# SPL and sensitivity

Discussion in 'Amps and Cabs [BG]' started by pedroferreira, Feb 9, 2004.

1. ### pedroferreira

Feb 10, 2003
Portugal
Cab A sensitivity - 100dB
Cab B sensitivity - 103dB

If you're delivering x Watts into cab B, you have to double the power (Watts) to get the same SPL from Cab A.

Am I right?

2. ### kmacleish

Nov 19, 2003
Atlanta, GA
You are correct, sir.

3. ### Finger Blister

Jul 8, 2003
In theory that is correct.

In practice it is Hogwash.

In actual A/B testing with the same amp at the same settings:
I have heard a 98db rated cab smoke at 104db cab in volume & tone.

4. ### inazoneSupporting Member

Apr 20, 2003
Lets say cab A is 8ohms and cab B is 4ohms with the same watts, does that make them both equal in sensitivity, in theory?

5. ### Joe_Atlanta

Sep 13, 2001
Stone Mountain, GA
6. ### Richard Lindsey

Mar 25, 2000
SF Bay Area
No. It means that a SS amp will probably be able to deliver more power (watts) into one than into the other, but that's not at all the same thing.

Sensitivity is typically given as dB measured at a distance of 1 meter with an input of 1 watt. For the sensitivity figure to have any meaning, the distance and the input have to be the same.

7. ### rickbassSupporting Member

If only there was an independent source to measure all these goosed-out, tricked-up, measurements from those with a financial interest....maybe like a "Consumers Report" magazine for gear.

8. ### bgavin

May 3, 2001
Orangevale, CA 95662
These numbers are called "small signal" values, and only have meaning at small power levels, i.e 1 watt.

One watt is more meaningful than 2.83 volts, because wattage is independent of the speaker load. For example, 2.83 volts into an 8 ohm speaker is 1 watt, but 2.83 volts driving a 4 ohm speaker is 2 watts.

Most sensitivity ratings are measured where they most benefit the manufacturer, typically 1,000 Hz. This is bullsh*t, because as a bassist, my primary focus is 40 to 200 Hz. The sensitvity here is a huge amount less. The only meaningful specs are plots of actual measurements taken across the useful frequency spectrum.

Bass drivers are severely limited in the amount of power they can accept, due to cone excursion limits. Typically, the voice coils will accept far higher power than the limits of excursion. Just because a driver is rated at 700 watts before meltdown, does not mean that driver will accept 700 watts without destroying the cone. Cone excursion is not a factor at 1,000 Hz, which is another convenient reason for taking SPL measurements here.

Feb 10, 2003
Portugal