RE: Re: [OT] Understanding speakers & watts.

["Mark Harrison" <Mark.Harrison@xxxxxxx>]

The purists will probably kill me for being too simplistic here, but
this "mental model" has been good enough for me to get through a
series
of jobs. I'm not going to use any formulae or equations here, this is
"plain text" ;-)

The executive summary is "don't worry - the speakers will work - just
don't play them LOUD - Loud will be fine, though."


Most (indeed - nearly all) domsetic amplifiers work by multiplying
voltage. An input voltage of up to 2 volts comes in from, say, a CD
player on the "phono" input, and an output voltage goes out
across the
loudspeaker terminals.

How high you've got the volume knob cranked determines the multiplier.
So at _very_ low volumes, and multiplier of 1, the output voltage will
range up to 2 volts. At high volumes, the multiplier might be 30, so the
output voltage will range up to 60 volts.

Now, there are two monkeys:

1: CD manufacturers, particularly Sony, tend to operate outside the
"normal" spec for the phono connectors, so _their_ CD players
might
output up to, say, 2.4v. This is naughty, in the sense that it might
overload your amp's input circuitry, and forces amp manufacturers to
over-specify rather than relying on source manufacturers to stay within
spec.

This is also cool, because on "blind" tests, most people's
emotional
reaction is to prefer the louder source over the quieter. So, flipping
between a Sony and a non-Sony CD player on a "which do you
prefer" means
that Sony's sell a lot more equipment.

2: What your loudspeakers fundamentally do with this voltage is pass it
through some electromagnets, which causes a fluctuation in the
electro-magnetic field around them. A normal magnet which you can think
of as being on a spring sitting in this field reacts to this by
physically moving to establish a new equilibrium between the higher (or
lower) magnetic field pulling it one way and the spring pulling it the
other.

The magnet is attached to the centre of a paper (or aluminium, or
kevlar, or whatever) cone. The centre of cone moves back and forth with
the magnet. The outside of the cone stay fixed, by virtue of being
attached to a big bit of wood (the speaker case). This movement pushes
air back and forth. The air pushes other air back and forth, which
pushes more air back and forth, until we get to some air that pushes
bits of your skin back and forth. (At normal volumes) you only notice
this as it pertains to bits of skin inside your ear, which causes some
electrons to flow up into your brain which then processes that movement,
along with the other electron flows just before it to think "ah -
that's
Robbie Williams".

The problem is that moving all this "stuff" (the skin in your
ear, by
the expedient of moving the air, via the expedient of moving the cone,
via the expedient of moving the magnet) takes energy.

One measure of "how much energy" it requires is the impedance
figure
quoted. The lower the figure, the more energy needed.

As such, your proposed 4 ohm speakers are harder to drive, in fact,
twice as hard to drive, as the 8 Ohm speakers that your amp manufacturer
was expecting.

The rating of your amp is a rating of how fast it can put out energy. If
it's operating within its tolerance, then it'll do it gracefully. If
it's not, then something will give - generally loudly with a sort of
bangy noise, and expensively.

However, don't worry. The reason that amp manufacturers quote a figure
into 8 Ohms is that, historically, this was the most common sort of
loudspeaker, and if everyone quotes the figures in the same way, then
it's possible to make an objective comparison.

The amp will still work with your speakers. However, don't turn it up
stupidly high, and if you notice the sound distorting, then it probably
means it's turned up too loud.

Mark Harrison
Head of Systems, eKingfisher


-----Original Message-----
From: jcom10 [mailto:jcom10@xxxxxxx]
Sent: 2 January 2002 17:14
To: ukha_d@xxxxxxx
Subject: [ukha_d] Re: [OT] Understanding speakers & watts.


Thanks for the info guys!
Just went in to buy them, then noticed they say 4 Ohms. I'm sure my
amp says 8 Ohms. What's that all about?

Justin.

--- In ukha_d@y..., "Phil Harris" <phillip.harris1@v...>
wrote:
> I had great success in my "in car audio" days using good
quality and
> high(ish) powered amps on line fit speakers. I had used 4 x 40w
Rockford
> Fosgate amps on speakers which were supposedly rated at 8w and never
> blew one of them - even though they were used quite hard. They were
> filtered to restrict the lower end of the frequency range as too
much
> bottom end through them would kill them as it ripped apart the
> suspensions but that was about it.
>
> On the other hand I have seen loads of speakers destroyed by using
cheap
> and crappy amps which when driven into clipping simply spend most of
> their life putting out almost square wave DC (clipped AC waveforms)
> which - as Keith has said - destroys tweeters in seconds and mid
bass /
> subwoofers in hours!
>
> Phil
>
> > -----Original Message-----
> > From: Keith Doxey [mailto:ukha@xxxxxxx...]
> > Sent: 02 January 2002 14:01
> > To: ukha_d@y...
> > Subject: RE: [ukha_d] [OT] Understanding speakers & watts.
> >
> >
> > If you turn it up way too high then you can damage the
> > speakers, but an amp that is too small can damage the
> > speakers because when an amp is overdriven the resultant
> > clipping causes an excessive amount of high frequency energy
> > that kills tweeters pretty damn quick.
> >
> > On overpowered amp driven sensibly is much less dangerous.
> >
> > Mordant Short normally have "Positec" protection which
are
> > self resetting fuses that cut out if they are overdriven. (My
> > MS3.10's do anyway)
> >
> > HTH
> >
> > Keith
> >
> > -----Original Message-----
> > From: jcom10 [mailto:jcom10@xxxxxxx...]
> > Sent: 02 January 2002 13:46
> > To: ukha_d@y...
> > Subject: [ukha_d] [OT] Understanding speakers & watts.
> >
> >
> > I have been looking for some new surround speakers, and
> > recently saw a Mordaunt Short "Premier" package in
Richer
> > Sounds. SWMBO was with me and insists we get them because,
> > they are unobtrusive and "they look nice"! I would have
to
> > agree, but I don't think they are man enough for the job.
> >
> > The speakers are rated at 50W but my AV amp is, IIRC, 80W.
> > My assumption is that the speakers will be knackered if the
> > volume is turned up too loud. Is that correct?
> >
> > They aren't on the MS site (strange) & I can find very little
> > information about them on the web. Anyone have any experience
> > of these?
> >
> > Any recommendations for other speakers? The keyword here is
> > SMALL. I fancy the Bose Acoustimass ones but they are a bit
pricey.
> >
> > Cheers,
> >
> > Justin.
> >
> > PS: Happy new year to everyone!
> >
> >
> >
> >
> >
> > For more information: http://www.automatedhome.co.uk
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