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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
kalali's avatar
kalali
1,977 posts
 
+1 Al

Thank you. People need to learn to express their opinions without the need to insult others, especially the ones whose knowledge and experience as well as their contributions are unique in this industry. 
cj1965
124 posts
 
" Thank you. People need to learn to express their opinions without the need to insult others, especially the ones whose knowledge and experience as well as their contributions are unique in this industry. " - kalali

If I had known that atmasphere was some "world class" amplifier designer, I probably would have used a different circuit analogy to make my point. In this case, I didn't have a clue who he/she was which re enforces a point I've been making elsewhere - when it comes to sharing accurate information with others, the credentials of the person attempting to share  information are irrelevant . Only the facts and accuracy of the information matter.

Secondly, when you are a professional in an industry and put yourself out on a forum sharing "facts" to help educate others, you should accept the possibility that you will be "incorrect" or "wrong" on occasion and all of the downside associated with that potential. This underscores the need to be  careful, exercise restraint, and double check your "advice" before you give it out. The outcome can solidify your reputation for expertise or weaken it - that's the inherent risk in sharing with others.
timlub
2,044 posts
 
Wow, I am soooo glad that I didn't spot this thread before now..... 
giving way to all the theory and mathematics,  
@williewonka 
If all things are equal,  meaning a 4 ohm 8 ohm and 16 ohm driver would all sound equivalent in a given cabinet, Paralleled wired speakers sound better overall than series.  I would also recommend that you add a simple impedance correction circuit.   Many amplifiers react better to a consistent impedance.  Not all, but No amplifier sounds worse with it. (unless you are dropping impedance too low for a few tubes) still within tubes impedance operating range,  even tubes sound better with impedance correction circuits on speakers.  
NO PROOF,  this is my experience. 
Good Luck,  Tim 
almarg's avatar
almarg
9,670 posts
 
CJ1965, I believe that what your analysis about phase differences between voltage and current in reactive circuit elements may not be taking into account is that the motion of a dynamic driver results from the current it is conducting, rather than from the voltage that is applied to it. And the current in a series circuit is of course identical at all points in the circuit, aside from the consequences of the propagation delay that will exist along that path. Which in turn will be completely negligible for path lengths that would be present in a home environment, putting aside reflection effects for which timing may have relevance in digital applications.

Regards,
-- Al

almarg's avatar
almarg
9,670 posts
 
CJ1965 4-17-2018
"So if you have a 97 db 1 watt/1 meter 8 ohm driver, two in series will have the same efficiency (since each is absorbing 1/2 watt) while the sensitivity is 94 db. If you put the two drivers in parallel for a 4 ohm load, the efficiency is the same as 1/2 is absorbed by each driver if 1 watt is applied. However the sensitivity is now 100db. " - atmasphere

With that, you clearly blew it.
Ralph’s (Atmasphere’s) statement is entirely correct, if (as he is assuming, consistently with commonly seen usage) efficiency is defined on a 1 watt basis. And if sensitivity is defined on the basis of 2.83 volts.

Strictly speaking, I would define speaker efficiency as being the ratio of acoustic power out to electrical power in. But that definition would have little practical use, and the term is widely (and IMO very reasonably) used to refer to the SPL produced at 1 meter in response to an input of 1 watt.

Regards,
-- Al

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