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PostPosted: November 1st, 2018, 8:30 am 
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Is there any advantage in connecting two identical drivers in series vs. parallel in a single channel of a speaker when connected to a transformer coupled output tube amp?

In my case, it will become an 8Ω or a 32Ω speaker. Since my application will connect the 8Ω load to the 4Ω tap, or 32Ω load to the 16Ω tap, because I need to reflect a greater impedance back to the output tube plates, I'm wondering which is the better approach?

I know that in series, the ~3dB efficiency gain one gets when parallel connecting is lost. But I'll have adequate power, even giving up the 3dB in efficiency.

On the other hand, more of the output winding of the transformer is used.
Don't know if that is significant.

No other drivers will be connected to the amp outputs. I know that the Zobel network will need to change.

Thoughts?


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PostPosted: November 1st, 2018, 9:12 am 
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The POWER sensitivity goes up by 3dB regardless of which connection you use. The VOLTAGE sensitivity goes up by 6dB with a parallel connection, and 0dB with a series connection.

Roscoe


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PostPosted: November 1st, 2018, 11:35 am 
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Isn't it simpler to view both power and acoustic sensitivities separately.

impedance is additive when speakers are connected in series and divisive when connected in parallel.

ie: if two speakers of 8ohm are connected in series, the total impedance on will be 8+8=16 ohms
and if connected in parallel, the total impedance will be (8*8)/(8+8) = 4 ohms.

On the acoustic side, a pair of parallel speakers will result in +6dB gain and no gain in serial speakers.

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PostPosted: November 1st, 2018, 11:40 am 
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Cogito wrote:
On the acoustic side, a pair of parallel speakers will result in +6dB gain and no gain in serial speakers.


That's only accurate if they're fed with a constant VOLTAGE. The power sensitivity increases by 3dB either way...

Roscoe


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PostPosted: November 1st, 2018, 1:29 pm 
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As stated efficiency is not a concern.

Is there an advantage or disadvantage to series connection of voice coils?

Is there an advantage to using 100% of the OPT secondary vs. 50%?


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PostPosted: November 1st, 2018, 2:28 pm 
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I've read many opinions in this thread -- some are right on some are not.

Output transformer impedance taps -- the output tap that gives the best result is what the power tubes would prefer in terms of reflected impedance.

In my case, the 16-ohm taps (SET 845) give the best sonic results with my 8-ohm nominal speakers. A friend with Magneplanars with a 4-ohm nominal impedance discovered that the 8-ohm taps on his Williamson (KT-88) amps. fleshed out the mid-range and sweetened the treble.

Play with it -- do trial runs to determine the best result.

Acoustic power output power -- Parallel drivers delivering the same bandwidth will yield double the acoustic power output (+3 db) regardless of whether they are wired in parallel or series.

The decision to wire in parallel or series is more dependent on what works best (sounds best) and what the amplifier prefers and/or tolerates.

:character-oldtimer:

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PostPosted: November 1st, 2018, 2:31 pm 
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SoundMods wrote:
[color=#BF0000
Acoustic power output power -- Parallel drivers delivering the same bandwidth will yield double the acoustic power output (+3 db) regardless of whether they are wired in parallel or series [/color]


For the same electrical power in...

Roscoe


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PostPosted: November 1st, 2018, 2:33 pm 
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Roscoe Primrose wrote:
SoundMods wrote:
[color=#BF0000
Acoustic power output power -- Parallel drivers delivering the same bandwidth will yield double the acoustic power output (+3 db) regardless of whether they are wired in parallel or series [/color]


For the same electrical power in...

Roscoe


10-4

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PostPosted: November 1st, 2018, 3:38 pm 
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An easy way to look at it:

Suppose speaker impedance is 8ohms and voltage of the signal is 20V.

For single speaker:
Using Ohms Law, Current: I = V/R = 20V/8Ohms = 2.5 A
Power = VI = 20 * 2.5 = 50W

For two speakers connected in serial:
Using Ohms Law, Current: I = V/R = 20V/16Ohms = 1.25 A
Power = VI = 20 * 1.25 = 25W

For two speakers connected in Parallel:
Current = 20V/4Ohms = 5A
Power = VI = 20 * 5 = 100W

So, a low power tube amp which can drive 8 ohms speakers nicely might struggle driving a 4 ohm speaker or two 8 ohm speakers connected in parallel.

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PostPosted: November 1st, 2018, 3:54 pm 
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Cogito wrote:
An easy way to look at it:

Suppose speaker impedance is 8ohms and voltage of the signal is 20V.

For single speaker:
Using Ohms Law, Current: I = V/R = 20V/8Ohms = 2.5 W
Power = VI = 20 * 2.5 = 50W

For two speakers connected in serial:
Using Ohms Law, Current: I = V/R = 20V/16Ohms = 1.25 W
Power = VI = 20 * 1.25 = 25W

For two speakers connected in Parallel:
Current = 20V/4Ohms = 5W
Power = VI = 20 * 5 = 100W

So, a low power tube amp which can drive 8 ohms speakers nicely might struggle driving a 4 ohm speaker or two 8 ohm speakers connected in parallel.


Actually, since the power sensitivity went up by 3dB, it ought to be EASIER for the amp to drive the 4ohm load created by two 8ohm speakers in parallel, assuming the OPT has a 4ohm tap. You're only looking at 20V across all three scenarios if you don't change output taps or use an amp (SS probably) with a vanishingly low output impedance. Remember, if you use the 16ohm tap to drive the series connection, and the 4ohm tap to drive the parallel connection, you're only getting half the voltage at the amp output for the same power delivered to the speakers.

BTW, it would be a lot simpler to follow if you just used V^2/R for power ;)

Roscoe


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