Amount of acoustic treatment for an audible difference

[Grayson Dere]

Recently I was browsing the web for images of fantastic looking professional recording studios and state-of-the-art home theater interiors. While seeing all the effort and science being put
into practice in installing acoustic treatment it made me wonder... if you started taking away both absorption and diffusion panels one by one, and were blindfolded (a friend would be doing the work), what would be the minimal treatment left when you could actually make out that the room now sounded borderline okay/unpleasing?
Anyways, I think it would be a fun exercise for those with time to spare : )

 

[Sonnie Parker]

I think it might be a mixed bag of opinions, as I have encountered guys who prefer to let the walls do their thing to the music (perhaps one of those guys who has been in my room might eventually chime in)... then there are naturally a host of listeners who like acoustic treatment, especially to kill first reflections to the primary listening position. You may or may not like what you hear. There is also the chance that there may not be much of a difference based on your type of speaker and speaker placement. REW can measure reflections. There are also those that use panels to tame the response and/or response issues, which can actually be measured with frequency response sweeps.

When Wayne was reviewing some of the MartinLogan speakers in my room... (can't remember which ones it was)... he setup a flat solid panel at the wall behind my ML's (basically covering the acoustic panels) and adjusted them with a mirror to reflect the rear wave back at the main listening position. I've used them with all of my ML's since and I believe it does give me a better sense of depth acuity. I don't know that I personally could A/B the difference though... I think I'd fail most of those tests for sure. It has to be pretty drastic for me to notice a difference.

The next evaluation meet we have here at the house, perhaps this is something we could all experiment with and even measure response and reflections in REW each time we remove a panel. Need better ears in here to do the test, if you know where I'm coming from.

 

[Grayson Dere]

Thanks for your thoughtful response, Sonnie : )

 

[AustinJerry]

Sonnie makes a good point--it is very difficult to make an A/B comparison because of the time it would take to remove and replace treatment panels. Such comparisons are only useful if the change is immediate, unless, of course, the difference is significant. And then there is the question, "What sounds better?" There is an app developed by Harmon called "How to Listen" than trains a person what to listen for, and what might make certain sounds more pleasing. If you are interested, check out http://harmanhowtolisten.blogspot.com/2011/01/welcome-to-how-to-listen.html.

REW measurements can help evaluate the differences, the Waterfall for detecting bass resonances, the ETC for examining reflections, and the RT60 for determining the "liveliness" of a room's acoustics. But in the end it all boils down to preference, and the answer to what sounds better is elusive. I have one friend who has over-treated his room to remove all reflected sound--he believes that movie sound tracks have ambiance built in and the room should not contribute any additional information. Not hard to conclude that music sounds terrible in his listening room. And I have another friend that insists in preserving reflections from side walls in order to maintain the width of the sound stage for musing listening.

 

[Mike-48]

I agree with @Sonnie and @AustinJerry that the user's taste is the deciding factor. As background for what follows: My taste is to reduce local room sound so I can hear the music and ambiance that have been recorded. I do retain a little room sound and make sure the treatments have some diffusion or reflection, so no recording sounds dead. Users who listen to highly processed releases, in particular, may prefer to let the local room add more of its own ambiance.

Anyway, in my 2-channel systems, about 15 yrs ago. I changed to more expensive speakers, and at home was frustrated that they sounded like the speakers they replaced -- all the same issues. ASC sent a room- treatment plan, which I followed in stages.

The first step was two tower traps in the front corners and a couple of 24" x 48" flat panels for first reflection points. The difference was huge, mostly in reduced smearing and irritation. One of the Stereophile Test CDs has the ASC music articulation test, and the improvement in clarity was obvious. More importantly, on music.

Each addition of acoustics (about six panels across the rear; some half-rounds above the speakers; then other traps on the front wall) made a difference.

I still have many of those products, and I reused them in my current room at the other side of the country. (You can see them in my Showcase post.)

To answer your question directly, I'd say bass traps in two or four corners and combination absorption/diffusion panels at sidewall reflection points will make a big improvement to any home system, at least one in a closed room, where bass decay time is typically too long without trapping. (I have no experience with rooms open on one side or another, nor do I have experience that is specific to AV systems.)

I hope that helps, or at least gives food for thought.

 

[DanDan]

There are some rules of thumb knocking around. From memory about 20-30% surface area treated or changed say from carpet to bare or vice versa becomes audible.
Coincidentally, maybe, about 30% perforation of a metal sheet renders it acoustically gone, transparent.
DD

 

[Grayson Dere]

I agree with @Sonnie and @AustinJerry that the user's taste is the deciding factor. As background for what follows: My taste is to reduce local room sound so I can hear the music and ambiance that have been recorded. I do retain a little room sound and make sure the treatments have some diffusion or reflection, so no recording sounds dead. Users who listen to highly processed releases, in particular, may prefer to let the local room add more of its own ambiance.

Anyway, in my 2-channel systems, about 15 yrs ago. I changed to more expensive speakers, and at home was frustrated that they sounded like the speakers they replaced -- all the same issues. ASC sent a room- treatment plan, which I followed in stages.

The first step was two tower traps in the front corners and a couple of 24" x 48" flat panels for first reflection points. The difference was huge, mostly in reduced smearing and irritation. One of the Stereophile Test CDs has the ASC music articulation test, and the improvement in clarity was obvious. More importantly, on music.

Each addition of acoustics (about six panels across the rear; some half-rounds above the speakers; then other traps on the front wall) made a difference.

I still have many of those products, and I reused them in my current room at the other side of the country. (You can see them in my Showcase post.)

To answer your question directly, I'd say bass traps in two or four corners and combination absorption/diffusion panels at sidewall reflection points will make a big improvement to any home system, at least one in a closed room, where bass decay time is typically too long without trapping. (I have no experience with rooms open on one side or another, nor do I have experience that is specific to AV systems.)

I hope that helps, or at least gives food for thought.

I was at a recent SF Bay Area hifi meet and ASC did a talk there explaining what happens to a room acoustically...they said exactly what you experienced with the front smearing that often occurs if no treatment is given for the front of the room. That's cool you had first hand experience in instantly getting rid of that smearing and irritation when you followed their steps for setting up the 2-tower traps + first reflection flat panels.

 

[Grayson Dere]

Interesting readings about this subject when you Google for Michael Green room tunes

RoomTune | mysite

www.michaelgreenaudio.net

Thanks for the link..I haven't seen this before.

 

[DanDan]

Sorry, but I can't avoid objecting to inadequate products. That RoomTune stuff is all too small to work well. The minimum treatment I would recommend anywhere would be the standard 2'x4'x4" fibre absorber, PLUS a 4" airgap or even better, straddling corners. Let us note well that straddling corners greatly 'amplifies' the efficacy of such traps. So four corners straddled, floor to ceiling, is a great start. 2 to 4 for the cloud, 2-4 each side.
So, minimum treat for a generic small room 8 foot ceiling...... 14-18 traps.
DD

 

[gregory]

Onken altec 414