How do you figure out watts/spl output of a speaker?

[Tripqzon]

If you know the sensitivity of the speaker, how do you figure out how many watts it will take to get a specified spl level output from the speaker?

Example:
Speaker: HPM-100 rated at 92.5db at 1watt/1 meter

How many watts would it take to get an spl of 110db at 1 meter.

There has to be a formula but I can't seem to find it.

Thanks,
Paul

[joelongwood]

Every time you double the power, you add 3dB.
92.5 @ 1 watt
95.5 @ 2 watts
98.5 @ 4 watts
101.5 @ 8 watts
104.5 @ 16 watts
107.5 @ 32 watts
110.5 @ 64 watts

Hope this helps. :D

[FalconEddy]

If you know the sensitivity of the speaker, how do you figure out how many watts it will take to get a specified spl level output from the speaker?

Example:
Speaker: HPM-100 rated at 92.5db at 1watt/1 meter

How many watts would it take to get an spl of 110db at 1 meter.

There has to be a formula but I can't seem to find it.

Thanks,
Paul


For the HPM-100 it would be just a bit under 64 watts

. . Falcon

[Tripqzon]

Oh my god. I should have known that. Someone kick me in the head!

The reason I ask is because I was messing around one night last weekend with a Radio Shack digital spl meter and it hit 117db. I was just wondering how watts it took to do that. I hadn't opened up my Emotiva amp to that extent prior and was curious. I was actually measuring at about 5' from the speaker but that's ok. I know these meters are not the most accurate but I did make an initial measurement with 1 watt (2.83v) in and the meter was jumping between 92 and 93db at just over 3'. So I figured it was close enough to get a decent measurement.

Thanks,
Paul

[mamboni]

Oh my god. I should have known that. Someone kick me in the head!

The reason I ask is because I was messing around one night last weekend with a Radio Shack digital spl meter and it hit 117db. I was just wondering how watts it took to do that. I hadn't opened up my Emotiva amp to that extent prior and was curious. I was actually measuring at about 5' from the speaker but that's ok. I know these meters are not the most accurate but I did make an initial measurement with 1 watt (2.83v) in and the meter was jumping between 92 and 93db at just over 3'. So I figured it was close enough to get a decent measurement.

Thanks,
Paul


Of course JoeLongwood is correct, for anechoic however. In room, the power requirement does not quite double for every +3db increase in loudness, because of energy storage by the room. So, you might have achieved 117 dB with far less than waht is theoretically perscribed.

Please tell us about the Emotiva amp. I for one cannot believe they sell for so little $$$ given their build and parts quality, power rating and specs - they just might be the best deal in new-retail high end audio today - seriously.:tresbon:

[Tripqzon]

Of course JoeLongwood is correct, for anechoic however. In room, the power requirement does not quite double for every +3db increase in loudness, because of energy storage by the room. So, you might have achieved 117 dB with far less than waht is theoretically perscribed.

Please tell us about the Emotiva amp. I for one cannot believe they sell for so little $$$ given their build and parts quality, power rating and specs - they just might be the best deal in new-retail high end audio today - seriously.:tresbon:

I understand what you're saying about the anechoic chamber. I was mainly looking for a general rule of thumb.

As far as the Emotiva amplifier, I'm not sure exactly what information you're looking for. Here is a link to info on it. http://emotiva.com/rpa1.html

I posted a review here http://www.audiokarma.org/forums/showthread.php?t=136113 as well.

One thing I will say is that Emotiva has proven to me that you can get top quality gear at a price that is attainable by the average Joe such as myself. I will be a loyal customer for years to come.

I've called them at least 3 times since I've owned their gear and they are very nice to talk to. They don't make you feel like you're bothering them. In fact I spoke with Lonnie, I believe he is the head engineer, today about the new amps they are coming out with and I was on the phone for over 20 minutes with him. He never made me feel like he was being bothered or rushed. I could of spoken with him longer but I was on my break at work and my time was up. If you look through the Emotiva forums, there is a statement by Lonnie somewhere that states that nobody has ever paid for a repair and they weren't about to break a record now.

Hope this helps.

Paul

[electroking]

Of course JoeLongwood is correct, for anechoic however. In room, the power requirement does not quite double for every +3db increase in loudness, because of energy storage by the room. So, you might have achieved 117 dB with far less than waht is theoretically perscribed.
...


This statement is puzzling. Why would energy storage in the room cause
such a generation of 'free power'. The speaker, room and furniture can
be regarded as a linear circuit driven by the amplifier, and energy storage
in the room can be accounted for by reactive components (capacitors
and inductors) in that circuit. However, in order to double the power
level in any resistor in the circuit, you still have to double the source
(i. e. amplifier) power. Or maybe this aging engineering physicist is
missing something. Please do enlighten me.

[jhal]

Also, keep in mind that speaker output will drop some as the voice coils heat up and increase in resistance at high power levels. Power compression is the term for this occurrence.

[Tripqzon]

Would the level reading be more accurate if you took the speaker outside where there are no boundaries for sound to reflect off of or am I way off here?

[mamboni]

This statement is puzzling. Why would energy storage in the room cause
such a generation of 'free power'. The speaker, room and furniture can
be regarded as a linear circuit driven by the amplifier, and energy storage
in the room can be accounted for by reactive components (capacitors
and inductors) in that circuit. However, in order to double the power
level in any resistor in the circuit, you still have to double the source
(i. e. amplifier) power. Or maybe this aging engineering physicist is
missing something. Please do enlighten me.

Reflected sound and room modes will add to the anechoic sound output of the loudspeaker and be reflected in a higher SPL reading by the meter. I am speaking of real world sound, not a theoretical simulated circuit that obeys Kirchoff's rules.

For the same energy input, your loudspeaker will "sound" louder in your room than when sitting in the middle of a flat open field, given the same distance to to the listening position, no?

[electroking]

Reflected sound and room modes will add to the anechoic sound output of the loudspeaker and be reflected in a higher SPL reading by the meter. I am speaking of real world sound, not a theoretical simulated circuit that obeys Kirchoff's rules.

For the same energy input, your loudspeaker will "sound" louder in your room than when sitting in the middle of a flat open field, given the same distance to to the listening position, no?

That's understood, of course. And at some frequencies, in a very poorly
designed room, you could also have the opposite effect, destructive
interference causing dead spots. But the question is, if you get reading
x with the meter in a certain position, how could x vary by anything other
than 3 dB when you increase the amplifier power by that same amount?

P.S.: I should say 'how could x increase by more than 3 dB when...', as it is understood that
heating in the speaker coil could actually decrease efficiency. So I understand
the reading could increase by somewhat less than 3 dB, but never by more
than 3 dB in the scenario stated above. Regards.

[charliemcd]

Lots of variables here to affect the answer to Tripqzon's question, as already noted by other posters. Here's my cheesy attempt to show the math.

P = PE * 10^((SPL- Eff)/10)
P = (1 watt) * 10^((110-92.5)/10)
P = 10^(1.75)
P = 56.2 watts

where
P= power needed for SPL you want
PE = power at efficiency rating = 1 watt
SPL = Sound Pressure Level you want = 110 dB
Eff = speaker efficiency = 92.5 dB

and 10^1.75 means 10 to the 1.75 power

[x_25]

That's understood, of course. And at some frequencies, in a very poorly
designed room, you could also have the opposite effect, destructive
interference causing dead spots. But the question is, if you get reading
x with the meter in a certain position, how could x vary by anything other
than 3 dB when you increase the amplifier power by that same amount?

P.S.: I should say 'how could x increase by more than 3 dB when...', as it is understood that
heating in the speaker coil could actually decrease efficiency. So I understand
the reading could increase by somewhat less than 3 dB, but never by more
than 3 dB in the scenario stated above. Regards.

Don't forget that the walls of an anechoic room are designed to absorb sound. While the walls in a normal room usually reflect a lot of sound so it sort of sticks around a bit longer. (then again that is my high school physics level of understanding of this.)

[mamboni]

That's understood, of course. And at some frequencies, in a very poorly
designed room, you could also have the opposite effect, destructive
interference causing dead spots. But the question is, if you get reading
x with the meter in a certain position, how could x vary by anything other
than 3 dB when you increase the amplifier power by that same amount?

P.S.: I should say 'how could x increase by more than 3 dB when...', as it is understood that
heating in the speaker coil could actually decrease efficiency. So I understand
the reading could increase by somewhat less than 3 dB, but never by more
than 3 dB in the scenario stated above. Regards.


I think I understand your insight: even after factoring in room effects, and assuming that the room, represented as some combination of resistance, capacitance and inductance, remains linear vis-a-vis power; then yes, a +3dB increase in average sound level should result from each doubling of [amplifier] power input. I wasn't clear in my comment about loudspeaker SPL and anechoic versus non-anechoic rooms. Stated simply, a 90 SPL loudspeaker fed 1 watt will output 90 dB at 1 meter, by definition, under anechoic conditions. In a typical room, output will be greater than 90 dB - considerably more so in a small hi-Q (reflective) room. I think we are in agreement. Of course, loudspeaker manufacturers generally spec out SPL at 1 kHz - and this is a far cry from describing the true efficiency of the loudspeaker whish is equally a function of it's bandwidth.

The beauty of physical science is that there is but one version of the truth.

[Tripqzon]

So which is the proper method of testing. Do manufacturers use pink noise or a 1kHz tone?

Thanks,
Paul