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Old 29th August 2013, 11:44 PM   #9241
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Quote:
Originally Posted by ra7 View Post
Umm... not quite. Well, not for me anyway. I have a similarly large tractrix horn and I've tried it with a BMS4592. Sure, there is extension, and yes, it is point source. But the horn still determines the dispersion. In other words, it beams like a laser in the HF, and gives unstable imaging.
Hi
We use a lot of the 4592’s (some of the speakers at work have1, 3 and 4 of them) but the 4592 has an internal geometry and exit large enough to already be defining the directivity up high and the high on axis sensitivity is partly a result of that driver beaming at 20KHz even without a horn.

Another issue I have found it that the acoustic phase or time relationship makes it very hard to have a summation without crossover phase shift like the normal Synergy horn crossovers (which sum into what looks like a single driver w/o crossover).

You might look at the 4550 which has an unusually low resonant frequency and impedance bump while also having good hf response.
We use hundreds of those at work and they are also a very reliable driver.
The one inch exit will fill out up to about a 50 degree conical horn at 20KHz too and radiates a curved (expanding) wavefront due to its internal geometry.
Best,
Tom Danley
Danley Sound Labs
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Old 30th August 2013, 07:14 AM   #9242
jzagaja is offline jzagaja  Poland
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Quote:
Originally Posted by ra7 View Post
But the horn still determines the dispersion. In other words, it beams like a laser in the HF, and gives unstable imaging.
This horn beams less

Minphase

I have ready crossover for 4590.
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Old 30th August 2013, 08:04 AM   #9243
Jmmlc is offline Jmmlc  France
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Hello Jack,

As Tom Danley, explained, the HF part of the 4592 compression driver defines itself its own beaming so the beaming in HF will be the same on the Azura and on the Minphase.


We have a lot of experience here in France with large Le Cléac'h round horns. We succeed in reducing the effect of the beaming inherent to that kind of horn rotating the axis of the horns to cross in front of the listeners head. Depending on the distance between the 2 loudspeakers , the crossing point of the horns axis can be from 80centimetres (30 inches) to 120 centimeters (50 inches).

Such horns should never be listened with parallel axis or small angle axis.

Additionally, that kind of set up allows a nearfield listening with 3D image effect.

Best regards from Paris, France

Jean-Michel Le Cléac'h

Jean
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Old 30th August 2013, 11:08 AM   #9244
3GGG is offline 3GGG  Australia
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Interesting points thank you Jean-Michel
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Old 30th August 2013, 12:10 PM   #9245
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Quote:
Originally Posted by Jmmlc View Post
We have a lot of experience here in France with large Le Cléac'h round horns. We succeed in reducing the effect of the beaming inherent to that kind of horn rotating the axis of the horns to cross in front of the listeners head. Depending on the distance between the 2 loudspeakers , the crossing point of the horns axis can be from 80centimetres (30 inches) to 120 centimeters (50 inches).
That's anyway how BD-Design recommends their Oprhean Mk2 horns for BMS4592 to be used - crossed in front of the listener. In a small room you can get a good result in any other way.
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Old 30th August 2013, 05:32 PM   #9246
ra7 is offline ra7  United States
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Quote:
Originally Posted by Tom Danley View Post
Hi
We use a lot of the 4592’s (some of the speakers at work have1, 3 and 4 of them) but the 4592 has an internal geometry and exit large enough to already be defining the directivity up high and the high on axis sensitivity is partly a result of that driver beaming at 20KHz even without a horn.

Another issue I have found it that the acoustic phase or time relationship makes it very hard to have a summation without crossover phase shift like the normal Synergy horn crossovers (which sum into what looks like a single driver w/o crossover).

You might look at the 4550 which has an unusually low resonant frequency and impedance bump while also having good hf response.
We use hundreds of those at work and they are also a very reliable driver.
The one inch exit will fill out up to about a 50 degree conical horn at 20KHz too and radiates a curved (expanding) wavefront due to its internal geometry.
Best,
Tom Danley
Danley Sound Labs
Tom, agree with all you say. What I meant with the horn determining dispersion is that you need a smaller horn for the HF, or a diffraction slot to control dispersion with the BMS dual concentric drivers.

Large horns and 2" exit drivers have their benefits. Incredibly gorgeous midrange is one. But they certainly have their problems. BMS has perhaps fixed the bandwidth issue -- there is no droop or breakup (maybe) like the classic large format drivers, but dispersion is still a problem.

If you choose not to use the 2" driver up high, then the crossover becomes a problem. Too much separation between the sources both vertically and in depth. The compromise I've landed on is a 1.4" driver and the SEOS-24.

I have tried the 4550 and it is an excellent driver. But it just doesn't have the LF extension I'm looking for. TAD-2001 is a good candidate, but I'm not paying that much for a driver.

Of course, your Synergies will solve all these problems, and I wanted to try and build a Synergy this summer. Alas, I haven't been able to the time. I'm hoping BWaslo will provide an update soon on his new build. And one can always hope for a kit from DSL

Last edited by ra7; 30th August 2013 at 05:35 PM.
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Old 31st August 2013, 10:24 AM   #9247
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has anyone compared BMS 4550 with B&C DE250 which is a good and affordable candidate for home use in a 2-way from 800hz on..... however i've never been fully convinced with DE250 tone so i'm after something more lively, sparkling and less dry (in a OSWG)....
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Old 31st August 2013, 11:30 PM   #9248
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Quote:
Originally Posted by Jmmlc View Post
We have a lot of experience here in France with large Le Cléac'h round horns.

We succeed in reducing the effect of the beaming inherent to that kind of horn rotating the axis of the horns to cross in front of the listeners head. Depending on the distance between the 2 loudspeakers, the crossing point of the horns axis can be from 80centimetres (30 inches) to 120 centimeters (50 inches).

Such horns should never be listened with parallel axis or small angle axis.

Additionally, that kind of set up allows a nearfield listening with 3D image effect.

Best regards from Paris, France

Jean-Michel Le Cléac'h

Jean
In the quite small listening room where the single 15" 416-Alnico and AH425/Radian745 were auditioned, the optimum listening angle seemed to be with half or less of the phase plug visible from the sitting position, which resulted in the axis crossing about the same distance in front of listener as mentioned in Jean-Michel's post above.

Since my strongest design influence has been the BBC research of the late Fifties, Sixties, and Seventies, I've always followed the BBC-stereo practice of the axis crossing a moderate distance in front of the listener. The exact distance is a function of dispersion and tolerance of diffraction artifacts.

I started designing low-diffraction loudspeakers in 1979, as a result of building a prototype for Audionics that looked like a pair of really big vitamin capsules. That was a fun experiment: if the room was darkened, you might actually walk into the speakers while they were playing, since the music seemed to float in the air without any apparent physical source.

That taught me that the apparent "pinning" of music to the loudspeaker is a result of diffraction around the sharp edges of the front baffle; if you reduce the diffraction below a perceptual threshold, not only does a lot of tonal coloration go away, but the spatial impression of sound coming from a speaker-like enclosure goes away too.

The comb-filtering of diffraction (as seen by ripples on the FR graph) is the least of the problems with diffraction; the time-domain reflections are far worse, and severely degrade the spatial impression in stereophonic playback.

This is also why I never seriously audition a loudspeaker in (single-speaker) mono; the spatial impression is completely different with a single-speaker presentation, and there's no way of telling how bad diffraction is. In stereo, if you're familiar with the sound of a very low diffraction loudspeaker, you can easily hear how much diffraction is impairing the spatial presentation. Most commercial speakers fail this test rather badly, but then again, very few reviewers and audiophiles have ever heard a loudspeaker with low diffraction and a fast-decay time signature.

Although magnetic-planars and electrostats can have fast-decay time signatures, the planar shape with hard edges isn't necessarily low diffraction. So the sound often seems to come from somewhere behind the planar, as if it were a window, instead of floating in the air, like it does with a truly low-diffraction loudspeaker.

Conversely, you can have a speaker with little or no diffraction, like the MBL and Walsh omni-radiators, but the time signature can be stretched-out and lengthy, thanks to diaphragm and structural resonances. This results in a diffuse and "swimmy" spatial impression. Room treatments can reduce the "swimmy", too-large sensation, but cannot improve the time response of the loudspeaker itself. (A true-omni radiator is a particularly good candidate for digital FIR correction, since the corrected time response is good in all (horizontal) directions, unlike a conventional array of drivers.)

The goal with this system is to have a rapid settling time, low diffraction, and high efficiency, with a slightly warm spectral balance (about 1~2 dB tilt from 100 Hz to 10 kHz).

Last edited by Lynn Olson; 31st August 2013 at 11:52 PM.
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Old 1st September 2013, 12:31 AM   #9249
ra7 is offline ra7  United States
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Quote:
Originally Posted by anubisgrau View Post
has anyone compared BMS 4550 with B&C DE250 which is a good and affordable candidate for home use in a 2-way from 800hz on..... however i've never been fully convinced with DE250 tone so i'm after something more lively, sparkling and less dry (in a OSWG)....
I did just such a comparison using the SEOS-18 horn.
1 inch CD Comparison (SEOS18)

The BMS has slightly less ripple, more output and less distortion in the lower octaves. Both are excellent, IMO. I was using them with a 800 Hz LR 6th order target. This is too low for either driver, even in the home.
Attached Images
File Type: jpg B&C_BMS.jpg (259.5 KB, 448 views)

Last edited by ra7; 1st September 2013 at 12:33 AM.
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Old 1st September 2013, 01:32 AM   #9250
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Hi Lynn, all
I can expand on Jean-Michel’s observation so far as aiming and the Stereo image.
If you think of a polar pattern as an “equal loudness contour”, most loudspeakers or horns that have directivity, have the maximum level at the zero zero on axis. In the olden days in commercial sound, the rule was you put the speaker in the air and aim the speaker at the farthest seat
Once the “polar pattern” came to be, the next step was to figure out the optimum height and angle so that the listeners were partly on the bottom side of the lobe. If one had the lobe angle and height “right” the spl in the audience plane did not change with the inverse square law but much slower.

In the listening room, if you have a couch, one can aim he right speaker at the left seat and vis versa and this puts the R listener in the R seat in a slightly lower level than normal and since part of the stereo image is loudness based (as in a pan pot say), one has a wider sweet spot.

I would offer too that your impression of “sound through a window” IS what one wants if reproducing a stereo image or in commercial sound maximizing voice intelligibility (the latter is a property that can be measured with a STIpa measurement).

The reason is the radiation of spatial q’s are what let you hear the source’s physical depth if your eyes are closed, are not part of the input signal. This works best with one speaker. Take the loudspeakers physical distance clues away and the sound, sounds “up close” on a dry mic recording or off somewhere in a reverberant recording. Listen in stereo and the speaker with spatial q’s produces a mono signal as a center phantom AND a right and left source. Take away the loudspeakers spatial q’s and you have a strong mono phantom and no apparent right or left source.

If you had planar speakers well enough behaved to produce that lack of spatial identity, then in spite of whatever edge diffraction, the direct energy is far greater than the spatial ques. Keep in mind that to the degree such a source can replicate true piston motion; it would have a LARGE amount of directivity up high. Also, it’s what you measure where you’re sitting that reflects what you hear where you’re sitting, a high degree of directivity delivers something to the listening position much closer to what one measured at one meter say.

While you can’t measure stereo imaging as that is entirely subjective, what one can predict is intelligibility of words as that depends on preserving the signal information / keeping it intact at the listening position.
The STIpa measurement I mentioned here and a number of posts elsewhere here is an audio Modulation Transfer Function Measurement, actually the STIpa figure is the result of 7 MTF’s across the speech band.

Like with optics, an MTF is a measurement of resolution, “how fast” the image can transition from black to white. In the audio version it is the rate of amplitude modulation of what ever signal F one is interested in. If one measures the MTF’s of a loudspeaker (with say ARTA), one picks the carrier F and then it measures how deep the modulation depth is at higher and higher rates.

Things like ringing, energy storage as well as distortion and reflected sounds (and more) limit the rate of modulation. This MTF view is a relatively new way of looking at loudspeakers, there is no “figure of quality” yet it is easy to tell if something you did, made it better or worse. On the other hand, the STIpa measurement which is a number of MTF’s has been proven to be a reliable language independent way of predicting the intelligibility in larger scale sound. In the home, one can clearly see the difference between different loudspeakers such as you mentioned.

I couldn’t agree more about the point source, it doesn’t have to be Omni, it can have directivity but it HAS TO radiate simply as if it’s origin were an acoustically small source and was producing simple (clue free) spherical radiation.

At work, our business is large sound systems but I have applied the same hifi goals to those systems. AS you might imagine, as the loudspeaker system gets larger and the acoustic power goes up, this is more and more difficult to do, but it is still possible. If you go to football games, you have heard just “how good” the sound quality is when you have 50,000 - 100,000 seats and a concert sound system. Anyway, if you want to hear some “single point sources” in a larger room, you can get some idea with headphones and the Video’s below (from LSU tiger stadium). Using that CD radiation lobe and choosing aligning the pattern, the spl only varies about + - 3dB over the entire stadium and it “sounds the same everywhere”.
Best,
Tom Danley

https://www.dropbox.com/sh/nmmmdtum82lyig9/QnEaYWlnDE
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