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SAC · 6th February 2010

Have you read what has been posted????
Apparently not, as you ask things that were clearly stated in the initial posts and you keep bringing up issues that are non sequitur to the issue! And you seem to be disagreeing by positing the same room response which I asserted from the beginning - except you seem to focus on the 'room' while I was focusing on the additional problems the speaker propagation would generate...both leading to (I think) a similar conclusion. But then you keep talking about a small room as opposed to a small room - as if thee is any other space or spaces involved other than a Schroeder "small acoustical space" which determines the rules at play.

Spaced, non signal aligned transducers reproducing the same passband will interact destructively if they are further apart than 1/4 wavelength of any reproduced frequency. And while we see comb filtering in the frequency domain, spatially you have polar lobing anomalies. In other words, if the original dispersion was cardioid or even omnidirectional, you will now have a response wit the total dispersion area divided into lobes. And the higher the frequency, the more lobes you will have.

PERIOD.

That will be the nature of the direct signal propagated by the spaced sources. Add to this the room modal behavior and you will have a mess - compounded by the spaced sources. The problem with comb filtering and polar lobing could be, in large part - but not totally, mitigated by close packing or vertical close packing within 1/4 wavelength of a floor-wall boundary.

Where do you get the idea that ANYTHING bypasses small room issues! It it TOTALLY conditioned by the acoustical behavior of a Schroeder defined Small Acoustical Space! And since we are assuming reproduction of music to 30 Hz, that means any space less than about 250,000ft^3!!!

And if you understand the nature of measurements, they were taken in a "large open space" precisely to eliminate the additional reflections and comb filtering and polar anomalies introduced by additional boundaries aside from those specifically to be included in the test scenario! Rather than compromise the conclusions, this very consideration provides yet more substantiation!

And do reflections act as virtual sources???? You have to ask this? Of course they do! That concept if fundamental to the entire discussion of reflections! And yes, the spacing/time offset introduced by the real and virtual sources will introduce still additional comb filters and polar lobing in addition to the various other combination of transducer spacings!

And the distinction of the room in which measurements were taken?? It is about the same as size as the one illustrated in the example with the 4 spaced woofers mounted vertically in the walls! It is STILL a "small acoustical space" as defined by Schroeder that determines the acoustic principles at play in the space! But the significance is that rear wall reflections were not an issue! Only reflections from the near boundary surfaces. If far wall surface reflections were considered, the response would be WORSE, as you would have yet another source of superposition..

And as the measurements show, we have a combination of room modes and comb filtering and polar lobing.

And Whatever Floyd Toole wrote has NO bearing on the topology of the 4 widely spaced woofers (both from boundaries and other drivers) in a single vertical boundary! Just because he experimented with four spaced subwoofers mounted adjacent to boundaries evaluated on the horizontal plane has little to do with the topology they have built!...aside from the fact that they employed the number 4 as well. Or did Floyd also evaluate the distribution of modes on the ceiling (a VERY short wall) near the center of the room assuming a vertical boundary placement. Funny, he never mentions that.

What is fascinating is how you have created yet another acoustic space unknown to science where apparently acoustics behaves as if in some realm of the Twilight Zone.

The result in the space is a strong modal presence compounded by comb filering and spatial polar lobing.

"Essentially, you have strong interactions between your "comb filtering and polar lobing" and your "modal behavior" when considering several spaced LF transducers in a typical listening room."

Duh! You think?!?!?!? ;-)))

That has been my contention from the first post onwards! You don't simply have room modes! You have additional frequency and spatial errors as well made worse by the non-optimally spaced drivers!!!! And these frequency and spatial errors are worse than if you had just one transducer or several tightly packed drivers!

6th February 2010	#19
SAC Registered User Joined: Dec 2009 Posts: 2,622	Have you read what has been posted???? Apparently not, as you ask things that were clearly stated in the initial posts and you keep bringing up issues that are non sequitur to the issue! And you seem to be disagreeing by positing the same room response which I asserted from the beginning - except you seem to focus on the 'room' while I was focusing on the additional problems the speaker propagation would generate...both leading to (I think) a similar conclusion. But then you keep talking about a small room as opposed to a small room - as if thee is any other space or spaces involved other than a Schroeder "small acoustical space" which determines the rules at play. Spaced, non signal aligned transducers reproducing the same passband will interact destructively if they are further apart than 1/4 wavelength of any reproduced frequency. And while we see comb filtering in the frequency domain, spatially you have polar lobing anomalies. In other words, if the original dispersion was cardioid or even omnidirectional, you will now have a response wit the total dispersion area divided into lobes. And the higher the frequency, the more lobes you will have. PERIOD. That will be the nature of the direct signal propagated by the spaced sources. Add to this the room modal behavior and you will have a mess - compounded by the spaced sources. The problem with comb filtering and polar lobing could be, in large part - but not totally, mitigated by close packing or vertical close packing within 1/4 wavelength of a floor-wall boundary. Where do you get the idea that ANYTHING bypasses small room issues! It it TOTALLY conditioned by the acoustical behavior of a Schroeder defined Small Acoustical Space! And since we are assuming reproduction of music to 30 Hz, that means any space less than about 250,000ft^3!!! And if you understand the nature of measurements, they were taken in a "large open space" precisely to eliminate the additional reflections and comb filtering and polar anomalies introduced by additional boundaries aside from those specifically to be included in the test scenario! Rather than compromise the conclusions, this very consideration provides yet more substantiation! And do reflections act as virtual sources???? You have to ask this? Of course they do! That concept if fundamental to the entire discussion of reflections! And yes, the spacing/time offset introduced by the real and virtual sources will introduce still additional comb filters and polar lobing in addition to the various other combination of transducer spacings! And the distinction of the room in which measurements were taken?? It is about the same as size as the one illustrated in the example with the 4 spaced woofers mounted vertically in the walls! It is STILL a "small acoustical space" as defined by Schroeder that determines the acoustic principles at play in the space! But the significance is that rear wall reflections were not an issue! Only reflections from the near boundary surfaces. If far wall surface reflections were considered, the response would be WORSE, as you would have yet another source of superposition.. And as the measurements show, we have a combination of room modes and comb filtering and polar lobing. And Whatever Floyd Toole wrote has NO bearing on the topology of the 4 widely spaced woofers (both from boundaries and other drivers) in a single vertical boundary! Just because he experimented with four spaced subwoofers mounted adjacent to boundaries evaluated on the horizontal plane has little to do with the topology they have built!...aside from the fact that they employed the number 4 as well. Or did Floyd also evaluate the distribution of modes on the ceiling (a VERY short wall) near the center of the room assuming a vertical boundary placement. Funny, he never mentions that. What is fascinating is how you have created yet another acoustic space unknown to science where apparently acoustics behaves as if in some realm of the Twilight Zone. The result in the space is a strong modal presence compounded by comb filering and spatial polar lobing. "Essentially, you have strong interactions between your "comb filtering and polar lobing" and your "modal behavior" when considering several spaced LF transducers in a typical listening room." Duh! You think?!?!?!? ;-))) That has been my contention from the first post onwards! You don't simply have room modes! You have additional frequency and spatial errors as well made worse by the non-optimally spaced drivers!!!! And these frequency and spatial errors are worse than if you had just one transducer or several tightly packed drivers!