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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
kijanki's avatar
kijanki
3,575 posts
 
This is exact quote from cj1965 post:

In theory, half the voltage applied to a driver will result in half the sound pressure in the output (-3db).

almarg's avatar
Ag insider logo xs@2x
almarg
8,673 posts
 
Thanks, Kijanki.  Here's another interesting quote, this one from the thread Tim referred to above:

CJ1965 4-19-2018
For some people, "results" means using antiquated 80 year old technology that is highly vulnerable to changes in performance depending on what it's connected to. And for some folks, the lack of bass and exaggerated highs, coupled with increased harmonic distortion when using this ancient "technology" is "pleasing" or "desirable". Similarly, others see the pops and ticks, rapid wear, uneven high frequency performance, limited dynamic range, increased distortion, wow, and flutter associated with ancient vinyl technology as "more authentic". Unfortunately, we can't confine such individuals who promote and buy this junk to padded cells. We pretty much have to create invisible "padded cells" that effectively allow ourselves to ignore them.

Best regards,
-- Al
 
atmasphere's avatar
atmasphere
7,068 posts
 
This is exact quote from cj1965 post:

In theory, half the voltage applied to a driver will result in half the sound pressure in the output (-3db).
Res ipsa loquitur, huh?

Obviously he didn't actually do the math, but based this on belief instead- the exact thing of which he was accusing others...


erik_squires
5,268 posts
 
For a single driver : The change in dB in input voltage is equal to the change in output SPL in dB.

Voltage dB can be calculated in this fashion: 

dB = 20 x log ( Vnew / Vold )

in the case of half the voltage:

20 x log ( 1 / 2 ) ~= (- 6 dB)

Also, you can use this handy web gizmo:

http://www.sengpielaudio.com/calculator-gainloss.htm
erik_squires
5,268 posts
 
Also, we are so far from the OP's original topic, maybe we should let this thread just die. :) 
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