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.

 

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?

 

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.

 

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.

 

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?

 

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 ]

 

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 ]