sub #1 = 75dB, sub #2 = 75dB, #1 + #2 = ?

SlowcarIX
SlowcarIX Posts: 887
edited August 2008 in Subwoofer Hookup & Bass Management
assuming no cancellation...

how many dBs will 2 subs put out total if they both output 75dB?
my 7.(1x4) HT setup
TV - Mitsubishi WD-65734
AVP / Amp - Onkyo PR-SC885P / D-Sonic 2500-7
Front - Emerald Physics CS2
Center - JTR Triple 12LF
Surround L/R / Back - Polk RTi4 / Polk FXi A4
Sub - 4 X Hsu ULS15 playing nearfield
DVD / CDP - Sony PS3/40GB / Sony SCD-XA9000ES
Belkin PURE AV PF60 / UPS
Buttkicker

http://www.polkaudio.com/forums/showthread.php?t=60612
Post edited by SlowcarIX on
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Comments

  • McLoki
    McLoki Posts: 5,231
    edited August 2008
    If within 1/2 a wavelegth of each other 6db gain. (15' apart at 20hz - need to be closer for 6db gain at higher frequencies)

    Further apart then 1/2 wavelength - 3db gain.

    With my subs about 3' apart - I got exactly a 6db gain.

    (I read the 1/2wavelegth thing here, so I may be mistaken or may have misinterpereted them.)
    Mains.............Polk LSi15 (Cherry)
    Center............Polk LSiC (Crossover upgraded)
    Surrounds.......Polk LSi7 (Gloss Black - wood sides removed and crossovers upgraded)
    Subwoofers.....SVS 25-31 CS+ and PC+ (both 20hz tune)
    Pre\Pro...........NAD T163 (Modded with LM4562 opamps)
    Amplifier.........Cinepro 3k6 (6-channel, 500wpc@4ohms)
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  • suprafantx
    suprafantx Posts: 249
    edited August 2008
    Interesting question. Between 75 and 150 dB. Just kidding. I am waiting for a phycist answer you question.
    Living room
    Speakers: McIntosh XR100 Fronts, LSIM707 Fronts, LSIM 706 Center, LSIM 703 Surrounds, LSi/FX Surround backs.
    Player: Oppo 95.
    Amps: Bryston 4B SST, B&K Ref 200.7 S2.
    Pres: B&K Ref 50 S2, Paraound P5.
    Subs: Dual Rythmik F15HP subs.

    Man Cave
    Speakers: Martin Logan Vistas.
    Player: OPPO 105.
    Preamp: B&K Ref 50 S2.
    Amp: B&K Ref 125.2 S2
    Sub: Rythmik F12.
    Sub management: SMS-1.
    Headphones: HD800, HD380, RS220, SRH-1840. Headphone amp: Woo WA2.
    Room treatment: GIK Room Kit #1.
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  • Dennis Gardner
    Dennis Gardner Posts: 4,861
    edited August 2008
    Michael is pretty much right. In an open area, a 3dB gain is the result of either twice the power or twice the surface area. The 75 watts into each speaker is irrelevant to the dB increase as long as the amps will push the wattage. It doesn't matter that there are 2 amps, just that there is 75 watts to each, (it could be coming from 1 amp and would have the same level.

    The 6 dB gain that Michael experienced could have been due to room gain from corners matching the wavelength of the frequency.
    HT Optoma HD25 LV on 80" DIY Screen, Anthem MRX 300 Receiver, Pioneer Elite BDP 51FD Polk CS350LS, Polk SDA1C, Polk FX300, Polk RT55, Dual EBS Adire Shiva 320watt tuned to 17hz, ICs-DIY Twisted Prs, Speaker-Raymond Cable

    2 Channel Thorens TD 318 Grado ZF1, SACD/CD Marantz 8260, Soundstream/Krell DAC1, Audio Mirror PP1, Odyssey Stratos, ADS L-1290, ICs-DIY Twisted , Speaker-Raymond Cable
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  • Sami
    Sami Posts: 4,634
    edited August 2008
    That's how the math goes:

    75dB + 75dB = 78dB (x + x = x + 3)

    That's the optimum situation, in practice you're going to run into cancellation where the waves run in different phase.
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  • Gaara
    Gaara Posts: 2,415
    edited August 2008
    I thought the math went: z = 10 log (10^(x/10) + 10^(y/10))

    x is the first db level
    y is the second db level
    z is the combined db level
    The Basement HT
    PC Rig
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  • Sami
    Sami Posts: 4,634
    edited August 2008
    Yes, I guess I should have specified the math for the given example. x + y != (x+y)/2 + 3
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  • Ron Temple
    Ron Temple Posts: 3,212
    edited August 2008
    Without the math...co-located subs within 6 - 8 feet (in phase) will get up to a 6db gain. Non co-located subs (in phase) will get up to 3dbs.

    Combo rig:

    Onkyo NR1007 pre-pro, Carver TFM 45(fronts), Carver TFM 35 (surrounds)
    SDA 1C, CS400i, SDA 2B
    PB13Ultra RO
    BW Silvers
    Oppo BDP-83SE
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  • bigaudiofanatic
    bigaudiofanatic Posts: 4,415
    edited August 2008
    I don't like math I can not do in my head epically when it comes to audio its music.
    HT setup
    Panasonic 50" TH-50PZ80U
    Denon DBP-1610
    Monster HTS 1650
    Carver A400X :cool:
    MIT Exp 3 Speaker Wire
    Kef 104/2
    URC MX-780 Remote
    Sonos Play 1

    Living Room
    63 inch Samsung PN63C800YF
    Polk Surroundbar 3000
    Samsung BD-C7900
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  • ShinAce
    ShinAce Posts: 1,194
    edited August 2008
    McLoki got it right the first time.

    Double up on the subs and double up on the amps, you get 6 dB.
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  • SlowcarIX
    SlowcarIX Posts: 887
    edited August 2008
    so...i tried using both conquest and danley together but just cannot get a flat response no matter what i try...phase, moving them around a little - gave up and and just went with the danley, nearfield :)

    DSC01426.jpg

    ignore my wiring mess :o
    my 7.(1x4) HT setup
    TV - Mitsubishi WD-65734
    AVP / Amp - Onkyo PR-SC885P / D-Sonic 2500-7
    Front - Emerald Physics CS2
    Center - JTR Triple 12LF
    Surround L/R / Back - Polk RTi4 / Polk FXi A4
    Sub - 4 X Hsu ULS15 playing nearfield
    DVD / CDP - Sony PS3/40GB / Sony SCD-XA9000ES
    Belkin PURE AV PF60 / UPS
    Buttkicker

    http://www.polkaudio.com/forums/showthread.php?t=60612
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