how does it sound good?

[rscamaroboy89 10+ year member]

ok my friend has two 15" rockfordfosgate 4 ohm p3 subs with a rms of 500 watts.his amp is a ma audio hk398.ok the specs are 600 watt 2 channel amp

150 watts x 2 chan@ 4 ohms

250 watts x 2 chan@ 2 ohms

600 watts x 2 chan@ 4 ohms bridged

so if hes only putting 150 watts to each sub how does it sound good? or am i retarded and dont understand how it works. can he bridge it to both subs and get 600 watts to both subs or what thanks.

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[efm80 10+ year member]

first off what kind of car is it?? If its a hatchback, I have seen those hit so hard without that much wattage just because of the acoustics of the car. And second off its 600watts x 1 chan@ 4 ohms bridged. Not 2 channels so NO he could not bridge the amp to get 600 watts to each channel. Although I believe the P3's are dual voice coil 4 ohms so he could wire the subs in series and then both subs in parallel to the amp to get a bridged 4 ohm load. Then he would see 300 watts per sub. correct me if I am wrong experts....

eddie

 

[SSS 18734 5,000+ posts]

You might want to elaborate on what you mean when you say "sound good."

 

[rscamaroboy89 10+ year member]

their in a mitsu eclipse so yea hatchback.by sound good i guess i really mean very loud.you cant hear the words in the song but the bass will rattle your eyeballs out.

 

[helotaxi 5,000+ posts]

Power isn't everything, or even the most important thing. First, he has 2 15s. That's a lot of cone area. Cone area is important in getting loud. It's installed in a hatchback. The car's acoustics are important in getting loud.

For a daily driven system where there is some room to play with, it's usually easier to get loud with more cone area an less amp power than the other way around. When you start adding lots of power you quickly reach the point of diminishing returns where you have to add a ridiculous amount of power to get just the tiniest increase in output. Adding cone area makes a big difference every time. Doubling power theoretically adds 3dB, but power compression (caused by voicecoil heating, reaching suspension limits, etc...) keeps you from getting most of this, especially as the power starts getting up there. Doubling cone area also nets you 3dB and with careful cone arrangement and the reduction in power compression afforded by dividing the power among more drivers the gain can be more than that.

Since doubling power gets you 3dB it makes since that the most gains are made at lower power. Your friend is only running 300w but that is a power doubling of over 8x and a gain of over 24dB compared to 1w. To see the difference between 1 and 300w watts again you'd have to increase power to over 76,000 watts.

 

[MTXman 10+ year member]

You've never heard a loud car, I can tell you this right now.

Not being able to hear the words is a bad thing. Tell your friend to invest in some quality components.

 

[efm80 10+ year member]

Power isn't everything, or even the most important thing. First, he has 2 15s. That's a lot of cone area. Cone area is important in getting loud. It's installed in a hatchback. The car's acoustics are important in getting loud.
For a daily driven system where there is some room to play with, it's usually easier to get loud with more cone area an less amp power than the other way around. When you start adding lots of power you quickly reach the point of diminishing returns where you have to add a ridiculous amount of power to get just the tiniest increase in output. Adding cone area makes a big difference every time. Doubling power theoretically adds 3dB, but power compression (caused by voicecoil heating, reaching suspension limits, etc...) keeps you from getting most of this, especially as the power starts getting up there. Doubling cone area also nets you 3dB and with careful cone arrangement and the reduction in power compression afforded by dividing the power among more drivers the gain can be more than that.

Since doubling power gets you 3dB it makes since that the most gains are made at lower power. Your friend is only running 300w but that is a power doubling of over 8x and a gain of over 24dB compared to 1w. To see the difference between 1 and 300w watts again you'd have to increase power to over 76,000 watts.

always love your posts helotaxi. got some great info, but I am just a little confused on a few ideas if you wouldn't mind explaining more...

1.) Why does power compression keep you from getting that increase in DB's from more power, how does it do that, and why is it more of a factor at higher volumes??

2.) "Your friend is only running 300w but that is a power doubling of over 8x and a gain of over 24dB compared to 1w. To see the difference between 1 and 300w watts again you'd have to increase power to over 76,000 watts.. I do not understand that statement and how you got those numbers.

sorry for being dumb and thanks for your insight....by the way I see you are from Vegas. me too, whereabouts are you??

eddie

 

[helotaxi 5,000+ posts]

1)Power compression comes from a few different places. The two big ones are voicecoil heating and the fact that you run out of motor strength as the cone moves farther from the center position of the cone's travel. Because of the first, the resistance and thus impedance of the coil increases and the actual power sent to the sub is decreased because the amp is seeing a higher impedance. The second means that even more power is needed to get the sub to travel any farther. Eventually you get to a point where the motor can no longer overcome the compliance of the suspension and it won't move any farther regardless of how much power you pump into it.

2)Multiply 1 by 2 8 times. You get 256. Remember that you theoretically get 3dB every time that you double power. You doubled power 8 times getting from 1 watt which is the sensitivity standard and 256 watts. 3 times 8 is 24 which gives you a theoretical 24dB increase from the reference level. At that low power level, you'd probably actually get all that increase because of minimal power compression. To get the next 24dB you'd have to double power 8 more times. I started with 300w and multiplied by 2 8 times and got a bit over 76,000. You wouldn't get hardly any of that increase becuase even if you didn't smoke the sub, power compression would severely limit your actual gains.

I'm up in the northwest corner of Vegas near the intersection of 215 and 95.

 

[rscamaroboy89 10+ year member]

thanks for all the info helo.im thinking of buying one of those amps to power two 12" p3 rockford fosgate subs.theyll be in the trunk of a grand prix though so idk how theyll sound.could you reccomend a better setup? i want bass that i can feel but im more for sq than spl.

 

[helotaxi 5,000+ posts]

If you care about SQ do yourself the favor of not getting Rockford subs.