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Multi-Way Conventional loudspeakers with crossovers

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Old 23rd August 2012, 05:36 PM   #7831
DeonC is offline DeonC  South Africa
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I would like to second this suggestion. With a second woofer working below bafflestep, the overall efficiency could be increased to about 103 - 106dB SPL. However this might mean a reworking of the XO, so I don't think Lynn would consider this.

OTOH, I must say that Lynn has me salivating when reading about these speakers. The description of the sound reminds me of the reason I got into this hobby in the first place- the sheer love of music. I just want to sit in front of the system and get carried away. That is what makes music so special. So with or without the extra woofer, this sounds like the kind of system that would make me take a step back from the mad rush that is this interesting hobby, and just spend more time listening to music.

Deon
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Old 23rd August 2012, 08:21 PM   #7832
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Quote:
Originally Posted by DeonC View Post
I would like to second this suggestion. With a second woofer working below bafflestep, the overall efficiency could be increased to about 103 - 106dB SPL. However this might mean a reworking of the XO, so I don't think Lynn would consider this.

Deon
Actually, I am considering this, although probably not for myself, since the cabinet would then grow to 9 cubic feet, most likely with dual Altec/GPA 416B's in a side-by-side configuration (same layout as the Altec 9844 and JBL Everest DD66000, except with a free-air horn on top).

Another dual-woofer configuration would use one or two open-back boxes filled with dense Bonded Logic UltraTouch filling, which changes the bass radiation pattern to a quasi-cardioid. These have interesting properties midway between pure dipoles and closed boxes; they are much more efficient than dipoles, since the deep bass cancellation is only 3~6 dB compared to the 20 dB loss of a pure dipole, which in turn would allow a second (bass-fill) woofer to offset the losses of the first (cardioid) woofer. When I visit Gary Pimm in a few weeks time, I'll discuss how the math works on these things, and what kind of EQ a dual-15-woofer configuration would require (taking into account the floor image as part of the radiation load).

The first thing is to build my own personal pair of the system described in previous posts (which is up and running, but is not in my house) and keep fine-tuning it. It's about 90~95% there.

The bass cabinet for the single Altec/GPA 416B-Alnico has a slot vent on the floor, the same trick I used on the Ariel to extend the deep bass through mirror-image floor coupling. The front face is slanted 22~30 degrees, to match the aim point of the AH425 on top of it, with small angled side panels, which decrease diffraction on the woofer panel. The width of the bass cabinet is 25"; any narrower, and the midbass becomes too thin. The 25" width sounds about right; I can see why traditional cabinets from the 1950's used widths like these.

Last edited by Lynn Olson; 23rd August 2012 at 08:32 PM.
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Old 23rd August 2012, 11:10 PM   #7833
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Originally Posted by Jmmlc View Post
Hello,

I think that there is some mistake in your idea that a tractrix could possess a better dispersion than a Le Cleach horn. For the same cut-off frequency both of them have nearly the same polar patterns.

See the attached graph which presents the comparison between simulation performed with Hornresp of the polar maps of
a tractrix (upper half of the diagram) and a Le Cléac'h horn (bottom half of the diagram).

An advantage of the Le Cleac'h horn upon the tractrix being smaller diffraction effects at the mouth (in some case that diffraction can give a fake impression of better dispersion though). But I fully agree with Lynn that diffraction is the firts thing to avoid in horns and this is one of the main goals of the Le Cleac'h horn

Best regards from Paris,

Jean-Michel Le Cléac'h
Thanks for your clarification, Jean-Michel. It seems I was indeed mistaken.
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Old 24th August 2012, 12:17 AM   #7834
Decker is offline Decker  United States
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Can someone point out a post or page number that discusses how the box volume and port size were determined? I have run the 416B T/S specs through WinISD using a 4.5 cubic foot box size, but I'm not sure that my results are what were intended. Also, is the slot for the woofer acting as a "variovent", or is it a port with stuffing? (Or maybe that is a distinction without a difference?)

Last edited by Decker; 24th August 2012 at 12:20 AM.
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Old 24th August 2012, 07:14 AM   #7835
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great to see variations based around a killer setup
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Old 24th August 2012, 08:56 AM   #7836
DeonC is offline DeonC  South Africa
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Lynn, I have a question concerning low bass. Do you think these speakers will work better with say a high-pass at about 50Hz - 60Hz and good subs like the Rhythmic Audio motional-feedback units. This will relieve the mid-bass units from low bass, with possibly better midrange. The XO could maybe be higher, say 70Hz - 80Hz, but I have read a number of people who say this is too high, and it interferes with the low-mids. What are your thoughts?

Thanks,
Deon
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Old 24th August 2012, 03:03 PM   #7837
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I reckon if people build this as prescribed by Lynn, they will fall off their chair and give themself an uppercut for having doubted
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Old 24th August 2012, 03:16 PM   #7838
DeonC is offline DeonC  South Africa
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I don't doubt that, but if you relieve the midbass from low-bass duties, you reduce the excursion-related distortions (like doppler, TIM (?) and others). Just a thought.

Deon
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Old 24th August 2012, 03:44 PM   #7839
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At 90dB you do not see the woofers moving while listening to music.
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Old 24th August 2012, 04:05 PM   #7840
DeonC is offline DeonC  South Africa
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I'm not disagreeing with that. But when referring specifically to the Rhythmic Audio subs with their motional feedback, they will be better in the bass than just about any non-assisted woofer. And I still contend that relieving the midbass from frequencies below circa 60Hz, which is below the area where tone is developed, will have benefits higher up. JMHO. YMMV.

Deon
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