Building Myself a Speaker cabinet.

[wishbone]

An 8 ohm speaker is an easier load than a 4 ohm one, so will not kill the amp. You'll get less power from the amp though.

Mixing different types of speaker to cover the same region of music is never a good idea - the different speakers will have different responses.

If I was in your position I'd sell the 3 drivers on ebay and buy a speaker designed for your application. Download winISD to model a box for any drivers you want. You'll need the thiele small parameters to do this though.

The jbl amp should have a low pass you can use to blend the bass in with your mains. Make sure you buy a wiring kit to get it installed safely. Theres loads on ebay for better than halfords type prices.

Rob.

edit: car audio direct seem to offer good prices. I've bought from them before and they're pretty good service.

http://www.caraudiodirect.co.uk/index.php

[nero279]

Out of those my personal choice would be the fusion. Then the Fli (made by vibe who have a very good reputation) or pioneer. The JBL's and pioneers tend to be a bit power hungry. The JBL's can also be a bit loose, so loud but at the expense of tonality.

Fusion are relatively new to the market(3-4 years as a major player in the UK market), and i'm always prepared to give the newbies a go, as they gotta have a reasonable product to make an impact in a well established market. It's also the closest match to the amp.

Mutant are cheap and cheerful, and also are in a similar position to fusion, but a bit newer. I wouldn't choose them at the moment, but purely because i've never been impressed with the build quality on their ready built packages, have a look at one of their twin ported boxes. Often the ports are loose, the carpet not cut right or stuck down well, and often the perspex is cracked and scratched around the screws which are sometimes not in a straight line aswell. So that's why i wouldn't choose mutant. Although i did run a mutant amp for as a temporary thing but soon replaced it with a JBL, not because i had problems with it, but it was never powerful enough to do what i wanted, which i knew when i bought it.

I was hoping you was gonna say the 2 10s were wired in series. As i could've then been pretty confident that they would run 4ohms impedance. The parralel wiring has thrown me as most home stereo, and PA/instrument amps are designed to work with an 8ohm load.


A speaker in a circuit, forget the fact that it produces sound, is effectively a resistor. Current goes in, meets resistance in the voice coil(electromagnet), and comes out. In a home speaker the resistance met is usually 8 ohms. In a car speaker the resistance met is usually 4 ohms. An amp will not cope with pushing the current it puts out through twice the resistance it's designed for, or at least not for very long. The opposite is also true if the amp meets too little resistance it will over-drive it's self and burn out. Which is why i'm sceptical about offering advice as to how to wire the 2 10s to the head unit without knowing what they are. What guitar amp were they from?

[nero279]

Has the head unit even got a pre-out to allow it to connect to the power amp?

Well spotted that man. I just looked it up on the sony site, and it doesn't appear to have any pre-amp outs, which means you will have to wire the amp to the speaker wires, i'm pretty sure the JBL amps have all got high level inputs aswell as low level RCA ins, so that shouldn't be a major problem. The only thing is that leaves no spare speaker wires. I really can't think how the best way to do it would be at the moment, I don't think the GTO 2000 is tri-mode compatible. I'm gonna have to look up the stuff you got already and work out the best way of doing it.

[wishbone]

A speaker in a circuit, forget the fact that it produces sound, is effectively a resistor. Current goes in, meets resistance in the voice coil(electromagnet), and comes out. In a home speaker the resistance met is usually 8 ohms. In a car speaker the resistance met is usually 4 ohms. An amp will not cope with pushing the current it puts out through twice the resistance it's designed for, or at least not for very long. The opposite is also true if the amp meets too little resistance it will over-drive it's self and burn out. Which is why i'm sceptical about offering advice as to how to wire the 2 10s to the head unit without knowing what they are. What guitar amp were they from?

Amplifiers have trouble supplying current (amps). Thats why amplifiers that can put power into 1 ohm, or even 0.5 ohms are expensive. They need to deliver big current (amps). the lower the ohms the closer to a short circuit you get. Big current means big expensive power supplies.

An 8 ohm speaker will draw 1/2 the amps of a 4 ohm speaker at the same voltage output. It's an easier load. Honest guv. Thats why you end up with lower watts out of the amp. Lower watts, less power drawn, easier load.

example using ohms law ( Volts = Amps x Ohms)

40V = 10A x 4 ohm : Watts( Amps x Volts ) = 400Watts output. (4 ohm speaker)

40V = 5A x 8 ohm : watts = 200 output. (8 ohm speaker)

btw most decent pa amps are running at 4 ohms, not 8.

Rob.

[nero279]

I'm not convinced, but i'm willing to stand corrected if i'm wrong.

[wishbone]

http://www.caraudiodirect.co.uk/esup...ndetails&_i=20


http://www.whathifi.com/newsMainTemp...ewssectionID=3

http://www.1388.com/articles/tech_un...ge2/page2.html


Rob.

[nero279]

http://www.caraudiodirect.co.uk/esup...ndetails&_i=20


http://www.whathifi.com/newsMainTemp...ewssectionID=3

http://www.1388.com/articles/tech_un...ge2/page2.html


Rob.

Chees rob i'll have to have a read through them.

[plumb bob]

I think the halfords guy will shat himself if he sees anything other than a stadard OEM set up ( they are noy trained for subs and amps)

I put my sub facing forward into the rear seat to protect the cone from my GSD. seems to work ok.

[nero279]

How did you get on at halfords?

I still can't get my head round that ohmage stuff rob. I guess i'll learn it someday.

[MattF]

I still can't get my head round that ohmage stuff rob. I guess i'll learn it someday.

Simplest way to design with amplifiers is that you can use a speaker of equal or larger *impedance* than specified on the unit. The higher the impedance, the lower the output, but it's safe. If you drop the speaker impedance below the minimum speaker ohm rating of the amp, something will burnt out. That's why wiring in parallel is generally a no go, unless you use higher impedance speakers to compensate for the effect.

[nero279]

OK so my understanding was a little mis-guided, but only a little.

The reason you will still want to keep you impedance at 4 ohms then, is because that's what the power ratings are generally given at. Unless you're talking class d monoblocks and Dual voice coil / 2Kwatt competion subs. So, you could wire up to give more resistance, but chances are then you'll end up driving amps hard as the speakers will not be coming close to their distortion levels. Thus amps will start clipping and running above RMS ratings whilst speakers are still quite happy and within their boundaries? So it's not because you're amps are going to burn themselves out trying to work harder it's because your average joe will drive them outside of their capabilities without realising it. OK so if you understand then, what's already been said then work out your power ratings and go for it with wiring above 4 ohms. Use the VU meters on the amp to ensure it's not clipping and all will be ok?

[wishbone]

What you need to look at is what the speaker wants. I have some 15" drivers that can handle 600w input. However, at 300W in the low bass region they'd already be clacking from the cone being over excursion. 300w at deep bass levels will push the driver beyond its limits, whereas 300w at midbass will be ok for the driver.

It doesn't matter what the speakers impedance is to a point, only what the amp is doing. If you want to put more than the amps capable of into a speaker then you'll clip the amp. If the speaker can handle more power then you've bought the wrong amp for the speaker and it's your own fault.

Its popular in pa circles to buy an amp at twice the speakers rms rating. This is so the speaker always gets a clean signal from the amp. Of course you need to set it up so you don't push the speaker past its limits.

JBL markets 4 ohm / 8 ohm / 16 ohm versions of some of its drivers so you can pick the right ones for your application. Amp choice would also play a big part.

Rob

[nero279]

So run too high an impedance, you get poor performance? Run too low an impedance you get cooked amps?

[wishbone]

So run too high an impedance, you get poor performance? Run too low an impedance you get cooked amps?

Well I never mentioned poor performance from the high impedence..

If you've decided to use a 200 watt 8 ohm speaker for a sub, and want to use it to its limit then you'll need an amp capable of delivering 200W into 8 ohms.

If you buy a 200W 4 ohm speaker and want to run it into it's limit, buy an amp capable of pushing 200w into 4 ohm.

If you buy a 200w 8 ohm speaker and drive it with an amp that'll push 80 watts into 8 ohm, realise you won't be able to push the speaker to it's limits.



If you're intending to drive your subs to their limits you'll probably not be too bothered by sound quality so a bit of clipping wouldn't be noticed anyhow


fwiw I'm planning to put 2 of my 15's in my surf, powered by an amp that will push 700watts into 2 ohms. The subs are dual 8 ohm voice coil, so they'll all be paralleled at the amp. Each speaker will get 350w which is just enough to push it to it's linear limit. I doubt they'll even get close to their limit keeping distortion nice and low.

Rob.

edit: If you was to clip an amp into a speaker you'd not kill the amp. They all have thermal cutoffs to shut themselves down. You may kill the speaker, though it'd be difficult on a sub. Clipping a tweeter will kill the tweet easily.

[nero279]

If you've decided to use a 200 watt 8 ohm speaker for a sub, and want to use it to its limit then you'll need an amp capable of delivering 200W into 8 ohms.

so in terms of car audio amps an amp with a minimum quoted RMS of 450w into 4 ohms?

Then even the JBL GTO 4000 would struggle at 400w RMS, 1000w PMPO



As far as i'm concerned driving a sub to it's limits means driving it to the point immediately before it starts to distort. If it's distorting it's gone past it's limits.

I've done nothing on the surf, my last car had several installs in but finished with this lot in the boot. 2x JBL GTO 4000 amps, 1x 1.5 Fahrad Power Cap, 2x10" kicker comp c10 subs in sealed boxes, 1x12" JBL GT4 1000w sub in sealed box, Autoleads circuit breakers and fused distribution boxes. No Treble in the rear as anything i put in got ripped apart by the subs, Infinity components in the front doors, all running from a Pioneer DEH-MP7600 headunit. Never had any distortion problems until it was cranked to within the top few figures on the headunit volume and still by far one of the loudest systems in ashford, and indeed at southend cruise i was asked to turn it down by event organisers and by the police as it was attracting too much attention.

This photo was taken before i completed the build, i had everything in, but still had some work to do with tidying up, and finishing off.