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KEF R3 Speaker Review

QMuse

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Im sorry to say there is a problem. Just consider the wavelengt of 10000 Hz . How much does a tweeter have to vibrate to play that frequency ?
But you are right that the problem is much lesser when crossing over at 400 Hz, than fullrange.

I don't have a problem with that there might be a problem with coaxial design, I don't even own such speakers. But I would like to see some proof for your claim. With your model it shouldn't really matter where XO point is. Let's assume it is at 1.8kHz and you are testing IMD with 400Hz (played by the mid) and 4000Hz (played by tweeter). Do you have any proof coaxial driver will have high IMD in that scenario?
 

tuga

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Genelec discusses coaxial drivers in a piece published by Resolution (attached):

Although conventional coaxial designs provide several key advantages, they also present drawbacks. The woofer cone movement causes intermodulation and Doppler distortion to the tweeter radiation. The larger the cone displacement the more intermodulation will be produced. The directivity, although improved at crossover, may not be uniform at higher frequencies. Also, most current common tweeter-midrange driver constructions have inherent acoustic discontinuities, which show up as an uneven on-axis HF response. Whether these are judged to be important depends totally on the application and the degree of desired perfection. As history shows, the benefits have exceeded the drawbacks.

The common challenge in all coaxial designs is how to avoid the aforementioned acoustical discontinuities and their effects on the response. Diaphragms have to move, there have to be gaps, but sound is easily diffracted from such discontinuities and so on. The following picture shows the typical situation with a somewhat uneven response.
 

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Tangband

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Genelec discusses coaxial drivers in a piece published by Resolution (attached):

Although conventional coaxial designs provide several key advantages, they also present drawbacks. The woofer cone movement causes intermodulation and Doppler distortion to the tweeter radiation. The larger the cone displacement the more intermodulation will be produced. The directivity, although improved at crossover, may not be uniform at higher frequencies. Also, most current common tweeter-midrange driver constructions have inherent acoustic discontinuities, which show up as an uneven on-axis HF response. Whether these are judged to be important depends totally on the application and the degree of desired perfection. As history shows, the benefits have exceeded the drawbacks.

The common challenge in all coaxial designs is how to avoid the aforementioned acoustical discontinuities and their effects on the response. Diaphragms have to move, there have to be gaps, but sound is easily diffracted from such discontinuities and so on. The following picture shows the typical situation with a somewhat uneven response.
Very interesting :)
 

BYRTT

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No problem think its good enough points you have there @Tangband but also think as long its nothing that tech talk we in speculation land or gossip : ) also why is that point never a argue for dual point sources where one could imagine just because tweeter sits 10-15 centimeter away will not free it from a woofer range of acoustic storm, guess for each build case those numbers could be tested and documented and also there could be a few tricks in electrical domain to stiff motion on tweeter.
 

aarons915

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Im sorry to say there is still a minor problem. Just consider the wavelengt of 10000 Hz . How much does a tweeter have to vibrate to play that frequency ?
But you are right that the problem is much lesser when crossing over at 400 Hz, than fullrange.

It's not lesser, it's non-existent from what I've seen. The issue only happens in 2 way coaxials since they're playing deeper bass, 300Hz isn't moving a woofer cone much at all. I think the best test of this would be to play the 1st tone around 100Hz since this is around the highest excursion in most ported speakers, then with that tone playing a frequency sweep can be played to test for any IMD distortion up to 20k. If anyone knows a program to do this let us know, I've only seen the typical multi-tone tests.

Either way, it is only a problem for some people who listen very loud and don't use a proper crossover, I use a 4th order high pass at 90Hz on the LS50 and they sound clean at my loudest levels, about 85db at my listening position.
 

infinitesymphony

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I think the best test of this would be to play the 1st tone around 100Hz since this is around the highest excursion in most ported speakers, then with that tone playing a frequency sweep can be played to test for any IMD distortion up to 20k. If anyone knows a program to do this let us know, I've only seen the typical multi-tone tests.
There are a number of ways to do this. You could use Audacity (free) to generate a chirp (sweep) from 100 Hz - 20 KHz and then generate a tone at 100 Hz. I just did that. Here's a WeTransfer link to the 4MB 24-bit WAV file:

https://we.tl/t-0upvdhm7Lf

Both the amplitude of the sweep and tone are at around 50% each. There's probably a happy medium where you could have the tone louder and the sweep quieter over time to simulate the downward EQ slope of most mixed music. Audacity can do that too -- there's a starting and ending amplitude.
 

aarons915

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There are a number of ways to do this. You could use Audacity (free) to generate a chirp (sweep) from 100 Hz - 20 KHz and then generate a tone at 100 Hz. I just did that. Here's a WeTransfer link to the 4MB 24-bit WAV file:

https://we.tl/t-0upvdhm7Lf

Both the amplitude of the sweep and tone are at around 50% each. There's probably a happy medium where you could have the tone louder and the sweep quieter over time to simulate the downward EQ slope of most mixed music. Audacity can do that too -- there's a starting and ending amplitude.

Awesome thank you. My next question is can I use that tone in REW and still have it display IMD distortion? I've been wanting to do this for awhile since the LS50 should be one of the worst offenders in IMD distortion, even though I haven't heard it myself. I was hoping to run the test full range and then see how various crossovers lower the distortion.
 

phoenixdogfan

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It is not the effect I am hearing or scoring on. But obviously that radiation pattern makes a difference with respect to what I hear in the room.
It is not the effect I am hearing or scoring on. But obviously that radiation pattern makes a difference with respect to what I hear in the room.
I would think a narrower directivity speaker like the Kef R3s would be better for smaller rooms and/or near/midfield listening than the Revels.

I too like a fatter bottomed speaker (owned Aerial 10ts for 15 yrs), but with a little judicious eq, or a sub, I think it would be possible to tease out a very pleasing bass response on them.
 

napilopez

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What you heard was the Kef midrange vibrating and modulating the tweeter. A problem with all loudspeaker drivers with the tweeter in center of the midrange. The midrange membrane is acting like a waveguide to the tweeter. As the membrane is vibrating , the waveguide for the tweeter constantly changes, changing the frequency response of the tweeter when playing music. The measurements may look fine, though.

I've been wanting to do this for awhile since the LS50 should be one of the worst offenders in IMD distortion, even though I haven't heard it myself. I was hoping to run the test full range and then see how various crossovers lower the distortion.

Of course, logically, it makes sense that a woofer acting as a moving waveguide for the tweeter isn't ideal. But it not being ideal is a very different thing from it being a significantly audible problem. And I certainly don't see how it's a more audible problem than vertical lobing on regular speakers.

I very, very much doubt that the KEFs sounding uninvolving to a few users here has anything to do with IMD. I mean you could make an argument about SPL levels perhaps, but 'uninvolving' is certainly not an attribute I see people apply to KEF in general. They are subjective impressions that, as most things, likely boil down to directivity and frequency response.

If we're going by subjective impressions, then mine are generally the opposite - that KEFs are some of the more 'engaging' speakers I've heard, and certainly more engaging than non-coaxials designs in their price brackets.

Following the IMD theory, the LS50W should be even less 'involving' than the the LS50 because it reaches significantly lower in the bass and thus asks more from the little woofer, yet in my experience it's very much the opposite.
 

thewas

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As said, when coaxials are used in a 3-way configuration and crossed around 300-400 Hz the travel of the mid cone is not more than 1 millimetre at very high SPLs so IMD isn't not a real problem and not really worse compared to a classic loudspeaker where the radiation of the tweeter without waveguide is also affected by the movement of the woofer.

Comparative IMD measurements can be easily done with the REW RTA and newer versions have even a several multitone signals in their audio generator. I personally use multitone signal I have created according to the EIA-426B standard (which is decreasing in higher frequencies to be more similar to music spectrum) and similar to the one used at the Sound & Recording magazine monitor measurements by Prof. Goertz.
 

Sancus

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I know most coaxials are not as well-engineered as Genelecs, but the IMD that S&R measured for the 8351a indicates that it is at least entirely possible to design a 3-way such that IMD is completely irrelevant, unless you think 2% at 100hz is audible. Which seems unlikely, though I haven't seen much in the way of studies about what level of IMD *is* audible.

Genelec-8351A-Studiomonitor-Messungen7.jpg
 

tecnogadget

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I know most coaxials are not as well-engineered as Genelecs, but the IMD that S&R measured for the 8351a indicates that it is at least entirely possible to design a 3-way such that IMD is completely irrelevant, unless you think 2% at 100hz is audible. Which seems unlikely, though I haven't seen much in the way of studies about what level of IMD *is* audible.

Genelec-8351A-Studiomonitor-Messungen7.jpg

Great contribution Sancus!

Listening to music through speakers (ANY speaker) IS A COMPROMISE. We all agree on that one, right?
Given the above statement plus the provided measurements by Amirm and the generous knowledge shared by other members, I think its time to give it a break with the constant criticism (as mentioned by another member in another post) against KEF and Coaxials, let's call it a truce at least.

Speakers are a compromise and in such a realm, Coaxial-Concentric's are a proven formula for better integration between mid-woofer & tweeter crossover points, great Horizontal and Vertical dispersion patterns, point source quality, time-aligned drivers, etc.

In this particular review, I can't stress out Kef has gone through 12 iterations of UniQ drivers over the spread of several decades (the final number is larger since every generation had different product ranges)

Like in everything else, there are cheap and well-engineered Coaxial-Concentric drivers. Addressing the key players of this technology, you get well beyond a Century of combined experience and research: KEF, TANNOY, GRADIENT, GENELEC, DEVIALET, CABASSE, etc. This is a well-matured technology.

I encourage to address further criticism with measurements and proven data in order to expand our knowledge. When using unproven beliefs or vague theories it's kinda better to address it with a question on the subject instead of a statement on the subject.
 

maverickronin

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Listening to music through speakers (ANY speaker) IS A COMPROMISE. We all agree on that one, right?

No, "we" don't. Lots of music isn't made with live play in mind.

Well it depends what he means...

I certainly agree that there is lots of music not made with live play in mind. (Beside, introverts like me don't even enjoy live music...)

OTOH there is no speaker at any price that can keep up with the performance of a $100 DAC so in that sense any speaker is a compromise...
 

q3cpma

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Well it depends what he means...

I certainly agree that there is lots of music not made with live play in mind. (Beside, introverts like me don't even enjoy live music...)

OTOH there is no speaker at any price that can keep up with the performance of a $100 DAC so in that sense any speaker is a compromise...
Well, I'd say Genelec's 8351B or MEG's RL901K with well integrated subwoofers and extensive room treatment might be close to perfection.

But the real problem is that there's no circle of confusion for DACs. Technically, it's not impossible at all to hear exactly what was heard in the mixing/mastering studio.
 

maverickronin

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Well, I'd say Genelec's 8351B or MEG's RL901K with well integrated subwoofers and extensive room treatment might be close to perfection.

I'm not to familiar with the MEG's, but the Genelec coaxials do look amazing...for speakers...

If a DAC measured like the 8341A it would get a decapitated panther.

You don't even need to bring the circle of confusion into it. Physical transducers can't match the electronics in any aspect. You need to actually worry about what deviations are audible because they don't blow past all limits of human hearing. Even the Genelec coaxials have their limitations, most notably max SPL. You'll want something from the 12xx line for that instead, but it comes at the expense directivity.

There are certainly excellent loudspeakers but nothing that could be called perfect at any position along the circle of confusion.
 

QMuse

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If a DAC measured like the 8341A it would get a decapitated panther.

No offense M8 but you keep stating the obvious. The analogy between DACs and speakers simply cannot be made as they are very different in their construction and they do very different tasks.
 

napilopez

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I know most coaxials are not as well-engineered as Genelecs, but the IMD that S&R measured for the 8351a indicates that it is at least entirely possible to design a 3-way such that IMD is completely irrelevant, unless you think 2% at 100hz is audible. Which seems unlikely, though I haven't seen much in the way of studies about what level of IMD *is* audible.

Genelec-8351A-Studiomonitor-Messungen7.jpg

And more than just audibility, we cant seem to pinpoint how much distortion sounds bad in music. I mean, it probably doesn't sound too bad when listening to metal...
 
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q3cpma

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You don't even need to bring the circle of confusion into it. Physical transducers can't match the electronics in any aspect.
But you do, because the speakers your music was mixed on aren't different in that regard. So you can (emphasis on can) get the same sound quality as the studio, and hear what the musicians/sound engineers want you to hear.
 
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