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Old 1st December 2012, 10:30 AM   #111
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Superposition still holds. Impulse response at point of measurement is sum of each source impulse response measured at same point. Very same mechanism that allows us to locate sources also blinds us the highly correlated multiple sources.



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Andrew
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Old 1st December 2012, 10:44 AM   #112
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Crosstalk cancellation techniques often require stringent speaker setup and testing, which once met typically improves perceived performance more than the crosstalk processing.

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Old 1st December 2012, 04:47 PM   #113
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Hi Barleywater
I am not sure you looked at the phase part of the curve, there is no “all pass” crossover phase shift like Butterworth, linkwitz riley and other named slopes produce.
The high pass hf crossover alone for example has a 4th order ultimate slope which normally would put 360 degrees phase rotation centered around 1200Hz which is not present. The phase response is as if it were one driver, not 7 with a 3 way passive crossover.

Here is an old link to some square waves if curious;
Making Square Waves?

DSP correction has been commonplace in commercial sound for a long time and for one single location, it can perform miracles and can appear to be “perfect acoustic bondo”, but does not fix root or acoustic source problem.
The problem is that if one has separate sources producing the same signal (like a multi-way speaker at crossover), one has separate path lengths to the ear.
DSP can easily fix time and can correct a multi-way loudspeaker but the larger the spatial problems it’s is accounting for (the larger the acoustic spacing relative to a quarter wl), the smaller the “corrected zone” is and usually the result is worse everywhere else.
A multi-way speaker that produces an interference pattern (lobes and nulls) will still be producing an interference pattern with DSP correction because it can’t fix problems in horizontal or vertical placement unilaterally, only locally for one point in space.
Think on the large scale like concert sound, it usually sounds good or fair at the mix booth and different everywhere else.

The SH-50 (Synergy horns) are unusual in that they can be very largely phase correct without DSP and by radiating a segment of a sphere over a wide band act / measure /sound like as if it had one crossover-less driver and so it presents a very uniform spectrum across the listening area.

While the coherent addition of drivers makes it an ideal thing to unilaterally correct the remaining time/phase with DSP (and that works great!), the market demand is much more for a passive speaker “if” it sounds good without being active.

I guess I would say the goal here was to fundamentally fix the acoustic source radiation and you fix many problems like lobes and nulls etc all at once.

The speakers I mentioned are much more powerful than hifi speakers and are normally used say 30-100 feet from the audience or larger distances. As you probably have observed, most loudspeaker problems become larger, faster than the signal you want so if your audience is 19 times farther away, you need 100X the acoustic power to reach the same level.
The audience plane is usually as wide or wider than the coverage of a single box and so, the object is to have the sound field be as identical as possible everywhere within the pattern.

Also, confining as much of the total acoustic power to the design radiation angle is a very important thing, the larger the room, the less natural absorption there is and the more of a limiting factor reflected and reverberant sound is so far as understanding words so a constant/ high directivity design was also needed. In a living room, the directivity means the mag/phase response and impulse response at the listening position is much more like the 1 meter measurement. When you can confine most all of the energy into the front pattern, the direct field and intelligibility zone is maximized in large spaces..

If I recall the picture of your speakers, they would be nearly / mostly onmi directional up to the higher frequencies and would radiate from nearly a single point in space with a simple pattern.
If they only had a tweeter that was smaller still but covered the entire frequency range, then the radiation would for the most part be a simple sphere and then portion of a sphere, largely a single point in time and space.. From that (the shape of the point source radiation envelope) it would seem that your point source speakers are actually similar to the Synergy horns which is curious, those being more or less the whole pie, while the Synergy horn is as much as possible just a slice of pie..
While the company is so far not interested in hifi, I am and that is what drives the designs, why I mentioned it here..

The Synergy horn radiates like that except the angle is bounded by a solid wall (tangent pressure boundary forms an acoustic mirror image of the rest of the sphere) with a confined angle less than a flat baffle.
What radiates begins at highest frequencies at the apex at a dimension too small for the sound to have any directivity and so the angle is set by the horn wall.
AS it progresses out of the driver into the horn and at a dimension suitable for lower frequencies, the mid energy is added in synchrony with the highs and then further down, again according to the acoustic dimensions, the low frequency energy is added.
That time /phase offset the crossover normally causes is offset by the drivers inverse physical locations so the result is what is in time and space like one driver and not a 3 way system.
What radiates is a segment of a spherical radiation, not the entire sphere and as if it were a single (but impossible) horn driver.

The “spherical-ness” is audible too when you place two of them side by side hard packed, you cannot hear a seam where one box ends and the other begins, only possible by radiating as if it were a point at the very back of the cabinet (in fact from a point where the horn walls would intersect).

Best,
Tom
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Old 1st December 2012, 04:56 PM   #114
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talking of crosstalk, I had last night my first go ever at ambiophonics. Olasonic speakers, VST pluggin on foobar. WOW!!!!
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Old 1st December 2012, 04:59 PM   #115
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Quote:
Originally Posted by Tom Danley View Post

If I recall the picture of your speakers, they would be nearly / mostly onmi directional up to the higher frequencies and would radiate from nearly a single point in space with a simple pattern.
If they only had a tweeter that was smaller still but covered the entire frequency range, then the radiation would for the most part be a simple sphere and then portion of a sphere, largely a single point in time and space.. From that (the shape of the point source radiation envelope) it would seem that your point source speakers are actually similar to the Synergy horns which is curious, those being more or less the whole pie, while the Synergy horn is as much as possible just a slice of pie..

Tom
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Old 1st December 2012, 05:15 PM   #116
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Quote:
Originally Posted by lolo View Post
talking of crosstalk, I had last night my first go ever at ambiophonics. Olasonic speakers, VST pluggin on foobar. WOW!!!!
Wow! It's really starting to catch on now!
Hahaha!
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Old 1st December 2012, 05:22 PM   #117
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Now try it with the Orions lolo.
Go ahead, don't be scared
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Old 1st December 2012, 06:35 PM   #118
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Quote:
Originally Posted by Tom Danley View Post
Hi Barleywater
I am not sure you looked at the phase part of the curve, there is no “all pass” crossover phase shift like Butterworth, linkwitz riley and other named slopes produce.
The high pass hf crossover alone for example has a 4th order ultimate slope which normally would put 360 degrees phase rotation centered around 1200Hz which is not present. The phase response is as if it were one driver, not 7 with a 3 way passive crossover.

Here is an old link to some square waves if curious;
Making Square Waves?

DSP correction has been commonplace in commercial sound for a long time and for one single location, it can perform miracles and can appear to be “perfect acoustic bondo”, but does not fix root or acoustic source problem.
The problem is that if one has separate sources producing the same signal (like a multi-way speaker at crossover), one has separate path lengths to the ear.
DSP can easily fix time and can correct a multi-way loudspeaker but the larger the spatial problems it’s is accounting for (the larger the acoustic spacing relative to a quarter wl), the smaller the “corrected zone” is and usually the result is worse everywhere else.
A multi-way speaker that produces an interference pattern (lobes and nulls) will still be producing an interference pattern with DSP correction because it can’t fix problems in horizontal or vertical placement unilaterally, only locally for one point in space.
Think on the large scale like concert sound, it usually sounds good or fair at the mix booth and different everywhere else.
Hello Tom

This problem is the same for "classic" IIR designs: good design will try to have phase coherency between two drivers troughout their crossover (say one octave around the crossover point) by targeting perfect symmetrical Linkwitz-Riley acoustical slopes (for both amplitude, and most importantly phase), by resorting to EQ or asymetrical electrical slopes. But of course the further apart the drivers and the worst it will get off axis (the coherency will be lost). In this regard your design is of course vastly superior!

Concerning DSP correction (convolution) I think there is two ways of doing it:

- the automated way (DRC) which if not done correctly (ie multiple measurement points and great care with what to correct and what to leave untouched) can lead to what you describe (sound get better for one location, but worse anywhere else). I think too aggressive and poorly made automated corrections (like measure, inverse, convolve...) have given this approach a bad reputation, but with care it can be quite efficient (cf DRC-FIR)
- the manual way, base on linear phase filters and/or phase correction of an existing (and already phase coherent) IIR system (including bass reflex phase shifts, etc.). If done correctly the coherence (between drivers) will be the same as an IIR system, but the phase will be linear throughout the whole spectrum. I have developed a software that tries to follow this approach (manual corrections and/or linear phase filtering):
rePhase, a loudspeaker phase linearization, EQ and FIR filtering tool
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Old 1st December 2012, 07:58 PM   #119
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What Tom describes as "a slice of the pie" has other benefits over the whole pie (omnidirectional ) approach for stereo image in a listening room. A controlled directivity allows for time-intensity trading to provide an image that is relatively immune to the position of the listener. You can'ttoe-in an omni speaker! (see Article about setting up controlled-directivity waveguide type speakers)

So, Tom, how are people to get the hifi advantages of the Synergies with the company doing only the pro market? The DIY approach is a difficult path on those.
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Old 1st December 2012, 08:27 PM   #120
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Quote:
Originally Posted by Tom Danley View Post
Over a broad band, the speaker radiates a portion of a sphere about 50 by 50 degrees.
Have you ever considered an even narrower directivity speaker (20°x30°) for home theater?
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