how do you measure the stereo output?

[_N_]

how do you measure the stereo output

OK, I got me a good multimeter, 40$ from Jaycar, has a temp probe which is really good,

Anyway, I saw a pair of Sony 4" 80W Dual Cone speakers at 60$ for a pair, and that got me thinking. Cause my current speakers in my car are full of distortion at more than half the volume (they are like 6W) so I wan't get something better. They have to be 4" cause I don't wanna do any big mod's to my car to fit the speakers in.

If I was to get some better speakers, I wanna know what's the output on my car radio. I was thinking of turning the radio right up, without the speakers and measuring the V and I and getting P from it. But then I thought to myself, there is something wrong with this. So how would I got about measuring the Power output? That way I can know what speakers to get and if I need amps etc.

And I can't find the power output written anywhere on the stereo.

[_N_]

come to think of it (after a couple of minutes),
doesn't the speaker have a certain R
and then i can just measure the V and get the power supplied to it??

[Solid Snake]

Yup, I am pretty certain that most car stereo speakers are set at 4 ohms. Some go as high as 8 ohms...

[_N_]

yep It's 4 ohms,

but, when I measure the V accross the speaker it was 0, but I think I did it right, I measured in parallel across the terminals,

with no speaker it was doing about 0.5V at max,

How big can the current get? don't wanna fry my multimeter.

Also, what are some good 4" speakers around? I'm looking at the 50-60$ a pair type,

are these any good?

sony xs f1022
60$ repco

Coaxial 2 way
Woofer 10cm, polypropylene cone type
Tweeter 2.5cm,
PEI balance dome type
Max input 80W
Rated input 25W
Impedance 4ohms
sensitivity 88dB/W/m
Frequency response: 45-22000HZ


4" 150W 2-Way Speaker Pair
"Green Devil" Performance Series
50$ http://www.cheapcarspeakers.com/4040b.shtml

Hybrid Polymer cone
100mm Woofer
25mm Tweeter
Peak output power: 150W
Continuous output power: 120W
Normal output power: 60W
Frequency response: 60Hz-19kHz
4 Ohm

[mird-OC]

you need a test tone such as a sine wave to measure the power output... but chances are if the headunit is reasonably new (i.e. less than 7 years old) the power output would be around 5W RMS, plus or minus 3W RMS.

the xplods will probably do you fine, but you'd benefit from hooking up a capacitor inline to your speakers to create a high pass filter. those 4 inch speakers just can't deal with bass, and most music these days is full of it.

[_N_]

sweet, well, as for bass, In the long run, I might get a sub and amp, also I'm not going for some really loud hardcore expensive sound system, just a resonable quality so I can listen to something on the way to and from UNI which is about an hour a day.

[dustyslapper]

A most aftermarket CD headunits put out around 4 * 25W.

[mird-OC]

Originally posted by dustyslapper
A most aftermarket CD headunits put out around 4 * 25W.
25W what? not RMS i can tell you :)

[dustyslapper]

Sorry - that should be 45W RMS

[2 much thinking]

the 45w is rated max music power, not rms, so it is not a true indictation. this is because companies test their speakers and amplifiers under different conditions-load, power source, and at different frequencys. hence the different ratio of max to normal power between the green devils and sonys

i wouldn't hook up the capacitor to the speaker as it would sound crap. your better to leave it and just turn the bass on the headunit down a bit

what headunit do you have?

[mird-OC]

Originally posted by 2 much thinking
i wouldn't hook up the capacitor to the speaker as it would sound crap. your better to leave it and just turn the bass on the headunit down a bit
yer wot? putting a capacitor inline to the speaker will have the same effect as turning the bass down on the headunit, except when it comes time to add in some bass the 4inches will be able to handle the full signal.

[fatsanchez]

just be careful you dont underpower the sony's with the ****ty amp in the headunit, the distortion as the amp strains away will kill them pretty quick

[2 much thinking]

Originally posted by mird-OC

yer wot? putting a capacitor inline to the speaker will have the same effect as turning the bass down on the headunit, except when it comes time to add in some bass the 4inches will be able to handle the full signal.

well if u want a 4" tweeter go for it:)

[mird-OC]

Originally posted by 2 much thinking


well if u want a 4" tweeter go for it:)
dude, it only need be a 100-120 Hz cross-over point... i.e. the frequencies 4" speakers are no good at reproducing. if it's not distorting trying to reproduce bass frequencies it'll sound a lot nicer doing what it does well.

[_N_]

well, I was talking to my friend and told him about getting the speakers, and then he offered me his two old 150W subs for 20$ for the pair, I bought it before he could change his mind,
pluged them in without an amp and they sound ok, so I'm off to make an amp. I think buying one of those kit's is that best way to go?
unless someone has a cheap amp around?
so I've put off the speakers for a while, I wanna get the subs finsihed first,

[2 much thinking]

Originally posted by mird-OC

dude, it only need be a 100-120 Hz cross-over point... i.e. the frequencies 4" speakers are no good at reproducing. if it's not distorting trying to reproduce bass frequencies it'll sound a lot nicer doing what it does well.

what capacitor rating would u use for filtering sub 120Hz?

I spent a bit more money on descent speakers cause i hate distortion (besides my guitar amp:D )

[2 much thinking]

Originally posted by _N_
well, I was talking to my friend and told him about getting the speakers, and then he offered me his two old 150W subs for 20$ for the pair, I bought it before he could change his mind,
pluged them in without an amp and they sound ok, so I'm off to make an amp. I think buying one of those kit's is that best way to go?
unless someone has a cheap amp around?
so I've put off the speakers for a while, I wanna get the subs finsihed first,

what size subs are they?

D.I.Y amps are ok but your better looking for one in a second hand paper whatever its called in Auckland

[shag]

Errr... trying to remember stuff from about 7 yr's ago here...

isn't the impeadance (restistance) for a capacitor got by this formula? z = 1/ 2*pi*f*C

I think thats it. So if u can get it to give around 4 ohms @ that frequency of 100 hz then that should do the job. I think :-)

I can't find my old text books and I have to go back to work so someone else will have to look this up for me to make sure I got that right. :rolleyes:

Oh, and make sure u get a non polarised capacitor.

[mird-OC]

thanks to the almighty google:

Speaker Crossover Chart and Capacitance vs. Frequency Calculator(High-pass) (http://xsspl.tripod.com/Audio/1HiChart.htm)

and for all sort of info about crossovers:

www.the12volt.com - Car Audio - Passive Crossovers (http://www.the12volt.com/caraudio/cross.asp)

so 120Hz for a 4ohm speaker = 330 microfarads. although since the slope is pretty shallow (6db/octave), you could probably go up to 150Hz (265mF).

[_N_]

k, well anyway,
the two subs which cost me 20$ for both are:
8" 4ohm, 150W, First Choice brand, yes I know, not too great, but hey, this is my first project and I wanna learn from the mistakes on this before getting anything better.

so, anyway, wen't into Jaycar, got me a 50W amp kit for 30$, the guy also gave me the catalouge and the CD for free, plus I learnt heaps, can't compare it to DSE, :D :D :D

I'll have to make up a 36V PSU, my friends got some coils and I'll manage it.

and at the end of the day, I'll have some good subs to add to my computer speakers to give the extra bass, and probably for about 80$ for the PSU, amp and subs.