50Hz ring, 60Hz hole, best material to treat?

[pns]

hello lights
boy these guys ^^^ sure do know their freq responses
quick question...
what software is generating the graphs ?
any pointers for using it effectively?
thanks in advance!

[Lights]

Hi PNS. Welcome to Gearslutz. The software is called Room EQ Wizard and it's free from hometheatershack.com (I think that's the URL anyway). There are a bunch of stickies and threads in this subforum that will walk you through the process. You need a sound presure meter ideally and also a proper measurement mic (the Behringer ECM8000 is the cheapest one and it's the one I have).

Basically after you've calibrated REW with your audio interface and selected a canned mic calibration file (since you can't possibly calibrate a mic without an anechoic chamber) you just set up your mic in the listening position, click "Measure" and you're good to go.

[DanDan]

It's Room Eq Wizard. A free downloadable program. It works on all computers but you are probably best to use the internal Apple sound chips, which are of perfectly good enough quality. Problems with some external interfaces.
The manual is a brilliant piece of writing, but this may help get you going quicker.
http://www.gearslutz.com/board/studi...er-v2-1-a.html

Skip the calibration and loopback correction. Just dive in.
DD

[Lights]

Hey guys: check out my (hopefully) final piece of acoustic treatment:

Can I convert this couch into a giant bass trap??

[Lights]

Well guys, I hit a brick wall in my efforts to deal with that last 43Hz null in the left speaker.

Early indication by going around the room with a SPL meter while the speaker produced a 43Hz tone was that I perhaps could soak up the reflection by converting my couch into a giant bass trap by making the frame porous (with a hole saw) and stuffing it with pink fiberglass insulation. However I did a quick test to see if that would really help things by laying out the insulation on a plastic sheet where the couch is and running a sine sweep. No change at 43Hz. Moved the pile-o-fiberglass around the room and no position changed the waterfall.

So I'm stuck. :(

[nms]

Did you move your speakers closer to the wall again? how far are they spaced off the front wall? That's a BIG cause of low nulls. Another huge spot to treat is the front wall to ceiling edge. Those two things really improved my worst low end holes. I'm all about treating my front end heavily now and getting the speakers in close to the wall.

[Lights]

They are midway between the front wall and the front of the desk. It seemed to be a good trade-off as moving them all the way against the wall resulted in an early reflection on the desk surface and moving them too far forward resulted in a bigger null at 43Hz.

I'm going to move them around a bit more and see if moving them further back helps.

I will also try temporarily treating the wall-ceiling corner on the front wall and see if that has an effect.

[nms]

In a room that size you'll probably have best results with your speakers tight to the wall and heavy treatment all up the front. The LEDE concept is intended to be dead at the front end where all your first strongest reflections live and live at the back. Where desk reflections are concerned that's exactly why it can be so worthwhile to build a custom desk with the minimum amount of surface area you need and angle the top as much as possible without your mouse sliding off the desk. Low end issues are difficult, but good monitor placement is the easiest way you'll ever find to improve the sound of a room.

[localhost127]

Originally Posted by nms

In a room that size you'll probably have best results with your speakers tight to the wall and heavy treatment all up the front. The LEDE concept is intended to be dead at the front end where all your first strongest reflections live and live at the back.

where did you obtain such information regarding LEDE?

...and how are the strongest reflections incident off the front wall?

[nms]

Look up LEDE. The lower the freqs, the less directional they are so naturally your sub bass will be hitting the wall behind, above, below, and beside your speakers hardest. The boundaries closest to the speakers will have the most powerful low end reflections.

Google is your friend:

"To prevent stray reflections, the wall areas behind and directly adjacent to the speakers are normally treated with a sound absorbing materials such as acoustical foam or wall panels to provide a "dead" end to the room. The opposite or back wall is left "live" and can be treated with sound diffusers to break up any possibility of standing waves within the room. This will create a small early time gap between the time of arrival of the direct sound and the arrival of the first highly diffused sound from the live end. This technique is known as "live end/ dead end acoustics" and has been the standard in professional listening environments for many years.

This design will create a very clean recording environment with better sound clarity, improved stereo imaging and smoother frequency response."

[Jens Eklund]

Originally Posted by nms

Look up LEDE. The lower the freqs, the less directional they are so naturally your sub bass will be hitting the wall behind, above, below, and beside your speakers hardest. The boundaries closest to the speakers will have the most powerful low end reflections.

Google is your friend:

"To prevent stray reflections, the wall areas behind and directly adjacent to the speakers are normally treated with a sound absorbing materials such as acoustical foam or wall panels to provide a "dead" end to the room. The opposite or back wall is left "live" and can be treated with sound diffusers to break up any possibility of standing waves within the room. This will create a small early time gap between the time of arrival of the direct sound and the arrival of the first highly diffused sound from the live end. This technique is known as "live end/ dead end acoustics" and has been the standard in professional listening environments for many years.

This design will create a very clean recording environment with better sound clarity, improved stereo imaging and smoother frequency response."

In a good LEDE design, you avoid broadband absorption and use redirection of early energy instead. The RFZ concept (that is also an LEDE design) takes this idea to the limit but the basic idea was used in LEDE designs before Peter put a name on it ("RFZ").

[Lights]

I will temporarily move some of my fiberboard bass traps between the left speaker and the front wall and see what kind of result I get. Between that and the foam I will have 6" of trapping. I'll report back.

[Lights]

Well guys I put bass traps behind and above the left speaker with the offending null and while it did even out the frequency above 150Hz a bit, it did nothing to rectify the null at 43Hz.

I moved bass traps around to multiple other places and while I did see minor changes at higher frequencies I again saw no change in that low null.

I also moved the speaker all the way to the front wall and that didn't have any effect either. This, plus the fact that the right speaker does not exhibit a null at 43 makes me believe it's the result of the asymmetry in the back half of the room and not the front wall reflection. But this is just a guess based on the data I have and the limited knowledge I have picked up from the experts here.

[DanDan]

Try moving the speaker side ways. Side Wall BIR. Also vary the height.
DD

[Lights]

I already tried sideways. Same null. To the left of the speaker is 2ft of insulation

I will change the height. What are we talking? 6in? 3ft?

[DanDan]

6 inches at a time should be enough.

DD

[localhost127]

Originally Posted by nms

Look up LEDE. The lower the freqs, the less directional they are so naturally your sub bass will be hitting the wall behind, above, below, and beside your speakers hardest. The boundaries closest to the speakers will have the most powerful low end reflections.

Google is your friend:

"To prevent stray reflections, the wall areas behind and directly adjacent to the speakers are normally treated with a sound absorbing materials such as acoustical foam or wall panels to provide a "dead" end to the room. The opposite or back wall is left "live" and can be treated with sound diffusers to break up any possibility of standing waves within the room. This will create a small early time gap between the time of arrival of the direct sound and the arrival of the first highly diffused sound from the live end. This technique is known as "live end/ dead end acoustics" and has been the standard in professional listening environments for many years.

This design will create a very clean recording environment with better sound clarity, improved stereo imaging and smoother frequency response."

just because one reads it on the internet does not necessarily make it true.

[localhost127]

Originally Posted by amishsixstringe

Local, thanks for that comment. I unchecked t=0, but the result ended up exactly the same for time and amplitude after subtracting the peaks. I have heard this before from SAC, but never understood why this should be set this way. Can you please explain it for me and others?

you need to uncheck t=0 (which will utilize loopback) such that you can accurately determine the total flight path for the indirect specular reflection. when you have t=0 and the direct signal corresponds to 0ms on the graph, you cannot simply utilize the given time difference between the direct and indirect signal, as is it not linear!

Originally Posted by amishsixstringe

As for measuring from the center of the speaker and not the tweeter, I agree. I never thought of it that way before, but I will at least take it into consideration when doing SAC style 'string theory' measures in the future.

Thanks for your input in this thread.

Neil

a proper thread which could be considered mandatory reading:
Above the Schroeder Frequency. Diffraction.

[nms]

Originally Posted by localhost127

just because one reads it on the internet does not necessarily make it true.

So you're saying you insist that in LEDE the rear wall behind you is supposed to be the dead one?
You can google it and find plenty of results saying the opposite. How about sweetwater's glossary page.. are they to be believed? http://www.sweetwater.com/expert-cen...ossary/t--LEDE

The reflections are strongest in the front half of the room. This is fact. In a properly designed studio without parallel surfaces and the proper angles to deflect the energy things are much better, but in a typical room full of square angles you're likely to get better results treating any of the front L,R, ceiling, floor corners than the rear ones.

To the op.. For your probs with the left speaker null try treatments near the right speaker and see if that affects anything.

[Jens Eklund]

Originally Posted by nms

So you're saying you insist that in LEDE the rear wall behind you is supposed to be the dead one?
You can google it and find plenty of results saying the opposite. How about sweetwater's glossary page.. are they to be believed? Glossary: LEDE - Live End, Dead End | Sweetwater.com

The reflections are strongest in the front half of the room. This is fact. In a properly designed studio without parallel surfaces and the proper angles to deflect the energy things are much better, but in a typical room full of square angles you're likely to get better results treating any of the front L,R, ceiling, floor corners than the rear ones.

To the op.. For your probs with the left speaker null try treatments near the right speaker and see if that affects anything.

The LEDE (or RFZ) design strives to achieve an ISD-gap (useful range from about 12 ms to 25 ms and energy within this time frame at -20 dB down or lower compared to direct) followed by a termination (preferably about -12 dB or higher, compared to direct) and following this, an exponentially decaying (semi) diffuse sound field. The energy terminating the ISD-gap should optimally arrive laterally (from the rear sides of the room).

If you have different view of what the LEDE/RFZ is, I suggest that you consult the appropriate literature (... not Sweetwater …)



EDIT:

Originally Posted by Jens Eklund

RFZ and LEDE are identical in terms of the criteria for the acoustic response. The RFZ is simply a geometric solution that makes it easier to meet the LEDE criteria, totally avoiding porous absorption if possible and instead relies on redirection of early energy thus making it easier to reach the level of termination of the ISD-gap. The use of angled walls was used before Peter named it “RFZ” but he successfully managed to link the term to his geometric solution. In other words; LEDE = RFZ as far as acoustic response criteria. RFZ does not replace LEDE, it’s a way of getting there.

[nms]

I definitely respect your advice typically Jens, but is this really LEDE? I've always believed it to be more prudent to treat the front half of the room where treating square angled rooms. It's usually the first place recommended to start and in testing I've always found superior results. A google search seems to pull up a lot of mention of LEDE being defined by a dead front end.

[Jens Eklund]

Originally Posted by nms

I definitely respect your advice typically Jens, but is this really LEDE? I've always believed it to be more prudent to treat the front half of the room where treating square angled rooms. It's usually the first place recommended to start and in testing I've always found superior results. A google search seems to pull up a lot of mention of LEDE being defined by a dead front end.

Yes, a common way to do a LEDE room is by treating the front half (if not the whole room for some reason) of the room using absorption at specific reflection points and/OR by splaying walls thus redirecting the early energy away from sweet post, and the back wall using 1D diffusers (assuming that the room is long enough to support the desired ISD-gap) to scatter energy to the sides that later arrive back to the sweet spot laterally.

[localhost127]

Originally Posted by nms

So you're saying you insist that in LEDE the rear wall behind you is supposed to be the dead one?
You can google it and find plenty of results saying the opposite. How about sweetwater's glossary page.. are they to be believed? Glossary: LEDE - Live End, Dead End | Sweetwater.com

i think you may be slightly confused or misguided with respect to LEDE acoustical model, and you may be taking the "live end dead end" name too literally. there are specific, specular requirements of which to achieve (based on measured acoustical behavior of the room - not simply assinging one boundary "live" and another "dead" (whatever those vague terms mean)).

50Hz ring, 60Hz hole, best material to treat?

soffit mounting of the speaker is quite fundamental to LEDE concept - so LF reflection off the front wall doesn't exist. absorption on the front wall is generally limited to the elimination of edge diffraction.

Originally Posted by nms

The reflections are strongest in the front half of the room. This is fact. In a properly designed studio without parallel surfaces and the proper angles to deflect the energy things are much better, but in a typical room full of square angles you're likely to get better results treating any of the front L,R, ceiling, floor corners than the rear ones.

i think you are confusing modal and specular behavior issues...

Originally Posted by nms

I definitely respect your advice typically Jens, but is this really LEDE? I've always believed it to be more prudent to treat the front half of the room where treating square angled rooms. It's usually the first place recommended to start and in testing I've always found superior results. A google search seems to pull up a lot of mention of LEDE being defined by a dead front end.

LEDE is quite well misunderstood, as are many sub-topics related to acoustics. the concept of making one boundary "live" and another "dead" most certainly does not constitute a LEDE room/response. Jens summed it up nicely, and the AES paper out there gives some of the high-level fundamentals of the model. you may wish to research this particular model directly from the relevant source(s), vs random google searches. this is becoming something tantamount to the 'telephone game'.

again, it's not about blind treatment of boundaries ... it's about achieving a total specular response within the bounded space.

[nms]

Jens just corroborated what I've always thought to be defined as LEDE.

In any case, best not argue over the term. Do any of us believe it's not sound advice to prioritize treating the front half of the room first? I certainly have never had as much result as found on the front half.. Particularly the front corners and wall to ceiling/floor edges.

[localhost127]

Originally Posted by nms

Do any of us believe it's not sound advice to prioritize treating the front half of the room first? I certainly have never had as much result as found on the front half.. Particularly the front corners and wall to ceiling/floor edges.

i would not say there is any priority to treat the front half of the room, nor any other specific boundary over the other in some sort of linear fashion. the room's actual acoustical behavior is measured via the waterfall plot (frequency response + time-domain (LF decay)) for the LF/modal region, and the ETC (in the time-domain) is generated to identify boundaries incident of early arriving high-gain indirect specular energies - gain with respect to time vs that of the direct signal in the specular region. once measured (eg, actual) issues are identified, then one can work to apply appropriate treatment and adjust source/listener placement to mitigate said issues.

see my statement above regarding soffit mounting re: LEDE.

if one is utilizing porous insulation as a LF absorber, then the porous absorber is typically placed in the corners (as first priority) such that the large wave is forced through the insulation - especially as the corners touch on 2 or all 3 axial modes (2D, 3D corners respectively).

for the specular region where energy can be ray-traced (modeled as light), there is likely no reason to treat front corners. there is generally no early-arriving, high-gain indirect specular energy (first-order) incident off of the front wall/corners (dependent upon speaker selection), unlike that from the sidewall, ceiling, rear wall, etc, of which are usually the priority to address (along with any early-early energy such as that incident from the working surface, edge diffraction etc). if one were forced to make such prioritization, i would say the front wall boundary is further down the list than the rear wall, side-walls, ceiling, etc, as energy will be incident from those boundaries and superpose at the listening position before incident energy from the front wall will do the same --- but measurements dictate this based on the actual behavior of the acoustical space.

[Lights]

In my case (as the OP ) I have such a nonstandard sized room, that I think we're into trial and error mode.

If someone wants to look at the specific room and judge where the 43-44Hz null is coming from (left speaker only--but the L speaker is on the right side of the diagram), I'll do my best to trap that area. Keep in mind that I just tried putting 6" of trapping (with 2-4" of airgap) above and behind the speaker (behind = between the front wall and the speaker) and the null didn't change at all.

[Lights]

As promised, I ran some additional tests to see if the height of the left speaker had any impact on the null around 43-44Hz.

It did. Albeit small.

Attached is a waterfall of the speaker at its normal height taken first as a "control" and then the speaker raised 14 inches. I also raised it 11in and up to about 19~20in but the best result was 14in.

I also tried holding a bass trap directly above the speaker and mic as I recorded to simulate a "cloud" and while the frequency response at higher frequencies in the waterfall improved somewhat, the null stayed there.

[DanDan]

Lights, when I suggest moving speakers or mic, my intent is interrogation of the room measurement. Make a move, see a change, CONNECTED.
Post 106 you moved your speaker away from Front Wall by six inches. I believe you called it the back wall, can we agree the wall in front of you is the FW and the one behind is the Back Wall. Many see it the other way round.

In any case, small move, quite a change in the notch, worse.
Sideways or vertical moves seem to show less of an effect.
Presuming the frequency of the null does not change with listener position,
I would conclude that the null is caused by by a reflection from a wall on axis with the move. The Front Wall seems too near to do a 40Hz notch. Must be the Back Wall.

DD

[Lights]

I have to redo the tests moving the speaker to the front wall and then forward on the desk toward the listening position. I don't think I can reproduce the null starting to go away anymore.

If the reflection from the back wall is causing the problem, I'm stumped as to which back wall it is. I have lots of back walls back there because of the odd shape of my room :(

[DanDan]

Well, try playing a Sine Wave at 40ish. Walk about and try to find nulls and hotspots.
DD