Speaker power question

[BobG]

In the tube amp days, we had big theater speakers because the amps
were wimpy. Now we have big powerful amps, speaker size and mass are
probably more important than effciency. Especially if you are loading
them in and out of a truck with no lift gate. If the only thing you
are worried about is blowing speakers, that is almost purely a thermal
problem... a 1" voice coil can handle about 100W, a 2" vc about 200,
and a JBL 4" vc with square wire might handle 400... so you get an rms
reading meter with a very slow time constant, and keep the long time
average rms level about 1 or 2 db below what the speakers will handle
heat wise. Big 20dB peaks like rim shots should go right through,
contribute thier little bit to the rms, and keep on chuggin.

 

[Bob Masta]

On Tue, 06 Nov 2007 13:55:14 -0800, Uriah <uriahsky@hotmail.com>
wrote:

I can buy a 300 watt speaker or a bunch of 150 watt speakers much
cheaper. Can you run the 150 speakers in such a way that they put out
300 or more watts of power, or loudness? Do two 150 watt speakers put
out as much loudness as one 300 watt speaker? If so how would you
wire it up? They are all 8ohms and in RMS.
Just not sure about this.
Thanks
Uriah

As others have noted, the efficiency of the speaker is important here.
This is given as the SPL output at 1 meter for 1 watt into the
speaker. The specs may just say something like "Sensitivity: 98 dB",
or they may put "1w/m" or some such after that. If you look at a lot
of speaker specs, you quickly discover that there is a rather wide
range in sensitivity values, and that sensitivity is usually directly
correlated with magnet weight, and likewise with price.

Also note that each 3 dB increase in sensitivity is the same as
doubling the input power, and it comes without additional heating in
the amp or the speaker. I'll bet if you check the sensitivity numbers
you'll find that you need quite a lot of the cheap speakers to equal
the expensive speaker in output, assuming 1 watt into each of them.
(Actually, if you are adding speakers with the exact same program
input, then two speakers with the same power output will produce
a 6 dB increase in sound where they are in phase... see below.)

Again as others have noted, even if all else is equal there can be
drawbacks to having multiple speakers. For midrange and high
frequencies the image will be smeared out because the sound will not
be coming from a point in space. Worse, with two or more sources
producing the same frequency, there will be locations where the two
sounds add together in phase and others where they cancel, leading
to peaks and dips in the frequency response that vary with location.

For low bass (below 100 Hz or so) there is not an imaging
problem because we don't localize these low frequencies very well.
That's why many systems can have a single subwoofer that combines
both left and right channels. (And recorded music rarely has much
low-frequency difference between channels anyway.) There probably
won't be a phase cancellation problem either, as long as you keep the
two drivers close together. (Phase issues arise when the separation
is more than a significant fraction of a wavelength. You may find it
educational to compute the wavelengths of a few selected audio
frequencies, just to get a feel for this. The speed of sound depends
upon temperature and humidity, but just for a simple approximation
use 1000 ft/sec.)

Best regards,


Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!

 

[Phil Allison]

"Uriah"

I can buy a 300 watt speaker or a bunch of 150 watt speakers much
cheaper. Can you run the 150 speakers in such a way that they put out
300 or more watts of power, or loudness? Do two 150 watt speakers put
out as much loudness as one 300 watt speaker? If so how would you
wire it up? They are all 8ohms and in RMS.
Just not sure about this.

** Using multiple, similar speakers will make LOUDER sound than a single
speaker can manage - just like using a larger diameter speaker makes more
sound than a smaller one.

The power rating of a speaker is its INPUT power - which does NOT tell
you how much sound it can deliver.

You need to provide a link for the make and model of the speakers and say
what YOU intend to use them for to get any useful advice.



........ Phil

 

[Jon Slaughter]

"Uriah" <uriahsky@hotmail.com> wrote in message
news:1194386114.367483.113390@e34g2000pro.googlegroups.com...

I can buy a 300 watt speaker or a bunch of 150 watt speakers much
cheaper. Can you run the 150 speakers in such a way that they put out
300 or more watts of power, or loudness? Do two 150 watt speakers put
out as much loudness as one 300 watt speaker? If so how would you
wire it up? They are all 8ohms and in RMS.
Just not sure about this.
Thanks
Uriah

Not really... There is more to a speaker than just its wattage which is just
how much electrical power it consumes. You can easily connect your 150 watt
speakers to form the 300 watt in the sense of "electrical equivalency" but
they won't necessarily be equivalent sound wise.

For example, you can build a wall of tweeters that use the same power as
your 300 watt speaker but its surely not going to sound the same.

You need to weigh cost, size, quality, etc... to get a better answer.

 

[Nobody]

On Tue, 06 Nov 2007 13:55:14 -0800, Uriah wrote:

I can buy a 300 watt speaker or a bunch of 150 watt speakers much
cheaper. Can you run the 150 speakers in such a way that they put out
300 or more watts of power, or loudness? Do two 150 watt speakers put
out as much loudness as one 300 watt speaker? If so how would you
wire it up? They are all 8ohms and in RMS.

If you connect 2 150W 8Ohm speakers in series, you get a 300W 16Ohm
speaker. Because of the increased resistance, you'll actually get less
power from a given voltage. If you want to increase the power, you'll need
to increase the voltage.

If you connect 2 150W 8Ohm speakers in parallel, you get a 300W 4Ohm
speaker. Because of the reduced resistance, you'll get more power from a
given voltage, but you will need an amplifier that can supply the
increased current.

You can adjust the effective resistance using a suitable transformer (one
designed for audio, not mains), although this will add to the cost.

Or you could connect 4 75W 8Ohm speakers to get a 300W 8Ohm speaker by
wiring pairs of speakers in series and the two pairs in parallel:

|
|
+--+--+
| |
- -
| | | |
| | | |
- -
| |
- -
| | | |
| | | |
- -
| |
+--+--+
|
|

Each "leg" will be 150W 16Ohm, giving 300W 8Ohm overall.

Lower power speakers will tend to be physically smaller, and will tend to
be less efficient at low frequencies, so you'll tend to get less bass that
way.

Oh, and you need to connect all of the speakers with the same polarity,
otherwise they will tend to cancel each other out, reducing the overall
volume.

 

[BobW]

"Uriah" <uriahsky@hotmail.com> wrote in message
news:1194386114.367483.113390@e34g2000pro.googlegroups.com...

I can buy a 300 watt speaker or a bunch of 150 watt speakers much
cheaper. Can you run the 150 speakers in such a way that they put out
300 or more watts of power, or loudness? Do two 150 watt speakers put
out as much loudness as one 300 watt speaker? If so how would you
wire it up? They are all 8ohms and in RMS.
Just not sure about this.
Thanks
Uriah

Uriah,

You have to tell us more.

How much power can your amplifier put out into 8ohms? 4ohms? 2ohms? 1ohm?

What is the efficiency of the 150W speaker vs the 300W speaker?

Bob

 

[Uriah]

I can buy a 300 watt speaker or a bunch of 150 watt speakers much
cheaper. Can you run the 150 speakers in such a way that they put out
300 or more watts of power, or loudness? Do two 150 watt speakers put
out as much loudness as one 300 watt speaker? If so how would you
wire it up? They are all 8ohms and in RMS.
Just not sure about this.
Thanks
Uriah

 

[Uriah]

Thank you everyone. I do now think I have enough info to make a
decision .
I appreciate all of the input, and I am double checking things,
especially the
sensitivity part that I wasn't aware of how it worked. I haven't even
got to the
amp part. I wanted to make sure I understood the speaker part first.
The speakers are sold through a local liquidation place and I have to
go
back there to get more details. It seems there is a little bit of
conflicting
advice but the bottom line is that yes wired correctly and powered
correctly
I should be able to produce more db from multiple speakers then from
just a single
speaker given that all things are equal or ideal. Quality of the sound
is not at
issue in this setup.
Thanks again
Uriah

 

[BobG]

If they are cheep enough, buy a couple extras for spares in the
future, and a couple to 'test'. Play your favorite cd into the fft
analyzer in cooledit and get an idea of the general shape of the
spectrum to be reproduced, then play the cooledit pinknoise generator
thru a graphic eq with about the same shape. Read the volts with an
rms voltmeter and run your test speaker and see if they'll take 50w
for 30min or so. Let em cool down for a while and turn it up 3db to
100W and see if they'll last for several minutes. When the smoke comes
out the bass port, subtract 3db from the power setting and use that
number to calibrate your limiters.

 

[Bob Masta]

On Sat, 10 Nov 2007 12:27:34 -0800, Uriah <uriahsky@hotmail.com>
wrote:

Thank you everyone. I do now think I have enough info to make a
decision .
I appreciate all of the input, and I am double checking things,
especially the
sensitivity part that I wasn't aware of how it worked. I haven't even
got to the
amp part. I wanted to make sure I understood the speaker part first.
The speakers are sold through a local liquidation place and I have to
go
back there to get more details.

I wouldn't be at all surprised if the liquidators don't have
sensitivity specs to provide.

It seems there is a little bit of
conflicting
advice but the bottom line is that yes wired correctly and powered
correctly
I should be able to produce more db from multiple speakers then from
just a single
speaker given that all things are equal or ideal. Quality of the sound
is not at
issue in this setup.

Ahh, but with speakers things are always a lot farther from "equal or
ideal" than with any other part of the system. If you are unable to
get sensitivity specs, the best you can probably do is go by weight,
magnet weight in particular. This is also fraught with problems since

different types of magnets have different strength-to-weight ratios,
and because manufacturers often include the magnet "structure"
in their weight numbers (if any). But in general a manufacturer who
is trying to make a cheapo speaker won't put a lot of metal into it if
it can be helped. So if you see a big difference in magnet weight,
that might be a good indicator.

Best regards,


Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!