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Multi-Way Conventional loudspeakers with crossovers

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Old 15th October 2011, 02:34 PM   #31
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Quote:
Originally Posted by pieter t View Post
Yes, we know about possible lobing issues with the MTM configuration.
That's why we tried all these options, just to see (hear) if practice meets theory.
In the end however the MTM simply sounds best, and from the listening position the sound is just very coherent without pointing in the direction of these lobing issues.
D'Appolito configurations are based on point sources as far as I know.
The TPL150 as a treble unit is not a point source but will more behave like a line source for frequencies over 3 kHz or so.
The midranges are about 40 cm apart centre-centre, so there is line source behavior from a little under 1 kHz upwards.
Maybe all this is responsible for the "click" we reached with this setup.
Mr.Achenbach, which sells the SON-B , made comparisons between the two configurations. One , using one driver only up to 400hz, and the second, using both drivers up to crossover frequency of the Beyma AMT. He reported no relevant perceivable difference.
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Old 15th October 2011, 02:42 PM   #32
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Quote:
Originally Posted by angeloitacare View Post
Mr.Achenbach, which sells the SON-B , made comparisons between the two configurations. One , using one driver only up to 400hz, and the second, using both drivers up to crossover frequency of the Beyma AMT. He reported no relevant perceivable difference.
Interesting that our experience is confirmed.
The nice thing with both midrange speakers working up to the same crossover is that it matches the sensitivity of the TPL150, so it not only eases the crossover network but not having to attenuate the TPL150 is good for sound quality.
By the way, our setup is open baffle woofer - MTM bi-amplified.
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Old 15th October 2011, 04:27 PM   #33
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Quote:
Originally Posted by pieter t View Post
By the way, our setup is open baffle woofer - MTM bi-amplified.
Any pictures?
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Old 15th October 2011, 09:44 PM   #34
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Here is my friends set up; open baffle bass still under development.
He prefers the TPL150 horn loaded (actually more a waveguide); I prefer it without.
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Old 16th October 2011, 05:32 AM   #35
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Originally Posted by angeloitacare View Post
The Germans do let one of the two 8" or 10" midbass drivers work up to 400hz, and the second one to crossover frequency to the TPL-150. So that evitates lobing.
would play up to 400hz:
I would expect a traditional TMW speaker stack with the T=TPL150, M= 8" midbass, and W=18" to perform better. For WAF, the pipe stand on the German MTM would likely get a lower rating that a bass cabinet.

I'm still a fan of using a wide bandwidth midbass to cover more of the vocal range, roughly 80 Hz to 1100 Hz (that is, E2 to C6) for normal male and female voices together.


There are several physical limitations in using one standard speaker over a wide bandwidth.
1) Frequency response and quality of sound.
2) horizontal and vertical polar response (beaming)
3) IMD Intermodulation distortion (doppler) from summing low and high frequencies
4) adequate SPL levels

STILL.. there is a large full range speaker group that accepts these compromises over crossovers.

When you run through the equations, it looks like 3-way with an 8" or 10" midbass speaker is the best option to cover a low of (80-100Hz) to a high of (1,200, 1,500Hz). IMD start to increase rapidly even with the xover dropping just from 100 to 80Hz. Constant directivity degrades rapidly with the xover increasing from 1,000 to 1,500Hz. A midbass with a curvelinear cone profile has ~10% superior directivity.

Several 98-100 db/watt high efficiency old school speakers with a 300Hz crossover used two 15" woofers, a 10" midbass like the JBL 2012H, and a 1" compression driver with a 90 x 40 constant directivity horn. I have found that accepting a 94-95 db/watt SPL efficiency and a 1,400-1,600Hz crossover to a suitable tweeter allowed me to use a light cone 8" midbass to pull detail over the vocal_range, or a 10" midbass to put more weight behind vocals with additional compromise in dispersion. I have Tang Band W8-1808 and Lambda TD10M.


As you would expect, a full range 8" with decent Xmax can be used as a wide bandwidth, good dispersion midbass.
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Old 16th October 2011, 10:30 AM   #36
Scott L is offline Scott L  United States
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Default Off set bass drivers

Quote:
Originally Posted by pieter t View Post
Here is my friends set up; open baffle bass still under development.
He prefers the TPL150 horn loaded (actually more a waveguide); I prefer it without.
I like the way you have your bass (or in my case mid-bass) drivers off set.
I used this same approch a few years ago, and intend on going back to it. Sounded really nice.
(ps disregard the MTM video speakers in the pic, and then notice the similarities)
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Old 16th October 2011, 10:55 AM   #37
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Originally Posted by Scott L View Post
I like the way you have your bass (or in my case mid-bass) drivers off set.
I used this same approch a few years ago, and intend on going back to it. Sounded really nice.
(ps disregard the MTM video speakers in the pic, and then notice the similarities)
In this situation the woofer offset is done to limit total height of the complete rig.
Maybe some kind of U or H frame might have done the bass job, but I am not sure if that sounds good up to some 200 - 250 Hz.
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Old 16th October 2011, 03:04 PM   #38
Scott L is offline Scott L  United States
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Default cross-over frq

Quote:
Originally Posted by pieter t View Post
In this situation the woofer offset is done to limit total height of the complete rig.
Maybe some kind of U or H frame might have done the bass job, but I am not sure if that sounds good up to some 200 - 250 Hz.
In the system pictured above, that was crossed at 500Hz then feeding the twin 5inchers in that waveguide. 500 Hz = 2 feet, and the 2 drivers are within that distance as well as the distance to the above mid. That's why I offset the drivers in that particular system.

Since then, however, I have lowered the x-over to 250hz and changed over to a single 10" midrange. The 10 inch moves a lot more air, which IMO is required at that low of a crossover frequency. I am mulling over whether to lower the x-over freqency even more, say to 190Hz.
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Old 16th October 2011, 03:17 PM   #39
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i have positioned the TPL-150 horizontally, instead vertically, as usual. I did not perceive any dispersion difference or deterioration. That would make it possible to bring the two midrange cone drivers closer together.
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Old 16th October 2011, 06:58 PM   #40
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Not for sweet spot listening, but off-axis there will be HF drop IMHO.
Having the midrange speakers further apart than theory predicts, but nevertheless sounding and blending that well was a surprise. We have a "don't touch anymore" thing with this
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