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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
erik_squires
15,657 posts
 
Hey Willie,

You know, you could grab a speaker crossover simulator and try this out for free, it may help you. I use XSim. There you can use the virtual 8 Ohm drivers to explore various different wirings and output. 

Yes, the amp matters. If it's a tube amp, you probably want to shoot for 8 Ohms. 

If we compare a single 16 Ohm driver vs. 2 in parallel, you get 8 Ohms, but +6 dB in output. 

If you wire 2 x 16 Ohms, you end up with 32 Ohms, and no gain in sensitivity. 
williewonka OP
3,067 posts
 
@erik_squires  - if I understand you correctly...

I will be using drivers that ....
- have a sensitivity of 96 db
- and come in 4, 8, or 16 ohms impedance

To get a total impedance of  8 ohms my choice would be...

2 - 16 ohm drvers in parallel  - which gets me a 6db increase -  102 db

Whereas...

2 - 4 ohm  drivers in series - simply stays at 96db?

I hope I have interpreted you correctly

Thanks - Steve 
erik_squires
15,657 posts
 
Double check the sensitivity on each! :) It is very unusual that the same driver has the same sensitivity regardless of impedance! It's not impossible, but usually manufacturers cut the sensitivity by 3dB as impedance doubles. 

Yes, your math is correct.  Again, I encourage you to grab XSim Crossover Simulator for PC or equivalent to try these ideas out. 

Best,

E
toddalin's avatar
toddalin
155 posts
 
If the amp puts out x watts at 8 ohms, and you split it between two speakers totalling 8 ohms, each speaker sees the half the power and puts out the same dB level.  When you add them together, the net result is the same.

That said, I would think that, if the net volume in dB for the speakers truly are the same regardless of the impedience, two 16 ohms speakers would be the better choice.

Speakers in parallel work independent of each other.  Speakers in series work together and can have an effect on each other.

Also, speakers with higher impedience tend to have a high Bl, and therefore follow the signal more accurately.
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