KEF T301C Review (Ultra-thin Speaker)

[Vladimir Filevski]

that's not true. if you have 2 slices only, you cant recreate the whole 3d response from it

My bad explanation, I mean this:
Klippel system measures whole 3D space around the loudspeaker and reconstructs both horizontal and vertical frequency response graphs. Directivity Baloon from post #58 (and #1, of course) is the result of both reconstructed "horizontal and vertical" single frequency response graphs at any point in 3D space. As far as I know, the Klippel system can extract and present detailed frequency response (20 Hz - 20 kHz) at any point in the 3D space. But in the case of a center loudspeaker, it is not necessary - ordinary horizontal and vertical "on-axis" frequency response graphs are all you need. All center loudspeakers have good vertical dispersion, and given the small vertical height difference between tweeter and listener's ear (loudspeaker below the TV), the vertical listening angle is most certainly less than 15 degrees - and that frequency response is not much different than on-axis. So, for seating position of the listener anywhere in the room, knowing horizontal frequency response graph is all you need, eventually plus some small correction at the highest frequencies from the vertical response graph (there may be some additional differences around the crossover frequency).

 

[KMO]

On the contrary, "Selecta-mount" reduces the bass, making the prominent treble even worse:
https://us.kef.com/explore-kef/kef-innovation/selecta-mount

Why would it do that?

That page is more detailed than anything I've found for the T series - but it's talking about the KHT9000, which it says engages a filter when placed on wall mount.

The T101 and T301 work the other way around - they have a filter in their floor stand. I think it's safe to assume it performs the desired effect of lowering the treble. Not found anything specific, but the diagram from the T series blurb someone posted earlier indicates that they expect response is weaker below 1.5-2kHz when free-standing, so it should be reducing frequencies above that to match.

 

[Vladimir Filevski]

"Selecta-mount" is the same technique which KEF uses in both KHT9000 and T301 - it reduces bass. Loudspeaker with flat anechoic frequency response (T301C is "flat" between 180 Hz and 3 kHz) when mounted on-wall will exhibit SPL gain below 1 kHz - bigger in lower frequencies (up to 6 dB), so it needs to be reduced to be flat again. Besides gain at the bass, wall mounted loudspeaker will also exhibit one prominent dip below 500 Hz.

 

[KMO]

"Selecta-mount" is the same technique which KEF uses in both KHT9000 and T301 - it reduces bass. Loudspeaker with flat anechoic frequency response (T301C is "flat" between 180 Hz and 3 kHz) when mounted on-wall will exhibit SPL gain below 1 kHz - bigger in lower frequencies (up to 6 dB), so it needs to be reduced to be flat again.

"Selecta-mount" is a marketing name they used (briefly) for "engage a filter or not depending on mounting".

If you can understand that a "crossover" might be at different frequencies, or a "filter" can be "low-pass" or "high-pass", then maybe you can understand that a "Selecta-mount" might use different filter types and/or frequencies.

The basic KHT9000 is tuned to be freestanding, so its "Selecta-mount" uses a bass-reducing filter when on a wall.
The basic T301 is tuned to be wall-mounted, so its "Selecta-mount" uses a treble-reducing filter when on its custom stand.

 

[Vladimir Filevski]

Do you have any measurement to support your thesis?

 

[KMO]

Do you have any measurement to support your thesis?

No, just common sense.

All the blurb talks about and shows diagrams of how the speaker has less bass when freestanding, below 1.5kHz, and how they've put a filter in the floor stand to compensate for that.

My claim is that the filter will be reducing the treble, because that's what needs to be done, and they're not stupid.

Your claim is that the filter will be reducing the bass because they're using the same "Selecta-mount" name as a different speaker that engages a filter on a wall. And presumably you think they're stupid enough to put a bass-reducing filter into the stand.

Here's the limited details from their technology paper:

WALL-MOUNT BASS EXTENSION

The sound of a loudspeaker will vary depending on where it is positioned relative to the walls of a room. Generally, loudspeakers sound best when they are positioned in “free space”, for example, on a stand, more than 0.5m from any walls.

This is what produces a natural sound, in the same way that the sound of someone speaking or playing a musical instrument will be best when they are well away from the walls and corners of the room.

When a loudspeaker is positioned “on-wall” the sound changes in a relatively predictable way: the upper bass is enhanced and a dip appears in the midrange – this is what we instinctively recognize as the “wall effect”. However, if we know that a particular speaker will generally be positioned “on-wall” we can correct for these effects and ensure that the speaker will sound natural in that position.

Selecta-Mount

Because the T Series satellites are designed to match the new generation of super slim TVs and will generally be mounted “on-wall” using the supplied bracket or positioned very close to the wall on the desk stand, they have been specifically balanced for the “on-wall” location. However, for those occasions when they are used on the floor stand - when they will be a significant distance from the nearest wall – the KEF Selecta-mount system automatically adjusts the balance for an “off-wall” location. This is accomplished by a clever connection arrangement in the stands which introduces an extra filter section ahead of the speaker’s crossover network to switch the speaker into its “free-space” balance.

 

[PeteL]

No, just common sense.

All the blurb talks about and shows diagrams of how the speaker has less bass when freestanding, below 1.5kHz, and how they've put a filter in the floor stand to compensate for that.

My claim is that the filter will be reducing the treble, because that's what needs to be done, and they're not stupid.

Your claim is that the filter will be reducing the bass because they're using the same "Selecta-mount" name as a different speaker that engages a filter on a wall. And presumably you think they're stupid enough to put a bass-reducing filter into the stand.

How does wall or stand mounting affect the treble? yes maybe but it's minimal, the effect on frequency response is mainly in the bass. We can't assume any "common sense" solution that a stand mount filter would fix. If there was already too much bass there could be a fix but I don't know why you automatically assume they want to change the treble response. Filtering the treble won't give you better bass response.

 

[KMO]

How does wall or stand mounting affect the treble? yes maybe but it's minimal, yhe effect on frquency response is mainly in the bass. We can't assume any "common sense" solution that a stand mount filter would fix. If there was already too much bass there could be a fix but I don't know why you automatically assume they wan't to change the treble response.

By "treble" I meant "higher frequencies" generally (probably should have said "non-bass") - I don't know exactly what their filter profile is. I'm assuming it's restoring bass balance by lowering midrange and treble. (Cutting frequencies is all that a passive filter can do, and that's what they've put into the stand).

You can at least see some hint of the filter effect in the specs in the back of the manual - sensitivity is listed as 91dB wall-mounted, 88dB via the floor stand. Depending how that's worked out, that would be consistent with a 3dB-6dB shelf filter at some midrange frequency, similar to what Amir did via EQ.

 

[More Dynamics Please]

So it seems the best results for the KEF T Series when tested free standing rather than on wall would be achieved by measuring it in its purpose designed Selecta-mount. Measuring it free standing without its Selecta-mount would produce skewed measurements as would testing it on wall with its Selecta-mount. The review here states:

The kick stand is loose which doesn't give me confidence that it won't fall over although it did not during all of my testing.

 

[Vladimir Filevski]

No, just common sense.

All the blurb talks about and shows diagrams of how the speaker has less bass when freestanding, below 1.5kHz, and how they've put a filter in the floor stand to compensate for that.

My claim is that the filter will be reducing the treble, because that's what needs to be done, and they're not stupid.

Your claim is that the filter will be reducing the bass because they're using the same "Selecta-mount" name as a different speaker that engages a filter on a wall. And presumably you think they're stupid enough to put a bass-reducing filter into the stand.

Your common sense is wrong.
No, all the blurb talks about how the speaker has more bass when wall-mounted (read carefully the Selecta-mount page). That frequency response is like bass tone control (in amplifiers) turned up 6 dB at 100 Hz. Midrange frequencies are much less affected than bass (midrange dip due to out-of phase cancellation aside). Tweeter frequency response is unaffected with wall mounting. So the common sense tell us that we should equalize the bass response, not treble.

 

[PeteL]

By "treble" I meant "higher frequencies" generally (probably should have said "non-bass") - I don't know exactly what their filter profile is. I'm assuming it's restoring bass balance by lowering midrange and treble. (Cutting frequencies is all that a passive filter can do, and that's what they've put into the stand).

You can at least see some hint of the filter effect in the specs in the back of the manual - sensitivity is listed as 91dB wall-mounted, 88dB via the floor stand. Depending how that's worked out, that would be consistent with a 3dB-6dB shelf filter at some midrange frequency, similar to what Amir did via EQ.

Sure, but we don't know unless we see measurments because that rise as frequency goes up in the treble could have been fixed in the first place because it won't change, and the bass boost that will occur when you will place it on wall, will not automatically save this frequency response, and actually will not automatically be beneficial. We can see that we would like to tame the mids and treble, but we'd probably want to tame those on wall too. to know I'd like to see measurments, before that it's just speculation.

 

[KMO]

Sure, but we don't know unless we see measurments because that rise as frequency goes up in the treble could have been fixed in the first place because it won't change, and the bass boost that will occur when you will place it on wall, will not automatically save this frequency response, and actually will not automatically be beneficial. We can see that we would like to tame the mids and treble, but we'd probably want to tame those on wall too. to know I'd like to see measurments, before that it's just speculation.

Indeed. This test doesn't reveal on-wall response, and we don't have a good idea of rebalanced off-wall response. Apart from it's clear that it needs to be rebalanced - with either the stand or some other EQ. (A miniDSP solution would probably be cheaper than the stands, and could definitely be better!)

It would be interesting to see a spin and preference score with EQ. If whoever's been doing those could step in...?

 

[Vladimir Filevski]

The boost in wall-mounted speakers is mainly at bass frequencies, so T301C will have dip between 1 kHz (or lower) and 3 kHz when wall-mounted, although bass will be leveled with highs. All-in-all, a bad design.
True wall-mounting loudspeakers should have flat frequency response above some 800 Hz and shelf-like down-response below, when anechoic measured. To compensate for limited tweeter dispersion above 8-10 kHz, that region should be elevated on-axis in anechoic measurements.

 

[pseudoid]

Thank you @amirm for this review but I am having second thoughts as to why this unit was even considered to be tested.
One look at this T301c unit (before even instrumenting it) hints at the outcome.
IMHO; it appears that sum1 is trying to bend the laws-of-physics.
It also seems that you are being too kind to this manufacturer.
I'd volunteer to break the other arm of this PinkPanther, so you do not have to rate this cheezer as a headless PP.

 

[pseudoid]

Your common sense is wrong.

Please don't insult other ASR members with such low blows. I am not sticking up for anyone but I am selfish and it hurts my eyeballs when such things are posted. Thank you!

 

[Vladimir Filevski]

I apologize. In my defense, common sense occasionally is in conflict with the facts.

 

[Vladimir Filevski]

Thank you @amirm for this review but I am having second thoughts as to why this unit was even considered to be tested.
One look at this T301c unit (before even instrumenting it) hints at the outcome.

Don't judge a book by its cover. Jamo A505 has astonishingly flat frequency response (sans crossover dip) and is only 2" deep.

 

[abdo123]

so T301C will have dip between 1 kHz (or lower) and 3 kHz when wall-mounted

except that there is a gigantic peak between 1KHz and 3KHz in the sound power, why would that energy disappear once the speaker is wall mounted?

 

[Chromatischism]

On-wall installation won’t change much except that the on-axis response will become very similar to that of the sound power.

We don’t know whether that psychoacoustically changes things as no research has been done on that particular use case before.

Bass directivity, extension, output (mostly due to directivity) will change on-wall and make this a much more balanced speaker. Psychoacoustic testing has been done at Harman proving nearly everyone would like the speaker more with increased bass.

Treble can also change with a speaker near a wall due to the wall directing treble emanating from the cabinet at you. Treble directivity can also change on-wall if thin enough (wall becomes an extension of the baffle).

All of this makes the speaker sound quite different.

 

[abdo123]

Bass directivity, extension, output (mostly due to directivity) will change on-wall and make this a much more balanced speaker. Psychoacoustic testing has been done at Harman proving nearly everyone would like the speaker more with increased bass.

Treble can also change with a speaker near a wall due to the wall directing treble emanating from the cabinet at you. Treble directivity can also change on-wall if thin enough (wall becomes an extension of the baffle).

All of this makes the speaker sound quite different.

I super imposed these two graphs below and the sound power were nearly identical(+/- 1 dB) (makes sense since displacement and voltage is the same). The only thing that's changing is the on-axis response. Sure they will sound different obviously, but the comment I was replying to was basically saying that the measurements are pointless / irrelevant just because they're not done in 2pi and that's obviously not the case.