Greg Monfort ML-TL Design Update for Alpair 10.2

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I'd suggest reconsidering very shallow depth enclosures for any wide-band driver, and most particularly very thin metal cone units such as any of Mark's drivers or the new Jordans for example.

Could you elaborate?
Shallow cabs not only look better and are easier to place (not sticking into the room so much), they also have advantages wrt bafflestep and portloading.
So what are the problems?
 
Reflections off the back wall coming through the cone / modulating its resonant behaviour can be a problem in some cases. The same applies to very narrow boxes, except there it's reflections off the sidewalls. Sometimes tricky to damp out. Not likely to be an issue here though -Greg knows what he's doing. ;)

BTW -not everybody thinks that wide / shallow boxes look better. Some prefer narrow, deep boxes. Subjective taste. I like both. Depends what the design requirements are.
 
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Oh, it's just that. Reflections are worse from sides in my experience. Most FR units have so large magnets that the backwave are sent mostly to the sides anyway. Not that you should put the driver all the way to the back-wall though.

Deep cabs to me just smack of retail speaker emulation. Because that's how most speakers in the shops are done. I guess they have convinced the salespeople, who in turn can convince the wives, in the heat of the moment at least, that that is The Right Way (tm).
Wide cabs are much more unashamed and unapologetic about themselves. If you have made a nice finish why not show it off? And they are, in the long run, much less intrusive in a living room. /My two cents.
 
Hmm, I managed to miss Chris's post, which opens up a 'can o' worms' WRT acceptable performance trade-offs and in this scenario, damping material choices.

FWIW, I’ve built many tower/column [now TL or MLTL] alignments where the driver was a slight force fit to both keep the cab as flat as practical and to mass and compression load/support the driver, ie. physically as high an aspect ratio as practical. Damping was either Celotex, thick felt carpet padding or acoustic fiberglass insulation.

All these have a much higher, wider BW damping performance curve, so compression, early reflections are pretty much moot till down in the cab's gain BW curve where I want[ed] it since maintaining as much acoustic efficiency as practical was/is one of my prime performance goals.

Celotex is long gone and finding/affording the kind of density, quality felt I used way back when makes it a poor bang/buck choice and folk’s acoustic fiberglass insulation health concerns is a real ‘head scratching’ one for me since it’s designed for lining ventilation ductwork to reduce its TL ‘vent’ noise, ergo to my way of thinking, the obvious choice for damping speaker cabs, especially high aspect ratio ones whether horizontally and/or vertically.

Anyway, the pioneers of audio concluded that as the aspect ratio increased beyond ~1.2732:1 in an undamped horn, measurable pattern distortion increased with increasing ratio to the point of pattern ‘flip’ and anyone who’s ever heard different shaped horns has experienced its impact on signal accuracy, so it seems reasonable to me that this would impact a driver’s ability to accurately track a signal over an increasing portion of its mids, HF BW with increasing aspect ratio when placed in such an acoustic environment if not properly damped.

This is why my default recommendation is a golden ratio since folks mostly prefer polyfil or similar stuffing nowadays.

GM
 
Oh, it's just that. Reflections are worse from sides in my experience. Most FR units have so large magnets that the backwave are sent mostly to the sides anyway. Not that you should put the driver all the way to the back-wall though.

Yes, generally sidewall reflections are the more problematic. It doesn't often happen off the back-wall, but it's not unheard of (the PAWO had problems along these lines IIRC), so if nothing else, as GM says, it's a reminder to ensure the box is properly damped. ;)


Deep cabs to me just smack of retail speaker emulation. Because that's how most speakers in the shops are done. I guess they have convinced the salespeople, who in turn can convince the wives, in the heat of the moment at least, that that is The Right Way (tm).
Wide cabs are much more unashamed and unapologetic about themselves. If you have made a nice finish why not show it off? And they are, in the long run, much less intrusive in a living room. /My two cents.

You could say the same (retail emulation) about wider boxes forty years or more back. ;) DIY generally reflects the commercial vogue of the age. Nothing new about that. For better or worse. Usually worse these days, unfortunately.
 
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Scott - yup it was the original PAWO that caused us come issues:

- the CSS FR / WR125 drivers had vastly more motor strength than the suspension could handle, and it was very easy to exceed the linear excursion limits with flatulatory results - in extreme cases the bottom of voice coil former might even be damaged, but I don't recall having done that ourselves - these drivers worked better for us in highly resistive vented designs (the original mini-onken and a bipole MLTL for example)

- we changed out the drivers in a pair of bamboo enclosures to Fostex FE127, and needed to add a solid wood supra-baffle to cover the recessed frame cut-out for the CSS driver - this provided almost another full inch of clearance behind the driver
 
Hi Squeak

To avoid raising frequency caused by baffle step you need an extremely wide baffle. A small baffle would still need some compensation, but starting at a higher frequency.

MJK´s models predict the result in your listening room and also has a model for a Baffle Step Circuit.

Take a look at the articles on Martin´s page.

But if you design the speaker to be shallow in depth which permits you to put it close to or all the way up against the wall, you will get a very large baffle.
Most speakers are placed against a wall if not for practical and WAF reasons then to get boundary loading.
With the beaming of most FR drivers corner or wall placement is usually not the problem it is with tweeter equipped speakers.
 
Hi Greg,
No progress with the Alpair builds as I have taken a detour.
I have been playing with vintage drivers and open baffles and am absolutely thrilled with the results.
Also I built a 45 valve amp recently and the MA drivers are not quite sensitive enough.
I am holding on to both Alpair drivers however and still hope to build your designs down the road. Best, Jason
 
Understood! While modern low Vas, Qms drivers are technically more correct for OB, there's a certain 'relaxed' sound to the old high Vas drivers, especially when coupled to a high output impedance, not to mention their rising suspensions let you know well in advance of impending doom unlike MA's and other brand drivers with XBL^2 or similar motor designs that 'announce' it with a sharp 'clang' even though not playing all that loud, but just has a 'fast' transient spike [assuming the amp doesn't clip it first].

GM
 
Cool! When did this begin?

It' not that there's no chance, just that it's doubtful anyone would pay what it costs since there's a 10 k minimum diaphragm order at $100/ea. IIRC back in the late '90s. Factor in AlNiCo and the retail cost shrinks their marketability to = a very expensive labor of 'love'.

GM
 
IIRC about 6 months back. The ones with the arrestor have an 'A' in their name, e.g. Alpair 10A (Gen. 3) etc. Pretty neat actually -it makes a whistling sound when you get near the limits to let you know.

Ouch. Yeah, I can see that giving some pause. Pity. Hopefully somebody will step up to the plate eventually if they can take the long-term / small sales volume view & price accordingly. Not that I could afford them at present, but I live in hope.
 
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