I helped Mark T fit his rear speakers and HU last weekend and I like his 5.25" rear speakers (Kenwoods I recall) and it made me ponder about my JBL P42s I've currently got.

I took mine out on the Sunday and refitted them more securely with nuts and bolts but I find that if I listen to something quite bassy (e.g. Electric Six) that the rear speakers distort, perhaps "bottling" (I think that's the term ) when I crank the volume up above 20. I'm only 6 foot (ok, ok, 5'11.5") and so my seat isn't rammed up against the speaker (probably a couple of inches of clearance?) so is the problem caused by (a) having cheap 4" speakers (b) not giving the rear speakers enough juice (i.e. I need to fit an amp) or

 

I get this too, I am sure its down to crap rear speakers, not the size but the quality.

 

What are your rear speakers Marc? (I can't see them listed in your sig)

 

polk I think. They were the real basic ones offered by Lucid when they first set up.

 

I think it's more to do with the space that the speakers are fitted in behind the rear plastic panels. There really isn't much space for them to move any air back there. I have 5.25s and they sound fine, but my seat squeaks against them

 

Interestingly the rear panels that Mark bought off Frankyknuckles had the air ducts taped off - would this improve the sound or make it worse on the basis that the air would not circulate as well?

 

Now we're on to the tricky subject of porting. You see this on smaller loudspeakers that have a hole (port) in the speaker cabinet to allow air to move.

I don't profess to be an expert in porting, but it does allow a smaller speaker to move more air with less effort ( I think ) I also know that for porting to work properly, the port should be tuned to the specific speaker.

AFAIK By taping the air ducts up, your speaker will have to work harder to move as much air.

 

I have P42s and I have never noticed any problems.

Did you wire them up correctly? It isn't obvious on the JBLs which is the power and which is the Gnd terminals.

 

[QUOTE]Originally posted by StevenM
I have P42s and I have never noticed any problems.

Did you wire them up correctly?

 

If the speakers are distorting at high volume, it's one of 2 things.
1) The amp can't cope and the output is clipping.

2) The speakers aren't controlled under high load because they are designed for a cabinet with a smaller volume or lower power, so they are hitting their 'end-stops'.

The two sound different, but I can't really put it in words well. With the former, you the speakers still sound quite punchy, with the latter, the sound is a bit fluffy. (see what I mean about not explaining it well?)

If it's the former, then get an amp, although the 13.8V wiring to your H/U will also play a part (i.e. if you wire your H/U up with bell wire, it will never deliver decent power). You should be able to work out if it is this based on the power rating of the speakers.

If it's the latter, then if the speakers are low power ones get better ones. If not, and the speakers are expecting to be mounted in a low volume enclosure, then you can either reduce the amount of free air behind the speaker, with some form of soft filling which may help, or you can get a speaker with a higher power rating, and lower sensitivity which means the speaker coil will move less for a given input power.

Of course, it could be the rear panel, in which case you can get damping material that you can stick to the panels to stop this.

The key is, that all three forms of distortion are different, so you need to identify which one it is first.