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Alpair 7P & Alpair 12PW combination.

Hello Lads (Ladies also....I guess there should be some in audio)

Now comes the real fun.........getting the best system combination by bringing together the Alpair 7P with the Alpair 12PW. There are some very interesting features to consider:

Where to cross.
The responses of both drivers give a great deal of choice. The 12PW will easily allow those system designers who prefer to cross higher, outside the telephonic band high point of 4kHz, you should be able to achieve your desire using the 7P/12PW combination. Equally for those who prefer further down, around 400Hz for example, your needs can also be accommodated by combining these 2 drivers.

Remember that you're working with 2 very similar drivers. Both have inclined shallow cone profiles that emit similar dispersion patterns. The Alpair 7P effectively becomes a super-sized tweeter while the 12PW is a wide bander capable of emitting to +10kHz. Don't assume that many of the "standard" cross-over methodologies are a "default" good fit. Experiment by starting off with simpler designs. Don't go nuts with complex cross-over designs with bucket loads of components, as both drivers power-trains are ultra sensitive. They will pick up increased signal deviation caused by the more complex cross-overs.

There's allot of cross-over designs and a ton of theory that can lead to a great of heated debate. Remember to be "reasonable" when debating ideas. Those who post with a "know-all" attitude risk be delated. Experienced members familiar with Markaudio drivers could be a good source of advice and ideas - thanks in advance guys.

Box designs.
Regarding box layouts, remember to isolate the Alpair 7P from the 12PW. Otherwise you risk cone blow-out on the 7P. For those crossing higher, allow 4 to 5 litres of internal compartment space for the 7P, mostly to avoid internal reflection. Those crossing lower <1kHz, allow 5 to 7 litres, assuming your not going under 400Hz.

Driver positioning......try to keep the drivers as close together as possible. The less distance between the drivers, the better.

I've got to rest now guys....



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Gee, the 12PW's response looks pretty darn useable to well past the normal "telephone band"

At the risk of asking an indelicate question, do you have off axis measurements for the two new paper models? For some folks that could be an important factor in their consideration of crossover implementation.

Further, and thinking out loud here - always dangerous :eek:- its more limited excursion capacity taken into account, I wonder if the A6P might also be a good candidate for matching with the 12PW?

In any case, I certainly can't be alone in eagerly awaiting the opportunity to get my grubby paws on a set or two of both of these new models.
Hi Chris,
Good to hear from you. I've took the feedback from many of the Diy guys who liked the Woofer No.6 (EL166) where their dislike of most woofs was a kicked up rising response usually around 3-kHz upwards. Always makes me chuckle looking at woofs and mid bass units with phase plugs fitted......a case of good looks at the expense of practical acoustics.

Yep, the point about the 12PW is it should be easy to get a decent bass output in a sizeable box without needing allot of complication, or a ton of power and cross wherever your pleasure suits. There's plenty of heavy duty AG's (atmosphere generators) available so no point me going there.

I'm hoping to do off axis once we've moved to bigger premises later this year. I'm in and out of medical clinics these last months so having time to do everything I'd like isn't possible.

Yes, 6P is also an interesting partner candidate. But its high range is less than the 7P, but maybe enough for many.

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Depends on what you're trying to achieve -response, speaker type & positioning in-room etc. It's not possible to give a simple 'yes' or 'no' without more information unfortunately.

Blame me for suggesting to Mark that a new midbass should provide a reasonably smooth, extended FR sans large breakup peak at the top end. Plenty of drivers like that around, far fewer at present without. Should make life easier for people who like low-order filters.
A smallish question (when you can etc)
If wanting to run a pair of 12PW's with one 7P per side, would you recommend wiring the woofers in parallel?

provided of course that the driving amp(s) will have no issue with the approx 4ohm load - that's not always a sure thing

and friends don't let friends eat McDs - most particularly the "fish-like" protein sandwich :eek: - but it could be worse - Arby's? :D

Bob Brines

2003-01-31 10:11 pm
The A7P and the A12PW sure look like candidates for as 1st order series XO. Pretty much pick your XO point anywhere for ~200Hz to 5kHz. IMO best choices seem to be at the baffle step, which the A12PW looks to take care of on its own, or 3-5kHz where the A12PW starts to go away. The problem with the high XO is going to be dispersion (maybe, since we don't have off-axis plots yet). The problem with the low XO is it wastes the bulk of the range of a very smooth midrange driver.

So, back to IMO. The A12PW looks to me to be a super choice for a wide range mid in a 3-way with a real woofer below, say, 100-150Hz and a real tweeter in a wave guide above 5kHz or so. The A7P is pretty much a drop-in for the A7.3. You get the difference in sound of the two cone materials, which I won't be able to comment on for 2-3 months after Madisound sends me the drivers.

Here's my logic on not using the A12PW in a FAST implementation. Chest thumping takes 85dB @ 80Hz at the listening chair. I have discovered this by experimentation. Any less volume, no thump. Now Mark has been very straight forward advertising the A12PW as a light weight driver. It's not going to survive as the bottom end driver at a frat party. So I will be crossing my FAST to a pair of 12" heavy duty woofers. Those of you who know my listening habits know I would never spend any time listening at over 75dB average for any time, but demos are demos and shows are shows. (BTW, young'ns, if you are listening at chest-thumping levels, you are destroying your ears. I am 70 years old. I never listened to rock and high levers or whet to concerts and I can still hear above 12kHz. You will never get that chance.)

The A7P will go straight into my little folded TL. I never did a BR for the A7.3, and I have no interest in something like that. I do think that the A7P might do well in a small stand mounted BVR with F10 around 50Hz or so. I might give that a try.

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I'm not sure I'd entirely agree that the BW potential of the 12PW would be wasted if crossing near the baffle-step frequency. Depends on the slope, but 1st order is likely to be popular & was mentioned above. Which is fine, but 1st order filters are a (very) slow 6dB per octave and for their potential to be fully realised, you either need drivers with a wide linear BW, or be prepared to accept extra complexity in the form of notches etc.

Many systems with very simple filters are nothing like as effective as they could be, usually due to insufficient suppression of breakup modes in the bass / midbass driver. Assuming an XO frequency of, say, 600Hz, with 1st order acoustical slopes you're only going to be 21dB down at 4.8KHz. That's not actually all that much, and if you've got an uncorrected +15dB breakup mode at, say, 4KHz in the midbass unit (which is not unheard of) you're in trouble because your low-pass transfer function and the overall frequency response have just gone to bits. Ergo, a reasonably well behaved wideband unit should be advantageous in helping to attain a linear response through the midrange without needing a bunch of extra components for supressing problems in the stop-band.
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Ultimately, but not in the first octave. Of course one must consider the mechanical roll-off when doing crossovers.

Ok kind of understood and I guess I wasn't clear either. I assumed that when you add in acoustic roll off (at one end of a drivers bandwidth) then that could add potential phase issues with a 1st order i.e. better to keep the crossover in the middle, 400hz or so
Here's my logic on not using the A12PW in a FAST implementation. Chest thumping takes 85dB @ 80Hz at the listening chair. I have discovered this by experimentation. Any less volume, no thump. Now Mark has been very straight forward advertising the A12PW as a light weight driver. It's not going to survive as the bottom end driver at a frat party. So I will be crossing my FAST to a pair of 12" heavy duty woofers.

Use more than 1. The design i have in the books will use 4.