A different kind of perfomance mod

I've got an ex-police s70... do you know what alternator I will have?... I'm running a 800w(4x200) amp at the mo, but it's running too many speakers.... (front door and rear decks are running in parrallel, Sub bridged accross the other 2).... I want to get a new amp for the sub so I can put the fronts where the sub is now and get that on a seperate amp.....how much power can I get b4 i start to get problems? (Head unit for other speakers is 4x40w)

Reading this thread, I realise how bad my car system is!... I like my home system tho.

Andy.

[foggyjames]

>do you know what alternator I will have?...

It usually says on the plate on the alternator itself, but as a guide that guy who did the dubious rear blue light mod (keith?) had a 100A alternator, which he seemed to think was an uprated one.

>I'm running a 800w(4x200) amp at the mo, but
>it's running too many speakers.... (front door and rear
>decks are running in parrallel, Sub bridged accross the
>other 2)....

4x200w! thats a big mumma amp! and quite a rare combination. is that peak power or RMS. If its RMS it seems a bit odd for a 4ch amp, cos most people use those for their mains - and you dont need that much for those....or course you could drive 4 subs with 200w...or 2 with 400!

You may not being doing that at all - it all depends on the minimum impedance handling of the power amp. Most vaguely big car amps can handle 2ohm per channel - some can do 1ohm or less. In other words if your two pairs of speakers are 8ohm or 4ohm each, and they are in parallel, the amp will see 4 or 2 ohms respectively - which the amp will be only too happy with, provided that its cooled adequately. My apologies if this is obvious to you.

>I want to get a new amp for the sub so I can
>put the fronts where the sub is now and get that on a
>seperate amp.....how much power can I get b4 i start to get
>problems? (Head unit for other speakers is 4x40w)

As long as you HPF out the bass to the 4ch amp, you should be fine with that combination (as long as you dont go crazy with the bass amp!). From the point of view of power draw, car amps are actually pretty efficient (dont know the exact figure, but its much better than hifi stuff - no power supply section to rob power). Lets say you have 60A of that 100A available - thatll give you 40-50A to drive the sub amp (that should give you a 400-500w mono (or stereo bridged) amp, and 10-20A for the mains, which is all they will draw, even at crazy levels. This leaves plenty free for you rear screen demister, etc, etc.

My only feeling is that 200w on your mains is going to be a bit of a waste - 50w would be adequate, and 100w will take your ears. few mains can take more than 100wpc anyway (not that that is a big problem anyway). If I were you (and assuming that you are not too attached to the 4x200w amp, and that it is reasonably saleable), I would flog it, and buy either a 4x50 (or 4x100) for the tops and a ~500w amp for the sub, or alternatively a 5ch amp, which will have four lower power channels (50-100w) and one big one (300-600) for the sub, all with the appropriate filtering.

I cannot stress highly enough though, how important it is to take the bass off your mains if you have a sub - I cannot count the number of blown speakers I have been called to look at, and its because the bass boost has been applied (globally) at the head unit, rather than on the sub amp, so those little 4" door speakers have been wetting themselves trying to produce huge levels of those bootlid shaking frequencies. Again, apologies if you are familiar with this.

Anyway, to summarise, you should be fine for power (unless you go crazy!), and unless you want control of front/back balance, you probably dont need to alter a thing.

cheers

james

Thanks for all the info....
The amp is peak... and it can take 2 ohms... (I think it's rating is for 2 ohm... cheap amp u see).. and I have 2 fans (badly) placed next to it to keep it cool.

The reason I wanted to split into different channels was mainly so I could introduce filters etc....
I have put kenwood speakers in the mains (16cm front, 17cm rear) which are all rated at 200w... but I think I am getting too much bass for the ones in the doors... the amp has a built in HPF for the sub, but no LPF... but if I put an LPF on all my mains will I loose out on upperbass that the sub isn't good at, but my rears are?

it's loud as it is... but not offensively so...I'm sure the 100w amp I put in my old fiesta seemed louder...I just now want a bit of clarity at volume too!

oh.... you'd probably know this....
Which is better for a sub... Sealed Box, Ported Box or Tube?

[pettaw]

Just my two pennurth, and perhaps a stupid question, but are you sure that your sub is in phase with your mains, and are the mains in phase with each other, ie are the fronts in phase with the rears etc. If they're not, you'll get a weak lumpy bass and you'll be cranking up the bass to try and compensate. Check by throwing your sub in and out and checking if the bass feels 'tighter' with the sub in or not, if it feels tighter with the sub out than in then the sub is out of phase, rectify by swapping round + and - line level inputs for the sub, or perhaps you have a phase control on the head unit.

This is where James and I start to disagree. I don't like Low pass filters. I believe that you should run full range to your speakers and then simply supplement the depth and extension of the bass with the sub. 200W should be plenty of power, even if it is peak, I think that works out at about 75-100W RMS so thats loads of power. You are right, I believe, in that you may well lose the upper parts of the bass that the sub may not handle well.

I would set all of the EQ controls neutral first without the sub, then don't touch them again, and just adjust the power of the sub to extend the bass depth, setting the filter to roughly where you think the main speakers are starting to drop out.

If you do find that the mains can't handle the full range output, you will have to filter them with a low pass filter. The problem is that subs can quite often sound boomy because they put out too much upper bass and the way round this is to set your high pass filter low, to about 60 Hz. Of course this won't work if you want to run a sub-sat system, 'cos you'll be setting your crossover point from sub to sat at about 120 Hz and to do that the sub has to work well at those frequencies. A poor handling sub can't be cancelled out by any amount of EQ, in fact it'll just make matters worse.

IMHO a good sealed box seems to offer better sounds for the money, because the porting has to be done properly for it to work.

Hope that helps a bit. Different guys may have different opinions LOL

Andy

When I wired it I just made sure + went with + etc ... i tried different postions for my sub (10" tube) but never tried it in the other phase... might go out and try it in a min...
I went very much for cheap stuff, so neither head unit nor amp have phase adjustments and the amp just has "Subwoofer On/Off" as it's HPF!

I think I agree with you that Sub should be there for additional depth, but I think i need to take a little bass from the mains... They usually sound fine until vocals come in along with bass which is when it struggles (they are 3 way speakers too)

IIRC i should be able to put a capacitor across/inline with the inputs of the speakers to filter sub from the mains.... anyone know what range of values will filter what?

Andy.

Just checked phases... and it's defo better as it was!

Are you there at the do tommorrow?

Andy.
Ps. a15htn ... sorry for trying to steal your thread! :p

[foggyjames]

>This is where James and I start to disagree. I don't like
>Low pass filters. I believe that you should run full range
>to your speakers and then simply supplement the depth and
>extension of the bass with the sub.

Time to fess up....I am doing exactly this (full range to mains, boost on sub), as I have found that the mains are so gutless if the EQ is set flat that theres virtually no bass coming from / going to them anyway!

I am coming at this from a pro-audio point of view, where you just dont have the power / cone displacement spare to do this. Same with PA subs - you *have* to cut the bass out at the bottom end (20-40hz) or you will waste power and blow cones like crazy!

The only sound quality query I can make re: filtering bass on tops is that if a cone is pounding away, it can introduce severe phase anomolies upon any higher frequencies it is producing (it obviously affects all frequencies, but sounds worst around 1k-3k

The cones are unlikely to be moving enough to cause these problems anyway.

>The problem is that subs can quite often sound boomy because
>they put out too much upper bass and the way round this is
>to set your high pass filter low, to about 60 Hz
>A poor handling sub can't be cancelled
>out by any amount of EQ, in fact it'll just make matters
>worse.

Certainly agree about the boomy midbass (60-150hz ish) of these smaller cones. The trick is to get them boosted at around 40hz, then gradually 'slope' them out above 50 or 60hz ish. Bear in mind this is supposed to be SUB-bass - most people run their subs out of their operational frequency area.

And an EQ is there to straighten out acoustic anomolies, not bad components, so agreed again :)

>IMHO a good sealed box seems to offer better sounds for the
>money, because the porting has to be done properly for it to
>work.

Agreed. Ported boxes are largely pointless, because the 'cabin effect' of the car (that is a recognised acoustic phenomenon BTW) gives huge gain to lower frequencies (below 50hz). In other words, a sealed box will not be significantly quieter, and will give a tighter sound.

cheers

james

[foggyjames]

Just a thought having re-read your posting...

If the mains are struggling to produce + vocals then too much bass is going to the mains. Ways to sort this:

1) Dont boost bass on HU - do it on amp via volume control + LPF, or via bass boost ON AMP if it has one. This just boosts bass to the sub, not to all yer speakers, which is a bit pointless since the sub is there to take the bass load off your mains

2) are they 6x9s on the parcel shelf with the sub in the boot? if so, box off the bottoms of the 6x9s, as the air pressure coming out of the sub has been known to pop 6x9 cones right out :) this forced displacement will result in horrible horrible sound!

3) use HPFs on the mains, but this shouldnt really be neccessary.

cheers

james

ps: i have literally 30 mins ago put one of my 2x10" pa cabs in the boot. hence the size of my grin!

[pettaw]

Nice one, try not to annoy the neighbours LOL. As for the phasing at least you know that you're in the correct phase so we've elimnated one problem.

Are you boosting bass on your HU. Don't use the EQ controls at all on the HU. Set them absolutely neutral, then crank up the bass on the sub amp control.

Agreed with James that in a PA environment where there's lots of power around, it's better to filter off the bass to the subs, and, frankly but no offence meant, people aren't that bothered with quality and smoothness of crossover points etc. they just want it LOUD LOUD LOUD.

Good luck and happy fiddling!!

Andy