New way for absorbing back wave?

[ted99]

Rich--I appreciate your informed opinion. The manufacturer of the foam claims an absorption which appears to me to be equal to that of the minitrap HF down to 280 Hz, the crossover frequency of the 'stat panel. As I get time, I think I'll remove two of the layers, bow the foam layer to the back, away from the 'stat panel, and rerun the YPAO to see if it still reports the speaker polarity as correct and to compare the gain needed to level compensate to the three layers. Running the YPAO is time-consuming, so i'll wait until my second sub arrives (on order) and combine the two tests.

 

[nsgarch]

I'm curious to what others might think.... If this speaker sounds better by stuffing absorption material directly behind the panel as noted above... Why didn't Martin Logan just enclose the stat - and stuff the cabinet full of foam? I don't think any electrostat is built like that - I may be mistaken - but, I thought part of the magic from this speaker was from its dipole design.

This is my position exactly. As a matter of fact, the curved ML panel means the (focused) rear wave becomes a lot of harmless cancellation hash before it ever reaches the wall anyway

Rich, to be honest, statements like this simply baffle me: "I just know that my speakers in my listening room image much better than any concert hall orchestra I have ever listened to." What?? So I used the term 'hyper-imaging' to express what I understood you seek from your system's reproduction. Maybe I'm just old school, but stopping short of Phil Spector`s Wall Of Sound , I prefer the enveloping environment of a live performance. I have no trouble locating the instruments.

Though I must admit, you made me consider the fact that even when the recording captures it, not everyone is interested in re-creating the live event.

 

[twich54]

I prefer the enveloping environment of a live performance. I have no trouble locating the instruments.

Totaly agree, but I'm fortunate to be but a hours drive from Verizon Hall

Though I must admit, you made me consider the fact that even when the recording captures it, not everyone is interested in re-creating the live event.

On reason I believe......is the number of people that have benifited from real world concerts of unamplified music is not that great (percentage wise) with respect to those that listen to amplified reproduced music.

 

[amey01]

Ted,

The pic makes it much easier to visualise to what you were referring.

I wouldn't be doing that. It is too close to interfere with the speaker's operation.

Question: Are you doing this for any sound benefit, or just because the Yamaha is telling you that you are out of phase?

If it is the latter, then now that you've satisfied yourself that you are in phase, remove those things! Room correction systems are not human ears and can rarely cope with dipole speakers.

If you are hearing a benefit, then you need to experiment further. As you can see, there are varying opinions on whether to absorb or refract the rear wave. MLs are designed to operate in real-world rooms without any tweaking, however you can seriously improve the sound by improving your acoustics.

Diffusion AND absorption are both valid:
1: Depending on your room
2: Depending on yoru preference
Experiment and keep what you like best.

Good luck.

 

[TrumpetDoug]

Photo is attached of the top of the Ascent, with three thicknesses of RPG foam behind panel. So, as I thought, it is not a new idea, but it is a more recent way to use a currently available generic material. I will not comment on the diffusion/absorption/bi-pole arguments. Others have covered these arguments is some detail and I suspect that this is a subject much like "high-end" cables and power conditioners: there are as many opinions as there are users.

The only thing that may concern me about this foam is that it seems to come apart a bit. I can see bit and pieces on the black frame. I would be terribly afraid that this would get in between the mylar and the medal stat panel and eventually damage the mylar. Perhaps you may want to try the cloth hanging technique I described earlier. I suppose let your ears cautiously be your guide.

Doug - out

 

[Gordon Gray]

Well my time to chime in. My system in this current house is bordering the edges of a very large picture window. Not my choice of course, the last house had a dedicated audio room in a finished basement. We are currently working (meaning the early planning stages) on putting a room above the garage for such a space.

Well folks,

Here's my take. I have a large window on the backside of my ML's and the Summit panels are 5' from the window. My listening chair is about eight feet from the panels. I have five - five foot tall plants between the window and the back of the speakers. I guess you would call that diffusing the back wave.

I am very happy with this setup. Rich has also heard my system and his only comment concerned the fact that the speakers were spiked directly into the floor allowing bass notes to transmit through the floor causing a less defined low end. As a result of Rich's observations, I purchased the BDR pucks, which were installed between the spikes and the wood floor.

Result. Much less vibration coming through the floor and a better defined mid bass / lower bass.

I must admit that I've never tried materials that absorb because I also have a nice view out the window and wish not to obstruct that view.

Anyway, the sound is somewhat live but images very well with great low end punch, a liquid midrange, and a transparent top end with no sibilant artifacts.

GG

 

[jfm]

I seem remember an article in Stereophile about 10 years ago concerning suppression of the backwave. In the article one of the reviewers had a a pair of MLs for review (not sure which model) and Gayle Sanders came over to help with setup.

I think the reviewer put some kind of damping material behind the panel and mounted on top of the woofer cabinet. Apparantly Gayle Sanders was surprised at how good the sound was without the backwave and was going to look into this idea further.

http://www.stereophile.com/floorloudspeakers/145/index6.html

 

[Neil H]

If the brain combines the two, that's when imaging goes to hell. The standard that has been established is that an echo, to be heard as an echo, must arrive at least 7 msec after the direct sound. If you divide 1180 ft/sec by .007 sec, you get 8.25 feet (difference in path length.) )

I take it that this would mean a distance from the back wall of about 4.15 feet ie. 4.15 for the sound to get to the wall and another 4.15 for it to get back to the speaker.

I have no rear damping in my room at present and found that those distances were about the point where I have found the speakers to sound at their best. I first had the speakers at about 3 feet but when I moved them to 5 the sound snapped into place.

Of course that could just be an anomally of the room or it just so happened that by the time I moved them to 5 feet breakin had gone just a step further.

I have a reasonably large room so that distance is not a problem, and I actually have them at about 6 feet at the moment.

 

[benleeys]

......Although orchestras sound great, I have to admit I have never experienced the kind of pinpoint imaging and soundstaging with an orchestra that I get with my Summits. It is just an entirely different experience.

Rich,
As a regular concert goer, I agree with what you say. My view is that our sitting position in the hall determines the kind of sound we hear of the orchestra (otherwise there wouldn't be various classes of seats).

The mics used for the recordings are placed at various perceived optimum positions for the recording process and therefore capture the sounds in the way the recording engineer wishes it to be. Together with post recording manupulations in the studios and whatever, the final result we experience at our home setups will surely be quite different from the overall sound we hear at our seats in the hall.

That's why I have always been a bit sceptical of the pronouncements of people like Harry Pearson of TAS that the ultimate quality of the sound from our equipment has to be judged against that of real unamplified sound in a concert hall environment.

 

[twich54]

That's why I have always been a bit sceptical of the pronouncements of people like Harry Pearson of TAS that the ultimate quality of the sound from our equipment has to be judged against that of real unamplified sound in a concert hall environment.

The what IS the benchmark from which we judge ??

 

[Rich]

Benleeys,

Thank you for expressing my point in a much more concise and clear manner than I was able to. Stereo recording is it's own beast and reproducing that recording on a pair of speakers is inherently different from listening to live instruments in concert hall.

Dave,
It is O.K. to use live unamplified music as your benchmark, if you really need a defined benchmark to enjoy your music. But you must do so with the understanding that the physics of stereo audio recording and reproduction are inherently different from the physics of sitting in a concert hall listening to live instruments. You are never going to recreate that exact sound on any two-channel listening system, so it is a little disingenuous to say that is your benchmark because it is ultimately not achievable. And that is not to say that the live music will always sound better in every respect than the recording. Engineers can do amazing things with recordings and some aspects of the stereo recording can sound much better than it did live.

Now, having said all that, I don't mean to dispute Neal's point that in a large enough room where you can get the speakers far enough from the back wall and side walls, that the delay will reduce comb filtering and allow the music to sound better. I have listened to Gordon's system and thought it sounded very good. His speakers are five foot or so out from a glass wall and very far from both side walls in a room with cathedral ceilings.

But after hearing my Summits with absorption behind them, I still feel the echoes of a live, reflective room hamper ML speakers from producing their best sound. As someone said above, this issue is dependent on individual room acoustics and individual taste, which is why everyone should test both diffusion and absorption before deciding what works for them.

As a matter of fact, the curved ML panel means the (focused) rear wave becomes a lot of harmless cancellation hash before it ever reaches the wall anyway.

Neil, what do you mean by this? If this were the case, why would we need diffusers or a certain distance from the rear wall anyway? For that matter, why would the Stage speaker design work at all? The rear wave focuses to a point behind the speaker and then reverses itself and continues traveling in a continuous waveform, which will be deleterious to your perception of the sound of the front wave unless it is diffused, absorbed, or delayed long enough (although I still believe that even with delay it is a problem, just less of a problem).

It seems funny to me how people are always trying to get their background noise floor to be a dead quiet "black" background, but then there is supposedly no problem with all these reflective echoes of sound hampering the stereo image of the front wave. I don't buy it, but that is just my opinion.

By the way, I do get a completely enveloping experience listening to well-recorded orchestral music, and I also get very precise imaging. As I have said, in some ways what I hear in my system is much better than what I hear live. But they are different. One can never be a completely accurate facsimile of the other, in my experience.

 

[slowGEEZR]

The what IS the benchmark from which we judge ??

Originally Posted by benleeys
That's why I have always been a bit sceptical of the pronouncements of people like Harry Pearson of TAS that the ultimate quality of the sound from our equipment has to be judged against that of real unamplified sound in a concert hall environment.

Great question! After all, if the sound of a home system sounded precisely like the same acoustic performance at a concert hall, how would it sound with a great jazz performance at a small night club? One would think that accuracy is accuracy, so that if a system captures and presents all the acoustic queues from a perfectly recorded (even possible?) concert hall performance, then it should be able to capture and present all the acoustic queues from a a perfectly recorded night club performance. I think that HP is saying that if a system can capture the real sound from a concert hall environment, that is the most complex and therefore any other performances would be easy to replicate.

 

[benleeys]

The what IS the benchmark from which we judge ??

The point I'm trying to make is that there are too many variables in the recording/production chain that affect the sound we ultimately get to hear at home as compared to the orignal. So who's to say that this recorded piece is accurate and that is not quite so?

Even if one were to be present on the occasion the recording was captured and sitting in the exact position where the mics were placed, I doubt if one can really remember every bit of nuances in the performance to eventually pass fair judgment on a piece of equipment or system, assuming that the recorded sound is accurate in every respect. With memory retention so shortlived, at best one can only generalise.

Further, high-end equipment/system these days are so refined and differences in sound quality so minimal that it is not really fair to pronounce one is more ACCURATE than the other. IMHO, the ultimate judgment that can be passed is whether one can live with and enjoy one's acquisition.

My apologies if my expressions seem to make little sense, but English is really not my first language. Hopefully, you should get the gist of what I'm trying to say.

 

[Rich]

My apologies if my expressions seem to make little sense, but English is really not my first language. Hopefully, you should get the gist of what I'm trying to say.

No worries there, Ben. You write in English more eloquently than many for whom it is a native tongue.

 

[twich54]

maybe benchmark is the wrong word, maybe..."a point of refrence", whatever. One must have one or the other for without it it's impossible to make qualitative and good judgement.

My point is simply this, IMO, unamplified music, chamber music, full orchestra, Pops ensemble, piano soloist, etc , etc is the benchmark/refrence that we try to get as close as possible too. There's no denying that the "Memorex Moment" is still recorded music, but without decent prior listening experience one really dosen't know what the differences are between our home audio setups and the "real thing".

As an example those that have a love for Club Jazz for example can do their best to tailor their system to replicate that as close as possible, but first they would have had to experience it live.

 

[BobF]

Gordon,
Where did you get the BDR pucks?
Thanks,Bob

 

[Gordon Gray]

Gordon,
Where did you get the BDR pucks?
Thanks,Bob

Hi Bob,

Available through Music Direct. Be advised that the BDR "pits" that I purchased are a bit pricey and you can find other products that basically do the same thing (decouple the speakers from the floor) for less money, but these puppies do a stellar job for their intended purpose. See my system description for the specific model purchased.

FYI, Music Direct has a 30 day money back policy on most items, including the BDR items. Should verify before purchasing.

If you choose to purchase this type of decoupler, with four required per speaker, it may take a bit of work to get all four items to couple "securely" to the spikes.

FWIW, this is "off topic". If you wish additional info, please send me a PM. Will gladly provide.

Gordon

 

[timm]

Ok - would it be crazy for me to say...'My system sounds better than the live event'.... I guess what I am saying is this - in any live venue that I have EVER been at - whether it be amped/not amped etc.... There is all of this other 'noise' going on - people talking/crunching paper,squeeky seats... you name it. Then you have the ambience of the hall to deal with. Then your seating position... At my house, it is me, I can control all exteriour noise,my seating position etc...

In the recording studio - you have towels/blankets/rugs on the floor for damping material, sound proof rooms. Then of course you have the engineer - and there is only 1 seat in the house - the engineeers chair - and it is dead center - void of all of these problems

I honestly think most of us use our systems as the 'benchmark' - then go to a live performance and base comparisons to it.

I wonder what the THD at a live event is 5 percent?

I think the discussion of the 'live event benchmark' is flawed in the sense - 'Who's live enent? What venue? What seating position? Hall design?' Empty hall/half empty hall/ full hall? So after that - you have to determine the benchmark of the benchmarks.... good god man...... I think our systems may have fewer variables - which I think is something that defines a good benchmark....So lets argue about that one!!!

 

[Rich]

I agree with you totally, timm and I have argued this same point in previous threads. Live music is totally variable and suffers from all kinds of issues that detract from its sound quality. To some, live music is this holy grail hallmark of ultimate sound that their systems must be compared to and always fall short of. Personally, I think my system sounds better than most live music I have heard as far as actual quality of the sound goes. And I am including orchestral arrangements, chamber music, live jazz, and bluegrass ensembles, in many different venues, in that comparison.

I also do not believe that you have to use live music as any kind of benchmark or reference to judge your system by. If you have listened to lots of different music on lots of different systems, and know particular recordings backwards and forwards, you can evaluate the quality of your system's sound independent of any reference to the sound of live music. Such a reference is faulty at best anyway, in my opinion.

 

[Bernard]

Personally, I think my system sounds better than most live music I have heard as far as actual quality of the sound goes. And I am including orchestral arrangements, chamber music, live jazz, and bluegrass ensembles, in many different venues, in that comparison.

I just wish that the enginners had not lost what they learned when they recorded those Mercury Living Presence disks. There is a quality to the strings (I think it's referred to as "rosiny") that is rounded and almost purrs, that I hear on Mercury but nowhere else.