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Old 28th April 2002, 08:20 AM   #1
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Smile help with driver selection?

Hello,

Im planning on redoing a set of speakers that i have sitting around (80's RSR 3ways) that have nice cabinets but crappy drivers and crossovers. I dont have ready access to many woodworking tools, so i want to try to use even the stock baffles for now. The cabinets are 1.21 ft3 and the baffles have one 8-3/8" hole, one 5-1/4" hole and two 4-1/4" holes (they had two cone tweeters each... wierd). Anyways, what im trying to ask is does any one know of any good two or three way designs using an 8 that would work well in this size of enclosure? WinISD says that the Parts Express #295-100 8 is a pretty good match ported and tuned to 45hz. Since the Dayton Silk Domes are out of stock for a while at PE, what tweet would you guys recommend using in a two way with it? or would a three way be better? in that case, what mid would you recommend?

Thanks,
Non

btw: im looking at spending around $300 for the drivers and _cheap_ crossover components for this project, and then if i like them, ill buy nicer crossover components.
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Old 29th April 2002, 03:44 AM   #2
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Sounds like fun. Anyways, 8 3/8" may be too small for 295-100. The speaker will fall right through the hole. Look at the hi-vi F8, it will work very nicely in your box, and it has an enormous lip giving it a 9-7/16" nominal diameter. I am finishing a project with that same driver in a .75 ft3 box (much too small) and am very pleased with them. At $60 they are a steal. If you like my idea I will go upstairs, get my book and tell you how to tune them. I cannot think of any other 8" driver that could be mounted in that size of hole. The F8 gets excellent midrange as well. My design is a two way using Vifa's D25AG alum tweeter crossed at 1.8 kHz, and the other I crossed at 4.5kHz just for fun. 4.5 sounds amazing, voices come to life, until you move a little bit off axis, where thr mids drop off. At 1.8 kHz, it sounds equally good, just a little different, ALL over the room. Absolutely no need for a midrange with this 8" driver! What are you going to do with the midrange hole?
Tweeter: 4 1/4" hole
That is going to be tough. My tweets are slightly smaller than that. Dayton's are not big enough. You're going to need a tweeter with as close to a 5" nominal diameter as possible. Let's see...
Hi-Vi RT1C-A...$60...4-3/4"
-planar tweeter, cannot be crossed below 3k
I can't find a damn thing; not even sure about the planar tweeter. What you could do is cut out a wood ring and mount it to the box, and then mount your tweeter to the ring.
Let me know what you think,
andy
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Old 29th April 2002, 04:24 PM   #3
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I just realized that i was very unclear. What I should have said in my first post is that the drivers are kind-of-flush mounted. the actual holes are an inch smaller than i said, and then there is a 1/2" recess around the holes and the outside of that was where i was getting those measurements, which was kinda dumb. Now that i've (hopefully) made that a little clearer, you'll see that the F8 is actually a little too big for my baffle. Actually, I would prefer to use it, but there actually isnt room for me to enlarge the hole enough. It is an impressive driver though. WinISD says 33hz in my enclusure, ported. that's pretty decent.

Anyways, what would you think of using the 295-100 w/ a morel MDT-20 maybe? the 20 has a pretty low Fs, so i was thinking crossing them around 900-1khz with maybe a generic 2nd order LR to start with? Actually, I've never designed a crossover before, so any help in that area would be very welcome.

As for the mid hole, ill probably just plug it with something. I guess it depends on how i decide to do the ports. I was thinking front firing, using two 1-7/8" dia 4" long ports, and using the wood rings you mentioned to mount one in a tweeter hole and one in the mid hole. It wouldnt be pretty, but i wont really ever be able to take off the grills of anyways, or my cat would maul them.

Thanks for the help
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Old 29th April 2002, 08:25 PM   #4
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Ok, its now looking like the Peerless 850136 CSX is a even better match for my box. now, this eight extends way up to almost 3k pretty well, so that gives me a much better selection of tweeters to use. any suggestions?
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Old 29th April 2002, 08:59 PM   #5
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Boy, I must be getting a kick out of talking to myself! Actually, I just want to write things out, it helps me think them through. Ok, the tweeter i think im going with is the Peerless 812978 1". It seems like a good match, and its cheap, and its shielded. Now im thinking about crossover. these have pretty wide bandwidth, should i go first of second order? Im leaning towards first right now... then i just need to figure out if i should put in baffle step...
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Old 2nd May 2002, 10:54 PM   #6
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I have relpied to this post three times now,and it has not come up. Am I doing something wrong?
Ok, now for your questions, I have answered them thrice already so I'll be brief; go for 2nd order. It is hard to get a first order crossover right, and they are very sensative to time alignment. Go for 2kHz.
-andy
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Old 3rd May 2002, 02:31 AM   #7
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Thanks for going through so much trouble to help me with this! That's wierd that your postsdidnt show up. Very wierd. Anyways, thanks. I'll do that. I actually already ordered parts for a generic 1st order, but I'll just pick up some more stuff, and try a 2nd order out.
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Old 3rd May 2002, 10:58 PM   #8
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Do you know what component values to use for a 2nd order?
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Old 4th May 2002, 12:26 AM   #9
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PE has a chart @ http://www.partsexpress.com/resources/xover.html that says .9mH and 7uF for 8 Ohms. www.speakermania.com give slightly different values. I was gonna go with the PE ones first. I do have a couple of questions though. For a zobel, are the resistor and cap in parallel with the driver? Also, how do i do baffle step compensation? Do i simply add a coil in series w/the woofer and then pad down the tweeter a little bit more?

Thanks
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Old 7th May 2002, 10:06 PM   #10
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First, you need to adjust the rising impedence of the woofer with a CR circuit. The value of c is 26 uf, and the value of R is 10 ohms. These values should work, but it is recomended to experiment with slightly different values. Simply wire the cap and the resistor together (in series) and attatch to the + and - terminals of the woofer(in parallel). I would get the Dayton cap because it's 10% tolerance will not be a prob. And it is cheaper than solen.
Now that we have a "good 'nuff" 8 ohm impedance we can determine xover component values. Using the wiring diagram of the second order xover at partsexpress,
L1= 1.3 mH
L2= 1.3 mH
C1= 5 uf
C2= 5 uf

I would get a couple 18 guage air cores for 5 bucks each, a couple solens (5% tolerance is wanted here) for 3 bucks each, and youre set.
Baffle step? i wouldn't worry.
andy
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