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Multi-Way Conventional loudspeakers with crossovers

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Old 31st May 2007, 08:07 PM   #931
mige0 is offline mige0  Austria
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Hi

Brian, Thanks!
I will search around a little more and have a look how I can digest that "self alignement".

Greetings
Michael
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Old 31st May 2007, 08:53 PM   #932
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Brian, thanks again for your comments to this thread. This has been extremely illuminating for me, and answered a lot questions I've always had about servo-feedback systems for loudspeakers.

Readers who've read my comments about feedback on the Nutshell pages might wonder about my enthusiasm for Brian's work - well, my issues with feedback topologies are generic transistor amps with low slew rates, inadequate phase margin with reactive loads, a forward path with high-order nonlinear transfer functions, and slow thermal (feedback) tracking for the Class AB transition on the output devices. This collection of disorders covers most transistor amps, and the problems are not visible with steady-state THD testing. (Note these are almost all problems in the midrange and higher frequencies.)

Servo-feedback subwoofer amps are another animal entirely - the main issue is system stability, and the care and feeding of the voice coil in the woofer. The comment I saw earlier about gradually removing the servo feedback above 100 Hz makes a lot of sense.

Mid and high-frequency servo feedback in loudspeakers has always been a nearly intractable problem, thanks to the "sensing problem" of where to detect the feedback for a diaphragm that is moving differently on different parts of the cone. At least for a low-bass woofer, the voice-coil former has a close relationship with the cone - get much higher in frequency, and parts of the cone start to decouple from the voice coil.

---------

Hmm ... thinking about the waveguide/WR driver comments made earlier. I have a utilitarian view of horns - I'm not really a horn fan, and haven't really warmed to their sound that much. I appreciate the efficiency and low distortion, but don't like the HOM, horn-edge diffraction, and other time/dispersion maladies - and those are very difficult challenges that a lot of smart people have been working on for a long time.

The HF horn is there - well, because aside from the exotic prosound ribbons, there is no alternative if you want 97+ dB/metre efficiency and low IM distortion. I don't see a vertical line array of dome tweeters as a realistic alternative, with their intrinsic problems of non-synchronous arrival times at the listening position.

But a horn for frequencies lower than the HF horn is an esthetic choice, not a technical one. Below 1~2 kHz, arrays of direct radiators can do the same thing, but with somewhat different tradeoffs. The midbass horn will have (much) lower IM distortion, but at the expense of (inevitable) HOM modes and associated transient disorders. The cone array will have better impulse response and broader dispersion, but not as clean IM distortion. You pays your money and you takes your choice.
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Old 31st May 2007, 09:09 PM   #933
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Hi Brian,

I was not refering to phase linearity in high-pass filters, but to the EQ boost at sub-bass.

Where the phase shift of any EQ boost is adjustable, and can be shifted from lagging to leading say through +/-30 degrees wrt to phase linearity, then there is only one setting where reproduction suddenly clicks together. Either side of the correct setting and it starts to sound like simple sub-bass boost applied to a falling driver response which might seem optimum for any system 'as is', yet not actually be correct when compared to a phase linear arrangement; unless it fortuitously hits the sweet spot.

In my experience absolute phase is most important, but I am not going to argue about it.

Cheers ...... Graham.
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Old 31st May 2007, 09:31 PM   #934
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Quote:
Originally posted by Graham Maynard
Where the phase shift of any EQ boost is adjustable, and can be shifted from lagging to leading say through +/-30 degrees wrt to phase linearity, then there is only one setting where reproduction suddenly clicks together.
My argument is there is no linear phase for HP filter so that reference does not even exist. Am I missing something here? A simple example of phase linear is when you double the frequency, the phase shift also doubled. That just cannot happen with HP filter.
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Old 31st May 2007, 10:11 PM   #935
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Hi Brian,

I repeat; I am not writing about the phase linearity in a HP filter, but about sub-boost EQ.

Maybe you are arguing about the method of using a conventional HP filter as way of generating sub boost via a separate channel, which of course cannot be phase linear.

Though of course no matter what sub-bass arrangement is used, there will always be a amplitude/phase compromise through the crossover range.

Cheers ....... Graham.
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Old 31st May 2007, 10:29 PM   #936
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Quote:
Originally posted by Graham Maynard
Hi Brian,

I repeat; I am not writing about the phase linearity in a HP filter, but about sub-boost EQ.


Cheers ....... Graham.

I understand your point now, although I may not agree. But that is just fine.
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Old 1st June 2007, 12:27 PM   #937
SunRa is offline SunRa  Romania
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Lynn,

I've mentioned earlier, in the weaveguide post, but maybe you missed it; I hope I'm not annoying though...

Do you consider any more Gary Pimm's subwoofer design and if yes, where can we find some references about it?
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Old 2nd June 2007, 01:58 AM   #938
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Quote:
Originally posted by SunRa
Lynn,

I've mentioned earlier, in the weaveguide post, but maybe you missed it; I hope I'm not annoying though...

Do you consider any more Gary Pimm's subwoofer design and if yes, where can we find some references about it?
Gary's pulled his audio page off the Web - he's taking a vacation from hi-fi, but I still chat with him on the phone every now and then.

The Gary Pimm subwoofer, if memory serves, was a straightforward W-baffle with Parts Express 15" woofers (2 per box) selected for a Q of 0.6 or a bit higher. The whole thing was separately amplified, of course, and a heavily modified DCX was used for EQ to the room and the dipole rolloff. Gary found the stock op-amps and electrolytic caps were so bad that simply connecting the DCX in parallel with the main system (and the subs turned off) quite audibly degraded the sound. The culprit turned out to be the electrolytic caps, which were "contaminating" the main signal path, even though they were simply connected in parallel. A complete replacement of the audio board with high-quality 1:1 line transformers cured that problem, with the transformers replacing ALL of the opamps and coupling caps, both input and output.

He changed the system from a standard dipole to more of a cardioid by extending the back of the box about a foot and filling the open rear space with recycled cotton filling, the same that is used for non-irritating building insulation. He auditioned it with no filling - thus more of a dipole - and filling, producing more of cardioid pattern - and preferred the cardioid. Both variations equalized flat to 16 Hz with the DCX, of course.

I should add Gary's listening room is fairly small, and we only listened about 6 feet away from the speakers (and the W-baffle subwoofers). The preference for dipole vs cardioid, or no filling vs filling, might easily change in a bigger room.
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Old 2nd June 2007, 09:34 PM   #939
jzagaja is offline jzagaja  Poland
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Yesterday I was in Mr. Manger house and we listened bipolar Mangers. He opened the balcony doors and we was walking around with birds singing everywhere. The stereo image was like a hologram - the same from any direction. What's more normal transducers in comparison with MSW have a noise which is annoying and you can easily detect it when clapping your hands. Everything is fine except the Science that cannot explain why two speakers measured similarly (JXR6 and MSW) sounds so different (a good speaker must measure well anyway). There is a new AES article where Schoeps reveal microphone ringing by using MSW as one polarity stimulus (which is required for the task).
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Old 3rd June 2007, 05:05 AM   #940
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Default The Story Continues ...

This is a Quad-12 array, more attractive looking than the previous drawing, and it offers the possibility of one 18Sound 12NDA520 or 12ND710 (the latter available in 8 or 16 ohms) for the widerange driver, one ToneTubby 12" Alnico in 16 ohms, and two ToneTubby 12" Ceramics in 16 ohms.

In terms of connections, the HF and 12" WR share a high-quality amplifier, the 12" Midbass and Bass share an amplifier (possibly a 35~60 watt tube amp), and the subs are independently powered.

If the 16-ohm ToneTubby's are chosen for the MB and B drivers, the Bass drivers can be wired in parallel, low-pass filtered by a single series inductor, and the 2x12 Bass array (with filter) wired in parallel with the single 16-ohm MB ToneTubby. At the lowest frequencies the combined impedance is about 4.5 ohms, the efficiency is about 103 dB/metre, Fs is 78 Hz, and Qts is 0.85. For the cost-conscious, no, it's not a cheap speaker, but the ceramic ToneTubby's are half the cost of the Alnico version - and TT themselves recommend mixing-n-matching the two flavors.

Downsides? I wouldn't expect a lot of linear Xmax from guitar speakers - although I can say from personal experience a single widerange ToneTubby plays really loud, and with none of the usual cone-breakup crud. A 3x12 array of these things would probably put you on stage with the musicians.

P.S. I received an e-mail from Lowther America recently, and they mentioned that there's a version of the Lowther with no whizzer cone - an obvious candidate for a ribbon tweeter to take over at 8 kHz. For those allergic to horns, the Lowther+ribbon would certainly be an alternative in the 1 kHz-on-up range. Now THAT would be an offbeat speaker - a trio or quartet of ToneTubby guitar speakers for the bass, MB, and low-midrange, and a whizzerless Lowther above that.
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