Help designing custum enclosure, and possible making my own crossover

[Johnny25]

I am a fanatic when it comes to working on anything electronic, especially speakers. So here I am with matching three way speakers (.5" tweeters, 4" midrange, and 12" woofer). (Pictures attached) I purchased these when a faulty wire fried the mids and tweets on my other speakers, luckily the 15" speakers stayed alive on both. I would like to combie the two working three way speakers and the other two 15" subwoofers into two matching single enclosures. All of the speakers are rated at 8 ohms. I would also like to make my own custom four way crossover since the fifteens handle the low end much better than the twelves. I'm not sure where the cutoff should be between the two woofers, I was thinking somewhere around 30Hz maybe a little higher. However, is it a problem that the 12 is ported and the fifteen is in a sealed enclosure? Maybe with the crossover cancelling out some of the 12's low end, the port might become somewhat useless, and a sealed encloser for it might be possible? I'm sorry about all of the questions, but I wanted to make sure every detail was acounted for. I'm sure this will involve a lot of work, but that just makes it more interesting for me. I will gladly accecpt any and all suggestions regarding the wiring of the speakers, and any kind of enclosure whether it be simple or creative.

[sreten]

Hi,

you should rebuild the 12" 3 way as a sealed box. Use the original c/o.

Personally I'd use the 2 15's in seperate sub boxes with one plate amp.

If you build the sub + speaker boxes together I'd still use a plate amp.

Low frequency c/o design is hideous due to the huge inductors
required and the effect of the bass resonances of the speakers.
Do not go there.

/sreten.

[Johnny25]

I've never heard of plate amps, though after looking them up online I recognize them from home theatre subs i've seen in stores. After looking at them, I agree that they are the way to go. Though, are the plate amps able to suport two subs on a single channel or do they come with left and right speaker outs? Would it be better to buy two amps? Lastely, do you have any suggestions on an amp with good sound quality and lots of features, like EQ settings?

[spock]

Check out parts express and/or gr research. They should have a wide enough selection to get you started. You should know the power handling capability of your drivers B4 choosing an amp. You can drive both drivers with the same amp, if you wire them in parallel it will cut the impedance in half. 2 amps would be better, then you could have stereo subs.

[AJinFLA]

Johnny,

you mentioned about everything except the most important thing.
Budget?
Here's my advice. For a little more than $200, buy two of these:
http://www.rythmikaudio.com/nonservo...t.htm#250basic
Forget building a giant box for all those speaker drivers (with no T/S parameters ). Use the boxes that they are in. They were designed for them.
If you must build some speaker boxes, do it for the 15's using the same size enclosure or slightly larger. Mount the plate amps to them.
If using old boxes, be careful to pay attention to the +/- coding when you open the box to disconnect the old woofer wiring to mount the plate amps (Make sure the old wires are not left hanging by the new ones). It could be the standard red+ and black -, but you never know. Hopefully you will be able to tell + from -, it's important. Connect + terminal on the plate amp wire to the 15's + terminal. Use solder if you can.
The 12" boxes should be wired to the speaker out terminals on the plate amp itself. It would be a good idea to keep the 15's close to the 12's as practical - if you can. To get a good blend, you will have to adjust the level (output) and the XO frequency on the plate amps. Phase should be ok if you keep 'em close. The manual with the amps should be of help for the adjustments.
Good luck.

Cheers,

AJ

[Johnny25]

Well, I have definitely decided to use the plate amps, and i'm going to make a sealed enclosure for the fifteens. I recently looked at the Rythmik Audio site and was looking at the specifications of the amplifiers. Without getting too technical, what is "dampening factor" and what would I use a phase shift for?

[rythmikaudio]

Originally posted by Johnny25
Well, I have definitely decided to use the plate amps, and i'm going to make a sealed enclosure for the fifteens. I recently looked at the Rythmik Audio site and was looking at the specifications of the amplifiers. Without getting too technical, what is "dampening factor" and what would I use a phase shift for?

The nonservo A350 amps (including the basic version and SE version) use the damping factor to control the boost at the rumble filter corner frequency that is often need for various sealed and vented box design. Mid damping setting has 1db boost, and low damping setting has 3db boost. It can also be used to fine tune the frequency response. It is not to be meant as a replacement for room correction. It is more for adjusting the native response (without room gain) of the sub.

The damping setting on the servo amp serves a different function. It is used to set the time domain response time. High damping has the fastest response time and low damping has the longest. Some people likes "fast" bass and some it slow. (Sorry there will be a lot of debates over what is fast bass)

The phase shift is used as a fine control to align the phase angle at the XO point. Ideally, the phase difference between your front speaker and sub should be 0 phase difference at the xover point. Some people use filter of various orders to achieve that. But each additional order in the filter function add 45 degrees at the xover point. What if the optimal requirement is only 22 degrees. The phase control comes very handy for this purpose because it gives a very fine incremental control. Of course this function is only necessary when you don't have HT receiver. Most HT receivers already have delay adjustment which serves the same function.

Brian D.
Rythmik Audio