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Im building some new cabinets/need some help...

Discussion in 'AV Stands, Cabinets, Seating & Furniture' started by freesey, Nov 25, 2002.

  1. freesey

    freesey
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    There is a little bit of story attached to this so please skip ahead if you like; basically I had some cheapo speakers with a 40 watt paper cone woofer and a 3 watt (yes 3 bloody watts) tweeter. That was until I blew out the foam surrounding the woofer. So I went to my hifi shop and bought some new woofers and tweeters. What I ended up getting were 2 X 8" 80 Watt woofers by Crown (A Canadian company I cant seem to find any support online for) and 2 X 100 Watt Peerless soft dome tweeters, 1 inch I believe. I was messing around on the www like any good dork, and I figured out that it probably should sound better than before due to better components(I hope). So I pull out the drivers again since replacing them, and take a look at the wire - yep ghetto 20 gauge wire with some really bad insulation, also notable was the 4.7 uF / 50 volt cap for the tweeter and the piece of wood glued to the back of the cabinet that should have been taken out when the holesaw drilled the hole for the woofer. Brutal. Anyways; I figured what the hell, why not replace all the garbage including the spring clip binding posts with some nice gold plated ones and some 12 gauge OFC wire as well. Sorry this post is so long (well if anyone cared to read it :) , my question is should I still be using that 4.7 uF / 50 volt cap for the tweeter? Or can I buy a Xover from partsexpress for say 3000 Hz and let it go from there? My specs are as follows if it helps :

    [Tweeter] Peerless (cat no:811528) : 8 Ohm; 91 dB; 95x95mm; 31mm deep; 26mm vc; 100 watts; 980 Hz fs; 3.5-20KHz; Qc 000926

    If some of those specs dont make sense feel free to make fun of me as Im not too sure exactly what they mean anyways I just found them on a site selling these.

    [Woofer] Cambridge Crown 800: 8 Ohm; RES. 40 Hz; Freq. RES. 30-2.5Khz 80 Watts RMS

    Ive tried reading a lot of how to's on the web and Im afraid I cant understand a lot of it, its my limited brain capacity. Thanks for anything. Thanks for any advice/opinions you can give me, I appreciate it!
     
  2. BK Electronics

    BK Electronics
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    Its not advisable to use that 4u7F cap as this was intended for use on the old tweeter, you may need a higher grade crossover say 12dB/Oct or even 18dB/Oct. Also if the woofer is less sensitive than the tweeter (They usually are) then you will need an L pad attenuater on the tweeter as well.

    I'm at work at the moment, but when I get time tonight I will research the components and if I can get the right info I require design a bog standard butterworth crossover which should suffice.
     
  3. BK Electronics

    BK Electronics
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    Ive looked for the spec on the peerless 811528 but cant find any details, I need a plot and the Th-Sm parameters to see if you can drive it lower than 3.5 kHz with a steeper filter. You seem to have a 1kHz gap between 2.5kHz and 3.5Khz that will need filling some how.
     
  4. BK Electronics

    BK Electronics
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    Found a plot of the peerless and the Th/Sm, the crown 800 is 87dB so the tweeter will need to be reduced by an L pad by 4dB. All I need now is the Th/Sm of the crown.
     
  5. freesey

    freesey
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    Wow you really know your stuff; since you seem to know what I need could you tell me what I should get from partsexpress.com and what configuration I should use to wire it? If not I already appreciate your input! I just want to make these cheap boxes not sound as bad as they are! Do you suggest any damping material in particular? Anything else I havent considered? Thanks again!
     
  6. BK Electronics

    BK Electronics
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    I will have a look at PartsXpress tonight and see if there is something suitable. I have come up with a design for the tweeter but without the Th/Sm for the woofer it would be down to guess work for that part of the design .

    The plot I got for the tweeter shows it is well able to go to 2.5kHz so a good compromise may be to feed full range into the woofer ( No crossover inline) and allow for the natural roll off of the speaker. Then just put a high pass filter at 2.5 kHz in line with the tweeter. Its not the ideal situation but it is cheap and simple.

    Whatever happens you will need the L pad attenuator, this is only two resistors, nothing to flash to worry about.
     
  7. BK Electronics

    BK Electronics
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    I had a look at Parts Express and this crossover seems to be the only 2.5kHz 2 way croosover suitable. I do not like iron cored inductors as they can saturate at high powers and cause all kinds of nasties.

    http://www.partsexpress.com/pe/show...51&St3=47156703&DS_ID=3&Product_ID=5621&DID=7

    I'll sort out the values and a circuit diagram so you can wire the two L pad resistors in

    As for something to deaden the box, try lead flashing from Wikes. Its got adhesive on, so easy to fit and really does make a difference..
     
  8. freesey

    freesey
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    Holy crap how do you know all this stuff?! Im really impressed by your knowledge - even tho I dont understand all of it! I can get my electrician friend to help me with that! Thanks for your help!
     
  9. BK Electronics

    BK Electronics
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    Hi There

    here's a circuit of the L pad attenuator. Good luck
     

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  10. freesey

    freesey
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    Muchos gracias! Thisll be fun :)
     

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