Power Mad! Choosing an Amplifier.

[Cloud]

If you can't be arsed to read this whole post, just skip to the last line for a summary.

This is driving me nuts; give me a big heavy lump of metal covered in grease and oil and I know what I'm doing. Talk to me about electrical resistance, speaker impedance, root mean square outputs, and so forth, and I'm lost in a sea of confusion. Nevertheless, I'm going to try and set up some audio stuff for in and out of my car.

I like versatility and application adaptability. Which is why I like the E30, a car that can do the weekly shopping trip to Sainsbury's, and come home again via Silverstone. So what I'd like is a decent setup for the car, that can be taken out of the boot and used to do club and DJing nights in Gloucester.

The basic idea is to have car tweeters and car speakers fitted permanently into the car, and have seperate "ordinary" cabinet tweeters/speakers to do the club nights with. The only thing that will be used for both is the sub-woofers, and the amp. I've got almost all the speaker gear already, just waiting on woofer cabinets. It's amps that confuse me.

I don't really know what I'm looking at. I've totalled up the RMS of the speakers I have, both in and out of the car, and they're roughly the same, it comes to about 1800watt RMS, or around 3600watt max. All the equipment (bar a set of 4ohm 6x9s in the car) is 8ohm, be it speaker, tweeter, or woofer. Now it's time to get an amp to run it all, and though my speaker setup isn't exactly large, I'm sure some on here will laugh at the idea of doing a club night with just 1500watts RMS @ 8ohm, it seems even the insanely powerful amp units aren't entirely up to the job. The max wattage isn't the issue, but it's the RMS that seems lacking.

I've been looking at a 5000watt 6-channel amp unit, now 5000watt seems like enough, but it'll only serve 570 RMS. This means it'll run the speakers fine, but not the tweeters or the woofers, without going above its rated RMS. So then I'm looking at a 10000watt amp, and to me this seems like "overkill 9000" not just in max power, you could electrocute a rhino with that much, but in price as well. I know that having enough power to do a club night isn't going to be cheap, but it seems like far too much for the speakers I've got.

In my Capri, I've got a fairly modest 180watt system, and this is running 4x 100watt speakers. This seems pretty loud, it wouldn't impress a chav and it's far from club volume, but it's not bad for the car. I never drive with music too loud anyway, so the obsession with absolute volume is more about the events than the E30. Car amps seem to give a bigger output for the money than hi-fi type things, and they're more suited to what I want, though I wouldn't be adverse to having a more domestic amp if it were cheaper or better in some way.

This is the gear I need to power:

Car:

2x 6x9s
- 260wMAX 125wRMS 4ohm three-way speakers
2x 6x6s
- 300wMAX 150wRMS 8ohm three-way speakers


Club:

2x mid-range cabinet speakers
- twin 12" 300wMAX 150wRMS 8ohm speakers
- twin 60mm 300wMAX 150wRMS 8ohm tweeters


Both:

2x bass woofers
- single 12" 300wMAX 150wRMS 8ohm woofer
- single 60mm 300wMAX 150wRMS 8ohm tweeter


So with speakers that have a combined demand of 3600w max or 1800w RMS, could I still get decent volume with a smaller amp, or would it need to be something massive like 5000w or 10000w or perhaps even bigger?

[chu346]

It don't/won't work like that. My advice is to do things the normal way and just use normal car speakers for the car and put the dj stuff in the back seats when your going dj-ing.

Dj bass speakers are tuned to different to car subwoofers. Car subwoofers only cover a narrowband (80-30hz) in comparison and use the cars natural bass responce to boost the lower notes. Dj speakers are tuned to play to a bigger area and in comparison play a widerband (500-50hz) and flater frequency curve.

Also, car amps work slightly differently. Most car amps work at 4ohms and if a 8ohm speaker is used it will halve the given output. So for a 150wrms 8ohm speakers you would need a 300wrms amp. Another thing is that if you want 1800wrms you will need another battery(s) and either uprated and/or additional alternator. The standard alterantor is about 80amp which might do for 900wrms or so.

Why not just get some decent £70 5.25" speaker up front and one or two 12" speakers in the boot and a secondhand rockford fosgate four channel amp? you'll be happy with that.

Oh and bin 6x9's too.

[Cloud]

Thanks!

Zone was down so I couldn't reply, but for the most part I've taken the advice. I've now got 4x 15" bass PA cabinet units for the DJing, a proper rack-mount amp, the 6x9s are in the pile of "stuff to be offered on ebay" heap, and I'm going to go for subs under the front seats in the car.

[chu346]

LoL, how much room is under the seats?

Have you looked into this?

[Cloud]

I've got a sub under the passenger seat in my four-door E30, originally with comfort leather seats I'm not toooo certain if it'll go under a sport seat in a convertible, but then I haven't begun to measure anything up just yet. I'll have to do that before I do anything else. But the car is low priority, I needed some DJ gear for the summer and thought I might be able to use it in the car at a later date. Shelved that idea now, for the best I think.

If a sub will go under the seat, I'll probably go for that option (new ones, ideally) rather than a sub in the boot, for quality, boot space, and so on. Unless there's a reason not to?

When I got the four-door, it had a suspicious green switch on the dash that I didn't touch for weeks. Curiosity got the better of me on a drive, and that's when I found out about the sub. Didn't even know it was there until it started throbbing away.

[chu346]

A normal sub won't fit.

If you like how it sounds in the 4door, you should take it out to find out what model it is and try to find another. Also whilst it's out you could test fit it in the convertible.