Eminence Open baffle design help pls!

[soundemon]

I found a nice deal on a "kit" of (stereo pair of each)
- Eminence Alpha 15a (15" woofer)
- Eminence beta 12 LTA (12" full range)
- Philips ribbon super tweeter.

I did a little searching and found some really cool looking open baffle designs for these speakers. The fellow I bought them from assured me there were some plans with them, and crossover components. it turns out that the plans are just a wiring diagram; basically a coil in line with the woofer, and a cap in line with each of the full range and the tweeter.

I know very well that the design of the baffle has a huge effect on the FR of the drivers, and so also the crossover design. But I haven't been able to find any "full design" info ie: use these values with this baffle style / width etc.

I've built quite a number of speakers, but all are from pre-planned, established designs. I have no measurement equipment, (excluding a simple mic etc for REW and a rat-shack SPL meter) so don't really want to start trying to experiment and find my own values.

Anyone here have OB experience with these drivers?

TIA!!

[JonMarsh]

None on my side. What model of Philips tweeter is it? Usually, mating a ribbon tweeter directly to a 12" woofer can be problematical- - the minimum operating frequency of the ribbon tweeter being higher than what the 12 works to cleanly. And just series pass caps on the mid and tweeter driver is not a crossover, it's just a basic protection circuit so you don't blow them up...

The Eminence drivers are good parts for the right application, but I think you'd may need to start researching designs using those drivers, and maybe you'll come across something usable for them- but it might not be open baffle. And you are quite, quite right- the dimensions and shape of the mounting baffle is a critical aspect to the design of a dipole speaker- and the roll off from the open back usually requires some substantial compensation in the crossover circuit. It COULD be that the upper end response of these drivers is so well controlled and complementary that upper range roll off isn't necessary, but it COULD be that you could also make this open baffle design into a nice glider using lifting body effects. Neither are likely.

Perhaps you should try to get more information and links from the guy who sold you this stuff?

BTW, some info on the 12" Eminence Beta.



No dispersion plots here- a 12" drivere is going to be very directional above 1kHz.

[soundemon]

Thanks for the reply Jon!

the 12 is actually the 12LTA, which is "full range" listing FR as 48Hz to 8kHz

http://www.eminence.com/pdf/Beta_12LTA.pdf

http://www.parts-express.com/eminence-beta-12lta-12-full-range-pa-driver--290-409

As I understand, there are designs out there using just this driver without crossover. I guess the idea behind the wiring diagram was to just knock the highs away from the woofer and the lows away from the 12. (and even moreso the tweet)

I'll get the model number info off the Philips when I get home this evening.

[Face]

The Eminence Alpha 15a is the "go to" for a budget orientated open baffle woofer. https://www.google.com/search?q=Emin...5a+open+baffle

Either follow the schematic you received or build something else as I doubt you'll find plans for another speaker that uses the same exact drivers.

[soundemon]

OK the tweets are Philips AD 21600 RT8

I'm seeing a pair on Ebay for more than I paid for the entire kit so that's pretty nice.

I'm thinking something real simple like this:

http://www.iol.ie/~waltonaudio/ob.html

and add the ribbon. I'll wire it up the way its been suggested, and go from there...

[JonMarsh]

Hopefully it will put you in the ball park... there's no substitute for measurements and knowing for sure just what is going on. The Philips were used as super tweeters by some VMPS models, so that notion of an 8 kHz crossover is likely in order- what were the cap values in in the instructions you were given? The Beta might be a good target for a column PA speaker- certainly an adequate range for voice. Lots of squiggles in that impedance curve, though! :W

[soundemon]

It shows a 22uF cap in line with the tweeter, 220uF in line with the beta, (the beta is shown wired in reverse polarity to the woofer and tweeter) and a 14mH coil in line with the woofer