Using car speakers in a cab

[JoeB]

Folks, all of you seem to forget one important thing..

PSU from PC are 12V.. PS in car when car is running is really closer to 14V!!! It's only when the car is off, is it even near to 12V!!

If you guys want to do it right, your best bet is to go to a local pawn shop or thrifty store (or flea market) and get a 12V Power supply!

I found mine at a local pawn shop, and paid 30$CDN for it (which is less than 20$US) and I got a PSU that supplies 13.8V constant 10AMPS (or 12AMP peak).  That translates to about 138W RMS!!! (Which is probably close to 300W peak).  And all this for less than the cost of any decent PC PSU!  (not to mention that any decent 12V PSU will come with build in thermal protection, build in voltage cutoff/spike protection, etc.. goodies that a regular PC PSU will not have!)

LK

[Tehrasha]

Folks, all of you seem to forget one important thing..

Nothing been forgotten.  Math for current and wattage remains the same.

If you guys want to do it right, your best bet is to go to a local pawn shop or thrifty store (or flea market) and get a 12V Power supply!

Your risk of 50/60 Hz hum increases greatly when using generic 'power supplies' as car amplifiers have no built-in filtering for powerline freqs.

I found mine at a local pawn shop, and paid 30$CDN for it (which is less than 20$US) and I got a PSU that supplies 13.8V constant 10AMPS (or 12AMP peak).  That translates to about 138W RMS!!! (Which is probably close to 300W peak).  And all this for less than the cost of any decent PC PSU!  (not to mention that any decent 12V PSU will come with build in thermal protection, build in voltage cutoff/spike protection, etc.. goodies that a regular PC PSU will not have!)

13.8V at 10A is 138 Watts..period.  RMS has nothing to do with DC voltage/current/power measurements.
Peak of 15A would bump you up to 207 Watts.  Figure in a generous 60% efficency for the amplifier and divide for 2 channels of audio.
Maximum peak output 62 Watts/channel.  41 Watts/channel nominal.

As for voltage regulation and shutdown safety, yes computer PS have these as well, in fact the voltage regulation is most likely far superior to generic 12v power supplies.
They have to be.  Your computer is alot pickier about its voltage levels than an audio amplifier is.  A car amplifier will chug right along even if the supply voltage dips to 6 Volts (albeit quieter and less efficient).  Try that with your computer sometime and see what it does.

[Silverwind]

Folks, all of you seem to forget one important thing..

PSU from PC are 12V.. PS in car when car is running is really closer to 14V!!! It's only when the car is off, is it even near to 12V!!

If you guys want to do it right, your best bet is to go to a local pawn shop or thrifty store (or flea market) and get a 12V Power supply!

I found mine at a local pawn shop, and paid 30$CDN for it (which is less than 20$US) and I got a PSU that supplies 13.8V constant 10AMPS (or 12AMP peak).  That translates to about 138W RMS!!! (Which is probably close to 300W peak).  And all this for less than the cost of any decent PC PSU!  (not to mention that any decent 12V PSU will come with build in thermal protection, build in voltage cutoff/spike protection, etc.. goodies that a regular PC PSU will not have!)

LK

not forgetting at all

If you run your car stereo with the engine off it's approximatly 12.9 volts..
with it on.. it's usually between 13.8 and 14.4 volts...  

but you try to use what you have available.. if you have a free computer PSU handy.. you would use that.. not as much voltage as you would like maybe.. but hey it's the free method..

I also agree that PC power supplies typically have higher standards applied to them..  it's a must when dealing with sensitive electronics..  

[AlanS17]

I've had plenty of problems with unshielded speaker magnets. I personally think a good set of computer speakers is ideal. Nobody is gonna see them anyways. They'll never know.

[Carsten Carlos]

Your risk of 50/60 Hz hum increases greatly when using generic 'power supplies' as car amplifiers have no built-in filtering for powerline freqs.

A big condensator between + and - of the powersupply should help.
Anyway, I'll know more the next days, when I connect my speakers!

[Dr. J]

I've had plenty of problems with unshielded speaker magnets. I personally think a good set of computer speakers is ideal. Nobody is gonna see them anyways. They'll never know.

Not unless you want them too  

BTW,  I haven't had any problems with the magnets.  I just kept them away from the PC and the monitor.

[JoeB]

But what about the fact that almost all power supplies for PC's out there are SWITCHING power supplies? (hence can't really supply the rated wattage at a constant rate for a long period of time)

e.g. saying one has a 300W power supply might in reallity have only a 150-200W constant PSU.  To top it off, since it is 12V (and not 14 like a real power supply, which by the way, my 30$CDN got me a brand name) will require a higher current to hit the same wattage as a real 14v psu!  GET IT? You might think your pushing a certain current, but in reality, require a lot higher current to get the same wattage.. a higher current which might damage the car amp!

To top it off, I've never seen a PC power supply that monitors its own temperature, and resets itself during spikes and what not...

Sure, some people would go with a PC because they have it around, but in no means is it close to being the best thing (nor the cheapest!)  Heck, look at eBay.. if you're in the US, you can get some really sweet deals on very good PSU's for dirt cheap!

And for those of you with really big amps, that want to push 2 speakers and a couple of car subs.. a dedicated PSU (non-PC) is your *ONLY* choice.. so why not make it right from the start???

LK

[Tehrasha]

But what about the fact that almost all power supplies for PC's out there are SWITCHING power supplies? (hence can't really supply the rated wattage at a constant rate for a long period of time)

e.g. saying one has a 300W power supply might in reallity have only a 150-200W constant PSU.

There is no almost about it.  All PC PSUs are switching types.
A 300 Watt powersupply is 300Watts but that is across all of voltages. +12 and +5
So yes, a 300 Watt supply may only put out 200 Watts to its 12v side.  And unless you are playing a 1KHz tone at full volume, you arent going to be pulling those kinds of current levels for more than a couple hundreths of a second anyway.

A math lesson and a dirty little secret about car amplifiers.

12v (car battery)... ok, for argument, ill use 14v.
14 volts from the car connected raw to an 4 ohm speaker will draw 3.5 Amps.
14 volts at 3.5 Amps is 49 Watts.  So how do car amplifers manage to crank out things like 100, 200, 500 even 1000 Watts per channel???  

Each one has a switching powersupply inside it, bringing the 12..er 14 Volts up to whatever it needs.

To top it off, since it is 12V (and not 14 like a real power supply, which by the way, my 30$CDN got me a brand name) will require a higher current to hit the same wattage as a real 14v psu!  GET IT?

I got it from the beginning, what is your problem?  You seem to be obsessed with WATTAGE and loudness.  Yes, my setup under an ideal power situation should be capable of 80W/channel into the main speakers and 150W/channel into the subwoofers.  But I value my hearing to much to want to stand 12" from that while playing games.

You might think your pushing a certain current, but in reality, require a lot higher current to get the same wattage.. a higher current which might damage the car amp!

Current is the limiting factor for the PSU.  The car amplifier cannot suck more (possibly damaging) current out of a supply than the supply can provide.

Reasonable listening volume will never come close to that kind of level, let alone the rating of the car amplifier or PSU.

To top it off, I've never seen a PC power supply that monitors its own temperature, and resets itself during spikes and what not...

Odd, we just had a posting from a fellow whose PSU cut him off at high output levels.  By the very nature of switching supplies, spikes have little effect on output.

Sure, some people would go with a PC because they have it around, but in no means is it close to being the best thing (nor the cheapest!)  Heck, look at eBay.. if you're in the US, you can get some really sweet deals on very good PSU's for dirt cheap!

Last I knew 'free' was cheaper than $anything.  As for the 'best thing', I dont think anyone in this thread has said that PSUs were a best choice. They were simply one solution to a question.  They have their problems, as do standard 'real' power supplies.

And for those of you with really big amps, that want to push 2 speakers and a couple of car subs.. a dedicated PSU (non-PC) is your *ONLY* choice.. so why not make it right from the start???

Why mess with powersupplies and amps?  For that kind of volume and power output the best choice would be a home stereo rig.

As with most ppl building cabinets, we deal with what we have available.
And custom, kludged, hacked, slashed, mangled, spindled, and dare I say 'unique' solutions are par for the course.

--Teh

Tune in next week when I tell about the switching supplies inside the cockpit displays that I repair for a living.  (and I dont mean arcade cockpits)

[Dr. J]

As with most ppl building cabinets, we deal with what we have available.
And custom, kludged, hacked, slashed, mangled, spindled, and dare I say 'unique' solutions are par for the course.

Amen to that.  I didn't have a clue how to "professionally" do any of this stuff.  I just rigged up the best I knew how with some help from friends and here.