Corona Plasma Tweeter, Lansche Horns & Open Baffle

[MCMXC A.D.]

Hi guys, i need some help with specific measurments to construct open baffles.

I have the opportunity to put together a set of Corona Plasma tweeters with their matching Lansche compression horns. For the bass i want to stack 4 - 15" Eminence bass drivers per side (8 in total) in an open baffle arrangement.

The tweeters go down to 2.5khz, the midhorns (which are 50cm wide) go down to 500hz.

The idea is to put each 15"driver in a backless cube & stack the cubes on top of each other, like a tower with the horns mounted on the side. The bass is supposed to go down to 30hz.

Can someone help me with some the measurements of the cubes?

I'm hoping someone can advise what size they should each be and the help will be very much appreciated.

Looking forward to your feedback on this design.

Cheers.

[keyser]

It's going to be difficult to run the 'subs' as high as 500 hz without problems, because a U-frame has a resonance at a quarter wave-length (in practice the mode turns out a bit lower). An H-frame would be better in this configuration, but I'd suggest you use three of them in a U-frame up to about 100 hertz, where the fourth takes over.
The deeper the frame, the higher the efficiency. Maybe you could get away with 40 cm depth (in the configuration I proposed above), but you'll have to experiment with that.

[cuibono]

Are you looking for physical measurements, or acoustic?

Keyser has a point about the u frame resonance - although it may be permissable to use the resonant portion of the driver's response. In my experience this hasn't been a problem.

BUT, up to 500 Hz is pushing it. Past the resonance, the frequency response will really degrade, particularly with multiple drivers - in fact I think you should seriously consider the effects of driver spacing - IMO, both crossover frequencies are too high with regard to the inter-driver spacing, particularly at 500Hz. My rule of thumb is that you want to keep the driver spacing less than half the wavelength of the XO frequency - so for 500Hz, that is about 1 foot. Your midrange response might end up looking abdominal. I highly recommend MJK's mathcad worksheets to help you determine your dimensions and desired acoustic response - I've tried lots of different software, and nothing is near as good as them.

I think my second point is that designing something on paper first is important, but acoustic measurements (semi-anechoic, and in room) are vital to a successful design. Doing a first time build is a long process, so don't kid yourself.

Third, there may be an issue with an omni tweeter and monopole mids and dipole bass (fairly irregular power response). Not sure if your tweeter setup will be omni though... I've always wanted to try the plasma tweeters though! I hope you success with them!

[MCMXC A.D.]

Thanks guys for your advice.

I'm looking for physical measurements.

The tweeter is a horn a and the mid horn has been matched by the manufacturer.

I"ll look into the H design and keep the spacing in mind.

I like the idea of using 3 of them at 100hz & have the other take over. Off to check out some mathcad.

Cheers.

[tvrgeek]

Might look over the Orion design that Sigfried published. He discusses these problems extensively.

[MCMXC A.D.]

Originally Posted by tvrgeek

Might look over the Orion design that Sigfried published. He discusses these problems extensively.

Thanks tvrgeek, i have been reading his website the last few days, great info & has helped with making decisions.

Jut need to put together a prototype and try it out.

[MCMXC A.D.]

Hi guys,

I now have my tweeters and horns.

The baffles are not u or h design, the are solid & 150mm thick. The holes for the 4 -15" drivers are just bored through the baffle.

What do ya think, any comments on what the holes bored through will do for the 15"?

[el`Ol]

12" drivers will be perfectly alright for 500 Hz x-over.

[MCMXC A.D.]

Originally Posted by el`Ol

12" drivers will be perfectly alright for 500 Hz x-over.

I've got 15" drivers.

[el`Ol]

Too much lobing.