Radiant Acoustics Clarity 66 Speaker Review

[Cogito]

The main selling point of Acoustic Clarity 66 is extremely low harmonic distortion - it beats Revel Performa F226Be, KEF R11 Meta, Sonus Faber Sonneto V G2 and MFi Sourcepoint 10.
I didn't find distortion measurements on other 3 loudspeakers, but I would bet they are worse than Acoustic Clarity 66 , especially in the low frequency region.

If the absolute lowest harmonic distortion levels are your primary criteria in choosing a speaker, then I'd expect the Clarity 66 speakers to be a reasonable choice. Then again, I've never seen a review of any of the speakers I listed where they complained about the harmonic distortion levels.

​

 

[Matt_Holland]

Then again, I've never seen a review of any of the speakers I listed where they complained about the harmonic distortion levels.

That’s because none of the reviewers had experienced Clarity 66.

 

[henz]

That’s because none of the reviewers had experienced Clarity 66.

Right!
The absence of distortion in the speaker part of the playback chain is a revelation in my (admittedly) humble opinion. After all, there’s a reason the brilliant @Lars Risbo has spent 10 years or so achieving it with Purifi’s drivers.

Most, if not all, speakers the size of our Clarity 66 have so much distortion that it’s really not worth touching upon in a normal review. It would be like mentioning that a car pollutes in every review of every car… That’s just how it is - and has always been. Well, until now.

I know it’s a tired trope but… it really has to be experienced.

 

[amirm]

Important note:

Klippel NFS requires manual tweaking of its parameters when the low frequency radiation sources are very far apart. Such is the case here with the port down low and rest of drivers way up. I noted this at the time of performing the robotic measurements. But then forgot when it came time to computing the results. My apologies for that. The review is updated with the new measurements, showing much extended low frequency response:

I have updated this and the rest of NFS measurements in the review.

 

[amirm]

@Maiky76, I have updated the results export. Please re-compute your results and update the post. Thanks!

 

[AudioJester]

If the absolute lowest harmonic distortion levels are your primary criteria in choosing a speaker, then I'd expect the Clarity 66 speakers to be a reasonable choice. Then again, I've never seen a review of any of the speakers I listed where they complained about the harmonic distortion levels.

​

Probably a primary criteria among other factors.
People usually turn the volume down because of unpleasant sounding peaks - due to distortion, and end up at modest listening levels.
Clarity at reasonable loud volume is addictive!

 

[henz]

Important note:

Klippel NFS requires manual tweaking of its parameters when the low frequency radiation sources are very far apart. Such is the case here with the port down low and rest of drivers way up. I noted this at the time of performing the robotic measurements. But then forgot when it came time to computing the results. My apologies for that. The review is updated with the new measurements, showing much extended low frequency response:

I have updated this and the rest of NFS measurements in the review.

Thanks for updating, Amir! Now we can see the port doing its job

 

[pma]

Klippel NFS requires manual tweaking of its parameters when the low frequency radiation sources are very far apart. Such is the case here with the port down low and rest of drivers way up. I noted this at the time of performing the robotic measurements. But then forgot when it came time to computing the results. My apologies for that. The review is updated with the new measurements, showing much extended low frequency response:

Great! Are the responses merged at 100Hz?

 

[Lars Risbo]

The NFS fits an spherical harmonic function expansion model of the measured pressure field. This is done per frequency point so not a merge across frequency but a sum of SH contributions

 

[Lars Risbo]

Thank you @amirm -really appreciated!
Now we have an excellent match with our published measurements and we see the flat extended bas response.

 

[Lars Risbo]

Great! Are the responses merged at 100Hz?

such tall slim floor stander has a fundamental standing wave in the 100-150Hz region and this is what we see here, although it’s heavily damped by the carefully optimised placement of the iCell damping material. it’s a challenge to apply damping at these low frequencies since porous materials lose their effect down here. i spent the first couple of month working on the damping layout and port placement to get to this point. Also, the damping material should not add distortion from its physical motion induced by the huge sound pressure (air speed) inside the box.

 

[Matt_Holland]

Right!
The absence of distortion in the speaker part of the playback chain is a revelation in my (admittedly) humble opinion. After all, there’s a reason the brilliant @Lars Risbo has spent 10 years or so achieving it with Purifi’s drivers.

Most, if not all, speakers the size of our Clarity 66 have so much distortion that it’s really not worth touching upon in a normal review. It would be like mentioning that a car pollutes in every review of every car… That’s just how it is - and has always been. Well, until now.

I know it’s a tired trope but… it really has to be experienced.

My main experience of a very low distortion full range speaker was the Meridian DSP8000SE. I worked for the manufacturer so had lots of time with all their products and the 8000 stood apart with its total lack of sense of dynamic limitation and a resolution at low frequencies that brought a sense of three dimensionality to the recorded space that other speakers didn’t.

 

[Lars Risbo]

such tall slim floor stander has a fundamental standing wave in the 100-150Hz region and this is what we see here, although it’s heavily damped by the carefully optimised placement of the iCell damping material. it’s a challenge to apply damping at these low frequencies since porous materials lose their effect down here. i spent the first couple of month working on the damping layout and port placement to get to this point. Also, the damping material should not add distortion from its physical motion induced by the huge sound pressure (air speed) inside the box.

and i forgot the most important: the damping material must not cause losses to the port efficiency at the tuning frequency (31Hz). that is a bit conflicting requirements when we also want to have max damping at 100Hz. That was a challenge to solve.

 

[Space is the place]

I think this speaker is a remarkable piece of engineering. When you you compare it to many high end well known brands these look like the money has been spent in the right places, nothing fancy or showy just a carefully constructed and engineered speaker.
Peter Lyngdorf is an interesting guy, in the early years of Lyngdorf/Tact they were quite keen on DIY and experimentation, open baffle and corner subs etc, all controlled by DSP, they were way ahead of the game. Lyngdorf has become different now of course, but these latest ventures including Purifi show he's a true enthusiast.

I like to ask Mr Risbo if he has a speaker or piece of hifi, or listening experience that set him on this path in life?

 

[capslock]

and i forgot the most important: the damping material must not cause losses to the port efficiency at the tuning frequency (31Hz). that is a bit conflicting requirements when we also want to have max damping at 100Hz. That was a challenge to solve.

What happens when you plug the port like in many current KEF products which are delivered with foam plugs and do a 80 or 100 Hz 2nd or 4th order low pass to add a sub. Would that approach be not advisable because of the damping mateiral?

Bonus question: do you have a distortion measurement of the 6.2 or 4.2 similar to the one on page 31 of the deep dive? I still think one of the smaller models might be a better fit for me, unless the the improvement in midrange distortion by the alu cone is substantial. Unfortunately, all I have at this point is Erin's measurement, and I don't think his microphone and preamp are good for measuring low low distortion (there is a discussion on diyaudio about his mic).

 

[amirm]

What happens when you plug the port like in many current KEF products which are delivered with foam plugs and do a 80 or 100 Hz 2nd or 4th order low pass to add a sub.

Given the size of this port, you almost need a football to shove in there to block the port.

 

[Lars Risbo]

LOL

The port narrows to around 75mm diameter in the middle (waist). One foromist was concerned about if his kat could be trapped inside the speaker.

foam in the port is aiming at damping the parasitic pipe modes that can be quite strong for a long port. This is again a compromise between not damping the port fundamental mode but hit the parasitic. It takes a surprising amount of lining of the port to be effective. Other tricks are to drill holes in the port.

On the 66 we utilise the tall box as a damped transmission line and place the port away from the woofers. this attenuates the higher frequencies very effectively and there is less energy feeding the pipe modes. The transmission line effect also means the port can be made shorter for the same tuning which helps move the pipe modes up in frequency where they get less energy. Finally, the extreme flaring we do is dispersing the pipe modes.

 

[Penelinfi]

Bonus question: do you have a distortion measurement of the 6.2 or 4.2 similar to the one on page 31 of the deep dive? I still think one of the smaller models might be a better fit for me, unless the the improvement in midrange distortion by the alu cone is substantial. Unfortunately, all I have at this point is Erin's measurement, and I don't think his microphone and preamp are good for measuring low low distortion (there is a discussion on diyaudio about his mic).

You could possibly compare Erin's measurements of both versions of the March Audio Sointuva. WG uses paper cone, AWG uses aluminium cone.

 

[jaakkopetteri]

foam in the port is aiming at damping the parasitic pipe modes that can be quite strong for a long port. This is again a compromise between not damping the port fundamental mode but hit the parasitic. It takes a surprising amount of lining of the port to be effective. Other tricks are to drill holes in the port.

I think the question was about blocking the port, not just damping it

 

[Lars Risbo]

ah yes thanks. then you dont have to worry about port losses or pipe modes. instead of plugging the port, i would use EQ in many cases. Except that a sealed speaker gives more output than ported at frequencies well below the port tuning - the only 2nd order roll off wins at low frequencies well.