Room Treatment Guide

[HIFI]

What books or reference can you suggest for understanding and treating a 2 channel listening room?

[AudioDoctor]

Jim Smiths book.

Computer Audiophile - Get Better Sound (Without Spending A Fortune)

[mayhem13]

Best not to do this blindly. There's no substitution for measuring and understanding your space BEFORE treating it. Dayton Omnimic system is an invaluable tool.

[mitchco]

Good comments so far. This might help to get you part way there: Speaker to Room Calibration Walkthrough - Blogs - Computer Audiophile

[HIFI]

Thanks for all help!

I have Jim's book and have studied the book, my room, speaker placement.

Because my room rings I have set up some temp treatments to knock some of the ringing. I have a long rectangle room and plenty of compounding bass on front wall and rear wall. Triangular Mondo Bass traps in front wall corners and one in one rear corner. I cant treat the other corner. Speakers on the short wall. I sit at about one third overall room distance for, what is now, optimum listening. My room is 13 wide, 28 long with 10ft ceiling. With many of the temp treatments the room is starting to shape up. Because this is my family home I will not be able to do anything with wall/ceiling joints other than two corners on front listening wall.

Things sound pretty good if I elevate my listing chair about a foot. This cannot be done because it looks stupid to my wife.

Has anyone had an issue like this and were you able to do anything to correct?

[mav52]

If you need some reading material on audio acoustics, here is lots, and lots of articles.

Acoustic Room Treatment Articles - eCoustics.com

[mayhem13]

Do you have some sine wave sweeps of 20-20 to post so we can possibly identify the problem area? Most nulls are pretty self evident to the untrained eye.

[Jim Smith]

Do you have some sine wave sweeps of 20-20 to post so we can possibly identify the problem area? Most nulls are pretty self evident to the untrained eye.

This will look different depending on where the mic was located.

Which is why finding the best location for the smoothest bass - the listening position - is step one before looking at generic curves.

[mayhem13]

This will look different depending on where the mic was located.

Which is why finding the best location for the smoothest bass - the listening position - is step one before looking at generic curves.

Sorry, I just assumed the OP knew to measure at the LP without mention.

[HIFI]

I have solved my problem by moving my audio cabinet from between speakers to side wall. I know this sounds easy/obvious but it was very complicated.

Short story . . . Wife wanted cabinet there. I wanted it here. Lots of pleading and crying on my part. Bribed wife and painted room in house and agreed to re-tile two bathroom floors and a utility room. In short it looks like a simple yet expensive room treatment but everyone is HAPPY.

[REShaman]

I have solved my problem by moving my audio cabinet from between speakers to side wall. I know this sounds easy/obvious but it was very complicated.

Short story . . . Wife wanted cabinet there. I wanted it here. Lots of pleading and crying on my part. Bribed wife and painted room in house and agreed to re-tile two bathroom floors and a utility room. In short it looks like a simple yet expensive room treatment but everyone is HAPPY.

In Jim's book, and DVD, he makes a point of admonishing not to put cabinet(s) between the speakers. In fact the only thing that should exist between the speakers are the speakers. Did I get that right Jim?

Offered in support of HIFI's correct "adjustment" re cabinet placement.

Best,
Richard

[jackfish]

Acoustic Primer. GIK Acoustics. Acoustic Panels and Bass Traps.
Acoustic Treatment and Design for Recording Studios and Listening Rooms
Cardas Audio

[Jim Smith]

In Jim's book, and DVD, he makes a point of admonishing not to put cabinet(s) between the speakers. In fact the only thing that should exist between the speakers are the speakers. Did I get that right Jim?

Offered in support of HIFI's correct "adjustment" re cabinet placement.

Best,
Richard

Well, low profile items such as amps on ampstands don't seem to be a problem.

Alas, so many of the rooms I visit initially on voicing sessions are entirely too dead. I don't know whether the owner was sold too much by the vendor, or what.

Usually, in a room in which simple voices sound dead or otherwise uninteresting (in conversations with people that you know), the musical reproduction will lack presence and energy. Basically a b-o-o-o-r-i-n-g experience.

A bit like going to hear a concert in a theatre acoustically optimized for drama. Yuck.

[Part-Time Audiophile]

Well, low profile items such as amps on ampstands don't seem to be a problem.

Alas, so many of the rooms I visit initially on voicing sessions are entirely too dead. I don't know whether the owner was sold too much by the vendor, or what.

Usually, in a room in which simple voices sound dead or otherwise uninteresting (in conversations with people that you know), the musical reproduction will lack presence and energy. Basically a b-o-o-o-r-i-n-g experience.

A bit like going to hear a concert in a theatre acoustically optimized for drama. Yuck.

+1 to what Jim said. Too much treatment = boring and lifeless.

[dallasjustice]

Alas, so many of the rooms I visit initially on voicing sessions are entirely too dead. I don't know whether the owner was sold too much by the vendor, or what.

Jim, do you have any standard recommendations for measured reverb time? I am just wondering how you define "too dead." Do you recommend RT60 to be even across all frequencies or do you prefer them to to vary depending on the frequency? What is your cutoff?

[Jim Smith]

I know this goes against Audiophile Common Knowledge, but for me, I've never found RT60 all that useful or even measurable in the sorts of rooms most audiophiles have.

For me, it's just an organic thing - how does it feel/sound?

An article that sort of agrees with me - and some don't - is here:

Room Acoustics

A part of the relevant info from that article is below:

Reflectivity:

In simple terms, reflectivity is the apparent "liveness" of a room. Professionals prefer the term reverb time or Rt-60. Rt-60 defined, is the amount of time (in seconds) it takes for a pulsed tone to decay to a level 6OdB below the original intensity. A live room has a great deal of reflectivity, and hence a long Rt-60. A dead room has little reflectivity and a short Rt-60.

Rt-60 measurements are most useful in determining the acoustic properties of larger spaces such as churches, auditoria, etc. In smaller environs the Rt-60 measurements become so short as to be useless. In these confined spaces, individual reflections from nearby surfaces dominate the sonic picture and are the primary focus for the audiophile.

Reflections can be both desirable and detrimental. This depends on their frequency, level and the amount of time it takes the reflections to reach our ears following the direct sounds produced by the speakers. Our brain blends together all of the sounds reaching our ears within 5-30 ms of the original. Reflections arriving approximately 30-50 ms or more after the original will be perceived as separate sounds. This phenomenon is known as the Haas effect[3]. It is these initial reflections that are most important to the brain in determining the apparent size of the listening room. By manipulating the ratio of direct vs. reflected sound, we can fool the brain into thinking we are listening in a larger room than actually exists. The idea is to reinforce the direct output from the speaker with reflections of the proper level, frequency and arrival time, while eliminating the detrimental ones. This can be accomplished by proper positioning of the speaker and listener, and through implementation of various acoustic correction products such as those made by Acoustic Sciences Corporation, RPG and others.

Comb filtering is another form of unwanted reflection. This condition is created when a speaker is placed near a reflective surface (wall, floor, furniture etc.). The result is image smear and/or frequency response anomalies. The comb filter effect occurs when the direct sound and the reflected sounds arrive at the listeners' ears out of phase, thus canceling each other. This problem can be avoided by placing your speakers well away from reflective surfaces, or by treating nearby problem areas with absorptive and/or diffusive materials.

[dallasjustice]

Before I treated my room, the RT times were more than 2 seconds and it sounded awful. Wouldn't you agree that good room treatments could competently deal with all first order reflections such that comb filtering is a nonissue? My listening room is slightly smaller than the American Airlines center (14'6" x 24' x 9'3"). You wouldn't approve of an RT time over 2 seconds for a room this size, right? Are you saying there are no useful measurements or standards applicable to decay time in a room this size or any normal sized listening room?

[Jim Smith]

Before I treated my room, the RT times were more than 2 seconds and it sounded awful.

WOW - that would have been rough!!

Wouldn't you agree that good room treatments could competently deal with all first order reflections such that comb filtering is a nonissue?

Yes.

My listening room is slightly smaller than the American Airlines center (14'6" x 24' x 9'3"). You wouldn't approve of an RT time over 2 seconds for a room this size, right?

Right.

Are you saying there are no useful measurements or standards applicable to decay time in a room this size or any normal sized listening room?

There are too many issues to go into here. Just getting a room quiet enough to perform the measurements is one thing.

(Here's where I get into trouble with the acousticians and mathematicians), I've never found a set of measurements that are officially and universally approved that work in every room. Well, maybe with nothing in the room but the spreadsheet. But once actual furniture and varying numbers of people are in there, all that math is useless to me (maybe not to others brighter than me, I'm only speaking for myself here).

In fact, without a doubt, some of these rooms that have been measured and adjusted to death produce nice sound, but are not musically compelling at all. IMO, of course.

Rooms smaller than yours (which is a little larger than I typically encounter) are difficult to evaluate with RT-60.

I have the feature on my RT, but I mostly tune for what sounds most involving, rather than what some acoustician sitting at a desk in another state has set as the arbitrary decay number we must have in a room that he has never seen or heard.

Although I have hundred of clients who love the results of these voicing sessions, it doesn't mean that I hold any special mathematical knowledge - it's most organically empirical experience, whatever that means.

So there's probably no need to argue our positions further.

[bdiament]

Hi HIFI,

What books or reference can you suggest for understanding and treating a 2 channel listening room?

For a short starter, I hope this article is of interest and provides food for audio thought.

Best regards,
Barry
Soundkeeper Recordings
Barry Diament Audio

[HIFI]

Thanks to all for input and resources.

I am truly limited in my 11.5ft wide x 29 ft long and 10ft ceiling room as to treatments because it is my family house. What I can do, with speakers placed on short wall, is front wall corner traps and some absorbing panels on same front wall. I am limited on side walls as well because the entire right side is large windows and the front entry door. Left side is all wall except opening that leads to rest of house. Therefor my side wall treatments will not be same but I need something. Absorbers on left wall in imeadiate area and use the wood plantation louvers in a fashion to redirect first reflections. Because back of room is untouchable I will always be disappointed in overall sound.

I have surrendered to making the best of what I can do. My hope is low frequency treatment up front will make a large enough difference. I am also hoping to reduce the ringing sound in room that is fatiguing to listen too. I am hoping absorption will do contain the ringing as I am not allowed to put large diffusers on walls.

[bdiament]

Hi HIFI,

In my experience, it takes quite a bit more than traps in the front corners to control room modes.

If you can't address the acoustics, my best suggestion is to use a smaller triangle (speaker-speaker-listening position) and listen in the near field or something close to that.

For room issues above the bass, imagine the walls, ceiling and floor are mirrors. From the listening position, any place you see a reflection of a loudspeaker on any of those surfaces, needs something soft in order to control the reflections.

If the ringing you describe is in the bass, the only solutions I know are to either treat the room (all corners as well as the mid and quarter points of each wall) or to turn the volume way down. If the ringing is in the treble, absorption at the reflection points is the solution.

I recommend avoiding diffusion where early reflections would take place as this only *ensures* those reflections will reach the listening position. Diffusion is best used to treat *late* reflections (i.e. sounds that have already been around the room) and is what keeps a sense of "life" in a room, without interfering with the sound from the speakers.

Best regards,
Barry
Soundkeeper Recordings
Barry Diament Audio

[REShaman]

Recognizing the positive potential in any given situation (the key to making it happen), HIFI and others with room acoustic problems who present in this thread have the attention of two experts, to wit, Jim Smith and Barry Diament, and we all get to learn about different acoustical problems and how various solutions resolve those problems. Obviously there is more to discuss, design and implement, and then apply and test to confirm. So far, as we are able to witness the exchanges, the criteria and thoughtful suggestions/principles exposited by our experts, Jim and Barry, in this thread are very useful.

Thank you to those who present problems seeking to do something about them as many of us have to contend with similar/same problems. And thank you Jim and Barry for your time and responses and sharing articles that further advance some of us with understanding of what's in play (pun intended).

Looking to give boosts (strokes) whenever possible (there are enough boots -- kicks) as more of that is welcome to most members. Not ignoring the usefulness of lively discussions and the exchange of different views.

Best,
Richard

[bdiament]

Personally, I would consider reflection delays on the order of 30 ms to be something that should be addressed. In my experience, they will be perceived as separate from the direct sound.

An example some may be familiar with: If anyone knows Stevie Wonder's work from the mid-70s - I'm thinking "Songs In The Key Of Life" - there is a particular sound on the horns. In the song "Sir Duke" and others on this album, the horn section has a distinctive, "razzy" sound. This is achieved by "doubling" the horn section - i.e., making say, three players sound like six - by adding a ~20 ms delay to the raw horn track(s) and mixing the delay with the raw tracks.

To my ears, a 20 ms delay (i.e., reflection in the listening room) will add a similar "razz" to the sound. This is easily remedied by adding absorption at the reflection points. (If used *only* at the reflection points - there is one per speaker per room boundary - and not indiscriminately all over the place, as we see in some ads and in photos of some "studios", the room will never suffer "deadness".)

Best regards,
Barry
Soundkeeper Recordings
Barry Diament Audio

[mayhem13]

[QUOTE=
Comb filtering is another form of unwanted reflection. This condition is created when a speaker is placed near a reflective surface (wall, floor, furniture etc.). The result is image smear and/or frequency response anomalies. The comb filter effect occurs when the direct sound and the reflected sounds arrive at the listeners' ears out of phase, thus canceling each other. This problem can be avoided by placing your speakers well away from reflective surfaces, or by treating nearby problem areas with absorptive and/or diffusive materials.[/QUOTE]

While i agree with most of your post, in order for room boundaries to produce actual comb filtering to a 180 degree phase shift, you would have to intentionally place theese boundaries very precisely to produce actual comb filtering. early reflections are another issue which do exist in common listening spaces but more important, you'll find the most destructive component is the speaker whether it's poor polar response, erratic directivity or a poorly implemented crossover slope. A typical flush mounted dome tweeter is a prime example of poor directivity by design, but how many speaker systems use them just that way?.....and not just from a directivity position but phase alignment where the acoustic centers of the drivers are off by 2" or more due to the recessed voice coil of the cone and the protruding surface of the dome. Wanna take most of the room out of the question?.....horn or waveguide loaded HF devices or true dipole radiation is a good start.

Complaints about poor LF response will always be abound until folks realize that usually the worst place for LF devices to be placed often the best positioning for the mains! But most 'audiophiles' accept this as the lesser evil than sub integration difficulties. What's worse is the odd order HD reaching close to the fundamental as these systems try and produce 40hz and below content from a 5-6" transducer. At reference level, these little woofers are so far from linear, not to mention the smeared up midrange that's usually playing to 2khz. Put the LF back where it belongs with larger drivers with acceptable levels of linear excursion.

[Julf]

I guess there is a reason I still love my old Isobariks with their "indirect radiation" second set of mid and tweeter aimed upwards, Carlsson-style.