Paper Lawyer

Cheers Steve, more food for thought. Hmmm, punchy of fluffy

Paul(UK)

I've got Kenwood dual mags in the rear. I have the head unit running with no bass lift and the fader slightly to the front as my door speakers (Infinity Kappas) can take everything the head unit can output, whereas the dual mags are unhappy with the head unit up high unless they are faded down slightly.
The small sub in the boot makes up for the dual mags lack of bass.
I have no problems with this system turned up and the roof down unless I reset the fader and then the rears start to crack up on anything with a beat.

Paper Lawyer

The JBLs seem to have a pretty high output rating for 4" speakers - 120 peak (I know that's not the same as RMS, but its peak rating is greater than almost every other 4" speaker I could find). I'm worried at the thought of working out which amp I need - its all so confusing!

Karl2k

Not convinced an amp is the answer. I have the same problem as Paul(UK) - I have to fade slightly to the front. I reckon that the fronts are meatier because they are in an enclosed space, whereas the back have a lot of work to do in such a big space. An amp will increase the high end, but bottom out on the bass still (if not worse that at the moment).

Neil has a point about the porting, but I don't agree that small speakers need a port to move more air - true if the small speaker is in a small space, but because the rears in the S are in such a large space, they need the opposite to get a 'thud'. You either need to do one of two things:

a) get a speaker/amp set up capable of moving the amount of air behind the panel (and we are talking more an 8" speaker here) or
b) reduce the air (such as taping the vents).

If you really want to get nerdy, you calculate here how much air or how big a speaker you need...

I haven't tried taping the vents, but it does sound an interesting idea... There must be a reason whay the vents are there - will taping them cause any problems such as dampness (the only reason I can of for there being vents) - or are the vents only there to assist with areodynamics when reversing???

Gonna go for a lie down now...

Paper Lawyer

Cheers guys, only just read your advice and coincidentaly I tried to change the bass and treble settngs today and realised that I had the Defeat function on i.e. factory defaults. I switched it off and made some tweaks (no need to fade to the front) and it sounds much better. Bizarre as I think I ended up increasing the bass

Karl2k

IIRC 'defeat' switches to mono. Running it in stereo will certainly help...

Strange how this would bottom out the speaker though... Anybody got any thoughts about the vents in the rear panels?

steve_the_greek

Actually, it's the opposite - the back doesn't have much work to do because there is a big space behind it, which is why it's more likely to hit the end of its travel and distort...

If a speaker has very little air behind it, then it will struggle to push against it (when the cone is going backwards, and compressing the air in the 'cabinet'), or pull against it (when the cone is going forwards and expanding the air in the cabinet). What this gives you is a tight sound, with little distortion, but also low volumes. So, you can give the speaker more welly and you get your volume, until you burn your speaker coils out.

In the case of the rear S2000 speakers, there's a good possibility that because there's loads of air in the gap between the panel and the rear bulkhead (or whatever you want to call it), the speakers have an easy life moving backwards and forwards, and hit the end of their travel at very low power outputs.

Blocking the air vents sounds like quite a good starting plan to restrict the air. If that has good results but you think it needs more, then you can try stuffing the space around the speaker with hollofibre (the stuff in duvets/pillows).

With respect to porting, this is used when you want a small speaker cabinet - one that is so small it leaves too little air for the speaker to move. So you make a hole in the cabinet and stuff a pipe in it. The speaker can now suck and blow air from outside of the cabinet, but not so much that it's like being in free air. I think it's a bit of a black art designing ported cabinets - all sorts of things like how long the tube is, what diameter to use, how far from the speaker, which way it points etc.