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post #91 of 637 Old 08-21-2013, 12:41 PM
 
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Originally Posted by arnyk 
From a consumer viewpoint, efficiency is defined by how loud the speaker can get while playing music and/or dialog before his amplifier generates audible distortion.

Are you not confusing efficiency for sensitivity?
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post #92 of 637 Old 08-21-2013, 01:05 PM
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Originally Posted by goneten View Post

Are you not confusing efficiency for sensitivity?

That was my thought...I thought having a jagged Frequency Response Curve that dipped considerably below 4 Ohms wasn't really an efficient speaker. Klipsch Marketing Calling it an "8 Ohm Compatible" speaker was how they got away with it that because the majority of the spectrum is conducted by the Horn tweeter. What has been reported is that the RF-7s sound okay at lower SPL levels on lower end AVRs but it's not till you raise the volume to a certain point that it starts to sound bad...
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Klipsch has been IMO playing games with speaker efficiency claims for a long time. I seem to recall a speaker of theirs that dipped down to 2 ohms. Sounds dire, but it may or may not be as dire as it looks.

From a consumer viewpoint, efficiency is defined by how loud the speaker can get while playing music and/or dialog before his amplifier generates audible distortion. The amplifier may not even be the major source of audible distortion in his system because speakers generate copious amounts of distortion. Amplifier clipping with music is not just one number, but potentially a family of numbers that varies with program material and amplifier. Remarkably little intelligence about this issue is revealed by steady pure sine wave bench tests involving resistive loads.

I read the article that Wayne linked to but don't have the math skills to know how my Home Theater fares in that regard but feels it may be relevant...That said, I remember reading that Klipsch comes up with their Sensitivity numbers by using a steady pure sine wave and that is how they come up with the RF-7 being 101 dB/ 1 meter.
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post #93 of 637 Old 08-21-2013, 01:40 PM
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Originally Posted by Zen Traveler View Post

I read the article that Wayne linked to but don't have the math skills to know how my Home Theater fares in that regard but feels it may be relevant...

Unfortunately, even if you have a full grasp of it, it's still hard to find specific info on specific products to help the consumer make specific decisions. I think if you had impedance/phase plots of the speakers, and maybe something like Aczel's power cube tests for the amps it would help...but come to think of it, even power cube testing is limited. I give up.
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post #94 of 637 Old 08-21-2013, 01:52 PM
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Quote:
Originally Posted by arnyk 
From a consumer viewpoint, efficiency is defined by how loud the speaker can get while playing music and/or dialog before his amplifier generates audible distortion.

Are you not confusing efficiency for sensitivity?

They are very closely related.

Strictly speaking efficiency is measured in percent. For real world speakers it runs from about 1 to 10 percent.

Sensitivity is really the same thing with different units (given as you know in dB/watts.)
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post #95 of 637 Old 08-21-2013, 02:19 PM
 
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Quote:
Originally Posted by arnyk 
Sensitivity is really the same thing with different units (given as you know in dB/watts.)

As I understand it, efficiency is power output, which includes all directions, for a specified power input. It has more to do with radiated acoustic power. Sensitivity is power output but only for on-axis, 1 meter, for a specified power input. If you have two speakers with equal sensitivities of 90dB/2.83V and one has a 4 ohm nominal impedance and the other has an 8 ohm nominal impedance, the latter speaker will have a higher efficiency, since the 2.83V will represent half the number of watts.

A speaker of lower sensitivity may have improved efficiency in the way it radiates sound. Horn-loaded speakers are pretty efficient and also tend to have a high sensitivity, so while a very high sensitivity could mean improved efficiency and probably does, it's not a given in my opinion.
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post #96 of 637 Old 08-21-2013, 06:49 PM
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Quote:
Originally Posted by arnyk 
Sensitivity is really the same thing with different units (given as you know in dB/watts.)

As I understand it, efficiency is power output, which includes all directions, for a specified power input. It has more to do with radiated acoustic power. Sensitivity is power output but only for on-axis, 1 meter, for a specified power input. If you have two speakers with equal sensitivities of 90dB/2.83V and one has a 4 ohm nominal impedance and the other has an 8 ohm nominal impedance, the latter speaker will have a higher efficiency, since the 2.83V will represent half the number of watts.

If you are talking about efficiency as the spec that is usually given as "so many dB per watt", then the convention is that the dB number is measured on axis in an anechoic chamber. That means that in the real world a dipole puts out twice the acoustic power as a monopole with the same efficiency. This difference generally does not show up in any spec. Thing is the spec that is usually given as "so many dB per watt" is generally called sensitivity.

I generally agree with this web page:

http://www.sengpielaudio.com/calculator-efficiency.htm

Note that they convert sensitivity to efficiency by mathematical means and without adding any other information about the speaker. So efficiency and sensitivity are not the same thing but they track each other very closely.
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A speaker of lower sensitivity may have improved efficiency in the way it radiates sound. Horn-loaded speakers are pretty efficient and also tend to have a high sensitivity, so while a very high sensitivity could mean improved efficiency and probably does, it's not a given in my opinion.

Very high sensitivity always means very high efficiency all other things being equal.

To expand on your example, building speakers with horns increases both their sensitivity and efficiency.

BTW horns or waveguides obtain higher efficiency through the intersection of a number of different technologies. The driver portion of horn loaded speakers can be far more efficient than the comparable element of a direct radiator. And additional measure of efficiency or sensitivity comes from the horn itself - it works like an acoustic transformer that matches the impedance of the driver to the air better than we see with direct radiators.
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post #97 of 637 Old 08-21-2013, 10:40 PM
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Originally Posted by arnyk View Post

If you are talking about efficiency as the spec that is usually given as "so many dB per watt", then the convention is that the dB number is measured on axis in an anechoic chamber. That means that in the real world a dipole puts out twice the acoustic power as a monopole with the same efficiency. This difference generally does not show up in any spec. Thing is the spec that is usually given as "so many dB per watt" is generally called sensitivity.

I generally agree with this web page:

http://www.sengpielaudio.com/calculator-efficiency.htm

Note that they convert sensitivity to efficiency by mathematical means and without adding any other information about the speaker. So efficiency and sensitivity are not the same thing but they track each other very closely.
Very high sensitivity always means very high efficiency all other things being equal.

To expand on your example, building speakers with horns increases both their sensitivity and efficiency.

BTW horns or waveguides obtain higher efficiency through the intersection of a number of different technologies. The driver portion of horn loaded speakers can be far more efficient than the comparable element of a direct radiator. And additional measure of efficiency or sensitivity comes from the horn itself - it works like an acoustic transformer that matches the impedance of the driver to the air better than we see with direct radiators.

I think it was Bob Lee of QSC who corrected me early in my time here to be sure not to call sensitivity (dB per watt, sorta) efficiency . . . . efficiency is how efficiently the speaker turns electricity into sound. Most get, as you said, well less than 10 percent of the power in the signal turned into sound, and the rest becomes heat. Sensitivity, which is indeed the other side of the same coin, is how much sound the speaker creates with a given input. And is, like most specs manufacturers quite, highly manipulable. When they own the information they can bend it any way they want. So some give you sensitivity at 1 KHz, which might be 3 ro 6 dB more than sensitivity at, say 40 Hz.

That's especially dandy in the musical instrument world, where telling me the speaker's sensitivity at 1000 Hz is nearly meaningless if the speaker is going into a cabinet that will sit under my bass amp . . .
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post #98 of 637 Old 08-22-2013, 06:36 AM
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Originally Posted by arnyk View Post

...To expand on your example, building speakers with horns increases both their sensitivity and efficiency.

BTW horns or waveguides obtain higher efficiency through the intersection of a number of different technologies. The driver portion of horn loaded speakers can be far more efficient than the comparable element of a direct radiator. And additional measure of efficiency or sensitivity comes from the horn itself - it works like an acoustic transformer that matches the impedance of the driver to the air better than we see with direct radiators.

What about in the case of the Klipsch RF-7 that has been referred to? They have a horn tweeter but is mated to dual 10" LF drivers... Bill Fitzmaurice in the speaker forum is always mentioning they can't be as Sensitive as the Klipsch specs show and going back to the article that Wayne linked to earlier which states they also may not be as efficient as those number indicate...For the record, the RF-7s also have a power handling rating of 250 watt RMS 1000 watt Peak...In the old days there was a formula using those numbers to get how much of an amp was needed, but if I remember correctly the discrepancy between that and the Sensitivity numbers is pretty drastic on the RF-7s.
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post #99 of 637 Old 08-22-2013, 07:47 AM
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Originally Posted by arnyk View Post

...To expand on your example, building speakers with horns increases both their sensitivity and efficiency.

BTW horns or waveguides obtain higher efficiency through the intersection of a number of different technologies. The driver portion of horn loaded speakers can be far more efficient than the comparable element of a direct radiator. And additional measure of efficiency or sensitivity comes from the horn itself - it works like an acoustic transformer that matches the impedance of the driver to the air better than we see with direct radiators.

What about in the case of the Klipsch RF-7 that has been referred to? They have a horn tweeter but is mated to dual 10" LF drivers... Bill Fitzmaurice in the speaker forum is always mentioning they can't be as Sensitive as the Klipsch specs show and going back to the article that Wayne linked to earlier which states they also may not be as efficient as those number indicate...For the record, the RF-7s also have a power handling rating of 250 watt RMS 1000 watt Peak...In the old days there was a formula using those numbers to get how much of an amp was needed, but if I remember correctly the discrepancy between that and the Sensitivity numbers is pretty drastic on the RF-7s.

Cone drivers can be built that are around 100 dB/W sensitivity, but only with some compromises. The usual compromise relates to bass extension versus the size of the enclosure.

The first compromise is shifting from an overhung voice coil to an underhung voice coil to boost efficiency.

http://en.wikipedia.org/wiki/Voice_coil#Overhung_.26_underhung_coils

"
Overhung coil
• Coil height is greater than the gap's height.
• This method keeps the number of windings within the magnetic field (or flux) constant over the coil's normal excursion range.
• Higher coil mass, sensitivity medium to high.‡
• Soft non-linearity as the coil exceeds limits.

Underhung coil
• Gap's height is greater than the coil's height.
• This method keeps the magnetic flux that the coil experiences, constant over the coil's normal excursion range.
• Low coil mass, sensitivity low to medium.‡
• Hard non-linearity as the coil exceeds limits.
"
The second compromise is shifting from a high mass cone to a low mass cone. This has a side effect of increasing the enclosure size for a given bass extension.

High efficiency and high Xmax mean a stronger, wider magnetic field in the magnet assembly, which means more metal, most of it being that expensive magnet stuff.

If you check into the world of live sound you can find systems in the 100 dB/W range that probably meet spec, but the boxes are large for their bass extension. For example the EV ZX-5 is a nice robust speaker in a 27 x 16 x 17.5 enclosure which is an easy 2 cubic feet. Its -3 dB point is about 60 Hz, which is very high if this were a speaker for home audio of this size. http://www.electrovoice.com/product.php?id=252
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post #100 of 637 Old 08-22-2013, 08:20 AM
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Originally Posted by arnyk View Post


High efficiency and high Xmax mean a stronger, wider magnetic field in the magnet assembly, which means more metal, most of it being that expensive magnet stuff.

I will need to study some of the things you said and thanks for posting...That said, it is interesting that the original Klipsch RF-7s are heavier than the newer RF-7IIs and that weight was attributed to a larger magnet in the former...I haven't heard the newer models but given they were made as Klipsch was looking for buyers in the company I always thought they may not be an "upgrade" to the previous model and the bottom line needed to look better on the spread sheet.
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post #101 of 637 Old 08-22-2013, 10:39 AM
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Originally Posted by Zen Traveler View Post

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Originally Posted by arnyk View Post


High efficiency and high Xmax mean a stronger, wider magnetic field in the magnet assembly, which means more metal, most of it being that expensive magnet stuff.

I will need to study some of the things you said and thanks for posting...That said, it is interesting that the original Klipsch RF-7s are heavier than the newer RF-7IIs and that weight was attributed to a larger magnet in the former...I haven't heard the newer models but given they were made as Klipsch was looking for buyers in the company I always thought they may not be an "upgrade" to the previous model and the bottom line needed to look better on the spread sheet.

The weight of a speaker is not proof of anything. The speaker magnet is only part of the weight of a speaker, and not all magnetic material has the same ratio of magnetic force to weight. Furthermore we have a long history of speaker manufacturers adding size and weight to speaker magnets for errr, marketing purposes.
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post #102 of 637 Old 08-22-2013, 07:04 PM
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Well, I am back to square one and feel that the link Wayne provided seems to address why a speaker that has such a high sensitivity rating as the RF-7 would need more current to drive than just relying on that spec alone...
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post #103 of 637 Old 08-23-2013, 05:26 AM
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Well, I am back to square one and feel that the link Wayne provided seems to address why a speaker that has such a high sensitivity rating as the RF-7 would need more current to drive than just relying on that spec alone...

Along the way someone mentioned Aczel's power cube, and it caught me by surprize. I thought that I had read everything he published, but I missed this critical item.

http://theaudiocritic.com/plog/index.php?op=Default&blogId=1&&page=3

Here is the Aczel powercube for an expensive amp, the Parasound Halo A 21 ($2,229)



(with the vertical scale equalized to match the other amps in my article)



and another one Bryston 875HT ($3,200):



Note that these amps aren't as different as the pictures may seem, as the second picture has a VASTLY different vertical scale that favors the Bryston. I did a rough job of stretching it in the third picture.!

Now, here's Aczel's Powercube for a cheap power amp, the Behringer A500 ($229):



An ideal power amp would have a Aczel Power cube like this: (bad art particularly perspective my fault)



Note that the Parasound amp has far higher actual power output than the other two.
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post #104 of 637 Old 08-24-2013, 05:04 AM
 
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Hey Arny, if I'm ever in the States, we should make contact. Would be nice to meet you. Plus you could show me your testing methodology for evaluating gear, how it's done etc. biggrin.gif
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post #105 of 637 Old 08-24-2013, 08:51 AM
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Hey Arny, if I'm ever in the States, we should make contact. Would be nice to meet you. Plus you could show me your testing methodology for evaluating gear, how it's done etc. biggrin.gif

I don't have any problem with Face-to-face meetings in public places. However, the USA is a big place. I still remember a guy I worked with from France. One of his first observations is that the trip from France to the US (JFK airport in New York) and the trip from JFK to San Diego via Dallas (airline hub) (where we met) were about the same sized trip.

NY city USA -> Los Angles via Dallas (American Airlines hub) 3272 miles

London UK -> NY city USA 3459 miles
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post #106 of 637 Old 08-26-2013, 02:40 AM
 
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Are these speakers difficult to drive?



I think they have a power handling of 500 watts. Also, they reach down to 25 Hz. Surely that would require a big amp with big current for the low frequencies?
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post #107 of 637 Old 08-26-2013, 04:44 AM
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Originally Posted by arnyk View Post

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Originally Posted by Heinrich S View Post

Are these speakers difficult to drive?



I think they have a power handling of 500 watts. Also, they reach down to 25 Hz. Surely that would require a big amp with big current for the low frequencies?

Why not do your own research? What does their impedance curve look like?
What is their efficiency? What is the intended use?
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post #108 of 637 Old 08-26-2013, 05:10 AM
 
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I can't really make out what the measurements are saying but :

http://www.stereophile.com/content/bw-802d-loudspeaker-measurements

I'm asking the question more out of curiosity than anything else. Many people on the net say these speakers are power hungry, so I just thought I would ask the experts. Most people use these speakers in a dedicated stereo system.

I figure that since they can reach down quite low, they would need a beefy amplifier.
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post #109 of 637 Old 08-26-2013, 08:34 AM
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I can't really make out what the measurements are saying but :

http://www.stereophile.com/content/bw-802d-loudspeaker-measurements

I'm asking the question more out of curiosity than anything else. Many people on the net say these speakers are power hungry, so I just thought I would ask the experts. Most people use these speakers in a dedicated stereo system.

I figure that since they can reach down quite low, they would need a beefy amplifier.

What do you mean by reach down quite low? Frequency response or impedance curve?

I don't find their frequency response to be particularly deep, especially compared to a good modern subwoofer costing a fraction of the price.

The dip in the impedance curve is pretty usual these days.

There's a lot of colorful prose by JA in the review you cite, but he bases way too much of what he believes on sighted evaluations and a 1970-80's view of audio.

When it comes to giving a picture of the load driving abilities of power amps, the best thing I've seen lately is Peter Aczel's Power Cube: http://theaudiocritic.com/plog/index.php?op=ViewArticle&articleId=22

Several amp reviews on that page show that good performance into reactive loads is actually pretty common these days because of advances in power transistor capabilities. You don't need a super-expensive or extra-beefy amp to get it.
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post #110 of 637 Old 08-26-2013, 11:09 AM
 
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So I guess AVRs are out of the picture with these speakers then?
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post #111 of 637 Old 08-26-2013, 11:23 AM
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So I guess AVRs are out of the picture with these speakers then?
Based on what? Are you even reading anything that's being written here, or are you just trolling?

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post #112 of 637 Old 08-26-2013, 11:30 AM
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Are these speakers difficult to drive?



I think they have a power handling of 500 watts. Also, they reach down to 25 Hz. Surely that would require a big amp with big current for the low frequencies?

B&W 802? I had a pair of the earlier 802 matrix speakers. I drove them with a 50 watt per channel amplifier. It was way more than enough for my application. I didn't find anything about them that was difficult to drive. Perhaps the newer ones incorporate some changes. I don't know.
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post #113 of 637 Old 08-26-2013, 11:47 AM
 
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Are you even reading anything that's being written here, or are you just trolling?
Don't you remember who what that member is?
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post #114 of 637 Old 08-26-2013, 11:49 AM
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So I guess AVRs are out of the picture with these speakers then?

??????????

You get so many things wrong that I sometimes wonder why I answer your posts.
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post #115 of 637 Old 08-26-2013, 11:49 AM
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Don't you remember who what that member is?
Nope, and that link doesn't tell me anything.

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post #116 of 637 Old 08-26-2013, 02:15 PM
 
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Nope, and that link doesn't tell me anything.
http://www.avsforum.com/t/1425262/are-audio-companies-all-involved-in-a-huge-conspiracy/1710#post_23052240
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post #117 of 637 Old 08-26-2013, 02:16 PM
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Nor does that one. Stop wasting my time.

If you can't explain how it works, you can't say it doesn't.—The High-End Creed

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post #118 of 637 Old 08-26-2013, 02:18 PM
 
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Are you even reading anything that's being written here, or are you just trolling?
Given his posting record, it's most likely the latter.
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post #119 of 637 Old 09-06-2013, 06:17 AM
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I don't want or need "a shiny new amp" and think the AVR-4311ci drives my Home Theater nicely...I can't comment if it's overkill or not and reported what I and others were experiencing with lower end AVRs driving their system and postulated a theory on why it sounded extremely, unlistenably, bright at the higher SPL levels I was accustomed.

Fwiw, the actual dips in the RF-7s go down to 2.8 Ohms a couple of times and in my 9.2 Home theater have 5 other large speakers (and 2 smaller ones) that I assume have similar Response Curves, but may not dip as low. I primarily listen to Multichannel music and that is more demanding than movies...That said, do people with 4 Ohm speakers and less than 90 dB Sensitivity benefit from an AVR that is rated for 4 Ohm loads or does it really not matter? I don't mean this facetiously and am asking to get a better understanding...

I know some of you don't get out of this section but if you have an opinion it would be greatly appreciated if you could post it in this thread in the Speaker section which includes the charts for the newer RF-7IIs (which, btw show only dips down to 3.7 Ohms): http://www.avsforum.com/t/1412510/klipsch-rf7-ii-measurements I really am trying to come to sensible reasoning why a speaker with a 101 dB/1 meter Sensitivity rating would require/benefit from an external amp instead of a power supply capable of the impedance dips that are reported.
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post #120 of 637 Old 09-08-2013, 03:45 AM - Thread Starter
 
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Originally Posted by Zen Traveler 
I really am trying to come to sensible reasoning why a speaker with a 101 dB/1 meter Sensitivity rating would require/benefit from an external amp instead of a power supply capable of the impedance dips that are reported.

Just be careful not to use an underpowered amplifier. You have more chance to blow the amp and speakers with an underpowered amp driven into clipping than having too much clean undistorted power.
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