I think I am going to build an Imperial.  Just the wood to do it is going to cost a lot.  Can I use a 12” and 15” instead of 2 15” speakers?  (I have them lying around).  I would eventually put 2 good 15” speakers in, but that would be after I get some money.

Will there be any serious problems with using a 12” woofer and 15” subwoofer in an imperial?  (With a horn on top)

I thought about doing that, mixing a 12" and a 15" to get better high frequency output (from the 12") but I was worried that having 2 different size drivers in essentially the same enclosure might cause some problems.  The 15" moves so much more air I thought it might create enough pressure in the cabinet to overpower the 12".  Eventhough the enclosure is open to the horn , plenty of pressure build up inside, as I witnessed while playing just one of the 2 woofers installed in the imperial.  The second woofer was moving a bunch, kinda like a passive radiator.

I'm not sure if I'm thinking about this correctly, so you engineers out there set me straight.  I guess if the force per unit area generated by each driver were the same (ie pressure) then it wouldn't matter.  Maybe you should just try it an find out.

Jim

My plan was to take the speakers from 2 PA cabinets I really don’t like.  They have inefficient drivers, and they have little resale value.  (I didn’t know they were bad until after I bought them.)  I have 2 Nady PFW12’s and 2 Nady PSW15’s.  I cant sell them at guitar center for any decent money, so I thought they would be good to experiment with.  I could take a 15” speaker from a sub and a 12” speaker from a monitor.  I would build an imperial with the front easily changed for when I get money to get real speakers.

I would drive each 15 with at Nady SPA850 amp bridged mono (600 watts), and each 12 with one channel of a Samson F1200 (400 watts).  (All 3 are cheap amps, but they are reliable, none have given me any problems yet.)

Drivers aside, how should the drivers in an Imperial be crossover-ed for PA use?  I have a Behringer CX3400.  It uses a slope of 24 dB/octave.  Is this too steep for an imperial?  (I would put a horn on top.)

Would I be better just using the PSW15’s drivers in one imperial as a sub to see what happens?

Thank you all for your help

Stv

Why not just use the 1 15in and when you get the cash replace the cheap 15in and later as you get a bit more $ add the second 15in. Why waste time on the 12in,just a thought

I don't have the plans so I don't know if this would work, but you could screw on the front panel. Make sure you use a quality weather stripping on the back side to seal it. Once you've decided on what you like, glue the piece in.

Jason

The effect of the amp is only part of the equation.  The enclosure and the drivers themselves are important too.  Sure you can find el cheapo speakers with different size drivers sharing a common airspace, but it is not ideal and you will never find that in a good speaker.  

If you insist on wanting to use 2 different size drivers, I think a better option would be to put a divider in the center chamber.  How to allocate the compression chamber volume between the 2 drivers is beyond my knowledge.

John F,

How does the air space in the imperial work?  In the PDF plans for the imperial, Brace B is solid.  It is on each end of the chamber behind the speakers, as well as between the two 15” speakers, so it looks like the chamber is already divided.  (If I am looking at the plans wrong, please tell me)



John K,

I am not going to bother building an imperial with the 12” speaker.  I was more interested in the control of the speaker.  I will start with the 15” speakers I have, and when I get some money add in a Peavey Scorpion.



Thank you both for your input; it helps with getting ideas together.

Stv

Steve,

The two chambers are indeed separated by a solid brace, and connected only throught the slot exiting to the horn.  Even so, there is a lot of interaction between the drivers.  I noticed this when building my Imperial.  I had two woofers installed but only one hooked up.  The other acted like a passive radiator and it was movin!  The result on the sound was to make it boomy.  My point is that those two chambers are not really very isolated from each other from the point of view of the drivers, which is why I was leary about running 2 different size drivers in one cab.  

I think your choice to use 2 15s and upgrade later is a good one.  I was wondering how cheap you could go and still get good sound. One of the drivers i used was an Eminence Gamma 15 and I think it was around $70.  I noticed a Pioneer 15" woofer in Parts Express that has good specs for the Imperial, but only 100/200 W power handling.  Its only $49.95.  

BTW, I'm putting the finish on my half Imperials.  I'm hoping to have them done by the 18th for our next Open Jam.  A word of advice:  Make sure you can fit the imperial through the door of your shop or you may end up with a kickin shop sound system and nothing in you livingroom.  Mine was a much closer call than I wanted, and it took three people and lots of grunting to get the job done.

Good Luck!

Jim P