Klipsch RF7 II Measurements - AVS Forum
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post #1 of 19 Old 05-27-2012, 11:57 AM - Thread Starter
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I recently auditioned the Klipsch RF7 IIs and was impressed. Since then I have been trying to find out any impedance and frequency measurements. Finally, I ended up buying the review from a German Audio magazine. I have attached the measurements to this thread.

There are a few issues I was concerned about. First, The impedance dips down to about 3.7 ohms, which should not be a problem with my Mcintosh MC275. However, what concerns me more is that the impedance curve shows to obvious wrinkles in the midrange, possibly indicating bad resonance in the range. Also, it seems the high frequency driver's resonance is at about 18 KHz. When auditioning, I did not pay particular attention to this and did not notice it. Is it possible that you would notice these issues more with certain recordings? And if so, would for example the resonances cause congestion?

Finally the waterfall also shows some irregularities in the 12-18K range, not sure if this is again related to the domes resonance frequency.

Would appreciate if someone can comment not this. Are the midrange resonances and HF driver's resonance at 18 KHz big issues or are these trivial issues and should not be big deal?

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post #2 of 19 Old 05-27-2012, 12:11 PM
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I would say the first two wrinkles in the impedence curve are more likely to cause audible resonances than the higher frequency wrinkle at around 18khz.
LL
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post #3 of 19 Old 05-27-2012, 12:11 PM
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Looks pretty good to 30 degrees off axis, outside of that weird 1khz dip at 10 degrees? I'm guessing whatever is going on at 12/18khz is why these speakers can be fatiguing to certain people.

The impedance and measured response just shows why the manufacturers rating is misleading. 100-200hz is the most demanding region when a speaker is crossed at 80hz, and most receivers wont perform well here. This speaker is also only 90db....
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post #4 of 19 Old 05-27-2012, 12:21 PM - Thread Starter
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the measurements were obtained supplying 2.0 volts to get 90dB. They did mention that sensitivity goes up to 96.3 with 2.83volts, still significantly lower than the advertised 101dB sensitivity

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post #5 of 19 Old 05-27-2012, 12:23 PM
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Quote:
Originally Posted by gago1101 View Post

the measurements were obtained supplying 2.0 volts to get 90dB. They did mention that sensitivity goes up to 96.3 with 2.83volts, still significantly lower than the advertised 101dB sensitivity

Alright, that's MUCH better
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post #6 of 19 Old 05-28-2012, 07:52 AM
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Quote:
Originally Posted by gago1101 View Post

First, The impedance dips down to about 3.7 ohms, which should not be a problem with my Mcintosh MC275.

So the dark line is impedance and the green line is phase, right?
Thanks for this. Settles a question that comes up often. The older RF7 had a dip to 2.7 ohms, as I recall, so these are not as hard to drive.

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post #7 of 19 Old 05-28-2012, 08:35 AM
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Some people might be worried about the 2kHz "bubble" or "peak" in energy? Indicating possible "brightness" in sound and possibly causing listener's fatigue?
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post #8 of 19 Old 05-28-2012, 09:45 AM
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Quote:
Originally Posted by gago1101 View Post

However, what concerns me more is that the impedance curve shows to obvious wrinkles in the midrange, possibly indicating bad resonance in the range. Also, it seems the high frequency driver's resonance is at about 18 KHz. When auditioning, I did not pay particular attention to this and did not notice it. Is it possible that you would notice these issues more with certain recordings? And if so, would for example the resonances cause congestion?

I'm thinking that these resonances may be contributing causes to the honkiness and listening fatigue that many people have experienced with modern Klipsch home speakers. That resonance at 400 Hz happens to correspond precisely to the outer circumference of the horn, which must not be adequately braced and damped, allowing the horn to literally ring like a bell. And the 1200 Hz crossover frequency for the high-frequency driver means that its colorations, whether detectable in these measurements or not, will be present throughout the midrange.

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Originally Posted by gago1101 View Post

Finally the waterfall also shows some irregularities in the 12-18K range, not sure if this is again related to the domes resonance frequency.

These are pretty massive, whatever their cause--I figure that they must be audible in some way.

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Originally Posted by Jay1 View Post

Looks pretty good to 30 degrees off axis, outside of that weird 1khz dip at 10 degrees?

Well, the legend says "10*hoch" and hoch means high in German (while seitl means side), so it's a vertical off-axis measurement, in which case the curve makes a lot more sense.

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Originally Posted by Jay1 View Post

I'm guessing whatever is going on at 12/18khz is why these speakers can be fatiguing to certain people.

Probably so, and the ringing of the horn is probably a big reason the speaker sounds honky. A speaker using horn-loaded drivers doesn't have to sound this way, or at least nearly as much, anyway--this one just has some major deficiencies (not as much as the Synergy series does, though). I dunno, for $1600/speaker, one would think that it would be designed and built better....
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post #9 of 19 Old 09-06-2013, 07:05 AM
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I saw this thread and picture and was totally impressed with what Gago did to these speakers: http://www.avsforum.com/t/1451372/better-value-then-the-klipsch-rf-7-ii-package-ideas/180#post_23643316

That said, with the information in the original graphs above of the RF-7IIs, what would be a sufficient power supply, Amp, or AVR to drive these speakers efficiently in a 2,000 to 2500 cu ft room?
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post #10 of 19 Old 09-06-2013, 08:36 AM
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Quote:
Originally Posted by Matts View Post

I would say the first two wrinkles in the impedence curve are more likely to cause audible resonances than the higher frequency wrinkle at around 18khz.
LL

I suspect that cause and effect are reversed in the comments above. The wrinkes in the impedance curves are clearly effects, not causes. The probable causes of the wrinkles would be acoustical or mechanical resonances in the drivers or their environments.

While most people can hear pure tones at 18 KHz if they are loud enough, that's not the most important thing. We now know that masking often trumps simple audibility. With all but a few pathological musical sounds sounds at lower frequencies from 7 to 13 KHz are often stronger than those above that range, but even if they aren't stronger, they can still mask sounds from 13 KHz and up because they are more audible per Fletcher and Munson.
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post #11 of 19 Old 09-06-2013, 08:36 AM
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Wow, I am impressed with what Gago did to his RF-7ii's! Does anyone know what compression driver he upgraded the mid-range horn to? I saw where the measurement graph said it was a Radian, but I am not sure of the model? Also, can anyone share anything about those Fostex tweeters that Gago used?
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post #12 of 19 Old 09-06-2013, 08:49 AM
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Quote:
Originally Posted by gago1101 View Post

There are a few issues I was concerned about. First, The impedance dips down to about 3.7 ohms, which should not be a problem with my Mcintosh MC275.

Given that few if any tubed amps have low source impedances that are even in the same zip code as what is common with good but even inexpensive SS amps, I would expect the sound of the MC275 to find them more problematical than a good modern AVR.

Here are some relevant facts: These are frequency response curves of a MC 275 with various loads:



Here are comparable frequency response curves that I would expect from most good SS amps including those found in mainstream AVRs:

http://www.stereophile.com/content/marantz-pm5003-integrated-amplifier-measurements



The vertical scales are comparable so it is reasonable to compare the size of the differences in the response curves.

Not only are the response curves for the AVR closer together by a factor of almost 3, so is the size of the waviness in the response into a simulated speaker load.

It is therefore concluded that even an AVR is many times more resistant to speaker-induced colorations than the classic and it its day quite good tubed amp.
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post #13 of 19 Old 09-06-2013, 10:12 AM
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Quote:
Originally Posted by arnyk View Post

Here are comparable frequency response curves that I would expect from most good SS amps including those found in mainstream AVRs:

http://www.stereophile.com/content/marantz-pm5003-integrated-amplifier-measurements



The vertical scales are comparable so it is reasonable to compare the size of the differences in the response curves.

Not only are the response curves for the AVR closer together by a factor of almost 3, so is the size of the waviness in the response into a simulated speaker load.

I am not sophisticated enough to understand the graph but are you saying that any mainstream AVR should be able to drive the RF-7IIs efficiently regardless of it's jagged Frequency Response and dips lower than 4 Ohms? Also, if anyone has the chart for the Original RF-7s which reportedly dip down to 2.8 Ohms could you provide the link?
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post #14 of 19 Old 09-06-2013, 05:31 PM
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Quote:
Originally Posted by gago1101 View Post

the measurements were obtained supplying 2.0 volts to get 90dB. They did mention that sensitivity goes up to 96.3 with 2.83volts,
If 2V into a given load gives 90dB, 2.83V will give 93dB.
Quote:
Originally Posted by gago1101 View Post

still significantly lower than the advertised 101dB sensitivity
Klipsch have played very fast and loose with specs since the great PWK died. They deserve one of his infamous badges.
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post #15 of 19 Old 09-06-2013, 05:58 PM
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Here's what I notice from the plots:

1) Sag in the midrange at 1kHz when vertically off-axis by 10 degrees. Lots of speakers, if not most, have issues like this due to vertically stacked drivers interfering. It can be avoided with coincident drivers (like KEF). Its audible significance is debatable.

2) General upward trend from 2kHz to 20kHz may make them seem bright.

3) Off-axis humps ("flares") in freq resp from about 4 or 5 kHz to about 10kHz may make them seem bright and/or forward in the mid-to-high treble.

4) Large peak around 20kHz is likely the tweeter resonances frequency. I can't hear that high. You might? Very little program material energy there, so of questionable significance.

5) Glitches in the impedance plots at 150Hz and 300Hz are likely from cabinet resonances. Tough to determine whether or not these are audible. Depends on their Q factor, magnitude, surface area, and many other factors.

6) Glitch in the impedance plot just below 20kHz is the tweeter resonance frequency. Audibility in question as described above.

6) Impedance magnitude drops below 4 Ohms from about 100Hz to 200Hz. This will draw a relatively high amount of current in a region with a lot of energy (mid to upper bass). But is ameliorated by the speakers relatively high sensitivity. In a big room, playing very loud, will stress an amp, but otherwise OK.

7) Impedance phase angles are all over the place and often exceed 50 degrees. This could make them a tough load. Fortunately, phase angle is low where the magnitude is low (100Hz to 200Hz), so not as big as issue as it could be. Still, pretty high phase angles, so it will be somewhat taxing on the amp. I would get a good solid-state amp or AVR rated to 4 Ohms.

8) The waterfall/CSD plot shows big ridges of resonance at around 12kHz and 18kHz. The lower of the two might be more audible as a very high frequency ringing. Not much program energy at this high frequency, but could be audible as a sharp piercing quality to the sound if the resonance is excited. The higher one is too high for me to hear but could do the same thing as the lower one if it's excited.

Overall impressions: Meh. I've seen worse measurements from that site. I've seen better too.
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post #16 of 19 Old 09-06-2013, 06:09 PM
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Interesting mods he did. Should fix some of the high-frequency issues of the originals.

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post #17 of 19 Old 09-07-2013, 06:55 PM
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Thanks beaveav, for the response. The reason I resurrected Gago's old thread was threefold: One, I too was impressed with the work/effort he's done. The second was trying to figure out how important the ability to drive 4 Ohm loads helped the RF-7s, and thirdly how much influence does the modern EQ programs help the deficiencies in these speakers. Insofar as the second is concerned, I do feel like lower end AVRs can't drive Rf-7s in a multispeaker configuration to near Reference volume from my experience...

That said, I have a Denon AVR-4311ci which has Audyssey MultEQ Xt-32 and it drives them as loud as the THX Ultra II Denon AVR-4806ci did (slightly, 3-6 dB louder) on everything yet it doesn't seem to have the power supplies of the AVR-4806ci.

For a year between those units I had a Denon AVR-3805 driving this system and with my Rat shack meter it was obviously 6 to 8 dB lower before it started sounding bright and I was trying to figure out the science to what I was hearing/measuring....I also had a couple of mid-priced Yamaha units prior to these and it couldn't drive them efficiently at loud volumes and I came to find that they weren't rated to drive 4 Ohm loads so that is where I started from {Note: Not a bash against yammis--they had really good processing on the various sound modes and lower volume.}
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post #18 of 19 Old 02-18-2014, 04:00 PM
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Does anyone know where I could find corresponding measurements for the original rf7? So far i tried with google to no avail frown.gif
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post #19 of 19 Old 04-16-2014, 10:38 AM
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Quote:
Originally Posted by Levil View Post

Does anyone know where I could find corresponding measurements for the original rf7? So far i tried with google to no avail frown.gif

I remember there was a graph in the original Sound and Vision article which had them on it's cover when they first came out but can't find it on the internet either--Anyone? I also remember that they dipped down to 2.8 Ohms at a frequency above where I would want the sub to take over, but it appears the RF-7II doesn't dip that low unless the measurements were done differently.
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