Does anyone have nearfield measurements of an Eminence Alpha 15A? - diyAudio
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Old 19th June 2008, 12:31 AM   #1
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Default Does anyone have nearfield measurements of an Eminence Alpha 15A?

Or (and this is the question I'm trying to answer), how high can it be used when crossing over to a midrange?
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Old 19th June 2008, 02:55 AM   #2
BHTX is offline BHTX  United States
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http://www.prodance.cz/protokoly/alpha_15a.pdf

I probably wouldn't use it above 300 Hz or so, actually more like 150-250hz, as I prefer to choose a mid that can cover as much as possible, depending on how efficient I want it to be. There are plenty of 8-10" mid drivers around 95-100 dB/watt that work well for this. Even many 12" drivers are suitable, depending on where you're planning to xover to the high freq driver. I suppose you could use the Alpha 15 quite a bit higher though if you really wanted to.
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Old 19th June 2008, 04:06 AM   #3
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Thanks. I already have a midrange driver I'd like to use (Audax PR170M0), and I'm trying to keep the project cost under control. These will be on an open baffle, and the 0.5mm Xmax of the Audax is the reason why I'm looking for a woofer that'll go up to 4-500Hz. I'll use an active XO, so the efficiency doesn't need to match.

Another option (that I just started looking into) is the Peerless 830669. Its Sd * Xmax is similar to the Alpha15, and it looks like it might be cleaner in the higher frequencies? It'll need more EQ in the bass, of course.

Other options I've considered:

* AE IB15/12 - It almost gets to 500Hz, and I may end up going with this, it has more swept volume than anything else I've looked at

* 2 x RS270 - This will probably work, but at $160/side, it's pushing my budget

* 2 x Peerless 830668 - Slightly more Vd than a single 830669, ~ double the cost. About the same cost as an IB15, much less Vd, so the only reason to pick this would be if its 500Hz response is cleaner

* Lambda, Ciare, B&C, BMS, 18Sound... all outside my budget
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Old 19th June 2008, 06:04 AM   #4
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Isn't Physics CS2 alphas are crossed at 1kHz ?
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Old 19th June 2008, 03:05 PM   #5
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I was looking into that, and I believe they are. Does anyone know if it's a stock Alpha15 in those speakers, or custom/modified in any way? That gives me hope that a 4-500Hz XO might work. On the other hand, I don't know how much DSP/EQ correction has been applied to get that woofer to play up to 1kHz.
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Old 19th June 2008, 04:33 PM   #6
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I believe it's a stock alpha 15 run to 1k. Sounds like a bad bad idea to me!
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Old 19th June 2008, 08:29 PM   #7
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Quote:
Originally posted by BHTX
http://www.prodance.cz/protokoly/alpha_15a.pdf

I probably wouldn't use it above 300 Hz or so, actually more like 150-250hz, as I prefer to choose a mid that can cover as much as possible, depending on how efficient I want it to be. There are plenty of 8-10" mid drivers around 95-100 dB/watt that work well for this. Even many 12" drivers are suitable, depending on where you're planning to xover to the high freq driver. I suppose you could use the Alpha 15 quite a bit higher though if you really wanted to.

If you want serious bass then go for an 18 inch driver.
However, they can be expensive.
15 inch drivers are much less expensive than 18 inchers.

I built a folded horn 18 inch enclosure and the bass is massive.
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Old 19th June 2008, 11:00 PM   #8
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Saurav: TBH, I think the Alpha 15A is most likely the best OB woofer for the money that is widely available, although there are others that will disagree. I've seriously debated trying out myself in the past, but I've since come to the conclusion that OB bass just doesn't cut it for me. I want the directivity, but the max spl is so low for the SD, not to mention the size of baffles often required to get the most out of it. But yes, the Alpha 15A for OB is the ticket. Model it in Xbaffle.xls and see for yourself. I would suggest 2 of them.. one on top of the other with your Audax in a TMWW config, and run the Audax as low as you can.. likely around 400 Hz or so, as you've already stated. My only concern is that in setups like this, I've often experienced negative effects of running the woofer(s) too high, and it tends to mess up the soundstage and imaging for me. String bass instruments especially.. everything gets shifted down too low towards the floor. That's the main reason why I said what I did earlier.. I like to keep as much of the most important stuff in one spot as much as I can. But there will have to be some sacrifices made with the Audax PR170M0. As for using a single Alpha 15 and mounting it up higher as close to the Audax as possible.. I think there would be less to be gained from doing that versus running two of them wired in parallel.

Anyway, I say go for it. It's one of the few drivers that will get you down to a solid 40 Hz on a narrowish baffle (lower in room, albeit at low output levels, as with all OB bass setups). Download Xbaffle or similar simulation programs and model it with a bunch of other potential candidates. On top of this, consider the money involved, and you'll soon find out that it's a tough one to beat.

Also.. I have yet to see the result of someone removing the dust cap from an Alpha 15A. You could certainly try that and add a phase plug, with a good chance of improvement in frequency response. It's not that big of a deal really.. especially for under $60 each (and I've seen them go for MUCH less than that on eBay).
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Old 19th June 2008, 11:45 PM   #9
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Thanks for the advice. I have Xlbaffle, MJK's worksheets, and ABCDipole, and have spent the last couple of months running simulations with various drivers.

Up until very recently I was reluctant to use 15" woofers because I think they'll look really big in my room, and 2 15's will be a bit much.

The current 'front-runner' is a custom driver that John at AE Speakers is experimenting with. It's based on the IB15, but is 12" (since I didn't want a 15" driver), with reduced Mms, and he's trying some tricks to see how high he can push the top end. If that works with a 4-500Hz XO, that's what I'll go with. Yes, it'll require more EQ than the Alpha15, but with 18mm Xmax, I can EQ it without worrying about bottoming it out. I'll have an active XO and an SS amp on the woofers. It'll probably handle a lower XO to a monopole subwoofer than the Alpha, which would be a bonus.

Yes, it'll cost ~2x the Alpha15, but it's within my budget for what I was thinking of spending on the woofers. And at that price, I haven't found anything else that comes close for swept volume. So... I think this might work, we'll see how it goes.

If it doesn't work, I'll probably try the Alpha 15. Many people have used it on OB, though other than the CS2 I'm not aware of too many who use it above ~250Hz. I've performed dustcap surgery on drivers before, so that's an option.

Quote:
My only concern is that in setups like this, I've often experienced negative effects of running the woofer(s) too high, and it tends to mess up the soundstage and imaging for me. String bass instruments especially.. everything gets shifted down too low towards the floor.
I've heard others say that too. I'll see how it works out, that's something to keep in mind.

Quote:
As for using a single Alpha 15 and mounting it up higher as close to the Audax as possible.. I think there would be less to be gained from doing that versus running two of them wired in parallel.
Agreed. I'll probably want the floor's help with an OB woofer, no matter what driver I try.

Here's what my rough idea looks like for now (the top cone is a compression driver on a waveguide):

Click the image to open in full size.

Even this is ambitious for my woodworking skills, so we'll see how this goes. Might need shorter wings, or wings that extend symmetrically in front of and behind that baffle... I'll work all that out once I start building and measuring some test baffles.
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