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Old 20th January 2010, 08:42 AM   #1
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Default Mark Audio Alpair 7 application

I bought a pair of Alpair 7 drivers, searching for a good enclosure, now.

Since, the Alpair 7 is the newest driver of the Alpair family, I didn't find any pracitcal recommendations for an enclosure.
There's a modification of the Pensil ML TL by WoddenDesign which is attractive to me, but the port seems to be tuned a bit high (only 19 mm long ?).
Sorry, I don't have any mathcad sheets for calculation.

Other choice could be Needle Deluxe design by oaudio.de
But the line of this TQWT seems to be too long (as many builders say, Needle was tuned to low, gain in bass wasn't effective).

So any recommondations for application (ML TL design would be prefered by me). Maybe anybody has got some practical information about enclosure for Alpair 7, he has already tried out.
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Old 20th January 2010, 12:48 PM   #2
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The Pencil 7 is not a modification of anything, it's a dedicated design for the Alpair 7. Fp is 64Hz, anechoic F10 ~42Hz. The Pencil alignment is very specific; designed for a very flat impedance & a slightly raised plateau between Fp & 200Hz which, with the lift engineered into the driver's midband & typical room gain, self-corrects for step-loss. That's why I ended up calling that range of boxes damped air couplers, rather than MLTLs, to reflect their design brief / behaviour.
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Last edited by Scottmoose; 20th January 2010 at 01:17 PM.
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Old 20th January 2010, 01:15 PM   #3
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Thank you Scottmoose. What makes me wonder about the tuning is that the port opening is 15,2 cm x 3,5 cm (53,2 qcm) when converted to circular port this would be 8,23 cm port diameter. Port length in Pensil series is only 19 mm (right ?). With a port length of only 19 mm you get a 8 db peak at 80 Hz falling down very strong in lower bass.
(sorry, I only filled in these data in bassreflex calculator to get a comparison, maybe mathcad ML TL calculation comes to different solutions here)
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Old 20th January 2010, 02:44 PM   #4
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Your BR calculator is assuming an empty cavity, with a uniform internal air particle density, no standing waves, and no damping. The exact opposite of the Pencil in other words, where the cabinet dimensions and transmission-line stuffing is critical to how it functions. The Pencil 7 is not a bass reflex enclosure, so trying to model it as such will give completely inaccurate results. As I mentioned, I even decided not to call them MLTLs, because they're such a specific alignment / have a specific design criteria.
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Last edited by Scottmoose; 20th January 2010 at 03:10 PM.
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Old 20th January 2010, 04:05 PM   #5
joern is offline joern  Europe
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Hi,
Quote:
Originally Posted by jockel77 View Post
I bought a pair of Alpair 7 drivers, searching for a good enclosure, now.
in the CHR-70 application thread i shared a 8L BR-enclosure-plan for the CHR70.
Imageshack - chr70istmasbox02text

The Alpair runs very well in that enclosure too, as one may see in the sim's .
(sorry, text in german, pics and sim's and plan will speak for themself).

In the moment I run the Alpair seven in a 5-Liter BR enclosure tuned to 55-56Hz. Nice as a small monitor positiones near the wall, but I feel, a little bit of air would make him "rounder".

The 8L-enclosure isn't ready by now... hope to finish it soon.

Try it, very nice sounding speaker !
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Old 20th January 2010, 04:22 PM   #6
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I have an unreleased A7 box (small) in the works, as does Scott (big).

Small sealed, 5-6 litres, will get you to the mid 80s if you are XOing to a woofer.

dave
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Old 20th January 2010, 04:36 PM   #7
Svein_B is offline Svein_B  Norway
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Quote:
Originally Posted by Scottmoose View Post
The Pencil 7 is not a modification of anything, it's a dedicated design for the Alpair 7. Fp is 64Hz, anechoic F10 ~42Hz. The Pencil alignment is very specific; designed for a very flat impedance & a slightly raised plateau between Fp & 200Hz which, with the lift engineered into the driver's midband & typical room gain, self-corrects for step-loss. That's why I ended up calling that range of boxes damped air couplers, rather than MLTLs, to reflect their design brief / behaviour.
Any chance you might have some FR and impedance graphs to share with us ?

(I have searched)

Svein_B.
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Old 20th January 2010, 09:54 PM   #8
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I generally gave up posting graphs a couple of years ago to avoid headaches. However:
Attached Images
File Type: gif Pencil 7.GIF (10.3 KB, 1144 views)
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Last edited by Scottmoose; 20th January 2010 at 10:16 PM.
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Old 22nd January 2010, 07:30 AM   #9
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Thank you for the simulation, Scottmoose.

The sims show the rising plateau in upper bass area, you mentioned.
On the other hand the enclosure design doesn't support the lower bass area.
I wonder if there's enough lower bass hearable.
Maybe, someone already has build the Pensil and can post his practical experience ?

There's another interesting design called "Torretta" by RumoH Zelfbouw Luidsprekers, postet in the CHR-70 application thread.
The CHR-70 doesn't need LCR correction in this design (the enclosure disigner says)
this is the plan: http://www.diyaudio.com/forums/attac...retta-tqwt.jpg
Torretta is a TQWT design like the needle. A bit smaller (shorter line) than the Needle and the port is on the backside of the cabinet.
It's tuned to 50 Hz and should give fine bass response with CHR-70.
My question: What should be changed on the Torretta design when ALPAIR 7 is used?
(Comparing the Pensil series for CHR-70 and ALPAIR 7, the ALPAIR 7 has a smaller enclosure).
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Old 22nd January 2010, 08:23 AM   #10
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Quote:
Originally Posted by jockel77 View Post
The sims show the rising plateau in upper bass area, you mentioned.
On the other hand the enclosure design doesn't support the lower bass area.
I wonder if there's enough lower bass hearable.
45 Hz F10 isn't bad for such a compact enclosure... if you want more you need to use a bigger box.

dave
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