I have a question... There are some acoustics experts who think that it is not a good idea to deaden a room too much (Toole and Geddes, for example) so you don't lose the desirable sense of spaciousness). It seems to me that higher intelligibility comes at the expense of broadband reduction in reverbration. There are also those who advocate a dead front and live rear in the room (most, I think), and some who promote the opposite (the sound should wash over your ears and never come back). So what do you recommend, and what do you think is the right balance?
Listening Room Intelligibility Test
- Thread starter Art Noxon
- Start date
Personally I prefer the RFZ approach. While one cannot get a really reflection free zone, my goal is typically to get the amplitude of the first and second reflections away from the initial launch path so as not to smear the direct sound through excessive filtering. I normally try to deflect the first HF reflections and have a combination of absorption and diffusion in secondary points. Why? Well, most domestic loudspeakers are voiced for normal domiciles. They are meant to make use of boundary effects for both amplitude and the sense of space so for me deadening the room will leave you with sound that is biased towards the low end. As frequency drops the propagation changes. As these change, new sets of treatments specific to those frequencies come into play. Once we get into the bass range we'll find that areas aside from the nodes in free space, the junctions between boundaries, are excited most. No surprise that bass traps are typically found in corners since this is where they are most needed. I wish it was as simple as slapping panels of compressed fiber everywhere but it isn't. To me, one must take into account the propagation and that is why I feel ray tracing is extremely useful and I dare say, should be used.
Hopefully the net effect is to keep reflections outside of the precedence effect time window. Note that I mention a time window here. Above the time window, first reflections are picked up by the brain (mine at least) as added ambiance since they are easily precessed as follow on events or basically how we are accustomed to receiving aural input in everyday life. Inside the time window and we get sums and cancelations that are destructive of intelligibility right out of the starting gate. Simplistically, think of an echo where outside the window you get Hello, hello, hello and inside it's Hheheellolohhhellelo. By deflecting the HF which incidentally carries the sounds of consonants and most leading transients you get to preserve the initial wave launches from top to bottom, from your loudspeaker to your ears. Couple this with treatments that cumulatively drop the reverberation times across the width of your frequency range and you get sound that is easily identifiable, intelligable and is again hopefully, truer to the signal without sounding unnatural because the third, fourth.....nth reflections are now low enough in amplitude so as not to mask what is newly coming out of the loudspeaker. Getting nothing but direct sound may be great for working on a track but for purely recreational listening, I've found, can be overwhelming to the point of fatiguing.
Legend has it that Art has an entire warehouse full of his early experiments. Those that didn't make the grade so to speak, in contrast to the right designs he has now been making available for quit some time. Is this true Art? Did you really keep the test panels and traps for posterity?
Hopefully the net effect is to keep reflections outside of the precedence effect time window. Note that I mention a time window here. Above the time window, first reflections are picked up by the brain (mine at least) as added ambiance since they are easily precessed as follow on events or basically how we are accustomed to receiving aural input in everyday life. Inside the time window and we get sums and cancelations that are destructive of intelligibility right out of the starting gate. Simplistically, think of an echo where outside the window you get Hello, hello, hello and inside it's Hheheellolohhhellelo. By deflecting the HF which incidentally carries the sounds of consonants and most leading transients you get to preserve the initial wave launches from top to bottom, from your loudspeaker to your ears. Couple this with treatments that cumulatively drop the reverberation times across the width of your frequency range and you get sound that is easily identifiable, intelligable and is again hopefully, truer to the signal without sounding unnatural because the third, fourth.....nth reflections are now low enough in amplitude so as not to mask what is newly coming out of the loudspeaker. Getting nothing but direct sound may be great for working on a track but for purely recreational listening, I've found, can be overwhelming to the point of fatiguing.
Legend has it that Art has an entire warehouse full of his early experiments. Those that didn't make the grade so to speak, in contrast to the right designs he has now been making available for quit some time. Is this true Art? Did you really keep the test panels and traps for posterity?
My speakers are CD waveguides and are far enough from the boundaries that first reflections from there are not a problem. The cathedral ceiling, likewise, serves to eliminate the usual source of early reflections from there. However, the large ceiling area leads to a fairly long reverbration time overall. I am most interested in room treatments that blend in seamlessly. The Persian rug (with thick felt pad) and large couches are a couple of examples of those. I presume you are suggesting a mix of different treatment types to "cumulatively drop the reverberation times across the width of the frequency range". I have been thinking about adding some membrane absorbers (perhaps on the lower part of the ceiling above my listening position) to improve things in the modal region. Some additional Mid- to HF absorption in the front of the room (or perhaps on the front half of the ceiling) would help to cut down some of the excessive echo and improve imaging and intelligibility, I think. I would be interested to lean more about Art's designs.
So would I but I would respect it if he didn't give his secret sauce recipe. One thing for sure is that his ASC panels (I own 10) are different, very different from the usual fiberglass in a frame treatments home made or sold. Going by weight alone you can tell that it's some kind of foam but it is a heavy one. A primitive test I do is to hold a panel a couple of inches in front of my face and talk into it or if it is mounted I walk up to it and talk into it. One shouldn't be caught on video doing this lest one end up being committed. 
It's difficult to describe but if you try this at home away from prying eyes going from say, bare wall, to drapes, to existing usual suspect panels you'll know what I mean. Talking into ASC panels is like talking into a big space in the way stuff comes back at you. That's what makes it different IME.
If there is a downside, they aren't exactly easy to hide. The bass traps more so. To those that don't mind however, the cumulative effects of a full package on a room and how they allow equipment in it to perform near or at their full potential makes the aesthetics inconsequential.
What's interesting with directivity loudspeakers is that even huge ones work well in small rooms and yes high and mid-high frequencies are definitely LESS prone to damaging early reflections because well, by design there really are less of them when compared to point and quasi-point sources. What bothers me about some acoustic treatment manufacturers is that while early reflections are important to deal with, not enough emphasis is put on late reflections. Early reflections have been turned into a marketing slogan. Same goes for bass traps where the more the merrier also has become one. The goal should actually be to make the room behave as though it were larger and to do this one has to deal with the entire spectrum. What really burns my butt is when there is nary a query on the room itself and the loudspeakers seeing as the construction of the room and the radiation pattern of the loudspeakers and what goes in the room, including people, already have reflective and absorptive properties intrinsic to it. It isn't like anybody is going to cover the entire room. When the furnished room isn't taken into consideration before treatment all one can realistically expect is different but not necessarily better although it may seem that way at the beginning until suck outs rear their ugly head. These are steps ASC and other true acoustical companies always look at and it is a reason I respect ASC. Their results are predictable and spot on.
It's difficult to describe but if you try this at home away from prying eyes going from say, bare wall, to drapes, to existing usual suspect panels you'll know what I mean. Talking into ASC panels is like talking into a big space in the way stuff comes back at you. That's what makes it different IME.If there is a downside, they aren't exactly easy to hide. The bass traps more so. To those that don't mind however, the cumulative effects of a full package on a room and how they allow equipment in it to perform near or at their full potential makes the aesthetics inconsequential.
What's interesting with directivity loudspeakers is that even huge ones work well in small rooms and yes high and mid-high frequencies are definitely LESS prone to damaging early reflections because well, by design there really are less of them when compared to point and quasi-point sources. What bothers me about some acoustic treatment manufacturers is that while early reflections are important to deal with, not enough emphasis is put on late reflections. Early reflections have been turned into a marketing slogan. Same goes for bass traps where the more the merrier also has become one. The goal should actually be to make the room behave as though it were larger and to do this one has to deal with the entire spectrum. What really burns my butt is when there is nary a query on the room itself and the loudspeakers seeing as the construction of the room and the radiation pattern of the loudspeakers and what goes in the room, including people, already have reflective and absorptive properties intrinsic to it. It isn't like anybody is going to cover the entire room. When the furnished room isn't taken into consideration before treatment all one can realistically expect is different but not necessarily better although it may seem that way at the beginning until suck outs rear their ugly head. These are steps ASC and other true acoustical companies always look at and it is a reason I respect ASC. Their results are predictable and spot on.
Steve williams
Site Founder, Site Owner, Administrator
I too am an ASC believer Jack and I have over 30 tube traps/bass traps in the room with the front wall panelled with Art's Sound Planks
http://www.whatsbestforum.com/showt...-Of-Steve-Williams&p=3412&viewfull=1#post3412
http://www.whatsbestforum.com/showt...-Of-Steve-Williams&p=3412&viewfull=1#post3412
I would think so as weight distribution is even. Fillers like rock wool and fiberglass tend to sag with gravity over time. Some of the traps I've handled are many years old, no sagging whatsoever.
Where's Art at anyway?
Where's Art at anyway?
Bruce B
WBF Founding Member, Pro Audio Production Member
garylkoh
WBF Technical Expert (Speakers & Audio Equipment)
I too am a firm ASC believer. My room is all ASC tube traps and CinePanels. That it doesn't measure as intelligible as Bruce's is due to a lack of treatment. But also, I design speakers in that room, and designing for a perfect room I think is far easier than designing for a realistic living room. Hence, I do intentionally have the room a little more "live" than would be optimal.
Agreed my ceiling bass traps are 703. I was referring to the countless DIY prism type copycats I've encountered.
Hi guys,
Yes, where's Art? I've been asking that question myself. Being out of the loop for the last week, and honestly, I found myself missing our visits. The stress of running a business sometimes just overwhelms me, and I forget to remember to do what I love to do, which is to dream about carving and cultivating sound.
And yes, I can't throw those old traps and projects away. A while back the shop was so busy that it needed more production space. they wanted to rent one of those 40' shipping containers and move all my acoustic museum junk out into the parking lot. Thank goodness, the recession hit just in time. The orders for our strange acoustic widgets dropped off and the shop doesn't need to move me out of the building any more.
This addresses Jack’s comments. Much of what he is talking about is consistent with what I might be saying.
1) Treble and bass act differently. Ray tracing works on treble and not on bass. Bass acts like sloshing water. Treble sound flys straight lines and bass sound spreads out (diffuses by itself)
2) Yes, bass loading (efficiency) of the woofer depends on where the speaker is relative to the room boundaries. When adding bass traps near speakers, it is always important to not dampen the wall loading bandwidth and only dampen the upper bass wall reflection comb filter range. An interesting topic for the future.
3) RFZ, means “reflection free zone” and it is a concept where early reflections, those which occur within the Haas effect, precedence or sound fusion time window (first 1/30 sec following arrival of direct signal) are eliminated. It is fatiguing if that is all someone listens to.
Comment, RFZ is a treble effect, not a bass effect and it is very fatiguing. That’s why recording studio design is LEDE, dead early reflections and diffused late reflections. Dead early reflections gives perfect signal perception but is fatiguing, adding late diffusive reflections backfills sonic space with a presence that is sufficiently time delayed to not connect with the direct in the early reflection time period.
4) His goal is to keep reflections outside the precedence time window. It is correct to say that late reflections give a sense of ambience. But here, things get smeared. Let me straighten things out a little.
When we talk about early and late reflections we need to keep track of the difference between early and late reflections.
A) One strong early reflection creates the comb filter effect, sorta like the coloration of sound you hear when you talk through a tube.
B) Many not-so-strong early reflections have no comb filter coloration effect. However, they do increase the perceived loudness of the direct signal.
C) Intelligibility is not ruined by many early reflections, it is enhanced. Intelligibility is ruined by many late reflections.
D) Intelligibility is ruined because of “sound masking”. There are two types of sound masking, spectral masking and temporal masking.
a) An echo, a strong and very late reflection causes sound masking by upsetting, confusing the tempo of a sound sequence.
b) The best sound masking signal is a set of late reflections that sound just like the direct signal but that are phase and time scrambled, as if it became reverberation.
c) Reverberation is like a noise floor, which also causes sound masking. Reverberation is not a reflection, but a condition of sonic space, where all organization of a sound has been lost. The spectral energy is still in the room but without any sense of direction or timing.
d) Early phase and time distorted reflections, inside the 1/30 second Haas window, are pretty difficult to create. It takes time to capture and rearrange the timing of reflections enough to “scramble” reflections. The time it takes to do this is enough delay that it turns the early reflection into a noisy, sound masking late reflection.
E) Yes, excess treble damping leaves a room dull and bass heavy. This it how many AV rooms have been built. Walls and ceiling covered with 1” fiberglass panels. This kills 500Hz and up and barely touches the idea of bass damping. This is why most AV rooms sound awful in audio playback, besides 5 channels.
So, I agree in general with what Jack is saying. However, I do think he got things a little confused when it came to the effect of early and late reflections.
It is true that late reflections create ambience and are desirable in listening room. But all late reflections are not equal. The subset of late lateral reflections (across the ears) actually make up the ambience effect. Late vertical and rear wall reflections, non lateral late reflections, act as a noise floor for the detection of lateral reflections. They replace the perception of ambient space with ambient noise. I invented the Bastoni product line as a way to sort out the good lateral late reflections from the bad late reflections. It was a large polycylinder that had sound absorbing shelves fit into the poly face. It visciously attenuated vertical reflections, side scattered front to back reflected and diffused side to side reflections. Alan Goodwin and an AV dealer in Florida bought the ones I made but no one reordered any. Probably my fault, I don't do marketing very well.
This business about what part of sound we are customarily processing needs some clarification. Yes, late reflections tell us about the ambience of where we are. However this idea: “Inside the time window we get sums and cancellations that are destructive of intelligibility right out of the starting gate.” This just isn’t how it goes. Lots of early reflections just makes the overall sound brighter, and any phase scrambling problems disappear after the first few early reflections.
Absolutely, hearing the full attack transient, the low level high frequency detail, is very good for the perception of musical sound. This is what the MATT test measures
Yes, where's Art? I've been asking that question myself. Being out of the loop for the last week, and honestly, I found myself missing our visits. The stress of running a business sometimes just overwhelms me, and I forget to remember to do what I love to do, which is to dream about carving and cultivating sound.
And yes, I can't throw those old traps and projects away. A while back the shop was so busy that it needed more production space. they wanted to rent one of those 40' shipping containers and move all my acoustic museum junk out into the parking lot. Thank goodness, the recession hit just in time. The orders for our strange acoustic widgets dropped off and the shop doesn't need to move me out of the building any more.
This addresses Jack’s comments. Much of what he is talking about is consistent with what I might be saying.
1) Treble and bass act differently. Ray tracing works on treble and not on bass. Bass acts like sloshing water. Treble sound flys straight lines and bass sound spreads out (diffuses by itself)
2) Yes, bass loading (efficiency) of the woofer depends on where the speaker is relative to the room boundaries. When adding bass traps near speakers, it is always important to not dampen the wall loading bandwidth and only dampen the upper bass wall reflection comb filter range. An interesting topic for the future.
3) RFZ, means “reflection free zone” and it is a concept where early reflections, those which occur within the Haas effect, precedence or sound fusion time window (first 1/30 sec following arrival of direct signal) are eliminated. It is fatiguing if that is all someone listens to.
Comment, RFZ is a treble effect, not a bass effect and it is very fatiguing. That’s why recording studio design is LEDE, dead early reflections and diffused late reflections. Dead early reflections gives perfect signal perception but is fatiguing, adding late diffusive reflections backfills sonic space with a presence that is sufficiently time delayed to not connect with the direct in the early reflection time period.
4) His goal is to keep reflections outside the precedence time window. It is correct to say that late reflections give a sense of ambience. But here, things get smeared. Let me straighten things out a little.
When we talk about early and late reflections we need to keep track of the difference between early and late reflections.
A) One strong early reflection creates the comb filter effect, sorta like the coloration of sound you hear when you talk through a tube.
B) Many not-so-strong early reflections have no comb filter coloration effect. However, they do increase the perceived loudness of the direct signal.
C) Intelligibility is not ruined by many early reflections, it is enhanced. Intelligibility is ruined by many late reflections.
D) Intelligibility is ruined because of “sound masking”. There are two types of sound masking, spectral masking and temporal masking.
a) An echo, a strong and very late reflection causes sound masking by upsetting, confusing the tempo of a sound sequence.
b) The best sound masking signal is a set of late reflections that sound just like the direct signal but that are phase and time scrambled, as if it became reverberation.
c) Reverberation is like a noise floor, which also causes sound masking. Reverberation is not a reflection, but a condition of sonic space, where all organization of a sound has been lost. The spectral energy is still in the room but without any sense of direction or timing.
d) Early phase and time distorted reflections, inside the 1/30 second Haas window, are pretty difficult to create. It takes time to capture and rearrange the timing of reflections enough to “scramble” reflections. The time it takes to do this is enough delay that it turns the early reflection into a noisy, sound masking late reflection.
E) Yes, excess treble damping leaves a room dull and bass heavy. This it how many AV rooms have been built. Walls and ceiling covered with 1” fiberglass panels. This kills 500Hz and up and barely touches the idea of bass damping. This is why most AV rooms sound awful in audio playback, besides 5 channels.
So, I agree in general with what Jack is saying. However, I do think he got things a little confused when it came to the effect of early and late reflections.
It is true that late reflections create ambience and are desirable in listening room. But all late reflections are not equal. The subset of late lateral reflections (across the ears) actually make up the ambience effect. Late vertical and rear wall reflections, non lateral late reflections, act as a noise floor for the detection of lateral reflections. They replace the perception of ambient space with ambient noise. I invented the Bastoni product line as a way to sort out the good lateral late reflections from the bad late reflections. It was a large polycylinder that had sound absorbing shelves fit into the poly face. It visciously attenuated vertical reflections, side scattered front to back reflected and diffused side to side reflections. Alan Goodwin and an AV dealer in Florida bought the ones I made but no one reordered any. Probably my fault, I don't do marketing very well.
This business about what part of sound we are customarily processing needs some clarification. Yes, late reflections tell us about the ambience of where we are. However this idea: “Inside the time window we get sums and cancellations that are destructive of intelligibility right out of the starting gate.” This just isn’t how it goes. Lots of early reflections just makes the overall sound brighter, and any phase scrambling problems disappear after the first few early reflections.
Absolutely, hearing the full attack transient, the low level high frequency detail, is very good for the perception of musical sound. This is what the MATT test measures
Steve williams
Site Founder, Site Owner, Administrator
If there were clapping emoticons I would've used a bunch of 'em. That's what being out of the loop for a decade gets you. Thanks for getting my rusty brain back on track Art.
Bruce B
WBF Founding Member, Pro Audio Production Member
So now... if you could.. Tell each of us, by looking at the graphs and photos of our rooms, how we can improve each of our rooms.
Hi guys, I actually wrote a very long answer, going into lots of detail and then I decided I was just meandering and needed to stay focused, so I wrote the streamlined version posted here. One thing I went into during my long answer, that I forgot to even mention here, is the following. Google the term QSF Quick Sound Field for fun and browse around. It is a recording technique that is dedicated to making lifelike sounding tracks. It fills the Haas, precedence effect or sound fusion time window up with lots of early reflections.
The human is in effect a corrolation detection system. What appears to be a very dirty electronic signal, one with lots of early reflections polluting the prized direct signal, is actually very nice sounding, loud and clear and normal sounding to us. We humans epend on early reflections. If you want to hear what the world sounds like without early reflections, go stand on a sand dune in the middle of nowhere, or go stand on top a small hump in the ground with nothing else around, like in some park somewhere. And talk to yourself, and hear how empty you sound to yourself, compared to saying something in an office or room. Jut keep harping on the notion that early reflections are something bad. they are very good.
However, for some purposes, they do cause some trouble. Strong very early reflections, those within a couple ms following the direct signal cause imaging shifts. Later early reflections, those within the haas effect time window shape the sound stage, width and depth. Too many early reflections fog the image, changing it from a hot spot to a floating fuzz ball. I think we should spend some time talking about and sketching out our sound stage. We do this by playing mono music. If everything is in sync we have a center image that stays put and stays small throughout the musical presentation. However, it's fun to watch the image ball move around according to the tone. If you can try runing your system in mono and watch image changes and report in on your experiences. ..............................art
The human is in effect a corrolation detection system. What appears to be a very dirty electronic signal, one with lots of early reflections polluting the prized direct signal, is actually very nice sounding, loud and clear and normal sounding to us. We humans epend on early reflections. If you want to hear what the world sounds like without early reflections, go stand on a sand dune in the middle of nowhere, or go stand on top a small hump in the ground with nothing else around, like in some park somewhere. And talk to yourself, and hear how empty you sound to yourself, compared to saying something in an office or room. Jut keep harping on the notion that early reflections are something bad. they are very good.
However, for some purposes, they do cause some trouble. Strong very early reflections, those within a couple ms following the direct signal cause imaging shifts. Later early reflections, those within the haas effect time window shape the sound stage, width and depth. Too many early reflections fog the image, changing it from a hot spot to a floating fuzz ball. I think we should spend some time talking about and sketching out our sound stage. We do this by playing mono music. If everything is in sync we have a center image that stays put and stays small throughout the musical presentation. However, it's fun to watch the image ball move around according to the tone. If you can try runing your system in mono and watch image changes and report in on your experiences. ..............................art
OK, I will pick on someone and let's see what happens. I did spend some time describing in general terms what I was seeing.
ONE IMPORTANT THING: We are currently going through the test CD, because of a few complaints we received about timing, before we print our next edition (to be handed out at THE Audio Show in a couple weeks. We discovered to my horror that the test timing had changed many years ago but the text accompanying the test did not change. Quick overview is that the test starts actually at 17 Hz not 28 Hz and tuns up through 790 Hz, not 780 Hz and it's faster than before, running 20 Hz/second frequency change rate. Example: starting at 17 Hz, after 2 seconds, the tone being played is 17 + 2 x 20 = 57 Hz. I haven't tracked down where exacty in our history the change happened. I have found the edition that did start at 28 and run through 780 as the literature says, but the downloadable test and the Stereophile test CD #2 both run faster and wider, between 17 and 790 Hz. I'm very sorry that our accompanying literature did not keep up with the changes in the test bandwidth. I know that when subwoofers came into the market we wanted to widen the bandwidth of the test to get down in the the full subwoofer bandwidth. I'd say 17 Hz is low enough. Such is life in the fast lane...
.............................art
Where will you be, Art? I don't see ASC listed as an exhibitor on the show site page. Presumably, you're working in tandem with one (or many!) CE's.
We are with Magico/Spectral in Maier Shadi's room (Audio Salon). We are not doing much else at that show, unfortunately. We are doing lots at Cal Audio show, in SF next month. I can't even go to THE Show, prior commitment. I was down there couple weeks ago and scoped the place out and designed the acoustic system. I'll talk about it after the show is over. I can guarantee you guys one thing, I never did anything like this before...and I've got the pre showtime jitters. The wave breaking system is all behind scrim and even if you saw it, you probably couldn't figure out what the heck I am doing, unless you mapped the whole thing out, then you can make a good guess. Hint: It's in Newport BEACH right, ........ so just think about what happens when big waves hit a BEACH? That room is huge. There is no way to "TubeTrap" anything that big. A completely different approach had to be used, something affordale and doable. And it didn't matter what it looked like and I had just about all the room I wanted to work in. Usually everyone loves to complain how ugly and expensive acoustics is, and now behind a scrim, anything goes, it's like high end street fighting. Fun, fun, fun.
Maier is a great person to work with. He is so into real sound and what it takes to get there. He's always asking questions, but not randomly. They are always tightly connected to what just happened. We talk and cook something up and he thinks about what we have talked about and calls me back up the next morning and asks focused questions and presto we take it yet another step even further. Over and over, weaving constraints into need and this acoustic monster is the net result. I sure hope I don't let him down.
Remember, be honest, gentle but honest with me if you get to go. I do want to know if we did these great manufacturers justice. I wish I could remember the rest of the chain. I'll edit this when I remember.
We will have hand out packages there in the staging room for those who are interested in serious room conditioning. All the MATT CD support material will have been straightened out and will be available there also. Thanks for asking....Why didn't I even think of mentioning this adventure to you guys....mebad Art
Maier is a great person to work with. He is so into real sound and what it takes to get there. He's always asking questions, but not randomly. They are always tightly connected to what just happened. We talk and cook something up and he thinks about what we have talked about and calls me back up the next morning and asks focused questions and presto we take it yet another step even further. Over and over, weaving constraints into need and this acoustic monster is the net result. I sure hope I don't let him down.
Remember, be honest, gentle but honest with me if you get to go. I do want to know if we did these great manufacturers justice. I wish I could remember the rest of the chain. I'll edit this when I remember.
We will have hand out packages there in the staging room for those who are interested in serious room conditioning. All the MATT CD support material will have been straightened out and will be available there also. Thanks for asking....Why didn't I even think of mentioning this adventure to you guys....mebad Art
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