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MeloManiac

John DeVore goes on a rant about the High End Audio lie that inspired him to start his company

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This video is about the lie concerning sensitivity and efficiency of speakers. Although I'm technically challenged, I understood enough of it to cherish even more my 1972 Heresy speakers (8 ohm) and my 12 Watt Leben CS300. 

This is the first time I watched a John DeVore video and I think he is a great guy, and he surely chooses the same side as the Klipsch speaker design!

 

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 I've been subscribed to his You Tube channel for a while. He has some interesting perspective and rants. I enjoy listening to the opinion of many to help form my own.

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Fun anecdote/story. 

 

When I lived in Brooklyn/Prospect Heights I would see John from time to time out and about. He has a sweet Cadillac CTS-V wagon that he parked on the street in the neighborhood. I was tempted to leave a note on his car to see if I could get an invite to his factory in the Navy Yard. 

 

I found myself with Forte III's -- inspired by the Devore O93/96 design approach. I was wanting to find a nice speaker to pair with my McIntosh MC240/MX110. But I was not prepared to spend $8400+ on speakers (yet) -- hence my foray in to Klispch (I could not be happier). 

 

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Yeah.  Cool.  He has a point, but maybe overstated. 

 

I'm unsure of the effect all that has on tube amps, but its a lesser problem with solid state.  A SS amp *simulates* a voltage source at most power levels.  That is, it boosts input voltage by x and supplies whatever current the speaker *draws* at the voltage applied to it.  It is a valid speaker design technique to use a lower impedance driver to make up for a little lower sensitivity.  Early Cornwalls are an example; the 4 ohm woofer *draws* extra power so it can keep up with the squawker and tweeter.   A practical speaker design has limits on this trick and I'd say Heresy 1s push that limit with about 128 ohms in the midrange.  In its case the higher impedance in the midrange *draws* (impedes current flow) less current (and power) so the 107 dB squawker is not too loud. 

 

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Who the heck is John devore?

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I saw the video. There a couple of misconceptions in his rant. First of all, it was the audio engineering society that change the spec and it was for some very valid reasons. First. Amps are constant voltage devices. Second drivers for most all cases do not have a constant impedance. In the real world when you switch speakers ons switcher, the speaker with the highest sensitivity spec will always sound louder. I was glad with the AES made this change. It is a real world spec for the real world. 
 

he does have some good points. Amplifiers have to be robust and be able to handle freq dependent impedances from as high as 50 ohms down to 4 ohms. 
 

sensitivity does not equal efficiency. 

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7 hours ago, Chief bonehead said:

sensitivity does not equal efficiency

 

I've read this before, here on the forum and elsewhere, so - being technically challenged - I thought the time had come to do some more research about this to finally get a grip on this. I found this place, where it is explained in a pretty good way, with an nice table to conclude: https://www.quora.com/Are-sensitivity-and-efficiency-in-speakers-the-same-thing#:~:text=Sensitivity is the sound pressure,power applied to the speaker.

Sensitivity is the output sound pressure level that is measured at 1m when 1 Watt of power is being consumed. It is expressed in dB.

Efficiency is the ratio of acoustical output power to electrical input power, measured in watts, expressed as a percentage. The acoustical measurement is taken at 1m from the loudspeaker.

main-qimg-9823a98c72ee90d961df0588d375bfca

This table helps me better understand things now. 

For instance, why my Klipsch RP160M (95dB) speakers are easily driven by my 12 W Leben amp, while that same amp struggles with the KEF LS50 Meta (83dB). The klipsch are 10x more efficient.

Now I also understand how it is possible to drive monster size speakers like the Klipschorns  and La Scalas with a measly 3 watt amplifier: these speakers have a 105dB sensitivity, so a lot of the 3 watt you put in, comes out as accoustic energy.

 

I guess most speakers companies will use the first column to 'brag' about their speaker. "Hey, this is our $20,000 speaker set with 83dB sensitivity" sounds much better than "Hey, this is our $20,000 speaker set with 0.125% efficiency."🤣

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11 hours ago, Chief bonehead said:

First of all, it was the audio engineering society that change the spec and it was for some very valid reasons. First. Amps are constant voltage devices.

Most amplifiers are voltage feedback devices.  Transconductance amplifiers (such as the First Watt F1, F1J, F2, and F2J, etc.) are effectively current feedback devices--like the modified Howland "current pump" circuit (which any amplifier can be turned into using external networks).  There is an interesting book on this subject:

 

51vzOuc6A1L._SX331_BO1,204,203,200_.jpg

 

The reason why I mention this is not to disagree, but to point out that acoustic drivers of the types used by Klipsch are all current-driven devices.  The problem, of course, is by using only voltage feedback amplifiers, you also introduce the effects of load back-EMF, which sounds like distortion. I have been exploring the use of these type of amplifiers for driving large compression drivers in order to clean up the output to free it from the effects of back-EMP feedback.  There are downsides to using these type of amplifiers for bass frequencies, but the subjective fidelity gained on HF drivers/horns is documented...by Nelson Pass.

 

Chris

 

 

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  I sometimes use Hovland current pump amplifiers to drive my LS II’s. Cannot say that topology is better the voltage output.

  These are Mauro Panasa’s My_Ref variants. The Full Evo drove B&W 801 Matrix II very easily to high output levels. 

  From reading reviews, the measured efficiency of DeVore speakers is lower than the factory specs.  But seem to be popular with owners of low powered tube amps. 

  

  

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Not trying to start a fight here, but hoping to learn: why do some speaker designers (and consumers) choose for low-sensitive speakers and high powered amplifiers? Is it just to be able to show off with big numbers, is it to push the consumer into spending more on heavy equipment, or  is there actually an advantage on the level of accoustic quality and sound quality for low sensitive speakers?

Why, for instance, did KEF design the highly successful LS50 (Meta) speaker, which is 85dB and requires a hefty, powerful amplifier?

 

Edit:

"In general the main reason to design a less efficient speaker is to enable more extended bass out of a smaller speaker. This has been the popular trend for the most part ever since higher power SS amps started to make their mark." (https://forum.audiogon.com/discussions/is-there-any-advantage-to-lower-efficiency-speakers-87-or-below)

 

If someone could elaborate on this, I would appreciate it.

 

 

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9 minutes ago, MeloManiac said:

why do some speaker designers (and consumers) choose for low-sensitive speakers and high powered amplifiers?

You can answer that yourself:  most people want loudspeakers that defy physics...and are just too small to handle the frequencies that they're trying to reproduce.  So they go smaller and the price they pay is higher required power, much lower dynamic range, and greatly increased modulation distortion (among other issues). 

 

11 minutes ago, MeloManiac said:

is there actually an advantage on the level of acoustic quality and sound quality for low sensitive speakers?

No.  Just the opposite.  I've called it "Klipsch's law" but it goes something like this:

Quote

The more efficient the loudspeaker, the lower the distortion, all other factors being equal.

 

12 minutes ago, MeloManiac said:

Why, for instance, did KEF design the highly successful LS50 (Meta) speaker, which is 85dB and require a hefty, powerful amplifier?

Because the affinity for too-small loudspeakers by consumers knows no bound...

 

Chris

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22 minutes ago, Sadie42 said:

I tried the LS50 Meta. In spite of their stellar measurements, they didn’t do it for me. The math said one thing but my ears said something different. I didn’t think they sounded as good as the ATC SCM12 Pro or the Klipsch RP-600M. 

 

Yes, but they do look like a UFO from outer space!

😉

 

I understand you point of view. This morning I put time in switching my RP160Ms with my Heresy's. My wife and I had gotten used to the Heresy's in the living room, but I decided to switch anyhow. After some heavy labour by both of us, I finally hooked up the smaller RP160Ms. Within one second we were both shaking our heads and ...switched them back again.

The Heresy's + Leben CS300 are perfect for our larger living room, while the RP160Ms+H/K430 are a perfect match for our den upstears.

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1 hour ago, Sadie42 said:

 


I tried the LS50 Meta. In spite of their stellar measurements, they didn’t do it for me. The math said one thing but my ears said something different. I didn’t think they sounded as good as the ATC SCM12 Pro or the Klipsch RP-600M. 

The klipsch RP-600M  is nowhere near an  ATC SCM12 Pro  -

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14 minutes ago, Sadie42 said:

 the KEF LS-50 Meta.  

 the technology behind the KEF-LS-50

 

 

 

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27 minutes ago, Sadie42 said:

I once heard Klipschorns in a small room (with very good equipment), and it didn’t sound good at all.

That's a poor choice for comparison's sake.  Try Jubilees instead(time aligned).

 

Chris

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1 hour ago, Sadie42 said:

 

In a smallish room sitting 8 feet away, 85dB/2.83v loudspeakers can be driven to decent levels with 60wpc. 


I tried the LS50 Meta. In spite of their stellar measurements, they didn’t do it for me. The math said one thing but my ears said something different. I didn’t think they sounded as good as the ATC SCM12 Pro or the Klipsch RP-600M. 


System setup can make or break any loudspeaker..!!!!

 

It would very informative if you post a picture of the setup so we can see the conditions for comparison...?

 

miketn.

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Within their design limitations I found the KEF LS50 performance very impressive when implemented as a near field setup where they would disappear as a sound source with excellent life size imaging and very musically involving reproduction.

 

miketn

 

 

8414E39A-ECA0-48E6-A14D-9F755D120083.thumb.jpeg.8c62f194688d23c74a99a333113e9184.jpeg

 

 

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On 2/6/2021 at 1:01 PM, Sadie42 said:

There is an old audio saying, while not always true, especially now days, still works as a general rule: big room big speakers, small room small speakers.

This is because small loudspeakers don't work very well in large rooms...not really the other way around. 

 

Most people equate large loudspeakers with ones that have very distantly separated "ways" (drivers and horns are separated from each other by more than 1/4 wavelength at  crossover frequencies), i.e., something like this that takes the separation of drivers/horns to the extreme (and resulting sound quality reflects this, too):

 

maxresdefault.jpg

 

You'd have to back off to 15-25 feet or more before this soundstage image coalesces into a cohesive whole because of the separation of sources alone (and we haven't discussed time alignment here yet). 

 

In a small room, you're sitting so close to the loudspeaker that these separation distances cannot be resolved within a very short listening distance (such as a Khorn).  If instead, you put a time-aligned Jubilee (no passive crossovers here, only DSP to time align) or a well designed but very large MEH of the size of an SH-96 into a very small room:

 

TheHardpop SH-96s.jpg

 

(here for scale, SH-96 on the bottom--about the size of a K-402/KPT-305):

 

472912526_derekdanleycropped.thumb.jpg.0ee1f2a4e7778ebb4d0122d86225cda3.jpg

 

...then there isn't a problem at all, in fact, I'd predict that you'd have the best small-room listening experience that you've ever had.  There is no minimum listening distance with these--you can put your head inside the horn aperture and it still sounds cohesive. 

 

So the real issue is "how well are the large loudspeakers designed/implemented to keep the driver/apertures coincident or within 1/4 wavelength of each other at their crossover points?".  This is the issue--not the size of the loudspeaker itself.

 

Chris

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32 minutes ago, Sadie42 said:

Mike, I have no way to take a picture. I just use a PC. Nothing much to see really, it’s just a small Den packed with books, boxes, and a recliner. There is a window but with thick drapes. My stands are well off the back and side walls, and foam on the sidewalls for the first reflections. I am a minimalist at this point in my life. Don’t get me wrong, the LS50’s were fun, but overall the RP600M delivered a more satisfying experience, especially for movies. The LS50’s would choke out fairly fast with some of my more demanding material and better blu-rays. 
 

Thats’s a very impressive room. 

 

Thanks

 

I would definitely recommend a sub/subs paired with the LS50 if high spl and movie reproduction is desired. My daughter runs LS50 and Sub for movies and again I find it to be a very impressive system.

 

miketn

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2 hours ago, Sadie42 said:

I have an SVS SB2000. I don’t know. Maybe I wasn’t patient enough. 

 

The main thing is you found what works best for your unique situation and taste...👍🙂

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