[8thnerve]

Also, if you ever do an impulse response measurement of a room, you can see exactly where the reflections are in time and hitting the refleciton points at those time points for first reflections absolutely does minimize those impulse 'blips.'  While you may not hear them specifically as an echo, you can absolutely hear/see the change in image specifity.

I would disagree with your interpretation of that data.  The reason those 'blips' reduce in level is because the overall high-frequency content of the room is reduced with the first reflection treatment in place.  I see the same impulse reduction without first reflection treatment when proper corner treatment is installed.

-Nathan

[8thnerve]

Perhaps 8th nerve is using a special kind of unidirectional fiberglass - Since it is reflective on one side, that must mean that it allows sound to pass through going toward the wall, yet magically knows to absorb it on the way out!?    And I guess since it is offset from the wall slightly, it also knows to let the sound in, but traps it effectively on the way out!?

I apologize if I am being unclear.  One side of the product is a hard reflective surface.  This is the part that faces into the room.  The other side is where the fiberglass is, facing into the corner.  Sound travels past the gap around the edge of the product into the corner.  Very little sound energy is lost as can be verified by taking measurements in front of, and behind the product.  Once the sound reflects back from the corner, it travels into the fiberglass and reflects off the the back of the reflective layer on the front of the product and travels back into the corner again.  This process repeats until the energy is gone.

Because of the shape of the product, the small gaps around the product consist of only about 5% of the available area that the return corner wave will hit.  Therefore, about 95% of the sound is trapped and cycled to nothing.  Is this more clear?

If you think my answers are pixie dust then I am not explaining them adequately.  These products work and I am happy to explain the solid, scientific processes that enable this.  Simply because it's new doesn't mean it's wrong.

-Nathan

[8thnerve]

Listen to any small room with an adequate amount of Eighth Nerve treatments and you'll change your mind. 

Hey, maybe I would if you'd ever check your PMs!   Any of those summer deals left?

Sorry Rob.  This new Audio Circle software doesn't pop up a box when I have new messages and so I never notice.  It's also much harder to see what is new and what I've already read.  The sale page indicates to email me and that is certainly the best way to go.  I don't get PMs nearly as often.  If you are having trouble reaching me via email (meaning you've sent me two emails already, and the second one said, "Hey Nathan, where are you?") then shoot me a PM (and include your email address so I can compare) to make sure your mail isn't getting lost, but that shouldn't happen, I go through ALL my spam mail to make sure I don't miss anything.

At any rate, you have a PM. 

Best,

Nathan Loyer
Eighth Nerve

Yeah, I'm noticing that, too.  But I also did email you and didn't get a response.  Maybe it's your spam filter, or maybe a problem on my end.  Anyway, I'll check my PM.

I responded back several times, your spam filter must be eating my messages.  I sent you a PM.

-Nathan

[John Casler]

John,

> If the brain can hear the frequency combination of direct and reflected sound then it can certainly hear the differing arrival times. <

Yes, when the delay is long enough. At short delays, less than 20 ms (or whatever) the main issue is the skewed response caused by comb filtering. I'm not disagreeing with you, because you hit the nail on the head! Time-based problems are at least as damaging as frequency response problems.

Hi Ethan,

I have a tendency to agree with that, except that I have heard significant sonic difference from the reflection of a simple marble table that used to sit "only" a few feet in front of me, meaning the angle of deflection and the delay time was "extremely" short.

Removing that table made significant improvement.

> I make an extreme distinction between a two channel audio playback environment, and the goals involved, compared to trying to make a HT, and other venue type acoustic environments, provide accuracy, and enjoyment. <

I know it's conventional wisdom that a 2-channel room should be more live than a home theater. But as I've added more and more treatment over time in my living room I've come to realize that one room can indeed sound excellent for both. It comes down to the opposing philosophies of whether the room should or should not impart its own character onto the reproduction. I have come to the conclusion that it should not. As soon as the room adds its own sound to the playback, you are no longer hearing what the mix engineers intended. The key is to avoid all early reflections. Once that's done you are hearing what the mix engineers intended. For the most part, and assuming bass and other resonances are also tamed.

--Ethan

Actually, the hard part is "what do the engineers intend you to hear"?

I feel the breadth of recording processes, environments, and engineering, cause us to choose which type of recording we wish to be most "true" to.

I choose to lean towards the "live" recordings as being the "Reference" for my system.

That requires that I reduce room distortion to a minimum, when and if possible.

[8thnerve]

And I cannot accept the concept that the brain will "ignore" or "reconstruct" the sound.  If the brain can hear the frequency combination of direct and reflected sound then it can certainly hear the differing arrival times.

Please know that I don't dispute the possibility of this sounding pleasant, or to some even preferable, but it is difficult to understand a statement of similarity of an Anechoic Room versus a Full Spectrum Reflective Room, when listening to music with "time domain" function.

It's not a matter of sounding pleasant.  It measures better.  In the frequency AND time domains.

This is a hard thing to conceptualize, but I'll give it a shot.  The biggest problem that everyone has is this erroneous concept that somehow there is a sound about to get to our ear and another one right behind it.  Sound moves way too fast for that and takes time to actually develop in our brain.  It takes a 60th of a second to simply create ONE cycle of a 60Hz wave, a sound that would barely be perceptible.  So just one cycle of this wave travels 5.6 meters in that 60th of a second period.  In most rooms, this one cycle has already been reflected around the room several times just to propagate itself.  And let me be clear, the wave isn't bouncing around the room, it is all the sound in the room during that time period.  The entire room crests and troughs to create that one cycle, at all points in the room.  Yes, the crests and troughs of the waves are in different states at different points in the room, but it is still the same wave, the same sound, the same cycle.

Saying that the first reflection contains a different sound or a delayed copy of that sound is overly simplistic and misleading.

-Nathan

[Ethan Winer]

Nathan,

> I have a tendency to agree with that, except that I have heard significant sonic difference from the reflection of a simple marble table that used to sit "only" a few feet in front of me, meaning the angle of deflection and the delay time was "extremely" short. <

Sure - I have a hand towel draped over the glass drink table on front of my couch for that very reason. Let's say the sound reflected off the table travels 2 feet farther so it's delayed about 2 milliseconds compared to the direct sound from a loudspeaker. That equates to one cycle at 565 Hz, but it's the half-wave that matters (180 degrees of phase shift) so the first null in the comb filter series is at 283 Hz. That's very audible! And directly explainable. I just rewrote the Frequency/Distance Calculator program for the RealTraps site, so this is all very fresh in my mind.

--Ethan

[John Casler]

Interesting thoughts John.  Again, you're thinking in terms of frequency response when you're addressing my 'dull and lifeless' comment.  I was speaking more of a lack of room ambience regardless of FR.

Hi Bryan,

I trust I know what you mean, but that "room ambiance" you speak of is nothing but "room distortion", to the original signal.  

Having spent much time in a room that has "reduced interaction", I can now "hear" every room I walk into.  From a Basketball Gym, to a well clothed closet, every room has a sound that you can hear.

Again, it might sound pleasant, but it degrades the accuracy of the original signal to varying degrees.  

Kinda like wearing "rose colored" glasses everytime you watch a movie.  You might get used to it, and it might even look good, but it isn't closer to the original source.

If I'm treating a room for a mix of 2 channel and HT use, I tend to leave the rear of the room a bit more live and use a mix of a bit of absorbtion mixed with diffusion as I described earlier.

If I had to combine systems, I would probably consider a similar arrangement (LEDE) since one of the greater goals in HT is "sonic envelopment" through multiple sound sources.

You'd probably find it amusing, that I consider diffusers, mechanical noise generators.

I'll agree that you'll never get a residential room to create an original venue - much less all venues.  But I do think one can make it more capable without absolutely killing it. 

Well getting back to "2 channel" only, the less room interaction, the more the "system" will provide you with recreation of the original venues, since you get to actually hear them without your room degrading them.

 To me, a completely dead room is very uncomfortable to be in and I find 2 channel music listening similar to listening to headphones.

Actually, a room that has less ambient noise will be very comfortable, and if you sit in it for any period of time without the music playing, you will likely fall asleep.

I have heard the old "myth" about how listening to music in an "anechoic chamber" is horrible, but when we try to find out who has made this evaluation in a reduced interaction room, under critical listening conditions, we find that not one "qualified" person has spend weeks or months, listening this way.

In fact, they haven't spend any time at all.

Admittedly, it is startling to really hear what is on a recording in a reduced interaction room, but your comment about headphones is pretty close, except, in a well designed room, the imaging and soundstage are "staggering" in their ability to sound realistic.

However, a "Studio Recording" will sound like a studio.

One other thing, to me, the trick in being able to 'listen deeply into the recording' is by designing the room to be quiet - not necessarily dead.  This is why isolation is so important.  It's not all about keeping sound from getting out.  IMO it's more important to keep it from getting in and mucking up the ambient noise floor of the room.  A very quiet room with a moderate amount of treatment and good bass control will allow good, relatively smooth frequency response at many different spots in the room - not just one sweet spot.

Bryan

Of course it is all a matter of "degrees", and preferences, as well, as I mentioned earlier, addressing your "Reference" material, along with any "compromises" one needs to make.

I have many times likened "high performance 2 channel listening" to High Performance Driving or Racing.

A BMW M-5 is a compromise (a good one, but a compromise just the same) compared to a Formula One car.

One is comfortable, seats 5, is very fast, and can be driven to the SuperMarket.  The other is brutal in its performance, seats one, and specializes in what it does best, but can only do its thing on the track.

I think all of us, and you guys as "Acoustics Experts" find what level of performance, preference, and compromise fits the situation and then we move to achieve that level.

I like driving an M5, but I prefer the performance of the Formula ride

As many have said before: YMMV

[bpape]

I think we're in somewhat agreement John.  I think we're just using different terms.  My point of the quiet - not dead is what I was referring to as lowering the noise floor in the room.  50db noise floor, 100db max system output, can't have more than 50db dynamic range.  30db noise floor, 100db output, max 70db dynamic range - and we've done nothing to change the internal absorbtion/reflection/diffusion in the room.

Let's try this...

When the engineer mixes the recording, HE is the one that is hearing and modding things (adding ambience, changing levels, EQ, etc.) to get the sound he wants.  He is listening in a room that is not the original venue.  It's treated similarly to what I desribed - dead front, early reflection control, scattered absorbtion/diffusion in the rear.  The only way to hear exactly what he did (and intends) is to listen on his system in his room (not terribly practical).  What we can do is emulate the enviornment in which he made his decisions.  Our system will be different but our room can be made closer - though I'm not advocating having a 2 channel room as dead as a studio control room...

Ethan - exactly.

Nathan - so what you're saying is that if I kill the wall totally behind my listening position and leave the reflections untreated that I'll see the spikes in the impulse response disappear just because I've absorbed the highs in the room overall?  What if I use 12" thick OC703 on the back wall that produces a very even absorbtion curve across the spectrum - do I still see them then because I didn't just absorb highs?  Just want to make sure I'm understanding your point - though I don't agree with it.  If it wasn't an issue then why did you remove the table?  That reflection should have just blended right in - correct?

Also, the information coming off the side walls at the reflection points absolutely positively is different from that coming directly at you.  Why?  Because there is no speaker made that has the exact same off axis response as on axis response.  As frequency changes, therefore, I have more or less reinforcement/cancellation/blending of the direct and  reflected sound at different frequencies - which changes the tonal balance of the perceived sound.

I'm glad we're all keeping this civil.  It's an excellent discussion of the hows and whys and different implementations to reach the same end.

Bryan

[8thnerve]

Sure - I have a hand towel draped over the glass drink table on front of my couch for that very reason. Let's say the sound reflected off the table travels 2 feet farther so it's delayed about 2 milliseconds compared to the direct sound from a loudspeaker. That equates to one cycle at 565 Hz, but it's the half-wave that matters (180 degrees of phase shift) so the first null in the comb filter series is at 283 Hz. That's very audible! And directly explainable. I just rewrote the Frequency/Distance Calculator program for the RealTraps site, so this is all very fresh in my mind.

Yes, the math is very straightforward.  And for a test tone, if you were in a free space environment with a table, you would see that exact result.  However there are an incredible amount of conflicting geometries in a room and as you've said before, a large comb filter series results at any given point in the room.  With complex sound however, (speech, music, basically anything other than test tones) the 565 Hz signal is only 565 Hz for an incredibly short amount of time.  By the time that delayed 565 Hz wave reaches the listener, the direct 565 Hz wave most likely will have changed though.  That, and it will be reduced in level by what, 2-3db?  There is no question that sound bouncing around the room causes comb filters and frequency and phase irregularities.  I am simply making the case that these minor irregularities pale in comparison to the amplified and distorted return energy from the corners.

And I still don't see how absorptive treatment makes a positive impact on the sound.  It reduces the energy of those waves that contribute to the comb filter, but all the waves in the room contribute to the comb filter.  Changing the frequency content because of non-linear absorption can cause even more serious and random comb filtering.  It just doesn't seem like a good trade off, and the in-room measurements with absorptive treatment up don't look any better than without treatment, at least when you address the largest areas of distortion first.  They have always looked worse.

-Nathan

[8thnerve]

Nathan - so what you're saying is that if I kill the wall totally behind my listening position and leave the reflections untreated that I'll see the spikes in the impulse response disappear just because I've absorbed the highs in the room overall?  What if I use 12" thick OC703 on the back wall that produces a very even absorption curve across the spectrum - do I still see them then because I didn't just absorb highs?  Just want to make sure I'm understanding your point - though I don't agree with it.  If it wasn't an issue then why did you remove the table?  That reflection should have just blended right in - correct?

Disappear, no.  Reduce in level as was stated, yes.  If you put absorption up, you'll see a reduction in all sound levels, but the level of reduction will be different across the band.

Also, the information coming off the side walls at the reflection points absolutely positively is different from that coming directly at you.  Why?  Because there is no speaker made that has the exact same off axis response as on axis response.  As frequency changes, therefore, I have more or less reinforcement/cancellation/blending of the direct and  reflected sound at different frequencies - which changes the tonal balance of the perceived sound.

Of course, but does that mean changing the signal even more is a good idea?

-Nathan

[bpape]

Change the signal?  No.  Keep keep some of the signals that are out of time/phase and drasitically different in frequency response from mucking up the direct signal?  Yup. 

As for the rear wall thing, well, we'll just have to agree to disagree on that one.  Lowering the overall level in a room doesn't change the relationship of direct to reflected sound from an untreated reflection point - it just brings the whole thing down.  But the time difference and difference in level (and frequency response of the off axis signal) is unchanged.

Bryan 

[Rob Babcock]

Odd.  I've seen some measurements of rooms before and after a set of RealTraps, and the measurements with the 'Traps is extremely good.  Flatter fr & reverberant envelope.

[bpape]

Guess I should be more clear Rob.  I was referring to the FR of the off axis sound from the speakers bouncing off the reflected surface vs. the direct signal.

Bryan

[ZooDog]

I'm bringing this thread back because I had an interesting experience over the weekend. 

I had the opportunity to set up my NHT Xd speakers in a large (aprox 30 x 20 x 11) room.  Pics:





At first I set up the system with no treatment.  The Xd has the best power response of pretty much any speaker in existence, and I have understood that the better the power response of the speaker, the less need there is for treatment at the first reflection points since the reflected sound is more similar to the direct sound, and therefore less confusing to the brain.  With this knowledge I figured that I could get the system to sound great without using any treatment at the side walls.  I have some foam up in my own room, but it was there before I purchased the Xds so I wasn't sure if it was making any real difference in the sound.

After I first set up the system and played with the toe-in and listening position a bit I got ok sound, but definitely not as good as I have with the speakers in my own room.  It was a bit shrill and fatiguing, and the center image lacked focus.  I decided to bring in my 4 GIK 244 panels and set them up at the first reflection points along the side walls (the ones in the corners are 247s).  Boom - everything snapped into focus.  The sound was now incredibly pure and detailed, and the soundstage became positively huge.  The sound now easily surpassed what I have in my own room, and is right up there with the best I've ever heard.  Ambience increased because I was now hearing more of the recording and less of the room.  Orchestral music is now tightly organized across the stage instead of appearing as a diffuse blob.  Though it's kind of silly, one of the songs that best demonstrated the improvement in imaging/soundstaging is Madonna's Vogue.  It uses q-sound which manipulates phase in order to make sounds appear to come from just about anywhere - behind your head, from the side, out in the backyard etc.  I've found that the better a  system can image, the more convincing q-sound is.  Well, in this case, the song is all over the room.  It's a fun thing to freak out non-audiophiles with. 

I wanted to share this because I now believe that even with a speaker that has excellent power response, treating the first reflection points is still beneficial, if not crucial.  I've now also learned that I need to do some more work on my own room to get it "there".

Edit:  I just want to add that I am starting to believe that the vast majority of "problems" that audiophiles encounter are room related.  IMHO, audiophiles who cycle through countless amps, cd players, cables etc. are merely spinning their wheels.  Get yourself some competent speakers and take care of the room. 

[nodiak]

     
    "...I am starting to believe that the vast majority of "problems" audiophiles encounter are room related."
   
    Thanks for that. I think that quote could be inserted in the vast majority of "discussions" about equipment. Just from changing rooms along the way it's been extremely obvious how different the system sounds room to room. But it's rarely brought up in equipment comparisons.
    I've finally come to my senses and will put my attention on the room, and will begin diy treatments right away.

Don

[ZooDog]

nodiak,

Though it finally seems that acoustic treatments are working their way into the audiophile mainstream it is still frightening to see pictures of rooms with 5 or 6-figure systems in them with bare walls and floors. 

I did not attend the RMAF but from the pictures I've seen it looks like many rooms were left untreated.  What are these people thinking?   

[Carlman]

Edit:  I just want to add that I am starting to believe that the vast majority of "problems" that audiophiles encounter are room related.  IMHO, audiophiles who cycle through countless amps, cd players, cables etc. are merely spinning their wheels.  Get yourself some competent speakers and take care of the room. 

Some of us try really hard to treat the room to no avail... it's just a bad room and that's what we got. 

Using cords and amps are a way to work around the fixed sonic qualities of a room.  Many people dismiss this as using gear or cords as 'tone controls' but it's a lot more than that... such as comb filtering, peaks, suckout, and all the subjective terms of the listener. 

I'm using a TacT and have sound treatment on just about everything in my room.  It's STILL not perfect.  But it's very, very good.

Anyway, the other problem with sound treatments is the looks.  Those GIK panels stand out more than a 300 lb. gorilla would in that room.  Not everyone is willing to sacrifice looks for sonic nirvana...

I do agree that reviewers should note the sound character of their room as part of the equation.  However, most reviews state the size of their room.  A little math lets me know what they're probably going to hear. 

-C

[John Casler]

Anyway, the other problem with sound treatments is the looks.  Those GIK panels stand out more than a 300 lb. gorilla would in that room.  Not everyone is willing to sacrifice looks for sonic nirvana...

I do agree that reviewers should note the sound character of their room as part of the equation.  However, most reviews state the size of their room.  A little math lets me know what they're probably going to hear. 

-C

Carlman is 100% correct.

While a perfectly treated room likely does not exist, we can be sure, that there are none that have maximum sonic benfits, while maintaining aesthetic apeal to the common person.

Many times I cringe, when seeing some of these rooms, for I already know how destructive they are to the sound.

If one must live with a system, that is placed in a "beautiful" room, the single best advice I can think of, is listen as "nearfield" as possible. (6-7 feet)

Anything less and you will be hearing the room and not the system.

Now that said, some "wish" to hear their room, and find the sonic enhancements euphonic.  There is much to be said for this viewpoint.

[nodiak]

Very good point about aesthetics, and about listening nearfield.
 
I know I'm going to end up with some goofy looking panels in awkward positions. Part of my plan is to hide them partially behind plants.

BTW, a thread about room reflections and ob has been started, if any are interested it would be good to here from the experienced, especially with ob and acoustic treatment.

http://www.audiocircle.com/index.php?topic=33241.0

Don

[ZooDog]

Anyway, the other problem with sound treatments is the looks.  Those GIK panels stand out more than a 300 lb. gorilla would in that room.  Not everyone is willing to sacrifice looks for sonic nirvana...

I agree with you about the looks thing.  The GIK panels would definitely be unacceptable as a permanent fixture in that room.  Acoustic treatment firms like Realtraps, Echo Busters, and ASC need to somehow come up with solutions that can fit in with room decor better or their customer base will be forever limited to recording professionals and hardcore audiophiles.  Simply coming up with different color options is not enough, IMO.

Using cords and amps are a way to work around the fixed sonic qualities of a room.

Can't agree with you 100% on that one.  Maybe tube amps can help in some cases, but certainly not cables.