Ideas on improving my mains...need input.

Discussion in 'Archived Threads 2001-2004' started by dave shreve, Jan 3, 2002.

  1. dave shreve

    dave shreve Extra

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    I want to improve my mains and build a center channel to match them later this year. I guess I could just buy new speakers, but what fun would that be?

    My speakers are kinda old, mid-90's vintage, and were made by the now defunct Blues speaker company. They also made car audio. Anyone remember them? They sound okay, but they just seem like something is missing compared to some of the nicer speakers I have been auditioning in the audio stores(I really like Paradigm stuff). Anyways, they are an MTM setup with dual 8's and a dome tweater in a ~55 liter rear-ported enclosure tuned to about 40Hz according to my rough measurements with a tape measure. However, since I will be building a sub, I am not against plugging the ports if necessary to get the right enclosure style for the components.

    The most obvious slution , to me anyways, is to buy the components from a similar kit and transplant them into my cabinets. Any ideas on how well this would work? I was kinda thinking about the Adire Kit 281 stuff, but my drivers are aligned vertically and my enclosures are a bit smaller. How would this affect the end result? Any other kit speaker transplant candidates come to mind?

    -dave
     
  2. KevinMcL

    KevinMcL Agent

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    Have you tried all the easy fixes already? Adding bracing, damping, internally/externally re-wiring using top-quality wire (preferably DIY Cat-5 braided!), upgrading the x-over components, or adding a bag of sand to the bottom of the enclosure? I did these to my towers, and it opened the sound right up. Just checking- hope this helps![​IMG]
     
  3. dave shreve

    dave shreve Extra

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    Actually, no, I haven't done anything to them.

    I thought about upgrading the crossovers, but I don't really know a whole lot about crossovers(yet). Maybe I'll open them up tonight and look at the cross-overs to see if I can diagram the circuit--or describe it and let you all help me interpret it--and then maybe you folks here can help me figure out where to go next?

    What does adding the bag of sand to the enclosure do, though? I can see it would decrease the size of the enclosure, but what beyond that?

    -dave
     
  4. Michael R Price

    Michael R Price Screenwriter

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    Of course, you can do the Kit281, if the drivers fit (you'd also have to replace the crossovers, and check the box alignment/tuning to make sure it works out with the 281 drivers. I don't know how much of a difference the tweeter offset makes. I think it has something to do with baffle edge diffraction affecting frequency response, and being able to place the woofers closer together. Of course, if you could build cabinets from scratch, that would be better... I think 40hz might be a bit high of a tuning for a 281 cabinet of that size. (Adire has a 61 liters tuned to 29Hz in their recommended alignment, mine are tuned to 25Hz or so.)

    You could of course try the usual tweaks, like internal re-wiring (or re-building a good quality crossover), or even just experiment around with some driver replacements I guess.
     
  5. dave shreve

    dave shreve Extra

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    Okay, I started taking things apart and poking around a bit. First, the speakers are Blues BCS-882 with 2 8" drivers and a 1" fabric dome tweeter. 8 ohm impedance and 200W RMS powerhandling according to the placard on the back of the cabinet. There is no internal bracing, but the cabinets are made of 3/4" particle board. About 2/3 of the internal surfaces have a layer of polyfil sheet over them.

    The Drivers:

    On the backside of the woofer cone are the numbers 240-0845-003, and on the side of the magnet is 71193BL84. These are fairly heavy drivers with coated paper cones and fome surrounds and center caps(with 'Blues' printed on them). On the backside of the tweeter are two lines of text. The top line is BDT25 and the bottom line is 433TND. Can anyone identify the origins of these drivers so I might find some T-S numbers for them?

    The crossover:

    The crossover is on a board stamped with '164-1'. The schematic of the circuit also doesn't look any of the examples in the speaker book I borrowed from a friend('Great Sound Stereo Speaker Manual With Projects' by David B/ Weens).

    Tweeter Filter: The tweeter has a long box that I am assuming to be a resistor in series with it imprinted with the following:'COLBER 5 OHM 5% CW10'. The tweeter/resistor circuit are in parallel with an inductor, I think--it's a red coil of wire around a black bar(just shorter than the long box resistor(?) mentioned above) with a band of white tape around the center and no identifying marks. One side of this coil is soldered to the negative terminal, and the other side(the leg where the resistor is between the coil and tweeter) is connected to a blue metallic can. This can is a capacitor, I think, imprinted with the following'6MFD 100V NP'. The other side of this capacitor(?) goes to the positive terminal.

    Woofer Filter: The two 8" drivers are connected in series, with one wire going to the negative terminal and one to the positive trminal, i.e. they are in parallel with the leg the coil and capacitor in series(with the tweeter/resistor(?) leg in parallel with the coil).

    Confused yet? If not, then what order and type is this crossover? Any guesses on cross-over frequency? If any of you want to see it, I can take some digital pics and e-mail or post them.

    Is that crossover worth upgrading? Are these decent drivers? The cabinets seem to be pretty solid except for the lack of bracing and cheap spring terminals for the connections...

    -dave
     
  6. dave shreve

    dave shreve Extra

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    The porting is done via 4 5" long 2" diameter ports. Closing off a port or three would lower the tuned frequency. Running the numbers on LSPcad, closing one port drops the tuning frequency from ~43Hz to ~38Hz, closing two drops it to ~31Hz, and closing 3 out of 4 gives ~25Hz. Even with three of them closed, the port speed doesn't get really high until you drop under 30Hz.

    Hmmm...this playing with the ports deal is giving me an idea or three. With the current tuning, LSPcad predicts a 5dB bump around 60Hz, but closing 2 of the ports cuts the magnitude of the hump in half. That would explain some of the boominess of the speaker--and a possible solution. I'm going to go experiment with closing some ports and speaker placement some...

    -dave
     
  7. NathanP

    NathanP Supporting Actor

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    Hey dude,

    Earlier when I was into HT, To upgrade my vintage 1970's I bought some cheap radio hack crossovers, patched up the speakerboxes, and put new screws intho the speakers and it sounded a million bucks better!
     
  8. Dave Poehlman

    Dave Poehlman Producer

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    I'm trying to figure out the layout of those crossover parts. The fact that theres a resistor, capacitor, and what sounds like an inductor attached to the tweeter... that sounds like a notch filter. Probably used to tame a resonance peak on that tweeter. If there are no other parts in there, perhaps they are just using the driver's natural rolloff rather than a crossover. Not an uncommon practice with manufacturers to cut costs. (and since Blues is now defunct... sounds like they should have cut a few more [​IMG]). If you could scribble a quick diagram with the ratings.. that would be helpful.
    Anyway.. I would recommend putting together a crossover at around 2000 - 2500 Hz. Even a simple first order will probably make a big difference and the parts aren't all that expensive.
    It sounds like you are looking to keep the cabinets, but, if you are feeling industrious.. I would recommend an MDF cabinet.
    Thats my $.02
     
  9. dave shreve

    dave shreve Extra

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    I've decided that I just want to do whatever I can cheaply to these, i.e. no new drivers. It's just not worth buying new drivers to settle with for the compromises of this cabinet. I would be willing to build or (preferably)buy new crossovers(no soldering skills) and do the other cheap tweaks.
    Here's a sketch of the crossover in the speakers now...
    http://www.seidata.com/~dshreve/XO1.bmp
    Please explain how it works and what each component does.
    -dave
     
  10. dave shreve

    dave shreve Extra

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    NOTE: I just realized I have the position of the capacitor and inductor switched in the illustrationj above.

    -dave
     
  11. Patrick Sun

    Patrick Sun Moderator
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    The capacitor and inductor work as an electrical 2nd order high pass filter. The resistor is there to pad down the tweeter output to normalize the output with the woofers' output for supposedly a flat frequency response.

    It seems the designer is counting on the natural roll off of the woofers for that portion of the crossover for the woofers, thus, no components for the woofers.
     

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