hannan36 Posted July 22, 2004 Share Posted July 22, 2004 What is the difference between Sensitivity and Max Acoustic Output ratings ? Seems like older models use the Sensitivity rating in speaker specs, but newer use Max Acoustic Output ratings which makes it hard to compare. For example, how would I compare 2 woofers with the following ratings ? MAX ACOUSTIC OUTPUT: 109dB @ 30Hz 1/8 space, 1 meter vs SENSITIVITY: 95dB @ 1watt/1meter Thanks, Ken Quote Link to comment Share on other sites More sharing options...
Frzninvt Posted July 22, 2004 Share Posted July 22, 2004 Those are two entirely different rating types. One is indicating overall efficiency and the other is providing you the maximum output capability. For example a Khorn has an efficiency of 104db w/1watt input measured at 1 meter distance. On the flipside it is also capable of delivering 124db continuous output with 100 watts input. Hope that helps some. Quote Link to comment Share on other sites More sharing options...
D-MAN Posted July 22, 2004 Share Posted July 22, 2004 The 1/8 space is possibly refering to corner placement; that is, 2pi/r solid angle, if memory serves. This tends to boost bass output and therefore increase efficiency. The MAX output rating is the maximum (or loudest) achievable sound pressure level measured at a stated frequency attained in decibels at a given distance. Note that it lacks a wattage value required to achieve the stated output. However, in your example, the 30Hz at 109 db rating means that the bass at 30 Hz (really low) is damn loud at 1 meter; this is appropriate applications where overall efficiency is not a major concern. In the case of powered subwoofers and the like, the power rating is relatively senseless because the amplifier in question is actually part of the speaker itself. Also (IMO) the built-in amps are of such a "nature" that rating them like a "real" amp is relatively pointless. The traditional sensitivity rating is rather more clear in that it states the power in watts usually defined as 1 watt (sometimes also a voltage rating is given where watts=voltage*current) and tests for the loudness level in decibels achieved at a stated distance, typically one meter. It does not have anything to do with the maximum output, but indicates the relative sensitivity to wattage (and the resulting efficiency) of the speaker in question. The higher the decibel rating at 1 meter from 1 watt electical input, the more efficient the speaker. The MAX output rating is usually stated for subwoofers, PA and large format installations, such as stadium, concert stage, theater or such venue where the output level is typically close to its maximum anyway, and efficiency really does not matter. DM Quote Link to comment Share on other sites More sharing options...
D-MAN Posted July 22, 2004 Share Posted July 22, 2004 I forgot to add this tidbit: In MAX output values ALWAYS expect that the amp employed is also being operated AT ITS MAXIMUM OUTPUT. i.e., a subwoofer as above with a 200 watt built-in amp means that the amp is at 100% of its rated output when the measurements were taken. DM Quote Link to comment Share on other sites More sharing options...
dougdrake Posted July 22, 2004 Share Posted July 22, 2004 Also, sensitivity is usually reported/measured at a given frequency, typically 1000hz. It would be best if the frequency was stated along with the measurement. Different frequencies will give different sensitivity results. Quote Link to comment Share on other sites More sharing options...
hannan36 Posted July 22, 2004 Author Share Posted July 22, 2004 OK, I understand the difference now. Makes sense! I suppose the question becomes, why isn't sensitivity listed for something like the RSW-10 ? I assume it must be because it doesn't matter much since it's an amplified sub, vs an externally powered sub speaker. Thx KEn Quote Link to comment Share on other sites More sharing options...
artto Posted July 22, 2004 Share Posted July 22, 2004 Sorry to rain on everyones parade again, but all of the above are sort of correct, and also sort of wrong, or shall I say incomplete. Sensitivity is simply a measurement of acoustic output measured at a specified distance (hopefully under specified conditions), with specified input signal (level). Maximum output can mean any number of things. It might mean this is literally the maximum acoustic output the speaker is capable of. It might also mean this is the point where one or more of the drivers or components will probably fail, etc. The late & great Richard Heyser used to perform something called the cresendo test. Here the ratio of sound pressure level to drive power is measured for selected musical tones. Perfection occurs when the SPL precisely tracks the drive power. This measurement is also indicates what amount of discernable lateral shift of stereo image should occur with changes in drive level. All speakers compress their acoustic output with increasing drive power. Inefficient speakers tend to do this more than efficient ones. Basically, the approach from low level signals to maximum acoustical output is not linear. So just doing the math based on sensitivity verses drive power will not tell you the maximum acoustic output. Quote Link to comment Share on other sites More sharing options...
artto Posted July 22, 2004 Share Posted July 22, 2004 ---------------- On 7/22/2004 1:46:49 PM hannan36 wrote: OK, I understand the difference now. Makes sense! I suppose the question becomes, why isn't sensitivity listed for something like the RSW-10 ? I assume it must be because it doesn't matter much since it's an amplified sub, vs an externally powered sub speaker. Thx KEn ---------------- That is correct. Quote Link to comment Share on other sites More sharing options...
D-MAN Posted July 22, 2004 Share Posted July 22, 2004 I was wondering about the Klipschorn's sensitivity measurements... was it done with more than one mic? Was it measured at 1 meter directly in front with a single mic and then at the "side" and then the results averaged? I figure that a microphone 1 meter in front would not receive the full effect of the bass horn "mouths" as that would be rather indirect... Any ideas? DM Quote Link to comment Share on other sites More sharing options...
meuge Posted July 22, 2004 Share Posted July 22, 2004 The length of the bass sound waves is large enough to pretty much go around open obstacles, so I would not expect a huge difference as far as low frequencies go between placing a sensor right in front of the drivers, versus at a 90 degree angle. On the other hand if you do the same to a horn-loaded tweeter the difference should be clear. But i may be wrong. Quote Link to comment Share on other sites More sharing options...
artto Posted July 22, 2004 Share Posted July 22, 2004 This is what Richard Heyser wrote in his very detailed review of the Klipschorn in 'Audio', 11-86 "Doing a complete set of acoustic performance measurements on the Klipschorn is a tour de force for any reviewer. This is a corner horn loudspeaker system; hence it requires a corner. How does one make free-field measurements when there are no corners? Paul Klipsch solved the problem by building an anechoic chamber with insertable corners. The Klipschorn was also intended to be listened to at distances greater than 3 meters. The substantial size of this speaker and its geometry require that measurements be performed at such distance, and I have chosen 3.5 meters, since this is the distance at which I listened to these units. Even assuming I could lift it, I could not haul the Klipschorn out of doors for lower frequency measurements since it needs corners to reproduce low notes. I puzzled over this problem for quite some time and then decided to resort to computer software and physics." The whole article is available in the papers I prepared last year for Forum members. Forum member Justin scanned them and it is available in PDF format from his website www.soundwise.org as "The Papers" Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted July 29, 2004 Share Posted July 29, 2004 There is also the ERC or Elastic Rebound Characteristic, which is the distance a component will bounce after being dropped from a height of one metre onto a marble slab. Quote Link to comment Share on other sites More sharing options...
KGeist Posted July 30, 2004 Share Posted July 30, 2004 Sensitivity measurements are typically made at three meters and then converted to a one meter measurement (add 9.5 dB). You want to be in the farfield of the loudspeaker in order to be sure the drivers are aligned properly. The one meter measurement is simply a more convenient way to state sensitivity. Sensitivity in a "powered" subwoofer doesn't mean a lot in the traditional sense because the input is fed through the internal power amplifier. Subwoofer amplifiers are generally highly equalized and therefore one number doesn't easily apply. On the other hand, stating subwoofer output for a given line input does make some amount of sense. For example, for a 100 mV input at 40 Hz, the subwoofer will generate 90 dB under 1/2 space conditions. The only problem with this approach is that it doesn't reflect the efficiency of the loudspeaker because the amplifiers voltage gain (amplifier sensitivity) is now included in the measurement. Kerry Quote Link to comment Share on other sites More sharing options...
Deang Posted July 31, 2004 Share Posted July 31, 2004 Pretty funny. I stit 12 feet away from my Klipschorns, and I call it nearfield. Quote Link to comment Share on other sites More sharing options...
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