What causes a speaker to have low sensitivity?

[type]

Why are some speakers more efficient than others? What actually causes a speaker to have low sensitivity, the tweeter, woofer, crossover and/or cabinet?

[bigwill]

Weak magnets

Heavy cones

Cones too small

Badly designed enclosures

etc

[tungsten]

Efficiency=(constant) x volume x (f-3)^3

Read: if you want f-3 to change from 40 to 20 hz with an unchanged box volume, your speaker will have to be eight times less efficient. This is known as "the iron law" - unbendable, unless you fiddle with active electronics.

The constant is unchanged for a given type of bass loading (larger for reflex than for closed box)

Efficiency is in acoustic power (W), not a logarithmic dB scale.

[tungsten]

Bigwill: remember that small, heavy cones driven by weak magnets is the only way to get decent bass from a small enclosure - which is why these boxes invariably are inefficient.

Increase magnet strength, and your Q goes down, and the bass goes down - for a given enclosure.

[bigwill]

Originally posted by tungsten
Bigwill: remember that small, heavy cones driven by weak magnets is the only way to get decent bass from a small enclosure - which is why these boxes invariably are inefficient.

Increase magnet strength, and your Q goes down, and the bass goes down - for a given enclosure.

It's funny that, you'd think it would be the opposite (low Q drivers making more bass)

[Rademakers]

The 2 formulas used to calculate the efficiency:

5,44 e-4 x BL^2 x Sd^2 / (Re x Mms^2) and/or 9,6 e-10 Fs^3 x Vas / Qes
9,6 e-8 to get the answer in %

So to get a high efficiency you want:

High: Vas, Sd, Fs, BL

Low: Qes/Qts, Re, Mms/Mmd

Sensitivity is directly derived from the efficiency (n0), by 112 + 10 x log (n0)


Wkr Johan

[tungsten]

Originally posted by bigwill



It's funny that, you'd think it would be the opposite (low Q drivers making more bass)

Yes, because low Q drivers look so potent with that big magnet. But looks deceive...

[demon2091tb]

Like the above said, Hoffmans Iron law, You can change 2 of the 3 specs. Effeciency, box size, and low end extension. You can have a small box size and great low end extension, but your effeciency is going to be your weakness, or vise versa b/w any of the three specs.

[sreten]

Originally posted by type
Why are some speakers more efficient than others?

Hi,

because you have an amplifier power available, speaker bass
capabilty, output capability and speaker cabinet size budget.

For moderm amplifiers 50w is typical. Low efficiency allows small
speakers with reasonable bass, and given the size of the bass
driver allows 50w of drive without overloading the driver.

In all cases simply increasing efficiency will reduce bass.
So for a given amount of power you trade loudness with bass.

If you want to keep the bass you have to make the cabinet bigger.
And typically higher efficiency speakers are not the smallest.

But if your amplier is only 5 or so (single-ended) watts, then
lowefficiency is a no-no due to limited loudness capability.
High efficiency requires far bigger boxes than normal, or
smaller speakers with relatively no bass compared to normal.

/sreten.

[infinia]

A different way to to look at it

If you could keep the VC in the sweet spot in the gap under all operating conditions with a fixed magnet size you will have high spl. Ok to do this and still have Low Fs cone needs to be big with a stiff suspension and small Xmax. This also means a big box to keep system Fc low.

Ok now every one wants a speaker that goes low but it also has to be small.
So start with the same magnet and smaller cone. Since the cone is smaller it has to move further to push the same volume of air.
So this means Xmax must be bigger, If Xmax is bigger with the same magnet gap the coil is not fully contained in the sweet spot
all the time so spl suffer.

It's all a tradeoff