Specification Questions

fdpatriot1
fdpatriot1 Posts: 4
edited October 2003 in Car Audio & Electronics
Ive been thinking about buying a new amplifier to push my 4 polk subs and am curious as to what slew, dampening is and what there values should be near. Ive also been reading a lot about xmax sd and vd. If xmax is how far the speaker moves in one direction, and sd is the effective surface area of the speaker, and vd is those 2 multiplied together, shouldnt the speaker with the highest vd be in theory able to produce the highest spl? Please correct me if im wrong cause im not fully understanding this. Especially since if you preform that math on the dx12-8 subs, the vd doesnt equal the vd that polk specifies for that sub. Could someone please elaborate? Any knowledge is appreciated.
Post edited by fdpatriot1 on
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  • sntnsupermen131
    sntnsupermen131 Posts: 1,831
    edited October 2003
    how much money are you wanting to spend on an amp?
    and for what purpose? (subs or smaller speakers like 6 1/2s)
    -Cody
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  • fdpatriot1
    fdpatriot1 Posts: 4
    edited October 2003
    Hopefully less than 600 for the amp. I was looking at the us amps 2000 to push 4 polk dx12-8 wire is parallel so the amp would see a 2 ohm load. But i still really would like to know more about how all those specification effect the performance on an amylifier so i can make these decisions on this amp, as well as amps for other systems in the future.
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  • sntnsupermen131
    sntnsupermen131 Posts: 1,831
    edited October 2003
    that us amps has crazy good specs
    your "avg" amp will have specs similar to these at 4 ohms
    damping factor: >200
    slew rate: 30volts/ms
    that amp you mentioned will put those numbers to shame though
    -Cody
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  • fdpatriot1
    fdpatriot1 Posts: 4
    edited October 2003
    but what do those numbers actually mean?
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  • HBombToo
    HBombToo Posts: 5,256
    edited October 2003
    Originally posted by sntnsupermen131

    your "avg" amp will have specs similar to these at 4 ohms
    damping factor: >200
    slew rate: 30volts/ms

    is this a typical slew rate for car audio because I'm familiar with u(microsec) rather than m(millisec). just seems low to me but I guess the power system is key here....


    confused as hell over here

    Twin
    ***WAREMTAE***
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  • HBombToo
    HBombToo Posts: 5,256
    edited October 2003
    change in voltage divided by time defines a slew rate. Total voltage swing your amp can do and provide the current without clipping... is my guess

    Twin:confused:
    ***WAREMTAE***
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  • PoweredByDodge
    PoweredByDodge Posts: 4,185
    edited October 2003
    slew rate = change in voltage over change in time.

    and its normally in micro (u) seconds. an amp that is rated in milliseconds (m) will be pretty **** -- 30v / ms is horrible. that's like 0.03 v/us.

    the usamps is at 150 v / us which is abnormally high. the norm is around 20 to 50 v / us --- some really nice amps are like 60 - 90 v / us --- anything over 100 is just damned pimp :)

    nothing i own is over 20...lol... i'm pathetic aint i?
    The Artist formerly known as PoweredByDodge
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  • PoweredByDodge
    PoweredByDodge Posts: 4,185
    edited October 2003
    ohh -- and i used to run four polk DX 12 - 8 ohm subs in parallel.

    i'll tell ya -- anything over about 300 - 350 watts per sub was just not doin it. actually anything over 300.

    they sounded like garbage... had them off an mtx 81000D -- potentially i had 375 per sub at my disposal, but i doubt i ever broke 300 per sub before i started to see problems with them over-excurting and what not.

    i would suggest a USamps 1000 --- that'll give you like 1200 watts x 1 at 2 ohms... or 300 w / sub. wouldn't waste my cast on the 2000 since you're almost guaranteed never to use all that power. they wont do their rated 400 -- i tried and tried and tried to get them to and they jsut would not.

    however that may be due to the quality of the amp.

    although i did go to the extent of just running one of them at 8 ohms off the amp, and still... i couldn't get it to do what i wanted it to do (power handling -wise). at 8 ohms even the81000D is "clean".
    The Artist formerly known as PoweredByDodge
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  • fdpatriot1
    fdpatriot1 Posts: 4
    edited October 2003
    i currently run my 4 on a earthquake thrust 4.5 amp.. its a 4 channel class ab tech amp. suposidly puts out 600x2 at 4 ohms.. which when i run 2 subs in parallel its 4 ohms across 2 of the 4 channels bridged.. i do the same with the other 2 subs and other 2 channels.. sounds damn good.. just want more.
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  • PoweredByDodge
    PoweredByDodge Posts: 4,185
    edited October 2003
    well if it really is putting out 600 /2 = 300 per sub, you really woudln't wanna go much higher.

    a sub will sound its best when its nearing its top power handling and then once u go past that it'll just turn to ****.

    but there's the deal of actual versus rated pwoer halding, and i'm talking actual.

    i dunno -- maybe i just had a bad experience with the 4 12's i had.... cuz my dx 10's took almsot 400 each and were only rated at 300.

    just be careful and dont trash yours like i trashed mine.
    The Artist formerly known as PoweredByDodge
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