Help treating my listening room

[Horacio Lewinski]

Hello.

New member, although been lurking for a while. I’m looking to treat my room and would welcome input from the experienced.
My listening room is also my living room, so treatments need to be stealth. The room is 16.6’ x 16’ x 8’. Pictures below. It’s a brick apartment building. Front and back wall are brick. Left “wall” is a glass sliding door floor to ceiling wall-to-wall. Right wall is a (white) panel door: I built with ¼” MDF + ¼” heavy acoustic barrier + 2” fiberglass panel + ¼” MDF – they are heavy! This right “wall” opens to another 16.6’ area surrounded by brick walls.

System: B&W 804S plus two 12” Rythmik subs in DIY sealed boxes. The system is active. The only source is an optimized computer running HQPlayer, that convolves digital filters built on Acourate: 3-way crossovers, plus room correction. Subwoofers are crossed over at 70Hz, run in summed mono. The woofers in the 804S have the passive xo removed and amps drive woofer directly (70 to 350Hz). The mid-to-tweeter passive xo is still in place and the tube amp drives this combo from 350Hz and up.

I’m interested in treating the room, within WAF constraints. I think I could fully treat the front wall and disguise the treatments. Maybe also diffusors in the front and back walls. Extreme treatment would probably be along the lines of hanging a large trap from the ceiling…NOT WAF-approved! But in my dreams.

I figured I should start making sure bass was good. I spent significant time playing with the Rythmik PEQ and other controls to get the flattest possible response. The wife wants the subs side by side with the rack…so no getting the drivers to mitigate the valley at 42Hz. I believe this is a consequence of the SW drivers being 68cm from the front wall. The red frequency response was taken with subs summed in mono, no treatments, from 18 to 100Hz, no DSP applied.

I was expecting the sliding glass wall would be basically transparent to bass waves and the decay would be rather fast…but was wrong. See the red waterfall. I’m thinking it’s not pretty. Am I right to believe I’m targeting a waterfall that decays to 50dB in 300ms?

I had 3 panels I built before which I tried: removed the SW from the front wall 7in and placed a 2” fiberglass panel behind each SW, separated another 2” from the wall. Plus a large 4” thick fiberglass panel, from floor to ceiling, 2’ wide placed across the front left corner. Hoping decay would improve. You can see the frequency response and waterfall chart in blue. Decay improved, but not much I think.

How do you think I should treat low frequencies? Slat absorbers on the front wall? Perforated panels attached to the wall? I’ve come across perforated drywall with 15 to 18%perforated area that could be used to disguise a bass trap behind. I guess the 45 and 35Hz resonances could be treated with Helmholtz resonators.

 

[ddude003]

Hmm... Seems like you have several issues to deal with here... Square room, subs not movable, lots of reflective surfaces... And I am wondering about where and why the woofers and subwoofers are crossed over where they are... Is this a HT or Audiophile only system... By the way, nice System and McIntosh tubed amplifier...

It would be interesting to experiment with your subwoofer placement just to see what could be accomplished just with placement... I know photos can be deceiving and are the speakers and subs centered to the back wall and side walls? It looks like the left hand side is 4 to 5 feet from the left wall and the right is 2 feet...

I would start with some traditional corner base traps and/or Helmholtz resonators and see where that gets you... Maybe drive your B&W 804S woofers a little lower... It looks like they will go down to 38Hz, maybe crossover at 45Hz or 50Hzish with the subwoofers...

I am interested in what others suggest...

 

[Tony V.]

In my opinion the subwoofer crossover at 70Hz is ideal I would even do 80Hz even though the speakers can do below that you put more strain on the amps driving the speakers lower and this could put you into distortion at higher volume levels. The subs are designed to take the lower frequencies much better than the mains.
Although visually the subs look good where they are I agree that different placement would yeild better results. Leaving one where it is and putting the other in the rear corner of the room for example could be much better.

 

[ddude003]

Hi Tony, We are not looking at an ideal environment here... With those B&W 804S sensitivity at 90dB and a McIntosh amp I would not worry about amp strain... I see the issues to be the dip of 5db at 40Hz and then the 20db peek around 57Hzish... My thinking was to drive the area around the peak with different drivers that may be moved physically or EQed from another source... Of course this is all just a thought experiment and some base traps might deal with the 20db peak just fine...

 

[Tony V.]

I wasn't necessarily talking about the amp going into distortion but the speakers could. Just because they are rated down to 35ish does not mean they are efficient at it. I still dont see any logic in using a speaker for stuff down below 60Hz if you have subs that are much more capable as specially considering the subs and speakers are located in virtually the same location..

 

[ddude003]

Hello again Tony, You had said "...put more strain on the amps driving the speakers lower and this could put you into distortion at higher volume levels..." I addressed the amp strain issue... And did not discuss the speaker distortion issue which I will address here...

The B&W 804S woofers are a pair of pair of 6.5″ drivers that utilize Rofacell... In my opinion this configuration will distort less than a single 12" driver driven into low frequencies... Reading the OPs description of how these woofers are already driven by a separate amp (read bi-amped) I would expect these woofers will be clean down into the 45Hz or 50hz range as I suggested above as the crossover between these woofers and the Rythmik subwoofers...

The OP also suggested that he used the "Rythmik PEQ and other controls to get the flattest possible response" from the subwoofer... Yet still having the dip at 40Hz and peak at 57Hzish...

Not seeing any suggestion for the use of this system by the OP as an HT and having left out a hint of center and surround channels I assumed this to be an audiophile stereo system... Hence the classic Dolby or THX 70Hz or 80Hz crossover may not apply...

Further constraints of the WAF limit subwoofer movement where I assume speaker movement/placement to be available... And in my experience even inches of movement of speakers from walls and toe-in can make big differences in acoustics...

There will still be the need for acoustic treatments and EQ... Lets see what other information the OP will provide about the system and his requirements...

Another can of worms... ;^)

 

[Tony V.]

It's fairly obvious by the pictures that it's for music listening not movies as I see no display or soround speakers.
None the less I still don't agree that lowering the crossover would benafit his situation. I do fully agree that some room treatments would go a long way

 

[Horacio Lewinski]

Sorry I didn't reply earlier. It had been a while and was getting no answers and stop checking. Thanks for answering!!

The system is audio only.
Moving subs definitely helps...but that's a constraint. I plan to add one or two additional 12" Rythmiks on the back wall (driver super close to the wall, at 90 degrees) and that will help smooth the valley around 42Hz (it's a multiple of the distance from existing subs to front wall).
The woofers in the B&W can certainly go lower, aren't strained, and the dedicated 400W amps aren't strained either. I play around with xo points within 80 to 60Hz. Had it at 80Hz until recently. But xo are 6th order so quite steep. Maybe making them 2nd order to allow the 6 drivers playing in the trouble region is a good option to explore.

But my key question is around room treatments. No tube traps allowed (built those, wife...emmm...didn't approve. And FWIW they didn't do much for sound either).
I'm thinking of covering the front wall with treatments. A mix of devices tuned for different frequencies, probably. And diffusion too. But first focusing on getting enough low-end absorption. Thinking perforated panel absorbers with varying degrees of perforation % and slat panels. Would that be on the right path?

There was a mistake in the measurements I took: I left enabled frequency dependent windowing to 10 cycles from an earlier measurement of a driver, so redid the measurement today, attached. Note the attached measurements were take with digital room correction turned on. My room definitely needs help with absorption below 110Hz.

 

[Wayne A. Pflughaupt]

Low frequency treatment is difficult, and the necessary absorption often requires large room-encroaching devices. I think I’d be more concerned about those nulls in the 79-90 Hz region, as far as getting an audible improvement goes. At least for starters.

Regards,
Wayne

 

[Horacio Lewinski]

Yeah, those nulls look ugly. In fact I'm looking 70 to 120Hz. The narrow 35dB drops at 74Hz and 87Hz are huge in magnitude yet narrow, making me wonder about their audibility. But those nulls also correspond with ringing seen on the waterfall, so my thinking is absorption should reduce ringing therefore also reducing the null.The same can be said for the null from 105 to 120Hz, although this one is wider and more likely audible.

I guess there's no better way than trying something out. Following Alton Everest Master Handbook of Acoustics, I'm looking at building a perforated panel absorber with 0.2% perforated area, perforated panel 1/2" thick, 6" of air space behind it, with 2" of fiberglass. According to Alton's equation the resonant frequency would be 50Hz or so, but reality tends to shift this higher and fiberglass more so. Sounds like a good/bad idea?

If good, any guidance for how much area I should cover with these? My plan is to use modules tuned to different frequencies, but how much area should be used for each frequency?

 

[Wayne A. Pflughaupt]

The narrow 35dB drops at 74Hz and 87Hz are huge in magnitude yet narrow, making me wonder about their audibility. But those nulls also correspond with ringing seen on the waterfall...

It’s physically impossible for a null to show ringing. If you’re looking at that little protrusion at 80 Hz, it’s not the 73 Hz null. It’s the small, sharp peak just north of it. Regardless, it’s too far down in level to be anything remotely audible.

Your crossover is set for 70 Hz, which is right in the area of those nulls. It may well be that the only thing needed is a simple phase adjustment to time align everything. Can your crossovers accomplish that?

The problem between 35 and 60 Hz can probably be equalized, as can the room mode at 35 Hz.

Regards,
Wayne A. Pflughaupt

 

[ddude003]

Hello Horacio, Those new charts and data help a little bit and I am wondering if you could get some samples without any correction applied so we could maybe see more of the room... Much of your low frequency issues are from corners and I would start there... Treating the forward and rear walls will help if that is all the WAF will allow... Are you referring to the devices in chapter 12 figure 12-42 for base and wide band absorption? If so, those should work as designed and I would look to cover 1/4 to 1/3 of the wall(s) surface if you are not treating the corners... Build two at a time and see how they work after placing and adjusting each pair... You can also toss them under the couch and love seat too... You can visualize what frequencies your room has issues with and where the most energy is, read where to place absorption, with the https://amcoustics.com/tools/amroc room calculator... I would tune the room first then apply EQ...

 

[Horacio Lewinski]

It’s physically impossible for a null to show ringing. If you’re looking at that little protrusion at 80 Hz, it’s not the 73 Hz null. It’s the small, sharp peak just north of it. Regardless, it’s too far down in level to be anything remotely audible.

Regards,
Wayne A. Pflughaupt

Good point. Thanks for noting!

 

[Horacio Lewinski]

Hello Horacio, Those new charts and data help a little bit and I am wondering if you could get some samples without any correction applied so we could maybe see more of the room... Much of your low frequency issues are from corners and I would start there... Treating the forward and rear walls will help if that is all the WAF will allow... Are you referring to the devices in chapter 12 figure 12-42 for base and wide band absorption? If so, those should work as designed and I would look to cover 1/4 to 1/3 of the wall(s) surface if you are not treating the corners... Build two at a time and see how they work after placing and adjusting each pair... You can also toss them under the couch and love seat too... You can visualize what frequencies your room has issues with and where the most energy is, read where to place absorption, with the https://amcoustics.com/tools/amroc room calculator... I would tune the room first then apply EQ...

I have the Fourth Edition. In it chapter 12 is about refraction so I'm guessing you have a different edition. I'm looking at perforated panel absorbers in chapter 9, figure 9-33.

Since the system is 3-way active using Acourate to generate filters than include crossovers and room correction I cannot run a full sweep without DRC. That's why my initial post was showing up to 100Hz thru subs only: I connected the subs to a soundcard connected to the laptop with REW and played the subs without room correction. Will do again, but will be in a couple days.

I plan to treat the front wall including corners. However the treatment will be on the front wall, 6" thick, and flush to the side walls. Can't do the triangular cross section for corner treatment. It will include, though, the whole edge between floor and front wall and FW and ceiling...which are also corners.

 

[ddude003]

I have the fifth edition... Copyright © 2009, 2001 by The McGraw-Hill Companies, Inc. Sorry, the devices I see are indeed perforated panels which are described as an adaptation from modules used by the BBC... These are tuned by perforation layout and distances per the equations for the given frequencies you are looking to absorb... Your plan to treat the front wall including the corners as you describe will help a lot with excess base and broadband energy...

No rush with the the subs without room correction data...

 

[Matthew J Poes]

I have the Fourth Edition. In it chapter 12 is about refraction so I'm guessing you have a different edition. I'm looking at perforated panel absorbers in chapter 9, figure 9-33.

Since the system is 3-way active using Acourate to generate filters than include crossovers and room correction I cannot run a full sweep without DRC. That's why my initial post was showing up to 100Hz thru subs only: I connected the subs to a soundcard connected to the laptop with REW and played the subs without room correction. Will do again, but will be in a couple days.

I plan to treat the front wall including corners. However the treatment will be on the front wall, 6" thick, and flush to the side walls. Can't do the triangular cross section for corner treatment. It will include, though, the whole edge between floor and front wall and FW and ceiling...which are also corners.

Hey Horacio could you do a full measurement of your system setup as you listen full range. Measure the left, right, and both with the subs and if possible, with the subs turned off. If you can post the mdat file I can take a look and see if the issue is your sub phase, placement, or modal.

Just for testing purposes you may want to consider buying some packaged wall insulation and sticking it in he corners in the package. Then measure. Around me I can get something called Safing insulation. It’s a fire Safing insulation for walls, 8lb density rockwool, and is perfect for bass traps. If you can’t get that even the low density fluffy insulation is ok if it’s still packaged. That can help you see what is going on.

Now as for how to measure and assess, because this is minimum phase ringing will always coincide with peaks. That means the waterfalls are not very valuable. I’ve totally stopped using them (other than to make a point) and strongly believe the obsession with them in room treatment is totally misplaced. I’ve never seen a situation where there is ringing that doesn’t coincide with peaks that I can’t explain (such as noise or bad measurements). Instead I suggest using two other methods. I use filtered impulse responses that i filter near the area of a peak Or dip I’m trying to treat. I then compare the shape and tail of the impulse before and after. I use the overlay tool to compare. The pair treatment should be more symmetric and have a shorter tail.

The second method I use is wavelet. This is recent for me. I knew what it was but treated it like waterfall. After a member on this forum suggested using wavelet for other reasons, I decided to re-analyze some past room data looking at wavelet. I suddenly found I could see reflections, ringing, etc much more clearly.

 

[Horacio Lewinski]

Hello Horacio, Those new charts and data help a little bit and I am wondering if you could get some samples without any correction applied so we could maybe see more of the room...

Please find attached the frequency response, waterfall, and mdat file for a sweep without DSP applied, only the subs playing in summed mono, with the subs' PEQ enabled, 15 to 100Hz (despite subs being xo around 70Hz when the system runs full-range).

 

[Horacio Lewinski]

Hey Horacio could you do a full measurement of your system setup as you listen full range. Measure the left, right, and both with the subs and if possible, with the subs turned off. If you can post the mdat file I can take a look and see if the issue is your sub phase, placement, or modal.

Sorry won't be able to run these until the weekend, but attaching the mdat of a full range sweep done last weekend with both left and right and subs summed mono playing simultaneously. Does this help some?

 

[Matthew J Poes]

Sorry won't be able to run these until the weekend, but attaching the mdat of a full range sweep done last weekend with both left and right and subs summed mono playing simultaneously. Does this help some?

I’ll take a look as soon as i can. I literally just got back from a talk I did in DC so may not get to it right away.

 

[NBPK402]

A little bit unrelated of a question... how do you like you air conditioner in the first pic? What brand is it, and did you install it yourself?

 

[Horacio Lewinski]

A little bit unrelated of a question... how do you like you air conditioner in the first pic? What brand is it, and did you install it yourself?

Why do you say unrelated?

It's an LG which I've had for 10 years. Like it very much. Truth be told it's not used on a daily basis at all. I had someone install it for me.

 

[NBPK402]

Why do you say unrelated?

It's an LG which I've had for 10 years. Like it very much. Truth be told it's not used on a daily basis at all. I had someone install it for me.

I had said unrelated, because your post was about room treatment. Is it pretty quiet...I am asking because we might need to get an AC unit, and would like to hear from someone who has one. I was wondering if it is very noticeable when listening to music, or movies.

 

[Matthew J Poes]

Sorry won't be able to run these until the weekend, but attaching the mdat of a full range sweep done last weekend with both left and right and subs summed mono playing simultaneously. Does this help some?

I apologize for the very long delay in reviewing your results.

I've looked at your results and found a few things.

First, it looks like your subwoofer has significant time delay associated with it. The poor integration at the crossover point is likely a result of this. It appears to be delayed by about 100ms at 80hz, where there is a spike, and about 50-60 ms over the rest of the range. This even shows up in the wavelet spectrogram, where the peak in the LF's doesn't smoothly transition to a greater delay (as you want to see) and instead has a sudden and abrupt shift. At 80hz it juts out to 40ms for the peak. It is normal for the peak SPL to be more "delayed" at LF's, but this is excessive and unusual. Filtered IR's show the same thing, at 63hz the peak is around 40ms. You need to either remove 40ms of time delay from the subs or add it to the mains (roughly, being exact here isn't too important).

The EDT shows that there is an uneven amount of absorption in the room. It looks to me like most typical untreated rooms or rooms treated using basic absorption panels. There is a bias toward the mid and high-frequency absorption, some spikes, and a lack of LF absorption. Again, looking at the filtered IR's also shows the large difference in decay. We expect this to a point, but it is large in this room. This kind of behavior is so ubiquitous with untreated rooms that I give the exact same advice to everyone without seeing measurements, you need some bass traps. It isn't to fix modes or smooth the response, it's just to rebalance the room decay to be more even at LF's.

I see some evidence of reflections but some of them don't make a lot of sense to me and make me think this might be the delay at LF's. So with a 250hz 1/3oct filtered IR I see a doubling of the IR peak at 4.5ms and 40ms. That difference in distance is equal to nearly 40 feet. That doesn't make a lot of sense to me unless it is caused by the delay issue. I doubt you have such a huge LF reflection at 250hz that is 40 feet away. The ceiling/floor reflections show up as a difference in distance of 4.3 feet, which makes sense.

I apologize if you already explained this, but why might I see so much delay in the subwoofer? Are you using DSP?

 

[Horacio Lewinski]

I apologize for the very long delay in reviewing your results.

I've looked at your results and found a few things.

Thank you for taking the time to look into this!! Much appreciated!

Great opportunity to learn, as I have no idea how you are arriving at these conclusions.

First, it looks like your subwoofer has significant time delay associated with it. The poor integration at the crossover point is likely a result of this. It appears to be delayed by about 100ms at 80hz, where there is a spike, and about 50-60 ms over the rest of the range. This even shows up in the wavelet spectrogram, where the peak in the LF's doesn't smoothly transition to a greater delay (as you want to see) and instead has a sudden and abrupt shift. At 80hz it juts out to 40ms for the peak. It is normal for the peak SPL to be more "delayed" at LF's, but this is excessive and unusual. Filtered IR's show the same thing, at 63hz the peak is around 40ms. You need to either remove 40ms of time delay from the subs or add it to the mains (roughly, being exact here isn't too important).

Where/how do you see this?
Indeed, I'm using DSP. But no time delay is introduced through it - that I know of. Might it be the phase adjustment in the subwoofer PEQ?

The EDT shows that there is an uneven amount of absorption in the room. It looks to me like most typical untreated rooms or rooms treated using basic absorption panels. There is a bias toward the mid and high-frequency absorption, some spikes, and a lack of LF absorption. Again, looking at the filtered IR's also shows the large difference in decay. We expect this to a point, but it is large in this room. This kind of behavior is so ubiquitous with untreated rooms that I give the exact same advice to everyone without seeing measurements, you need some bass traps. It isn't to fix modes or smooth the response, it's just to rebalance the room decay to be more even at LF's.

What kind of traps would you recommend? Last weekend I built, but haven't finished, perforated panel absorbers tuned to 38Hz, with perforated area of 0.13%. Will finish them this weekend and post some pictures.

I see some evidence of reflections but some of them don't make a lot of sense to me and make me think this might be the delay at LF's. So with a 250hz 1/3oct filtered IR I see a doubling of the IR peak at 4.5ms and 40ms. That difference in distance is equal to nearly 40 feet. That doesn't make a lot of sense to me unless it is caused by the delay issue. I doubt you have such a huge LF reflection at 250hz that is 40 feet away. The ceiling/floor reflections show up as a difference in distance of 4.3 feet, which makes sense.

I apologize if you already explained this, but why might I see so much delay in the subwoofer? Are you using DSP?

Yeap, xo are done on Acourate (without delays) and also room correction is built into the filters.

 

[Matthew J Poes]

I’ll try to post some screen shots from REW of what i looked at to come up with this. For now let me give you some breadcrumbs to look on your own at least.

First, if you look up excess phase under REW help you will find an article by John that talks about its value for time alignment. Take a look at that first. Create a minimum phase version under group delay and then look at the excess phase plot. Note the rise in delay at LF’s along with all the peaks. That is the group delay caused by your filters. It appears that there is so much delay being caused by the filters that the Lf’s are averaging about 20-40ms of delay. Some peaks are out past 100ms. At LF’s we aren’t too sensitive to this but still that is pretty high. If you designed a speaker with that much delay you would probably consider it a bad property.

Second look at the RT60 screen and then look at TS. TS is the time of the peak of the impulse st a given frequency. It shows delay. We always see a little delay at LF’s and often see more delay in LF’s when subwoofers are in a system than with full range. However you still want to see that delay stay under 20ms and to be very smooth if possible. Sudden peaks or dips near the crossover are a sign that you may have too heavy a hand in the filtering.

Finally, go to the spectrogram window and create a wavelet with the Y axis and frequency and the X axis as time. This creates a classic DIRAC impulse graph. If you measured an ideal speaker outside you would get a symmetric Christmas Greer shape. A kind of swoopy pyramid. It shows the amount of energy over time that enters the system at each frequency. There is always an increase in energy over time as you get lower in frequency. Further, all real world systems will show a dog leg or dog tail shape at LF’s with a right temporal bias. This just means a slight delay in the LF peak. What you look for is a smooth transition and a relatively smooth buildup of LF energy over time. So while the peak may happen 20ms later below 200hz than above, you still expect this to be a smooth transition. What you often see instead is a sudden shift out by 20-40ms and the buildup happening later in time. This can only be caused by delay in the LF’s.

This delay is likely a kind of group delay. I think it could be caused by the filters but I don’t think it’s just an all pass filter. It’s an actual time delay.