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Eminence Alpha 15A bass reflex box calcs help + horn
Eminence Alpha 15A bass reflex box calcs help + horn
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Old 24th March 2017, 08:26 PM   #1
charlie2 is offline charlie2  England
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Default Eminence Alpha 15A bass reflex box calcs help + horn

Is there someone that can model with enclosure volume regards eminence alpha 15A bass reflex design,left over from open baffle project.and how low it will go given size constraints, have at disposal wood/4" vent pipe.

Last edited by charlie2; 24th March 2017 at 08:30 PM.
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Old 24th March 2017, 08:30 PM   #2
TBTL is offline TBTL  Germany
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What is the problem exactly?

With Qts=1.26 a sealed box is likely to give better results. Eminence suggests 71 - 85 liters.
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Old 24th March 2017, 08:35 PM   #3
charlie2 is offline charlie2  England
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Quote:
Originally Posted by TBTL View Post
What is the problem exactly?

With Qts=1.26 a sealed box is likely to give better results. Eminence suggests 71 - 85 liters.
different designs give different results and tuning, looking at building something for the old fellow rather than those skinny WAF things
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Old 24th March 2017, 08:58 PM   #4
boswald is offline boswald  United States
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Eminence Alpha 15A bass reflex box calcs help + horn
Look at the eminence box designs. They'll get you down to 6cuft vented, but look at that peak!
You can do it if you go active eq, but otherwise? I wouldn't worry about too much waf with a 15" anyway, unless you put it on the side and hide the volume in the basement. Maybe trade them for something with lower qts or sell and buy what you need. How about IB into the next room(keep the door closed)?
For flat vented, you are looking at 30 cuft!
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Old 24th March 2017, 09:28 PM   #5
John Busch is offline John Busch  United States
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Default Emi Alpha Vented box

Looking around, the most practical vented alignment would be a Thieile QT based.

Assuming your Alpha's are close to spec and a RG series resistance of 0.5 ohm your box works out as follows:

6.5 cu. ft. net internal volume (184 L)
9" dia. vent X 9" long.
FB and F3 are 41 Hz

A work sheet for this alignment format is here:

mh-audio.nl - Home

Good luck!
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Old 24th March 2017, 10:25 PM   #6
chris661 is offline chris661  United Kingdom
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Sorry John, but have you run a simulation of the cabinet you've suggested?
There's a very large peak at 70Hz.

Charlie, the Eminence Alpha-15 isn't a great driver. You might (might) persuade it into a ported box if you're prepared to get hold of measurement gear and undo all the peakiness that comes with such a weak motor. Even then, it's gonna be a lot of work.

Here's an alignment for you. The filters are compulsory, since they're acting as EQ for this particular simulation.
300L box, tuned to 21Hz.
Highpass filter: 4th order Butterworth, 18Hz.
Lowpass filter: 2nd order Butterworth, 17Hz.
Those are not typing errors. That'll get you a response that's flat from 55Hz down to about 19Hz, and will roll off with a 4th order slope above 55Hz.

Chris

PS - I've just tried a sim that appears to be +/-3dB from 30Hz up to 100Hz, so no EQ would be required. It's a zero-taper tapped horn (T-QWT IIRC), with a 4000cm^2 path area, and 2.3m overall path length. Might be fun, but it's around 900L. Very efficient, though, at ~100dB groundplane.

Last edited by chris661; 24th March 2017 at 10:31 PM.
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Old 24th March 2017, 11:13 PM   #7
John Busch is offline John Busch  United States
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Default Sim

Chris

Used the Thieile QT calc many times at NH which I have had excellent results from. May have made an input error... but don't think so. Ripple should only be about 1.5 db.

Have an Alpha around here somewhere.... will locate and play. Also happen to have a 7 cu. ft. test box too. Will let you know what I find out!

John
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Old 24th March 2017, 11:18 PM   #8
chris661 is offline chris661  United Kingdom
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Hi John,

It looks like the calculator just spits out box recommendations. I'd recommend running that in a simulator. With a Qts this high, the results with a bass reflex are rarely good.

Note that the tables don't go up to the Qts of 1.2 that this driver has. I'd only go as high as Qts = 0.5 before writing off ported boxes and going for something else.

Chris
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Old 25th March 2017, 12:14 AM   #9
boswald is offline boswald  United States
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Eminence Alpha 15A bass reflex box calcs help + horn
Thanks John. As we get to the edge of (and past) our models' ranges, there is no substitute for good old empirical testing. why don't you try tuning in 10hz or so increments from 10 to 80hz. Let's see what happens to the hump and the roll-off. We might luck into something easily eq'd.
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Old 25th March 2017, 02:13 AM   #10
Godzilla is offline Godzilla  United States
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I read recently that the Alpha 15 sounds good in a sealed 3cf box. I ran simms that did not look bad at all - just not as good as other 15" drivers. I think there was strong bass response to about 50Hz. I'd try it if a 3cf box works for you. Maybe you can make a 2-way and cross a horn tweeter around 800Hz or 1200hz? Or add a high efficiency midrange and horn tweeter to make a 3-way?
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