Author Topic: Sonic difference between 4 ohm and 8 ohm amplifier taps  (Read 3053 times)

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Offline raffya468

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Sonic difference between 4 ohm and 8 ohm amplifier taps
« on: Jan 27, 2017 at 10:34 AM »
My Line Magnetics  501ia has 4, 8 and 16 ohm taps obviously to properly match with the impedance of the speaker to be driven. I recently purchased a Dali Epicon2 which is a 4 ohm speaker and in my excitement I had inadvertently used the 8 ohm taps (the speaker it replaced was 8 ohms thus the speaker wires were already connected this way). I listen only at moderate levels so I don't have the volume knob go past the 10 o'clock range.

While I was very satisfied with the performance (fairly similar to the sound characteristics of this speaker driven by my ss amp) in terms of dynamics and overall tonal quality, the vocals seemed just a bit laid back and slightly off-center despite trying various speaker placements/positioning. This went on for about a month and while the epicon broke-in quite nicely, something seemed amiss. That's when I discovered that I was using the 8 ohm taps for a 4 ohm speakers.

Now that I have properly connected the wire to the 4 ohm taps the epicon exhibited a totally different character. Mids are more detailed and the vocals more upfront presence and pinned to the center stage. However, it seems to me to be slightly less dynamic sounding although I very much prefer the overall sonic presentation now.

My question is, of course aside from the obvious matching with the speakers, what in the amplifier design would lead to a difference in sonic character between the 4 and 8 ohm taps? What would happen if I used the 4 ohm tap to drive an 8 ohm speaker?

Appreciate in advance any insights the experts may give. I'm trying to keep myself educated in this fascinating hobby of ours.

Thank you.

Offline uvax

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Re: Sonic difference between 4 ohm and 8 ohm amplifier taps
« Reply #1 on: Jan 27, 2017 at 10:49 AM »
I was recently watching a youtube video by Audioholics and they gave a link to this article on their website:

http://www.audioholics.com/audio-amplifier/impedance-selector-switch-1

https://www.youtube.com/watch?v=Ou5bO8P2Drw
« Last Edit: Jan 27, 2017 at 11:11 AM by uvax »

Offline raffya468

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Re: Sonic difference between 4 ohm and 8 ohm amplifier taps
« Reply #2 on: Jan 27, 2017 at 12:42 PM »
Thank you for the links uvax. The YouTube video by Audioholics discusses how many mass consumer A/V Receivers purposely put the impedance switch for marketing purposes and employ technics that are shortcuts or workarounds rather than provide real tech solutions. I am hoping the LM 501ia being a dedicated audio gear which has individual output taps for 4, 8 and 16 ohms has not resorted to workarounds. Maybe the written article has a more detailed discussion and will read it thoroughly.

Cheers.

Offline lithium_deuteride

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Re: Sonic difference between 4 ohm and 8 ohm amplifier taps
« Reply #3 on: Feb 02, 2017 at 04:47 PM »
The lesser the impedance, the greater the capacity for current flow.  So using an 8-ohm amp on a 4-ohm speaker will limit the performance of that speaker as it won't be getting the amount of current it demands.  If it's the other way around (4-ohm amp taps on an 8-ohm speaker), wala siguro problema.  Maybe our resident experts can chime in.
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Offline meat_eater

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Re: Sonic difference between 4 ohm and 8 ohm amplifier taps
« Reply #4 on: Feb 02, 2017 at 05:12 PM »
The lesser the impedance, the greater the capacity for current flow.  So using an 8-ohm amp on a 4-ohm speaker will limit the performance of that speaker as it won't be getting the amount of current it demands.  If it's the other way around (4-ohm amp taps on an 8-ohm speaker), wala siguro problema.  Maybe our resident experts can chime in.

Mismatched impedance (pots) could result to an overworked amplifier. You will notice this kapag umiinit ng sobra ung transformers mo.

The best way to know which pot to use is to check if merong published measurements ung speakers. If the speaker dips to say 4 ohms better to use the 4 ohm tap kahit 8 ohm ung nominal impedance nia (declared ng manufacturer).
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Offline tony

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Re: Sonic difference between 4 ohm and 8 ohm amplifier taps
« Reply #5 on: Feb 02, 2017 at 05:35 PM »
it works because of the nature of music....

an 8 ohm or even a 4 ohm speaker is true only at one frequency,
at other frequencies they are no longer 8 or 4 ohms but can be as high as 300 ohms....
how do we defend our freedom? by the truth when it is assaulted by Marcos lies....

Offline uvax

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Re: Sonic difference between 4 ohm and 8 ohm amplifier taps
« Reply #6 on: Feb 02, 2017 at 05:49 PM »
The lesser the impedance, the greater the capacity for current flow.  So using an 8-ohm amp on a 4-ohm speaker will limit the performance of that speaker as it won't be getting the amount of current it demands.  If it's the other way around (4-ohm amp taps on an 8-ohm speaker), wala siguro problema.  Maybe our resident experts can chime in.

Actually if you read thru the Audioholics article this will only matter if you are driving the speaker at high volumes. The 4 ohms taps are there solely for legal safety compliance. Driving low impedance speakers can draw a lot of current and cause the amp to overheat and cause a fire hazzard. In effect the 4 ohms switch is a current limiter. This will have an effect in that if you are playing material with short bursts of intense volume it will clip the current causing distortion.

The guys at Audioholics recommend not to use the 4 ohms taps because modern amps and receivers have overdrive protection anyway so you can fully enjoy your amp.

Offline meat_eater

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Re: Sonic difference between 4 ohm and 8 ohm amplifier taps
« Reply #7 on: Feb 02, 2017 at 06:00 PM »
it works because of the nature of music....

an 8 ohm or even a 4 ohm speaker is true only at one frequency,
at other frequencies they are no longer 8 or 4 ohms but can be as high as 300 ohms....

True.

Or as low as 2 ohms as with most consumer floorstanders (declared as 8 ohm) (PSB Imagine X2t, B&W floor standers, etc).

Some speakers declare a 4 ohm nominal impedance, but measurements show otherwise - e.g. Dynaudio Excite X14 - Does not really go below 5 ohms and stay above 6 ohms - A benign load and very easy to drive speaker. :)
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Offline CoolTOYZPH

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Re: Sonic difference between 4 ohm and 8 ohm amplifier taps
« Reply #8 on: Feb 05, 2017 at 08:52 PM »
Very nice topic.
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Offline tony

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Re: Sonic difference between 4 ohm and 8 ohm amplifier taps
« Reply #9 on: Feb 06, 2017 at 07:57 AM »
Quote
My question is, of course aside from the obvious matching with the speakers, what in the amplifier design would lead to a difference in sonic character between the 4 and 8 ohm taps?

what happened here was you were asking the amp for more power, and being kt88's, they are capable of more power...
if you want some math, we can do that....;)
the drawback here could be higher distortions, but if that was a 3rd harmonic, then better for the bass....

if you did that to an el84 amp, then things might have been different....the el84 would have clipped sooner than a kt88...


Quote
What would happen if I used the 4 ohm tap to drive an 8 ohm speaker?

then the amp will be loafing around and delivering less power...
distortion will be lower, but then for tube amps, that is usually
not an issue as long as you can not hear it....

lastly, for solid state amps, this speaker matching is not such a big
issue, ss amps have output impedances below an ohm, see the damping factor specs for ss amp....

tube amps have much higher output impedances, (lower damping factors...) the 4 8 and 16 ohm taps in a tube amp is not the output impedance of that tube amp, they are OPT secondary taps for
connecting speakers....
« Last Edit: Feb 06, 2017 at 08:33 AM by tony »
how do we defend our freedom? by the truth when it is assaulted by Marcos lies....

Offline raffya468

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Re: Sonic difference between 4 ohm and 8 ohm amplifier taps
« Reply #10 on: Feb 06, 2017 at 02:51 PM »
Many thanks for the replies and inputs gentlemen. Lots of research and reading for me to do.

@tony - thanks for the clear explanation on the points I raised. The LM 501ia employs 4x  kt120's and the amp outputs 100w per manufacturer's claim. I'm certain the condition you described applies to these as well. No need to do the math as I'm sure it would just fly 10 feet over my head! I appreciate the offer though.

I had a very good friend who's based in the U.S. visit me yesterday to listen to my set-up. By way of background he is a trained sound engineer who works as r&d head for a global car stereo brand that supplies its equipment as OEM for major car companies. He gets to test and sign off on new equipment they had developed that are installed in various car brands. Needless to say, his passion for quality sound extends to his home set-up.

After ample warm-up time with the 4-ohm Dali Epicon2 connected to the 4-ohm taps of the LM 501ia we listened to material he is intimately familiar with in both vinyl an cd versions. He would listen at levels that were louder than what I was used to with the volume at about 50-60% mark and during certain passages go to about 75% level! Frankly I was getting nervous watching the volume meters banging the reds consistently. I could sense he was looking for certain sounds and he was straining trying find it. He was trying his best to be polite but I too found the sound wanting at those levels.

We then tried using the 8-ohm taps and it was day-and-night transformation. My friend started nodding his head, tapping his feet and began describing what the sound engineer was attempting to do in terms of conveying the various layers of the recording. As I had described in my original post, the 8-ohm taps provided a more open and dynamic presentation with great detail at the bass notes. As expected and pointed out by you fine gentlemen, the amp was showing signs of struggling at the volume levels and we had sensed clipping at about 60-65% volume level. I never reach that in my normal listening mode.

So for now it stays on the 8-ohm taps. I'll continue to experiment with speaker placement to address the slightly left of center vocals this set-up exhibits.

Your comments, suggestions and insights would be most welcome.

Thanks.

Offline tony

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Re: Sonic difference between 4 ohm and 8 ohm amplifier taps
« Reply #11 on: Feb 06, 2017 at 04:15 PM »
Quote
@tony - thanks for the clear explanation on the points I raised. The LM 501ia employs 4x  kt120's and the amp outputs 100w per manufacturer's claim. I'm certain the condition you described applies to these as well. No need to do the math as I'm sure it would just fly 10 feet over my head! I appreciate the offer though.

kaya naman pala minani lang nya ang 4 ohm into the 8 ohm tap...
kt120 is 1.5 times a kt88....
but if the circuit and the voltages used in that amp is the same
as the kt88's then power will be the same as a kt88....
not to despair though, a kt120 used in a kt88 circuit will not bring
more power, but it will be more robust and yield a longer tube life...it is still powerful as it is...
if i can see the design schematics, i can tell with more surety....

and did i tell you that i stopped counting the watts a long time ago? as long as you are happy with your setup, then that is it...
how do we defend our freedom? by the truth when it is assaulted by Marcos lies....