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Old 15th March 2008, 12:12 AM   #1
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Default Multiple drivers; check my thinking.

I am making a tube guitar amp for my grandson and wanted to make a multiple speaker cabinet with dissimilar drivers that could be switched for different tone and different sensitivity.

I initially thought of one low efficiency driver (93dB/W) and a more normal 99-100dB speaker. In this case I would have to provide for padding down the high eff speaker when run with the low eff speaker. However a thought occurred to me.

I already have two of the 93dB speakers so why not a triad using the two 8ohm 93dB drivers and one 16ohm high 99dB driver. I could have it switchable for one 93, one 99, two 93s in series and two 93s in series then paralleled with the one 99.

Since the amp will have switchable output imp (tranny has 4,8,16 ohm taps) the total output power would remain the same but I should gain some by running both 93s.

PUNCHLINE: Since there is no increase in power the two 93s in series should give me 96dB right? If so this is starting to get close enough to the sensitivity of the other driver to make the tonal contributions of both speakers audible in all likelihood wouldn't you think?

mike
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Old 15th March 2008, 12:22 AM   #2
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My first thought would be to do it as a tapered array. The three speakers in a vertical line. Put the 99 db in the middle and the 93 dbs above and below. Wire the 2 93 dbs in series to get 16 ohms, then parallel them with the 99 db to get a total of 8 ohms. By the way, speakers only increase in sensitivity if you wire them in parallel.
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Old 15th March 2008, 04:28 PM   #3
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Quote:
Originally posted by happy.gringo
By the way, speakers only increase in sensitivity if you wire them in parallel.
Do you mean efficiency?
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Old 15th March 2008, 05:23 PM   #4
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This sounds like a nice concept, but as I read, I can only ask - Why?

Is this really what your grandson is likely to want in a guitar speaker?

Also, the change in various levels depending on the speaker combination, is that really going to give a valuable subtlety that can't be achieved by simply turning the amp up or down. Then combine a simple volume control with the likely various special effects (buzz boxes, whaa-pedals, etc...) and it seems to render this subtlety kind of pointless.

I think your grandson would much prefer a straight forward (pardon the expression) kick-*** speaker cabinet.

Again, I'm not saying that it is a bad concept, or an unworkable concept, I'm just questioning whether it is really necessary.

Admittedly, I don't know your grandson or the style of music he is likely to play, so there may be more to this idea than I am able to know. But on general feeling, I say stick with the basics. Don't build in a cool feature that is never going to be used.

I remember building this cool pair of 4x12" speaker cabinets for a friend to use as a PA. As I was building them I got this idea that would allow the speakers to be hooked to other speakers in either a series or parallel combination just by plugging into a different speaker jack. It seemed very simple to me, but no matter how many times I explained it to him, including diagrams, he still didn't get it and ended up hooking speakers together in a willy-nilly fashion.

Sometimes, good ideas just aren't appreciated.

It sounds like a cool thing to do, but ask yourself, is it necessary, and will the grandson understand it well enough to apply it or is he just going to turn everything on and crank it up?

Just a thought.

Steve/bluewizard
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Old 15th March 2008, 05:55 PM   #5
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I think you are right Blue Wizard. I will probably build him a big cabinet with two high efficiency 12"s for the big gigs and a little single 12" low efficiency one for the smaller club settings.

He is what I think you would call a metal head.

mike
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Old 15th March 2008, 06:14 PM   #6
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Making an even broader analysis than BlueWizard's already good suggestion (and also making some sweeping assumptions), I question your grandson's appreciation of this gift for him, unless he's very involved with the details of this project from the beginning.
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Old 16th March 2008, 01:18 AM   #7
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Wes is very much in the loop and very excited about the project. I agree however that simplicity has its virtues in this case. That is why I am going with cathode bias for example so that he won't have to worry about bias adjustments and all of that.

mike
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