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Alpair 7P & Alpair 12PW combination.

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#41
Even with tight nesting, stacked lamination with plywood would be a rather inefficient yield, and I'm personally of the opinion wouldn't necessary sound better than a well braced skeletal frame wrapped with bending ply. (think racing monocoque vs Abrams tank)

You might want to consider a small TL or resistively vented enclosure for the A7- ported out the back. I've built quite a few enclosures with the metal versions, but as far as I can remember, not yet a sealed.
 
#51
2 Way PDF plan - Alp7P/Alp12PW

Hello Guys,
Here's a plan for a 2-way using Alpair7P and Alpair 12PW. Many thanks for Dr. Scott for originating this idea. Thanks for Evan Yu for making a start-up drawing (Dave D might have time to make a posh version - thanks).

Note the gentle filter. The idea is to allow for a large merged frequency output area in the lower-mid to higher-mid bands, desirable due to the similarity in the driver's operation.

Be prepared to tweak the filter's component values as this is an experimental box.

Thanks
Mark.
 

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#56
How about making something like "Pensil" enclosure for A12pw, and then just "add" A7p on its sealed box on top?
If I wanted to be creative, I'd opt for a "Pensil A12Pw" and a spherical enclosure for A7P on top. Painted black, of course 🙂
 
#57
Vix said:
How about making something like "Pensil" enclosure for A12pw, and then just "add" A7p on its sealed box on top?
If I wanted to be creative, I'd opt for a "Pensil A12Pw" and a spherical enclosure for A7P on top. Painted black, of course 🙂
Click to expand...

A pensil box for the 12PW is not really viable in size terms.

Cheers for the drawing Dave. 🙂 Guys, just to reiterate a couple of points above: this should be an easy-to-build project, but it is deliberately done in such a way that there is plenty of room for people to adapt / play with it as they wish. The cabinet loadings are quite nice -not exotic, but they'll work well. The filter is also supposed to be very simple to give people a starting point, but leave lots of room for changing if / as desired. Do carry on.

One point for clarity. I would not throw extremely expensive components at the filter (whatever you settle on). Reasonable quality, fine, but you don't have to go mad.
 
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#58
Looks really good!

I've already asked Dave about 7Pen and I will buy a pair of these when they become available.

This is the kind of speaker I had in mind, but I can't help thinking there should be two of the 12PW to keep up with the 7P?

I see there is a 1ohm series resistor, but it looks like it has about 90-91db sensetivity in the midrange.

And the 12PW has a sensetivity of 88-89 db's, and then you have the baffle step...

For me the 100-300hz is the most important area. I think that is why I'm so fond of Harbeth speakers. They are some of the most correct speakers in this area.

Cbarth
 
#59
This is the kind of speaker I had in mind, but I can't help thinking there should be two of the 12PW to keep up with the 7P?

I see there is a 1ohm series resistor, but it looks like it has about 90-91db sensitivity in the midrange.

And the 12PW has a sensitivity of 88-89db's,
Click to expand...

Both are much of a muchness at the bottom end, hovering around the 90dB point with some minor variations apiece. The 12PW rolls off slightly above ~800Hz, shelving itself down a few dB on average, again notwithstanding a little variation as you'd expect.

and then you have the baffle step...
Click to expand...


Two 12PWs would be a completely different design and significantly increase cost. This was supposed to be a simple 2 driver speaker.

Re baffle-step, not for everybody there isn't. The problem with correcting for baffle step is that just sticking in a generic quantity can be as problematic as anything else in speaker design. It's not like the energy has vanished. It's still there, albeit dispersed. Which is the point. For example, in many UK & Japanese rooms floor space is at a premium, and the enclosures are in very close proximity to boundaries to the point where little or no compensation for step-loss is actually needed. Hence the comment in my last:

The filter is also supposed to be very simple to give people a starting point, but leave lots of room for changing if / as desired. Do carry on.
Click to expand...


However, a few broad suggestions:

The 7P & 12P have very broad dispersion characteristics, so edge diffraction may (may) become problematic. You could put a nice round-over on the edges, or even double the side baffles to allow a larger round-over, which will help. Likewise, covering the front with felt can assist somewhat.

Baffle-step problematic if the enclosure is well out from boundaries? Fair enough, that can be addressed. For example, the LF inductor value can be kicked up to 2mH, and we can look at making some simple changes to the high pass. For example, we could up the value of the padding resistor to 3.9 ohms, halve the value of the shunt inductor & add a couple of ohms in series with that. Then play from there. All good, harmless fun.
 
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