no bass from rear left speaker - run out of ideas!

[geoff46]

I've just upgraded the rear speakers and on testing I noticed that there was significantly less bass coming from the rear left speaker. I established this by shifting the front / rear balance to the rear, and then changing the left / right balance. There was a major difference between the 2 rear speakers.

I checked that the polarity was correct, then I swapped the L and R speaker connections at the head unit and the problem remained with the rear left. I then put the old speakers back in and the problem was the same. This problem may well have been present all the time as I have never tested the speakers individually.

This led me to think that there must be a problem with the wiring running to the rear left speaker so I tested the speaker terminals with a volt meter. The rear left showed about 0.02 V compared to 0.1 on the rear right. I disconnected and reconnected all the connectors at the head and speaker but still the same problem.

I guess this means the problem must be in the wiring running to the back of the van. Does anyone know if there is a particular culprit I should check out? I've read about problems with the wiring running to the speakers in the front doors but I'm assuming that the rear speakers wouldn't follow that path. I can't find route of the speaker wires to the rear.

Or is there another explanation? I've had a search on the forum but can't find anything.

Any advice would be greatly appreciated!

Thanks.

[Dodgey]

Have you swapped the two rear speakers over? The new ones? That would prove immediatelyif it is the speaker or not. Actually, scartch that, you tried the old speaker and it was also lacking in bass .

The only thing it can be is one of two things.

A) the left speaker is mounted in a way that is significantly less "sealed" than the right one. This would cause a drop in bass.

B) actually, im just not sure.

To eliminate a mounting issue, look at both speakers. If they appear to move about the same amount then it is a mounting issue.

[geoff46]

I didn't swap the two new ones over, but I did put the old one back in and there was the same problem.

[Dodgey]

I updated my reply above.

[turbodave]

Hi, sounds like a dodgy wire.....the signal is weaker going to the one side which suggests a flaw in the lead or connector at the device going to that side. you could remove the system, check connectors and if still unsure form a temporary connection from device to speaker and see if this improves matters. Dave

[geoff46]

Thanks.

I took both side panels out to fit the speakers and haven't put them back yet. The speakers are just in their mounting brackets, so I think they are both equally unsealed. I understand that until the panels are fully refitted I wont get the full bass, but I thought they should sound similar?

[geoff46]

Hi, sounds like a dodgy wire.....the signal is weaker going to the one side which suggests a flaw in the lead or connector at the device going to that side. you could remove the system, check connectors and if still unsure form a temporary connection from device to speaker and see if this improves matters. Dave

Good call! I'll run a cable straight from the head to the speaker and see what happens. Seems obvious now

[Jaws]

Also worth checking that the polarity is correct i.e. that all speakers are connected in the same way.

If the connections are swapped then the speaker will be out of phase and might cause this problem?

[321Away]

Also worth checking that the polarity is correct i.e. that all speakers are connected in the same way.

If the connections are swapped then the speaker will be out of phase and might cause this problem?

If the speaker is connected round the wrong way, it will only produce mid/high range sounds, it wont produce bass as it'll push when it should pull

Julian

[fatcatlawyer]

Could the settings on the Radio player have been altere3d by "little fingers". I found that my left rear speaker was not working and on investigation realised that my grandson had "played" with the settings.
Ian G

[haydn callow]

Could the settings on the Radio player have been altere3d by "little fingers". I found that my left rear speaker was not working and on investigation realised that my grandson had "played" with the settings.
Ian G

That's right..."Blame the kid"

[Simon Jones]

Also worth checking that the polarity is correct i.e. that all speakers are connected in the same way.

If the connections are swapped then the speaker will be out of phase and might cause this problem?

If the speaker is connected round the wrong way, it will only produce mid/high range sounds, it wont produce bass as it'll push when it should pull

Julian

True, when both rear speakers are in use as one will be moving outwards, while the opposite one moves inwards. This is how noise-cancelling technology works by emitting a sound wave that is opposite to the one being supressed. However, as soon as one speaker is disconnected, or the balance turned to just give a single channel output, then the problem will disappear. So, try just running the balance set to the 'good' side and then turn it the other way to the 'bad' side: if they sound the same on their own, then you can rule out phasing.

[geoff46]

Thanks for all the suggestions everyone.

I tried running a temporary cable from the head to the rear left - same prob.
I ran the temp cable (still from the rear left output on the head) to the rear right speaker - all ok. So head, temp cable and rear right speaker all ok.
Moved the rear right speaker to the rear left position with the same temp cable and same output - no bass! (am testing by moving the front / rear to rear, then switching between left and right)
Swapped polarity just in case and no difference

So as far as I can tell the only other variable is the speaker mount. The rear right is more enclosed than the rear left - the panel that accommodates the diesel filler pipe boxes the speaker in a bit. Is it possible that this is enough to generate more bass from rear right than from the rear left?

Have put the panels back in now so will see how I get on with it. Sounds better than with the old speakers so haven't wasted my time, but its going to bug me knowing that it isn't quite right!

[Dodgey]

Your testing has proven that it must be an acoustic problem, not electrical. Goes back to my original post - and yes, the enviroment in which a speaker is mounted makes a huge difference to bass production. Put it this way - speaker in no box - no bass. Speaker in sealed box = good bass. So there is a lot in between to consider.

[Jaws]

I would agree this could be an acoustic problem but would not agree that a sealed box is the only way to get good bass There are plenty of excellent open port bass units which use both forward and backward motion of the speaker cone to produce bass for instance. A sealed box (infinite baffle) design does not and cannot easily be placed around the existing speaker mounts.

However the speakers in the rear of a Bongo are mounted with the back face directed pretty much directly at a good sound reflector i.e. sheet steel. If the distance between speaker cone and side wall are there or there about then the reflected rear sound wave will cancel out the front. This might be the case for your rear right speaker. If you you have not put any acoustic dampening foam behind the speakers, try doing so. You might be surprised

PS any dense foam will do and one inch or more is preferable.