Audio Problems!!

I know nothing about cars; I wanted to start out with that. So I do have a
question and I hope someone can help me. The other day I was listening to
a CD in my car when the stereo stopped working. Well the radio turns on
and will play CD's but no sound is coming out. I recently bought new
speakers and I had a friend check to make sure the speaker wire didn’t
just fall out or something. But the speakers are installed correctly.
Then I though a fuse, but I'm not sure if they have a fuse, and none of
the fuses in the fuse box were dead. If anyone can help me it would me
much appreciated!!

 

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We know nothing about cars either . . . .

At least we know NOTHING about yours, nor the stereo you put in it. :-(
Move your WebCam a little to the left, or open the curtains a bit more
so I can see if it's a two-door or four-door.

'Curly'

 

Not enough info from what you provided.

Let me try to guess some situations for you.
First, I assume that you have a honda car with stereo head unit which has
amplifier built in. In this case, fuse is not an issue if you can still
turn on the car stereo. Maybe the amplifier section is bad and not pumping
out juice to drive the spaekers. Maybe the amplifier section is short
circuit and burnt your speaker.
Are you sue the speaker is in good condition? Did you try to put original
speaker back to check if the head unit is still working?

Second, you may have an external amplifier which is not connected correctly
or faulty cable. This is another case your speaker does not receive any
signal from amp--no sound.

 

What Curly is saying is that you're very unlikely to get any useful
information from Usenet unless you include a lot of specific
information and detail. You've given the experts essentially nothing
to go on with the message you posted. They don't have crystal balls
<amateur punsters, please refrain from the obvious>.

Ron

 

Ok I am very sorry for the lack of info I'm just not sure what is important
or not. I have a pioneer stereo and speakers. I know that the speakers
are find b/c I bought them a month ago b/c the old ones blew and they work
in my friends car...we tries just incase. Also I’m not sure how this is
relevant to my stereo but yes my car is a Honda, its a 1995 Civic Ex V-Tec
and (sarcastically) I know this must be important Curly but my car is a two
door!! I don’t have an amp.

 

Many times people install speakers with the wrong impedance. This bogs
down the IC amplifier. Usually before you know the IC fries and the only
replacement is to replace the audio deck or, if you're lucky, just the IC.

The impedance is usually written on the deck. 8-Ohm is a lot safer than
say, 2-4-Ohm speakers.

 

Mismatched speaker impedance can ruin an amplifier? It decreases the
efficiency of the system, but "frying an integrated circuit?" Are you
sure?

Ron

 

do the math. how much more current will sink through a 4ohm load
compared with an 8ohm load? and what is the formula for power?

bottom line, yes, wrong impedance can fry the ic.

 

If I = V/R, then the answer might be twice as much. Why am I to
deduce that this will "fry" the power amp? I'm not trying to be
argumentative because I have no special knowledge of car audio, but
I've simply never heard of an impedance mismatch actually damaging
audio equipment, and the statement didn't seem intuitive to me.

I've run mismatched speakers on home audio systems for years with no
problems at all. It can mean that you have to turn up the volume a
little and perhaps the power amp may work a little harder, but it has
never caused any damage. All the product manuals suggest matching
impedance if possible, for the sake of improving efficiency, but none
I've owned over the last thirty years has ever warned that serious
damage to the receiver may occur from the mismatch.
Are car audios that much different from home receivers?



Ron

 

yup. and P = I^2.R

it's not common for normal domestic use because you usually don't get
near the power limits very often, but once you get into a car, where
power is often substantially higher [cranking the stero up to cover road
noise, etc.] and temperature is often much higher, it starts to be a
problem.

as per the above, it's not usually a big deal in domestic systems, but
as you approach the output limit, things get all toasty. chip life
drops dramatically with increasing temp.

 

So P is doubled (2^2 * ½). It doesn't really seem that it would be
likely to "fry" anything.

I see the point (and had considered it before replying last time), but
have you actually seen a car stereo ruined by an impedance mismatch?

Ron

 

if it was 1A into 8 Ohms, that's 8W. 2A into 4 Ohms, that's 16W. if
your output is limited to say 30W peak, trying to suck 60W out of it
would be a massive problem that'll fry semiconductors quite nicely!
especially in a nice hot car where the output heat sinks are crammed
into a nice airtight little socket in the dash. semicons are just not
abuse tolerant.

yup. the plastic packaging on the output transistors melted and the
circuit board had gone from green to brown in the heat zone.

 

There are some issues that are less than obvious here. Power TO THE
SPEAKERS is not what counts, power dissipated in the amplifier is the
problem. Contrary to what one might think, power dissipated in the amp
is not at a maximum when power to the speakers is at a maximum (volume
cranked to max. (ours goes to 11)). It occurs when power to the speakers
is at about 40% of max. (Assuming amp output impedance is much smaller
that speaker impedance)

One might say that a dead short is also just an impedance mismatch, and
a dead short certainly can fry an amplifier. Furthermore, in car stereos
you usually don't have *matching* impedances. The output impedance of
the amp is usually quite low compared to the speaker impedance. Thus the
power delivered to the speakers will theoretically increase as you
decrease the speaker impedance until it reaches the amp output
impedance. As a practical matter, things will start to smell foul long
before the speaker impedance is low enough for an impedance match.
Given an amp with x ohms output impedance, max. power should be with
speakers of x ohms as well, but this is not really the design criterion.
Rather, given speakers of 4 ohms, max. power is obtained with an
amplifier output impedance of 0 ohms.

In video and RF, impedance matching is important to avoid reflections.
However, as a rule of thumb, if your cable is shorter than 1/4
wavelength, you don't really care. For audio, that means that your
speaker cables can be up to a mile and a half before you have problems
with reflections (assuming 20 kHz and signal velocity in speaker cable
of about 2/3 the speed of light in vacuum)

To compound the issue, home stereos usually have ample cooling;
Ventilated chassis and large heatsinks, sitting in a room where the
temperature is comfortable for humans. Head units in cars are not at all
well cooled. They are hidden inside the dash where there is no air flow
and in a car that might have baked in the sun all day.

A well designed amp will be short circuit protected and have thermal
shutdown, Even then, if it spends any amount of time close to but not
quite at the trip temperature for the thermal shutdown, it will have a
reduced service life.

Did the wrong speakers kill SaraKat's head unit? Speakers with less than
4 ohms impedance are unusual, and car stereos that can not handle 4 ohm
speakers are unusual as well. Perhaps several speakers were connected in
parallel on each output?

 

Resolution of the problem. Thanks. I understand better, now.



Ron