Welcome, Guest. Please Login or Register
Decware Audio Forums
11/28/14 at 08:51:29


Pages: 1 2 
Send Topic Print
12” and 15” in imperial (Read 6025 times)
stvcmty
Ex Member



12” and 15” in imperial
10/13/04 at 18:39:46
 
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)
Back to top
 
 
  IP Logged
Braggi
Ex Member



Re: 12” and 15” in imperial
Reply #1 - 10/15/04 at 16:09:36
 
Welcome to the forums.

You could certainly try it. Just remmber to let us know how it works out. The "mismatched" driver concept should hold for your idea. You can always replace the 12" later.

Best of luck!
Back to top
 
 
  IP Logged
JimP
Ex Member



Re: 12? and 15? in imperial
Reply #2 - 10/15/04 at 21:42:40
 
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
Back to top
 
 
  IP Logged
Braggi
Ex Member



Re: 12” and 15” in imperial
Reply #3 - 10/21/04 at 18:19:49
 
I've been thinking about this issue. (Dangerous, I know.) Seems to me it would work as long as the motors on the two drivers are of roughly equal strength with voice coils and magnet assemblies about the same size. As long as the drivers are wired in phase, they'll hit at the same time and should work together. If one of the drivers is a stout, 98 db, 150 watt pro woofer and the other is a vintage 15 watter, there might be serious problems.
Back to top
 
 
  IP Logged
stvcmty
Ex Member



Re: 12” and 15” in imperial
Reply #4 - 10/28/04 at 05:48:32
 
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
Back to top
 
« Last Edit: 11/29/04 at 05:24:53 by stvcmty »  
  IP Logged
Braggi
Ex Member



Re: 12” and 15” in imperial
Reply #5 - 10/29/04 at 05:30:08
 
You're just going to have to make multiple baffle boards so you can try various ways and tell us all about it and post pictures here. I think you should try each driver full range, solo, no xover. Also try them both together in parallel, no crosover. Then try all sorts of things with the crossover settings, with and without horns. Have a blast then let us know how it feels.

                              Grin
Back to top
 
 
  IP Logged
Johnk
Ex Member



Re: 12” and 15” in imperial
Reply #6 - 11/04/04 at 17:41:04
 
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
Back to top
 
 
  IP Logged
stvcmty
Ex Member



Re: 12” and 15” in imperial
Reply #7 - 11/04/04 at 18:07:35
 
Thank you John K,

That sounds like a really good idea.  Changing the size of a hole would be difficult once the cabinet was assembled.  Making a removable front board would probably weaken the cabinet.

You are right about wasting time.  Time is more expensive than wood or speakers right now.

The easiest thing to do will be to build a single imperial with the two 15” speakers I have and when I get money for speakers, buy a set of better ones, and build a second cabinet; each cabinet with a cheap speaker and a decent speaker.

Steve
Back to top
 
 
  IP Logged
morpheous85
Ex Member



Re: 12” and 15” in imperial
Reply #8 - 11/05/04 at 01:26:23
 
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
Back to top
 
 
  IP Logged
stvcmty
Ex Member



Re: 12” and 15” in imperial
Reply #9 - 11/05/04 at 23:31:55
 
Just thinking about the concept of two different sized speakers:

Some people think a possible problem would be the smaller driver being affected by air movement of the larger one.  This seems like a question of speaker control, which is affected by the amplifier’s dampening factor.  As long as the amplifier driving the smaller speaker has a good dampening factor, and sufficient gauge wire was uses, the smaller speaker should be well controlled.

Does this sound right, or am I missing the concept of dampening factor?

Thank you for any input.

Steve
Back to top
 
 
  IP Logged
JohnF
Ex Member



Re: 12” and 15” in imperial
Reply #10 - 11/06/04 at 14:17:13
 
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.
Back to top
 
 
  IP Logged
Johnk
Ex Member



Re: 12” and 15” in imperial
Reply #11 - 11/06/04 at 15:12:53
 
I would use just 1 cheap 15in in ea cab .When cash is available replace the 2 cheap 15in .After you get more $ add the second set of woofers.1 15in is plenty per cabinet.better 1 good driver per cab then 2 cheap ones.
Back to top
 
 
  IP Logged
stvcmty
Ex Member



Re: 12” and 15” in imperial
Reply #12 - 11/06/04 at 17:26:45
 
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
Back to top
 
« Last Edit: 11/29/04 at 05:25:13 by stvcmty »  
  IP Logged
JohnF
Ex Member



Re: 12” and 15” in imperial
Reply #13 - 11/07/04 at 16:25:37
 
It looks like some of the brace B's are solid and some are not.  In the pic of a construction in progress it looks like the center and 2 side B's are solid and where the drivers are aren't.  It would depend on your setup.  A single driver imperial would only have solid 2 solid B's at the sides.  2 equal size drivers would have a solid center B.  I'd think different size drivers would require the center solid B to be off center and make it more difficult later.  An alternative would be to center the solid B brace and add something in the smaller driver's chamber to take up volume to achieve desired tuning.
Back to top
 
 
  IP Logged
Jim_P_at_Work
Ex Member



Re: 12” and 15” in imperial
Reply #14 - 11/07/04 at 21:06:22
 
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
Back to top
 
 
  IP Logged
Pages: 1 2 
Send Topic Print