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The semi clone of JBL 3731's build thread

post #1 of 1381
Thread Starter 
OK guys this maybe a little premature because I have to wait for my HF sections to come. I am building my version of the JBL 3731. It will utilize the same waveguides and drivers that are in the 3731 but I am building BFM omnitop 15's(minus tweeters) for my 15 inch driver so I can have a fully loaded horn system in my theater. These will measure 62 x 30 x 17.5 when finished. I am going with either a biamped or triamped version. The biamped will utilize JBL's crossover for a smooth transition from the HF to the MF and I will use a DCX 2496 for the bottom section. If I triamp then I will utilize 2 DCX 2496's for all the crossovers. What do you guys think? Right now I am waiting for my woofers to come in and then the HF sections with compression drivers. I have the MF sections and woofers that go in them. I took a few pics of them but I have not started yet. Once I get the 15's I will start to build. I wanted to post a thread to maybe get some ideas from the members here.

I will take better pics when I get going.

This is what the boxes look like when it arrives. The big box are the 3 MF waveguides and the smaller box has six 6.5 inch woofers. The waveguide is built out of hard molded plastic.



Inside the woofer box



The MF waveguide that is bigger than most people's speakers.

post #2 of 1381
Nice!!!!!!!!!!!!
post #3 of 1381
This should be very interesting... Looking forward to the build.
post #4 of 1381
wow. lol. nothing else needed. should be epic
post #5 of 1381
Lolz! For one day I don't check out AVS and I almost missed this!

Should flavor it up around here with all the THT amd Spud talk. *yawn*

I very much look forward to your progress with this build. Subscribed.

Btw, what bass driver are you going to use with the BFM bottom? Eminence Kappalite3015LF or do you have some more JBL drivers laying about?
post #6 of 1381
I assume your goal here is to trade extension for efficiency by swapping out the JBL resonant cabinet for the OT15? I'm all for a 4-way horn loaded system where no single horn is asked to cover more than 2-3 octaves.
post #7 of 1381
I should add that the OT15 built per plans is also a resonant cabinet. You could omit the ports. I'm not sure what your lower cutoff would change to. Hopefully something your DTS-10s can easily crossover to. I think there is a graph on Bill's site somewhere in his forum showing the differences.
post #8 of 1381
I asked this in the danley thread, but are you ever worried you may have to fix your own spine someday due to your speakers system?
post #9 of 1381
Very cool.

Can you buy the entire kit with all waveguides, crossovers and speakers from JBL directly?

What about the cabinet?
post #10 of 1381
Thread Starter 
Hey guys, all the drivers will be from JBL. I do want an all horn loaded speaker. You can not order these from JBL and they don't sell them as kits.

MY HF section will be crossed at 1200hz and then the MF will cross over at 350 HZ so the LF section needs to cover the 80 to 350 hz region where I will have my processors crossover.
post #11 of 1381
Thread Starter 
Quote:
Originally Posted by stgdz View Post

I asked this in the danley thread, but are you ever worried you may have to fix your own spine someday due to your speakers system?

I have that about installing a small theater in my office just in case.
post #12 of 1381
Quote:
Originally Posted by Vinculum View Post

I should add that the OT15 built per plans is also a resonant cabinet. You could omit the ports. I'm not sure what your lower cutoff would change to. Hopefully something your DTS-10s can easily crossover to. I think there is a graph on Bill's site somewhere in his forum showing the differences.

This is an important point if MK wants to have an all horn loaded system.

MK you might want to ask Bill what the horn cut-off is with those OT15's.
post #13 of 1381
Thread Starter 
Excellent point. I started a thread about designing a horn for my 15 inch woofer(same JBL woofer) and I think everyone just said that Bill's design was easy and fits my needs. Maxmercy was working on a folded horn but I don't know if that is needed. I guess I will ask the same question here, Anyone want to design a horn for this 15? I could easily just put it in a sealed cabinet and be done but I really want a fully horn loaded speaker. The original JBL cabinet goes to 40 hz but I cross over at 80hz all the time to let the Danley's do there thing.
post #14 of 1381
[fix in process, hang on. update:scrubbed. for some reason, the driver parameters changed on me. back to the drawing board. sorry.]
post #15 of 1381
Man, you have come a long way from your M&Ks.
post #16 of 1381
Thread Starter 
The S-5000's are still one of my favorites
post #17 of 1381
Quote:
Originally Posted by MKtheater View Post

The S-5000's are still one of my favorites


True, but behind your screen is obscene enough already. You shouldn't even put up a permanent screen. You should cover your seating with heavy plastic. Give your guests the brown note, then lower the screen when the movie starts.

http://www.southparkstudios.com/clip...he+Brown+Noise
post #18 of 1381
MK I though you had depth limitation which counted out a front loaded horn with a 80hz cut off?

IIRC I think a 350hz x-over is less than optimal for a folded horn, but then again you do see them used that high on occasion.

Since you have a lot of height, maybe you could consider a J-horn. They look rather hard to design build though. They're basically a front loaded horn with a single bend so that their profile is J shaped.

http://jimmyauw.com/2006/10/17/horn-...r-with-fostex/
post #19 of 1381
MK,

This will be a fun thread to watch!!! Good luck on the build!


dbl
post #20 of 1381
Quote:
Originally Posted by dbldare View Post

MK,

This will be a fun thread to watch!!! Good luck on the build!


dbl

What size is the hole in the mf waveguide? I am trying to get some scale.
post #21 of 1381
Thread Starter 
I have as much room in depth as I want but if I can keep it less than 25 inches then that will be the icing. If it is more than I have to shrink my screen as I move it closer to the seats. I like the big screen.
post #22 of 1381
How low will the mid horn play?
post #23 of 1381
Thread Starter 
The woofers I showed are 6.5 inch woofers which 2 will go into the holes. The crossovers will be 1200hz and 350 hz. The mid section will cover 350 to 1200 hz.
post #24 of 1381
Thread Starter 
I am trying to see if I can buy the crossover but my guy is having trouble. If not I will buy 2 DCX 2496's. My biggest problem is designing the horn for the 15. I thought the omnitop was just a horn and not ported. I do want a front loaded horn.
post #25 of 1381
Quote:
Originally Posted by MKtheater View Post

I have that about installing a small theater in my office just in case.

Let me guess, JTR tripple 8's with THT's in the waiting room with a 120" AT screen looping the gas station scene of terminator salvation
post #26 of 1381
Thread Starter 
Think bigger and more powerful.
post #27 of 1381
Quote:
Originally Posted by MKtheater View Post

I thought the omnitop was just a horn and not ported. I do want a front loaded horn.

I'm only going on what Vinculum said.

Honestly Bill has a pretty average website and it's hard to tell exactly what's going on.

But what I do know is a front loaded horn with a 80hz cut off is going to be over 3 feet in length.
post #28 of 1381
Thread Starter 
The Max dimensions I would like it to be(if possible) is 36x30x25
post #29 of 1381
Thread Starter 
Here is a link to my other thread that involved building a horn for my 15.

http://www.avsforum.com/avs-vb/showt...9#post17767909

Post 37 was Bill's response to using his omnitop 15 with my driver.
post #30 of 1381
Quote:
Originally Posted by MKtheater View Post

The Max dimensions I would like it to be(if possible) is 36x30x25

I assume that's hxwxd... if so then you'll have to go with a folded horn and live with the compromises that involves.

Or you can move your screen forward and go with a FLH.

Only you can make that call..

BTW can provide us with a link to that omni 15 you were going to go with.

[edit] I see you've linked that in your post above mine.

It's really hard to tell what's going on. It looks like a front loaded horn, but since it's only 22x22x18 it must be a folded horn. Maybe bill can chime in.
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