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does Speaker sensitivity apply to all frequencies? (Read 455 times)
flargosa
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does Speaker sensitivity apply to all frequencies?
11/01/17 at 14:11:58
 
So speaker sensitivity is measured by feeding it 1 watt, playing one tone, a 1 kHz tone?  What does that mean?  So a speaker rated at 91 dB/Watt plays 91 dB at 1 kHz with 1 Watt? or 91 dB on all frequencies with 1 watt?

Many say low frequency need more power due to the increased amount of woofer movement needed to produce lower frequencies.  So will playing pink noise at 1 watt show an uneven slope frequency graph where the low end is at a lower dB than the higher freq?  

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Sources: 2Qute, Hugo, Rega P5, Marantz SACD 8005.
Amps: Decware SE84UFO2, Nelson Pass Aleph
Speakers: Klipsch Palladiums, Golden Ear Triton Two, Focal Elear.

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dank
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Re: does Speaker sensitivity apply to all frequencies?
Reply #1 - 11/01/17 at 17:47:05
 
The sensitivity is an average number, and it can be off by quite a bit.  Many things can contribute that aren't taken into account by the simple number you get when looking at speaker specs.  Things like room reflections, enclosure gain (ported box or horn load can change sensitivity at the lower frequencies by 3 to 6 db and if you ever hit a resonance point, all bets are off).  Most speakers will offer a graph of output volume at a fixed distance verses frequency when the speaker is given a fixed amount of power.  You should be able to see a correlation between that graph and the sensitivity number.  But even that can be off as many times the speaker is driven by a fixed voltage (2.828 V) and to get power you need to use the speaker impedance which also varies by frequency, even though the number you usually see is fixed (8 or 4 ohm).  That is also an average.

Then there is the human ear to consider.  It is less efficient at lower frequencies that at mid-range frequencies.  Pink noise takes this into account by putting more energy into the bass to make it seem like all frequencies are equal volume.  White noise is all frequencies at the same volume and that always seems a bit lacking in bass to the ear.

So, all these average numbers can really only be used as a ballpark starting point or in relative comparisons as a 94 db 4 ohm speaker really ought to be louder than a 91 db 4 ohm speaker - but even there you need to be careful (is it measured at 1w/1m or 2.83v/1m)

Dan
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flargosa
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Re: does Speaker sensitivity apply to all frequencies?
Reply #2 - 11/01/17 at 19:01:11
 
What do you mean by "The sensitivity is an average number, and it can be off by quite a bit."? So my speaker specs says  91dB/2.83V/m and Stereophile also measured the same dB(Golden Ear triton two).  So in an anechoic, if feed 2.83volts. Are you saying some freq will measure lower and some higher in volume ?

So if a speaker says  91dB/2.83V/m, will it sound louder or softer with 1 watt?    

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« Last Edit: 11/01/17 at 19:03:24 by flargosa »  

Sources: 2Qute, Hugo, Rega P5, Marantz SACD 8005.
Amps: Decware SE84UFO2, Nelson Pass Aleph
Speakers: Klipsch Palladiums, Golden Ear Triton Two, Focal Elear.

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dank
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Re: does Speaker sensitivity apply to all frequencies?
Reply #3 - 11/01/17 at 19:26:15
 
power = voltage squared divided by impedance.  So if the speakers are 8 ohms, 2.83v is 1w.  If the speakers are 4 ohms, 2.83v is 2w.  Obviously a 91db 4 ohm speaker driven by 2w should be louder than a 91 db 8 ohm speaker driven by 1w.

I really have no idea how the speaker sensitivity number is derived.  But I would hope that a number of different frequencies are measured and some sort of average is taken.  If I had to guess, being the pessimistic person that I am, I would imagine that the speaker manufacture comes up with a way to measure his speaker that makes it look the best.  A few years back a "new" series of raw drivers from Madisound appeared in the marketplace that had sensitivity numbers about 6 db higher than anything else comparable.  The one that sticks in my mind was a 15" woofer / subwoofer, 8 ohms, rated at 103 db 1w/1m.  Once purchased and installed the they sounded good, but the actual sensitivity was closer to 96.  A few years later these drivers from Madisound disappeared from the marketplace.  You can find them every once in a blue moon on Ebay.

Dan
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DB2
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Re: does Speaker sensitivity apply to all frequencies?
Reply #4 - 11/02/17 at 19:07:51
 
"Loudspeaker Sensitivity: a measure of Sound Pressure Level (SPL) at a specified distance for a specified input signal. This is usually specified for a loudspeaker in a non-reverberant environment, in dB SPL and referenced to 1 meter on the reference axis with an input of 2.83 volts RMS, typically at one or more specified frequencies (often 300, 400, 500, 600Hz or the average of these). Sensitivity should always be accompanied by an impedance specification."
www.audioholics.com/loudspeaker-design/loudspeaker-sensitivity
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flargosa
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Re: does Speaker sensitivity apply to all frequencies?
Reply #5 - 11/02/17 at 20:33:07
 
Is the sensitivity of the measured frequency ranges(300hz - 600hz) a good representation of the other frequency sensitivity?  I guess, maybe? Otherwise they would measure across a wider frequency range?
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Sources: 2Qute, Hugo, Rega P5, Marantz SACD 8005.
Amps: Decware SE84UFO2, Nelson Pass Aleph
Speakers: Klipsch Palladiums, Golden Ear Triton Two, Focal Elear.

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DirtDawg
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Re: does Speaker sensitivity apply to all frequencies?
Reply #6 - 12/02/17 at 21:41:28
 
DanK summed it up fairly well in his first answer.  Sensitivity is an average of usually several octaves of either pink noise or swept frequencies.

Often cheap speakers advertise a number and the closes to reality is what those speakers can do at 1KH, which is where many speakers have their peak efficiency. That is a little misleading in terms of the realistic usefulness of a speaker system.

To have any chance of interpreting a sensitivity number, let alone comparing that number with another published number from another manufacturer, all the ways they measured the sensitivity  must be a part of the question and disclosure of information.

To compare you must have enough information about how each manufacturer tested their systems in order to arrive at the "average" sensitivity to make sure you are comparing apples to apples, not oranges.
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« Last Edit: 12/02/17 at 21:46:43 by DirtDawg »  
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Lonely Raven
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Re: does Speaker sensitivity apply to all frequencies?
Reply #7 - 12/04/17 at 16:14:06
 

To add more to the above - speakers are dynamic analog devices. Just look at the impedance curve at different frequencies! The goal of a good design would be consistency, but being a dynamic analog device...well, you cannot change the laws of physics, captain!

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