Different approach to low frequency treatment - would this work??

[jdebonth]

Hi all, I am considering an ‘unconventional’ approach to addressing (low freq) response issues and would like to understand if this could work.

I have just replaced a set of PMC FB1i's (that go down to 28Hz) with the much larger EB1i's (down to 19Hz). The low frequency ‘weight’ of these new speakers is making very apparent all kinds of low frequency issues in my relatively small room (see image and dimensions below). Particularly in the listening position I seem to be sitting in a peak; the bass is extremely exaggerated. (I am currently not bothered by the first reflection points of the mid and high frequencies).

I understand the recommended best approach is to place superchunk type bass traps in all four corners; followed by additional rectangular bass panels where necessary. This will remove all nulls and peaks throughout the entire room. There are 2 issues with this:

1. This is my living room and I don’t really want to fill it up with treatment
2. I do 100% of my listening at the ‘sweet spot’ (couch on the right in the pic) and do not need to entire room to have a flat response; just in the listening location.

The question I have is the following: Is it possible that with a minimal amount of treatment I am able to level out the area in the listening position only?
I.e. would I be able to place large 5” bass traps on the wall behind and directly above the listening position to level out this area? Note the back wall is only about 80cm (30 inches) from the listening position.

Appreciate if anyone is able to help out with this! Ultimately I will buy a microphone and do SPL checks to confirm the treatment has worked; right now I would simply like to understand if there is merit to this approach.


Length (curtained wall): 12.7feet (3.9m)
Width: 13.7 feet (4.2m) although this opens up into dining room behind camera
Height: 8.7 feet (2.7m)
174 sqft (16.4 sqm)

[Gdupproductions]

Originally Posted by jdebonth

Hi all, I am considering an ‘unconventional’ approach to addressing (low freq) response issues and would like to understand if this could work.

I have just replaced a set of PMC FB1i's (that go down to 28Hz) with the much larger EB1i's (down to 19Hz). The low frequency ‘weight’ of these new speakers is making very apparent all kinds of low frequency issues in my relatively small room (see image and dimensions below). Particularly in the listening position I seem to be sitting in a peak; the bass is extremely exaggerated. (I am currently not bothered by the first reflection points of the mid and high frequencies).

I understand the recommended best approach is to place superchunk type bass traps in all four corners; followed by additional rectangular bass panels where necessary. This will remove all nulls and peaks throughout the entire room. There are 2 issues with this:

1. This is my living room and I don’t really want to fill it up with treatment
2. I do 100% of my listening at the ‘sweet spot’ (couch on the right in the pic) and do not need to entire room to have a flat response; just in the listening location.

The question I have is the following: Is it possible that with a minimal amount of treatment I am able to level out the area in the listening position only?
I.e. would I be able to place large 5” bass traps on the wall behind and directly above the listening position to level out this area? Note the back wall is only about 80cm (30 inches) from the listening position.

Appreciate if anyone is able to help out with this! Ultimately I will buy a microphone and do SPL checks to confirm the treatment has worked; right now I would simply like to understand if there is merit to this approach.


Length (curtained wall): 12.7feet (3.9m)
Width: 13.7 feet (4.2m) although this opens up into dining room behind camera
Height: 8.7 feet (2.7m)
174 sqft (16.4 sqm)

I almost have the same room size beside that mine is 1.90 in width + i also notice that the bass is way louder when i sit further from it.....wel you think you sit in a peak ? go stand in the corner with your home cinema on ;D.

5 inch trap - 5 inch spaced off the wal with 5 inch panels stradled or superchunks in the 2 back corners would help out alot.

[raticusfortuna]

Originally Posted by jdebonth

1. This is my living room and I don’t really want to fill it up with treatment
(snip)
The question I have is the following: Is it possible that with a minimal amount of treatment I am able to level out the area in the listening position only?

no

Ultimately I will buy a microphone and do SPL checks to confirm the treatment has worked;

you'll only know if it worked if you test before and after.


raticus

[audiothings]

Equalization is an option if you do not require a wide sweet spot. Have you considered DEQX? Of course, it'd be a shame to send the signal through all kinds of digital processes before it gets to that pair of beauties.

5" traps will most likely do absolutely nothing significant, in the frequency range you are talking about (30-100 Hz). Many of us do not understand why they call such things "bass traps". They can help with other stuff, tho'.

There are very few commercially available products that are effective in that range. Modex broadband comes to mind. Not cheap, but neither are your speakers Check out the other modex stuff as well, and the Primacoustic Fulltrap.

Couple of other suggestions...

* toe in your speakers as much as you can, to minimize side wall reflections.

* Put some small rugs or some such in the critically reflective area of the floor, between you and your speakers.

Think again about DEQX. Acoustic control in the sub bass region is a PITA... money, time and space hungry. Go easy on yourself. Everything is digital anyway.

[raticusfortuna]

Originally Posted by jdebonth

I have just replaced a set of PMC FB1i's (that go down to 28Hz) with the much larger EB1i's (down to 19Hz). The low frequency ‘weight’ of these new speakers is making very apparent all kinds of low frequency issues in my relatively small room (see image and dimensions below).

i'm curious to see if it's really the shift from 28hz to 19hz that's making the low frequency issues in that room apparent. all you've done is gone from astonishingly low to astonishinger-ly low. what ever room issues exist kicked in much higher than the 28hz.

the thing that has significantly changed is the speaker design. going from 4 drivers to 6. (or 5 and 7 w/sub) seems like adding a dedicated midrange speaker would radically change the balance/energy of the frequencies of the source material being played.

i would love to see room measurements of the different models playing the same source materials in that room. maybe the 'weight' comes from increased low-mids?

I understand the recommended best approach is to place superchunk type bass traps in all four corners; followed by additional rectangular bass panels where necessary. This will remove all nulls and peaks throughout the entire room.

all?
even so, if you don't take listening seriously enough to put those speakers in a room where you can actually hear what they can do, why bother? it's like buying a maserati and not bothering to get a drivers license. you're never gonna get that bad boy out of the garage.

raticus

[boggy]

Originally Posted by jdebonth

....
I have just replaced a set of PMC FB1i's (that go down to 28Hz) with the much larger EB1i's (down to 19Hz). .......

If you like to have flat response down to 20Hz you may use wideband absorber that works down to 20Hz but minimal depth is 1.2m. This is Tom Hidley / Philip Newell design, and you can find some rough calculations and reference papers in this post

I build smaller room than yours, that is fairly flat down to 4Hz, but speakers aren't port construction (Transmission Line in your case), but sealed, compression design, with second order slope at low frequencies, that ideally match existing "room gain" (acoustical LP shelving filter that exist in small rooms) below lowest room mode, then speaker and room sums flat down to ~4Hz... but... i spent about 30-80cm depth at all sides except ceiling for acoustical treatment... and this, for sure, doesn't like bedroom anymore, and there are still some remains of lowest room modes.

You can't get realistic response with your speakers in your room without serious bass treatment, and without spending more of your usable space for it.

Then, you may have two possibilities:
- use bigger room with enough space for serious bass treatement.... roughly you need usable height+1.5m, usable width+2x1.2m, usable length+2x1.2m

- buy a smaller speakers that can't cause that "wild" low frequency response in your room

In all cases you must try to find a best position for your ears and your speakers, using measurement microphone and some measuring software.

EQ may be an option, but only after (still) serious acoustical treatment, and don't expect spectacular improvements with it.

Hope this helps

Cheers,

Boggy.

EDIT: Here are Burst Decay analysis sonograms for left and right channel of this room I build:

[jdebonth]

Thanks all for taking the time to comment.

My take away is that I need to first really understand what the problem is and hence I will buy a measurement mic + preamp and take some measurements.

I do believe it is in the sub-bass region as I am only really bothered by the exaggerated bass when I play synthetic bass from dub/reggae and electronic music. I listen to alot of home-oriented dubstep and bass heavy electronic/experimental music and this simply becomes unlistenable due to the boomy bass...
Other genres such as rock/jazz and even hiphop are not really giving me problems.

[boggy]

Originally Posted by jdebonth

.....
I do believe it is in the sub-bass region as I am only really bothered by the exaggerated bass when I play synthetic bass from dub/reggae and electronic music. I listen to alot of home-oriented dubstep and bass heavy electronic/experimental music and this simply becomes unlistenable due to the boomy bass.......

I know what you talk about.
Contrary to many beliefs/expectations, serious (wideband) bass treatment below 100Hz down to 20Hz is probably most expensive and most precious part in any excellent acoustic treatment of control/listening rooms, because two reasons:
1. expected high cost of design/labor/material.
2. non expected costs of room space used for bass treatment that you can't use anymore for living/working. Excellent bass treatment may use about 40-50% of useful room volume in small rooms.

Also, your room has nearly square horizontal cross section, then you will have two room modes very close to each other, similar that I have in a smaller room that I build.... you can see it at Burst Decay sonograms... like two yellow/green lines near 50Hz/60Hz, yours will be near ~40Hz.

Hope this helps

Cheers,

Boggy

[avare]

Originally Posted by boggy

Contrary to many beliefs/expectations, serious (wideband) bass treatment below 100Hz down to 20Hz is probably most expensive and most precious part in any excellent acoustic treatment of control/listening rooms, because two reasons:
1. expected high cost of design/labor/material.
2. non expected costs of room space used for bass treatment that you can't use anymore for living/working. Excellent bass treatment may use about 40-50% of useful room volume in small rooms.

+1. An excellent summary!

Andre

[psykostx]

Aside from all mentioned above, heavier curtains (much heavier) and a thick persian style area rug (not the cheap kind) in front of the speakers would help tremendously. Also, I'm sure that the position of the footboard of the bed is causing some midrange mayhem, a carpet should fix that. A bunch of roxul wrapped in fabric and stuffed under your bed might fix a lot of the lower room modes also. Don't go nuts, the idea is to get them to sound good... perfection is not the goal for TV watching ... unless you are a millionaire. Beautiful speakers by the way.

[doctor sumatra]

Originally Posted by jdebonth

Thanks all for taking the time to comment.

My take away is that I need to first really understand what the problem is and hence I will buy a measurement mic + preamp and take some measurements.

excellent! now the fun begins! it would be interesting to compare the room measurements with some screen shots of an in the box equalizer graphically analyzing the tracks in question to see how low the fq's go on the tracks actual tracks.


raticus

[jdebonth]

Yes i would like to understand how low the freq goes in the problematic tracks. Is there a software with which I can do a spectral analysis and zoom in to the 20-100 hz region to see what's going into the speakers in this range?

[DanDan]

I don't see much point in measuring the room or the problem tracks if you cannot do anything about it.
Minimal treatment will have minimal effect.
In between we have small but quite effective LF treatment i.e. Modex Plate or Broadband. You would need quite a few to have any decent effect.
I had the PMC IB1's on trial here. Too bright, odd eh?
Judging from the picture the worst offender here is the listening position.
The back wall usually has the biggest bass build up.
If you don't mind losing some view, I would turn your room around. Speakers at the window. Listening spot out in mid room.
DD

[psykostx]

Originally Posted by DanDan

I don't see much point in measuring the room or the problem tracks if you cannot do anything about it.
Minimal treatment will have minimal effect.
In between we have small but quite effective LF treatment i.e. Modex Plate or Broadband. You would need quite a few to have any decent effect.
I had the PMC IB1's on trial here. Too bright, odd eh?
Judging from the picture the worst offender here is the listening position.
The back wall usually has the biggest bass build up.
If you don't mind losing some view, I would turn your room around. Speakers at the window. Listening spot out in mid room.
DD

Good point...

[audiothings]

+1 to DanDan. Turn to your right and face the glass window and you are most likely in a much better place. As you would probably have figured out, bass tends to accumulate at the boundaries.

You will need to reinforce your curtain to keep out the light when you are watching the television.

i'm curious to see if it's really the shift from 28hz to 19hz that's making the low frequency issues in that room apparent. all you've done is gone from astonishingly low to astonishinger-ly low. what ever room issues exist kicked in much higher than the 28hz.

+1. I doubt very much if the frequency response extension is causing the problem.

[Aof]

Originally Posted by psykostx

Aside from all mentioned above, heavier curtains (much heavier) and a thick persian style area rug (not the cheap kind) in front of the speakers would help tremendously. Also, I'm sure that the position of the footboard of the bed is causing some midrange mayhem, a carpet should fix that. A bunch of roxul wrapped in fabric and stuffed under your bed might fix a lot of the lower room modes also. Don't go nuts, the idea is to get them to sound good... perfection is not the goal for TV watching ... unless you are a millionaire. Beautiful speakers by the way.

His problems are with low frequency. This speakers go down to freaking 19Hz. I doubt even a 50 pound curtain will do any good.

You will need a LOT of acoustic treatment.
As others have suggested, try changing speaker and listening positions.

[jdebonth]

Guys, again thanks a bunch for all the feedback, I am new to this site and wow what a helpful community!

I will definately try rotating the setup 90deg as suggested, lets just hope the GF is OK with it.

Other than this as I use the mac mini as the source component I am able to apply EQ into the signal path very easily; the current playback software I use supports VST and ASU so I can apply a high quality software based EQ.

I will get the SPL mic and preamp just because I want to understand what is happening and what the exact frequencies are that are bothering me. I will then also be able to compare the response when I change around the room layout. Plus this will help me set up the EQ so that I get a flat response in the listening position.

Further I may be moving to a larger listening space in the near future and then it will also come in handy to be able to measure.

Thanks again guys!

[jdebonth]

I have just been playing around with a 31 band graphic EQ VST loaded into my playback software Fidelia. I have noticed that the issues I have been having is primarily in the 40-50 Hz region; if I knock these down -6dB the 'boomy-ness' is COMPLETELY gone. I must be sitting in a strong mode at this freq.

I think what I will do is address the 20-200Hz region by means of digital room correction (I will measure the exact response in listening position and apply the inverted response directly to the EQ) as treatment is simply not feasible/practical. I will then smooth out the response from 200Hz and above with treatment which will be much more 'living room friendly'.

I think this seems like a great compromise.

[DanDan]

I am afraid graphics wear off after a while. Parametrics, carefully used can be useful. I presume a Linear Phase one would be best. PSP Neon springs to mind but the latency may not work for movies. Room Eq Wizard is your friend in such an adventure. Do, try the 90 degrees. I'm betting you will be so happy with it that you will put up with the oddness of blocking the window.
DD

[Aof]

Originally Posted by jdebonth

I think what I will do is address the 20-200Hz region by means of digital room correction (I will measure the exact response in listening position and apply the inverted response directly to the EQ) as treatment is simply not feasible/practical. I will then smooth out the response from 200Hz and above with treatment which will be much more 'living room friendly'.
I think this seems like a great compromise.

Problem is, no matter how much EQ you use, you can't fix dips in your frequency response curve with EQ. Dips occur because there is destructive interference between audio waves. No amount of EQ will bring it up, because the interference is still there. Not only that, but you will put excessive strain on your amplifier.
Also, filter estimation is not so simple, you need computing power for that.
I suggest you check this program and the tutorials, so you know what you are dealing with:
Welcome to R+D

[raticusfortuna]

Originally Posted by jdebonth

I have just been playing around with a 31 band graphic EQ VST loaded into my playback software Fidelia. I have noticed that the issues I have been having is primarily in the 40-50 Hz region; if I knock these down -6dB the 'boomy-ness' is COMPLETELY gone. I must be sitting in a strong mode at this freq.

glad to hear it. thanks for following up.