Alpair 7 - good baffle thickness?

Related to this discussion in the Dec 14, A10.2, A6p, A6m have hit Madisound thread;

What would you say is a good baffle thickness for the Alpair 7, incl. bezel cover? 18mm? 20mm? More? ... Would you consider 15mm too thin and difficult to work with?

I'm having some wood cut for a Frugel-Horn Mk3. Might as well bump up the baffle thickness I think. How far to go, then?

Thanks!
 
Here is a set of dimensions for the Mark Audio drivers (no Alpair 10.2 or 6.2 yet). i just revised the Alpair 7s to reflect a unit on hand.

Attached is the A7 (2nd production run with (grey) superGasket) mounted in 12, 15, 18mm baffles. 12 would really require supplemental support on the magnet, 15mm is probably fine (we use 18mm baffle with A12, which in the end has about the same "meat" (althou will magnet support) -- especially if the driver is backstopped with a holey brace, 18mm would be a 1st choice.

The above assume good multiply. MDF is not nearly as strong, so would need to be thicker. if you use aluminum, i'd rear mount them, with a 45 degree bevel on the opening.

dave
 

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FWIW, if you're going down the MDF route (not recommended, but it's better than being tortured, thrown down a fire escape, and being danced on by gibbons) then you'll need 1 1/8in panel thickness to ~equal 3/4in of baltic birch or an equivalent thereof.


Scott, don't disparage being danced on by hairy apes - one of my fonder memories from high school grad (1969 - yes, really Grad '69 , but only in my hormone soaked dreams that night) :rolleyes:

For those using BB, Apple or any of the HD plywood types, 1" thickness is available, but due to reduced demand is substantially higher cost. OTOH, If you're planning on a lot of speaker projects, a single sheet would produce a lot of pairs of driver baffles.

But absent that, I've been laminating a small plate or ring of 9mm ply on the rear side of driver cut-out of normally 15 or 18mm baffles. Even with the wider than normal bezel/flanges on Mark's drivers, the location of the screw mounting holes doesn't leave a lot of core material if you chamfer the inside and rebate for flush mounting. Regardless of your philosophy on sound of the materials, this is where MDF or particle board or low density plywood "pro-core" sheet goods show their true colours.

As Dave notes, driver / magnet brace probably never hurts .
 
FWIW, if you're going down the MDF route (not recommended, but it's better than being tortured, thrown down a fire escape, and being danced on by gibbons) then you'll need 1 1/8in panel thickness to ~equal 3/4in of baltic birch or an equivalent thereof.

Hi Scott,
I'm waiting at Melbourne airport. Should get back to HK tonight/tomorrow (fingers crossed). Wrong kind of snow at Heathrow so many long haul planes in wrong place. My flight is the first leg of the Melbourne - London rout.

So........love the "gibbon" reference......ummmmmph. Well applies to the world of Airport management at Heathrow and some of central EU!

Glad to see U back on DIYaudio.

Merry Christmas

Mark.
 
Hope your flight runs OK Mark; if I don't get change to speak to you before, then all the best for Christmas.

Upper management. Most of the gibbering fiends are only interested in lining their pockets. Running an airport properly doesn't come into it. The government's no better. I'd rather the nation was run by Monty Python's Flying Circus.

(just as a clairifcation to my last post, the thicknesses I quoted above are from the average MOE specs.; the MDF will be rather denser of course, which still makes it inferior).
 

ExMathGuy

Member
2012-08-08 3:31 pm
Here is a set of dimensions for the Mark Audio drivers (no Alpair 10.2 or 6.2 yet). i just revised the Alpair 7s to reflect a unit on hand.

Attached is the A7 (2nd production run with (grey) superGasket) mounted in 12, 15, 18mm baffles. 12 would really require supplemental support on the magnet, 15mm is probably fine (we use 18mm baffle with A12, which in the end has about the same "meat" (althou will magnet support) -- especially if the driver is backstopped with a holey brace, 18mm would be a 1st choice.

The above assume good multiply. MDF is not nearly as strong, so would need to be thicker. if you use aluminum, i'd rear mount them, with a 45 degree bevel on the opening.

dave
Sorry for continuing on such an old thread, but this is the only reference to rear mounting Alpair 7 my search found.

I'm considering rear mounting Alpair 7.3's. The reason is aesthetics, but I won't do it if it has a negative impact on sound. In fact, I was about to conclude it was a bad idea based on zero evidence of someone doing it, until I found this post.

When rear mounting in aluminum, how much aluminum thickness is ideal/acceptable between the baffle surface and the Alpairs? (Deeper gives a more rigid mount but also more of a funnel/waveguide for which the drivers may not be optimised.)

Should the edges be routed with a 45 degree bit or a rounding bit? Should there be a "ring" on the inside of the driver (if so, how thick?) or just washer/screw? For the nut on the front, I was just going to cut a groove with the router, fit the (hex) nut in -- so top and bottom of the nut is aligned with the edges of the groove -- and fill the voids on the sides with epoxy mixed with carbon flakes. Any better plan?

While I'm at it -- this pretty much requires a removable back panel, right? Any good best-practice advice for that; especially if you want a rear support to stabilise the driver (yes, I have read your other posts :)) ?

If more info is needed, I'll volunteer some things now which I think might or might not matter. Baffle will not actually be a solid block of aluminum, but rather several aluminum sheets epoxy glued together (I happen to already have a stack of 0.7 mm aluminum sheets, and I'm too cheap to buy thicker aluminum when I have plenty of aluminum at home) or alternatively a sandwich with some layers of aluminum sheets as faceplates with a plastic core (it improves stiffness/weight ratio somewhat and saves gluing work -- I'm also lazy. The side walls will be sandwich for sure, but I can stand more work on baffle if there is a good argument for it).

It is a FAST arrangement with Dayton Audio RSS265HF-4 woofers and DSP-implemented cutoff, at a frequency to be determined experimentally, but certainly in the 80 - 250 Hz range -- sims suggest 170 Hz or so would work well.
 
I've been using Mark's drivers for a good while now, and my observation and suggests are that they are intended for front mounting and to be recessed for the flange to be flush with the front baffle. There is less than 10mm of clearance between the outside edge of surround and centre of mounting holes.

If you're determined to rear mount on an aluminum panel, I'd opine that a net thickness of 3mm should suffice. Any thicker than that and you'd probably want to deal with a chamfer or light radius such as found on the "optional" extra bezel that should be shipped with the drivers.

In the 7 years since my last post in this thread, I've built dozens of pairs of enclosures for the 7.3 and 10.3 /10Ps, and have long since stopped using those extra rings. I find that a single layer of 18mm BB ply with appropriate rebate works perfectly for front mounting. The hex head screws supplied with the drivers are excellent, and with proper pilot holes and pre-tapping before installation of the drivers are more than sufficient.
 

ExMathGuy

Member
2012-08-08 3:31 pm
If you recommend flush mount, then flush mount it is. I've read many of your excellent posts here and I'd like to take this opportunity to say I've learned a lot from them, and that they placed you as one of the few people on the internet that I actually trust. So thanks, not only for this answer, but for all the other stuff as well!