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  1. #1

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    Default db10 Sub box for home use...

    I don't know exactly where to post the topic so here it goes anyways.

    Here is the deal. I have a pair of db 10's, bought them back in 1998. I love them, sound great, have had like 4 different box configurations in 3 different cars.

    I started autocross and rally cross, and the subs needed to go. I did some work on the rear deck, and put the 6x9 MOMO 3 ways. Sounds great, nice bass and all. Not as much oomph as when i had the subs, but the clarity is sweet.

    Okie, so I have had the subs sitting in my room for about 5 months now. I currently don't have a sub for my home stereo. So I figured I would build a nice box for the db 10's becuase I have an mono-block amp to drive them(280watts @ 8ohms sub amp).

    I know the subs where designed for the car, but I figured if I tweaked the sub box design, I could get good response in the house with the stereo.

    I downloaded WinISD and have been using it to design some boxes for the subs.

    The last sub box plan I had was a bandpass design with the subs in a iso-barik push pull configuration. I thought of keeping a similar design. I plotted the design in WinISD, and wasnt impressed with the results, not great for home atleast.

    I was thinking of designing a box to use the subs in a push-pull configuration (Like the M&K's), but have spent 2 days searching the web with no results on designs for a box of that sort.

    So after much tweaking I have come up with the following specs on the box for the 2 db 10's, its a vented box.

    Driver : Polk Audio db10-4
    Vas : 31.8
    Qts : 0.38
    Fs : 26.70
    SPL : 85.00
    --
    Project by : DGoReck
    Project for : you
    --
    Number of drivers : 2
    Box type : Vented
    Box size : 4.000 ft^3
    Tuning frequency : 24.00 Hz
    Vent : 1 vent(s)
    11.48 in length for each
    4.00 in round


    Relative
    Freq Gain SPL
    [Hz] [dB] [dB]
    15.00 -17.87 70.14
    20.00 -6.44 81.57
    25.00 -0.47 87.54
    30.00 -0.64 87.37
    35.00 -1.18 86.83
    40.00 -1.38 86.63
    45.00 -1.41 86.60
    50.00 -1.35 86.66
    55.00 -1.26 86.75
    60.00 -1.16 86.85
    65.00 -1.06 86.95
    70.00 -0.97 87.04
    75.00 -0.88 87.13
    80.00 -0.80 87.21
    85.00 -0.73 87.28
    90.00 -0.67 87.34
    95.00 -0.62 87.39
    100.00 -0.57 87.44
    105.00 -0.52 87.49
    110.00 -0.48 87.53
    115.00 -0.45 87.56
    120.00 -0.42 87.59
    125.00 -0.39 87.62
    130.00 -0.36 87.65
    135.00 -0.34 87.67
    140.00 -0.32 87.69
    145.00 -0.30 87.71
    150.00 -0.28 87.73


    The outter box dimensions are (0.75 thickness):
    W 16.00
    H 26.00
    D 20.96

    Gain Plot:


    SPL Plot 1 watt @ 1 meter:



    Okie, so is this a feasible design? I'm looking for good low end, atleast 80db @ 1 watt @ 20Hz. Or is my logic flawed? Please help/advise.

    P.S. If you can provide any information on a push-pull configuration (non-isobaric) It would be appreciated.

    Dan

  2. #2
    Polk Customer Service
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    DGoReck,
    There are a couple of things that I would be concerned about
    this design that need to be addressed before going into production...

    #1 - The db10 uses a high mass cone and are not really designed to be used in a vented enclosure. They were designed to be installed small sealed enclosures. They will work in this application
    but make sure that there is a subsonic filter used and is set to 25 Hertz to prevent excessive cone displacement and prevent possible suspension damage.

    #2 - The combination of the cabinet volume and the the port tuning raises the vent air velocity to over 24 Meters per second with a applied input power of 150 Watts at the tuning frequency. The enclosure is tuned to 24.06 Hertz.
    This is a little high and you will be able to hear the port "breathing" or "chuffing"depending on the volume level.
    With our designs we try to shoot for a maximum level of 18 Meters per second at 150 Watts applied input power. This is a good reference level to use that will ensure a fairly quiet sounding enclosure.

    If your plans are to execute this design, then I would suggest changing the tuning of the enclosure by installing two 4" ports that are 19" in length. This will change the tuning of the enclosure to 27.23 Hertz and the vent air velocity at 150 Watts is significantly reduced down to less than 10 Meters per second at the tuning frequency.

    Happy Box Building,
    Kim

  3. #3

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    Originally posted by Kim

    #1 - The db10 uses a high mass cone and are not really designed to be used in a vented enclosure. They were designed to be installed small sealed enclosures. They will work in this application
    but make sure that there is a subsonic filter used and is set to 25 Hertz to prevent excessive cone displacement and prevent possible suspension damage.
    Thats a good point, I remember the specs for the old sealed box where like 0.7 cubic ft for each sub.

    I know you mention the filter and distortion, but unfortunately, I don't have the specificaton sheet handy, but what is the frequency range the drivers were meant to deliever? Was/Am I shooting to low of a tuning frequency?


    #2 - The combination of the cabinet volume and the the port tuning raises the vent air velocity to over 24 Meters per second with a applied input power of 150 Watts at the tuning frequency. The enclosure is tuned to 24.06 Hertz.
    This is a little high and you will be able to hear the port "breathing" or "chuffing"depending on the volume level.
    With our designs we try to shoot for a maximum level of 18 Meters per second at 150 Watts applied input power. This is a good reference level to use that will ensure a fairly quiet sounding enclosure.

    If your plans are to execute this design, then I would suggest changing the tuning of the enclosure by installing two 4" ports that are 19" in length. This will change the tuning of the enclosure to 27.23 Hertz and the vent air velocity at 150 Watts is significantly reduced down to less than 10 Meters per second at the tuning frequency.

    Happy Box Building,
    Kim
    Another good point, unfortuantely, it seems the software will not update the vent mach as you increase the wattage applied. So I did not forsee this.

    I have no problem changing my design. I have been tossing around some ideas , and this seems to give me the flatest response.

    Do you guys/gals have any suggestions as to the type of enclosure to use? I am planning on using it in the house mainly for music/tv listening(not home theatre). I am open to suggestion,.

    Thanks.

    Dan
    ~~Rallye Driven~~
    '00 Subaru 2.5RS Pearl Red w/ Polk Audio MMC690's in the rear deck
    2 -10" Polk db10 subs sitting at home with nothing to do yet =[

  4. #4

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    Forgot about this. The subs are 4 ohms each. I just realized today, that trying to run the subs in a isobaric configuration would cause a 2 ohm load, was fine in car, that amp drove 2 ohms, but the home amp is meant for 8/4. 2 ohm load I am looking for trouble. So am I stuck using using a normal setup(no isobaric), or any way for me to work around this.
    ~~Rallye Driven~~
    '00 Subaru 2.5RS Pearl Red w/ Polk Audio MMC690's in the rear deck
    2 -10" Polk db10 subs sitting at home with nothing to do yet =[

  5. #5
    Redford
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    If you wire them in series won't it run at 8 ohms?

  6. #6

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    thats what i was thinking, dont wire them in parallel, wire them in series, this will have an 8 ohm load instead of 2, unless you will not be getting enough watts to push them, but remember, you dont need as many watts in your home as you do in a car
    -Cody

  7. #7

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    I didn't think you could run the isobaric configuration in series. I was under the presumption that it needed to be run in parallel, as every configuration I have read about does so.
    ~~Rallye Driven~~
    '00 Subaru 2.5RS Pearl Red w/ Polk Audio MMC690's in the rear deck
    2 -10" Polk db10 subs sitting at home with nothing to do yet =[

  8. #8

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    i dont know why, but could be, i dont know too much about that particular configuration
    -Cody

  9. #9

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    could u just use two home sub amps that are rated at like 300 watts at 4 ohms (www.partsexpress.com) and make sure the input to those amps was identical (y splitter or whatever) ????
    "With your own attitude it is hard to survive here... But who gives a damn, we are here to change the world, and we dont need a password for that."
    - Anurag

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