Cheap but good 2ch amp and 1ch mono

chodecz · Post by **chodecz** » Sun Mar 26, 2006 5:50 pm

hey guys, Ive been looking at class D sub amps, and ones with subsonic filters are a bit expensive, compared to ones without!

What are the actual chances of my sub being fried in my 30-32hz ported box without the filter!!?????

Post by **GlassWolf** » Sun Mar 26, 2006 6:15 pm

chances are very good. the FAQ section has a thread I submitted that Jonathan wrote on ported boxes. it's worth reading. In short, when the sub plays notes below the tuned frequency of the port, the sub loses it's damping, or the suspension or "back pressure" supplied by the box itself. When that happens, it's like pulling the rug out from under your feet. The sub will suddenly act like it's not in a box at all, and without that "spring" effect from the box's suspension, the sub will over-excurt and exceed it's Xmech, tearing the coil or coil former right out of the motor structure and spider. In short, it fries the sub.

Jeremy, sorry you posted as I was writing my reply, so I didn't see yours till I hit the submit post button.
Yes everything after "more info;" was pasted, from the article I wrote for the FAQ section on amplifier fundamentals:
http://www.glasswolf.net/caraudio/amplifiers.html

I wrote it specifically to save me from re-typing everything every time I see the same questions arise.

sorry if it got confusing.

chodecz, most class D amps have an ISF now (infrasonic filter) though a few of the entry level lines still don't. It shouldn't be impossible to find an affordable, decent amp that has one though. Try elevation, planet audio, or avionixx to start. I'm pretty sure elevation has some entry level stuff at least.

JeremyC · Post by **JeremyC** » Sun Mar 26, 2006 6:22 pm

Nah dude its all good. I was going to say something about mine being the simple way to look at it, and that someone would have the more techinical way to explain it. (cough.............. jonathan or you)

Either way its nice having the extra info.

chodecz · Post by **chodecz** » Sun Mar 26, 2006 6:25 pm

Thanks glass.

As I look at more and more amp specs, I seem to get less and less idea of what the amp will put out at standard battery voltage. Some quote at 14.4 VDC, others at 13.8 VDC, some dont quote at all! Im interested in a JBL p180.2, but it doesn't quote input voltage at all, so i'm afraid the quoted 2x90rms might be exaggerated!

What voltage will my amps be getting maximum, from a standard battery and charging system on a small car? And if really pushed till lights start to dim *very slightly*, what would be a approximate voltage drop??

Please help.

Jonathan · Post by **Jonathan** » Sun Mar 26, 2006 6:35 pm

: I don't remember writing that *shrugs* May have been another Jonathan, or just a really long time ago.

JeremyC · Post by **JeremyC** » Sun Mar 26, 2006 7:12 pm

Yeah I think that was geolemon.

High Society · Post by **High Society** » Sun Mar 26, 2006 7:29 pm

Some one else just hopped on Kiki's bandwagon :)

Post by **GlassWolf** » Sun Mar 26, 2006 9:23 pm

find an amp with a PWM (pulse width modulated) or "regulated" power supply.
that will mean the output is fixed, regardless of input voltage within reason. better bet for a stock or near stock electrical system. that should help.

chodecz · Post by **chodecz** » Mon Mar 27, 2006 3:10 pm

Thanks guys.

But no one answered my question? Is it too much of a dumba** question or something?

"What voltage will my amps be getting, from a standard battery and charging system on a small car? And if really pushed till lights start to dim *very slightly*, what would be a approximate voltage drop??"

Please help.

Post by **GlassWolf** » Mon Mar 27, 2006 5:10 pm

use a voltmeter (VOM or DMM) and test it to see.
usually 12.5V from the battery and 13.8-14.4V above idle from the alternator.
when lights dim, it's usually less than 12VDC.