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I was contemplating a set amp to go with my speakers (focal utopia micros and I already have an old audion parrallel 300b)I was considering moving to a conventional single 300b per channel. some people have indicated that this can work since I dont listen to loud music. something I dont understand is the sensitivity /effeciency ratings of speakers which dont appear to be an effective measure of how easy they would be to drive. for example the grande utopia micros have an efficency of (2,8V/1 m) 92dB and my micros are 89db. but no one would consider driveing them with a 300b set.what am I missing. do they measure seakers at only a single frequency ie 1k hertz
Follow Ups:
with 89 dB speakers. Not very loud is 70-75 dB peaks. From rough calculations, you need 4 W from a single speaker at 3 m distance in open space to have 71 dB SPL. Because of room reflections and 2 channels, you practically need about 2 W/channel in a small-to-medium room. I use 14 WPC amplifier with 87 dB speakers, and for normal listening volume is at 9 o'clock, which I belive corresponds to 1-2 W.Important requirement is though that speakers perform well at low and very low levels. Speakers that specify minimum driving power are not of this kind.
The impedance and the efficiency both matter.First, some nomenclature. Manufacturers often use the terms "efficiency" and "sensitivity" interchangeably, which creates confusion. "Sensitivity" refers to the output level with a 2.83 volt input, and "efficiency" refers to the output level with a 1 watt input. The two are the same for an 8 ohm load, but different for anything else.
A sensitivity of 92 dB/2.83 volts/1 meter is ambiguous without knowing the impedance. If this is an 8 ohm speaker, then the efficiency is 92 db/1 watt/1 meter. But if it's a 4 ohm speaker, then the efficiency is really only 89 dB/1 watt/1 meter, because 2.83 volts into a 4-ohm load is 2 watts, not 1 watt.
It gets worse.
Very seldom does a speaker have a smooth impedance curve. Usually the impedance curve has peaks and dips, and these tend to make the load more difficult. Dips especially so, peaks less so (generalizing here). And it's not uncommon for a speaker to have an impedance dip down to barely over half its rated value.
So...
If our 92 db/2.83 volt speaker is a 4 ohm speaker with an impedance dip to 2.5 ohms around 150 Hz (where there's lots of music energy), then it's going to be a very difficult load for an SET amp.
On the other hand, if we have a speaker that's 89 db/2.83 volts/1 meter sensitive and the impedance curve stays between 6 and 12 ohms, it will be a much easier load and our SET amp will not only sound better but also play louder before clipping.
Hope this helps.
Close, but no cigar. "Efficiency" is a measure of just that... what percentage of an electric watt IN is converted into (fractional) acoustic watts OUT. You won't see "efficiency" specified much; most speakers are a few per cent efficient.Sensitivity is defined dB per watt (or, generally, at 2.83VAC, which is indeed 1W at 8 ohm but 2W at 4 ohm) at some fixed distance (typically 1 meter, but at 40 feet for the old EIA spec).
Your speakers are worth a try on a 300B SE amp (ca. 8W,usually), IMNSHO.
Well I think we have the same understanding but not necessarily the same usage of terms.To get really precise, "efficiency" is indeed a raw percentage. The convention is to use this percentage in prosound, but not in home audio. Most home speakers are less than 1/2% efficient.
You wrote: "Sensitivity is defined dB per watt (or, generally, at 2.83VAC, which is indeed 1W at 8 ohm but 2W at 4 ohm) at some fixed distance..."
In my opinion, using the term "sensitivity" to describe BOTH the 1 watt/1 meter AND the 2.83 volt/1 meter SPL rating is confusing. Likewise, interchangeably using the term "efficiency" to describe both is also confusing. As you point out, the voltage-based SPL spec changes as the impedance of the load changes - but the wattage-based SPL does not! That's because it's really power (watts) that drives a speaker, NOT volts!
The explanations of "efficiency" and "sensitivity" at the link you provided in your "scoop" post is very good, by the way. First describing the basis of 1 watt/1 meter specifications:
"The manufacturer measures the sound pressure level (SPL) that a speaker produces with one watt of power at a distance of one meter. But this measurement is actually a measure of a speaker's EFFICIENCY, and NOT its sensitivity." [emphasis Duke's]
And next, the basis for 2.83 volt/1 meter specifications:
"The manufacturer measures the SPL a speaker produces at 1 meter on 2.83V of input power. Today's solid-state amps do a pretty good job of maintaining their output voltage in comparison to older, tube-style amps. So the measurement of a speaker's voltage SENSITIVITY is considered a more accurate measurement." [emphasis Duke's]
My point being, it is appropriate to use the term "efficiency" when referencing a 1 watt input, and the term "sensitivity" when referencing a 2.83 volt input. If there's another convention the industry would like to use that doesn't promote confusion, that would be fine with me.
The confusion probably first arose when marketing departments for manufacturers of 4-ohm speakers realized they could hike their numbers by 3 dB just by switching from a wattage-based specification to a voltage-based one. Few people would dig deep enough to find out exactly what the impressively high "efficiency" or "sensitivity" specification was based on, especially if the terms are used as if they're interchangeabe. (Now some manufacturers are using "in-room" specs, inflated by yet another 3-6 dB!).
I maintain that since power (acoustic watts) is what comes out of a speaker, power (electrical watts) is the more appropriate measurement of what goes into it. Note that it is power (watts) that heats up voice coils. You don't see "voltage handling" specs - you see "power handling" specs, in good old-fashioned watts.
Getting back to efficiency as a percentage, if you know the percentage efficiency and the wattage input, you can easily calculate the SPL output (ignoring power compression). However, if you know the percentage efficiency and the voltage input you cannot reliably calculate the SPL output. You must also have the impedance of the load. Once you have the voltage and the impedance you can convert to watts and calculate the SPL output. So focusing on voltage this or voltage that is to a certain extent a distraction from what really drives speakers - which is watts. That tells us what the speaker can do. If the amp's power doubles into a four ohm load, fine - let that be part of the amp's specs, not the speaker's.
Just my $.02 - not enough to buy a cigar.
Duke
see below, or also:
http://www.jsdsound.com/sensitivity.htm
http://www.hometheaterhifi.com/volume_1_1/v1n1spk.html
all the best,
mrh
- http://www.crutchfieldadvisor.com/ISEO-rgbtcspd/reviews/20030722/match_speakers.html?page=3 (Open in New Window)
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