sub conundrum

[Johny]

Found out the other day that the left sub isnt running at the same rate as the right one.

Then found that if i disconnect one sub both of them keep going... and theres no noticeable sound difference, so concluded that maybe theyre bridged in the box.

Just took one sub out now to notice that theyre running completely seperately...

So what the flying follocks is going on? :speechles

[Turbo_Steve]

One may be out of phase - cancelling out the other.
The other possibility is that one of them is simply blown.

[Fully]

Come around Johny I will have a look at for you?

[dickytim]

One may be out of phase - cancelling out the other.
The other possibility is that one of them is simply blown.


I second this opinion.

The sub that is not running correctly could in fact not be running at all and the movement you see is caused by the working sub.

I am guessing that they are in the same space, i.e. not seperated from each other inside the box?

[Johny]

yeah its just a dual sub box

my other problem is while playing around with it today i migrated it from two channels to 4 then put the my boschmann gigas in and now its stuck in protection mode :|

hense why im seling them i dont think my amp likes those speakers lol

[dickytim]

have you bridged the amp ?

it is unlikely the amp "doesn't like" the speakers, it is more likely you have bridged the amp at a lower impedance.

alot of amps will allow you to bridge but if you bridge down to 2ohm then you will get the case you have here.

I am a little out of touch with the whole audio thing as it has been a few years but I will try to explain.

Bridging an amp is where you take the positive out of one chanel and the negative out of the other. This gives you a combined out put, for example if the amp was 200WRMS per chanel and you bridged 2 chanels then you would have 350WRMS for the one chanel, not exact but there is usually a bit of loss there. The down side is that the amp will get hotter when you are doing this.


When you run an amp at a lower impedance you generally have two speakers (subs) running off one chanel, this doesn't halve the power to each speaker but you get 180% of the power so approx 90% of the rated power to each speaker.

These figures are as an example only, some amps are more efficient others less.

Anyway when you push more power, i.e. current thru an amp it gets hotter.

Some amps allow bridging and others take lower loads, more expensive ones can do both at the same time, but it is generally not a good idea to do this as you are essentially overloading the amp all the time, those that have protection cuiruts will often go into protection mode.

So to test what you amp is doing you could,

first connect one sub up to a single channel unbridged, if the amp goes into protection mode then either your sub is faulty or the amp is.

If it works well, bridge the chanel then see if it still goes, if it does the problem is the amp doesn't like being bridged, if it still works then the problem was the amp being bridged and running at too low impedance.

I hope this helps, otherwise have a look at www.nzicemag.co.nz and search some of their tech articles, forums or sign up and ask the question

[Johny]

the amp is a 150wx4 and up until yesterday it was running both bridged absolutely fine (other than that weird sub issue)

yesterday i put it back into 4 channel mode with the subs on channel b and the speakers on channel a and it all worked for about 5 mins

Actually hmm maybe that means my amp is now broken :(

[dickytim]

it may sound weird but you could change the sub and speakers around, have the sub bridged on chanel a and the speakers on chanel b.

but it does potentially sound like there could be an amp issue or one of the speakers could have a problem, if one of the speakers has blown.

Best way to see is to change the speakers around detaching one at a time until the amp works correctly, you will then have narrowed down which speaker it is.

[Johny]

i took all the speakers out and had the same then now moved it back to how it was when it was working and now its still in protection mode and both subs are making annoying systematic thumps lol

[Turbo_Steve]

Your amp is going DC. At some point it's overloaded and is now gradually failing: the thumps will be killing your speakers and will burn them out quickly: DC offsets are not good!

Time for a new amp IMO.

[Johny]

yeah have checked all the connections and theyre fine and unplugged the rca's and wound down the levels to zero and still the same so guess its time for it to come out :( lol

[Turbo_Steve]

I'd suggest you invest in a small amp to drive the cabin speakers, and a dedicated one to drive the subs. Sound quality throughout will be improved, and a decent D-Class Monoblock will make your subs pound like an integrated amp never would. I'd actually venture to say that if you're using a four channel amp, there is little or no point in having two subs, as it isn't powerful enough to run a single cone properly.

A good monoblock will allow you to run both subs in 2ohm configuration and with decent output levels with no distortion, clipping or switching.
You will be astounded by how powerful your subs really are on a decent amp.

A good quality amplifier running the cabin speakers from it's own power supply will sound cleaner and distort less, as well, as it won't be suffering from every bass note.

[Fully]

4 channel amp could be used to power front splits and then bridged to the sub.
The thing to note is the 'impedence' (ohm) required for best power to run the subs. when bridging channels, unless the amp is very high quality, it will operate best running a 4ohm sub. when running at 4ohm bridged, each channel actually operates at 2ohm, 'sharing' the 4ohm load.

[Johny]

i have no idea how you even change the ohmage
i just originally had the amp bridged and each bridged channel running each sub
then before it broke i had it not bridged and running straight to each speaker and sub so i dont see how couldve changed the ohms?

[Roberto]

Are you running the subs in Parallel or series?

You need to be running them in Parallel to be running in 2ohm bridged mode.

If you have them in series, they are a combined 8ohms, which would not be good for the amp.

[Johny]

:speechles

[Roberto]

Do you have both " - " connected together at the amp and both " + " connected together at the amp.
Thats parallel, the way it should be.
If you have them mixed up or different, bridged mode will not work right for 2ohm mode.

Hope that makes a bit more sense.

[Johny]

the + are going to the plus and the - are to the negative:S

[Johny]

with the original conundrum could it just of been because my headunit only has one pre out and ive got the splitters set up so that the left channel is going into one sub and the right channel going into the other?

[Roberto]

Your starting to confuse me now.

If your head unit only has one RCA output, is that a dedicated one just for the Subs.
Which would make sense. And the way I have seen most headunits.

You would normally see 3 RCA outputs if it was designed to be used to drive Full range speakers (front and rear fill)

If so you will not be able to run the front speakers through that amp, using the RCA inputs.

If thats the case and you want to Amp the Fronts and rears.

The way I would go is, use the amp you have for both Fronts and rears, driven by the speaker outputs from the head unit.
And get a Sub Amp that can run 2ohms and use the RCA output to drive it and wire both subs in parallel.

[dickytim]

the + are going to the plus and the - are to the negative:S


If these photos are how you are running your subs this should be fine as it is only brighed and as long as your subs are 4ohm then it should be OK.

However, if this is one sub and your fronts then this could be the problem.

or even worse 2 subs and the 2 fronts this would explain you issue.

Is the amp very old, i.e. under warranty ?

[dickytim]

Actually have you disconnected all the speakers and checked if the amp is still in protection mode, you will have to disconnect all power usually to reset it.

This will tell you straight away if it is major problem with the amp.

Then all you have to do is connect a speaker until it returns to protection mode, this will tell you which chanel is fried if it is a single chanel.

[dickytim]

when running at 4ohm bridged, each channel actually operates at 2ohm, 'sharing' the 4ohm load.

This is a common misconseption, it is still running at 4ohms but sharing the power from both chanels.

[dickytim]

with the original conundrum could it just of been because my headunit only has one pre out and ive got the splitters set up so that the left channel is going into one sub and the right channel going into the other?

I would only expect this if you have the head unit only running to the left channel, i.e. using the fader.

Splitting the RCA's should not cause any real issues, my first sound off I was running my head unit this way splitting it 3 yeas for front, rears and 4 subs.

It would pay to check if your pre-outs are designated sub or just pre-out, however this shouldn't cause the issue you are having.

[Johny]

today removed all speaker cable and disconnected all power then put the power back in and still in protection... so i geuss its out with it lol

[Turbo_Steve]

they are a combined 8ohms, which would not be good for the amp.

Actually, an 8ohm load should be very easy to drive. It'll be extremely quiet, as the amp will effectively be running at half it's output, but the amp should be able to do this all day long without even getting warm: very inefficient, but shouldn't be a problem.



As already mentioned, I'd take your single RCA feed and splits, and feed a dedicated amp for the cabin speakers, and a monster monoblock for your subs.
With a proper pair of amps in there, you'll be astonished at the clarity you get from your cabin speakers, and the sheer depth and power of bass you'll get from your subs on a proper amplifier is likely to make your jaw drop (and, if the speaker box is any good, make your hair stand on end and potential difficulties breathing :D )

[Johny]

have sold off my giga's my other 6c9s and such now and brought some 6c9s till i can afford some decent ampage lol (could be a while...)