Building DIY Speakers on the cheap

Discussion in 'Home Theater Projects' started by Mike-Hatheway, May 24, 2004.

  1. Mike-Hatheway

    Mike-Hatheway Auditioning

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    Hey,
    I got turned on to the Partsexpress NSB buyout speakers by this thread: hometheaterforum.com/htforum/showthread.php?s=&threadid=198386. So on impulse (can be a bad thing, I know) I bought eight of them and some tweeters in hopes of making a very cheap, decent set of what will more than likely become shop speakers. Here are the links to the drivers:

    Woofers (if you can call them that [​IMG] )
    partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=269-570

    Tweeters
    partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=269-702&scqty=2

    The tweeters are pretty bad, I know. But I have some ELF 1.5's (no tweeter) and don't notice too much to be lacking from the music, so I figured I would just buy some cheap speakers (staying with the project theme) and see if I could integrate.

    I figured I would either put these in a TMMMM or MMTMM arrangement. I came up with some manageable dimensions and found I could get a maximum box volume of 1.125 ft^3, this will be ported to around 60Hz.

    At first I was not going to include a crossover of any kind, but seeing as I've never designed my own crossover (only built them from schematics included in designs) I thought that this would be the perfect project to start the learning process with, something with few reprecussions if I screw it up.

    My main questions are these. Any input on the design I have come up with? Any suggestions on what to change about it? Second, as far as a crossover goes what do you guys reccomend (remember these are meant to be a very cheap project, I have much larger things on my plate at the moment that require most all of my funds). Third, I think I figured out how to wire these to a 7.2 Ohm load, but I could be completely off base, I will include a picture If I can, so you guys can tell me if I'm doing it right.

    Here's a link to the picture:
    web.engr.oregonstate.edu/~hathewam/post.GIF

    Ok, here's the very crappy picture of the wiring. Basically I split the woofers up into groups of two. Two 8 ohm woofers wired in parallel, and two in series. The two sets of woofers are then wired in parallel with each other giving I think a 3.2 ohm load. This is then wired in series with the 4 ohm tweeter to give a 7.2 ohm load. Does this look right? Thank you very much for any input or advice you can give.

    Mike

    Argh, no links until a certain post count I see. Sorry people but you'll have to copy past the links :/.
     
  2. Aaron Gilbert

    Aaron Gilbert Second Unit

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    That wiring diagram needs some work. First off, you want your tweeter in parallel with the woofers. Also, I would wire the woofers slightly differently. I would put two pairs in series and then put those pairs in parallel. This will net your nominal 8 ohm load for the woofers, but your tweeter stays at 4 ohms.

    I think you might have problems using that tweeter, however. It's not really efficient enough to match up with four of those woofers. That said, if you don't mind a depressed top couple octaves, it looks to have a fairly smooth response. Due to the high Fs, you will want to cross it over rather high. I would say at least 5-6kHz if you are using a single capacitor as the crossover (first order electrical). That 8dB peak at 7kHz in the woofer is actually more troubling, it's the kind of thing that kind lead to sibilance issues (SSSSSS sounds emphasized).

    I don't have a way to scan or upload images at the moment, otherwise I'd draw you a proper circuit diagram, I'll try to remember later.

    Aaron Gilbert
     
  3. Mike-Hatheway

    Mike-Hatheway Auditioning

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    Shane, thank you for the links.

    Aaron, if I wire the woofers to an 8 ohm load, and wire the tweeter in parallel with them, is it safe to say that this will not drop the overall speakers impedance signifacantly? And why is this? Because the tweeter's voice coil is so small that it just doesnt provide a lot of resistance?

    Losing output on the upper octaves doesnt bother me much, though if I do need to cross the tweeter over so high to stay away from the Fs, which brings the woofer up to that 7kHz peak, then I'm a little worried.

    Is there any (non-complex) way to attenuate that peak in the crossover? And thank you very much for the generous offer of uploading a circuit diagram, whatever help you can give is very much appreciated. Thanks for your time.

    Mike
     
  4. Aaron Gilbert

    Aaron Gilbert Second Unit

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    What you need is a parallel notch filter. It can attenuate peaks such as the one on that woofer. I've never designed or used one myself. It's a resistor in parallel with a capacitor in parallel with an inductor, and the whole thing placed in series with your woofer. It will easily cost you quite a bit more than your woofers though, and reports are it can take quite a bit of tweaking to get right. I'd build the speakers first with a simple crossover (like a single capacitor and inductor) and see what you think. Spending hours and hours figuring out a way to make cheap drivers sound better often ends up costing your more in both money and time, than purchasing better drivers to begin with. I don't meant to throw despair into your project ideas, I'm the kind of simple crossovers and have no problem using inexpensive buyout drivers. This particular woofer is one that I myself would pass on, though.


    Aaron Gilbert
     
  5. Mike-Hatheway

    Mike-Hatheway Auditioning

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    Aaron, thanks for the insight. I guess I'll just wire them up as you suggested, and using one of the many crossover calculators online I'll choose an inductor and resistor to use as a very simple crossover. Does 5 kHz sound like a good crossover point? Thanks again for your time.

    Mike
     
  6. Aaron Gilbert

    Aaron Gilbert Second Unit

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    Mike,

    Darnit, I forgot all about drawing up a little diagram last night, sorry about that. 5kHz sounds like a good crossover point. I would strongly urge using a 2nd or 3rd order electrical crossover on the tweeter though, unless you are only going to be playing at low to moderate volumes.


    Aaron Gilbert
     

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