Re: speaker cab noise

I just wanted to add one thing, so I put it here so no one would have to
re-read the whole thing unless they wanted to. You correctly state that db
is a logarithmic ratio and the examples you quote below relate to that. It
is important to note that there is another customary use for the term db,
and that is in sound pressure. In this latter and different usage 0db
corresponds to the threshold of human hearing, a fixed point. From that
point forward all numbers follow the logarithmic ratio. I mention that
because it would be easy to draw some false conclusions from this:"> Note:
The following is rough and not 100% technically accurate, but I
hope it's good enough to illustrate the point.

Suppose for the sake of argument that putting 1W into a speaker gives 20dB
of "white noise" to the listener sitting in the middle of a room. If you
boost the power to 10W you will give him 30dB. To his ears the difference
in sound levels is that of rustling leaves compared to an empty movie
house (twice as loud).

To make *that* twice as loud you need 10 X 10W (100W). That moves you up
to a residential area at night. To double *that* you need 1,000W (quiet
restaurant). To double *that* you need 10,000W.

In other words 10X the power only makes it twice as loud. If you wanted to
make that white noise as loud as a rock concert (120dB) you'd need
10,000,000,000 watts.

While the ratios are correct, you DON'T need 1000 watts and forward to
approximate the noise level of a quiet restaurant. Just clarification, I
don't disagree with any of your post otherwise and the link does give both
definitions of decibel.

Gerry
"Jim Carr" <newsgroups@xxxxxxxxxxxxxx> wrote in message
news:0G8qk.30397$KZ.20236@xxxxxxxxxxxxxxx
Jose de las Heras wrote:

I may be a bit naive here... (?)
I don't have a practical knowledge about how much transient peaks can
amount to above the "continuous" output of the amp.
Intuitively I'd imagine that to pick a cab, I'd look at the "continuous"
value if tehre's such thing. That's what I want to be as high or above
the max output of the amp. the higher the better, and yes, if price is an
issue I'll compromise as to how high I go.
THEN, I'd probably want a limiter to tame the extreme peaks when they
occur... so I should be fine.
Or is this too naive?

There are continuous power ratings for speakers, yes. We're talking audio
for live music here, not car stereos, so ignore all the crap you see in
the sports section of the newspaper.

In the later part of your post you seem to get what I'm driving at.
However, I think you might need some education in power ratings and
decibels. Check out this link regarding power ratings, decibels and
perceived loudness.

http://tinyurl.com/5ntj28

Note: The following is rough and not 100% technically accurate, but I hope
it's good enough to illustrate the point.

Suppose for the sake of argument that putting 1W into a speaker gives 20dB
of "white noise" to the listener sitting in the middle of a room. If you
boost the power to 10W you will give him 30dB. To his ears the difference
in sound levels is that of rustling leaves compared to an empty movie
house (twice as loud).

To make *that* twice as loud you need 10 X 10W (100W). That moves you up
to a residential area at night. To double *that* you need 1,000W (quiet
restaurant). To double *that* you need 10,000W.

In other words 10X the power only makes it twice as loud. If you wanted to
make that white noise as loud as a rock concert (120dB) you'd need
10,000,000,000 watts.

For another example play something on your stereo right now (preferably a
mono track). Put the speakers next to each other. Mute one speaker. As you
toggle that speaker on and off that's about a 3dB difference. It's louder,
but not by much.

If you had an amp running at 50W continuously and had clean peaks at 100W,
the difference in sound levels is also about 3dB. Not much, is it? The
difference is the same as running at 500W with 1,000W peaks. If we wanted
to be able to cleanly handle 6dB peaks we'd need 2,000W (4x the power).
Think in terms of power ratios rather than counting watts.

Sure, you could buy speakers that could handle 2,000W continuously, but
why would you? You'd need something like a couple of Ampeg 8x10 cabinets.
But in the real world you could get away with a lot less in terms of
cabinets. This assumes, of course, that running at 500W continuously is
all you need, which for most gigs is probably more than enough. It has
been for this weekend warrior playing bars, clubs, and the occasional
festival with professional sound systems.

> The issue is not so much that teh amp should be rated X times above the
speakers... but that if using the right speakers for the venue (by this I
mean that they can handle ok the wattage required for the venue) one CAN
use an amp rated so many times above the rating of teh speakers because
one will NOT use all that power, and you will be running the amp in its
"comfort zone" as I called it earlier.

Yep. You'll have a system that provides adequate sound coverage with
plenty of headroom. You won't be hauling around (or paying for) cabinets
you really don't need.

Example (with made up numbers)... you figure you need 1000W to get the
right sound levels. The chosen speakers can handle that. Then your amp
may be 4000W, for instance. If you turn it up too high you'll probably
destroy your speakers... but you're not going to get even close, you'll
use the 4000W amp to reach the required 1000W, and this is achieved
without pushing the amp (clean headroom available)... no distortion, etc.

Yep.

This does make sense to me now. And yes, you can use speakers rated to
4000W or higher, but it'll be quite an extra expense and unnecessary (as
long as you somehow make sure that power amp doesn't get pushed above
1000W).

Right?

I'd say so.

And while we're on the subject, not all cabinets are created equal.
There's the sensitivity rating. For the sake of argument assume they are
accurate. Cabinet A might be rated at 97dB @1W/M. That means it puts out
97dB with 1W of power when measured at 1 meter. Cabinet B is 100dB @1W/M.
It's 3dB louder with the same power.

If you assume a perfect world, then in theory you'd need to drive cabinet
A at 1,000W to get the same "loudness" as cabinet B at 500W. That means
you'd need a more powerful amp to keep your headroom.

In the semi-real world my Hartke 2x10 is rated at 99dB @1W/M with power
handling at 200W. Behringer's version is rated at 95dB @1W/M with power
handling at 500W. In theory I need less power to get my Hartke as loud as
the Behringer.

In the real-real world who knows? You got frequency response curves and
all sorts of other stuff. The important lesson just because a cabinet can
"handle" more power doesn't mean it can go louder.

That's why I always buy amps and cabinets based solely on appearance.
Flashing lights and shiny speakers are the *really* important deciding
factors.


--
Write a wise saying and your name will live forever.
- Anonymous


.

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