Matching speakers - different sensitivity

[überfuzz]

Hi

I've got an idea of using a 15" speaker along with an 8" speaker in one of my builds. Anyone here with experience of matching different sized speakers, specially speakers with different sensitivity?

As of now I lean towards 2 jensen speakers. When I scouted for info I stumbled upon a Bode plotter on the Jensen site. The 15" is sitting roughly 6 dB higher than the 8" throughout most of the frequency range. Is this going to "drown" the 8 incher?

Thanks!

[Chuck H]

Hi

I've got an idea of using a 15" speaker along with an 8" speaker in one of my builds. Anyone here with experience of matching different sized speakers, specially speakers with different sensitivity?

As of now I lean towards 2 jensen speakers. When I scouted for info I stumbled upon a Bode plotter on the Jensen site. The 15" is sitting roughly 6 dB higher than the 8" throughout most of the frequency range. Is this going to "drown" the 8 incher?

Thanks!

I would think so. You could attenuate the 15" speaker though with a parallel and series resistor arrangement to get a more uniform output from each speaker. I don't know how to calculate the right values based on dB, but something like this:



Or you could choose an 8" speaker with half the impedance of the 15" so that the 8" speaker is carrying 2/3 of the watts. That would make the 15" only 3dB louder than the 8". Ah, but it would also make for an odd total speaker load figure.

[Leo_Gnardo]

Are you planning to run the 15 and the 8 in parallel? Some amps from "back in the day" did this, or similar. 15's & 8's in Sano amps intended for accordion, some Polytone SS amps marketed to the jazz market, 12 + 8 in some old Gibsons.

Every time I encountered these combinations, I added a capacitor in line to the smaller speaker, as a low-slope crossover (6 dB/oct.). 1: why stress the smaller speaker with low frequencies it's not designed to handle? And furthermore might wreck the speaker. B) Along the same line, let the small speaker act as a sort of "tweeter".

Which cap to use? What value? I'm lucky to have a collection of crossover caps so I can try a few out, see what works best. Typically somewhere between 6 and 20 uF. Unless you have a super bright sounding 15, like a JBL D/K/E 130, you will find the small speaker adds some clarity to the high frequencies, regardless of differences in the published sensitivities.

[J M Fahey]

Hi

I've got an idea of using a 15" speaker along with an 8" speaker in one of my builds.

Which is ?
Tube/SS , Guitar/Bass/Hi Fi? Which circuit?

Anyone here with experience of matching different sized speakers, specially speakers with different sensitivity?

Yes.
No real need to *match* them,this is not a Hi Fi setting (I guess) where we want flawless flat response across the full audible range, by any means.
Like Enzo says: "it´s a Guitar amp!!!!!"

As of now I lean towards 2 jensen speakers.

Which ones?

The 15" is sitting roughly 6 dB higher than the 8" throughout most of the frequency range. Is this going to "drown" the 8 incher?

It depends.
Probably not "drown" and only actual testing and your ear can tell.
Mount both on any old piece of plywood or chipboard you have lying around and test them.
4 ways possible:
* 15" alone
* 8" alone
* 15"+8" in parallel, impedance setting as both in parallel
* 15"+8" in parallel, BUT with a "crossover capacitor" in series with 8" speaker, to avoid wasting 50% of your Bass power into it , so you use it as a mid/high unit only.
In that case: impedance setting as the 15" speaker alone.
You can try a 47uF **bipolar** electrolytic in series with 8" speaker.
Nominal crossover frequency is 400 Hz but it´s a "slooowww" crossover so in practice speaker will work from around 200Hz and higher, which is fine.
It won´t try to reproduce frequencies <200Hz which certainly is done much better by the 15" one.

There´s an old Argentine tale about a homeless guy, who was wearing two full-of-mothholes sweaters on a cold day.
Somebody told him: "hey, those are full of holes!!!!"
The homeless guy answered: "true, but I am still warm, holes do not match!!!"

Same with speakers: even when one on average has higher sensitivity than the other, speaker curves in general are very rough, and chock full of peaks and dips all over the place: when 15" speaker dips and/or 8" peaks, at those specific frequencies 8" will be heard, contributing its own.

No need to attenuate 15" to match 8", but of course let your ears be the judge.

[überfuzz]

Thanks for all the input!

Definitively helpful when I start tinker with this set up.

Leo_Gnardo - Do you conciser the load of the speaker as a resistance, or as an impedance (a result of the resistance an inductance) of the smaller speaker?

[Leo_Gnardo]

Thanks for all the input!

Definitively helpful when I start tinker with this set up.

Leo_Gnardo - Do you conciser the load of the speaker as a resistance, or as an impedance (a result of the resistance an inductance) of the smaller speaker?

The speakers have impedance curves. The manufacturer may publish them, or if you want to go to enough trouble you can measure them yourself. HOWEVER - calculating with all that science is getting a little deep - these are just guitar amps after all. Most of the power of your amp is expressed in the lower frequencies, so if you have a cap blocking the amp's power from getting to the smaller speaker at low frequencies then the impedance of the larger speaker is what's most important. The smaller speaker only comes into play for the very highest notes of the guitar (or accordion... whatever) and also the overtones of the instrument's signal. In that frequency realm, the impedance of your "woofer" is rising considerably, now the cap admits signal to your "tweeter" to the point it starts to become a relevant part of the impedance picture, and the combination results in something close to your amp's rated output impedance.

Something to consider, (I'm sure you're aware already because of your question) all speakers have impedance curves, and in some part of those curves they rise considerably from their nominal impedance. For instance at and near resonance, and as we start looking at higher frequencies say 1 KHz and up. By some miracle amps still drive them well, we get good sound, there's a lot less to worry about than one might imagine. Otherwise we'd be "fixing" the overall impedance curves with zobels all over the place. You don't much see them in use, especially in MI equipment.

[Mick Bailey]

You could download WinISD to give a good idea of the overall response.

[Chuck H]

With all due respect for the experience and knowledge of my colleagues participating on this thread...

My impression on this forum starts with "guitar amp" unless otherwise stated. That said, I assumed the goal was to have a cabinet that offers a guitar amp through a 15" speaker AND a guitar amp through an 8" speaker. The capacitor in series with the 8" occurred to me, but I didn't mention it because that would be a guitar amp through a 15" speaker and JUST THE TOP END of a guitar amp through a 8" speaker. And since the 8" is already just 1/3 as efficient as the 15" any mismatch in output still exists.

I also have tried to take original information at face value. It was mentioned that there are dissimilar peaks and valleys in the response curves of dissimilar speakers. And this is very valid and true. But with a difference in efficiency of 6dB and the statement that this is "throughout most of the frequency range" I don't get the impression that the 8" will be asserting itself.

In this light I feel that just attenuating the 15" or intentionally applying more of the "load" to the 8" by staggering the impedance of the speakers may still be a viable option.

I think a better definition of the final goal might help.

[Enzo]

Speakers are not monolithic collections of specs. Just because one speaker is 8 ohms and another 16, it doesn't mean that all in all one is going to be precisely half as loud as another... or whatever. Speaker impedance is a nominal thing, meaning they take it at one particular frequency. But the real impedance varies WIDELY over the range. That 8 and 16 might otherwise sound pretty much the same...or not. You can't tell from one or two specs. And we haven't even considered pattern. Some speakers are beamers, some spread it around. Listening angle matters. Efficiencies? See "curve". In short, just hook up the speakers and see how it sounds. You may need nothing additional at all. SO what if one speaker is a little louder than the other? They may blend beautifully that way. WHen two people sing together, do you mix them by VU meter or do you mix them by ear?

[J M Fahey]

Agree and add: we still don´t know what speakers are and even less seen their curves.

[überfuzz]

Wooow! I don't think we need to get to technical about it. :-) I think we all know that a speaker is a coil with inductance and resistance. In addition to this we have the mechanical impedance (acoustic energy transfer from membrane to air). No magic in this! Set up the transfer function, plot the response and you see.

I was looking for hands on experience from you guys. Which I got and really appreciate, thanks again!

At the moment I plan to fix a baffle with a 15" cut out. In addition to this one 8 and one 6 inch cut-out. The smaller cutouts are