Designing a cabinet for Mark Audio Alpair 7.3 - Page 9 - diyAudio
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Old 6th February 2013, 03:00 PM   #81
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I do hope I'm not entirely the same as your wife (with all due respect to the good lady of course).
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Old 6th February 2013, 05:57 PM   #82
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Not at all Scott:
but back to StudioAu - any progress? came up with some construction already? c'mon, show us, we are waiting
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Old 6th February 2013, 09:47 PM   #83
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I glued on a piece to hold the mdf together and put together my dust extractor.

I'm building a cocktail cabinet at the moment which is takin up all my time. I will hopefully Cnc the parts, which needs some careful planning. I now have autocad installed and have started sketching it out.

Will turn the teardrop soon.

Also have purchased some MA ch70's.

And hopefully ordering a carton of Alpair 10.2 for kittin out a bar I am re-modelling.

Busy. Alpair 7's are happy in their base reflex cabinet for now.
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Old 22nd February 2013, 08:39 AM   #84
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Does anyone know how small a cabinet I can use for the A7.3's.

The Bar re-furb is going to need 6 Alpair 10.2 units and 6 much smaller speakers to fit in strange shaped ceilings and installed in bathrooms.

Looking at the 6M perhaps or the CHP 70 (I have the black one so I can test) Although would choose the metal cone for the final.

Anyone have any sims for the smallest useable box. Each will be in a room with at least one A10 so low frequency isn't too critical.

Thanks
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Old 22nd February 2013, 09:40 AM   #85
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Does anyone have an idea of the power rating for the 7.3 crossed @ 400hz?
(1st order)
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Old 22nd February 2013, 10:27 AM   #86
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Yes, it's exactly the same as if it wasn't.

High-pass filtering a drive unit does not change its power rating per se. The A7.3 is rated to 20w; adding a filter doesn't change that, but you will improve the overall system power-handling ability / dynamic range since it has to do less work in the < 500Hz region. For e.g., in a sealed box, Qtc 0.7, at the 20w rated input, you'll never get anywhere near the rated Xmax; just over 1mm is about the lot. Sans filter, at 100Hz in the same box for the same power input, displacement will be about 3x that (this is assuming you've dealt with the LF impedance peak). In other words, with the filter in place, you should be able to achieve the ~98.9dB (1m) theoretical maximum the driver is capable of at the rated input without running out of mechanical travel, which would normally prevent this being practically achieved.

Last edited by Scottmoose; 22nd February 2013 at 10:39 AM.
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Old 22nd February 2013, 12:19 PM   #87
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Sorry, I've worded that wrong- so this driver should be able to handle alot more than 20w/reach a figure in excess of 100dB if the crossover is high enough?

Last edited by Bill poster; 22nd February 2013 at 12:33 PM.
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Old 22nd February 2013, 01:24 PM   #88
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The nominal power-handling is still 20w. However, by high-passing the driver it no longer has to handle the low frequencies where the greatest power demands are, significantly reducing excursion. The limits therefore become thermal / electrical rather than mechanical. Sans filters, at 20w input you're rapidly running out of travel; with the filter in place, this is much reduced. See the attached deflection plots for the 7.3 at 1m/20w -yellow is QB3 vented box, blue Qtc .707 sealed box, purple Qtc .707 sealed box with 1st order high-pass at 400Hz.

Note that the 20w figure is a nominal; the A7 can handle somewhat more, but this isn't a free reign to come it the neanderthal; it's a large tweeter, not a 15in pro-audio woofer.
Attached Images
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Last edited by Scottmoose; 22nd February 2013 at 01:51 PM.
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Old 22nd February 2013, 02:23 PM   #89
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Thanks Scott, altho I'm more confused now I'll look at the graph.
I don't want to use it sans x/o, just if it can take more than 20W crossed @ 400hz 1st
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Old 22nd February 2013, 04:18 PM   #90
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Yes, I know you don't.

No. The nominal rated power input of the Mark Audio Alpair 7 is 20w. It can take a bit more than that in practice (probably ~30-35w for brief [repeat: BRIEF] bursts), but 20w is the nominal rated input. That doesn't change whether you high pass it, low pass it, bandpass it, or are on the northern polar cap of Mars dancing the tango with Rachel Weisz.

By high passing the drive unit at 400Hz, you are reducing the amount of power applied to it in the low frequency region, where most of the power demands in a musical signal are to be found. This results in lower excursion levels, since the driver is not being asked to handle these low frequencies, so you will not likely get near its mechanical limits. However, you still need to pay attention to the electrical / thermal limits since if you apply too much power beyond what it is rated at, you could burn out the voice coil.

Last edited by Scottmoose; 22nd February 2013 at 04:27 PM.
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