speakers on 4 ohm vs. 8 ohm taps - what's the theory?

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Postby noctilux » Fri Aug 20, 2004 2:55 pm

KD wrote:Is "mismatching" potentially harmful to equipment?


Only if you drive the gear beyond it's means. impedance mismatching leads to lower power in output transformer based amplifiers. if your amp were rated at 40 watts and you connect a 4 ohm load (average) at the 8ohm tap, you may get as low as 20 watts of effective output. Same goes with an 8 ohm rated speaker connected at the 4 or 16 ohm tap. If you get to overdrive the amp due to the lower output, this may or may not fry your amp. Anyway, when clipping occurs, just bring the volume down.
Best way is to check which tap (be it 4, 8, 16) gives you more dynamic range, that's the best match.
My rule of thumb, which may not be everyone's, if you have an amp killer for a speaker, don't use tubes. Amp killers have usually very reactive loads, of varying impedance and averages at 4 ohms. Either get a tube amp friendly speaker or get a Mark Levinson, Jeff Rowland or Krell.
Hope this helps
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Postby jo2 » Fri Aug 20, 2004 5:42 pm

Noctilux,

Forgive my ignorance. Could you please elaborate?

Medyo me kahinahan pong umintinde. :D


noctilux wrote:

My rule of thumb, which may not be everyone's, if you have an amp killer for a speaker, don't use tubes. Amp killers have usually very reactive loads, of varying impedance and averages at 4 ohms. Either get a tube amp friendly speaker or get a Mark Levinson, Jeff Rowland or Krell.
Hope this helps
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Postby noctilux » Fri Aug 20, 2004 10:39 pm

jo2 wrote:Noctilux,

Forgive my ignorance. Could you please elaborate?

Medyo me kahinahan pong umintinde. :D


noctilux wrote:

My rule of thumb, which may not be everyone's, if you have an amp killer for a speaker, don't use tubes. Amp killers have usually very reactive loads, of varying impedance and averages at 4 ohms. Either get a tube amp friendly speaker or get a Mark Levinson, Jeff Rowland or Krell.
Hope this helps
Noct


Sorry bout that, let me do this again. If your speaker is difficult to drive in terms of impedance, you will have to eliminate the use of a tube amp. Instead get a beefy solid state amp to drive that monster. Difficult speakers have very reactive loads wherein the impedance (measured in ohms) vary greatly in relation to the frequency played. some go below 2 ohms in the mid to high frequency range however stay above 8 ohms in the midrange and go down again in the low frequency. Medyo mahirap explain but let me try: if you tke a look at the graph of this type of impedance, you will not find a straight line but a series of bumps and dips. That's reactive.
The antithesis of this load is the pure resistive load like the old KEFs and the most magnepans wherein the impedance is practically fixed at 4 ohms. This is a relatively kind and predictable load to the amp despite being at 4 ohms. The amp won't be working too hard to track the impedance load of the speaker.
Solid state amplifiers which are designed corectly can handle the reactive loads more easily than tubes since the output impedance is commonly below one ohm. further, since they have naturally low output impedance, the output transfprmer is not required as against a tube amp.
Tube amps require output trannies to better match the impedance of the speaker to a "limited" degree only.
Whew, I hope not to have added to your confusion. easier explained in person than through this thread yata.
rgds
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Postby arnel90 » Sat Aug 21, 2004 12:44 am

Hyperion wrote:Noel_14,

Try it and see what happens. The Tino does not drop below 6 ohms I think so it is unlikely to benefit much from the 4 ohm tap.


tried the 4ohm tap last night on my tino/mv45a.... soundstage shrunk dramatically and had to crank up the volume to hear the music....definitely better in the 8ohm tap for my set up.
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Postby Hyperion » Sat Aug 21, 2004 1:53 am

arnel90,

Thanks for the info. I'll add this little tidbit to the ever growing sonus faber database hehehe :D ...
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Postby jo2 » Sat Aug 21, 2004 6:24 am

noctilux,

Thanks! :)
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Postby Noel_14 » Sat Aug 21, 2004 9:31 am

Yup, I agree with arnel90 :) at 4 Ohms load it lack the punch. The music sucks and lifeless.
cheers :)
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Postby diowee » Sat Aug 21, 2004 10:45 pm

same finding with arnel90 and noel14 when i used 4 ohm tap; tino + asl aq1010 int amp. much better in 8 ohm tap.
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Postby JackD201 » Mon Sep 05, 2005 3:05 pm

Mods please move to Tech Archive. Tnx guys!
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Postby rascal101 » Thu Nov 03, 2005 5:30 pm

Inputs from a newbie ...

Using 4ohm speakers - there is more current for the same signal. Since the speaker is an inductor (stores current), it is much more capable of driving the speaker cone ... more current ... more driving capability.

Comments please ...
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Postby JackD201 » Thu Nov 03, 2005 5:59 pm

4 ohm speakers have less DAMPING. They therefore REQUIRE more current (ohms law) wether run from the 8 or 4 ohm taps. The 4 ohm tap is there to provide you with an option if your loudspeakers have low impedance dips, an added bit of safety. It has little to do with quality. In other words the 4 ohm tap is better at stopping (which eats away at power reserves like a @*^$$%^ ! :lol:) and not driving the speaker cone excursions. Proof: In tube amps 4ohm output wattage is, in most cases, practically the same if not lower than their 8ohm output wattage unlike solid state designs.

;)
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Re: speakers on 4 ohm vs. 8 ohm taps - what's the theory?

Postby rascal101 » Thu Nov 10, 2005 10:26 am

troporobo wrote:Synergy gurus: can somebody help me understand this please? I have been reading on the 'net from time to time that some people deliberately connect their 8 ohm speakers to the 4 ohm taps, or vice versa. I have not been paying close attention, but maybe this is more prevalent with low power tube amps. What's the theory behind doing it one way or another?

I was thinking about this last night after hooking up a pair of speakers I have on trial (many thanks again to a kind pinoydiophile!). The impedance wasn't labelled and I had forgotten to check, so left my cables on the 4 ohm taps (on an 8 wpc EL34 SET amp). The speakers sounded terrible, really flabby bass, flat mids, recessed highs. Turns out the speakers are 8 ohm and only 86 or 88 dB sensitivity. So I changed to the 8 ohm taps . . . success! Bass tightened up dramatically, highs and mids were brought forward and balanced in proportion, all was right with the world.

What I want to know is, why is this? What is the speaker / amp interaction that's happening? And why would some people deliberately use a seemingly mis-matched connection?

Thanks in advance


Sirs,

For tube and solid state amplifiers, it is necessary that the output impedance must match speaker impedance for maximum power transfer. Since tube amplifiers have transformer coupled output stage it is easier to match impedance. As such, if output transformer impedance is 4ohm, speaker impedance must also be 4ohms. This is the same scenario for 8ohms.

In this configuration, if the amplifier is capable of delivering 10watts output power, 5watts each will be consumed by the amplifier and speaker corresponding to a 50% and 50% power ratio.

As an example, if there is impedance mismatch as follows:
output transformer = 4ohm, speaker = 8ohm

the power ratio will be 1/3 and 2/3. This is not good for the amplifier or speaker as they will be consuming less/more than necessary. In example above, 1/3 or 3.33watts for amp and 2/3 or 6.66watts for the speaker. This is bad for the speaker as it is consuming more power than required. For the opposite scenario (output xformer = 8ohms, spkr = 4ohms), 6.66watts for the amplifier would mean driving the power device eg vacuum tube 33.33% more than required. There is more power stress in the tubes.

In the impedance mismatch scenario, there is more current to the power device - vacuum tube, output transformer and speaker. This can't be good to either of them regardless if the design had extra margin.

As such, connect 8ohm speaker to 8ohm output terminal and 4ohm speaker to 4ohm output terminal. Amplifier or speaker life must always be considered before pleasure.

Hope this information helps.

Best regards,

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Re: speakers on 4 ohm vs. 8 ohm taps - what's the theory?

Postby JackD201 » Thu Nov 10, 2005 11:28 am

rascal101 wrote: Amplifier or speaker life must always be considered before pleasure.



I Agree. I have 6 ohm nominal speakers with a relatively stable and flat impedance curve but I connect to the 4 ohm tap. It was also the dealer's recommendation. If you want more air and bass definition, just move your speakers further away from the walls and sit nearer. :lol:
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Postby AnalogBuff » Thu Nov 10, 2005 12:24 pm

Fella's check this site out :)

http://wolfstone.halloweenhost.com/Tech ... ching.html

Cheerio!!
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Postby tony » Wed Nov 16, 2005 11:08 am

speaker impedances are nominal, they are true for only one frequency! an 8ohm speaker will have a dc resitance less than 8ohms,

this dc resistance is in series with the voice coil that has an inductive reactance that varies with frequency!

when the voice coils is moving, it can also have capacitive reactance, much like a synchronous motor!
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Postby JackD201 » Wed Nov 16, 2005 4:06 pm

joan2, that goes without saying. Earlier in this thread it was recommended that if one has doubts ask the loudspeaker manufacturer for the impedance plot of the particular model in question. Nominal means average over the spectrum i believe and not at any given frequency. In double or triple stack systems nominal impedances are given for each array.

Yes similar to a synchronous motor but more like a moving coil motor which pistonic drivers actually are.
Last edited by JackD201 on Wed Nov 16, 2005 5:17 pm, edited 1 time in total.
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Postby garp » Wed Nov 16, 2005 4:43 pm

I sometimes use the 4 ohm tap to experiment on the damping factor. Here's the scenario: I have an 8 ohm nominal load and using a push pull UL amp. I converted the amp to become PP triode instead. I got the mids I wanted but at the expense of slightly boomy low end. To compensate, I increased the damping factor by moving to the 4 ohm tap.
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Postby JackD201 » Wed Nov 16, 2005 5:14 pm

garp wrote:I sometimes use the 4 ohm tap to experiment on the damping factor. Here's the scenario: I have an 8 ohm nominal load and using a push pull UL amp. I converted the amp to become PP triode instead. I got the mids I wanted but at the expense of slightly boomy low end. To compensate, I increased the damping factor by moving to the 4 ohm tap.


Garp, did it solve the boominess? Did it come at the expense of dynamic headroom?

just curious. :)
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Postby garp » Thu Nov 17, 2005 7:01 am

It's tighter using the 4 ohm tap but idn't cure the boominess entirely. Altho tighter its not quite at par with UL.

As for dynamic headroom, its hard to tell. Along with the triode mod, I also disabled the NFB. This has the effect of increasing the sensitivity (gain?) of the amp so that now at my usual 10oclock pot position is now at 8oclock for SUBJECTIVELY the same volume level. The midrange is much clearer from the softest to the loudest passages in triode mod. Given this new config, I can't tell yet (I'm still listening) if I PERCEIVE a change in dynamic headroom when moving to the 4ohm tap.
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Postby tony » Thu Nov 17, 2005 8:29 am

an 8ohm tap on the output transformer will have 40% more turns than a 4ohm tap.
a 16ohm tap will have twice the number of turns for the 4ohm tap.
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