Room Treatment Guide

[REShaman]

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.

Following on the coattails of Julf, my KEF Reference 107, have the woofers facing up and at the "perfect" height to handle bass without the 50Hz room mode I experienced when adding two JL Audio F112s fed by a Bryston 10B active crossover with Low Pass frequency cards at 80Hz. Art Noxon of ASC analyzed as part of a larger perspective that I had to either raise the F112s significantly or change the crossover frequency cards to 50Hz as the KEF 107 (again at the right height for the woofers - facing up in the from chamber) can handle more bass and does need the help from the F112 at 80Hz. The change in frequency cards from 80Hz to 50Hz solved the 50Hz room mode.

Just offering this as a resource of information for others for consideration as a possible solution should you experience room modes of a certain order.

Best,
Richard

[HIFI]

Thanks to all for your experience and guidance.

So I go and make the best of what I have . . .

I am going to start with two front corners and I can treat one rear corner. I am leaning to ASC Tube 16" X 7 or 8 ft tall. It was also recommended I do one each 13" x 6ft tall behind each speaker on same front wall. I am thinking these first as they have diffusion properties as well. For the one rear corner I am looking for a cheap bass trap only. It does not have to look pretty as it will be hidden behind a dinning hutch. I see many people put broadband absorbing panels on their front wall. I will ask now . . . am I missing something? My brain thinks only diffusion belongs on front wall. My wife will not let me do large diffusion on front wall.

I am going to mount either one or two absorption panels on left side wall. I will be purchasing Art panels from GIK Acoustics. I can pick the artwork and they turn it into one, two or three broadband panels. I am hoping this will take care of some of the mid to high frequency ringing as well as first reflection currently present. I am also going to fabricate a portable broadband panel for my right side in front of windows. I can simply put up during a listing session and put away when done. I am going to do two portable panels for back of room as well.

Random thoughts . . . ASC Tube Traps are expensive. If they are as good as the price I have NO objection. I want to at least address any thoughts on absorbing panels on front wall. I really want to get front wall correct and I my brain won’t let me move forward. You help is appreciated.

Thanks

[HIFI]

This may need to be considered in my application . . . My speakers have Heil AMT that radiates front and rear of driver. Vertical dispersion is 20 degrees. Heil driver operates 1k hz and up.

[mayhem13]

Although you asked for guidance, i hope your plan of attack to solve your problems are based on something other than the replies posted here in your thread. Honestly, you haven't provided nearly enough information to begin to analyze what's going on in your space other than the AMT tweets which are dipolar in radiation. This means if properly positioned, the sound from the front and back should cancel at the sides of the system, leaving only very directional front and rear radiation. The very narrow directivity of the AMT accounts for you needing a riser at your seat to sound good......no room treatments in the world are going to solve this. Worse..you mention the speakers being 'on' the short wall?.....if that's the case, bad placement.....period. The rearward radiation of the AMT or any Dipole system needs to be at least 4x the wavelength of the lowest freq, in your case 5ft from any boundaries. if you can't accomidate the system, better to replace the speaker than treat the space.

As to bass response, there's much better methods for solving your or any problems than random trapping but you need to measure and understand your room response first. Any treatments in this area are no better than a lottery ticket purchase in regards to success. I'm also unsure of exactly which ESS's you have, but if it's the model with the passive radiator below the woofer, you've got your work cut out for you. Since passive radiators lack a motor, their transient response on LF content is awefull to begin with and forward firing one with the woofer just makes things worse.

Now i haven't read Jim's book, but have done enough installations to know that the two surfaces that have the greatest impact on in room sound are the two most commonly ignored and that's the floor and the ceiling. It took a while for speaker designers to catch on, but now that they have systems with symmetrical driver arrays above and below the HF device are appearing with greater frequency. Such systems address the fact that we don't listen in open ceiling spaces and shouldn't expect anything less than poor in room response from stacked woofer/mid/tweeter systems. In other words, given your circumstances, IMO the speakers themselves are more of the problem than the room. Good luck with your endevours.

[REShaman]

Although you asked for guidance, i hope your plan of attack to solve your problems are based on something other than the replies posted here in your thread. Honestly, you haven't provided nearly enough information to begin to analyze what's going on in your space other than the AMT tweets which are dipolar in radiation. This means if properly positioned, the sound from the front and back should cancel at the sides of the system, leaving only very directional front and rear radiation. The very narrow directivity of the AMT accounts for you needing a riser at your seat to sound good......no room treatments in the world are going to solve this. Worse..you mention the speakers being 'on' the short wall?.....if that's the case, bad placement.....period. The rearward radiation of the AMT or any Dipole system needs to be at least 4x the wavelength of the lowest freq, in your case 5ft from any boundaries. if you can't accomidate the system, better to replace the speaker than treat the space.

As to bass response, there's much better methods for solving your or any problems than random trapping but you need to measure and understand your room response first. Any treatments in this area are no better than a lottery ticket purchase in regards to success. I'm also unsure of exactly which ESS's you have, but if it's the model with the passive radiator below the woofer, you've got your work cut out for you. Since passive radiators lack a motor, their transient response on LF content is awefull to begin with and forward firing one with the woofer just makes things worse.

Now i haven't read Jim's book, but have done enough installations to know that the two surfaces that have the greatest impact on in room sound are the two most commonly ignored and that's the floor and the ceiling. It took a while for speaker designers to catch on, but now that they have systems with symmetrical driver arrays above and below the HF device are appearing with greater frequency. Such systems address the fact that we don't listen in open ceiling spaces and shouldn't expect anything less than poor in room response from stacked woofer/mid/tweeter systems. In other words, given your circumstances, IMO the speakers themselves are more of the problem than the room. Good luck with your endevours.

Not that you need validation, Art Noxon made preliminary recommendation re the 50Hz room mode I experienced with the F112s,and specifically referred to floor and ceiling as essential factors in the equation for resolving the bass rumbling because the F112s were too low on stands to the floor and thus too low from the ceiling allowing for those reflections which muddied up great base after inclusion of the Bryston crossover set to 80Hz. Reading your assessment helps to confirm these principles about which I learned how much I do not know. Thank you for the lesson.
Best,
Richard

[dkAudio]

...have done enough installations to know that the two surfaces that have the greatest impact on in room sound are the two most commonly ignored and that's the floor and the ceiling. It took a while for speaker designers to catch on, but now that they have systems with symmetrical driver arrays above and below the HF device are appearing with greater frequency. Such systems address the fact that we don't listen in open ceiling spaces and shouldn't expect anything less than poor in room response from stacked woofer/mid/tweeter systems...

Mayhem-

Can you expand further , or point me to some literature, on floor and ceiling reflections? I only have a fuzzy understanding of some low frequency reinforcement from floor reflections and I find what you said very interesting.

[Jim Smith]

Other than some basics such as tube traps (which have to be fairly large in diameter to have any hope for helping in the bass), I don't believe too much in predetermined room treatments. Oh, we will need them, but the question is where? We won't know that at first.

First we have to find where the bass is smoothest. If the bass is missing some notes and exagerrating others, we'll never be musically satisfied.

Most folks think that's done by moving the speakers around. And of course, that does have an effect. But that's not the first thing to be done. The room resonances (at this point, I'm only thinking of resonances below 300 Hz, with special concentration on about 200 down), left largely untreated, are going to show up in various planes in the room (including vertical planes).

This is a function of resonances from front to back, side to side, and floor to ceiling. I usually recommend trying to find locations where the bass is generally the smoothest. When I say locations, at this point I DO NOT mean the speakers. I mean the seating location. In fact, if I have to give up the bottom octave so that a bassist can go up and down the scales and the notes are sounding pretty good, but I'm gonna miss the deepest pipe organ fundamentals, then so be it. Getting the bass right - the very foundation of the music, comes first.

Measurement with the right equipment is fastest and most accurate, but there are other methods such as those I have written about and illustrated on the DVD.

You CANNOT get it done (at least not as well) with a Radio Shack Meter and a "corrected Radio Shack curve". To me, using a good omni-condenser mic that is flat and deep into the bass is far more critical than the sort of program that you run to look at the curve. The Radio Shack meter isn't predictable, it doesn't go deep, it doesn't do it linearily, it suffers from proximity effect and if you can get close enough to read it, you probably have affected its reading...

Once you know where a couple of likely seating options are, we can start to think about speaker placement.

After that starts to be somewhat dialed in, then room treatment becomes very important. But we cannot know where first (and second) reflections will be until we know here we will be seated and where the speakers will be.

IMO, this process is an interesting blend of art & science.

I think I went off track a bit, but I wanted to address the notion of knowing how things will automatically work from some formula that cannot possibly have taken the particular aspects of YOUR room into account.

One very short example. I voiced a client's system yesterday. The room was symmetrical, except for a short (5 or 6 steps) & narrow stairway at one side, somewhat near the end of the room, leading up to the next floor.

I was having a heck of a time finding a seating location that didn't have a pronounced 40 Hz suck-out.

Reversing the room, while it didn't totally eliminate that suck out, ameliorated it greatly. Not sure how a predertimined spread sheet would have ever figured that one out.

One last thing, in doing system/room voiving for over 30 years (well over 600 projects), I'd say that one thing happens more often than not.

It's really a bit analogous to the focusing a wide angle lens on a SLR camera. You have to rock the lens back and forth to get that correct focus. It seems music rooms are like this. More often than not, they go from not enough treatment, to too dead, and eventually (hopefully) to something more pleasing. Smaller rooms haven't worked with RT-60 for me, but I'll admit that someone more clever might get it to work.

Sadly, it's not just observing clients (consumers, retailers, manufacturers) folks go through this, I must admit to having done it myself, as well...

[HIFI]

Although you asked for guidance, i hope your plan of attack to solve your problems are based on something other than the replies posted here in your thread. Honestly, you haven't provided nearly enough information to begin to analyze what's going on in your space other than the AMT tweets which are dipolar in radiation. This means if properly positioned, the sound from the front and back should cancel at the sides of the system, leaving only very directional front and rear radiation. The very narrow directivity of the AMT accounts for you needing a riser at your seat to sound good......no room treatments in the world are going to solve this. Worse..you mention the speakers being 'on' the short wall?.....if that's the case, bad placement.....period. The rearward radiation of the AMT or any Dipole system needs to be at least 4x the wavelength of the lowest freq, in your case 5ft from any boundaries. if you can't accomidate the system, better to replace the speaker than treat the space.

As to bass response, there's much better methods for solving your or any problems than random trapping but you need to measure and understand your room response first. Any treatments in this area are no better than a lottery ticket purchase in regards to success. I'm also unsure of exactly which ESS's you have, but if it's the model with the passive radiator below the woofer, you've got your work cut out for you. Since passive radiators lack a motor, their transient response on LF content is awefull to begin with and forward firing one with the woofer just makes things worse.

Now i haven't read Jim's book, but have done enough installations to know that the two surfaces that have the greatest impact on in room sound are the two most commonly ignored and that's the floor and the ceiling. It took a while for speaker designers to catch on, but now that they have systems with symmetrical driver arrays above and below the HF device are appearing with greater frequency. Such systems address the fact that we don't listen in open ceiling spaces and shouldn't expect anything less than poor in room response from stacked woofer/mid/tweeter systems. In other words, given your circumstances, IMO the speakers themselves are more of the problem than the room. Good luck with your endevours.

Mayhem, It is clear you don’t like my speakers more than me. I know I have some issues but I will work with what I have. I also have a pair of AMT 1C’s with rear mounted passive. With either speaker pair I still have the ringing and low bass detail issues. I also have a pair of Theil 8 inch 3-way floor speakers that are accurate speakers but fail in same room. Regardless of speaker selection my room is a mess unless I turn volume down and do a triangular near field setup as mentioned by others here at CA.

Thanks for your tip on floor/ceiling treatments. I am still hopeful I can treat the room and get some acoustic gains. If I surrender my speakers for, say, something you like/own I would still have many of the room inaccuracies with no treatment . . . so I think all will not be lost/wasted.

What I was hoping for in my latest reply was opinion on bass traps. Your lottery observation is not an accurate accusation. I have spoken to three suppliers of room treatment products and offered room dimensions. They all come back with same suggestions on bass corner treatments and I have to believe I am pointed in the right direction. There are variations on other treatments with all three and I can experiment with those areas.

[HIFI]

Other than some basics such as tube traps (which have to be fairly large in diameter to have any hope for helping in the bass), I don't believe too much in predetermined room treatments. Oh, we will need them, but the question is where? We won't know that at first.

Jim, you mentioned diameter . . . What size does "help the bass"? I also am interested in the "diameter" statement you made. Is there a benefit to round tube trap design that out performs a triangle trap or a pannel trap mounted diag in corner?

Love your book and thanks for your participation here!

[bdiament]

Hi HIFI,

Every room will have resonances in the bass. It will have a fundamental resonance for each dimension (length, width and height) and there will be corresponding harmonics of these.

Proper traps, such as Art Noxon's wonderful Tube Traps as well as some DIY variations on a similar theme, placed in all four corners will address the fundamentals. The first harmonic will peak at the half way point along each room boundary and the second harmonic will peak at the quarter points.

In order to properly treat the fundamental and the first harmonic, larger diameter traps are required than for the second harmonics at the quarter points.

All the good rooms I've worked in or listened in were treated this way. In domestic situations, room size doesn't matter as there will still be corners, half points and quarter points and this is where the maximum pressure for each fundamental and harmonic will occur.

Of course what I've described is only effective for the bass resonances. Early reflections in the treble (one per speaker per room boundary) must also be addressed. Lastly, applying diffusion for later reflections is also, in my experience, a good idea.

Best regards,
Barry
Soundkeeper Recordings
Barry Diament Audio

[Jim Smith]

Jim, you mentioned diameter . . . What size does "help the bass"? I also am interested in the "diameter" statement you made. Is there a benefit to round tube trap design that out performs a triangle trap or a pannel trap mounted diag0 in corner?

Love your book and thanks for your participation here!

In general, 16" diameter in front, and if possible, 20" in back.

The 11" and 13" shouldn't be called bass traps IMO.

They make a 24" trap, but it's for use for much larger rooms that I typically encounter on voicing sessions.

[mayhem13]

What I was hoping for in my latest reply was opinion on bass traps. Your lottery observation is not an accurate accusation. I have spoken to three suppliers of room treatment products and offered room dimensions. They all come back with same suggestions on bass corner treatments and I have to believe I am pointed in the right direction. There are variations on other treatments with all three and I can experiment with those areas.

Room mode calculators are a dime a dozen....the math isn't anything special. What is special....and neccessary is knowing how deep the actual nulls or high the actual peaks in the FR. Only then can you honestly devise a correction 'plan'......which whould require in room measurements after treating anyway to perform the required tweeks or eQ. And in the case of nulls, bass traps are useless. Sure, you'll soak up a 15db peak centered at 55hz but what about the null centered at 40hz that's down 20db? I agree it's nice to get rid of the rings and modes, but accepting lost content in the same octave? Anything less is a half measure solution AT BEST and given the cost of bass traps, completely and utterly wastefull IMO.

Why not invest a few $$ in a simple measurment system. i can gaurantee the return on this investment would be greater than any blind room treatment someone sells you. At least with some real world graphs, you can email the files to the experts or better yet, place the treatments and read the results, adjusting location or position as needed.

[mitchco]

Why not invest a few $$ in a simple measurment system. i can gaurantee the return on this investment would be greater than any blind room treatment someone sells you. At least with some real world graphs, you can email the files to the experts or better yet, place the treatments and read the results, adjusting location or position as needed.

Totaly agreed. REW is excellent free measurement software that can not only measure frequency response, but waterfalls (amplitude versus frequency over time - a 3 D plot if you will), where you can examine your specific in-room resonances, plus measure Energy Time Curves (ETC's), which will assist in locating early reflections, so you know where you are placing your treatments and can measure (and listen of course) the before and after, etc. REW has an excellent support forum.

I wrote a step by step walkthrough on how to get started.

Hope that helps. Cheers, Mitch

[hifitubes]

Great thread, any comments on using something like an all-in-one USB mic (Dayton OmniV2) vs. EMM6, or similar, at higher sample rates?

I was reading some comments that stated a higher quality converter and sample rate could be effective, but I'm guessing the Omni should suffice...

thanks
Jon

Totaly agreed. REW is excellent free measurement software that can not only measure frequency response, but waterfalls (amplitude versus frequency over time - a 3 D plot if you will), where you can examine your specific in-room resonances, plus measure Energy Time Curves (ETC's), which will assist in locating early reflections, so you know where you are placing your treatments and can measure (and listen of course) the before and after, etc. REW has an excellent support forum.

I wrote a step by step walkthrough on how to get started.

Hope that helps. Cheers, Mitch

[HIFI]

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.
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

I want to say thanks to all and ask a follow up question . . .

In all the tech reading I have done I have only understand a bit. Can I consider early reflections for absorbtion and later reflections for diffusion? Additionally is there a time span, in ms that should be titled an "early" and an additional time frame that would be titled "later"? My thought is to early, what ever my brain/ear can process, will adversly effect the original signal. Then at some "time window" it is too late to ruin a good stage image and I can difuse those later reflections so they would have no apperant source. That way I do not remove any unnecessary energy in my room. Logical or am I just hacken away again?

[bdiament]

Hi HIFI,

I want to say thanks to all and ask a follow up question . . .

In all the tech reading I have done I have only understand a bit. Can I consider early reflections for absorbtion and later reflections for diffusion? Additionally is there a time span, in ms that should be titled an "early" and an additional time frame that would be titled "later"? My thought is to early, what ever my brain/ear can process, will adversly effect the original signal. Then at some "time window" it is too late to ruin a good stage image and I can difuse those later reflections so they would have no apperant source. That way I do not remove any unnecessary energy in my room. Logical or am I just hacken away again?

In my experience, it is really much simpler than many make it out to be.
No numbers are required.

Assuming properly placed speakers and listening position:
The direct sound follows the path from the speakers *directly* to your ears.
Early reflections (those that should be absorbed) are the ones that bounce once after leaving the speakers and before arriving at your ears.
Later reflections (those that should be diffused) are the ones that bounce more than once after leaving the speakers and before arriving at your ears.

Every room boundary (walls, ceiling and floor) will have one early reflection per speaker. In a two speaker system such as we use for stereo, there are two early reflection points per room boundary.

A carpet or rug takes care of early reflections from the floor.
My article (linked to earlier too, I believe) provides hints on finding the early reflection points.

Early reflections and room modes are, in my experience, more important to address than diffusion. Ideally, of course, all would be addressed. Some trap designs will address all three in a single device. All you need is to have a sufficient number of them for full acoustic treatment. (Flat panels can be useful for early reflections but that, in my view, is about all they are good for. Further, with the type of trap that addresses all three room issues, flat panels are not needed anyway.)

Best regards,
Barry
Soundkeeper Recordings
Barry Diament Audio

[Jim Smith]

Agreed 100%.

[mayhem13]

Hi HIFI,



In my experience, it is really much simpler than many make it out to be.
No numbers are required.

Assuming properly placed speakers and listening position:
The direct sound follows the path from the speakers *directly* to your ears.


Best regards,
Barry
Soundkeeper Recordings
Barry Diament Audio

I wish we lived in a world where drivers radiated sound as you proposed but sadly, that's just not the case......and the 'on axis' material that does beam directly at the listener does so at the extreme expense of even power response. And....ehemm.....'proper' placement of a speaker is highly dependant on the individual speaker as much as it's relationship to the room. I find it very difficult to believe that a professional in the field of acoustics would recommend treating a room without adequate measuring of the speakers nearfield and farfield response.

[bdiament]

Hi mayhem13,

I wish we lived in a world where drivers radiated sound as you proposed...I find it very difficult to believe that a professional in the field of acoustics would recommend treating a room without adequate measuring of the speakers nearfield and farfield response.

Can you show me a post where I "proposed" how any particular drivers radiate sound?
As far as I can recall, I made no mention of anything of the sort. The topic is treating the *room*.

Unless one is interested in applying EQ to the speakers (something I would never do as I consider it less than fruitless), there is nothing gained by measuring speaker response, nearfield, farfield or otherwise.

Besides, most measurements make the (to my mind, fatal) assumption that what the microphone "hears" reflects what the listener would hear. This would only be the case if like the microphone, the listener had an extraordinarily narrow head with a single ear in the middle of their face. ;-} That doesn't apply to any listener I've ever known.

Proper placement for any speaker that isn't specifically designed to be placed elsewhere (something I would question from the start), is not very different from any other speaker. Dispersion and radiation characteristics of the individual design will determine only how severe the room effects are; it will not change *what* those room effects are nor will it change the locations at which they occur.

Every domestic size room, if it has walls, a ceiling and a floor is going to behave similarly to any other enclosure. Resonance frequencies will be determined by its dimensions but where the resonant modes build up in the room is unrelated to the frequencies of those resonances - the locations are always the same: at the boundaries for the fundamental in any given dimension, at the half way point for its first harmonic and at the quarter points for its second harmonic.

I am aware of other approaches but personally, have never heard one of these that I deemed supported by the audible results.

This is merely my own perspective of course, based on my own experience in my own studio/listening room, in other studio/listening rooms I've had and worked in and in studios and listening rooms I've designed for others.

Best regards,
Barry
Soundkeeper Recordings
Barry Diament Audio

[HIFI]

Back to room treatments and an additional question . . .

I have been reading about how to treat for bass issues. I have also sat in a professionally treated 2 Channel audio listening room and have experienced results at popular listening volumes. The science is understandable. Nowhere have I read anything that speaks about listening volumes. So my question is “how much” does the volume one listens at effect bass trap performance? I assume that there must be a limit of absorption to a bass trap that goes beyond a frequency range of absorption.

The reason I ask is for education and application. I listen to a variety of music including some very nice reference material. I like a small jazz trio in a small club recording. I can listen to a solo piano or acoustic anything for hours. I love the rich sound of Patricia Barber’s voice. When no one is looking I load up on the likes of Clash, Talking Heads, B-52’s, Ramones and I can’t help finding the limits of the amp and speakers. I just enjoy my hobby that way as well.

[bdiament]

Hi HIFI,

...So my question is “how much” does the volume one listens at effect bass trap performance?...

I can see such a question arising if one assumes room resonance modes are simply a matter of frequency response. In fact, that is a mistaken assumption. Resonance modes are *time-based* issues with the frequency response peaks and dips that result merely being among the several symptoms but not the core problem itself.

A resonance means the room "holds onto" sounds after they are "finished" in the source material. Another term for the resonance is "ringing". Proper treatment of room modes involves modifying the "Q" of the resonances, not simply absorbing excess energy. (Remember that in some locations, room modes will cause *dips* in response, a *lack* of energy.)

With the "Q" modified (changed to a lower value in this case), the ringing duration is shortened. As a *result* symptoms such as frequency response irregularities are ameliorated.

ASC makes a "test tone" (which was also on one of the Stereophile Test CDs) that is useful for hearing the extended duration manifested by ringing modes. The "tone" consists of a series of short bursts of sound. In a properly treated room (or via headphones, where there the effects of the room are non-existent), the silences between the bursts are plainly audible. In an untreated room, the silences are "filled in" by the ringing modes, effectively flattening out musical transients (i.e., making for less "punch" on the bottom) and also obscuring low level information that would otherwise be heard between louder sounds in the bass.

All this to say, louder playback volumes merely increase the excitation of room modes. In my experience, with these properly treated, the Q being lowered, the volume won't matter.

Hope this helps.

Best regards,
Barry
Soundkeeper Recordings
Barry Diament Audio

[REShaman]

Hi HIFI,



I can see such a question arising if one assumes room resonance modes are simply a matter of frequency response. In fact, that is a mistaken assumption. Resonance modes are *time-based* issues with the frequency response peaks and dips that result merely being among the several symptoms but not the core problem itself.

A resonance means the room "holds onto" sounds after they are "finished" in the source material. Another term for the resonance is "ringing". Proper treatment of room modes involves modifying the "Q" of the resonances, not simply absorbing excess energy. (Remember that in some locations, room modes will cause *dips* in response, a *lack* of energy.)

With the "Q" modified (changed to a lower value in this case), the ringing duration is shortened. As a *result* symptoms such as frequency response irregularities are ameliorated.

ASC makes a "test tone" (which was also on one of the Stereophile Test CDs) that is useful for hearing the extended duration manifested by ringing modes. The "tone" consists of a series of short bursts of sound. In a properly treated room (or via headphones, where there the effects of the room are non-existent), the silences between the bursts are plainly audible. In an untreated room, the silences are "filled in" by the ringing modes, effectively flattening out musical transients (i.e., making for less "punch" on the bottom) and also obscuring low level information that would otherwise be heard between louder sounds in the bass.

All this to say, louder playback volumes merely increase the excitation of room modes. In my experience, with these properly treated, the Q being lowered, the volume won't matter.

Hope this helps.

Best regards,
Barry
Soundkeeper Recordings
Barry Diament Audio

Just discussing this very subject Friday night with guests for various reasons. Thank you for a very clear explanation. Every time you refer to ASC, which is where I landed (not promoting Art) in getting advice and with the intention of following through, I am gratified to read commendable references.
Thank you, Barry,
Richard

[HIFI]

Hi HIFI,



I can see such a question arising if one assumes room resonance modes are simply a matter of frequency response. In fact, that is a mistaken assumption. Resonance modes are *time-based* issues with the frequency response peaks and dips that result merely being among the several symptoms but not the core problem itself.

A resonance means the room "holds onto" sounds after they are "finished" in the source material. Another term for the resonance is "ringing". Proper treatment of room modes involves modifying the "Q" of the resonances, not simply absorbing excess energy. (Remember that in some locations, room modes will cause *dips* in response, a *lack* of energy.)

With the "Q" modified (changed to a lower value in this case), the ringing duration is shortened. As a *result* symptoms such as frequency response irregularities are ameliorated.

Thanks for jumping back in.
Your explanation of “core” problem makes sense and has me more discouraged and at the same time encouraged.

I was sniffing around my room this past weekend. My front wall and left wall are interior walls and both are hollow. My brain said problem and now I want to say. . a “core” problem. Am I correct in suspecting this is a part of “core” problems? If so, aside from tearing down and rebuilding, would filling the void between studs with some “Magic Audio Acoustic” insulation help? If so who makes the “magic” potion?

[bdiament]

Hi HIFI,

Thanks for jumping back in.
Your explanation of “core” problem makes sense and has me more discouraged and at the same time encouraged.

I was sniffing around my room this past weekend. My front wall and left wall are interior walls and both are hollow. My brain said problem and now I want to say. . a “core” problem. Am I correct in suspecting this is a part of “core” problems? If so, aside from tearing down and rebuilding, would filling the void between studs with some “Magic Audio Acoustic” insulation help? If so who makes the “magic” potion?

They're two different things.

Room modes will exist (and ideally, be treated) in any domestic-size room, regardless of the wall construction. That is the space *inside* the walls.

As to the walls themselves, in my experience, they'll tend to be the lesser of the two issues. I don't know if I'd call any particular material a "magic potion". Sometimes, simply adding another layer of sheetrock can help. There are also commercially available materials to add as a "liner" between layers of sheetrock. (I believe ASC makes something like this but you'd have to check with them.)

Personally, I don't think the walls will be much, if anything, of a problem, provided the space inside the walls is properly treated. As I've said earlier, this will involve a lot more than two traps in the front of the room. (I may have also said that in my experience, the flat panels sold as bass traps are pretty useless below the treble.) A full treatment can involve traps (as close to floor-to-ceiling as possible) in all four corners, the midpoint of each wall and the quarter points of each wall. A rug or carpet can cover the floor. In some cases, ceiling traps are called for as well but I'd see what treating the walls and floor does first. In many rooms I've worked in and/or set up, this is sufficient.

If you do decide to address the walls, I suggest seeking to make them as rigid as possible. This is more important than filling the void between studs. But again, in my experience, this may well be moot once the space inside the room is properly treated.

Hope this helps.

Best regards,
Barry
Soundkeeper Recordings
Barry Diament Audio

[JWL]

As to the walls themselves, in my experience, they'll tend to be the lesser of the two issues. I don't know if I'd call any particular material a "magic potion". Sometimes, simply adding another layer of sheetrock can help. There are also commercially available materials to add as a "liner" between layers of sheetrock. (I believe ASC makes something like this but you'd have to check with them.)

Personally, I don't think the walls will be much, if anything, of a problem, provided the space inside the walls is properly treated. As I've said earlier, this will involve a lot more than two traps in the front of the room.

Anything placed inside the wall cavity will have very little effect on the sound inside the room, though it can definitely help reduce the amount of sound that gets outside the room. To improve the sound inside the room, you need acoustic treatment inside the room.

(I may have also said that in my experience, the flat panels sold as bass traps are pretty useless below the treble.)

I must respectfully point out that this is false. Our (I work for RealTraps) MicroTraps are flat panels, are a bit over 1" thick, and are effective down to about 250Hz. Thicker panels perform to lower frequencies; our MiniTraps (3" thick) are effective to below 80Hz, and our MondoTraps (4" or 6" thick) offer even more absorption down to below 50Hz.

A full treatment can involve traps (as close to floor-to-ceiling as possible) in all four corners, the midpoint of each wall and the quarter points of each wall. A rug or carpet can cover the floor. In some cases, ceiling traps are called for as well but I'd see what treating the walls and floor does first. In many rooms I've worked in and/or set up, this is sufficient.

In general our approach (or at least the first 2 and most important steps) is to add as much bass trapping to as many corners (including wall/ceiling and even wall/floor corners) as possible, and to create a Reflection-Free Zone at the listening position. It's important not to over-do high frequency absorption or the room will become too dead, but it's impossible to have too much bass trapping in a small room. The more bass traps you add, the flatter the room's response will get.

For details on our general strategies for listening rooms, see: RealTraps - Acoustic Basics

Also, we have several articles on room measurement that you might find useful, including a "shoot out" of various measurement microphones (including multi-thousand dollar mics as well as mics below $50):

RealTraps - Room Measuring Series
RealTraps - How Does That Sound Look?
RealTraps - Optimizing Acoustic Treatment using ETF
RealTraps - Measuring Microphones

Measuring a room is useful to show what YOUR room is doing in terms of the specific frequencies where you are having problems, but no matter where the problems are the solution is always the same. More bass trapping will clean up the frequency response by reducing comb filtering. Absorption at reflection points will clean up clarity and restore the stereo image/soundstage. So while measuring room can be fun if you are interested in such things, it's not really 100% necessary in my experience.

James Lindenschmidt
General Manager, RealTraps
RealTraps - Home