4 OHMS or 8 OHMS

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4 OHMS or 8 OHMS

Postby AnalogBuff » Tue Sep 06, 2005 10:45 am

Hi Jack!

Can you give me an affirmation or comment on this scenario I have experienced? My tube amp has the standard 4 and 8 ohms speaker outputs.I am using a fairly efficient 8 ohm nominal impedance speaker.

To my surprise upon recommendation of an audiophile reviewer I tried hooking the speakers up on the 4 ohm output with very good results. The bass is more controlled and tighter! Imaging has somewhat become more focused and spot on.

Now outside of the improvement in the sound quality can you give me some technical reasons as to why this came about. We in our klub would greatly appreciate what you and perhaps others may share to this phenomena. Thanks.
Last edited by AnalogBuff on Tue Sep 06, 2005 1:06 pm, edited 1 time in total.
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Postby amandarae » Tue Sep 06, 2005 11:13 am

Hello sir,

I am not Jack but allow me to speculate.

I think it is obvious that your speaker likes more power(and current) than you might imagine. At 4 ohms load, a stable amp will produce more power than at 8 ohms. Since the load is 8 ohms and you are using the 4 ohm tap, the amp(from the primary) is seeing a load of 4 ohm in parallel with 8 ohms in the secondary, which is roughly around 3 ohms. So what?
Since the amp "sees" this present load, it will summon the power supply to produce more current to sustain the spl level you prefer as oppose to the other configuration which in turn I supect your speaker (the crossover mainly) likes better.

I also think that "8 ohms nominal..." is the key here. 8 ohms nominal at what frequency? Depending on the design of the crossover, etc. an 8 ohm nominal driver can have an impedance swing on the audio spectrum. It can be 2 ohms at high frequencies or 12 ohms at bass frequencies etc. In that sense, I think your speaker sounds better at the 4 ohms tap because it can take care of this impedance swing easily(particularly tone and dynamics) if the amp gives more current or headroom.


I could be wrong....
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Postby audiophyte » Tue Sep 06, 2005 8:31 pm

but what is the danger in tapping 4 ohms of the tube amp when the speakers are designed for 8 ohms? will it break the speakers or the amp?

thanks so much.
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Postby AnalogBuff » Tue Sep 06, 2005 10:44 pm

audiophyte wrote:but what is the danger in tapping 4 ohms of the tube amp when the speakers are designed for 8 ohms? will it break the speakers or the amp?

thanks so much.


I feel there is no danger it won't break either because everything is fine with me (so far). In a worse case scenario there may only be some sound changes in the music you listen to. Depending on the speakers you are using.

Thanks amandarae for your inputs it does seem logical to realise that the speakers I am using are more shall we say friendly to variants in the impedance loads shifts.

Is it safe to say then this may not prove to be beneficial(tapping 4 ohm output into an 8 ohm speaker) to other systems let's say SET's?
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Postby rascal101 » Thu Nov 10, 2005 10:35 am

AnalogBuff wrote:
audiophyte wrote:but what is the danger in tapping 4 ohms of the tube amp when the speakers are designed for 8 ohms? will it break the speakers or the amp?

thanks so much.


I feel there is no danger it won't break either because everything is fine with me (so far). In a worse case scenario there may only be some sound changes in the music you listen to. Depending on the speakers you are using.

Thanks amandarae for your inputs it does seem logical to realise that the speakers I am using are more shall we say friendly to variants in the impedance loads shifts.

Is it safe to say then this may not prove to be beneficial(tapping 4 ohm output into an 8 ohm speaker) to other systems let's say SET's?


Sir Analogbuff,

This foray is dangerous as there is an impedance mismatch. The matching of impedance is there to ensure maximum power transfer. 50% power is consumed by the amplifier and 50% for the speaker.

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 xfrmer = 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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Postby jamants » Thu Nov 10, 2005 10:59 am

thanks! very helpful thread guys
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Postby AnalogBuff » Thu Nov 10, 2005 11:47 am

Rascal101

Who needs impedance mismatch if the speaker impedance goes down to 4 or even 2 OHMS I would surely prefer I tapped my amp at 4 OHMS.

Just like a gun better to have one and not use it than to need one and not have it :)
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Postby AnalogBuff » Thu Nov 10, 2005 12:21 pm

For further clarification on the subject you can check out this site fellas :)

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

Cheerio!!
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Postby tony » Sun Nov 20, 2005 2:09 pm

audiophyte wrote:but what is the danger in tapping 4 ohms of the tube amp when the speakers are designed for 8 ohms? will it break the speakers or the amp?

thanks so much.


i doubt that either your amp or your speakers will be damaged. if you are just listening to music and not doing it ala mobile disco.

average listening levels would be in the vicinity of 5watts or therabouts. more if your speakers are inefficient and less if they are very sensitive.

tapping an 8phm speaker to a 4 ohm tap actually raises the load impedance seen by the output tube, thus less power is available but distortion decreases.

what you did, you may actually have found the best match for your amp and speakers. so if you are happy with that setting, then go with it.

amp designers can not actually anticipate what speaker and end user will hook up to their amp, that is why they design to certein standards.

take the case of bose, they do not deisgn and sell amps per se, but they sell speaker systems with amps, that way, they are sure of the performance of their system.
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Postby Kier » Thu Jan 19, 2006 9:22 pm

How about a speakers with a nominal impedance of 6 ohms & a minimum of 4 ohms, where should it be tapped :?:
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Postby tony » Sat Jan 21, 2006 10:38 am

audiophyte wrote:but what is the danger in tapping 4 ohms of the tube amp when the speakers are designed for 8 ohms? will it break the speakers or the amp?

thanks so much.


when you tap an 8ohm speaker to the 4ohm tap, what happens is that the primary impedance increases, thus power is reduced some but distortion decreases. no problem here, you may even like it!

now when you tap an 8ohm speaker to the 16 ohm tap, the impedance at primary is reduced, thus more power can be generated at some increase in distortion.

all these actions will not damage your amp in any way if you just operate it at average listening levels. :D
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