108 DB from a single MM2104?

mrmsudawgs
mrmsudawgs Posts: 34
edited July 2005 in Car Subwoofer Talk
I just tested my system performance using a hand held DB meter, test tones, and the same chart as shown here for "In car Response" http://www.polkaudio.com/car/toolbox/subboxplans/subbox_plan.php?id=57&mesurements=standard

My performance was significantly better than what is shown on the chart. I noticed at the bottom of the page where Polk says the test is performed at 1 volt input. Why 1 volt? Why not 12 volts? I ask this because I got 108 DB at 60 HZ versus the published 85 DB at 50 HZ. What's the difference?

Mike
Post edited by mrmsudawgs on
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  • PolkThug
    PolkThug Posts: 7,532
    edited July 2005
    Simple, you have the volume turned up more (a higher input signal).
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  • neomagus00
    neomagus00 Posts: 3,899
    edited July 2005
    theirs is a reference... so when you see a sub that has a 'sensitivity' or 'efficiency' of, say, 85 db, that's where that number comes from, roughly.

    when you did your test, you did it at a voltage input of about 22 volts, not 1 :). the voltage refers to what's going in to the sub, which in your case is what's coming out of the amp... if you're pushing 300 watts, that's about 21.7 volts, in a car. you probably wouldn't even be able to see their sub moving when they did that 1 volt test, compared to yours at full excursion.

    fyi, if you're using the radioshack digital spl meter, you need to go out on the net and find a table of correction figures, because it's not perfectly accurate at all frequencies.
    It's not good, very fundamentally simply not good. - geolemon

    "Its not good enough until we have real-time fearmongering. I want my fear mongered as it happens." - Shizelbs
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  • mrmsudawgs
    mrmsudawgs Posts: 34
    edited July 2005
    I am indeed using the Radio Shack SPL digital SPL meter. Would you happen to have a link to the table of correction for this meter?
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  • swerve
    swerve Posts: 1,862
    edited July 2005
    i'm pretty sure he has the collector's edition 2104's....
    cats.vans.bag...
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  • PolkThug
    PolkThug Posts: 7,532
    edited July 2005
    Originally posted by mrmsudawgs
    I am indeed using the Radio Shack SPL digital SPL meter. Would you happen to have a link to the table of correction for this meter?

    "snapbug" is the one you seek. Go forth on your journey....
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  • neomagus00
    neomagus00 Posts: 3,899
    edited July 2005
    This is for the C-weighted mode, which is the one you use to tune. As a note, these are the corrections you apply, not the response of the meter... e.g. the meter is -7.5 dB at 20 Hz, so you need to add 7.5 dB to your 20Hz reading to get the real number.

    10hz.....+20db
    12.5hz...+16.5db
    16hz.....+11.5db
    20hz.....+7.5db
    25hz.....+5db
    31.5hz...+3db
    40hz.....+2.5db
    50hz.....+1.5db
    63hz.....+1.5db
    80hz.....+1.5db
    100hz....+2db
    125hz....+.5db
    160hz....-.5db
    200hz....-.5db
    250hz....+.5db
    315hz....-.5db
    400hz....0db
    500hz....-.5db
    630hz....0db
    800hz....0db
    1k.......0db
    1.25k....0db
    1.6k.....-.5db
    2k.......-1.5db
    2.5k.....-1.5db
    3.15k....-1.5db
    4k.......-2db
    5k.......-2db
    6.3k.....-2db
    8k.......-2db
    10k......-1db
    12.5k....+.5db
    16k......0db
    20k......+1db


    from http://www.htguide.com/forum/showthread.php4?t=13395
    this mod should level out the bottom end, if you want to do it. of course, that invalidates this table...
    It's not good, very fundamentally simply not good. - geolemon

    "Its not good enough until we have real-time fearmongering. I want my fear mongered as it happens." - Shizelbs
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  • mrmsudawgs
    mrmsudawgs Posts: 34
    edited July 2005
    Thanks for the info! Ya' know - I can not fathom how or why someone knows that correction factors are even needed for this meter. The fact that the information is out there proves that someone has put lots of time into it. Amazing....

    Thanks again!
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  • PolkThug
    PolkThug Posts: 7,532
    edited July 2005
    Originally posted by mrmsudawgs
    Thanks for the info! Ya' know - I can not fathom how or why someone knows that correction factors are even needed for this meter. The fact that the information is out there proves that someone has put lots of time into it. Amazing....

    Thanks again!

    Heh, you are heading down a path that many have traveled before you, just try not to get too wrapped up in measuring audio (like me) and remember to enjoy the music.

    Measuring bass in your car is a great way to learn how subwoofer position and other variables affect output. Try measuring the bass with your windows rolled up vs. down 1" vs. down 6", doh! there I go again... have fun!
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  • neomagus00
    neomagus00 Posts: 3,899
    edited July 2005
    pt, what did you find when you did the windows thing? how much worse do you think it gets when you take the whole roof off :p?
    It's not good, very fundamentally simply not good. - geolemon

    "Its not good enough until we have real-time fearmongering. I want my fear mongered as it happens." - Shizelbs
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  • PolkThug
    PolkThug Posts: 7,532
    edited July 2005
    Originally posted by neomagus00
    pt, what did you find when you did the windows thing? how much worse do you think it gets when you take the whole roof off :p?

    Rolling your windows down gives you more db's in the lower bass frequencies.
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  • neomagus00
    neomagus00 Posts: 3,899
    edited July 2005
    relative to the upper frequencies, or absolutely more? i'd find absolutely more hard to comprehend.
    It's not good, very fundamentally simply not good. - geolemon

    "Its not good enough until we have real-time fearmongering. I want my fear mongered as it happens." - Shizelbs
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  • PolkThug
    PolkThug Posts: 7,532
    edited July 2005
    Never measured or paid attention to the upper frequencies in that situation.

    Its a significant gain in bass SPL, you don't need a meter to notice it. (Assuming that you have a decent system to start with, and your car isn't leakier than swiss cheese :) )
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  • neomagus00
    neomagus00 Posts: 3,899
    edited July 2005
    okay, i'm trying to wrap my mind around this one, so let's be perfectly clear... you're saying that, with all the windows closed, if you hit 110 dB, you could hit 115 with all the windows open?
    It's not good, very fundamentally simply not good. - geolemon

    "Its not good enough until we have real-time fearmongering. I want my fear mongered as it happens." - Shizelbs
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  • PolkThug
    PolkThug Posts: 7,532
    edited July 2005
    Originally posted by neomagus00
    okay, i'm trying to wrap my mind around this one, so let's be perfectly clear... you're saying that, with all the windows closed, if you hit 110 dB, you could hit 115 with all the windows open?

    Yep, with the front windows open. Don't know about all windows if its a four door, could have an adverse affect.

    Just try it!

    Another note (don't know if it matters or not): I always use sealed sub enclosures.

    And another: Last two cars I've had subs in were a '99 BMW 323 and an '02 BMW 325
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  • neomagus00
    neomagus00 Posts: 3,899
    edited July 2005
    hmm... i'm trying to reconcile this with what i know about the transfer function of a typical car (which, admittedly, isn't a ton). accordingly, i'm going to throw out a couple ideas, and you respond, okay? okay, let's begin :) :

    bmws are european, therfore they're built like tanks... now how does that matter... hmm... what if the cabin was sealed up well enough to act as a larger sealed box on the front of the sub? that'd make it quieter... then, roll down the windows (i.e. cut big holes in the second box), and it'll be more free to radiate...

    what else... same thing, maybe the tank-like construction blocks enough of the sound from reaching the cabin that, with the windows down, you hear the sound that escapes the trunk and radiates outside the car in addition to the normal bass you get...

    i'm trying to compare it to a home sub in a big versus a little room, cause that's what's happening, basically - radiate from (sub -> trunk -> cabin) or (sub -> trunk -> entire planet). i don't have a car sub, but i do have a definitive tech supercube reference (i think it's a reference, or equivalent, it's several years old and very big). i can stick that in my trunk, see what it does... folding the roof down could be a problem, but we shall see... i have a saab, so it's equivalent to your beemer (sp?), and a friend has a p.o.s., i can test in both...

    could there be a transmission-line type of effect going on here?

    any other ideas?
    It's not good, very fundamentally simply not good. - geolemon

    "Its not good enough until we have real-time fearmongering. I want my fear mongered as it happens." - Shizelbs
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  • PolkThug
    PolkThug Posts: 7,532
    edited July 2005
    The Bimmer does seal very well. If you're driving down the highway and open the sun roof, it sounds like one of those Star Wars doors.

    I think the car seals well enough that it actually restricts cone movement of the sub. Roll down the front windows, and that pressure is relieved, resulting in more cone excursion, thus a higher SPL.
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  • neomagus00
    neomagus00 Posts: 3,899
    edited July 2005
    yeah, that's the idea i was geting after with the 2-sealed-box blathering :). i think it's definitely worth a couple hours of testing tonight... annoy the beejesus out of the neighbors, and test a bunch of variables - what car it's in, window and roof configuration, which compartment the sub's in, and which way it's facing, plus anything else i can think of.
    It's not good, very fundamentally simply not good. - geolemon

    "Its not good enough until we have real-time fearmongering. I want my fear mongered as it happens." - Shizelbs
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