Whats A Good Amp For A 500w Rms Subwoofer

If I have two 400 watt RMS subwoofers what size amp do I need? How can you tell?

Probably 800 watts at half the rated ohms of one speaker. Your amp must be able to push 800 watts at, say, 2 ohms if these are 4 ohm speakers or 800 watts at 4 ohms if these are 8 ohm speakers.It will say on the speakers what the impedance in ohms is.Get an amp that is specified with 800 watts or over, at an ohm rating that is SAME or UNDER…half the ohm rating of one of those speakers.That's the answer here's a short ramble:Almost inevitably you will be running the two speakers in parallel. Whether you have two outputs on your power amplifier; or if you go into one speaker then go out from that speaker to the next; the connection you don't see inside the speaker with in and out or inside the amp is a parallel connection. Parallel connections divide the impedance (ohms.) It takes a bigger amp to handle lower impedance, because lower impedance is lower AC resistance. Lower resistance means more amps flowing for the same output voltage. More amps requires a beefier output section. The actual equation for total speaker ohms of speakers wired in parallel is:Total ohms = 1/((1/ohms#1)+(1/ohms#2))…If you put in a third speaker there would be another similar term in the denominator, (1/ohms of speaker #3). More speakers, lower ohms…The amp will say what the watts and ohms are on the back, or at least in the manual it will tell you what it can handle. Be at or below the ohms, and above the watts.

What size amps should I get for a 15-inch subwoofer?

The most important part of this question is that it’s a subwoofer. You don’t need a lot of power to move a lot of air with a 15″, but it also depends on your subwoofer’s frequency response, and your required frequency response.In a sealed box, the woofer will roll off I think at -6dB per octave, while in a ported box, it will roll off much steeper. However, if it is a ported box, you don’t want to push the woofer hard below the box frequency. In this case, enough power is what you need. Average power will likely be 10 W or so, but when the large transients hit, you don’t want distortion, so for 15″, I would guess you’re looking for high SPL, so I would recommend no less than 200 W (quoted RMS amplifier rating).For a sealed enclosure, things become interesting. You can compensate the roll-off below the woofer’s low frequency response using a simple 2nd order low-pass filter on the input. So your LPF will have a -3dB frequency of, say, 2 octaves below Fb of the woofer (the woofer’s -3dB frequency on the low side). For example, if your woofer goes down to 40 Hz (-3dB), you can make a LPF at 10 Hz (-3dB). This will compensate the woofer, but you then need a lot more power, and the woofer driver needs to be able to handle that power. The further your filter frequency from your woofer frequency, the more power you need, but the lower (frequency) your response will be.To illustrate:As you can see, the -3dB frequency response of the woofer with the filter is 10 Hz, and it will respond down to about 5.5 Hz. But you need a huge amount more power (roughly 30 times more). For reasonable output, you need 16 W for a 93 dB sensitivity woofer (let’s assume sensitivity is accurately measured at 1 W). For the same power with the above filter, you therefore need 480 W. So there’s your answer - for a sealed woofer box with a -3 dB low frequency of 40 Hz, if you compensate this to respond as above, and the woofer can handle it, you need a 500 W amplifier. :) And know something for sure - that woofer excursion is going to be something crazy! And if it can manage the excursion and power, you’ll have one very thunderous woofer!Verdict: 200 - 500 W