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Old 30th July 2007, 02:30 PM   #1
GordonW is offline GordonW  United States
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Default Horn Flare/driver throat mismatch causing big FR dip?

OK. I've got a very strange problem.

I'm planning to use an Eminence Beta 10CX, with a higher-bandwidth driver (ie, one that can go LOWER) than the "normal" APT50 tweeter driver. A crossover point in the 1500 Hz range was my target.

My first test, was with the Beta 10CX, with a Selenium D210Ti horn driver. The driver shows very good response on the factory spec graphs... AND it tested VERY WELL on a "standard" horn I tried it on, for another project.

I have attached a graph, showing the response of the D210Ti on the "standard" horn (here's a link to a very similar, if not the exact same, horn flare: http://www.mcminone.com/product.asp?...%5Fid=53%2D880 ), and on the Beta 10CX. The top (red) plot is the driver on the "standard" horn, the bottom plot (purple) is on the Beta 10CX.

As you can see, there's SERIOUS problems at about 6KHz, with the D210Ti/Beta 10CX combination. My only cogent thought on the situation so far, is that somehow, I've got a really SERIOUS horn-throat-mismatch between the Selenium and the Beta 10CX. In fact, I don't think I've EVER seen a 20dB notch like, that EVER. Smaller notches, yes... but 20 dB? That's quite a HUGE notch!!

My current plan is to try other horn drivers (with, ostensibly, different shaped throat entrances), and see if any of them interface any better... but I hate the prospect of 'trial and error' blind parts swapping, without being able to do proper diagnostics of what's happening here. Has anyone seen this behaviour before, or has any good ideas (or even good speculations) on the mechanism that's causing this problem?

Thanks in advance...

Regards,
Gordon.
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File Type: jpg d210ti-freq-incoax-smallplot.jpg (67.9 KB, 868 views)
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Old 30th July 2007, 02:33 PM   #2
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How does the response look like with the original driver ?

Regards

Charles
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Old 30th July 2007, 02:36 PM   #3
GordonW is offline GordonW  United States
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BTW: Here's an impedance plot of the D210Ti on the Beta 10CX, just in case anyone is interested or needs it. I don't see anything in the impedance plot, that gives much of any clue of a correlation with the response problem...

Regards,
Gordon.
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Old 30th July 2007, 02:57 PM   #4
GordonW is offline GordonW  United States
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Quote:
Originally posted by phase_accurate
How does the response look like with the original driver ?

Regards

Charles
I don't have an Eminence APT50 (what they originally recommended- it's not included with the Beta 10CX- you have to buy it separately) on hand to try. I may try to pick one up, just to see. I'm also going to try an Eminence PSD2002 (the one recommended for the larger Beta 12CX) since I do have one of those available...

Regards,
Gordon.
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Old 30th July 2007, 03:46 PM   #5
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Greets!

Without taking any physical measurements or doing any tweaking, the throat/horn transition sure seems to be at least a contributing factor since the ~high Q notch around 1 kHz equates to a 6 k+ angular frequency notch, same as with Altec 1" drivers, which among other things I cured on one set of horns by replacing the cardboard gasket with a metal one and align honing the whole assembly. Makes me wonder how good the seal between the two is.

I've seen such notches in poorly loaded drivers though, so considering the lack of LF loading due to the fast flare constant, I'm wondering if reducing the rear chamber Vb to better damp that huge broadband impedance peak well below Fs might reduce it enough. That, or replace the rear cover with a well stuffed pipe.

Anyway, looking forward to your findings.

GM
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Old 31st July 2007, 05:34 PM   #6
GordonW is offline GordonW  United States
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Decided to try a couple of things, to alter/smooth, or change the dimensions of, the throat region.

Ordered one of the Selenium BOLT-ON D210Ti drivers, and a couple of bolt-on to screw-on adapters. That way, I can modify the adapters, to match the throat inside the coax.

Also, I ordered a couple of other decent drivers... B&C DE10, for one example. Maybe just a change in phase plug type/throat interface shape might make a difference too...

Much more testing to be done...

Anyone else got any ideas on further things worthy of testing?

Thanks!

Regards,
Gordon.
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Old 31st July 2007, 06:50 PM   #7
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Default Re: Horn Flare/driver throat mismatch causing big FR dip?

Quote:
Originally posted by GordonW

My first test, was with the Beta 10CX, with a Selenium D210Ti horn driver. The driver shows very good response on the factory spec graphs... AND it tested VERY WELL on a "standard" horn I tried it on, for another project.

I have attached a graph, showing the response of the D210Ti on the "standard" horn... and on the Beta 10CX. The top (red) plot is the driver on the "standard" horn, the bottom plot (purple) is on the Beta 10CX.

Is the response of the D210Ti only 85/90 dB SPL ???
Spec sheet shows 110 dB SPL w/ HL14-25 horn.
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Old 2nd August 2007, 03:01 PM   #8
GordonW is offline GordonW  United States
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Default Re: Re: Horn Flare/driver throat mismatch causing big FR dip?

Quote:
Originally posted by Inductor


Is the response of the D210Ti only 85/90 dB SPL ???
Spec sheet shows 110 dB SPL w/ HL14-25 horn.
We were running much less than 1 watt. Amp gain was set for a max of around 90 dB during the test. One watt would have run both of us out of the room.

Regards,
Gordon.
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Old 3rd August 2007, 12:05 AM   #9
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Another driver has the same problem you mention at 10k, DH200E.
I am using DT150, it seems to work better, with large and small flares.
Definitely PSD2002 is a very good driver.
I guess it's a problem of phase as GM sketch it.
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Old 31st March 2008, 01:29 PM   #10
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What happened with the other drivers, was there a solution found?

Also what is the recommeded driver to go with the Eminence Beta-12CX?
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