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Old 30th March 2006, 03:54 AM   #21
m@ is offline m@  Thailand
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polar response = crossover slope + driver separation (+ driver directivity + baffle + voodoo), yes. but even coaxial drivers don't sum perfectly. (and i believe they're usually 'incorrect' directly on axis.) I was talking about asking the sound sources to sum acoustically - using changing amplitude and/or phase of two sources (of different physical and tonal characteristics, not to mention frequency response variations). That summing is an ugly affair - hence the ragged polar response. Nor does it happen as models predict. nor is it completely worthless, of course, far from it, but why accept it when full/wide range driver technology has come so far?

anyway, is a crossover really bad? yes. there is much to be gained by getting rid of the tweeter/mid/bass tweeter/bass $500 cap and coil mess paradigm and producing speakers with an unsullied, coherent, point source middle band. mmmm, clear mids. it's like taking your ears out to get laid...



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Old 30th March 2006, 10:13 PM   #22
KCHANG is offline KCHANG  United States
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Hi swak,

I have not measured the directivity of the Audax driver at 7KHz. My guess is that the dispersion is not too good, but I have no data to show it. I listen to the OB speakers on-axis.


With the various projects I've tried, I actually prefer the OB bass over BR, but I use the JBL 4648 bass boxes because I have them. As you may know, my main system uses B&G RD75 line sources and eight 18" woofers on OB's for dipolar bass. To my ears, the bass generated by the JBL boxes does not sound as "clean" as the bass from the OB subs. A friend used Dayton 15" IB woofer on OB, and it also produced very nice bass, better (again to my ears) than that of the JBL boxes.

I have not had the chance to visit Dr. Geddes, but I definitely want to audition the Summas someday.

Best,

Kurt
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Old 31st March 2006, 01:48 AM   #23
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sorry to threadjack here, my gf falls asleep when i rant

Are you talking about the Geddes from Michigan? A friend of mine has just hired him to design some horns. How is the guy's gear?
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Old 31st March 2006, 02:17 AM   #24
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A friend used Dayton 15" IB woofer on OB, and it also produced very nice bass, better (again to my ears) than that of the JBL boxes.
Nice to hear that, IB subs is something I have considered as well.

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eight 18" woofers on OB's for dipolar bass.
Wow, I bet it souds good! How big is your room? I was thinking of 2x15"/ch for a 23m2 room. At what freq. at you crossing them over to the big planars? Going up to 300Hz I would be able to control the room modes efficiently, but on a W or H frame I would have to equalise at the top.

I would really want to try a midrange horn (conical) someday, but using high efficiency widerange mids (mayby even 2 or 3) seems much much easier. Have you tried several high efficiency mids?

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Are you talking about the Geddes from Michigan? A friend of mine has just hired him to design some horns. How is the guy's gear?
Kchang can give you more info, but if his designs incorporate as much as he knows abot speakers, I bet they are top noch.
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Old 31st March 2006, 03:29 PM   #25
KCHANG is offline KCHANG  United States
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Hi swak,

My main system using the B&G RD75 drivers and OB bass is in my basement, which is about 1400 sqft and undivided. Actually, all my speaker projects are in the basement, as they tend to be big and ugly, and no WAF. The speakers of the main system are placed at least 8 feet away from the side walls and 12+ feet from the backwall. The crossover is 180Hz 4th-order LR, using the Behringer DCX2496, and the bass boost is done using a Behringer DEQ8024.
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Old 31st March 2006, 11:29 PM   #26
BHD is offline BHD  United States
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Passive crossovers are bad if they're in the critical 500-5K range. If you can get them outside that, they do less damage. It's especially difficult to cross over in that middle range when the drivers are drastically different types (cones to ribbons or cones to horns, for example).

The PHY-HP KM-30 crosses over to a super tweeter at 8K or so, relieving the main driver of such duties. The Manger driver handles everything above 150-300Hz or so, leaving the low bass to drivers more suited for that job.

Others like VMPS are using wideband midrange drivers and crossing at 150Hz or so to a woofer and using a high quality supertweeter crossed over at 5K. I can think of many Fostex drivers that don't have great treble or bass response, but would be great crossed over to good woofers and super tweeters outside the 500Hz to 5KHz range.

You can also have drivers custom built that have the same sensitivity and naturally cross over to each other (like the Gallo Nucleus and the PHY driver above) eliminating the need for a passive or active crossover altogether. I think this is the best way to go, but a properly implemented active crossover is better in every way than a passive one if you can pay the extra freight in amp costs.
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