In article ,
wrote:

I've just bought a couple of Home Cinema receivers in the sales.
Need help understanding speaker watts.

Teac AGH550
Spec shown he http://www.homeaudiosuperstore.com/product460.html

This is a 5.1 unit. It has 5 independent audio amps that produce
up to 80 watts each. This includes a front right, front left,
center, rear right, and rear left. The subwoofer output is is
at line level, so the sub needs its own amplifier.

RX-V730RDS Home Cinema Receiver
Spec shown he
http://www.yamaha-audio.co.uk/homeci...0rds/index.asp

This is a 6.1 unit. It has 6 independent audio amps that produce
up to 75 watts each. They are the same as above, but with the
addition of a rear center channel.

I can't understand the meaning of ohms at all, tried looking at
various webpages with diagrams but it still doesn't make any sense.

As long as you connect a single speaker to a single output on the
back of the receiver, you can all but ignore ohms. All modern
hi-fi and home theater speakers are in the 4 to 10 ohm range, and
all amps can drive one of them per amplifier.

From what I can gather, most speakers and systems use 8ohms and if you
go lower than 4 it starts to get dangerous, risking damaging the amp??

As long as you go one speaker per amp, this basically true.

I think this means you can't put loads of speakers on the amp
otherwise you'll put too much stress on it. My AV receiver has wires
for the individual speakers (6.1) so 1 speaker gets plugged into 1
port. I guess I don't need to worry about ohms when buying speakers??

When you want to connect more than one speaker per amplifier, you
have to follow the laws of parallel and series speakers. For
example, if you want to connect two 8-ohm speaker, put them in
parallel to get 4-ohms, which these amps can drive OK. If you want
4 speakers, put two in parallel, then the other two in parallel,
and finally these two groups of parallel speakers in series. The
parallel groups each make 4-ohms, but by putting two groups in
series, you are back up to 8-ohms.

Also, I need help understanding speaker power in W's.

The RX-V730RDS Home Cinema Receiver is rated 125 W per speaker.

That number is when loaded at 4 ohms. The legitimate method of
rating power is based on 8-ohms. Use the 75-watt number, it is
more accurate of a representation.

My amp is rated 125w per channel, if i buy speakers that are rated
150w, 200w or 250w per speaker, will I lose out on the quaility?
Should I *only* be buying 125w rated speakers for the 125w amp?

Speaker power ratings are mostly foo-foo numbers, and are their
for marketing. They are supposed to mean the maximum amount of
power that the speaker can tollerate. In reality, even low levels
of dirty power can damage a speaker, and some speakers can handle
very high levels of clean power.

and for the Teac AGH550, it is rated at 80w per channel, does this
mean I should *only* buy 80w speakers? If I put 100w or 150w speakers
on the Teac, will it make any difference to quality?

Some (but not all) speakers have a range printed on the back for
example like 60w to 90w, others just have 90w.

In general, you can ignore the power ratings. You do want speakers
that can handle more power than what your amp can produce, but then
again, few people listen at extrememly high power levels. Even a
single watt of power going to your speakers is going to produce
ear-splitting volumes on reasonably efficient speakers when used
in home applications.

It is far more important to get speakers that sound good.

-john-

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John A. Weeks III 952-432-2708
Newave Communications http://www.johnweeks.com
================================================== ==================

In article ,



I can't understand the meaning of ohms at all, tried looking at various
webpages with diagrams but it still doesn't make any sense.

To get a given output sound level your amplifier puts a given voltage
across the speaker terminals. The speaker then demands a current.
Impedances in Ohms are simply the ratio between these.

So when you have a load with an impedance of X 'Ohm's, when your amp puts a
voltage of 'V' volts across the speaker terminals it has to supply the
speaker with a current of I = V/R amps.

Does that make it clear? Or have I missed the point?

From what I can gather, most speakers and systems use 8ohms and if you
go lower than 4 it starts to get dangerous, risking damaging the amp??

The problem is that with most speakers the effective impedance varies with
frequency. Hence to put a given a.c. voltage on its terminals at some
frequencies requires more current than at other frequencies. This means the
impedance value quoted for a loudspeaker is just a sort of 'average' of
'typical' value for what you get over a range of audible frequencies.

With amplifiers the powers quoted are when applying signals to a resistance
whose value is the same at all audio frequencies. Thus you can use the '8
Ohms' values as a general guide, but this hides details that are usually
unimportant, but sometimes matter. :-)


Also, I need help understanding speaker power in W's.

The RX-V730RDS Home Cinema Receiver is rated 125 W per speaker.

My amp is rated 125w per channel, if i buy speakers that are rated 150w,
200w or 250w per speaker, will I lose out on the quaility? Should I
*only* be buying 125w rated speakers for the 125w amp?

Nope. As John as already indicated, these values are also only really
'guides'. The power value given for the amp is (or should be!) the maximum
amount it can driver steadily into a stated impedance. The speaker values
are 'finger in the wind' estimates of the power levels you can expect to
get away with for brief periods.

In practice, most music consists of occasional brief high-power bursts with
a much lower mean level. Hence if you are using a 100W set of items it is
quite likely that the average power is well below this.

I suspect that on both the 'Ohms' and 'Watts' points you confusion may be
coming from the *different* ways that amplifier and speaker makers use
these values. Alas, we are stuck with this due to the way these things have
evolved in practice. :-)

Thus do not take the power or impedance ratings of items too seriously.
They are useful as a vague guide, but no more than that unless you get much
more detailed info on the units.

Hope the above helps.

Slainte,

Jim

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