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Critique of a Parts Express DIY Project

Discussion in 'Amps and Cabs [BG]' started by Thor, Mar 31, 2006.


  1. Thor

    Thor Gold Supporting Member In Memoriam

  2. joelb79

    joelb79

    Mar 22, 2006
    Lansing, Michigan
    hope you dont plan on using that for bass guitar ;]

    downward firing subs dont sound good on plush carpet. the carpet acts as a bass trap. Hardwood floors would work. should be similar cone area to a dual 8" sub. sharp roll-off on the lowend frequencies under 40hz. I would be suprised to hear deep bass out of it, but it would sound good for a basic sub in a small room.

    would i build it? no. i'd rather have a single 10" 500w sub for a home theatre. 12's are ok.. 15's are ok. just depends on how much shake i want. my home theatre is a small room, so i dont need much.
     
  3. seamonkey

    seamonkey

    Aug 6, 2004
    I've always wondered about this. The Acoustic Image amps have a down firing woofer. I've only tried one on a hard floor (tile). I hear different stories about how they work on carpet. I've heard some guys carry a board to put them on. But then I hear at the frequencies it puts out that it doesn't matter which way the woofer points. Confusing.
     
  4. Thor

    Thor Gold Supporting Member In Memoriam

    The reason it intriged me is that I have a space problem in the
    family room, and a 12" or 15" center sub is not an option.
    There is about 5" of clearance under my entertainment
    center, so this caught my attention.
     
  5. joelb79

    joelb79

    Mar 22, 2006
    Lansing, Michigan
    well that might work then.

    bass traps are usualy nothing more than a peice of movable fabric that absorbs the moving air from the woofer. in that sense, since carpet can vibrate, carpet *MAY* act as a bass trap, eating away at some of your lower notes but absorbing the moving air from the speaker.
     
  6. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    Carpet in and of itself is NOT a bass trap.
     
  7. joelb79

    joelb79

    Mar 22, 2006
    Lansing, Michigan
    true. i didnt say *ALL* carpet was a bass trap. i was stating that carpet CAN ACT as a bass trap. This would be dependant on its ability to absorb the energy produced by the speaker and its ability to absorb the floorboard reflected energy.

    but, then again, as long as the air volume moved and rarified by the speakers is as big as the volume of the gap/height away from the carpet which MAY be acting as a bass trap, then this would not be an issue now would it?

    in all honesty, looking at the design of that speaker, your going to loose a little 100-130hz content from firing it at carpet that you would not loose firing it at hard wood floors. yes you would be crossing it over at a higher frequency, but you would loose a little of the information that direct firing speakers would produce.

    mounting it on a wall in a corner with the port 6" away from the wall would be optimal, as the air would be less restricted on the speakers, and a natural room bass boost would happen due to corner loading.

    just my opinion, i cant back it up scientificaly without testing with some equipment that i cant afford on my college student/parent of two kids budget. but if you want to argue about if carpet is or isnt a bass trap:

    in and of itself, carpet is NOT a bass trap. thanks for clearing that up. ;)
     
  8. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    Time to read up on how bass traps are constructed. If carpet could act as a bass trap serious studios could have saved gazillions of dollars over the years on their control room and sound stages.
     
  9. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Not unless it's 12 inches deep. It does act as a midbass and midrange trap, and as such is very useful for soaking up the Doppler induced harmonic distortion that direct radiator subs produce.
    A little, but since a sub should be crossed over from 80 to 100 Hz anyway anything that sneaks through above that you want soaked up.
    Unless you positively had to have a box 5" deep I'd pass. Even then you could do this size box with two eights or one ten for a lot better performance at lower cost.
     
  10. Thor

    Thor Gold Supporting Member In Memoriam

    I was hoping you would say that.
     
  11. Thor

    Thor Gold Supporting Member In Memoriam

    What about the driver?

    Is this right?

    Specifications: Power Handling: 50 watts RMS/100 watts max *VCdia: 1-1/2" *Impedance: 4 ohms *Re: 3.6 ohms *Frequency range: 35-800 Hz *Fs: 35 Hz *SPL: 85 dB 1W/1m *Vas: .51 cu.ft. *Qms: 2.81 *Qes: .32 *Qts: .29 *Xmax 11.5 mm *Dimensions: A: 7", B: 5-1/2", C: 3-5/8"

    Isn't that the sensitivity figure, not SPL?

    Isn't that rather low? Is this basically a car audio driver for
    the Boom Boom Boys?

    Does that make this project a "Design a project to feature
    this product so we can sell more of them", rather than
    'Design a useful project and then find parts to achieve it"?
     
  12. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    That is sensitivity, but that's not an unusual figure for a hi-fi driver. The specs are OK, and if you could only use a 6.5 it's about as good as you can get. OK for a computer sub, for instance, But four of those only displace as much as two eights or one ten, and cost a whole lot more, so as to:
    I'd be inclined to say yes.
     
  13. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    I didn't even look at the rest of the specs, but it's obvious in this case that SPL refers to sensitivity - and it's not uncommon for home to see sensitivities that low.
     
  14. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    You could just build a Table Tuba you know.
     
  15. Thor

    Thor Gold Supporting Member In Memoriam

    *sigh*

    My house is having an addition, so no speaker building is on
    right now. But come this summer ...

    It will be nice to have a few projects lined up to keep me in my new workspace. hehe. Can't wait.
     
  16. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    Yeah, if I didn't have other priorities right now ... Bill's plans are cheap at three times the price - great, informed designs. And what you can learn about driver and cab design and cab building from them is more added value. Not to mention his forum. Lots of great support and knowledge there.
     

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