What about Double Bass Arrays??

[SAC]

Originally Posted by tINY

Please go back and read the premise of the study. Within the scope of the study, this is a resonable simplification (likely made to keep the presentation interesting to people other than those still reading this exchange).

You will also notice that they kept the woofers on the floor, placed woofers along the wall, and drove the identical woofers in-phase. This is how the majority of any commercially viable systems will be deployed.

Of course, you may not be interested in actually improving the system performance of sound systems sold to the masses, but that's what Harmon does. Specifically, they are looking to improve low frequency behavior in home theatres for multiple listening positions.

There is no reason these concepts can't be extended into non-rectangular rooms or into 3-dimmensional configurations where the woofers are deployed at heights other than on the floor.

The german concept, using front and back arrays driven with different signals, simplifies the problem by turning the room into a giant tube with cancelation at the back wall. This may be better in a lot of ways, but is hard to sell domestically (if you are married).





This is precisely why they included the study. Using a "RULE OF THUMB" is usually a massive simplification of a complex problem.

You'll notice in Slide 45 that they come to the same conclusion you do... Is there a point to bringing this up?





That is the point of using a mono subwoofer system with multiple, identical drivers. If you can reduce variation of frequency response over the seating area and then apply a couple of bands of equalization to normalize the response, you have improved the bass performance for the people trying to listen to the music or watch the movie.

I'm not sure what is so evil about moderating variations of the model - so long as the system you are designing can effectively employ the same techniques. Are you hoping for directional sub-woofer response in a small room?




I am not suggesting that the results of mulitiple time-of-arrival differences (lobing and comb-filtering) don't exist for low frequencies in a small room. I am suggesting that they are inconsequential when considered in such simple terms. All of the lobing and combfiltering you have alluded to have both constructive and destructive interference - this is the way all sound is in all acoustical spaces. It's the aggregation of all of the contributions that is important.

You still haven't applied your "better result" to model the relatively simple, practical application of the 4 woofers in the front wall of the german scheme. It's only 4 sources and 4 sources reflected off of 4 surfaces for a first approximation... 20 signals to superimpose. Did you do the calculations and find that it didn't support your argument?




Until someone actually wants to put forth the effort to do some modeling or build 4 or 8 subs and take some measurements in a room....

What?

Now you are focused on evaluating Harmon's model which is NOT equivalent to the case in point presented in the three! The closest they come to the case in point is the use of 4 subs!...

The closest our original model presented comes to this is if the Harmon model were playing to the 'ceiling' - which they admit is a mess and are thankful no one sits there! But they DO in our original model, as the original model is shifted 90 degrees!

And then you go off justifying what Harmon did to mitigate their particular scenario which again does not solve our original scenario as originally presented!

And to take this further, you then dismiss the additional destructive interference created by the presented model by saying who cares as there is always some interference!!!

The point was that both modal and comb filtering and polar anomalies exist - and were MADE WORSE by the use of multiple vertically mounted subs spaced greater than 1/4 wavelength from all of the other sources - real and virtual - of the same bandpass.

In other words, the method used by the original example in this thread of simply adding more drivers to create greater gain came with a significant increase in destructive interference that could have been accomplished more effectively and efficiently without incurring such a penalty.

Simply trotting out another study that differs substantially in its focus, methods and goals and then to subsequently rationalize the existence of various types of interference made worse by a particular method of increasing gain misses the point, as the original model did not learn from any of Harmon's lessons!

The initial point WAS that the manner in which the ORIGINAL folks did that DID so in a manner that incurred a penalty in the form of INCREASED interference! And if you doubt this, simply refer to Don Keele's evaluation of various array configurations made during the research for his AES article on Bessel Arrays. In fact, if you need specific data on any particular configuration, let me know, as I have the copy of ALL of the 4 inch thick tomb of measurements made by Mike Lamm in the process of doing the research for that article! All of the modeling and testing to which you refer has been done!

[tINY]

Since the one study you are hanging all of your arguments on is basically a red herring in response to the german concept, I have to assume you are simply playing devils advocate. That relatively simplistic study proves some concepts well, but applying it to a 8ft high and 10ft wide room takes a lot more than "see, boundary reflections cause comb filtering".

Since you didn't understand the point of canceling modal ringing and introducing multiple sub-woofers to even out the comb filtering effects over a listening area - forget Welti's presentation.

Instead, take all that you learned from your buddy Pat Brown and calculate the superposition of the first 20 arrivals for a typical listening position. You will see that at 80Hz, there are no comb filtering effects. (and if you demand a higher cut-off frequency for this, or your front wall is biger, add more subwoofers as determined here: Google Translate )

Want some real-world measurements?
Double Bass Array (DBA) - The modern bass concept! - Page 3 - AVS Forum


-tINY

[SAC]

Originally Posted by tINY

You still haven't applied your "better result" to model the relatively simple, practical application of the 4 woofers in the front wall of the german scheme. It's only 4 sources and 4 sources reflected off of 4 surfaces for a first approximation... 20 signals to superimpose. Did you do the calculations and find that it didn't support your argument?


Until someone actually wants to put forth the effort to do some modeling or build 4 or 8 subs and take some measurements in a room....

Nope! But you are welcome, along with the folks who designed the system, to think that they are way ahead of the curve on this - when in reality they are able to imagine this simply by virtue that they are so far behind as to simply have lost sight of those who have moved forward.

This has been beaten to death in practice and in theory!

Boundary interactions are well understood - going back to wave tank days! And the destruction interference inherent in spaced sources are also likewise well understood and utterly predictable.

But you dismiss the interaction of the direct signals with the aplomb of a seasoned Bose salesperson.

I am sorry that you are not familiar with this, but the interaction of spaced drivers without boundary additions, and within a bounded space has been explored!

It is funny that if one simply moves over to the pro-sound forums that this would be quickly dealt with with barely more than a shrug.

While you are apparently still waiting for folks who are ignore-ant of this to catch up to what the audiophile world, which is also not familiar with this - like so many who also comically extol the merits of listening to exorbitantly priced line arrays in the near field in their living rooms - thinks is a radical idea, the rest of us move on and utilize best practices to minimize destructive interference that are sourced by both real and virtual sources in bounded environments.

But then, these same folks feel that you cannot localize bass sources in the near field because LF are 'omni-directional'!! And they also neglect the psycho-acoustics of the near field direct signal propagation and polar lobing as they focus all of their efforts on the long term averaged pressure zone modal response of the standing wave (and your preoccupation with the focus on rear wall reflections) which utterly neglects transient based intelligibility in a non-steady state environment that is not focused on simply reproducing pink noise!!

But by all means, build lots of large thump car audio systems for the home! But you might also want to discover what made Richard Clarke's approach to car audio systems so radically different from the competition!

And re: the AVS 'eggthrowing' front/ rear wall delay system? You have got to be kidding, right? That is great if you are reproducing a steady state sine wave! But tell me how that helps if you are reproducing a time variant real world response? Delay and signal synchronization is indeed a critically useful tool. But one needs to understand how and when and where it is appropriate! And they talk of line arrays in the near field where there is a certain area one must be in where "you are effectively in the near field response but comb filtering is minimized. I suppose it's a function of the spacing between the woofers (the greater the spacing, the lower the low pass filter and the further away you must be)." There is NO near field position where comb filtering and polar lobing is not rampant! That is a fundamental limitation of ALL arrays other than the Bessel! Exactly the point of mentioning the Bessel!!! And still one needs to be at least 10X the inter-driver spacing from the Bessel before he soundfield congeals even with the Bessel!!

But hey, if they want to spend the money and time to reinvent the wheel, by all means have fun!!! The irony is why they didn't simply start with a 5 element tightly packed Bessel cognizant of the near field limitations where comb filtering and polar lobing dominates the direct signal!

[tINY]

I'll assume you really want answers here - and are making a few challenges. I'll try to leave out snide remarks (this has been hard).


-tINY

Originally Posted by SAC

This has been beaten to death in practice and in theory!

Boundary interactions are well understood - going back to wave tank days! And the destruction interference inherent in spaced sources are also likewise well understood and utterly predictable.

Yes, but the complications come when there are many drivers and the walls on more than 3 sides are too close to ignore. You haven't even attempted to solve for the simple case of 4 drivers in a baffle and 4 other walls.

But you dismiss the interaction of the direct signals with the aplomb of a seasoned Bose salesperson.

And you, sir, are a luddite who likely doesn't really understand any of this... (OK i've indulged once)

I am sorry that you are not familiar with this, but the interaction of spaced drivers without boundary additions, and within a bounded space has been explored!

It is funny that if one simply moves over to the pro-sound forums that this would be quickly dealt with with barely more than a shrug.

... because "pro" sound forums deal with large acoustic spaces. Launching a plane wave in a large space would be prohibitively expensive.

While you are apparently still waiting for folks who are ignore-ant of this to catch up to what the audiophile world, which is also not familiar with this - like so many who also comically extol the merits of listening to exorbitantly priced line arrays in the near field in their living rooms - thinks is a radical idea, the rest of us move on and utilize best practices to minimize destructive interference that are sourced by both real and virtual sources in bounded environments.

And, in your ignore-ance, you dismiss things that won't work in auditoriums out-of-hand. Even if the application is not an auditorium.

But then, these same folks feel that you cannot localize bass sources in the near field because LF are 'omni-directional'!! And they also neglect the psycho-acoustics of the near field direct signal propagation and polar lobing as they focus all of their efforts on the long term averaged pressure zone modal response of the standing wave (and your preoccupation with the focus on rear wall reflections) which utterly neglects transient based intelligibility in a non-steady state environment that is not focused on simply reproducing pink noise!!

That's a lot to throw out and hope something sticks...

I'm not sure what you think Psycho acoustics and near-field propagation have to do with each other in this case. Polar lobing isn't an issue if the whole room is in a single lobe.

As for your ideas on transient analysis, did you see the waterfall plots and energy decay graphs? Did you understand them?

"transient based intelligibility"? You do realize that, by dramatically decreasing decay times of strong resonances, you do improve intelligibility. You were the one referencing Schroeder's work - what happens below the frequency where resonances are tightly spaced?

But by all means, build lots of large thump car audio systems...[more self-indulgent fluff deleted]

I've spent enough time here - I have real things to do. Obviously you don't really care to debate this in terms where we and other people can learn something....

Have fun with your mono 15" 2-way sound system (OK, twice I indulged).



-tINY

[SAC]

I'll assume you really want answers here - and are making a few challenges. I'll try to leave out snide remarks (this has been hard).


-tINY





Yes, but the complications come when there are many drivers and the walls on more than 3 sides are too close to ignore. You haven't even attempted to solve for the simple case of 4 drivers in a baffle and 4 other walls.

I have already stated several times, that the additional surfaces act as additional virtual sources, and to the degree that the total source separation exceeds a total of ¼ wavelength (or 1/8 wavelength to the wall and back), their involvement in the superposition of the signals INCREASES the degree of comb filtering and polar lobing! Why do I need to calculate MORE when the source spacing is already too great a contribution while you simply ignore it and maintain that it doesn’t matter – or worse, that it helps remediate the already present destructive interference! - as you say it doesn't matter?

And you, sir, are a luddite who likely doesn't really understand any of this... (OK i've indulged once)

Don’t worry, you may as well, as you have little else…

Yup, and you have been doing acoustical analysis with time based measurement gear for HOW long know? 6 months? A year? 2 years? Ever? Many have been doing this with large and small acoustical spaces for 30+ years. And all of the measurements you site employ only frequency domain measurements! So...who is the Luddite? And why are so FEW even aware of the features of a free product such as REW beyond the waterfall and RT60 measurements in small acoustical spaces where no meaningful statistically reverberant field even exists?

And since you feel comfortable calling me a Luddite, just where/when did you get your degrees in physics and acoustics and start using time domain evaluation?

Sorry, but smoothed frequency plots establish NO grounds for any comments regarding polar lobing.

There are both modal and near field superpositional comb filtering and polar lobing anomalies. You keep citing modal waterfalls and nothing with respect to the superpositional issues regarding spaced sources and you only expect us to imagine them non-existent. Right... Did they employ faith-healing as well as EQ?


... because "pro" sound forums deal with large acoustic spaces. Launching a plane wave in a large space would be prohibitively expensive.

Complete and utter nonsense! So all spaces dealt with by Pro sound are larger than 250,000ft^3 for a response down to 30 Hz??? And folks, the average Large grocery store is around 60,000 ft^3 - if that gives you a rough idea...





And, in your ignore-ance, you dismiss things that won't work in auditoriums out-of-hand. Even if the application is not an auditorium.

...And you think that auditoriums have something to do with this. What do you think about Eskimos and dirigibles? Are they involved too? Absolutely hilarious. And we care about modes in large acoustical spaces why?


That's a lot to throw out and hope something sticks...

I'm not sure what you think Psycho acoustics and near-field propagation have to do with each other in this case. Polar lobing isn't an issue if the whole room is in a single lobe.

You haven't a clue. Polar lobing is the spatial correlative of comb filtering. Obviously you don't know this. And the near field propagation of the signal exhibits comb filtering (which you say is simply everywhere!) while you assert that there is no polar lobing of the direct signal. So which way to Oz, Scarecrow?


As for your ideas on transient analysis, did you see the waterfall plots and energy decay graphs? Did you understand them?


"transient based intelligibility"? You do realize that, by dramatically decreasing decay times of strong resonances, you do improve intelligibility. You were the one referencing Schroeder's work - what happens below the frequency where resonances are tightly spaced?

And psycho-acoustics…Hmmm. You keep mentioning reflections off rear walls as being constructive. Have you ever heard of the Haas Effect? And if they are destructive in other environments, please tell us why the later arriving reflections of the woofers would not be subject to the same time smear distortion described by Henry, Haas, and also Heyser.

Ah! waterfalls! More frequency domain analysis. Well, you certainly demonstrate that you do not understand them!

As if waterfall plots have ANYTHING to do with initial transients! Have you ever heard of Heyser? Ever read his stuff? And if so, out of curiosity, why do you totally neglect what he has said and avoid all time domain analysis? And waterfalls are not time domain measurements.

Did you know that you can measure both the modal analysis of the room as well as the near field behavior including the polar lobing of the direct radiated signal? And has anyone looked at the phase response of your "egg tossing" front-rear wall configuration? Do what????

Hmmm. Another use of terms where the meaning of the terms apparently don't matter. As you dismissed psycho acoustics earlier, it might confuse you more to know that intelligibility is a psycho-acoustic phenomena, and it is evaluated primarily in the time domain. And "below the frequency where resonances are tightly spaced?" Huh? The answer - you have more frequencies! That is meaningless. Again, you are simply looking at modes while talking about "spaced reflective surfaces" that act as virtual sources reinforcing additional comb filtering and polar lobing in the direct signal near field where most are listening in the room, which are then reinforcing the modal pressure response of the room. - Two sources of error. They do not somehow negate each other as you are want to believe.

Obviously you do not understand the quite intentional references to Bose, who likewise tried to trot exactly such a concept out with their direct-reflecting concept. A notion that was utterly and completely demolished in the SynAudCon Intelligibility Workshops conducted when systems featuring different Qs and installed by EV, JBL and Bose engineers were measured and evaluated.


I've spent enough time here - I have real things to do. Obviously you don't really care to debate this in terms where we and other people can learn something....

Apparently you mean simply ignoring behavior, known physics (superposition), how multiple spaced sourced interact (as the greatest separation between ALL elements (not simply adjacent elements), real and virtual, Must be within ¼ wavelength, and not simply a system claiming to have achieved a ‘flat’ response by heavy use of EQ while focusing Solely on modal analysis and presenting absolutely no nearfield polar or other analytical data. Nor has any form of system transfer function evaluating the differences between a known input signal and the real measured output signal been submitted.

Simple emotional assertions of no fundamental near field superpositional interference and claims of a unified single lobe are utterly unsupported. And i ewnd to lean toward objective measurements and not simply acts of faith.

Have fun with your mono 15" 2-way sound system (OK, twice I indulged).

I have not proposed any specific system as an alternative. Nor is it my responsibility in order to critically evaluate the physics of this nonsense. But a close packed vertically oriented 2 driver system would be more predictable and better behaved than the system they have trotted out - for half the cost for additional gain without much additional destructive interference.

Let's see. You can close pack and have all the sources couple and avoid the destructive superposition (up to the frequency where their spacing ceases be less than 1/4 wavelength - and a reason for a crossover!) by making sure all interdriver acoustical centers, including ALL combinations of real and virtual drivers, are within ¼ wavelength, or you can use a Bessel array in the far field and deal with the substantial phase issues at the crossover, or you can vertically stack close coupled drivers and minimize horizontal plane polar issues in the direct signal.

This system does none of that. Just looking at the drivers and their spacing relative to the far side wall as well as the diagonal spacing they exceed the spacing requirements necessary to couple.

But now we have folks claiming to be able to effectively overcome such superpositional anomalies with EQ. And you even claim the system lacks any polar spatial anomalies and propagates as a SINGLE lobe!

Absolutely fantastic! You system renders the Bessel array insignificant with your claimed accomplishments!

And it’s interesting to see that neither you nor the folks who made the system have chosen to address just how they will crossover the system. And they will address the phasing issues how? As such is never addressed, I suspect that they are still at "The what?" stage?

And thus far, in order to justify the design, you have cited a Harmon study which in no way justifies what has been done - in fact in many spots it directly refutes it, while you claim that 4 widely spaces drivers in a small room superpose in the direct near field to produce a SINGLE polar lobe - something that to date not even the prodigious Bessel array is capable of doing.

And it is quite easy to measure the transfer function of the system - where a know signal is input into the system and you measure and evaluate the output within the room to determine how much or little it resembles the original source in all respects.

Nothing of the sort has been provided.
But this system claims to accomplish this at least in part via equalization ([IMG]file:///C:/Users/Owner/AppData/Local/Temp/msohtmlclip1/01/clip_image001.gif[/IMG])

My suggestion...If you think it actually performs aw you Claim, (based solely upon frequency analysis!) by all means write it up and present it at ASA and AES. Folks will be waiting with intense interest to hear all about your widely spaced sources that create a soundfield devoid of nearfield superposition induced destructive interference that to date only the Bessel array has come close to doing - and then only in the far field!

The fact is, you (and they) have provided absolutely NO evidence of overcoming the destructive elements of superposition in the direct near field. And all you keep doing is talking about modal response that even Harmon cites would be an issue with such a system, as the closest they get to 'your' featured system is to listen to their drivers on the ceiling - which they admit would exhibit a disastrous response.

As I mentioned. We know how spaces sources act with regard to superposition, comb filtering and spatial polar dispersal. Increasing the sources of superposition does not improve that - just as everyone has learned as a result of the Bose direct reflecting chaos nonsense - and where the increased sources introduce INCREASED reflections that destroy intelligibility! The result of which is ABSOLUTELY NOT a single polar lobe.


And your frequency response does nothing to refute the above. And at worst, fails to even address any of the topics presented.

And then you go on to state that we have not evaluated the response of myriad array configurations.


I personally posses a stack of ~4 inches of TEF plots of various array configurations, as well as for 5,7,9, and 11 element Bessel arrays, made to compare and evaluate various array configurations performed by Mike Lamm in preparation for Don Keele’s study of Bessel arrays published in the AES Journal. You might do well to review the study and the conclusions drawn relative to the alternative array configurations.

But I think it’s cute that you claim that others have either not performed such evaluations or are ignorant of them. Obviously it is you and a few others who are ignorant of THEM.


And in regards to your complaint as to what I present as an alternative, I don't have to! I have the luxury of simply critically reviewing this approach! Presenting an alternative is a red herring. Just as referees in a basketball game are not required to jump higher or shoot better than Michael Jordan in order to evaluate his or anyone else’s performance, the critical analysis of such a spaced configuration does not require anyone to build a better system.

What do we know. In order to effectively sum in phase, all spaced sources, be they real or virtual must be within ¼ wavelength at their highest reproduced frequency. That means all boundaries must be within 1/8 wavelength at their highest reproduced frequency. If that is 80 Hz, then they must be within 4.25m or 53 cm. Such pertinent information is not provided, but they certainly do not appear to be such. And at distances greater than 1/3 wavelength, or 71 cm at 80 Hz, the summed pressure from the driver and wall reflection become weaker than that of the driver itself. And as such, the reflections cease to provide support or substantial cancellation either. So what is that about reflections from the back wall doing what exactly regarding comb filtering??? I know it sounds good, but does it mean anything?

To the degree they are not, comb filtering and the concomitant spatial polar lobing occurs. You do not have one without the other! They are correlative!

So please, present evidence to support your "one lobe" polar response without comb filtering anomalies in the direct signal near field; along with a well behaved phase plot allowing for an elegant high slope transition crossover.

But we will indeed be waiting for the presentation at AES:

A system with 4 widely spaced LF drivers is asserted to do what a Bessel array cannot do: Present a coherent response identical to the response of a single component driver without comb filtering and polar lobing in the Near field!

It well be most interesting to read your report that will certainly be presented at AES as you are effectively claiming to offer an array configuration featuring spaced drivers where comb filtering and polar lobing anomalies are non-existent. In other words, you are asserting a configuration that out performs the Bessel array using one less driver featuring even greater efficiency.

And even the Bessel is subject to comb filtering and polar lobing in the near field . The Bessel requires a presence in the FAR field of at least 10 X the largest inter-driver spacing before its soundfield congeals into a unified unchanging wavefront that is invariant with regards to distance. which constitutes distances less than 10 X the largest interdriver spacing interval. Only in the Far field does the soundfield congeal in a coherent manner.

And unfortunately, it takes more than a smoothed frequency response and a waterfall plot evaluating resonances to ascertain this. Nothing has been provided to support the assertion.

So I guess it must be the magic EQ that claims to remediate the room-speaker and speaker- speaker interactions!


And we have the assertion that while 2 drivers produce interference, many drivers do not – in fact, they remediate the destructive interference of 2 drivers. Yup, like the Bose direct reflecting system sort a makes you forget simple interference by virtue of rendering the entire sound field so chaotic that there no longer exists a ‘good’ spot that is objectively different from a ‘poor’ spot, as the soundfield has become so universally mediocre. And the seeming lack of difference becomes a new (low!) reference!


But you are right, far too much time has been spent debating a system that is asserted to overcome fundamental physical limitations regarding spaced drivers based simply upon ‘you have to believe’ statements and waterfall/frequency plots.


Sorry, but the system does not come close to the performance of a Bessel array, not in the far or near fields. But we will await the presentation at AES.

Have fun. Belief is a nice thing. Even if one has to suspend actively evaluating phenomena in order to continue to believe. But you fail to present any significant information that offers anything new.

Meanwhile, there are more effective ways to increase gain without incurring substantial destructive increases in interference.

And your claims of performance that exceed the Bessel array (no lobing errors!?!?!?!) without the limitations in the near field are impressive IF anyone can substantiate them! And just a suggestion, its going to take a bit more substantiation than a simple "Its a Miracle!"

[tINY]

Originally Posted by SAC

... and to the degree that the total source separation exceeds a total of ¼ wavelength (or 1/8 wavelength to the wall and back), their involvement in the superposition of the signals INCREASES the degree of comb filtering and polar lobing!

So, if two sources are 1/2 wavelength apart and equidistant from my head, how is lobing a problem?

So all spaces dealt with by Pro sound are larger than 250,000ft^3 for a response down to 30 Hz??? And folks, the average Large grocery store is around 60,000 ft^3 - if that gives you a rough idea...

We are talking about rooms on the order of 2000-4500 cu ft here. When was the last time you did any serious analysis on a room that small? Nothing is perfect, but some times an unorthodox approach can significantly improve performance. You may have some sniggly points, but if it sounds better, it is better.

I don't listen for clinical accuracy - but if I can significantly even out the bass frequency response, nearly eliminate modal ringing, and do this over a fairly wide listening area, I have just increased the performance of my subwoofer system in a small room. I don't care if I have to equalize the feed to the amplifier (you are probably old enough to remember HF equalization on horns...)

As if waterfall plots have ANYTHING to do with initial transients! Have you ever heard of Heyser? Ever read his stuff? And if so, out of curiosity, why do you totally neglect what he has said and avoid all time domain analysis? And waterfalls are not time domain measurements.

I guess I am enough younger than you to have had fairly powerful computer that can do FFT and inverse FFT without too much trouble. If you keep the phase information, you can step from frequency domain to time domain and back without too much trouble (you should listen to some of the convolution reverbs sometime). So, in my mind the only difference between time and frequency domain is what you use as a stimulus when you want to measure a transfer function.

Waterfall plots are just a convenient way of looking at time and frequency effects at the same time.

I know that I am not particularly sensitive to transient response below 100Hz, and judging by the popularity of ported subwoofers, most people are less sensitive than I.




-tINY

[SAC]

So, if two sources are 1/2 wavelength apart and equidistant from my head, how is lobing a problem?

Geesh! If two sources superpose that are greater than 1/4 TOTAL wavelength apart, they, by definition and in reality, result in comb filtering AND Polar Lobing! Simply restating this 20 times does not change the results!








We are talking about rooms on the order of 2000-4500 cu ft here. When was the last time you did any serious analysis on a room that small? Nothing is perfect, but some times an unorthodox approach can significantly improve performance. You may have some sniggly points, but if it sounds better, it is better.

What is this pathological preoccupation you have? I am specifically NOT talking about Large Acoustical Spaces!!! From the beginning I have harped on the fact that the acoustical behavior of Small Acoustical Spaces is distinct from Large Acoustical Spaces. But only here do a bunch of folks think there is something special about 2000-4500ft^3 spaces! They are and behave as Small Acoustical Spaces!

And since you are concerned with that, you might want to indicate that you have a clue about the very thing you claim to be cognizant of by dropping the "reverberant" notion of small Acoustical Spaces! As one of their determinate differences from Large Acoustical Spaces is the LACK of a viable statistical reverberant soundfield! But it is insane to keep listening to so many Scarecrows from the Wizard of Oz harp about - "But its a "2000-4500ft^3 room" as they then run to measure RT60s!!!

I don't listen for clinical accuracy - but if I can significantly even out the bass frequency response, nearly eliminate modal ringing, and do this over a fairly wide listening area, I have just increased the performance of my subwoofer system in a small room. I don't care if I have to equalize the feed to the amplifier (you are probably old enough to remember HF equalization on horns...)

Sorry, but this "I don't care if it is actually better, but if it is different and I like it it is better" rail sounds like someone who has just discovered Audyssey. The fact is, an understanding of acoustical physics can both make it sound "different" AND make it sound better.

And EQ HAS a legitimate place when dealing with minimum phase sources! All EQ is NOT bad! But speaker-speaker and speaker - room interaction within the room is NOT minimum phase! And here you can only EQ the direct signal! And as the reflection is also comprised of the direct signal, changing one does not change the other so that they somehow interact differently!




I guess I am enough younger than you to have had fairly powerful computer that can do FFT and inverse FFT without too much trouble. If you keep the phase information, you can step from frequency domain to time domain and back without too much trouble (you should listen to some of the convolution reverbs sometime). So, in my mind the only difference between time and frequency domain is what you use as a stimulus when you want to measure a transfer function.

Yes, if you are dealing with the impulse response which maintains all of the required information! And you might want to review the B&K domain maps to see how the domains (and subsequent measurements) are related!!! What I am talking about addresses this aspect directly! But unfortunately, you (and those folks) have not used ONE thing that an FFT or any other 'time domain' capable format affords in ANY of your measurements! So while you may 'remember them', - here's an idea, how about USING them and UNDERSTANDING them!?!?!?!? I have been SPECIFICALLY doing this for over 22 years beginning with TEF. Others who have studied this for longer! So your reference to FFTs are not anything new. They are fundamental to the POV to which I refer! That has been how we have come to understand exactly behavior of which I have been speaking! But yet you are content to look at frequency response lots ONLY - and a CSD/waterfall is nothing but a series of frequency samples! It is NOT a time domain measurement!!! How about using the tools you talk about to their potential?

Using the words is a great start. But please start understanding them.



Waterfall plots are just a convenient way of looking at time and frequency effects at the same time.

Nope. Take some time and find out why waterfalls are NOT time domain measurements.

I know that I am not particularly sensitive to transient response below 100Hz, and judging by the popularity of ported subwoofers, most people are less sensitive than I.

Now we shift the focus to bass reflex systems, as if they have anything to do with the topic... Time smear distortion (Heyser) is real. It is also addressed and important/fundamental in the realm of psycho-acoustics. And it specifically impacts the subject of "intelligibility". It is the basis for our dealing with the arrival times of various signals.

And it is curious to watch as the determinant criterion of a system below 100Hz seems to ONLY be "gain". I suggest that gain, without adequately addressing the concomittant sources of error resulting from simply adding additional sources is not the panacea many might assume. And this subject has been examined in quite some depth.

Selective attention can be a useful tool, as it allows one to ignore that which is inconvenient to notice. But intentionally ignoring aspects of behavior while claiming the resultant to be better is a flawed methodology.

The goal is to be cognizant of ALL of the behavior and to optimize the entire system. Not just to 'smooth' one aspect at the expense of another whose behavior we understand and whose behavior is detrimental.

[tINY]

You really like to be argumentitve without being helpful, don't you?



-tINY

[DanDan]

tiny

You really like to be argumentitve without being helpful, don't you?

SAC repeatedly engages in snide remarks, insults, pomposity, shifting goalposts, revisionist editing of posts, and so on. tiny, may I recommend that you do a search of posts by foxfyr and another on posts by SAC. You will find clusters of argument and unpleasantness which are quite unusual in GS. I think you will conclude that it is a complete waste time engaging with this guy. His sum is never ever positive. He hooks people with big words, name drops, derision of the the lesser educated, and all sorts of other loathesome techniques which he has refined. This place is the lesser for his presence, and I amongst many others who have communicated with me on this topic, wish to see him leave. ( As apparently his alter ego foxfyr has done, or perhaps been compelled to)
Sorry to be nasty but sometimes fire can be the best thing to put out a fire, or a foxfyr

DD

[SAC]

What about the superposition of sources greater than 1/4 wavelength separation is not clear?
This is like saying that at 32F water freezes, only to be treated to challenges of "but what about at 10 F? or -25F? or..."

Addressing modal issues is indeed important, but not at the expense of exacerbating additional issues. The best solution is one that mitigates all of the substantial issues, not one that simply focuses on one and ignores the others.

And unfortunately, the solution as proposed and explained literally sounds like the flawed rationale Bose used when alleging that Q and multiple driver coverage overlap (and hence the accompanying superposition) did not matter.

And there is plenty of specific documentation regarding that available as well by PM.

[tINY]

Thanks for the heads-up, DD.

It's not been a complete waste of time to check my assumptions and clarify a few details about things for my own understanding. Sometimes a ridiculous challenge is just what you need to get off your butt.



-tINY

[DanDan]

You're welcome tINY. I hear you re technical discourse/challenge. I have had a few reasonably robust ones with Ethan for instance. Normal communication skills, manners, were used throughout, which ended up strengthening a friendship. That is simply not on the menu in this case.

DD

11th July 2009, 07:03 PM
foxfyr
This message has been deleted by jayfrigo. Reason: repeated insults, bickering, and unnecessary escalation.