How does speaker sensitivity affect real world SPL?

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khachai44
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#1 How does speaker sensitivity affect real world SPL?

Post by khachai44 »

When it comes to mids and highs, efficiency (sensitivity) is a fairly
good indicator of output differences at the same power level. When it
comes to subwoofer performance, the driver's sensitivity is irrelevant
unless you are also specifying a box volume.

An efficient sub requires a larger box to achieve equivalent extension
to a less efficient sub. In a small box, the less efficient sub will
actually be LOUDER at low frequencies at the SAME POWER as the more
efficient sub.

Linear excursion is a very good indicator of ultimate output capability
(given sufficient power to drive the speaker to that point.) To make
sound you must move air; therefore, the more air you move, the more
sound you make. When comparing two speakers of equal surface area, the
one with greater excursion capability will play louder given sufficient
power.
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#2 Re: How does speaker sensitivity affect real world SPL?

Post by steve s »

Is your question is about subs or sensitivity in general ? ...don't forget transient responce is also important, the ability to follow the musical signal...
In my experence most lower efficiency cone drivers only pay lip service to transients no matter what frequency they are being played at ..
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Scottmoose
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#3 Re: How does speaker sensitivity affect real world SPL?

Post by Scottmoose »

Driver sensitivity per se has no influence on cabinet volume [as in size] for a given alignment. Driver sensitivity is a result of its electrical & mechanical properties only. Assuming you're targeting a specific alignment, then this, especially for box speakers, is dominated by Fs, Vas and [effective] Qt', i.e. Qts + any series resistance in the circuit. Hoffman's iron law; pick any two, but the laws of physics prevent you having all three:

-High sensitivity
-Small size
-Low bass

As far as boxes go, an effective Qt of around 0.312 should provide the greatest extension in the smallest box for a given Fs, Vas. Note that it's possible to have a driver with, for e.g., moderate - low sensitivity and a relatively high Fs, so it will not necessarily go any lower than an equivalently sized high sensitivity driver.

Linear travel (Xmax) can be a reasonable indication of outright dynamic range -however, if you're going to make comparisons, in addition to driver Sd you have to factor in the nominal sensitivity of the system if you're going to establish which is going to go louder in outright terms. Don't forget also that there is no standard definition for Xmax -I did a count of different methods a few years back, and gave up at seven. Driver manufacturers do not always state which they used, although in some cases it's possible to work out what they've done, and they all give somewhat different results if applied to the same driver.

I'd agree with Steve that transient response is vital (low driver VC inductance being the critical factor here), and a system Q of 0.5 being theoretically 'transient perfect' in the acceleration region, with (all other things being equal) higher efficiency units having the greater dynamic headroom.
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Nick
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#4 Re: How does speaker sensitivity affect real world SPL?

Post by Nick »

system Q of 0.5 being theoretically 'transient perfect' in the acceleration region
It will be critically damped I agree, but as its being fed a bandwidth limited signal is there not a advantage to having it under damped (Q>0.5) with respect to transient response?
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#5 Re: How does speaker sensitivity affect real world SPL?

Post by IslandPink »

Scott - so.... I thought the correct number we're aiming for in 0.7 , is this what is 'critically damped' ?
I know the solvers for sealed box calcs suggest you normally use Q = 0.7 and that was what James aimed for more or less with OB's too.
If so why physically is the transient perfect Q different to the critically damped Q ?
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#6 Re: How does speaker sensitivity affect real world SPL?

Post by Scottmoose »

Q = 0.7[07] is maximally flat. Q = 0.5 is critically damped. On-line calculators tend to use maximally flat (i.e. the lowest anechoic F3) because it looks nice on a graph. 0.5 = 'transient perfect' (or is considered to be as close as can be achieved) as it has no overshoot and therefore in theory the correct 'attack' / 'decay'. 0.577 Bessel has the fastest settling to rest after an impulse but a slight overshoot. The downside to critically damped is the large cabinet size needed and the high F3 -the rolloff is shallow but it starts high up, so if you want to go low, your driver needs a very low Fs. Some people find it too dry; not enough LF amplitude for that reason.

You do get some interesting twists on this though. John K pointed out some years ago that since lower Qs put the fundamental at a lower amplitude, a higher Q may be considered more accurate, at least as far as FR goes -transients a bit more open to question though. This is partly academic since room-response also will come into play when implementing, especially with a complex signal, so it's rarely as cut & dried as all that. Overdamped alignments can sound extremely 'fast' / 'tight' since there isn't time for the leading edge of the transient to be completed; that can match well acoustically with compression drivers given how highly damped they tend to be.
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