2. speakers
  3. 135359-1640

A Question on Speaker Driver Efficiency

I have been tweaking my guitar amps, by upgrading the speakers.

I installed a larger speaker (was 8" now 10") in my bass amp, but I made sure it was very efficient - net result
- not only is the bass much deeper sounding,
- but because the new driver was more efficiant I now play at a lower volume.

So I am now considering upgrading my other amp (i.e. used for my 6 string) and got to thinking about building a new cabinet that houses two speakers.

I know that connecting the speakers in ...
- series will double the impedance, i.e. 2 x 4 ohms would have an onverall impedance of 8 ohms
- parallel will halve the impedance, i.e. 2 x 16 ohms would have an onverall impedance of 8 ohms

But what I have not been able to get my head around is...
- what will each connection method (i.e. series or parallel) have on the "combined" sensitivity rating?
- e.g. if both speakers are rated at 96db sensitivity, will the overall sensitivity change due to the connection method or remain at 96db?

Since I can get 4 ohm or 16 ohm drivers - which connection method would be best? series or parallel?

in case it is a factor
- the amp is 15 watts into 8 ohm
- I am looking at employing two identical drivers each rated at 96db sensitivity
- 96 db (or higher) is the target for the combined sensitivity

Any help is appreciated - Many Thanks Steve
williewonka
ptss
1,964 posts
 
I get particularly displeased when a person is graciously made aware of a shortcoming— but carries blithely on.
I was taught that’s a true true sign of real ignorance. 
cj1965
124 posts
 
Al - Yes indeed. These are all just rewrite. Since power is proportional to the square of the voltage:

(0.5 x 0.5) = 0.25

Now, calculating power difference:

10 log (0.25) = -6 dB    - erik_squires

Wrong again. You cannot simply substitute the electrical power ratio into the sound power formula and call it a day.

The ratio of measured sound power to reference sound power is 1/2 - not 1/4. And if you multiply the area factor in the formula for sound power in a medium, the ratio goes back to 1 - yielding 0 db. And with that, I’m done giving out free lessons in first year electrical engineering. Find someone else to insult.
erik_squires
16,882 posts
 
Sorry, wrong is wrong. And with that, I have to move on. I have better things to do with my time.

And with that, I’m done giving out free lessons in first year electrical engineering. Find someone else to insult.

Well I must say some days a much more interesting here than others. :)

E
ptss
1,964 posts
 
Life is always interesting. Here again we have the one who is most insulting - to be the most sensitive... aw , darn shame ain’t it ...
almarg's avatar
almarg
9,670 posts
 
CJ1965 4-20-2018
Wrong again. You cannot simply substitute the electrical power ratio into the sound power formula and call it a day.

The ratio of measured sound power to reference sound power is 1/2 - not 1/4.
I posted the following in this thread, into which this debate had spilled over:
Almarg 4-21-2018
Regarding the debate about the relation between SPL and speaker input power, I found the following sub-page at the site which provided the calculators that were referred to earlier:

http://www.sengpielaudio.com/calculator-efficiency.htm

Entering various parameters into either of the two calculators closest to the bottom of that page (one entitled "Sound Pressure Level and Amplifier Power" and the other in the section entitled "Electro-Acoustic Sensitivity") clearly confirms what Atmasphere, Erik_Squires and I have all said on this subject. Namely that if the input power to a speaker is changed by a given number of db, SPL at a given listening distance will change by the same number of db. (As previously stated, this of course assumes that the speaker is not being driven hard enough to cause thermal compression in the drivers to become significant).

I also found the following writeup at PSB’s site, which provides additional confirmation. About 2/3 of the way down the page a table is provided showing power vs. volume for an unnamed 87 db speaker used as an example. Note that 40 watts results in a volume of 103 db, while a 6 db reduction in that power level (to 10 watts) results in a volume that is 6 db less (97 db). While a 3 db change in power, from 1 watt to 2 watts, changes the volume by 3 db, from 87 db to 90 db. And a 20 db change in power, from 1 watt to 100 watts, changes the volume by 20 db, from 87 db to 107 db.

http://www.psbspeakers.com/articles/Guide-to-Speaker-Specifications
Regards,
-- Al


More to discover