High quality 2-way (15" + CD) PA speaker design

[keyser]

I'm not sure about bottoming out a 1" CD. The problem with the higher crossover point is the change in directivity: the 15" woofer beams a lot at 1.5k, while most horns beam a lot less. At the crossover you want to match the directivity of both drivers.

[Dr.EM]

Sounds logical yes. The JBL system uses a 1.7kHz crossover interestingly. Not too sure why it has 70x70 radiation horn either, surely wide horizontal and narrow vertical is always more desireable in this sort of application?

With no off-axis graphs or polar plots for the RCF 15", how can we determine what a good crossover point should be? Would you say 1kHz is a good general frequency for a 15" to match the 90x40 horn?

[dirkwright]

Originally Posted by Dr.EM

Sorry, you must have posted while I was typing. Those are nice components, but a stretch too far budget wise. Looking at around £340 on drivers per cab; that CD+Horn leaves 0 budget for a woofer unfortunately.

They are cheaper here in America. Maybe someone can smuggle them into the UK for you?

[AllenB]

1kHz is a good start, probably not any higher. If you don't want to go down with the horn, you could think about smaller woofers.

[weltersys]

Originally Posted by Dr.EM

Sounds logical yes. The JBL system uses a 1.7kHz crossover interestingly. Not too sure why it has 70x70 radiation horn either, surely wide horizontal and narrow vertical is always more desireable in this sort of application?

With no off-axis graphs or polar plots for the RCF 15", how can we determine what a good crossover point should be? Would you say 1kHz is a good general frequency for a 15" to match the 90x40 horn?

Many manufactures use symmetrical pattern horns to avoid "pattern flip", where the narrow pattern actually becomes wider at lower frequencies.

For a 90x40 to maintain vertical pattern control to 1000 Hz, the mouth needs to be about 12" high (a full wave length of 1K), which presents other design difficulties and compromises.

All front loaded cone speakers begin to beam at a frequency dependent on the piston diameter.
A 15” has a -6 dB 90 degree dispersion at about 1200 Hz.
Dispersion varies with frequency, a 15” speaker is about -6 dB at 60 degree at about 1.8K, a 12” at 2.2K, a 10” at 2.8K.

A 15” has a 180 degree -6 dB beam width at around 600 HZ, a 12” at about 800, and a 10” at about 1200 HZ.

A 12” speaker is around 180 degree at 900 Hz, 90 degree at 1200 Hz, 50 at 2400 Hz, and 30 degrees at 4000 Hz.

[Charles Darwin]

If you wanna stick with 1" drivers BMS 4552Nd and 4550 should allow you to cross low enough for a 15" with a 90deg horn.

Overview

Overview

[Dr.EM]

Thanks for all the input, it's been very useful! Currently, my friend is having trouble raising money for this project. He needs to sell a pair of 3015LF drivers to get some funds. I say it's a shame they aren't the standard 3015 model as those would probably work in this design!

[Tajzmaj]

PD153er from precision devices....+ something like CP750nd or CP800 ......
Good combination
Regards, Taj