Akim711

Okay, i've been thinking about doin some bass upgrades to my system, and maybe even some speaker upgrades, and reading off the BOSE topic in this forum, brings me to this question.

I understand that an amp (2-channel, say) basically acts as a 2-port network, with input and output currents. If the load is 3-ohms, then it would draw more current from the amp that was designed for a 4-ohm impedance. Wouldn't attempting to drive that kind of current for extended periods of time blow a fuse? assuming that the device is not current limited?

i understand whats behind current limited amplifiers... did some stuff with passive, active, and linear filters and amplifiers... so i get the theory behind all this, but these amps use MOSFETS, which eh, which i'm not getting to till next semester.

basically, here's my situation. i got a JL 10-W6. its a DVC wired in parallel, to get 3-ohms. it's powered by a Rockford fosgate 800A4, just two channels bridged. the output sucks, and the amp gets super super hot, and i'll eventually blow fuses. its a 40amp fuse, which is a heck of a lot of current.

so what's the best way to test and see if my output is from my amp is working properly? i have a DMM with basic functions... that checks VDC, VAC, and resistance... but not current. I was thinking about getting hold of a function/tone generator and seeing if there's a gain by measuring the output AC voltage. what do you guys think?

also, what is the typical low pass cutoff frequency for woofer operation?

thanks.

Akim711

Another question:

I'm using a hi -> low converter tapped off the back speakers which acts as a line in for the amplifier. Do I then set the amplifier to full range, since everything but low range frequency has already been filtered?

Also, if i wanted to make my own low pass filter, what would be a good order for it?

MiK3Y

when you bridge an amp you need to cut the ohms in half. so your your amp isnt seeing a 3-ohm load...it sees 1.5ohms and the fosgate is rated at 2ohms, which would explain why your blowing fuses. you need a 8-ohm DVC or add one or two more 6-ohm DVC's.

BBsAcuraRacing

The easiest solution to the impdence problem is buy another speaker and wire the two speakers in series putting out 6 ohms load on the amp.
A fourth order is best but not as good a buying a low pass filter at line level before the amp at 18db/octave.

Akim711

fourth order? wow... okay, yeah, better to just buy one. 18dB/octave? wow... pretty steep. thought the typical was 20dB/decade (or -6dB/octave). guess thats just the way the amps are designed.

it just seems crazy though. If people in competition got 3 W6's (they usually do), then that would mean that they got a 1-ohm load (assuming they wired each in parallel and then again in parallel with each sub). Seems like an insane amount of current. What kind of amps are they using? I do indeed have an extra 10 W6 lying around... but at 6-ohms, it just doesn't seem efficient. What do you think?

VTEChump

With 3 JL W6's you wire series-parallel to get a 4 ohm total load. Wire each coil in series for 3 12 ohm loads, then wire 3 12 ohm loads in parallel for one 4 ohm load.

If you get this setup (3 W6's) make sure you have a lot of power. At least 250RMS for each woofer (750W RMS x 1 into 4 ohms). I have 3 10W6's and they sounded like crap with 450W RMS x 1 so I had to buy a bigger amp. Else you can buy a 1 ohm stable amp (very expensive) and wire them in parallel-parallel for 1, 1 ohm load.

[ 08-13-2001: Message edited by: VTEChump ]

jdl75

You can get your hands on an o-scope and check it out (if you don't know how, e-mail me, but if you are going to study MOSFET's, you had better already know how to run a 'scope!).
However, it sounds like you have some load balancing to do. This has been said once, but let me reiterate: If you bridge the amp, you drop your load impedance in half again.
Example: Two four ohm subs in parallel = 2 ohm load. Two ohm load across a bridged amp = 1 ohm load. Any comercial grade amp will get hot enough to cook dinner at 1 ohm load. Switch your subs to 8-ohm, or don't bridge the amp (or buy a competition amp).

[ 08-13-2001: Message edited by: jdl75 ]