SUB BOX HELP!

[clio_massive]

i have a double MDF box with two 12inch subs. the problem is that they bounce about and hardly any bass comes out, what could be the problem? the sides are all sealed etc.



cheers!

 

[BRUN]

what bounces about ?........the subs ?

what subs do you have ?........what amp ?........do you have decent cabling ?

 

[clio_massive]

yea the subs bounce

have 2 jbl GT4s

never happened when i was only running 1 of the subs

its the wiring i got with the wiring kit

its a 500watt amp

 

[NeiLD0wN]

If the subs are bouncing around maybe the hole is slightly to big/small for the subs, or maybe there are not secured in properly.

Also is the box secured down to the floor of the boot?

Hey BRUN, another talkaudio member

 

[BRUN]

Quote: Originally posted by NeiLD0wN on 19 August 2004


Hey BRUN, another talkaudio member

yup

how do you mean they bounce ?

are they actually moving out of the box, or do you simply mean the cone is moving but your not getting much bass from em


[Edited by BRUN on 19 August 2004 at 8:06pm]

 

[clio_massive]

the box is enclosed and they sound really crap, they distort alot.

isnt any holes from what i can see

 

[Dink]

out of phase???

 

[clio_massive]

simply mean the cone is moving but your not getting much bass from em



p.s brand new speakers got the other day

 

[BRUN]

id suggest trying a different amp then mate

i work at Motor World and those JBLs are definitely not crap and with the right amp you can get a decent amount of bass from them, enough to vibrate shop windows a little

is there a level/gain/sensitivity control on your amp ?.........it might be turned all the way down (dont turn it all the way up !)

what make is your amp ?

 

[clio_massive]

the thing is mate it sounded excellent when i only had 1 jbl sub in a single box, but now i have 2 of them it doesnt sound as good, sounds like they cancel each other out if u get what i mean

 

[Mole]

is the new box seperated for each sub, i.e a middle wall to make 2 enclosures.

if not then ones wired in the wrong polarity, whichll mean when 1 moves out, the other moves in, which wouldnt change the pressure inside the box, causing hardly, if any bass at all to be produced.

Quite easy to rectify, just change the wires around on one of the subs

 

[clio_massive]

there is a wall in the middle mate

 

[Mole]

what amp u got running these then, coz u might be using an amp that just isnt capable of driving both of them, and hows it wired up, i.e in parrellel or on 2 channels if its a multi-channel amp.

 

[clio_massive]

i used my car amp which is a 520watt 4channel and was wired up one channel per sub, then i decided to try it on my home amp (1000watt power amp) still the same thing

 

[BRUN]

probably not enough power mate, 130W per channel, probably only about 60W RMS, if that, which isnt enough to power a sub really

can you bridge the amp ?

does it have a crossover/low pass filter on it ?........to run the subs you will need it otherwise it will sound rubbish

its funny you mention having one sub and it soundin less powerful now you added a 2nd one, i had the same at work with a customer and an SPLx 1000W amp, when we changed the amp it was fine, summat was up with the amp

this car amp you have, what brand is it, what model is it

 

[clio_massive]

its a shark amp from maplin, not all that



its got bridge would that improve it?

 

[BRUN]

yes it would

bridge the channels to make it a 2 channel and see how that is, should be a lot better

it should be printed onto the side of the amp how to wire it to bridge it, but it usually goes

+ Bridged -

+ - + -

 

[clio_massive]

cheers mate

 

[BRUN]

with yours being a 4 channel its probably very similar to this

+ Bridged - + Bridged -

+ - + - + - + -

 

[Mole]

shark is pretty much a budget name aswell, bit like SPLx so id say get yourself a more powerful amp.. your prolly running the amp to the max and its clipping, making it sound awful

 

[Djw John]

Quote: Originally posted by clio_massive on 19 August 2004

the thing is mate it sounded excellent when i only had 1 jbl sub in a single box, but now i have 2 of them it doesnt sound as good, sounds like they cancel each other out if u get what i mean

This usually means they are running in phase. Thats when one goes out and the other goes in so cancelling out the soundwaves. Make sure that the positive on both subs go to the positive on the amp and obviously sam ewith the negatives. Other than that then it would be power issues.

 

[Irfan]

IN PHASE is when both subs move in and out together at the same time, provided both the subs are mounted the same way ie magnets are in the box.

OUT OF PHASE is when one sub moves in, whilst the other moves out. this can cause cancelling. again, only applies when the subs are mounted the same. if one sub is mounted with the magnet in the box,a nd the other sub is mounted with the magnet out, then they need to be out of phase to make the woofers move in sync with each other.

 

[BRUN]

hes already said his box has got a divider in it so messing with the phase shouldnt be an issue, jus wire em up to the amp + to + and - to - like you normally would

 

[Dink]

the sound would still be messed up if it has a divide in the box and the speakers out of phase. because the speakers would be creating oppersite pressures inside the car

 

[Irfan]

yup, the sound pressure in the boot wouldnt change if they werent in phase. it would be like having infinite baffle (try running your subs with the boot open and youll get the idea)

 

[BRUN]

Quote: Originally posted by Dink16v on 20 August 2004

the sound would still be messed up if it has a divide in the box and the speakers out of phase. because the speakers would be creating oppersite pressures inside the car

true