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Thread ID: 78241	2007-04-09 01:57:00	Since were talking about audio...	pine-o-cleen (2955)	PC World Chat

Post ID	Timestamp	Content	User
539127	2007-04-10 01:31:00	Most sub amps I have seen have their own inbuilt low pass filter, switchable in or out. So they can be used a a full range amp or just a sub amp. But 200 watts of bass in a boot area would seriously upset the cones of 6x9's that also vented into the same area, as I noted above.	godfather (25)
539128	2007-04-10 03:58:00	you can't isolate the amps from a common 12v source short of useing seperate sources. however you can beef up the power useing caps. they store power and, unlike batteries, release full power very quickly. this fills in the voltage dip which then allows the amp to run at full power :) Yes, I am aware of those limitations tweak'e, but I was thinking more of the amateur installation that shares a common supply cable, possibly of inadequate gauge as well. When you get up to the kinds of peak current demanded by high power car audio, then cable or terminal resistance, or even inductive effects are going to limit peak curent capacity, so on a shared supply, any other amp is going to see a voltage dip just when it is looking for stability. I earned my wings in this area installing 25W radio telephones into 6 volt vehicles and boats, and 6 volt switch-mode supplies would simply die when you triggered the transmitter if there was not a super-low impedance/resistance path back to the battery. High powered audio follows similar principles and makes similar demands, and I do wonder about the efficacy of these 1 or 2 farad caps because although their ESR is very low, once they have dumped their stored energy into a transient request from the amp, they then have to replenish their charge, and surely that will put a corresponding transient load on the battery? It would be interesting to simultaneously log the voltage at the input to the amp and at the cap in real time along with the audio demand to see what the dynamic situation looked like. No doubt somebody has already done this though. Conversion to 24 volt would make things so much easier, but that has probably been done as well. Cheers Billy 8-{)	Billy T (70)
539129	2007-04-10 08:27:00	Could possibly be cheap or previously overdriven speakers, now suffering from cone break-up and consequent intermodulation between low and higher frequencies . However it actually sounds to me like you are trying to create a Mercedes by grafting a Honda Civic onto an aging Toyota ute . Each on its own is competent, if not exactly outstanding, but grafted together they are considerable less than the sum of their parts . That said, if you want your 6x9s to act as midrange speakers then yes, you would need to filter off the lows via a crossover network . Maybe you should back off the lows a little to give your 6x9's a chance . You may have a separate amp and low pass filter for the sub, but if the amp feeding the 6x9s is fed from the same preamp/equaliser then it will very likely be overdriving them . In my opinion they are probably just being swamped by the lows you are providing for your sub . So if this is the case, I will definitley need a mid range filter . Any idea where I would purchase one? Mobile music isn't supposed to lift your rear wheels off the ground or cause nosebleeds! Cheers Billy 8-{) Oh don't worry, I'm not into nosebleeds either . Also, if your sub is boot-mounted and the 6x9's also use the boot as a "cavity" (i . e . they are OEM recessed into the rear parcel shelf) the large amount of LF pressure from the boot mounted sub will seriously affect the cones of the 6x9's . Ok, sounds like I have a problem then, the 6x9's are mounted on a 'plank-o-wood' that is attached to the sub housing, that sits in the boot, with the 6x9's sitting just under the standard speaker grills . So yes they are in the same cavity . I did this to keep away any unwanted attention . what input and ouputs does the amp have ? The amp has 2x RCA and 4x screw terminal inputs, with 4x screw terminal speaker outputs . That's not the point . The key issue is the sound mix going to the amp that feeds the 6x9s . If you have a single graphic equaliser and you have optimised it for the level of bass you want out of the sub (I assume you want to let everybody within a radius of 250 metres know you have this huge power level available) then the balance to your midrange speakers is going to be wrong and they will be over-driven at low frequencies . The midrange speakers also need to be isolated electrically, signal wise, and acoustically from the sub . "Electrically" includes the source impedance of the 12 volt supply too . At 200 or so watts, the sub amp will be taking 15-20 amp "bites" out of the supply and if it is on a common 12 volt source then the midrange amp could be suffering severe voltage sag on every bass beat . That will knurgle your sound quality something terrible through common-mode coupling . Of course you may already have all this sussed out and the right cabling etc installed, but it is worth mentioning just in case . Cheers Billy 8-{) The amp and the head unit are on separately fused outputs, coming directly from the battery, is this what you mean? Thanks for all the replies guys, it's all valuable information that would be hard to get anywhere else!	pine-o-cleen (2955)
539130	2007-04-10 08:54:00	Unless the 6x9's are "sealed" at the top to the standard grill openings (air-tight) they are running unbaffled and will be nothing short of horrible. Unless you can stop the air movement from front to rear of the speaker, its efficiency will plummet and it will have unwanted resonance. Add that to the fact they are in the sub cavity and I am surprised you get anything acceptable from them. Whatever you do, do NOT "enlarge" the existing holes in the rear parcel shelf though, I know of one person that did so, the effect was to write off the car. The rear shelf is part of the structural car shell, cutting some away destroys the integrity and it failed a warrant. The cost of repairs far outweighed the car value.	godfather (25)
539131	2007-04-10 09:17:00	How do you hear "audio distortion" with 200W of subwoofer and multiple channels at 50W in the small volume of a car? People outside can probably see the car panels physically distorting. :groan:	Graham L (2)
539132	2007-04-10 09:24:00	easiest way to fix the 6x9 is to diconnect them. after they do nothing for good audio, they screw up the sound stage. run decent front speakers and forget the rears. the amp will only run the sub (i assume your running in bridge mode).	tweak'e (69)
539133	2007-04-10 09:34:00	Yes, I am aware of those limitations tweak'e, but I was thinking more of the amateur installation that shares a common supply cable, possibly of inadequate gauge as well . When you get up to the kinds of peak current demanded by high power car audio, then cable or terminal resistance, or even inductive effects are going to limit peak curent capacity, so on a shared supply, any other amp is going to see a voltage dip just when it is looking for stability . I earned my wings in this area installing 25W radio telephones into 6 volt vehicles and boats, and 6 volt switch-mode supplies would simply die when you triggered the transmitter if there was not a super-low impedance/resistance path back to the battery . High powered audio follows similar principles and makes similar demands, and I do wonder about the efficacy of these 1 or 2 farad caps because although their ESR is very low, once they have dumped their stored energy into a transient request from the amp, they then have to replenish their charge, and surely that will put a corresponding transient load on the battery? It would be interesting to simultaneously log the voltage at the input to the amp and at the cap in real time along with the audio demand to see what the dynamic situation looked like . No doubt somebody has already done this though . Conversion to 24 volt would make things so much easier, but that has probably been done as well . Cheers Billy 8-{) the caps help even out the flow . most amps run PWM power supplies anyway . but batteries don't output high amperage at 12v, they drop to 11v where they can supply huge amounts . batteries like to deliver constant power not dynamical . however its harder for the amps to work at 11v or less . no need for fancy logging, just put a meter across the battery and watch it read in time to the music :)	tweak'e (69)
539134	2007-04-10 09:43:00	The battery won't supply a lot of current for long. It will handle a few hundred amps for starting, but that's only for seconds. The alternator is what is supposed to supply heavy loads for any period. Most (with an output of 35A) would be struggling to supply a big ampolifier at night with lights on.	Graham L (2)
539135	2007-04-10 09:52:00	Unless the 6x9's are "sealed" at the top to the standard grill openings (air-tight) they are running unbaffled and will be nothing short of horrible . Unless you can stop the air movement from front to rear of the speaker, its efficiency will plummet and it will have unwanted resonance . Add that to the fact they are in the sub cavity and I am surprised you get anything acceptable from them . Whatever you do, do NOT "enlarge" the existing holes in the rear parcel shelf though, I know of one person that did so, the effect was to write off the car . The rear shelf is part of the structural car shell, cutting some away destroys the integrity and it failed a warrant . The cost of repairs far outweighed the car value . I should probably have mentioned that the sup is 'pressed' up against the rear seats, pretty tight . So it looks like I need to find a way to seal the 6x9's up to the grill . I don't think this is going to be easy . . .	pine-o-cleen (2955)
539136	2007-04-10 09:53:00	the actuall average current is not huge, battery will last quite some time on is own. its the large peak current on the bass notes that are the problem. battery and sometimes even the alternator can't supply the current fast enough.	tweak'e (69)
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