Altec 604e/Alpha 15 Open Baffle?

[dgator]

I'm way over my head here but have an idea prompted by the recent OB thread.

I have a pair of 15" Altec 604e coax drivers in need of an enclosure. They are suited for a vented 9 ft box - but I don't want to do that and my wife really doesn't want that.

I was thinking about an OB with the 604e on top with two Eminence Alpha 15s to augment the bass. The 604e is not ideal in a narrow baffle (20"-22") OB - it's QTS is .21. So, from what I've read I would get an early rolloff especially on a narrow baffle - hence the two Alpha 15s. I understand that the Alpha (qts >1.0) is well suited for an OB.

This concept is kind of a cross between the Jamo 907, Stereophile: Home Page and the Emerald Physics 2.3.

[Brett]

Just seen this. MJK has a project (#7?) on his site with a pair of A15 and a Lowther. Seems that using that as a starting point would mean you're about 90% there, especially if you use an active xover A15-604.

[Cal Weldon]

dgator,

I really like your idea.

[planet10]

Certainly sounds like a way to get around a refrigerator size box. Go gor it.

Brett has already pointed to an excellent starting place.

dave

[dgator]

thanks to all.

MLK suggests the alphas are perfect for an OB but I am concerned about the Altec on and open baffle.

If the Altecs roll off too soon will I have a big gap?

[Pano]

They won't roll off that soon.
The 604 or 605 with helper woofer can sound very, very good. My buddy John took a pair to LSAF and they were very well liked. Just 1 15" helper, IIRC.

Maybe he'll post something here about them.

I have a pair if 604-8Ks here, but no helper woofers to try them out with, or I would. I does seem like a really cool OB rig.

[Cal Weldon]

Originally Posted by panomaniac

I have a pair if 604-8Ks here, but no helper woofers to try them out with

I'm coming for a visit. Put beer in the fridge.

[Skip Pack]

Inspired by John's speakers at LSAF in 2008, I have put together a pair
of OB 605B's. John used a single 18" Eminence (model unknown). Mine are on
a 22" square baffle on stands at present and get down to about 60 - 70hz. Very
pleasant at this point, but they will be better with a good bass solution. John's
were very very nice.

Skip

[John Bsuch]

Hello all....

Skip Pack... thanks for the positive comments... hope to get over your way soon and listen to your creation....

Back to main topic... yes ... an Altec duplex with helper woofer can work very well in a dipole application... you can see a bit more about what I put together for 2008 LSAF here.... Lone Star Audio Fest 2008 - Event Reports - Dagogo here.... lone star audio fest 2008 & here... CryoParts Lone Star Audio Fest 2008

I think there were a couple more show write-ups posted at the time.

Using both the 605A and 604-8K I built proto-type(s) it quickly became apparent the woofer to HF crossover was a key issue... I decided on the 605A because it had a bit higher QTS (.24 vs. .30) and both woofers had similar Xmax and FS. The 605 portion of LSAF system used a modified crossover inspired by Jeff Marquart (Thanks again Jeff for sharing your work!!), and worked remarkably well. Many were surprised by the dynamic yet smooth presentation.

For the helper woofer I used a pair of Eminence 18" (QTS of .22 & 6 mm Xmax!!) driven by a single plate amp (mono sum). A great 18 with a smooth forgiving response that unfortunately is no longer available. The crossover point from the sub to the 605A woofer was about 50 Hz. With out the plate amp running .... the 605A could deliver to about 60 Hz.

One trick I used on the plate amp... a 150 watt Keiga from Madisound IIRC, was to add a large inductor to convert the 2nd order built in roll off to third order which makes it SO much easier to mate the falling response of the Altec woofer. As in odd order with odd order.

BTW... I used a 25 wpc ASL class A tube integrated (EL34's) to drive the Altec portion of the system. It was easy to get 106 + db levels with out any sign of strain... Brad Baker made me do it (he had his Hawthorn set up a couple of rooms over and the SOB bribed me ... or is it plied me with beer!)... Also... the 605's had been re-worked by GPA on both the LF and HF end of things.

Bass from the helper 18 was solid to about 30 Hz and very clean. Didn't take much bass fill in the small hotel suite... I doubt we hit more than 20 watts per helper 18. Fun... Fun... Fun. I did play the system out doors out on my driveway back here in CA and was amazed at how much low end the system would deliver. Better than 100 db in the low 30's was so easy.

[Pano]

Originally Posted by Cal Weldon

I'm coming for a visit. Put beer in the fridge.

Bring woofers.


Actually.... I do have a funky pair of Altec 416s that I could try. And plate amps, too. But the 604s belong to John and he plans to sell them. Maybe if I'm quick enough.....