Alpair 12 - Studio Monitor Plan

[neutron7]

Do you have any plans for a (possibly smaller) near field monitor using Alpair 12?

[planet10]

neutron7,

I have unreleased plans for a Classic Golden Ratio Mar-Ken12. This will be part of the free releases for the Mark Audio miniOnken Series.

It is a tiny bit narrower (1/8"), a bit shorter (1.25") and almost half as deep.

eMail me if you'd like a pre-release copy... i need to finish off a few details before starting a thread.

dave

[neutron7]

That sounds just about perfect. I havent bought the speakers yet, but i have pretty much decided this is what i want to go with.
No hurry, ill wait till you release the final version.

btw, thanks for the quick reply.

[wushuliu]

I built a set of these Studio Monitors this weekend. Previously I was breaking in my A12s in an oversized BR. I'll have pics up later today. This is a great design. Much better than the simple BR I had. More balanced and really good bass. Have to admit though I also forgot to put damping in the lower chamber and did not construct a removable rear panel. So I shoved some polyfill in against the back wall with a broken hanger; at higher volumes the bass does start to overwhelm, but at my normal listening volume it's just right. I have about ~100hrs on the 12s. They sound almost as good as my Modula MTMs and better on some material. Two things niggle though:

There is a bit of an edge to vocals. Grainy. This has been the case, regardless of box or cable or amp, mass loading, etc (I've done a lot of swapping around). Finally I used some equalizer software on my PC and found that it went away if I reduced 6-10khz range. Less toe-in helps som, but then I lose the top end.

Second is there is till a touch of that radio-like, closed in sound on some recordings. Kind of hollow. It's a feature of FR drivers I think as I've heard it on other drivers, but was hoping it wouldn't be the case here. It's not as prominent as I've heard elsewhere, but still there at times.

Are these characteristics that may improve w/ more break-in?

Otherwise, they sound terrific...

[planet10]

Originally Posted by wushuliu

Second is there is till a touch of that radio-like, closed in sound on some recordings. Kind of hollow. It's a feature of FR drivers I think as I've heard it on other drivers, but was hoping it wouldn't be the case here.

I've most often found that to be box related. And the damping in the box.

MDF or Ply? Add any bracing? Champher the back of the driver cutout? And little or no damping in the 2nd chamber?

Alpair12eN here (in Classic GR Mar-Ken) are quite beguiling. Sometimes the system even fools the dog.

dave

[wushuliu]

Originally Posted by planet10

I've most often found that to be box related. And the damping in the box.

MDF or Ply? Add any bracing? Champher the back of the driver cutout? And little or no damping in the 2nd chamber?

Alpair12eN here (in Classic GR Mar-Ken) are quite beguiling. Sometimes the system even fools the dog.

dave

3/4" Baltic Birch. 1in. Acoustic Foam on all internal surface (upper chamber). Some poly-fill in the second chamber. No bracing. No chamfer on the back of the driver. It's flush mounted, leaving only ~1/4in., so chamfering would be a little dicey, no?

[chrisb]

Originally Posted by wushuliu

3/4" Baltic Birch. 1in. Acoustic Foam on all internal surface (upper chamber). Some poly-fill in the second chamber. No bracing. No chamfer on the back of the driver. It's flush mounted, leaving only ~1/4in., so chamfering would be a little dicey, no?

yup, Mark's use of thicker plastic based flanges than we're used to (particularly with Fostex stamped frames) does take some getting used to.

Since the thickest BB that's normally available will be 18mm, that doesn't leave a lot of meat for rebating an almost 12mm thick bezel. What I've started doing is laminating a layer of 6-9mm BB ply on the back side of driver panel. This leaves enough core for full rebate, mounting screws and chamfering, but depending on how you're overlapping panels, could mean adjusting size of other parts.



BTW, I quite like the hex head screws that are now included. With the plastic bezels, I'd be interested in trying to hear the difference that brass screws might make. (that's for Dave )

I'd guess that, yes - some of the issues you describe above will resolve with careful break-in, and others could benefit from the polka-dot cure. (relatively safe to DIY on most paper or plastic/compound cone materials, rather more risky on the thin metal alloy cones - I've already managed to crease 2 perfectly good drivers while testing brace fit )


and you might want to consider the Ultra-touch blue denim damping material instead of foam on a future build - it's a dream to fabricate with and seems to sound just right

[planet10]

Originally Posted by chrisb

and you might want to consider the Ultra-touch blue denim damping material instead of foam on a future build - it's a dream to fabricate with and seems to sound just right

Other than the damping, everything else is as it should. I don't use the foam, at the thickness you use it should be OK, unless it is reflective at the frequencies you are having issues with.

dave

[wushuliu]

Just want to add that I have really been impressed with the low end performance of this design. We just finished watching Alien and Aliens and the A12 monitors took the lows in stride. Shook the walls in our apt. The bass was nice and clean, not boomy. Mind you we were listening at moderate levels, 9ft equidistant. No bottoming out either until a THX promo popped up at the end of the disk without warning - no way they could handle that and I had to turn off the volume quickly.

Been lazy about getting pics up. Will do so soon. I still intend to replace the monitors with A6M FAST setup (to get that real 3-D stage and beautiful sweet mids), but the A12s certainly deliver. If my listening space/distance was larger they would be keepers.

[Krabbenkoenig]

Since I'm thinking about building a pair of Alp12 monitors, I was wondering if it would be also possible to do a circular BR port insted of the rectangular one.
Any ideas?
btw. where can I find the plans for the "Golden Ratio Mar-Ken12"?

Br