Q.
I have two subs and when I connect both they sound crappy. Once I disconnect one (either one) from the amp they work fine. I have checked the wiring, I have stronger in line fuse and music comes out fine. I need help to know what I could try next. Is my amp not getting enough power?
A.
Chances are you either have 1) a load mismatch (the ohm rating of the subs is not correct for the amp), or 2) one of the subs is connected backwards (positive and negative switched). If the subs are parallel connected (each sub has it’s own wiring going to the amp), option 2 is the most likely. If the subs are series connected (from amp to sub to sub back to amp), it could be either. If the subs work fine by themselves, it’s most likely a wiring issue.
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Q.
I have a question about an amp for my car. OK, lets talk RMS and max power between high quality and paper weight quality or so I’m told. One is a Polk Audio 2400w amp, RMS 4 ohms: 400 watts x 1 channel. The other is a Boss 2400w amp, RMS 4 ohms: 750w x 1 channel. What’s the difference? I know there’s some quality issues, but the Boss is $100-150 and the Polk is $300-350. Do I really need to spend 200 dollars more?
A.
Peak and RMS power numbers these days are like the horsepower wars of the 60′s – everyone is always trying to one-up each other. Basically, in the real world, peak power is meaningless. RMS is the more important measurement – it is the average, sustainable power output. The speakers need to be rated for (IMO) about 1.25 to 1.5 times the RMS (at the correct load, in this case 4 ohms) power of the amp to avoid being toasted.
More important for the sake of quality and clarity is the Signal to Noise Ratio of the amp – compare a really expensive amp to a really cheap amp of the same RMS output and you’ll see the difference. Signal to noise is, simply put, how much power output can be obtained “cleanly”; the higher, the better.
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Q.
I’m mounting a subwoofer (9.5” deep) in an enclosure that is only 10” deep (about .5” clearance from the magnet to the wall). Will this favor certain frequencies or give it a more flat response? Do nothing at all? If everything is to specs on the sealed enclosure cu/ft wise, will this matter at all?
A.
Yes, it will change the response of the speaker due to the standing wave reverb. Basically, a speaker producing a low bass tone is just moving air back and forth. That rate of movement creates the “standing wave”. The higher the frequency (say, 100Hz) the shorter the wave, and vice versa. Changing the distance from the speaker cone to the rear wall will accentuate different frequencies. Due to some pretty neat physics, you can effectively “fool” the sound waves into thinking they’re in a deeper enclosure by adding a foam backing to the rear wall – something that is lightweight and porous works well (cheap pillow foam works wonders and is real cheap, egg-crate foam works as well).
The sealed enclosure volume has a larger effect overall in this situation, but keep in mind the manufacturers spec’s are for a particular frequency – more volume will lower that frequency, less volume will raise it.
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