On Sun, 04 Jan 2004 19:47:06 +0000, Fleetie wrote:

"Form@C" wrote
If you put an orchestral peak at, say, 200dB (way too high, I know - it
would deafen the conductor.),

If by "dB" you mean the normal decibel used to measuring sound pressure
level (20 * log_10(p / 2.0E-5) ), then it would not deafen the conductor.
It would kill him and pulp his body.


Too true! 130dB is threshold of pain, is it not? I was thinking of
transients really, not actual output from the orchestra. 200dB is, of
course, ludicrous, but it is on the right (high) side of reality!


the SPL at your listening position at, say, 197dB (lost half of it) and
your speaker efficiency at, say, 60dB/w (fairly poor sealed boxes) then
you need 4W to hit the peak volume. A 5W amp is overkill. :-)

Erm, no.

You should not use the notation "dB/W" because it doesn't work like that.
Correctly, you should specify speaker sensitivity as "X dB at 1W input
power" (at some frequency). Some manufacturers instead say "X dB at 2.83V"
(being 2*pi) RMS input (at some frequency), which is a similar thing,
because P = V^2 / Z. If R=8 Ohms at the test frequency, then the power
will be 1 watt. But only if Z=8 Ohms at that frequency, and in general, it
won't be.


Point taken.
Right, the (transient!) SPL at the concert seat could hit around 190dB.

Example: Kef Coda 70: 2.83v/1m 91dB, 8R, frequency not stated (efficient
for small boxes). So at, say, 4m away you get 79dB at your listening
position for 1W at the speakers (it appears to be 6dB each time the
distance is doubled). So, for our 190dB we need 2.5W at the speaker? Ok,
not a lot of bass in that little box (-3dB at 45Hz), and they have a max
output of 109dB anyway, but you get the idea... 5W is still a lot.

--
Mick
http://www.nascom.info for Nascom & Gemini information
Also at http://www.mixtel.co.uk where the collection started.
Currently deserting M$ for linux... :-)

On Sun, 4 Jan 2004 17:41:14 +0000 (UTC), "David"
wrote:


I have often found that the easiest way to deal with bass is just not to
do
it at all! Small, sealed (infinite baffle) enclosures made with very
heavy
damped panels and a simple crossover using very high quality drive units
often sound fantastic (BBC monitor LS1 fans may now smile smugly) BUT
they
need vast amounts of amplifier power to produce any response below 100Hz
(and no - a subwoofer is not the answer)

Oh yes, it is! And BTW, those speakers can't *handle* vast amounts of
power, so you are stuck with no bass.
--

Hi Stewart

I think you are actually agreeing with me in an argumentitive fashion... but
thats OK.

Me, argumentative?................ :-)

My point is that it is often best to sacrifice the bottom couple of octaves
and concentrate on getting the rest "right" - something which small IB
cabinets do very well.
Introduce a sub into the room and pass the sick bags.

Introduce it *well*, and pass the paper hankies!

The idea is to find a system which sounds good WITHOUT anoying the
neighbours.

Buy a detached house in the country! :-)

Having the big power amp on hand means that the amp will be
cruising but will still have an iron grip of the speaker hence the need for
powerfull amps in the real world (and yes I have used 8 watt single ends
into big efficient cabinets with good results - but still no bass and
limited volume)

OK, so you had some badly designed big speakers! BTW, it's the output
impedance that determines the 'grip' on the speakers (below resonance,
at any rate), not the power output.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sun, 4 Jan 2004 17:41:14 +0000 (UTC), "David"
wrote:


I have often found that the easiest way to deal with bass is just not to
do
it at all! Small, sealed (infinite baffle) enclosures made with very
heavy
damped panels and a simple crossover using very high quality drive units
often sound fantastic (BBC monitor LS1 fans may now smile smugly) BUT
they
need vast amounts of amplifier power to produce any response below 100Hz
(and no - a subwoofer is not the answer)

Oh yes, it is! And BTW, those speakers can't *handle* vast amounts of
power, so you are stuck with no bass.
--

Hi Stewart

I think you are actually agreeing with me in an argumentitive fashion... but
thats OK.

Me, argumentative?................ :-)

My point is that it is often best to sacrifice the bottom couple of octaves
and concentrate on getting the rest "right" - something which small IB
cabinets do very well.
Introduce a sub into the room and pass the sick bags.

Introduce it *well*, and pass the paper hankies!

The idea is to find a system which sounds good WITHOUT anoying the
neighbours.

Buy a detached house in the country! :-)

Having the big power amp on hand means that the amp will be
cruising but will still have an iron grip of the speaker hence the need for
powerfull amps in the real world (and yes I have used 8 watt single ends
into big efficient cabinets with good results - but still no bass and
limited volume)

OK, so you had some badly designed big speakers! BTW, it's the output
impedance that determines the 'grip' on the speakers (below resonance,
at any rate), not the power output.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sun, 04 Jan 2004 19:10:08 GMT, "Form@C" wrote:

On Sun, 04 Jan 2004 17:32:20 +0000, Stewart Pinkerton wrote:

On Sun, 04 Jan 2004 12:31:32 GMT, "Form@C" wrote:

On Sun, 04 Jan 2004 11:09:48 +0000, Ian Molton wrote:

On Sun, 04 Jan 2004 08:27:50 GMT
"Form@C" wrote:

It's no use turning down a
100-200W monster amp because you arn't running them at their best.

what?

Sorry, it wasn't very clear was it? What I meant to say is that "high"
power amps are usually designed and set up to produce their best results
an appreciable way up to their rated power output.

No, they aren't.


Oh yes they are...

Oh no, they aren't!

Well, it *is* the panto season.................

You will almost always see distortion levels etc
quoted for a particular power output level. That power level is often
quoted at either full rated power or at least somewhere well above 5W
or so - very loud in most domestic rooms.

Yes of course, since that's conventional, and tells you how much power
the amp can put out.

(You may also notice that
manufacturers don't often quote exactly what the load was theat the amp
was driving when the measurements were taken. Some amps measure well into
resistive loads only.)

Very true! :-(

Only the better amps will quote specifications at
low power levels.

But any well-designed amp will have low distortion at low levels,
usually well below the noise floor.

They won't perform at
their best at a very low percentage of that level.

Absolute garbage!

Maybe, but its a fact! :-)

No, it's not. You are thinking of those nasty mid-70s 'Jap crap'
designs with excessive NFB and poor open-loop bandwidth, using
slow-switching output trannies. Doesn't happen with any decent modern
amp.

I *know* that many are
*supposed* to be class A at low levels, but they are generally not
designed as class A amps, and are not really running as such (the output
stage quiescent current is usually too low to allow correct class A
operation on a class AB amp).

Excuse me? A class AB amp *always* runs in class A up to some
predetermined level, which may be less than 1 watt or as many as 50 watts.
I use an amplifier which runs in true class A up to 50 watts into 8 ohms,
and in class AB above that level, up to its rated maximum of 400 watts
into 1 ohm. It sounds just fine at very low levels.

You are correct, but that predetermined level can be very vague in many
cases. There is no way for the user to tell when the amp changes out of
class A without getting a scope out, so manufacturers often "bend" the
quoted output to make the specs look good! An amp can be classed as AB if
it produces the first 50mW as class A of course...

Yes, and this is also *totally* irrelevant to how it sounds. I have a
low-bias Audiolab 8000P and a 'pure class A' Krell KSA-50 mkII, and
they are sonically indistinguishable into my pretty tough Apogee
duetta Signatures.

At 400W you are not
running an amp that I would class as average domestic. It will (should) be
running bloody hot too! (1) The majority of AB amps out there run the
no-load current at below optimum for usable class A use and don't apply
sufficient drive to push the output devices fully. It keeps the size &
cost of the PSU down and reduces the heat, making the equipment more
acceptable to the domestic market.

Yes, and it doesn't make a jot of difference to the sound quality.

Thus it is a mistake to judge low-power
audio systems by simply turning down the volume on existing "high" power
equipment & changing the speakers for more sensitive ones.

Depends on the amp......................

Oh yeah! There are a lot of really good amps, but you won't often find
them available through your local outlets. Even so-called "hi-fi" shops
tend not to carry the good stuff as stock - it costs far too much.

Nah, it starts with the Yanaha AX-592 and carries on from there.

(1) A note for thos who may not know what we are on about... Stewart will
know this already! Class A is always less than 50% efficient, typically
46%, so you should be producing well over 100W of heat, with no signal
present, to be capable of class A at 50W - not including valve heaters of
course! In class AB amplifiers one of the output devices is cut-off on
alternate halves of the waveform, giving a power saving. Class B
amplifiers always cut off one of the devices at some point. This is the
primary cause of the "transistor sound" - a lot of odd-harmonic
distortion.

Yes, my '50 watt' Krell draws 300 watts from the wall when idling. For
those of an enquiring mind, the theoretical efficiency limit for a
class AB amp is 78% at full popwer. Naturally, no *high quality* amp
has to worry about valve heaters............... :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sun, 04 Jan 2004 19:10:08 GMT, "Form@C" wrote:

On Sun, 04 Jan 2004 17:32:20 +0000, Stewart Pinkerton wrote:

On Sun, 04 Jan 2004 12:31:32 GMT, "Form@C" wrote:

On Sun, 04 Jan 2004 11:09:48 +0000, Ian Molton wrote:

On Sun, 04 Jan 2004 08:27:50 GMT
"Form@C" wrote:

It's no use turning down a
100-200W monster amp because you arn't running them at their best.

what?

Sorry, it wasn't very clear was it? What I meant to say is that "high"
power amps are usually designed and set up to produce their best results
an appreciable way up to their rated power output.

No, they aren't.


Oh yes they are...

Oh no, they aren't!

Well, it *is* the panto season.................

You will almost always see distortion levels etc
quoted for a particular power output level. That power level is often
quoted at either full rated power or at least somewhere well above 5W
or so - very loud in most domestic rooms.

Yes of course, since that's conventional, and tells you how much power
the amp can put out.

(You may also notice that
manufacturers don't often quote exactly what the load was theat the amp
was driving when the measurements were taken. Some amps measure well into
resistive loads only.)

Very true! :-(

Only the better amps will quote specifications at
low power levels.

But any well-designed amp will have low distortion at low levels,
usually well below the noise floor.

They won't perform at
their best at a very low percentage of that level.

Absolute garbage!

Maybe, but its a fact! :-)

No, it's not. You are thinking of those nasty mid-70s 'Jap crap'
designs with excessive NFB and poor open-loop bandwidth, using
slow-switching output trannies. Doesn't happen with any decent modern
amp.

I *know* that many are
*supposed* to be class A at low levels, but they are generally not
designed as class A amps, and are not really running as such (the output
stage quiescent current is usually too low to allow correct class A
operation on a class AB amp).

Excuse me? A class AB amp *always* runs in class A up to some
predetermined level, which may be less than 1 watt or as many as 50 watts.
I use an amplifier which runs in true class A up to 50 watts into 8 ohms,
and in class AB above that level, up to its rated maximum of 400 watts
into 1 ohm. It sounds just fine at very low levels.

You are correct, but that predetermined level can be very vague in many
cases. There is no way for the user to tell when the amp changes out of
class A without getting a scope out, so manufacturers often "bend" the
quoted output to make the specs look good! An amp can be classed as AB if
it produces the first 50mW as class A of course...

Yes, and this is also *totally* irrelevant to how it sounds. I have a
low-bias Audiolab 8000P and a 'pure class A' Krell KSA-50 mkII, and
they are sonically indistinguishable into my pretty tough Apogee
duetta Signatures.

At 400W you are not
running an amp that I would class as average domestic. It will (should) be
running bloody hot too! (1) The majority of AB amps out there run the
no-load current at below optimum for usable class A use and don't apply
sufficient drive to push the output devices fully. It keeps the size &
cost of the PSU down and reduces the heat, making the equipment more
acceptable to the domestic market.

Yes, and it doesn't make a jot of difference to the sound quality.

Thus it is a mistake to judge low-power
audio systems by simply turning down the volume on existing "high" power
equipment & changing the speakers for more sensitive ones.

Depends on the amp......................

Oh yeah! There are a lot of really good amps, but you won't often find
them available through your local outlets. Even so-called "hi-fi" shops
tend not to carry the good stuff as stock - it costs far too much.

Nah, it starts with the Yanaha AX-592 and carries on from there.

(1) A note for thos who may not know what we are on about... Stewart will
know this already! Class A is always less than 50% efficient, typically
46%, so you should be producing well over 100W of heat, with no signal
present, to be capable of class A at 50W - not including valve heaters of
course! In class AB amplifiers one of the output devices is cut-off on
alternate halves of the waveform, giving a power saving. Class B
amplifiers always cut off one of the devices at some point. This is the
primary cause of the "transistor sound" - a lot of odd-harmonic
distortion.

Yes, my '50 watt' Krell draws 300 watts from the wall when idling. For
those of an enquiring mind, the theoretical efficiency limit for a
class AB amp is 78% at full popwer. Naturally, no *high quality* amp
has to worry about valve heaters............... :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sun, 04 Jan 2004 19:35:50 GMT, "Form@C" wrote:

On Sun, 04 Jan 2004 17:17:32 +0000, Stewart Pinkerton wrote:

On Sun, 04 Jan 2004 08:27:50 GMT, "Form@C" wrote:

Have a look at any mid-price, fairly sensitive, half-decent speakers &
couple them with a little pure class A amp. Valves are nice...

No, they aren't - if you want *accurate* reproduction.


Maybe not, but do you want *accurate* reproduction or an amp that is good
to listen to? I, personally, would much rather listen to 2nd harmonic
distortion rather than 3rd!

Of course, the nice thing about SS amps is that you don''t have to
listen to either!

In any case,
how close would you be sitting to the orchestra to reach the dB level
for "several hundred watts" *at your seat*?

That's typically 100-105dB, so it depends on your room and your
speakers.

So, given fairly inefficient speakers of about 60dB/W you *need* less than
2W to reach that SPL. Double it to add some headroom. Say 5W. Even small
bookshelf speakers can be about 90dB/W, so this is loud.

Um, something wrong with your sums there, dude! with 90dB/w/m speakers
(which are well above the 86dB average), you will need 20 watts to
reach 103dB at one metre, which usually translates to 20 watts/channel
for the same level at the listening position in a small/medium room.
With 60dB/w/m speakers, you'd need a humungous 20,000 watts! Luckily,
I don't know of anything lower than 80dB/w/m (ATC SCM10s).

Remember to take the sqrt of the
power each time you double the distance back. You tend to sit far closer
to speakers than you do to the orchestra in a concert hall.

And the square law no longer applies once you are half way down the
room..................

No, it tends to get worse because of sound absorbtion (although there is
some reflected stuff too), so the SPL at your listening position is
probably less...

No no, it gets *better* because you are in the reverberant far field.
As noted above, in most small/medium rooms you'll get the dB/w/m
figure from a stereo pair at say 2 to 2.5 metres listening distance.

Try it. Use a
*good* low power amp and sensitive speakers. It's no use turning down a
100-200W monster amp because you arn't running them at their best. They
will be set up, probably anyway, to sound best at about 25-50% of full
output.

Absolute garbage!

Maybe for your amp... :-)

For any well-designed amp.

Remember that to double the volume you have
to square the power,

No, you need ten times the power.

Sorry, my mistake! I got carried away with sqrts....

so 250W is about twice the volume of a 25W amp, which in turn is
about twice the volume of a 5W amp! The more sensitive your speakers
are, the better.

Yes, but you still need good amplifier power to ensure adequate headroom
for peaks.

If you put an orchestral peak at, say, 200dB (way too high, I know - it
would deafen the conductor.), the SPL at your listening position at, say,
197dB (lost half of it) and your speaker efficiency at, say, 60dB/w
(fairly poor sealed boxes) then you need 4W to hit the peak volume. A 5W
amp is overkill. :-)

You really do need to read up on those sums! SPL is *logarithmic*, so
for every 10dB, you need ten times as much power. If you really had
60dB/w/m speakers, you would need 50 million *megawatts*!! That might
put a bit of a dent in your electricity bill..............

BTW, 200dB is about what you'd experience if a cruise missile went off
between your ears...................
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sun, 04 Jan 2004 19:35:50 GMT, "Form@C" wrote:

On Sun, 04 Jan 2004 17:17:32 +0000, Stewart Pinkerton wrote:

On Sun, 04 Jan 2004 08:27:50 GMT, "Form@C" wrote:

Have a look at any mid-price, fairly sensitive, half-decent speakers &
couple them with a little pure class A amp. Valves are nice...

No, they aren't - if you want *accurate* reproduction.


Maybe not, but do you want *accurate* reproduction or an amp that is good
to listen to? I, personally, would much rather listen to 2nd harmonic
distortion rather than 3rd!

Of course, the nice thing about SS amps is that you don''t have to
listen to either!

In any case,
how close would you be sitting to the orchestra to reach the dB level
for "several hundred watts" *at your seat*?

That's typically 100-105dB, so it depends on your room and your
speakers.

So, given fairly inefficient speakers of about 60dB/W you *need* less than
2W to reach that SPL. Double it to add some headroom. Say 5W. Even small
bookshelf speakers can be about 90dB/W, so this is loud.

Um, something wrong with your sums there, dude! with 90dB/w/m speakers
(which are well above the 86dB average), you will need 20 watts to
reach 103dB at one metre, which usually translates to 20 watts/channel
for the same level at the listening position in a small/medium room.
With 60dB/w/m speakers, you'd need a humungous 20,000 watts! Luckily,
I don't know of anything lower than 80dB/w/m (ATC SCM10s).

Remember to take the sqrt of the
power each time you double the distance back. You tend to sit far closer
to speakers than you do to the orchestra in a concert hall.

And the square law no longer applies once you are half way down the
room..................

No, it tends to get worse because of sound absorbtion (although there is
some reflected stuff too), so the SPL at your listening position is
probably less...

No no, it gets *better* because you are in the reverberant far field.
As noted above, in most small/medium rooms you'll get the dB/w/m
figure from a stereo pair at say 2 to 2.5 metres listening distance.

Try it. Use a
*good* low power amp and sensitive speakers. It's no use turning down a
100-200W monster amp because you arn't running them at their best. They
will be set up, probably anyway, to sound best at about 25-50% of full
output.

Absolute garbage!

Maybe for your amp... :-)

For any well-designed amp.

Remember that to double the volume you have
to square the power,

No, you need ten times the power.

Sorry, my mistake! I got carried away with sqrts....

so 250W is about twice the volume of a 25W amp, which in turn is
about twice the volume of a 5W amp! The more sensitive your speakers
are, the better.

Yes, but you still need good amplifier power to ensure adequate headroom
for peaks.

If you put an orchestral peak at, say, 200dB (way too high, I know - it
would deafen the conductor.), the SPL at your listening position at, say,
197dB (lost half of it) and your speaker efficiency at, say, 60dB/w
(fairly poor sealed boxes) then you need 4W to hit the peak volume. A 5W
amp is overkill. :-)

You really do need to read up on those sums! SPL is *logarithmic*, so
for every 10dB, you need ten times as much power. If you really had
60dB/w/m speakers, you would need 50 million *megawatts*!! That might
put a bit of a dent in your electricity bill..............

BTW, 200dB is about what you'd experience if a cruise missile went off
between your ears...................
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sun, 4 Jan 2004 19:48:06 -0000, "Roy" wrote:


"Stewart Pinkerton" wrote in message
...
On Sun, 4 Jan 2004 00:01:48 +0000 (UTC), "David"
wrote:

No. Highly efficient speakers are generally less accurate than "lowish"
efficiency speakers. They tend to become unlinear at high outputs.

Actually, the exact opposite is true. It's insensitive speakers that
have problems at high SPLs, for reasons which should be obvious.

Erm, remind me!!

They need huge amounts of power, and suffer from thermal compression.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sun, 4 Jan 2004 19:48:06 -0000, "Roy" wrote:


"Stewart Pinkerton" wrote in message
...
On Sun, 4 Jan 2004 00:01:48 +0000 (UTC), "David"
wrote:

No. Highly efficient speakers are generally less accurate than "lowish"
efficiency speakers. They tend to become unlinear at high outputs.

Actually, the exact opposite is true. It's insensitive speakers that
have problems at high SPLs, for reasons which should be obvious.

Erm, remind me!!

They need huge amounts of power, and suffer from thermal compression.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sun, 04 Jan 2004 21:56:33 GMT, "Form@C" wrote:

Point taken.
Right, the (transient!) SPL at the concert seat could hit around 190dB.

Nope, 105-110 dB absolute maximum.

Pick up a hand grenade, pull the pin, wait five seconds, and you'll
experience about 160dB - briefly.

Example: Kef Coda 70: 2.83v/1m 91dB, 8R, frequency not stated (efficient
for small boxes). So at, say, 4m away you get 79dB at your listening
position for 1W at the speakers (it appears to be 6dB each time the
distance is doubled).

Only in an anechoic chamber, and it's 3dB, not 6. In a big enough room
for a 4 metre listening distance, you'll probably get about 85-87dB/w,
depending on furnishings.

So, for our 190dB we need 2.5W at the speaker?

NO!!!!!!! Where the heck are you getting these numbers?

If you're getting 85 dB/w, then for 105 dB, you need 100 watts.

Ok,
not a lot of bass in that little box (-3dB at 45Hz), and they have a max
output of 109dB anyway, but you get the idea... 5W is still a lot.

No, it's pathetically inadequate.
--

Stewart Pinkerton | Music is Art - Audio is Engineering