Got another project I don’t need. Plus I have questions...


No longer a junior member
Hey guys. Facebook marketplace keeps trying to get me to buy stuff, well it worked at the end of last week. I saw these older PA speakers that were supposedly built for a church and never installed. Someone bought them at auction years ago and then was selling them.

What attracted me to them was the Baltic birch cabs. I have a lot of drivers and bad ideas, but cabinets are hard for me to come by cause I don’t have a place to build stuff. I thought these looked like they could be an easy refinish and rework.

I got them home and pulled the nice metal grills off. They contained what appears to be some variation of an Eminence Beta 15A woofer in each one, and a P Audio PHT-404 horn/compression driver combo. The network is simple. One 3.3uf poly cap and one inductor and a couple fuses. Woofers appeared to be wired to run full range.

The woofers are for sure Eminence, the code on the label makes them from 2004, 10th week, Monday. But I’m not 100% sure I’m model cause I can’t really find any info on a model 151312A. According to the website the 15 indicates the size, so I believe the 1312A is the model. Anyone have any knowledge? I can reach out to them this week.

Anyone have a good calculator to figure the volume and tuning of the trapezoidal cabinet? I’m thinking about using the 15’s, sealing up the horn opening that is there, and mounting one of my Emilar Bowtie pairs on top. The ports are dual, 3x1” round.

Here’s some pics. Anyone have any ideas or thoughts?

Here’s a link to the HF section. Apparently these are still available.

- Woody



No longer a junior member
Oh... I should mention cabinet dimensions are internally 14-14.25” deep. Front baffle is 17”x21.5” and the back is 11”x21.5” measuring to the seams which would be the inside back dimensions.

- Woody
I don't know a formula for calculating trapezoids but I'd think if you calculated the volume for the hypothetical larger cube that would exist if it was 17" front and back, then also calculated the volume for the hypothetical smaller cube that would exist if it was 11" front and back - you could average those together and arrive at your trapezoidal volume. Maybe my after dinner beer is clouding my judgement though...


No longer a junior member
Emailed Eminence about the driver specs... the guy that provides that stuff is out of town until next week, so I'll hopefully hear back next week from him.

- Woody


No longer a junior member
So I got the following back from Eminence yesterday. I am impressed with their customer service. I think it would have been much faster if he wasn't out of town, he was really quick to reply to another question... so what can you speaker building experts tell me about a box for this woof?


Your speaker was made for CGM Music in as an OEM and as such was never sold individually to the public. It consists of a 56 oz magnet, a RDM cone, and a 2.5” voice coil rated up to 200 continuous watts max safely.

The rest of your parameters are as follows:

05-RE OHMS 6.29
06-LE MH .82
07-QM 8.00
08-QE .600
09-QT .560
10-XMAX MM 1.60
11-BL TM 11.87
12-EFF % 4.71
13-FS HZ 49.36
14-MMS GMS 43.60
15-CMS mm/N .2384
16-RMS NS/M 1.6905
17-VAS LTRS 245.51
18-SD SCM 856.34
19-EBP 81.7
20-SPL dB 98.7

If IThis speaker would be closest to our Delta 15A, one size up due to the 56 oz magnet. They share the same size voice coil and magnet. can offer you any other information, just let me know.

Caleb M. Potts.
I'm very very far from a guru but after having just built some cabinets of my own I think at least one of the critical measurements there is #13 - Fs or freestanding resonance. You'll use that number to determine your interior volume and port size to get the tuning right. I used some old Altec literature/graphs to figure out mine.