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Cab Sensitivity Specs - What Does it All Mean?

#2
The sensivity is a measure of sound pressure level (in Decibels (dB)) with an input of 2.8 volts at a distance of 1 meter. For an 8 ohm cabinet, that's 1 Watt. IIRC, the industry standard frequency for this test is 1 KHz.

Assuming both cabinets are 8 ohms, the 101 dB cabinet will be 4 dB louder than the 97 dB cabinet and will sound a little bit louder.
 
#5
As I've posted before, I disagree with Bill on this. The RELATIVE SPL ratings have always correlated VERY highly in my experience with the general amount of power needed to drive a cab.

For those of you have have used all these cabs, I think you will agree...

Acme,EAVL series.... very low published SPL.... takes a lot of power

Bergs, Accugrooves, and some later EA's.... moderate published SPL's.... not as power hungry as the Acme's, but more than many other cabs

Epifani, Eden, Schroeder, etc.... high published SPL's.... and guess what!?!... loud as the beejebers with moderate wattage.


Of course, part of this it the amount of low end they put out, so I'm not totally disagreeing with Bill and others. However, the published SPL's are usually a pretty good piece of info to include when you are cab shopping. It's only one piece of info, though.

To say that they are 'useless' is silly.
 
#6
I agree - publish something. Investors will use the specs to help make a purchasing decision.
When investors use specs, Eventually one manufacturer will post a chart of their speaker verses another so you get a real idea of the full bandwidth sensitivity. They will probably include a few other brand speakers on the chart to show how their ratings may be skewed.
 
#7
NO single frequency can reflect the usable sensitivity.

The best by far is to use a band of pink noise with an average level of the standard 1W or whatever, and then measure the output over the whole bandwidth.

Any single frequency may be at a peak (if marketing is involved, they would probably want that) that is higher than the average level.

But, I totally agree with Kjung and Seamonkey on this. If there is NO spec, whatcha gonna use?

I would NEVER trust a dB or two difference very far. But if one is 95 dB and the other is 101 dB you are surely going to notice a difference.

ANY spec at least tells you what to expect....

"Is it about normal, same as most others"?

"Or am I going to have to trade off loudness vs tone with it, because its weak?"
 
#10
Smallmouth_Bass said:
So where does wattage fit in with these specs?
Will a higher watt rated amp with lower sensitivity be louder than a lower watt rated amp with higher sensitivity?
Click to expand...


all else being equal--and as others have been pointing out, all else is never equal--you need to double the power to make up for a difference of 3db lower efficiency.

which means 4X the power to make up 6db, 8X the power to make up 9db, etc. etc.

As you can probably imagine, you'll almost never be able to make up for a very large difference in efficiency. even if in theory you could do it with 5000 more watts, in practice the speaker probably won't like it very much.
 
#11
Smallmouth_Bass said:
So where does wattage fit in with these specs?
Will a higher watt rated amp with lower sensitivity be louder than a lower watt rated amp with higher sensitivity?
Click to expand...

Depends... As I wrote earlier, for 8 ohm cabinets, the sensivity is measured with a 1 watt input. 2.8 V across a 4 ohm load equals 2 watts (approximately).

I believe the theoretical formula for maximum spl would be something like:

SPL (in dB) = Sensitivity (dB) + 10 log (P max/Pref)

for an 8 ohm cabinet P ref = 1 watt so a 101 dB cabinet powered by a 100 watt amp would yield (at 1 KHz)

101 + 10 log (100/1) = 101 + 10 * 2 = 101 + 20 = 121 dB

or for a 94 dB, 8 ohm cabinet and a 500 watt amp...

94 + 10 log (500/1) = 94 + 10 * 2.7 = 94 + 27 = 121 dB

and employing our friendly "double the power = 3 dB louder" rule of thumb...

94 dB, 8 ohm cabinet and a 1000 watt amp...

94 + 10 log (1000/1) = 94 + 10 *3 = 94 + 30 = 124 dB; 3 dB louder than with a 500 watt amp...

Of course this can't go on forever...you ultimately run into mechanical and electrical limitations (Xmax and Pmax of the loudspeakers) and I believe that distortion can be an issue if the loudspeaker designer tries to squeeze too much efficiency into the driver.
 
#16
Smallmouth_Bass said:
Ooops, I meant the wattage rating of the cabinet and not the amp.
Click to expand...

Well, I kind of covered that too when I wrote..."depends" and "Of course this can't go on forever...you ultimately run into mechanical and electrical limitations (Xmax and Pmax of the loudspeakers) and I believe that distortion can be an issue if the loudspeaker designer tries to squeeze too much efficiency into the driver."
 
#17
BillyB_from_LZ said:
I believe that distortion can be an issue if the loudspeaker designer tries to squeeze too much efficiency into the driver."
Click to expand...
Distortion isn't that much of a concern, but response is. Getting more driver effficiency is easy, you increase the motor strength (bl) of the driver. The good news is you get more output, the bad news is that higher bl translates into lower Qts and that results in less bass response. That's another reason why referencing SPL at 1kHz is smoke and mirrors. Compare a Kappa Pro 10 and Beta 10. The Kappa Pro has a high bl, low Qts, 101 dB sensitivity at 1kHz, but its response drops like a stone below 200Hz. The Beta 10 has a low bl, high Qts and only 93dB sensitivity at 1kHz, but is a strong performer down to 50 Hz.

You can get high SPL at low frequencies with high bl drivers, and that's where your concerns come into play, as they require very high Pe and xmax/xmech ratings to so. One example is the Basson cabs. They have huge magnets, which gives high bl but low Qts, and therefore you need a huge amp to get any bass out of them. I wouldn't go that route with a traditional amp, but it does start to make sense with a 1kW class D amp that only weighs 10 pounds. I also wouldn't go high bl when that means using four or more drivers that weigh 30 pounds each, but the prospect of high bl 500 watt neo magnet drivers that weigh less than 10 pounds each makes the notion far more user friendly.
 
#20
billfitzmaurice said:
'Faster' has no technical meaning with respect to either speakers or drivers.
Click to expand...

Hm, yes, on second thought, naturally. :rolleyes: Otherwise they wouldn't be capable of producing a certain frequency.

But when we speak of an amplifier's damping factor, is it correct this has to do with how fast the amplitude of the signal can rise? (That's what I actually meant with "fast", the "punch" we always speak of)
And doesn't the speaker (magnet, coil, cone,...) itself has some influence on this? Or is it all the cab? (Why then would some speakers be more expensive than others?) Or is this also a nonrelevant question? :hiding:

Thnx! :)
 

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