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-   -   Crossover Design ! (http://www.diyaudio.com/forums/multi-way/13668-crossover-design.html)

postman 12th April 2003 03:02 PM

Crossover Design !
 
Just whipped up a quick layout of my new speakers im going to build, the woofers were originally in a 80 litre box with 2 of em, so im giving them about 40litres. Got some d19's lying around so i thought id use them.

I just need some help on how to make a crossover for them, a simple one if possible.

Heres the pic

http://members.optushome.com.au/soll...ewspeakers.jpg

Thanks !

SY 12th April 2003 03:35 PM

Let me start with an assumption: you're trying to take the trouble to make something really good. If that assumption is wrong, skip everything I have to say. I assume this because the cabinet design looks like something pretty ambitious.

You'll never get that driver combination to work really well. The problem is matching of dispersion characteristics of the two drivers at realistic crossover frequencies. The 8" will start having its dispersion narrowing at a frequency well below where you can reasonably cross over to the tweeter (unless you like distortion and fried tweeters). What will happen with any crossover that protects the tweeter is that the off axis frequecy response will show a big midrange dip up to the point where the tweeter cuts in, where the response will rise. So even if the direct sound is flat, the reverberant response won't be at all smooth. This has been the plague of all the 8" two-ways that I've ever listened to. Imaging and spectral balance suffer badly.

Consider using a smaller driver for the woofer (a 5" would match your tweeter well) or a tweeter that will go down much lower in frequency than a D19. By all means, use a high-slope crossover so that the woofer's break-up frequncy is well into the stop-band.

postman 12th April 2003 03:43 PM

Ok i get what your saying :)

Could you recommend a smaller woofer that would suit the tweeter i have, that also wont cost me an arm and a leg ??

Also for these speakers i was hoping to get a descent midrange and highrange out of them. They dont need to be heavy in bass since ill be using a small subwoofer with them. Could i use a midrange or midwoofer instead of a woofer ??

Im pretty new to speaker designing so excuse me if i say some wrong stuff

postman 12th April 2003 04:29 PM

Also about the complicated box design, the woodworking side of this wont be any problem for me. Its just the sound side i need help with :bawling:

I can get TC11SG-69-08 and P11MH-00-08 for pretty cheap, would they be more suited to the tweeters i have ??

SY 12th April 2003 04:55 PM

I don't know what's available in Oz, but I'd look for 130mm or 160-170mm drivers from Vifa, Audax, Seas, or Morel. You might browse around the Madisound website for some ideas about models and pricing.

I'm just the opposite of you- woodworking is something I can't really do well and I'm not equipped for. Too bad you don't live in California!

Nappylady 12th April 2003 11:25 PM

What about adding a midrange to the drivers you already have? That might be a cheap alternative, and then you're actually using everything you have...

postman 13th April 2003 02:29 PM

Adding a midrange would be ok but it does add extra costs, and then it would involve making a more detailed crossover, i was hoping to just get a simple project going :dodgy:

Im really new to crossovers and stuff, was hoping maybe just to use a cap or whatever.

Could someone just give me a simple way of linking the drivers together that i originally specified by using a cap, no crossover etc.

thanks in advance

Nappylady 13th April 2003 09:37 PM

Using a capacitor is not a bad start; after that, you can move up to using a cap and inductor. Lots of "professional" speakers survive using just a cap, or just a cap and an inductor.

The problem is that an 8" and a 1" have a hard time working together most of the time. Cone breakup makes the frequency response very uneven past the point of cone breakup. If you want to send these frequencies to the tweeter, you have to have a tweeter that won't completely die if you do so. With speakers as large as 8", this usually means a 3-way system, though not always. My friend Merrilee owns a studio, and her monitors are 2-way with an 8" paper cone / foam surround and a 1" titanium tweeter, and they seem to work pretty well for her.

Also, if the 8" has a larger voice coil, this helps defeat cone breakup. That's why you don't find 12"+ speakers with 1" voice coils (except in guitar amps); the cone breakup gets to be too much.

So why not make the voice coil speaker size and have virtually no breakup? Low efficiency. So, like everything in the audiophile world, it's a trade between two desireable traits.

Anyway. Tangent over. Measure the frequency response of the two drivers, and pick a crossover point that doesn't cripple either driver.

planet10 13th April 2003 10:43 PM

Quote:

Originally posted by SY
You'll never get that driver combination to work really well. The problem is matching of dispersion characteristics of the two drivers at realistic crossover frequencies.
What SY says is certainly true on the face of it... but there are quite a few counterexamples of 8" 2-ways with XOs in the same region that are quite good, and some that are 1st rate, so it is not an impossible situation. (althou they usually XO to a larger T.

What kind of woofer? What kind of cone material? (there are tricks you can do with a paper cone to improve its hi-frequency dispersion).

dave

Nappylady 13th April 2003 10:57 PM

Okay, I'm interested in hearing about these things with paper cones... are you talking about coating them, etc? I have some paper cone 15's outside that need to respond in the midrange better (I used a stock crossover--don't kill me!) and I'm interested in hearing this.


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