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Dumb question about impedance

4/1/1999 9:42 AM
Don Symes
Dumb question about impedance
In the case of an amp with selectable output impedances and a 4x12 switchable between 16 and 4 ohms:  
Is there a discernable sonic difference between matching at 16 and matching at 4?
4/1/1999 11:38 AM
Steve Dallman

Try it and see. Gerald Weber claims the 4 ohm will be brighter and the 16 ohm will be darker.
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4/1/1999 11:59 AM
The 16 ohm being "darker" kind of make sense because the signal is using more wire in the amps output transformer (higher inductance). R.G. does this make any sense?
4/1/1999 12:47 PM
Steve Dallman

That would be right.
4/1/1999 2:12 PM

Maybe a little. Actually, for a well-designed transformer, it probably won't make an audible difference, and it depends on whether there is a separate 16 ohm winding or a tap on a single winding for the different impedances. For poorly designed, cheap guitar output transformers, maybe.  
The difference would be in a higher leakage inductance, maybe a touch more self capacitance.  
The biggest difference is likely to be that most people use two 8's in series or four 16's in series/parallel to get to 16. Any time you put two speakers in series, they each lower the damping factor from amp to speaker for the other one, so they each have looser, boomier bass. Could be that Gerald heard that.  
For a 16ohm speaker on a 16 ohm tap verus a single 8 (or 4) speaker on a matched tap, if the speakers were equally good (an impossibility in the real world, naturally!) the differences should be very hard to hear.
4/3/1999 1:49 AM

Um.. You guys.. G. Weber was talking about parallel series and series parallel, two ways to still end up 16 ohms but brighter and darker respectively.. I am still deciding whether or not it is effective myself b.t.w.
4/3/1999 1:46 PM

"G. Weber was talking about parallel series and series parallel, two ways to still end up 16 ohms but brighter and darker respectively.."
Gerald has an occasional lapse.  
If you take four identical speakers, and hook them in two series chains, then parallel the chains and run audio through them (this is parallel series, right?) you could use an AC voltmeter to measure the voltage between the middle junctions of both series chains.  
If the speakers are identical, the voltage between the middle points must be and will be zero, because identical currents are flowing in each of the two identical paths. Makes no difference whether the speakers are good, bad, inductive, capacitive, resistive, just that they're alike.  
If you then connect the middles with an ammeter - yep, no current will flow, because there is no voltage between the two points. It makes no difference whether you connect the two middles (making a series-parallel connection, right?) because no voltage exists between the center points and no current flows.  
This is the fundamental theory behind all bridge measurement instruments. Maybe Gerald didn't read that book...
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