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Which ETC-curve should be preferred? Studio Monitors
Old 22nd July 2014
  #31
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Tip of the day

Sorry for my delayed answer.

Mctwins; In your post https://www.gearslutz.com/board/9455716-post165.html you also showed ETC graphs besides the waterfalls you showed above. The ETC without “floor flowers” showed a high peak at -5 dB / 1,7 ms and one at -12 dB / 1,9 ms and there are several between 2-2,5 ms close to -15 dB. In the ETC with “floor flowers”, these peaks have diminished down about -15 to -20 dB. (BUT at the same time when placing the “flowers” on the floor, impulses in the range 3-4 ms are about 5 dB worse than before and are now up to -18 dB as worst. This corresponds quite well with the size of the “flower”, 60x60x25 cm / 24”x24”10”, as 1 ms means a change of travel distance of about 34 cm / 13”.) All these reflection are probably in the range 1-8 kHz with wave lengths between 4,3-34 cm / 1,7-13”. If so, you could deflect them away from LP with something the size of a pocket book to LP case. Or, you could absorb the impuls frequency and kill it down to below hearing with a regular pillow. A pillow or two (or cooler looking, a stuffed spaniel) at reflection points will not deaden your room for these reflections, nor would it reflect and increase the already low reflections at 3-4 ms you started with.

Jim1961, I have followed your thread about acoustical fixes in your room. Interesting, even though I haven’t posted anything in it. I know for certain you have done more than a handful of measurements and adjustments to get where you are now …

Akebrake, well I started with a bare concrete bunker of 33 m³ / 355 ft², 72 m³ / 2542 ft³, which I wanted to make a comfortable listening and home cinema room out of. This together with meeting the soundfield parameters for assesments of 2 channel listening according to EBU standards. For my room size that would mean a decay time of 0,22 +/- 0,05 s (170-270 ms) 200-4000 Hz and early reflection not worse than -10 dB between 1-8 kHz 1/3 octave within the first 15 ms. To that, the visual end result mustn’t look too damn awful or weird. So far, most of the figures have been ticked off. Early reflections are at or below -20 dB, decay time in bass is a lot better than what EBU requires, frequencies above 1,5 kHz are fine, while 300-1500 Hz need to be improved with at least 0,02 s to reach 170 ms minimum. This can probably be done by adjusting some slat absorbers which I believe are too effective in that particular range.

I have found out I have some pretty nifty and cheap means for easy adjusting of the acoustics at the listening position. Tip of the day: Get some coffee tables as the pictures below. (The front has now been modified to a full face plywood front from the MLS sequence shown in the picture). I have 2 tables, each is L98xW50x54 cm (38x20x21”). They got wheels and are light weight, so are easy to move around to form 1 rectangular table or a square one. The table top is also removable in an instant. Cost was SEK 300:- / about USD 45:-. As you see from the pictures the table has a grid pattern of slats and open areas 21x21 mm. Open area varies 45-48% so a “naked” table is transparent to all audible frequencies of interest.

I glued a plywood sheet on 1 long side and let the other side be untouched, on the short sides, 50x50 cm I glued slats on the inside to cover some of the “open area columns” and followed an MLS sequence for this rendering a about 24% open area, partially reflective / diffusive for higher frequencies and transparent to mid and lower. => I can have a totally reflective side towards speakers, a MLS sequence or a 100% sound transparent side. At comfortable distance from the reclainer sofa, ie so I can have my feet on the table while listening or watching a movie, I get no measureable reflections in REW from the transparent table top. (Element height 78 cm, ears at 87 and distance 325 cm for me.)

The graphs below are for a rectangular setup, L196xW50xH54 cm. Light blue is with transparent front, dark blue one is with transparent front and a fluffy woolen table cloth. Light purple is with plywood front towards speakers and darker purple with the table cloth on top. As you see in REWs RT60 graph the decay changes quite dramatically depending on my choice.

A reflective front modifies the floor bounce and reflect it back towards front wall so I increase decay between 200-300 Hz, a table cloth on top and I increase decay between 70-100 Hz, = I am improving on the null from floor-ceiling bounce at common listening and room heights. At the same time with the table cloth I may decrease a peak in the 200-300 Hz range. (At least that is how I interpret the decay graphs.) If I turn the table around so the transparent side is towards speakers, I get another response in decay time for different frequencies. What I find cool is, it is easy to modify these frequency responses by stretching wires between the slats inside the table and throw in a piece of insulation of suitable air flow resistance. By adjusting the wire height and insulation thickness over the reflecting floor, I should be able to nail down a certain frequency range I wish to modify. At the same time all the ugly acoustic fixes are hidden away from sight and serves as furniture as well.
Attached Thumbnails
Which ETC-curve should be preferred?-009.jpg   Which ETC-curve should be preferred?-140721-transparent-side-towards-speakers.jpg   Which ETC-curve should be preferred?-140721-plywood-side-towards-spekaers.jpg   Which ETC-curve should be preferred?-140721-6-plywwod-front-towards-speakers.jpg  

Last edited by Adhoc; 23rd July 2014 at 12:14 AM.. Reason: some mispellings
Old 26th July 2014
  #32
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I have experimented and taken some REW-measurements with the grid table. I like the versatility the table provides. 6 of the measurements look quite similar with some small mode tails but 1 stands out and gives an exceptionally smooth low end end 40-200 Hz. Measurements where 1 without any insulation inside, the other 6 ones with 70 mm Isover Piano (about 7000 rayls/m) at 6 different levels with 5 cm / 2" increments between levels above the concrete floor.

The one I find best is the dark red graph, at level 3 = 27 cm / 10,6" above concrete floor.

Right now there is a dip close to 80 Hz, something which needs attention later on.
Attached Thumbnails
Which ETC-curve should be preferred?-140725-grid-table-empty-no-insulation-inside.jpg   Which ETC-curve should be preferred?-140725-grid-table-70-mm-isover-piano-level-1-17-cm.jpg   Which ETC-curve should be preferred?-140726-grid-table-70-mm-isover-piano-level-2-22-cm.jpg   Which ETC-curve should be preferred?-140726-grid-table-70-mm-isover-piano-level-3-27-cm.jpg   Which ETC-curve should be preferred?-140726-grid-table-70-mm-isover-piano-level-4-32-cm.jpg  

Which ETC-curve should be preferred?-140726-grid-table-70-mm-isover-piano-level-5-37-cm.jpg   Which ETC-curve should be preferred?-140726-grid-table-70-mm-isover-piano-level-6-42-cm.jpg   Which ETC-curve should be preferred?-140726-spectrogram-grid-table-70-mm-isover-piano-level-3-27-cm.jpg  

Last edited by Adhoc; 26th July 2014 at 10:10 PM.. Reason: Added some text
Old 27th July 2014
  #33
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****, one shouldn’t make measurements late at night when one is tired. The one I saw best was not smoothed to 1/48 as the other ones, but to 1/6, - no wonder it looked better … Still, one can notice that also small change in height above floor makes a difference in the waterfall. (Thanks akebrake for your sharp eye.)
Attached Thumbnails
Which ETC-curve should be preferred?-140726-grid-table-70-mm-isover-piano-level-3-27-cm-1-48-oct.jpg  
Old 27th July 2014
  #34
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Quote:
Originally Posted by Adhoc View Post
Sorry for my delayed answer.

Mctwins; In your post https://www.gearslutz.com/board/9455716-post165.html you also showed ETC graphs besides the waterfalls you showed above. The ETC without “floor flowers” showed a high peak at -5 dB / 1,7 ms and one at -12 dB / 1,9 ms and there are several between 2-2,5 ms close to -15 dB. In the ETC with “floor flowers”, these peaks have diminished down about -15 to -20 dB. (BUT at the same time when placing the “flowers” on the floor, impulses in the range 3-4 ms are about 5 dB worse than before and are now up to -18 dB as worst. This corresponds quite well with the size of the “flower”, 60x60x25 cm / 24”x24”10”, as 1 ms means a change of travel distance of about 34 cm / 13”.) All these reflection are probably in the range 1-8 kHz with wave lengths between 4,3-34 cm / 1,7-13”. If so, you could deflect them away from LP with something the size of a pocket book to LP case. Or, you could absorb the impuls frequency and kill it down to below hearing with a regular pillow. A pillow or two (or cooler looking, a stuffed spaniel) at reflection points will not deaden your room for these reflections, nor would it reflect and increase the already low reflections at 3-4 ms you started with.
Do you really think that we havent tried that out. We have put porous panels on the floor to take that reflection but scews the freq resonse in a negative way. The sound is also bad, to damped. We rather choose to not have anything on the floor and live with that reflection because it sounds better than having panels on the floor.

With the wings its a different animal all togehter. It sounds better and at the same time have killed that nasty reflection and makes the freq resp even better.

You seem to be good with numbers and writing so it looks good on a paper but treat a room in a practical way seems to be your weakest link. The effort and energy schould be put on that instead of giving us advice what to do.

Cheers
Old 29th July 2014
  #35
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The ETC graph is improving , slowly but steadily. I shall try to increase the reflections between 17 to 24 ms. I have an idea which might kill two birds with one stone, tests will show if it is possible.

Poohbecca: Read again what I wrote to Mctwins. The way he presents his measurements, the “floor flower” fixes 2 early reflections to better while with the same placement the “floor flower” worsens other reflections up to a higher level due to its size, all within the first critical 5 ms. This is obviously clear from his measurement postings.

You don’t inform on the size of the absorbtive panels you tried out and found to dampen the room too much. As I wrote, the absorbtive area does not need to be large in area or thickness to fix a reflex in the high frequencies, which means the porous absorbers you tried where unnecessarily too big if they actually damped down the room.

My projector lens gives a reflection at 5,8 ms. Fixing that reflection down -29 dB needed an absorber of size 30x24x3 cm / 11,8x9,4x1,2”, = smaller than my laptop. Now, do you think an absorber of that minuscule size will actually dampen a room of 7,86 x 4,19 m? If yes, you are more daft than should be permitted for anyone posting.

Poohbecca, you should leave the postings to your twin brother Mctwins. When he wants to, he can actually write something of a pretty good standard and also seems to be able to put 2 and 2 together, while you don’t. Perhaps you suffered from severe lack of oxygen during birth (?), and for this reason is a hopeless case for improvement. At any rate, I haven’t seen you offer anything of significance anytime, except being a GS major laughing stock. Sometimes it is even quite amusing, still rather tedious.
Attached Thumbnails
Which ETC-curve should be preferred?-140728-7-etc-schroeder-integral.jpg   Which ETC-curve should be preferred?-93-mini-absorber-30x24x3-cm.jpg   Which ETC-curve should be preferred?-94-140728-15-no-absorber-30x24x3-cm-5-8-ms-no-haas-kicker-17-1-ms.jpg   Which ETC-curve should be preferred?-95-cause-reflection-5-8-ms.jpg   Which ETC-curve should be preferred?-96-miniabsorber-place.jpg  

Which ETC-curve should be preferred?-97-result-mini-absoorber-140728-7-absorber-30x24x3-cm-5-8-ms-haas-kicker-17-1.jpg   Which ETC-curve should be preferred?-98-140728-7-red-15-light-blue-together.jpg  
Old 21st August 2014
  #36
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After a lot of measurements, thinking, shuffling around of furniture and stuff, I think I have reached the ETC limit in my room. The only added absorbtive materials is a piece of fibre glass, 30x24x3 cm / 11,8x9,4x1,2”, two pillows and a blanket on a seat cushion in the leather sofa. The rest of quenching non wanted early reflections where done with ray tracing, redirecting and screening with hard materials (an LCD screen at appropriate angle) moving some furniture, using speaker horns as scatterers / diffusers etc.

It is possible to get one strong -6 to -7 dB reflection at either 16,5, 17,7 or 28 ms. My gut feeling said it would be better with several strong reflections involving different frequencies within a short time range, instead of one single very strong spike of probably a singular frequency. Any comments on that gut feeling?

The diagrams below show current results with strong reflections grouped around 20 ms and 28 ms respectively. Reflections around 14,4 ms is of no consequence as the “culptrit” is the microphone tripod. Either group at 20 ms or 28 ms can be easily removed if that is seen as more positive than two reflection groups. (Changed color in the last diagram, for those 10% color blind green-red. Measurements are the same)
Attached Thumbnails
Which ETC-curve should be preferred?-140820-27-zoomed-out-right-ear-etc-decay.jpg   Which ETC-curve should be preferred?-140820-27-close-up-right-ear-etc-decay.jpg   Which ETC-curve should be preferred?-140820-26-close-up-left-ear-etc-decay.jpg   Which ETC-curve should be preferred?-140820-26-27-purple-right-ear-green-left-ear-etc-decay.jpg  
Old 21st August 2014
  #37
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Quote:
Originally Posted by Adhoc View Post

It is possible to get one strong -6 to -7 dB reflection at either 16,5, 17,7 or 28 ms. My gut feeling said it would be better with several strong reflections involving different frequencies within a short time range, instead of one single very strong spike of probably a singular frequency. Any comments on that gut feeling?
The LEDE model calls for an initial terminator followed by a tail. I am sure you already know this. So I think we need to think about the purpose of the termination in the first place. Part of that is to de-localize later arriving reflections. By preserving strong later reflections, you may be defeating this purpose.

In my case, I have one strong (-6db) at 24ms, and am quite pleased with my results. Admittedly, I haven't experimented with strongly arriving additional reflections. So I cant really comment from experience how having them will play out in actual listening.

If you know the source for each of the (3) reflections you describe, I would experiment by placing absorbers in front of 2 of the 3 and listen. See what it sounds like with only one. Then with (2), and then all three.

The other thing to consider is which direction these different reflections are arriving from. The laterally arriving ones are the ones id give priority to keeping.
Old 21st August 2014
  #38
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The group of reflections between 28-28,5 ms (right ear, purple / red) are coming from a 125 degree angle, laterally / behind, = more or less directly into the ear. For left ear (green) 210 degrees and from below. The ones at 19,6-20,2 ms (both right and left ear) are from about 170-190 degrees behind and from below ear. These cannot be easliy redirected so they arrive laterally and I do not think they are that noticeable by ear even though the mic show a stronger reflection for those.

Thanks for reply, time for bed now.
Old 21st August 2014
  #39
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Hi Jim, The reflections and source are actually the same for both the shown measurements with several spikes and the third one (not shown) with a single -7 dB spike at around 28 ms. The difference between my single spike ETC and the ones with several spikes with a bit lower amplitude, is only due to a very slight variation of the angling of Haas triggers.

Measurements were one for each ear with both front speakers hooked up. Setup was identical except moving the mic sideways about 27 cm. I used a dummy head, placed the microphone and made measurements close to each ear. For the reflections coming from the right side / behind at 125 degrees and around 28 ms, one can see the reflections are lower in amplitude and slightly later in time with mic placed at left ear. This corresponds to the width of the head (17 cm / 6,7”) obscuring reflection of “high frequencies” and partly obscuring a reflection of “lower frequency” with wave length larger than the head width. The mic was distanced away about 5 cm / 2" from ears.

Some murky pictures showing the setup for the 28 ms reflections. A laser meter is fixed on top of the right front speaker. The red dot / beam hits the mirror on the Haas kicker in the left back corner, bounces towards the mirror on the door to the right of LP, travels over the dummy heads right ear / head into a third mirror on an LCD screen (not shown in the picture) angled at an appropriate angle and ends up at the dummy heads left ear. The final spot at left ear is at around 35 ms and reflection strength is then low in amplitude. (I angled the LCD-screen downwards a bit to show “the principal” and a red dot on the head. How the Haas triggers need to be angled depends on the speakers radiation pattern).

The reflections around 20 ms come from the up angled table tops behind and below the top of the sofa. If I remove the tables, the reflection from the slightly down angled Haas triggers at the back wall ends up in the back of the sofa below ear level and bounces towards the back wall again, thus “nullified”.
Attached Thumbnails
Which ETC-curve should be preferred?-99-laser-meter.jpg   Which ETC-curve should be preferred?-100-ray-tracing-right-front-speaker.jpg  
Old 21st August 2014
  #40
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Quote:
Originally Posted by Adhoc View Post
Hi Jim, The reflections and source are actually the same for both the shown measurements with several spikes and the third one (not shown) with a single -7 dB spike at around 28 ms. The difference between my single spike ETC and the ones with several spikes with a bit lower amplitude, is only due to a very slight variation of the angling of Haas triggers.

Measurements were one for each ear with both front speakers hooked up. Setup was identical except moving the mic sideways about 27 cm. I used a dummy head, placed the microphone and made measurements close to each ear. For the reflections coming from the right side / behind at 125 degrees and around 28 ms, one can see the reflections are lower in amplitude and slightly later in time with mic placed at left ear. This corresponds to the width of the head (17 cm / 6,7”) obscuring reflection of “high frequencies” and partly obscuring a reflection of “lower frequency” with wave length larger than the head width. The mic was distanced away about 5 cm / 2" from ears.

Some murky pictures showing the setup for the 28 ms reflections. A laser meter is fixed on top of the right front speaker. The red dot / beam hits the mirror on the Haas kicker in the left back corner, bounces towards the mirror on the door to the right of LP, travels over the dummy heads right ear / head into a third mirror on an LCD screen (not shown in the picture) angled at an appropriate angle and ends up at the dummy heads left ear. The final spot at left ear is at around 35 ms and reflection strength is then low in amplitude. (I angled the LCD-screen downwards a bit to show “the principal” and a red dot on the head. How the Haas triggers need to be angled depends on the speakers radiation pattern).

The reflections around 20 ms come from the up angled table tops behind and below the top of the sofa. If I remove the tables, the reflection from the slightly down angled Haas triggers at the back wall ends up in the back of the sofa below ear level and bounces towards the back wall again, thus “nullified”.
Without a room diagram showing the bounce paths of the reflections in question, I cant really tell whats going on there.

All I can say is I believe a single terminator in the 20-28ms region approaching the LP from 110-120 degrees, followed by a tail would be the conventional design goal.

I will add that trying to get a good and even spectrum (1k and up) from more than one bounce is difficult. From 3 or 4 bounces, problematic. You want the kicker response to be as even from 1k and up as possible in other words.
Old 21st August 2014
  #41
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Quote:
Originally Posted by jim1961 View Post
The LEDE model calls for an initial terminator followed by a tail.
A lateral exponential diffuse tail.

The hard panels should be removed and replaced by quality diffusors. Even though a strong termination with such panels can create a locking effect to the direct signal, they are also detrimental to some degree. Diffusion is better and replaced the old hard panels in LEDE a long time ago.
Old 22nd August 2014
  #42
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Quote:
Originally Posted by bwo View Post
A lateral exponential diffuse tail.

The hard panels should be removed and replaced by quality diffusors. Even though a strong termination with such panels can create a locking effect to the direct signal, they are also detrimental to some degree. Diffusion is better and replaced the old hard panels in LEDE a long time ago.
My response was an over simplification, and also an attempt to not recite the entire theory concerning LEDE. But you are right of course.

Yes, diffusion is better. But reaching a -12db termination with diffusion alone is unattainable in most small rooms, much less a more preferred termination of -8 or -6db, much much less at the desirable >20ms timing.

Long story short, a fully implemented LEDE/RFZ model in a small room isnt happening. So using a specular return for termination becomes a substitute. Not a perfect one, but IMO, much better than none at all. Whether a specular "tail" is better than none at all is another matter.
Old 22nd August 2014
  #43
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Just as we are clear. A specular strong return isn't better then a weaker return with diffusion. Diffusion is best either way. Specular high gain reflections should be avoided, even late ones. A return of -6 or -8db isn't important and studies of Russ Berger shows that the ideal termination lies between 10-15db, but this also less important then the diffuse tail itself. One should focus more on quality diffusion (aperiodic sequence) rather then a strong termination.

It's possible to increase the termination in a normal room by using speakers with high Q that focuses the energy more. But either way; the termination itself isn't as imporant as treating late arriving specular reflections from the rear of the room. If one can't treat the rear with proper diffusion, perhaps a strong termination is better. Difficult to say and depends if the option is no diffusion or some. Though it locks the listener to the direct signal and thus removes the cues of later arriving specular reflections, it also introduces it's own coloration. If there's already some diffusion in place (which is the case here), it might be better to use some absorption for the last areas of specular return. I would experiment with both. If there's no diffusion at all, hard panels and a Haas trigger might be preferable to avoid the room becoming too dead (which only absorption would lead to). Anyway, that's just my personal opinion and I would advice experimenting with both. But remember that the strong termination with hard panels was used before diffusion was introduced and to avoid the room becoming overly dry. When diffusion came on the line, things changed. We had a better option. It was also discovered later that the use of Hass kicker with panels had some detrimental effect despite arriving late. You don't need a half circle of diffusion by the way, though that's nice. Treating only a great part of the back wall with diffusion will in most cases be sufficient.
Old 22nd August 2014
  #44
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Thanks for chiming in. You are both right as I see it. There are also some restrictions I have to take in consideration and haven’t taken up yet. (Too much text in a post may be too much to take in for participants, so not always good. I hope there isn’t too much now.)

There is a passage way between two opposite doors, so the sofa cannot be moved back more than 2 or 3 feet. If I do that, stereo and / or video perspective will also worsen a bit. Optimizing one collides with the other so I have settled for probably the best compromise.

Putting a proper QRD on the Haas Kicker’s face plate will reduce signal strength about 7 dB, a skyline type about 20 dB, if I understand RPGs info correctly => So Jim1961 is probably right there about signal strength return. Kicker face width is 60 cm / 2 feet now, max can be an increase with about 10 cm / 4”.
If I remove the corner Haas Kickers and floor speakers at the back wall completely, reflections show up in the 18-20 ms region but with “low” strength, roughly below -20 dB. 18 ms from the curved BAD in the middle, at around 20 ms from the 2 volumetric diffusors = those vertical columns between the ceiling and floor bass elements.

If I move the floor speakers at the back wall towards the corners, specular reflections will show up at 16,5 ms and about -18 dB, because of the polar pattern from the front speakers = a bit early. Back speakers close to centre line gives no reflections at 16,5 ms. The CD-rack in front of the curved centre BAD works as a scatterer and prevents a 18 ms return which is close to -20 dB.

With the curved centre BAD + the 2 volumetric diffusors, I belive remaining back wall reflections after termination can be seen as pretty much diffused. The volumetric ones are 80 cm wide and 30 cm / 11” deep with 3 stages in depth and close to 50% sight line between the columns. (The ones presented in the doctors thesis from Salford Univesity where 50 cm / 20” deep with 5 stages in depth. A link to the thesis has been on GS several times before.)

So, questions to save time and effort boils down to what should be preferred, based on others previous experiences / preferences.
1) Is a singular spike at about -7 dB at specified time better than 3 to 4 spikes very close to the same time, within 0,5 ms of it actually but weaker with about 5-7 dB. (My thinking, the singular might be picked up by a mic, not necessarily by the ear as the reflection doesn’t come from an ideal lateral direction.)
2) Is anyone actually “better” than the other -10,5 dB at 20 ms and from behind or -12,7 to -14,2 dB at 28 ms coming from the side / behind at 125 degrees.
3) Is it a very poor idea getting strong responses at both 20 ms (strictly behind) and 28 ms (behind /side), should one be scrapped. If yes, which one?

Listening to the options might be easy to say but switching between them cannot be done with the switch of a button. It takes quite a bit of time to readjust and a firm sound memory fades rather quickly and may not be “dependable” because of that.

Enclosed are some pictures of the back wall as it is now together with ETC entering the echo region around 50 ms. ETC reflections are with mic at right ear of the dummy head, originating from the Haas kicker / boob lady witht the horns in the pictures right corner => bouncing to an opposite door to the left (28 ms) + the other Haas kicker bouncing to a Haas kicker behind / below the sofa (20 ms) => bouncing further to the listeners right ear at LP.
Attached Thumbnails
Which ETC-curve should be preferred?-102-back-wall-view-2.jpg   Which ETC-curve should be preferred?-103-back-wall-view-close-up.jpg   Which ETC-curve should be preferred?-140820-1-haas-trigger-20-28-ms-entering-echo-region-50-ms.jpg  

Last edited by Adhoc; 22nd August 2014 at 09:21 AM.. Reason: Inserted a clarification
Old 22nd August 2014
  #45
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Quote:
Originally Posted by Adhoc View Post



So, questions to save time and effort boils down to what should be preferred, based on others previous experiences / preferences.
1) Is a singular spike at about -7 dB at specified time better than 3 to 4 spikes very close to the same time, within 0,5 ms of it actually but weaker with about 5-7 dB. (My thinking, the singular might be picked up by a mic, not necessarily by the ear as the reflection doesn’t come from an ideal lateral direction.)
2) Is anyone actually “better” than the other -10,5 dB at 20 ms and from behind or -12,7 to -14,2 dB at 28 ms coming from the side / behind at 125 degrees.
3) Is it a very poor idea getting strong responses at both 20 ms (strictly behind) and 28 ms (behind /side), should one be scrapped. If yes, which one?
1) I wouldn't recommend spikes from a rear direction.
2) The lateral direction is important, so that gets my vote. The strength, using specular panels, shouldn't be limited given you can double them up for more gain.
3) I am not a fan of multiple terminators.
Old 22nd August 2014
  #46
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Quote:
Originally Posted by bwo View Post
Just as we are clear. A specular strong return isn't better then a weaker return with diffusion. Diffusion is best either way. Specular high gain reflections should be avoided, even late ones. A return of -6 or -8db isn't important and studies of Russ Berger shows that the ideal termination lies between 10-15db, but this also less important then the diffuse tail itself. One should focus more on quality diffusion (aperiodic sequence) rather then a strong termination.

It's possible to increase the termination in a normal room by using speakers with high Q that focuses the energy more. But either way; the termination itself isn't as imporant as treating late arriving specular reflections from the rear of the room. If one can't treat the rear with proper diffusion, perhaps a strong termination is better. Difficult to say and depends if the option is no diffusion or some. Though it locks the listener to the direct signal and thus removes the cues of later arriving specular reflections, it also introduces it's own coloration. If there's already some diffusion in place (which is the case here), it might be better to use some absorption for the last areas of specular return. I would experiment with both. If there's no diffusion at all, hard panels and a Haas trigger might be preferable to avoid the room becoming too dead (which only absorption would lead to). Anyway, that's just my personal opinion and I would advice experimenting with both. But remember that the strong termination with hard panels was used before diffusion was introduced and to avoid the room becoming overly dry. When diffusion came on the line, things changed. We had a better option. It was also discovered later that the use of Hass kicker with panels had some detrimental effect despite arriving late. You don't need a half circle of diffusion by the way, though that's nice. Treating only a great part of the back wall with diffusion will in most cases be sufficient.
I have listened to the specular terminator at -15, -12, -10, -8, -6 and -4db. My preference for -6 to -8db is based on actual listening.

Also keep in mind that my comments are based on a listening room, not a mix or control room application. So what I want from my termination/tail is the best sense of liveliness/spaciousness, not accuracy. The stronger the termination, the more this effect or sense is present. For a otherwise dry/dead room, this is a compensating factor that may vary for others depending on the degree to which this compensation is needed or desirable.

These are my opinions as well. But they are based on listening, not merely quoting theory.
Old 22nd August 2014
  #47
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Adhoc, apologies slight thread drift, but am curious about your coaxial speakers. Are those a commercial factory product, or did you build the cabinets? They look great.

If you built the cabs, am curious what speaker they are loaded with and do you like them? I have been a fan of coax speakers for decades but never owned any. Quite a variety of coax components are available today, but have not auditioned any modern coax components.
Old 22nd August 2014
  #48
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Bjorn Omholt's Avatar
 

Quote:
Originally Posted by jim1961 View Post
I have listened to the specular terminator at -15, -12, -10, -8, -6 and -4db. My preference for -6 to -8db is based on actual listening.
Which is obvious since you don't use enough diffusors and thus lack a nice decaying diffuse tail.
Quote:
Originally Posted by jim1961 View Post
Also keep in mind that my comments are based on a listening room, not a mix or control room application. So what I want from my termination/tail is the best sense of liveliness/spaciousness, not accuracy. The stronger the termination, the more this effect or sense is present. For a otherwise dry/dead room, this is a compensating factor that may vary for others depending on the degree to which this compensation is needed or desirable.
Yes. That's important. For a studio I wouldn't recommend what you're doing since it has a negative effect on accuracy to some degree. In those cases it should be diffusion or attenuation. In a listening room one can do whatever suits one's preferences and what's possibly within the boundaries.
Old 22nd August 2014
  #49
Gear Addict
 

jcjr: The coaxial elements, left-centre-right front speakers, are Altec Lansings Duplex 604K. Bought them as new old stock, never used, about 9 years ago. They might originate through a member at this very forum as far as I understand, from a project that never came to existence. The K-version was produced between early 80:ies into the 90:ies. Might be from 1982 or 1992 as the serial number only show the production years last figure. Toolings from the original Altec Lansing factory was bought by some of the engineers / workers and new elements can be bought today from Great Plains Audio in Oklahoma. As far as I know, you can by elements as a private person directly from the factory with or without filters, as well as spare parts for original Altecs or getting old Alnico magnets remagnetized. http://www.greatplainsaudio.com/two_way.html

The speakers at the back are also Altecs, the 416B with 811B horns, same as in the Altecs Valencias, A7 and Model 19. Cabinets are DIY, the unorthodox top sticking out from the side was only meant as handles when I carried them up from the basement, later to be routed off. Still there though … Subs at front and back are from Acoustic Elegance. AE is a small rather specialized company in Wisconsin producing high quality elements. You can buy as a private person directly from the factory.

(I know there may be more accurate speakers than the old Altecs nowadays, according to some people at least. But what do they know … -It should be fun to listen also.)

bwo: That product you got a pdf from me about, a couple of them may turn up as a loan to a friend I know. In case I go over to him, I might make some quick measurements in REW with / without them at close range. I’ll let you know.

Jim, Thanks! Opinions from people who have used devices for a prolonged time are always welcomed until one has had the time to form a personal one.

Last edited by Adhoc; 22nd August 2014 at 05:23 PM.. Reason: Some additions
Old 22nd August 2014
  #50
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akebrake's Avatar
 

Quote:
Originally Posted by bwo View Post
Just as we are clear. A specular strong return isn't better then a weaker return with diffusion. Diffusion is best either way. Specular high gain reflections should be avoided, even late ones. A return of -6 or -8db isn't important and studies of Russ Berger shows that the ideal termination lies between 10-15db, but this also less important then the diffuse tail itself. One should focus more on quality diffusion (aperiodic sequence) rather then a strong termination……..
BWO, Which study of Russ Berger are you referring to? (Paper, article?)

Best

Ake
Old 22nd August 2014
  #51
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Bjorn Omholt's Avatar
 

Where do you cross over the 811 b horn Adhoc?

Here's a newer horn which I'm presently using. Oh yes, we love good horns!

Attached Thumbnails
Which ETC-curve should be preferred?-wp_20140822_001-large-.jpg  
Old 22nd August 2014
  #52
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Bjorn Omholt's Avatar
 

Quote:
Originally Posted by akebrake View Post
BWO, Which study of Russ Berger are you referring to? (Paper, article?)

Best

Ake
I can't remember the name of the article and my server (where the paper is at) is down at the moment. However, I couldn't find exactly what Russ Berger told me concerning this in that paper. Not sure why.

I also see that I have been somewhat incorrect about what Berger said. He said the reflections should be at least 10-15dB lower then the direct energy. Which is not the same as what I said. Sorry about that. Here's Berger's own words:
Quote:
An AES paper I presented with a former colleague, I forget when. but long ago, tested the veracity of the hard reflections and our results concluded that the energy from behind wants to be at least 10-15dB lower than the direct energy, with signal delay timing appropriate for the source material.
He also mentioned to me that an issue with the strong reflections from the panels was that it actually made the material played back in the presence of these strong reflections sound better than the original. And this is obviously not the goal when mixing. You want the environment to reveal flaws and inaccuracies in the micing techniques, recordings and mixing choices.

I think by the way I have given you the link to the AES paper before. I can post it again if needed after this weekend. It's recommended reading. Now it's time for cabbin and fishing.
Old 22nd August 2014
  #53
Gear Addict
 

Oooh? Crossover, I am not 100% sure anymore. I believe it is at 800 Hz, still use the original crossover. They are now only used as back surround speakers.

Bought them in 1976 as an exchange student in the US and had about 100 kg / 220 lbs over weight when going back. Problem was solved with some contacts a bottle of Scotch with no further costs. All the stuff was loaded onto a military transport flight with NATO seals and all to NATO headquarters in Brussels where major unloaded it over to a civilian Sabena flight to Stockholm.

Conclusion: Never under estimate the service mentality of people if offering them a good bottle of malt whisky! heh
Old 23rd August 2014
  #54
Lives for gear
Thanks for the info, Adhoc. Though I fear the knowledge of great plains audio might eventually cost me some money.

604's were the initial impetus of my lust for coax speakers, in the early 1970's, though I never got around to buying any. Had heard them in studios but never could justify buying for stage keyboard speakers because the price was rather high and the early models had (as best I recall) much lower power handling specs than those quoted in the current great plains docs. The old ones were loud enough to make you deaf in soffit mounted studio speakers, but feared they might be too easy to blow on stage. But current application would be home studio, so durability under power wouldn't be a concern.

Agreed that measurements indicate other speaker designs may be more flat and accurate, but there is definite ear candy from big woofers and hf horns.

The hf drivers in old altec voice of the theater cabs seemed at the time the closest pro audio full fidelity horn, having what seemed at the time excellent hf performance negating the need for discrete tweeters. Though the VOT metal horn of the time could be "ringy" and some people would encase the outsides of the metal horns in spray foam to damp that problem. And the altec driver was a bit too easy to destroy in PA usage, though it certainly sounded good treated gently.

A 604 or the new 12" version would seem easier to buy without hearing first, being a "known quantity". A driver I know ought to be acceptable unless my taste or ear has drastically changed. Even if some of the new brands of coax drivers might be better, the improvement would be merely theoretical unless I could audition one.

Had even considered loading a coax 15 in my roland kc500 keyboard amp (which never goes to gigs or gets played loud). There's nothing basically wrong with the cab or electronics, and the speakers are not terrible at moderate volume, but a good speaker would have to make it better. The speaker baffle board doesn't have sufficient area to turn the cab into a three-way. Can't find a small enough high efficiency mid driver that would fit in the cab. So a good coax might be ideal. Though the concept of mounting a $600 speaker in a $500 amp has so far been ludicrous enough to prevent serious consideration.

What I used for keyboards for about 1976-1984 were small sealed three way boxes. Four cabs, one pair with jbl D130 woofers, the other set altec 421ah. EV small diffraction horn in one set (as in klipsh heresy), mccauley lenses in the other set, using EV phenolic diaphragm drivers (rugged and difficult to destroy, but insufficient hf for a two way cab). Jbl slot tweets in one pair, jbl bullets in the other. Wish I still had em here to evaluate. I recall em sounding pretty good but perhaps today wouldn't think so anymore.

Apologies, I just can't stay on topic, just ignore and carry on.
Old 24th August 2014
  #55
Gear Addict
 

Jcjr: Going off topic a bit is OK as long as things doesn’t get totally derailed.

Quote: “Can't find a small enough high efficiency mid driver that would fit in the cab.” Now, I don’t know what small enough and high efficiency mid driver means for you. You may check out TD12M an Acoustic Elegance element, mostly a midbass one with a pretty good efficiency and it can be crossed over rather high as you see in the link: AE Speakers --- Superb Quality, Unforgettable Performance, Definitely. . There is also a 8", 10” and 15”. The TD15M is by many considered one of the very best midbass drivers money can buy but at a lower price than ie TAD or JBL and is usually found in ready made multi$-speakers. (Also better technically / sonically than the Altecs) John Janowitz at AE is a helpful guy if you need any assistance technically.

I damped my 811B aluminum horns with 4 layers of 3 mm / 1/8” of adhesive bitumen sheets (found at car shops ). Result: No ringing whatsoever, totally “dead”, looks a lot tidier than any spray foam too.
Old 25th August 2014
  #56
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akebrake's Avatar
 

Quote:
Originally Posted by bwo View Post
…...I think by the way I have given you the link to the AES paper before. I can post it again if needed after this weekend. It's recommended reading. Now it's time for cabbin and fishing.

Bwo, thanks for your effort and hope your weakend was fine!
I just wondered if you have found any new(old) information (later papers) from Russ B.
Pls send your link again (as I coudn’t find it). But I found one of my postings re the same matter.
https://www.gearslutz.com/board/8963889-post140.html

BTW There is an upcomming event at AES in LA in October that might be interesting
AES Los Angeles 2014
Old 26th August 2014
  #57
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Bjorn Omholt's Avatar
 

Quote:
Originally Posted by akebrake View Post
Bwo, thanks for your effort and hope your weakend was fine!
I just wondered if you have found any new(old) information (later papers) from Russ B.
Pls send your link again (as I coudn’t find it). But I found one of my postings re the same matter.
https://www.gearslutz.com/board/8963889-post140.html

BTW There is an upcomming event at AES in LA in October that might be interesting
AES Los Angeles 2014
Here you go:
AES E-Library

AES E-Library

Edit: I see they are the same ones you had in that link.

Yes. That AES event would be nice to join. However, a bit far away for me. Perhaps you can joing and give us a report :-)
SydAudcon are also planning some interesting events. Perhaps one with Russ Berger.

Adhoc:
Unless you specifically are trying to diffuse the sound from the surround speakers, why not move the two diffusors on the front wall to the rear wall next to the other two? Ideally, one should follow the barker sequence when using four but overall I still think this would be better.
Old 26th August 2014
  #58
Gear Addict
 

bwo: I or pictures must have been a bit unclear, -as you propose moving diffusors from the front wall to the back wall. There are no diffusors straight up front. At the 2 side walls there are curved ternary BAD-diffsorbers as RPG calls them, 1,22 x 2,44 m / 4’ x 8’ but these are fixed to the wall and cannot be moved. There are 8 BAD panels integrated onto one plywood sheet and a Barker code cannot be fitted in with 8 pcs, so I just made a random mix of positive and negative hole patterns in each plywood sheet and turned one upside down so they aren’t mirror images opposing each other.

The surround speakers for a 5.1 setups are 3 pcs / front surround channel. The old Altecs at the back are seldom used but are meant for back surround channels in a 7.1 setup if I wish.

The side BADs are a bit too long forward wise. Untreated I get a reflection from right front speaker and the left BAD. This was easily fixed to below -20 dB though by just placing a LCD screen at 14 degree angle versus the wall and facing towards LP. The reflection then goes to the centre of the back wall without passing any of the 2 main LPs. The other side wall reflection was fixed by absorbtion with a comfortable sheep skin chair, also below -20 dB according to REW.

I enclose a picture of the current front wall. The ceiling polys have been taken down as they did not do anything substantial, positive or negative.The angled corner sections are superchunks with a 82 cm / 32” wide diagonal, covered up with wood 170x21 mm and slots about 6 mm wide. They are not sealed at top or bottom, so not a Helmholtz device. As the wood is still quite fresh I’ll let it dry out and shrink for 6 months before I might make any adjustment of the slot width.

I will try out the late specular rear / side reflection from the Haas kickers for some time. Later on I might replace the Haas ladies and build some QRDs or perhaps try out Jens’ diffusers as they seem very price worthy even though I will only use about ½ of a regular set.
Attached Thumbnails
Which ETC-curve should be preferred?-87-ny-front-med-superchunks.jpg   Which ETC-curve should be preferred?-105-angled-lcd-redirects-side-wall-refelction-back-wall.jpg  
Old 27th August 2014
  #59
Lives for gear
Quote:
Originally Posted by Adhoc View Post
Jcjr: Going off topic a bit is OK as long as things doesn’t get totally derailed.

Quote: “Can't find a small enough high efficiency mid driver that would fit in the cab.” Now, I don’t know what small enough and high efficiency mid driver means for you. You may check out TD12M an Acoustic Elegance element, mostly a midbass one with a pretty good efficiency and it can be crossed over rather high as you see in the link: AE Speakers --- Superb Quality, Unforgettable Performance, Definitely. . There is also a 8", 10” and 15”. The TD15M is by many considered one of the very best midbass drivers money can buy but at a lower price than ie TAD or JBL and is usually found in ready made multi$-speakers. (Also better technically / sonically than the Altecs) John Janowitz at AE is a helpful guy if you need any assistance technically.
Thanks Adhoc, those AE speakers look nice. The speaker baffle board in that roland kc500 is very crowded. There might be room to mount an added component in up to an extra 4" hole, but an extra 3" hole would be easier to squeeze in. Haven't snooped inside the cabinet so far, but possibly there wouldn't be room for a 15" woof, 6" midrange, and bullet tweeter, even if I cut out the baffle board and custom-cut a new replacement baffle board.

Had been hoping that somebody makes an efficient 3" dome mid, at least 92 or 95 dB 1W 1m, capable of covering perhaps 500 to 2.5 K or higher. I have seen dome mids that might otherwise qualify, except that the ones I've seen claim no higher efficiency than the low-80 dB vicinity, which couldn't keep up with a decent woofer and tweeter.

Some people curse that roland keyboard amp. Apparently if you play them at full power on stage it is too easy to blow the Fostex tweeter in the thing. However, I've never heard a unit labeled "keyboard amp" that sounds nearly as good on keyboards copmpared to name-brand high-quality small 3 way PA cabinets. The Roland isn't fabulous sounding, though I have heard much worse equipment called "keyboard amps" from other manufacturers. I don't recall hearing any "keyboard amp" which sounds obviously better, but have not heard them all.

Was thinking about replacing the woofer with one of the usual suspects, and replacing the fostex tweet with a JBL bullet. But a two-way crossed over that high is far from ideal, with a 15" covering the bottom end of the two-way.

The cab and amp seems "close enough for rock'n'roll" if it had better speakers. Not that the speakers are bad, they just are not great. Perhaps equivalent to mid-range OEM eminence or jensen. I first got the thing for studio use only, as a bottom end to a motion sound rotary speaker, but it is fun to play synthesizers thru. On some sounds, better ear candy than studio monitors.

Quote:
Originally Posted by Adhoc View Post
I damped my 811B aluminum horns with 4 layers of 3 mm / 1/8” of adhesive bitumen sheets (found at car shops ). Result: No ringing whatsoever, totally “dead”, looks a lot tidier than any spray foam too.
Thanks, that is a much better idea than foam!
Old 27th August 2014
  #60
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Bjorn Omholt's Avatar
 

Oh I see. Some pictures confused me and I haven't read carefully enough.

A quite different approach then what I'm used to.

By the way, I just discovered a new UREI type of speaker. Presonus Sceptre:
PreSonus | Sceptre
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