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RF-7 and Amplification Exposed


tigerbalm

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Hi All.

I'm trying to understand the long-discussed issue of RF-7 and amplification concerns. I understand perfectly the theory behind efficiency and 2.83volts/meter but practically I bump into intriguing results.

Since the RF-7 are so efficient, why is it (told) rewarding to use a quality high-power solid-state rather than a quality 50watts?

What is this thing with the speaker's impendance dips in its lower frequencies? any measurments taken by somebody?

In practice, no one gets even near the clipping area of a 50watts amplifier, so why a 150watts amplifier of the same brand (with the same pre) sounds better in moderate volume levels?

Thanks!

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Hi All.

I'm trying to understand the long-discussed issue of RF-7 and amplification concerns. I understand perfectly the theory behind efficiency and 2.83volts/meter but practically I bump into intriguing results.

Since the RF-7 are so efficient, why is it (told) rewarding to use a quality high-power rather than a quality 50watts?

What is this thing with the impendance dips in its lower frequencies? any measurments taken by somebody?

In theory, no one gets even near the clipping area of a 50watts amplifier, so why a 150watts amplifier of the same brand (with the same pre) sounds better in moderate volume levels?

Thanks!

My take: its not the amount of watts, but the quality of the amplification, that makes the difference. My RF-7's are living quite happily right now with a 30 WPC tube/hybrid amp. Its ability to deliver stable amplification, with reasonably high current draw, gives it an edge over another of other amps, even higher WPC amps, that I have listened to.

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whell, thanks for your insight. I'm refining my question to refer only to solid-state amplifiers.

Adding more input: I've conducted an experiment with two different branded pre-amplifiers and four corresponding power amplifiers, e.g. NAD pre and Rotel Pre and NAD power 50 and NAD power 150 and Rotel power 50 and Rotel power 200.

Regardless of the pre-amplifier, I got quite different results with matching high-power amplifiers. This phenomena is repeated throughout the forum. The high-power results are flavoured with more punchy bass, faster dynamics. Indeed, each amplifier and its own characteristcs, but I'm talking about the greatest common divisor available.

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whell, thanks for your insight. I'm refining my question to refer only to solid-state amplifiers.

Adding more input: I've conducted an experiment with two different branded pre-amplifiers and four corresponding power amplifiers, e.g. NAD pre and Rotel Pre and NAD power 50 and NAD power 150 and Rotel power 50 and Rotel power 200.

Regardless of the pre-amplifier, I got quite different results with matching high-power amplifiers. This phenomena is repeated throughout the forum. The high-power results are flavoured with more punchy bass, faster dynamics. Indeed, each amplifier and its own characteristcs, but I'm talking about the greatest common divisor available.

The higher powered amp probably has a higher dampening factor (essentially the ability to control the power comming back to the amp) and can more easily handle the lower impedence.

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Hi All.

I'm trying to understand the long-discussed issue of RF-7 and amplification concerns. I understand perfectly the theory behind efficiency and 2.83volts/meter but practically I bump into intriguing results.

Since the RF-7 are so efficient, why is it (told) rewarding to use a quality high-power solid-state rather than a quality 50watts?

What is this thing with the speaker's impendance dips in its lower frequencies? any measurments taken by somebody?

In practice, no one gets even near the clipping area of a 50watts amplifier, so why a 150watts amplifier of the same brand (with the same pre) sounds better in moderate volume levels?

Thanks!

In a two quick words.....It's hogwash.

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I didn't mean in reference to whether you heard a difference. I wouldn't question that. I meant in reference to really needing the mega watt amps for RF-7's. I've heard them with quality 50 to 60 watt amps and no way in heck do they require more power. I bet in the end the higher powered amp is just simply a better amp and your not really using more the the 50 watter could provide if all other things in the both amps were equal.

Craig

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Hi All.

I'm trying to understand the long-discussed issue of RF-7 and amplification concerns. I understand perfectly the theory behind efficiency and 2.83volts/meter but practically I bump into intriguing results.

Since the RF-7 are so efficient, why is it (told) rewarding to use a quality high-power solid-state rather than a quality 50watts?

What is this thing with the speaker's impendance dips in its lower frequencies? any measurments taken by somebody?

In practice, no one gets even near the clipping area of a 50watts amplifier, so why a 150watts amplifier of the same brand (with the same pre) sounds better in moderate volume levels?

Thanks!

In a two quick words.....It's hogwash.

Definitely take Craig's word on this. He's certainly an expert, as

I suspect he's washed more than his share of hogs living up there in

Burton. [:D]

Seriously, the first time I heard my RF-7's on any

amp south of 100 WPC, they were being driven by a pair of Craig's

VRD's, and they sounded SUPERB!

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Hi All.

I'm trying to understand the long-discussed issue of RF-7 and amplification concerns. I understand perfectly the theory behind efficiency and 2.83volts/meter but practically I bump into intriguing results.

Since the RF-7 are so efficient, why is it (told) rewarding to use a quality high-power solid-state rather than a quality 50watts?

What is this thing with the speaker's impendance dips in its lower frequencies? any measurments taken by somebody?

In practice, no one gets even near the clipping area of a 50watts amplifier, so why a 150watts amplifier of the same brand (with the same pre) sounds better in moderate volume levels?

Thanks!

In a two quick words.....It's hogwash.

Definitely take Craig's word on this. He's certainly an expert, as

I suspect he's washed more than his share of hogs living up there in

Burton. [:D]

Seriously, the first time I heard my RF-7's on any

amp south of 100 WPC, they were being driven by a pair of Craig's

VRD's, and they sounded SUPERB!

I was there.

Actually it was at my house. It was the best I ever heard RF-7s and I believe they were with the stock crossover networks.

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Impedience dip. The RF7 and RF-83 have a 2.8 ohm dip at 170 hertz I believe so the problem is most recievers are good to around 6 ohms but when you are playing it relatively loud the reciever is in more demand for wattage that weaker ones cannot supply long term. Put it this way, if you had to haul say a boat and you had an engine that is just adequate for the job and one that has much more power, you would put alot more strain (higher rpm etc) on the just adequate engine while the more powerful engine might barely hiccup.

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I've seen a graph, dont know its source, at http://www.overton.ru/pressa_st.php?id_st=26 It's in russian, but can easily be (automatically)translated into English using AltaVista's babelfish.

The graph actually gives a dip of 3.8ohm at 107hz and another similar one at 10Khz.

Are there any known reliable measurments? It's not crucial at all, but once and for all it ought to be put into perspective, now that the RF-7 is sold out ;) maybe the justice will be given to its successor.

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Hi All.

I'm trying to understand the long-discussed issue of RF-7 and amplification concerns. I understand perfectly the theory behind efficiency and 2.83volts/meter but practically I bump into intriguing results.

Since the RF-7 are so efficient, why is it (told) rewarding to use a quality high-power solid-state rather than a quality 50watts?

What is this thing with the speaker's impendance dips in its lower frequencies? any measurments taken by somebody?

In practice, no one gets even near the clipping area of a 50watts amplifier, so why a 150watts amplifier of the same brand (with the same pre) sounds better in moderate volume levels?

Thanks!

In a two quick words.....It's hogwash.

Definitely take Craig's word on this. He's certainly an expert, as

I suspect he's washed more than his share of hogs living up there in

Burton. [:D]

Seriously, the first time I heard my RF-7's on any

amp south of 100 WPC, they were being driven by a pair of Craig's

VRD's, and they sounded SUPERB!

I was there.

Actually it was at my house. It was the best I ever heard RF-7s and I believe they were with the stock crossover networks.

I think I can simplify this and give a good answer to the question: Here's the deal....I'm your ordinary guy shopping for new speakers. I already have a nice receiver with a "kick ***" HT system (as compared to HT out of a box....like I actually HAVE a receiver). So, I'm all over the 'net and in the "big box" stores looking for a deal.....venture out to a "boutique" and hear some reference models.....OK..this is good, this is good....

So now I'm home....bragging to friends that I've got these "boutique" speakers (RF-7) set up....and WOW...listen to this. Sad thing is.....they aren't as good as I thought....maybe should have stuck to the CircuitCity/Best-Buy deals for the money.....I know my set-up is clean, healthy, and POWERful, ie, I have the Yamaha/Onkyo/Denon.....latest 27x,38x,8x something receiver.....and I read that Klipsch is so efficient=I don't know what's wrong...I just know it LOOKs cool but.....

I'm a college guy....no head-banger is going to have a better system than mine!!....so I start researching.....(actually, this is some what auto-biographical) ......start scratching beneath the surface and learn a little about amplification. Now, look guys....don't even suggest tubes to me...its alien. But I DO find out about getting "quality" amperage....who-the-hell knows what that means.....went back to the same store and for about only $800 turned my (now expensive) sound system into a monster!! Happened to be 200watts of Rotel.....could have been anything else probably, as long as it made up for the output sag from the receiver.

Bottom line, the fall-out reported on all the web sites leans heavily toward SS because that's what we all grew up with, we can buy it down the street, plug it in, and use it. You can search for the "quality amps" high and low....I don't doubt much that I've read in this forum...the best is usually the best. But for the average guy...who's not going to get "Dean-mods"...or learn about tubes....this IS the solution. And its NOT a bad solution. In fact it's a fantastic solution that so many RF-7 owners finally "get-it" and find some Watts......and finally get to enjoy a really good speaker.

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UFO, thanks for the illustration, but your assumption that tubes are better than solid-state, doesn't apply for everyone, regardless of what setup they've got. It's truly a matter of taste, sonic-education, etc.

I can understand the refinement you're capable of achieving by replacing tubes, etc. But my question was explicitly referred to solid-state setups. Note that solid-state equipment can get pricey as tubes. The example I gave with budget NAD & Rotel were just for experimental purposes, and do not bias the discussion towards mid-fi equipment at all.

Personally, I accept your thesis that if I dont really care that much then $800 rack equipment will do, I think it's consensus.

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UFO, thanks for the illustration, but your assumption that tubes are better than solid-state, doesn't apply for everyone, regardless of what setup they've got. It's truly a matter of taste, sonic-education, etc.

I can understand the refinement you're capable of achieving by replacing tubes, etc. But my question was explicitly referred to solid-state setups. Note that solid-state equipment can get pricey as tubes. The example I gave with budget NAD & Rotel were just for experimental purposes, and do not bias the discussion towards mid-fi equipment at all.

Personally, I accept your thesis that if I dont really care that much then $800 rack equipment will do, I think it's consensus.

Agreed with one exception..."if you don't really care that much then $800 rack equipment will do"....In fact, for most (including me) we do care and milk all the quality we can get...but let's face it...you have budget ceilings...other interests...etc. And finally, there's the WALL: what are you actually using it for? I'm still refining my ability to HEAR the difference in two versions of a Vivaldi concerto.....or the difference in a Bosendorfer vs a Steinway......and the quality of "rack equipment" is not factoring too much into this equation at the moment when applied to the source material, lest we forget why we buy this stuff anyway. But I really appreciate your question because I struggled with it and attempted to give credence to use of "mid-fi" solid-state. As always, I really enjoy the responses.

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My RF 7 amplfication saga. Went from a Rotel 990 [200w/channel] to a NAD C272 150w/channel. Went Back and forth between these 2 for months and finally sold the Nad since I thought the 990 sounded a bit better in the base. Then about 3 weeks ago I auditioned an Ayre SS amp. When I went to borrow it I thought it was going to be the 200w/channel version. Turned out it was the evolution Ayre [integrated] 60 watts. I had just driven an hour to get it and would have it for a week so I took it anyway. It drove the RF 7's beautifully without my $ 5000 tube SP11 pre amp in the system. Since I intended to keep the SP 11 and did not want to spend $2000 for the Ayre that ended the Ayre for me, but that is a very musical amp. Latest chapter.---- The Ayre dealer also is a Rotel dealer. He rated the current class D Rotel as the best amp they ever made and the RB 1090 as a close second. I bought a used1090 the next week 380w/channel and like it as the best.sounding. This is because of the build quality and components in the 84 lb 1090 not the extra watts so I 'THINK'. I am now selling the 990 which was just factory refurbished a few weeks ago.

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I've seen a graph, dont know its source, at http://www.overton.ru/pressa_st.php?id_st=26 It's in russian, but can easily be (automatically)translated into English using AltaVista's babelfish.

The graph actually gives a dip of 3.8ohm at 107hz and another similar one at 10Khz.

Are there any known reliable measurments? It's not crucial at all, but once and for all it ought to be put into perspective, now that the RF-7 is sold out ;) maybe the justice will be given to its successor.

OK, now who told the Russians about the RF7's impedience dip? What ever happened to national security.

Jay - If I find it was you, I will have you banned from this web site and deported.

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tigerbalm,

I have been very happy with a set of RF-7 pretty much since they were introduced. I find, as I have with any speaker/amp combination, all you need in power is enough to handle your peak demands, plus a 25% to 33% margin for loss of linearity as clipping approaches.

Figuring out the "peak demand" may be a bit tough. Fortunately for me, I had a digital oscilloscope and found with +/- 4V peak swings into my Forte-IIs I was driven out of the room. "Efficiency" of the RF-7 is a bit higher so I still consider +/- 4V to be all I generally use. If that +/- 4V happened to occur playing exactly the famous 2.8 Ohm frequency then the amp would require 1.43 amp and 5.72 Watts when playing that note. Add some margin for loss of linearity as clipping approaches and you're still under 10 Watts. In reality I use a 4 Ohm output on a 3.5 Watt tube amp most of the time, but I don't listen at levels used by some on this forum.

I suspect these are the kinds of numbers you are curious about. They do work.

Usual problems with amps and speakers (the RF-7s included) is high output impedance with tube amps, responding to the speaker impedance swings (I find the peak in the mid horn of the Chorus-II to be much more objectionable than the dip in the RF-7), and low power distortion with ss amps. There are tube amps with sufficiently low output impedance and ss amps with sufficiently low low-level distortion, but one has to select with some care. The amount of power you need is a function of how loud the sound is and making sure the worst case current/Voltage requirements are met.

Leo

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I didn't mean in reference to whether you heard a difference. I wouldn't question that. I meant in reference to really needing the mega watt amps for RF-7's. I've heard them with quality 50 to 60 watt amps and no way in heck do they require more power. I bet in the end the higher powered amp is just simply a better amp and your not really using more the the 50 watter could provide if all other things in the both amps were equal.

Craig

Excellent point, but it brings up another question. It's safe to say that it's the quality of the amp rather than power rating that makes the difference, but what specific quality makes one amp able to handle the impedance dip on an RF-7 better than another amp.

I guess it's easier with SS amps to go large, because then you get bigger power supplies, etc. and hopefully better components if you buy a good brand. That is a shotgun approach to the problem, as it may not be the power that fixes it, but another quality of the amp. We do know that the larger power SS amps tend to sound better with an RF-7, and that a high quality 50 watt amp can also sound great. What's the common denominator?

I'm going to be buying a new amp for my RF-7s in the near future, so I'm very interested to see what info we can come up with in the thread. [:)]

(as of now, my plan is for an Outlaw 7500 amp - 200W x 5 ch.)

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