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Old 19th September 2014, 09:59 PM   #1
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Default Impedance marketing?

I have some Klipsch Heresy II's with the round cup back where the binding posts are. A few years back I got some Sonicaps from Bob Crites and did the crossovers myself. I have had them hooked up to my Scott 299A mainly and have been using the 8 ohm tap regardless of the speakers saying nominal impedance 4 ohms. The amp sounds better to me with the 8 ohm taps rather than the 4. A friend was over and told me I was damaging my amp using it this way lol........anyway I know I am not damaging the amp but after some digging I haven't gotten a definitive answer. I have read two answers, one is that the woofer at lower frequencies is 4 ohms, and the other is that it was a marketing scheme at the time to boost sales to solid state amp users hoping to get more power from the 4 ohm load.

Maybe somebody can shine some light on this for me.

-Thanks
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Old 19th September 2014, 10:20 PM   #2
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Try measuring the frequency response from either tap at a decently high SPL. The "right tap" will depend on the speakers' impedance profile, which is not by any means resistive.

My guess is that the 4-ohm tap, which should have the lowest output impedance, is going to be the most accurate while the 8-ohm tap is probably measurably colouring the sound.

Last edited by RockLeeEV; 19th September 2014 at 10:23 PM.
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Old 19th September 2014, 10:36 PM   #3
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The only reason that your amplifier is still alive is because your speakers are incapable to produce true bass sound.
There is no true woofer drive in them.
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Old 19th September 2014, 11:23 PM   #4
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Originally Posted by Kiriakos View Post
The only reason that your amplifier is still alive is because your speakers are incapable to produce true bass sound.
There is no true woofer drive in them.

Please explain. Are you speaking in terms of high power levels? When you say "There is no true woofer drive in them" are you talking about the frequency response of the speakers or the amp? If you are talking about the speakers being rated down to 63Hz and not 20Hz are you saying if they did reach lower my amp would blow up?

Your response is very vague, and you have not presented any data to support your claim. Also your response does not remotely answer my original question. I am sure your systems bass is "superior".

I do have a subwoofer for supplemental bass when using with this system FWIW.
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Old 19th September 2014, 11:27 PM   #5
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Quote:
Originally Posted by RockLeeEV View Post
Try measuring the frequency response from either tap at a decently high SPL. The "right tap" will depend on the speakers' impedance profile, which is not by any means resistive.
Thanks I will give this a try. I am guessing the tap with the highest transfer at the lowest frequency is what I am looking for?
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Old 20th September 2014, 08:06 AM   #6
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Your large drives are wide range, this automatically translates to a minimal power consumption compared to a thee way speaker system with dedicated woofer.

Therefore by the numbers, speakers coils will collapse first but not the amp.
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Old 20th September 2014, 09:43 AM   #7
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Let's ask the right question! We know that valve amplifiers, which are current sources, dislike driving an open circuit, because they push more and more volts at the load to try and get some current flowing. Transistor amps, which are voltage sources dislike short circuit, because they push more and more amps at the load. These conditions will cause damage to the amps' output stage potentially.

Therefore if I am using the 8 ohm tap of a valve amplifier into a 4 ohm load, is this safe for the amplifier?

I think so. For a valve amp you are pushing it nearer to a short circuit load condition, which it won't mind. It won't be the most EFFICIENT setting, however and it won't go as loud overall.

Tonally, the sound will change with a significant amplifier output impedance. Feedback complicates this, but in general, output from the speaker will increase as the speaker impedance goes higher. Hence the effort to keep speaker impedance flat when designing a valve-friendly speaker. If the impedance is flat, the tone won't change with any sort of amplifier output impedance variation.

Hope I got that right!
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Old 20th September 2014, 01:54 PM   #8
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Originally Posted by system7 View Post
Let's ask the right question! We know that valve amplifiers ......
Wait a minute ...
I just realized that this topic is about an valve amplifier, and my first thought is to start running away as faster I can from it.

An valve amplifier is a different animal compared to transistors, and in this case instead of getting personally in a technical analysis, I would suggest a better reading of the Users manual or an email to be send to the manufacturer, only he is aware of the true potentials of this equipment.
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Old 20th September 2014, 03:53 PM   #9
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Originally Posted by system7 View Post
Let's ask the right question! We know that valve amplifiers, which are current sources, dislike driving an open circuit, because they push more and more volts at the load to try and get some current flowing. Transistor amps, which are voltage sources dislike short circuit, because they push more and more amps at the load. These conditions will cause damage to the amps' output stage potentially.

Therefore if I am using the 8 ohm tap of a valve amplifier into a 4 ohm load, is this safe for the amplifier?

I think so. For a valve amp you are pushing it nearer to a short circuit load condition, which it won't mind. It won't be the most EFFICIENT setting, however and it won't go as loud overall.

Tonally, the sound will change with a significant amplifier output impedance. Feedback complicates this, but in general, output from the speaker will increase as the speaker impedance goes higher. Hence the effort to keep speaker impedance flat when designing a valve-friendly speaker. If the impedance is flat, the tone won't change with any sort of amplifier output impedance variation.

Hope I got that right!
Great answer! And yes you did get it right. I do understand the theory, which would tell me the transfer would be less when using a 4 ohm load on the 8 ohm tap. But this isn't the case with these speakers, hence my question, I do NOT think the speakers in fact are a 4 ohm load but actually an 8 ohm load, which is why I think it was a marketing scheme to write on the back nominal impedance 4 ohms.

Anyway valve amps usually can take 100% mismatch in loads without doing damage.........but you will get performance differences. In my case I do not believe I am mismatching the load for the speakers are actually 8 ohms instead of the marked 4 ohms.

I guess I can try and contact Klipsch about this but my suspicions are that the speakers are in fact 8 ohms for I get the best transfer with the 8 ohm tap.
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Old 20th September 2014, 04:09 PM   #10
SY is offline SY  United States
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Quote:
Originally Posted by system7 View Post
...which are current sources
Only effects-box designs. When engineered, they're generally closer to a voltage source. 0.5 ohm is not unreasonable, and 1 ohm is a reasonable max. It *will* change the frequency response into a load with a varying impedance (99% of speakers), the question is how much and is it beneficial or a degradation for a particular speaker/amp combination. Very different than a current source which has a source impedance >> load impedance.
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