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Multi-Way Conventional loudspeakers with crossovers

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Old 11th May 2013, 12:28 PM   #8741
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Some inspiration for open boxes like discussed in #8720 and the following posts 2-way: Waveguide + Cardioid-like
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Old 11th May 2013, 06:38 PM   #8742
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Originally Posted by Lynn Olson View Post

. . . the Gary Pimm open-back boxes. Gary uses the Eminence Beta 8's . . . The box is really simple; it's about 15" wide, 12" high, 18" deep, and open on the back.
What is used for the treble? Also any XO info would be appreciated.
If I interpret the dimensions correctly, it's a horizontal cab (a really big one for the Beta 8 at that). I'm guessing that means a seperate horn on top?

Sorry all the questions; despite all the gear detail on Gary's site, there's nary a peep about the speakers.

Thanks!
-- Mark
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Old 11th May 2013, 07:47 PM   #8743
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Well, until recently Gary was using a Chinese ribbon (don't know which one) with a computer-based crossover and multi-amping, Beta 8 for the mids, and four 15" woofers in two open-baffle W boxes for the stereo-pair subs. (Four 15-inchers in all.) Very heavy EQ for the subs, pretty much no EQ for the Beta 8's, and not much for the ribbon tweeter.

I talked to Gary on the phone just a couple of days ago, and he's built a custom LeCleac'h wood horn for the Radian 475 1" exit compression driver, with a T=0.707 and entrance angle of 5.5 degrees to match the 5.5 degree exit angle of the Radian 475. The horn is a 1 kHz horn, and he's using a 2 kHz 4th-order highpass filter with a bit of in-band EQ.

He was previously using a commercial Tractrix horn with the 475, and he's much much happier with the LeCleac'h, reporting pretty much the same things I noticed with the AH425 ... very deep images, very natural spatial qualities, and vivid dynamics, with much less horn coloration than the Tractrix horn. He's really thrilled with the combination of a wood horn, the LeCleac'h T ratio of 0.707, and exact matching of exit and entrance angle between compression driver and horn ... very low measured diffraction, smooth response, and much more dynamic sound than the ribbon.

Since Gary has an electronic crossover, all he has to do is turn a virtual knob with the mouse at the listening position, using his big LCD TV screen as a monitor, to evaluate the sound of different crossover frequencies and (acoustic) slopes. With the 475, 1.4 kHz was a bit too low, and 2 kHz sounded great.

His next plan is for a bigger LeCleac'h horn, 425 Hz, or maybe even 360 Hz, since the maximum size of the AH425 was constrained by needing to fit into an Australian Post box for economical shipping from Australia. (FedEx would be about US$500 or more, while AusPost is about US$120 a pair) For the larger horn, Gary's considering either the Radian 745Neo or possibly the really big one favored by JMMLC himself, the 950Neo. One advantage of the 950 is you can get a 4" beryllium diaphragm for it right now, although they're not cheap.

Last edited by Lynn Olson; 11th May 2013 at 08:06 PM.
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Old 12th May 2013, 12:21 AM   #8744
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Originally Posted by Lynn Olson View Post
Well, until recently Gary was using a Chinese ribbon (don't know which one)
Hi-Vi planar. A sort of quasi-ribbon. 1st order high pass circa 5K, IIRC. It mated well with the Beta 8. Beta 8 had a small inductor in series to calm the slight rising response.
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Old 12th May 2013, 02:05 AM   #8745
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His next plan is for a bigger LeCleac'h horn, 425 Hz, or maybe even 360 Hz, since the maximum size of the AH425 was constrained by needing to fit into an Australian Post box for economical shipping from Australia. (FedEx would be about US$500 or more, while AusPost is about US$120 a pair)
There are some online courier services now that give better prices, which perhaps makes the 340Hz JMLC azurahorns worth looking at . eg a carton 52 x 52 x 40cm to USA (from Oz) is $175. 61 x61 x 49cm is $295. (interparcel.com.au via ups). A lot less to NZ or SE Asia. Still expensive but in terms of overall cost might make sense. BTW just a hobby for me.

martin
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Old 12th May 2013, 11:55 PM   #8746
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Is there any real advantage to a 340 Hz Horn compared to the 425 Hz version when using a 15" / 16" woofer?
the 340 is larger, heaver, more expensive, harder to ship, presumably has more beaming at higher frequencies.
In return, group delay and pattern control are lowered another 1/3 octave.
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Old 13th May 2013, 06:24 AM   #8747
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The exponential nature of sound really confronts you with horns. Perhaps the size difference is the best intuitive measure. Certainly it doesnt buy much on the linear scale of things. The 425 horn is a great landing spot for many reasons, but in the end it is the bass / mid reproducer that determines what you need. At least with Jean-Michel's curve the character of presentation is the same in all sizes. Add construction rigidity to advantages of smaller horns.
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Old 14th May 2013, 03:07 AM   #8748
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Originally Posted by Truetone View Post
The exponential nature of sound really confronts you with horns. Perhaps the size difference is the best intuitive measure. Certainly it doesnt buy much on the linear scale of things. The 425 horn is a great landing spot for many reasons, but in the end it is the bass / mid reproducer that determines what you need. At least with Jean-Michel's curve the character of presentation is the same in all sizes. Add construction rigidity to advantages of smaller horns.
Martin brings up important points about the size of the horn. Bigger is not always better; what you win in some areas is taken away in others.

What's a little unusual about the AH425 is that it's fairly compact (16.5" overall diameter) for a large-format compression driver. It's not a horn designed for a 500 Hz crossover; that would be about 45% larger, 24" or so.

I did a bit of research on the performance of direct-radiator paper-cone 12" and 15" drivers, and the versions that are not designed for PA use have pretty good performance through 1 kHz, with a broad, low-Q peak around 1.5 kHz. The pro drivers intended for high-power use have heavy, rigid cones, with complex breakups in the 1.2 kHz and higher regions.

I don't want to rely on digital brickwall filters to prevent power from going to complex breakup regions; I'd rather select drivers with are controlled and well-behaved from 1 to 5 kHz. The Altec/GPA 416 and 515 fit the bill, but there are other pro drivers designed for studio-monitor use that are suitable as well. I expected the JBL 2226 to be suitable, but it didn't audition that well compared to the GPA 416 Alnico.

Even though these drivers are being used in their piston band (flat-response region), there are pretty noticeable subjective differences between them. Some of the subjective differences may be the result of out-of-band artifacts, while others may come down to differences in surround, suspension, and magnetic-field geometry in the gap.

What I've learned about horns is that "stretching" bandwidth does not work well; a given driver and horn has a preferred working range, and trying to squeeze out a few more Hz at the bottom of the range isn't a good idea. The Radian 745 has a stiffer suspension (stretched Mylar) than the crimped-aluminum tangential suspension of the Altec/GPA 288, and this affects how low the compression driver can go before noticeable IM distortion starts creeping in. So I'm not sure that a 500 Hz crossover, along with a larger horn, is even a good idea for the Radian 745. The Radian 950 is probably a better fit for that setup.

It's the builders using folded bass horns that have to make some hard choices: many folded bass horns are in pretty bad shape by 500 Hz, never mind 700 Hz, where the response is a rumpled mess. Horns that have flat response (and good power-handling) down to 300~350 Hz are really big, in the 32~40" region, and the best driver is probably a cone, not a compression driver. Time alignment gets tricky with horn that deep ... it's either digital time correction and crossover, which implies multi-amping, or the loudspeaker itself starts to get quite large and quite deep. So there's a whole collection of tradeoffs when HF horn has to meet a folded bass horn.

The alternative is direct-radiator bass, with a choice between two 12" drivers (high efficiency but with a higher F3 frequency), a single 15" driver (good overall compromise), and two 15" drivers (cabinet starts to get large and heavy). An interesting option with a vertical array of two bass drivers is separate lowpass filters for each driver, which gives a provision for a moderate degree of time-aligning between upper and lower driver.

The two-drivers in a vertical array, with the lower driver almost touching the floor, has some interesting characteristics when the floor image is considered. At the lowest frequencies, there are effectively four drivers in a vertical array, with the lower two comprised of the floor images (carpet absorbs less than 1 dB in the 50 Hz to 500 Hz range). Yes, we're back to the line array, in a way, but it's lowpassed at 700 Hz.

Last edited by Lynn Olson; 14th May 2013 at 03:33 AM.
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Old 14th May 2013, 11:54 AM   #8749
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...or the loudspeaker itself starts to get quite large and quite deep.
Hey! I resemble that remark.
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Old 14th May 2013, 06:02 PM   #8750
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I keep hearing from the experts about how conventional dome tweeters are smoother than compression drivers and better in the home environment. So, I started experimenting with the Vifa XT25 ring radiator in a SEOS-12 waveguide. Results are promising. No problems with distortion or perceived dynamics, as long as you watch the low end on the tweeter. And you get that last octave in the top end, which is missing in most 1" CDs, and is non-existent in 2" CDs. It really makes a difference in terms of the ambiance of the recording.

The EQ required to flatten the response is substantial though, and I haven't gotten the overall balance right yet. But it does sound better defined than a CD. Instruments have distinct signatures, and notes have better precision/definition.

Has anybody else made similar comparisons? Are the response curves from CDs truly smooth? I guess we need high-res measurements (Toole recommends a 2 Hz resolution) that cannot be obtained through gating.
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