Room Treatments

Posted by: 2x6spds

Room Treatments - 11/05/16 02:24 AM

I have a wickedly unpleasant 800Hz spike in my living room. Major bass suckout as well. It's a peculiarly shaped room with ceiling which ranges from 12 to 20' and then a stairway which goes up to a landing which is 30' above the living room floor. Worse, there is a skylight which is a 3.5' x 3.5 'chimney' up to the slanted skylight. Acoustically, a nightmare.

So, I built one (building another) 7' x 4' framed treatment with 2" of rockwool behind a patterned fabric. I will try to post pictures.
[img]https://postimg.org/image/59j3dwyt7/[/img] [img]https://postimg.org/image/ijg47bz65/[/img]

I'm hoping this will tame the 800Hz. Ian suggested multiple subs for the bass problem. I have 1 EP600. Might be cheaper to get a new house.
[img:center]https://postimg.org/image/ijg47bz65/[/img]
Posted by: bridgman

Re: Room Treatments - 11/05/16 03:58 PM

Nice... like camo for a fine living room.

I was thinking that a Helmholz resonator tuned for 800 Hz and filled with absorbent material would be useful, but I had trouble finding dimensions that would cooperate.
Posted by: 2x6spds

Re: Room Treatments - 11/05/16 04:52 PM


Wise guy!

Of course, this's guy http://preserve.lehigh.edu/cgi/viewcontent.cgi?article=2015&context=etd master thesis agrees with your concept.
Posted by: bridgman

Re: Room Treatments - 11/06/16 07:41 PM

Yeah, I found that but it used long words and I was really tired.
Posted by: 2x6spds

Re: Room Treatments - 11/07/16 07:49 PM

Posted by: 2x6spds

Re: Room Treatments - 11/07/16 09:06 PM

Helped bass suck out ... 800Hz spikey better ... needs more help
Posted by: AAAA

Re: Room Treatments - 11/08/16 05:37 AM

If I had a better idea of your room I could help with the bass issue. The 800hz issue sounds like a mechanical resonance, not an acoustical one. If I had to guess the tweeter is under damped suffering distortion. Is this your EPOS setup?

The panels you put up will lower decay time and reduce parallel flutter issues. They cant fix a bass null issue or mechanical resonance. frown You have to move the speaker or listener for Bass problems.
Posted by: AAAA

Re: Room Treatments - 11/08/16 05:53 AM

Tighten up the drive units.
Posted by: Mojo

Re: Room Treatments - 11/08/16 11:51 AM

It's his tube amps. The natural frequency of a grid on a pentode is 800Hz.
Posted by: 2x6spds

Re: Room Treatments - 11/08/16 03:34 PM

Thank you fellas
I am using a pair of Emerald Physics EP100.2SE power amplifiers, a pair of Emerald Physics EP2.8 speakers with DSP.

Thanks for the suggestion about the tweeter and drivers!

The designer of these speakers is coming out this Thursday with an upgraded DSP and other goodies.

I'll report back
Posted by: 2x6spds

Re: Room Treatments - 11/08/16 03:48 PM

I got an EP600 subwoofer.

My Yamaha M80 amp is coming home after some upgrades and maintenance.

I am going to triamp these Emerald Physics using the EmPh100.2.SE monoblocks, the Yamaha M80 and the Odyssey Khartago. I would like to get a tube amp into the lineup at some point.

Serenity Now, thanks for the tip!
Posted by: bridgman

Re: Room Treatments - 11/23/16 10:06 PM

What I'm struggling with is that 800 Hz corresponds to a pretty short wavelength, eg 1/2 wave is maybe 8-9". Seems too short for the spike to be a room or speaker placement issue unless maybe you have speakers ~1.4 feet from a wall ?

Or your DSP has become self-aware, starting in the 800 Hz band.

Mojo - LOL !!

I don't *think* the skylight dimensions are right for it to contribute to the 800 Hz spike but I would be tempted to temporarily stuff it full of fiberglass or rockwool insulation just to be sure. If your 800 Hz spike becomes a suckout then you just take half the insulation out.

It does sound like the kind of room we would ask for more details about just because it would be fun watching you try to draw it smile
Posted by: 2x6spds

Re: Room Treatments - 11/23/16 10:33 PM

I swapped out the pair of digital amplifiers for the 5 watt per channel SET tube amplifier. The spike is gone. I don't get it as I am running the amps through the same DSP.

I picked up a second Antique Sound Labs MG SI 15DT. This one does not have the V-Caps I used to upgrade my first one of these amps, but it does have a pair of super Svetlana Winged-C 6550 tubes, don't know what 12ax7s it's running.

I figure I'll put my other ASL amp into the Emerald Physics system, and swap the Svetlanas for the Tung Sols. That amp uses some wonderful Mullard 12ax7s.

I just got my Yamaha M-80 (M stands for Monster I think) back from its tweaking at Vintage Audio. I'm going to tri amp the Emerald Physics EP2.8s, using the tube amp for the mids, the Yamaha for the bass driver, and maybe the Odyssey Khartago for the coincident tweeter/driver.

I ended up leaving the EP2.8s in the living room for the parties, no one put an elbow through any of the carbon fiber drivers. The system sounded just great.

Still a difficult room.




[img:center]http://img.photobucket.com/albums/v192/2x6spds/20161122_153757_resized%201.jpg?t=1479872215[/img]

Posted by: 2x6spds

Re: Room Treatments - 11/23/16 10:41 PM

The EP2.8s look like Daleks from Dr. Who. You can see the Axiom EP600 peaking out to the left of the left speaker in the picture above.


[img:center]http://img.photobucket.com/albums/v192/2x6spds/20161122_153757_resized%201.jpg?t=1479872215[/img]
Posted by: Mojo

Re: Room Treatments - 11/23/16 11:29 PM

I don't know what to say other than if you live in a restaurant, all bets are off for audio!
Posted by: bridgman

Re: Room Treatments - 11/24/16 12:42 AM

2x6spds dining room isn't much different from my living room in terms of "interesting" combinations of materials and dimensions. The tiniest change makes a difference:

Sound & imaging are fantastic with this setup (ignore the blur):


but dead and lifeless with this setup (blind on right hand window pulled down, sofa cushion moved down to floor):


BTW I just ordered a pair of M3v4 refurbs so I can do something a bit more like an apples-to-apples speaker comparison. I have always really enjoyed M3's every time I get a chance to listen to them.
Posted by: 2x6spds

Re: Room Treatments - 11/24/16 01:46 AM

Hey Bridgeman, you are my brother! Look at all those speakers!

That's a picture of my living room. I used the dining room for the buffet.

I rent the tables and chairs. I've been doing these pre-Thanksgiving dinners on Mondays and Tuesdays for over 20 years. After all, the turkeys are not getting any younger and nothing good is happening to the turkeys between Monday and Thursday.

Everyday is Thanksgiving!



I agree with you about the M3s. I love listening to them. I think they may be Axiom's best all-around speakers.

[img:center]http://img.photobucket.com/albums/v192/2x6spds/20161121_194017.jpg?t=1479883806[/img]

BTW, those are the magnificent Michaura M65s in the background. Incredibly solid hex shaped Rosewood cabinet and the familiar 6.5" drivers. They use Axiom's 0.75" Titanium tweeters. They are one of the few bookshelf speakers that I prefer to the M3s, although, it is a close call. The left speaker is sitting atop an EP500 subwoofer. The tube amp is the wonderful Antique Sound Labs MG SI 15DT with the V-Cap modification, Tung Sol 6550s and Mullard 12ax7s.
Posted by: AAAA

Re: Room Treatments - 11/24/16 04:05 AM

Floor center channel. frown

John, top down/bottom up honeycomb cellular shades are a great option for reducing window coincidence effect from near speaker placement. Works great.
Posted by: bridgman

Re: Room Treatments - 11/24/16 04:08 PM

Originally Posted By 2x6spds
That's a picture of my living room. I used the dining room for the buffet.


I guess that explains the speakers and the fireplace blush
Posted by: AAAA

Re: Room Treatments - 11/24/16 04:19 PM

Those are spoiled dinner guests either way. smile
Posted by: 2x6spds

Re: Room Treatments - 11/24/16 08:49 PM

Oh yes, Serenity, they surely were!
Posted by: bridgman

Re: Room Treatments - 12/02/16 01:21 PM

M3s are in and sound as great as I remembered. No time for serious listening yet but ran a few different CDs/genres through them as a quick check.

I wasn't sure how things like bass pedals were going to come through but White Mountain (Genesis) and Echoes (Pink Floyd) sounded really good. Not sure if the initial bass at the start of Echoes is pedals or bass guitar but sounds smooth & decently flat response either way.

Initially I put them on the stands and put the Sierra 1's on top of the M40s, but concluded that the M3's sounded better if they were a bit closer together.





Sorry for pic size, thought my phone used to make "small" pictures smaller than this when sending. Must be one of the recent Blackberry OS upgrades.

EDIT - that's interesting...pics seems smaller on the web page than when viewed locally, so ignore apology above.

Something to figure out on the weekend smile

BTW the new packaging is really good - Axiom may have finally come up with something that even a courier can't break, at least for the lighter speakers.

I guess you could still get damage if the driver practiced caber tossing with an M80 or M100 though.
Posted by: bridgman

Re: Room Treatments - 12/02/16 01:24 PM

The one thing I always find truly disturbing is thinking about how much money I would have saved if my first Axiom purchase had been M3s instead of M2s.

- wouldn't have needed to buy a subwoofer

- without subwoofer wouldn't have realized how good sound on modern DVDs was

- without that I wouldn't have been compelled to get AV receiver and surround speakers... or projector... or a few hundred DVDs/BluRays...
Posted by: bridgman

Re: Room Treatments - 12/02/16 01:49 PM

%^$#$#&$*^@!!

I have short pieces of 1x1 lath under the front feet of the M40s to angle them up a bit, since my ears tend to be further from the ground than most. This means that the top of the M40s angles back a bit.

So I'm working in the office, DSOTM is playing on the M3s. I hear a brief "grunk" kind of noise, wonder if I have volume up too high (driving them with 250 WPC amp) but don't hear any other noises so figure the noise came from outside somewhere.

I go back into the living room & sit down, notice that the imaging doesn't sound right. Looking at the speakers something doesn't look right either, one of the M3s is missing !

The right hand M3 vibrated towards the back of the M40 (angled surface + DSOTM) and fell off onto the rockwool bundle I'm using as an impromptu bass trap. No apparent damage though. The left hand M3 had slid to the back of its M40 and was still moving slowly.

M40s are now level and rubber dimples installed on the M3s. Hopefully everything will stay put now.
Posted by: Gr8_White_North

Re: Room Treatments - 12/02/16 02:01 PM

impressions of M3 vs Sierra's
Posted by: bridgman

Re: Room Treatments - 12/02/16 03:38 PM

Not much yet, still playing with setup. Sierras like to be toed in towards listener while Axioms seem better either toed in less or pointing straight ahead. I really need a speaker switch box, going to start another thread on that.

- Sierras sound a bit more neutral (a bit less midrange) but I don't know which is "right"

(but the slightly more forward midrange in the M3s is also something that gets a lot of positive comments re: detail)

- Sierras seem to have a bit more bass but M3s seem to distinguish different bass frequencies more readily

- Sierras hit volume limits at relatively lower level than M3s (surprisingly low on some electronica)

- didn't notice big differences in efficiency

- main thing I noticed about Sierras in comparison with larger speakers was more detail in complex passages (suspected less cabinet vibration but only a guess)... relative to M3s the difference certainly isn't as obvious, may not be there at all

(if I had to use short words I would say that the Sierras sounded more "solid" than the larger speakers but I haven't done enough testing yet to tell if that is still the case vs M3)

(this may be why I have always liked bookshelf speakers on stands - thought it was 2-way vs 3-way crossover but maybe it was small/rigid cabinet)

So far it's turning into one of those "they do sound different but I'm not sure which one I like better" things, but the differences aren't as big as they were between Sierras and larger speakers eg M60s.

EDIT - I was starting to think along the lines of the Sierras sounding a bit "bigger" than the M3s, but after I moved the M3s out to the stands and toed them in a bit more I started getting the same "big" sound from the M3s, at least as close to the same as I could detect when unplugging & moving speakers.

Speaker reviewing is hard, at least doing it well is hard.
Posted by: bridgman

Re: Room Treatments - 12/02/16 05:21 PM

Originally Posted By bridgman
Speaker reviewing is hard, at least doing it well is hard.

I guess it's a lot easier if you know what conclusions you want to reach before you start smile
Posted by: bridgman

Re: Room Treatments - 12/04/16 08:25 AM

OK, I have pretty much ground to a halt re: comparing M3s with Sierra-1s. The M3s are quite a bit more forward than the Sierra-1s (most reviewers describe the Sierra-1s as "warm" which AFAICS is the opposite of "forward") and it's really hard to tell if the other differences I hear are a function of frequency response or something else.

I can find passages where the Sierras sound less "annoying" than the M3s (generally busy passages with high vocals and edgy instruments at the same time) but in most cases I can hear the annoying sound on the Sierras, it's just quieter.

What I can say is that reviews talking about the extra detail you hear with M3s (and presumably even more so with Axiom speakers using the 5.5" driver) are spot-on - little things like finger movement on a guitar fretboard are noticeable on the M3s but go un-noticed on the Sierra-1s unless you really listen for them. The problem is that I wasn't sitting in the studio for the recording sessions so I have no idea which is more correct. There have been a few cases where I have been out of the living room, walk back in, make some kind of observation about how much better speaker X is and find that it's actually the other speaker playing (a short memory is a useful asset).

BTW I ended up moving the speakers around a bit more, so that both pairs were the same distance apart and I just had to move my head a bit to the left for M3s and a bit to the right for Sierra-1s. Makes one think about "Walk like an Egyptian".

I'm going to pick up some 2P2T relays and knock together an A/B switch box but without also having switchable EQ to take out most of the FR differences it's going to be hard to get much further. Hopefully someone makes a PC-based EQ that can apply 1/2 the EQ to one signal then on a key press apply the opposite EQ so that neither speaker has the advantage of being un-EQ'ed.

The one clear take-away from this is that M3s and Sierra-1s are both really nice speakers. I need to do some A/B testing with the M60v4s but at the moment I'm thinking there is something in my listening preferences that leans towards smaller speakers.
Posted by: bridgman

Re: Room Treatments - 12/04/16 09:33 AM

Listening to the end of "Cinema Show" from Selling England By the Pound I do get the impression that the balance of Sierra-1's might be a bit closer to "correct" than the M3's. There is a point near the end where bass guitar carries the <not really melody but most interesting part> and that gets lost a bit on the M3s but sounds just right on the Sierras.

Seems like I do need to start playing with EQ... I suspect we're only talking about a couple of dB here. Somewhere between the two is probably ideal...
Posted by: bridgman

Re: Room Treatments - 12/04/16 11:32 AM

There probably should be some kind of "yeah that's what it was supposed do sound like" web site where we get speakers and rock stars together...
Posted by: bridgman

Re: Room Treatments - 12/13/16 08:20 AM

Originally Posted By bridgman
OK, I have pretty much ground to a halt re: comparing M3s with Sierra-1s. The M3s are quite a bit more forward than the Sierra-1s (most reviewers describe the Sierra-1s as "warm" which AFAICS is the opposite of "forward") and it's really hard to tell if the other differences I hear are a function of frequency response or something else.


So I had one of those "Mein Fuhrer, I can walk !!" moments yesterday when I remembered that the receiver I was using had tone controls, although I had not touched them since... forever.

I turned the treble down just the tiniest smidge, maybe 1 dB (as small as I could do without the detent pushing it back to zero) and that shifted the balance maybe half way towards what I heard from the Sierras and seems to give just the sound I want.

Ian reminded me that I had already encountered a case where the optimum room treatment changed a bit depending on the speaker I was using (believe that was with the M60s and replacing the couch) so I'm going to revisit the blind from a few posts ago (the one that made Sierras sound dead & lifeless) and see if I can get similar results without tone controls when time permits.
Posted by: MatManhasgone

Re: Room Treatments - 12/13/16 08:40 AM

I am convinced that our ears and our brains are the worst enemies to our wallet when we get that itch for upgradeitus.

I think it is psyco-acoustic need for change that drives us. You go out and buy a setup and tweak and change until you get something that you convince youself is much better sounding than whatever you had before. And you live with it for 3-5 years and then suddenly your brain starts to tell you that it isn't good enough and there is something better out there. Be it from reading a review that said Speaker X is the best sounding or that Amp Y just improved the sound night and day. So suddenly you convince yourself that what you have isn't cutting it.

So you get into the position that Bridgman is in where he is testing two speakers that are different from each other. What one is better? Neither. they are different from each other. If you had been listening to the same sound feel for the past 3-5 years it is bordum in your brain that convinced you to change. So you get something new to change the sound that was perfect before but suddenly now is not.

Likely if you forced a change in the placement and treatments inside your room every 9-12 months, your brain will never get use to or tired of what you have and you could likely save yourself a whole load of money.

This of it like toys for a cat. If you leave your pet cat 10 toys out to play with, then it will play for a few days and then get boarded of all of them. If however you put out 1 toy for a few days then put it away and swap it for a different toy, then the cat would be entertained forever. by the time you get around to the 10th toy it would have completely forgotten about the 1st one and as far as it knows, this is a totally new toy.
Posted by: Gr8_White_North

Re: Room Treatments - 12/13/16 11:18 AM

Matt , you left out guys like me. Same speakers for 38 yrs , I have developed such a love of them that no other speaker makes me feel the way they do. I can relive my youth any time just by cranking up some Van Halen or Ozzy etc. But yeah , for the theater there is the constant search for that feeling I got when I got my HPM 900's , never had an urge to replace them and I listened too lots of speakers when I was younger and there were shops aplenty to audition speakers in.
Posted by: bridgman

Re: Room Treatments - 12/13/16 11:20 AM

In my case I had "perfect" sound 30 years ago (or at least as close to perfect as I could afford) back when I had a lot more free time to spend on speakers & room treatments. Then life got in the way.

Since then I have spent all my scraps of free time trying to get back to what I was hearing 30 years ago smile
Posted by: bridgman

Re: Room Treatments - 01/10/17 05:25 AM

Originally Posted By bridgman
Ian reminded me that I had already encountered a case where the optimum room treatment changed a bit depending on the speaker I was using (believe that was with the M60s and replacing the couch) so I'm going to revisit the blind from a few posts ago (the one that made Sierras sound dead & lifeless) and see if I can get similar results without tone controls when time permits.


Finally got a chance to try the M3's with the blind pulled down (the change that mucked up Sierra-1 imaging). As Ian hinted, it had exactly the opposite effect with M3s.. cleaned up the imaging and significantly improved the overall effect. First guess is that the wider dispersion of the M3s meant that more midrange energy was bouncing off the glass... and since the other side of the listening area was open space (and a sofa) the result was unbalanced sound until I pulled the blind down.

This leads to the slightly scary observation that A/B speaker testing in an asymmetrical listening area is going to potentially be unfair to one of the speaker sets if the A and B speakers have significantly different response/dispersion patterns... and even a perfectly symmetrical room may end up requiring slightly different room treatments for best results with each speaker.

This may help to explain why reviewers often seem to end up preferring their reference speakers to most of what they test - if the room treatments are optimized for their reference speakers then anything significantly different is going to be tested with sub-optimal room treatments.

To further complicate things, I was up near Axiom before the holidays and Ian invited me to stop in and do some double-blind testing with the Sierra-1's. That was eye-opening to the extent that I'm still trying to get my head around it.

We did a few rounds of tests and in the second round I was ABSOLUTELY sure that Debbie had switched in completely different speakers. I was thinking maybe LFR's and Mini-T's from the sound (bass response and imaging both seemed significantly different from the first round) but in fact it was the same speakers as before (M3s and Sierras) with the positions physically reversed, the volume turned up a bit higher (I did that because I felt the "new speakers" handled the volume better) and the ventilator noise cut down by stuffing a rag in the vent.

I was totally surprised when the curtain was pulled back.

The third round was equally interesting - this time Ian was working the controls; he also picked a different set of tracks from me. As the volume increased the M3's seemed to open up while the Sierra-1's started to sound "hard"... and the relative frequency response differences between the speakers seemed less. Ian noted that drivers can start exhibiting compression at surprisingly low sound levels and so managing the compression characteristics of (for example) woofer vs tweeter was one more important part of maintaining good sound at different levels.

It's hard to summarize everything in a couple of lines but it's clear that choice of music and volume level make much more difference when comparing speakers than I had previously thought. I was less surprised by the impact of moving the speakers around simply because I had done a lot of that kind of testing already. I was also surprised by how much "less different" (and how good) the two sets of speakers sounded in Axiom's listening room compared to mine - possibly because their room is relatively symmetrical while mine is off-center with room treatments on one side balancing open space on the other.

Anyways, it was very interesting and educational - thanks to both Ian and Debbie.
Posted by: Mojo

Re: Room Treatments - 01/10/17 08:42 AM

Interesting observation about the room and treatments. This may explain my impressions of the Dramcatchers vs the M3ti and M22ti in my 2.1 space. It will be interesting to compare the M5HP when you get them.
Posted by: AAAA

Re: Room Treatments - 01/10/17 08:18 PM

Thanks for the report. It would be fun to do that test and have the curtain reveal your mind was convincing you of who knows what. smile. I really like reading your impressions from your testing.

I have also found speakers take on a different character when they are pushed hard as well. Sometimes bad and compressed, sometimes boxy, sometimes spacious and weightless. In my setup with LCRs driven with 150wpc outboard amps my little center channel loves to be pushed hard, while my towers start to complain earlier. I think this is also due to cabinet resonances ringing like a bell at certain frequencies when pushed as well.

What I have also found, strangely enough, is that changing the amplfier gain to preout signal balance has a big impact on the perceived focus and clarity on my towers. My center likes more amp with lower pre setting while my towers like more pre with lower amp setting. I can effectively enhance the width of my soundstage and transparency by juicing up the amp, but at the expense of focus and pinpoint imaging. It has to be distortion related.

Since renting high powered amps I got curious and discovered I am able to vary the gain of my amp by opening it up and changing a jumper setting -leaving it completely variable. After a bunch of testing I concluded I was able to somewhat replicate the pro amp sledgehammer power required to approach "dread" but my speakers lose composure once asked to deal with all that power. The solution was to apply a higher preout voltage and turn the amplifier gain down. The end balanced spl at all channels is 75db, and pink noise measures the same on each relative amp setting once level matched. But with content they sure thud harder with more amp gain when applied. They dont seem to like it when asked to.... Lol.

Wait a sec, is this the synergy thing audio blokes get hung up on?

Again, I like reading your adventures, as I am a sidequest audio nutbar too. smile. Keep em coming.
Posted by: Thasp

Re: Room Treatments - 02/06/17 09:58 PM

Have you considered trying owens corning 703 instead of wool? Much better absorptive properties. I have about 16 panels in my room with 2" 703, and two in the corners as bass traps with 4" corning 703. It makes all the difference in the world, take them out and I almost feel like I'm listening to bose. smile

I was cheap so I wrapped mine in burlap in wooden frames we cut ourselves - but I'm sure there's some nice breathable fabric that would look great as well!
Posted by: Gr8_White_North

Re: Room Treatments - 02/06/17 10:12 PM

Roxul Safe & Sound works great also.
Posted by: 2x6spds

Re: Room Treatments - 02/07/17 01:52 AM

Wow, Serenity! That was an eye opener. I have my Yamaha M80 and Antique Sound Labs tube amp maxed, and control volume with the Sonic Frontiers SFL-1 preamp. For some reason, long forgotten, I figured that was the right way to go. I have to do some sperimenting!

Yo Thasp, I did some wandering around Al Gore's Interweb and read a couple of articles about DIY room treatments from folks who sure sounded like they knew what they were talking about. I went with Roksul (Roxul?) because I didn't want any fiberglass in my living room even if it were 'bagged.'

The treatments really help. I put some antiqued brass remote controllable picture lights on top of the panels and they sure look good.
Posted by: bridgman

Re: Room Treatments - 02/09/17 01:46 AM

Originally Posted By Thasp
Have you considered trying owens corning 703 instead of wool? Much better absorptive properties.

I originally started looking for 703 but it seems to be fairly hard to find in Canada, while the various Roxul products were broadly available. I did some poking around in absorption vs frequency values and IIRC Safe & Sound was pretty similar to 703 although 2x the thickness.

Roxul also makes a semi-rigid that I am using in a few places (guess I should get around to covering it with cloth eventually) but most of it is still in the wrapping acting as a bass trap in a hallway where a lot of bass seemed to be piling up. Nobody seems to talk about implementing bass traps by dumping a bale of fiberglass or rockwool in the corner (hey it comes wrapped in a free membrane), probably some petty aesthetic thing.

I need to get some treatments up in the HT area so will do another look around to see if I can find 703 this time.
Posted by: bridgman

Re: Room Treatments - 02/11/17 12:36 PM

Sorry, that "2x thickness" wasn't right - 3" S&S seems to perform between 2" and 3" OC 703, and closer to 3" if anything:

Code:
Product 	 	density 125hz 	250hz 	500hz 	1000hz 	2000hz 	4000hz 	NRC
RXL 80 		1.5"  	8.0 pcf 0.21 	0.64 	0.92 	1.00 	0.95 	1.01 	0.90
SafeĎníSound 	3"  	2.5 pcf 0.52 	0.96 	1.18 	1.07 	1.05 	1.05 	1.05

703, plain 	1"  	3.0 pcf	0.11 	0.28 	0.68 	0.90 	0.93 	0.96 	0.70
705, plain 	1"  	6.0 pcf	0.02 	0.27 	0.63 	0.85 	0.93 	0.95 	0.65
703, plain 	2"  	3.0 pcf	0.17 	0.86 	1.14 	1.07 	1.02 	0.98 	1.00
703, plain 	3"  	3.0 pcf	0.53 	1.19 	1.21 	1.08 	1.01 	1.04 	1.10

source

I am actually using Comfortboard IS rather than RXL 80, but apparently the two have very similar behaviour.

One thing I don't understand is that the absorption coefficients don't go up that much at high frequencies as thickness increases, but I was also under the impression that adding layers would more or less result in adding the absorption coefficients. I guess the latter belief must be wrong ?