BlieSMa T25A-6, T25B-6, T25D-6, T25S-6 - a comparison of dome materials

[headshake]

https://hificompass.com/en/reviews/bliesma-t25a-6-t25b-6-t25d-6-t25s-6

I thought this was a really neat writeup about some high-end tweeters. For me, the most interesting part was how silk performed.

T25A-6 = Aluminium + magnesium

T25B-6 = beryllium

T25D-6 = diamond

T25S-6 = silk

Thanks, hificompass!!!

 

[q3cpma]

What real conclusion can really be made, though? I'd say that soft domes are "obsolete" and beryllium is indeed as good as marketed. Aluminium seems good enough to my eyes (and ears).

 

[headshake]

What real conclusion can really be made, though? I'd say that soft domes are "obsolete" and beryllium is indeed as good as marketed. Aluminium seems good enough to my eyes (and ears).

"we are atoms that appreciate atoms" ...

I was just surprised to see how well diamond performed and how silk moves in and out of the performance of all of the materials.

Seeing this makes me think I need to hear a few domes before I make my 1st speaker (if i do at all).

The ringing of the aluminium was a another one that I did not expect to see so clearly.

 

[Dumdum]

"we are atoms that appreciate atoms" ...

I was just surprised to see how well diamond performed and how silk moves in and out of the performance of all of the materials.

Seeing this makes me think I need to hear a few domes before I make my 1st speaker (if i do at all).

The ringing of the aluminium was a another one that I did not expect to see so clearly.

If you read very closely... it is silk... but not the same as most tweeters, it is silk for the dome, treated to make it stiffer, and then a different silk for the surround bonded together...

I have just ordered a matched pair of beryllium for my car along with some Sb acoustics ceramic 15cm drivers for the dash bookshelf’s

 

[Katji]

silk for the dome, treated to make it stiffer

And that treating varies per design and manufacture, so there are variants of silk dome tweeters. ...And then how each variant performs may be affected by other parts of the tweeter/etc.

 

[andreasmaaan]

https://hificompass.com/en/reviews/bliesma-t25a-6-t25b-6-t25d-6-t25s-6

I thought this was a really neat writeup about some high-end tweeters. For me, the most interesting part was how silk performed.

T25A-6 = Aluminium + magnesium

T25B-6 = beryllium

T25D-6 = diamond

T25S-6 = silk

Thanks, hificompass!!!

All you're seeing in those step responses is the magnitude and Q of the break-up mode.

Since in all cases other than silk this is well above the range of frequencies we can hear, the comparison is misleading.

HifiCompass is great though, and I'm not saying they're wrong in general. But overlaying step responses of these tweeters with no other information about their performance is the wrong way to compare them.

 

[ZolaIII]

S

"we are atoms that appreciate atoms" ...

I was just surprised to see how well diamond performed and how silk moves in and out of the performance of all of the materials.

Seeing this makes me think I need to hear a few domes before I make my 1st speaker (if i do at all).

The ringing of the aluminium was a another one that I did not expect to see so clearly.

Silk is the smoothest from those but that are all actually traditional designed one's, planar -electrostatic-ribbon ones can go more up & be even smoother. Still a good old silk dome one is perfectly fine.

 

[Dumdum]

And that treating varies per design and manufacture, so there are variants of silk dome tweeters. ...And then how each variant performs may be affected by other parts of the tweeter/etc.

My point was more about the dome and surround being different materials... it may be more common than I think, but I’ve never heard of that practice previously

 

[headshake]

I did not have a silk dome on-hand, but I recently got to compare the Bleisma Be dome vs JBL Ti dome vs SBA Textreme dome.

The Be won for me, the textreme was darn close. I really could only hear a difference if I filtered the music to 2000hz and above.

All you're seeing in those step responses is the magnitude and Q of the break-up mode.

Thanks for pointing out what is audible. I was just counting peaks not knowing what could be heard.

 

[andreasmaaan]

I did not have a silk dome on-hand, but I recently got to compare the Bleisma Be dome vs JBL Ti dome vs SBA Textreme dome.

The Be won for me, the textreme was darn close. I really could only hear a difference if I filtered the music to 2000hz and above.

Thanks for pointing out what is audible. I was just counting peaks not knowing what could be heard.

No worries I would advise against drawing conclusions about what different dome materials sound like based on how different complete tweeters (that happen to use different diaphragm materials) sound.

The Bliesma Be domes are really exceptional tweeters, but so are their equivalent Alu/Mg domes (and also the Diamond dome in the case of the T25).

 

[ctrl]

Silk is the smoothest from those but that are all actually traditional designed one's, planar -electrostatic-ribbon ones can go more up & be even smoother. Still a good old silk dome one is perfectly fine.

One can also approach the evaluation somewhat differently.

The ideal would be a loudspeaker/chassis with constant directivity over the entire transmission range, which is not possible with a normal dome.

So the next best thing would be that the chassis behaves ideally for as long as possible during sound reproduction.
For this purpose, the real behavior of the tweeter is compared with that of an ideal tweeter of the same dimensions.

Here we compare the normalized (by hificompass) measurements of the silk dome and the Be dome with an ideal dome:

Update: Fixed T25B-6 diagram

 

[headshake]

@ctrl Can you do a t25d-6 vs ideal comparison? Thanks for making those!

I have 4ms gated polar of the t25b-6 measured 5cm from my test baffle. It is not flush ATM. This is what I got:

 

[ctrl]

Can you do a t25d-6 vs ideal comparison? Thanks for making those!

Would add to my statement in post#11:

So the next best thing would be that the chassis behaves ideally for as long as possible during sound reproduction.

... or behaves "better", i.e. more in the manner of CD.

But that's really just how I personally would rate the directivity of the tested drivers.

T25D-6 vs. ideal dome

 

[bigjacko]

@ctrl Do you know why the silk dome is the only one that does not behave like an ideal dome?

 

[valerianf]

Diamond is the winner but at a sky high price.
Aluminum is to avoid (parasitic resonance).
Then only Be and silk are reasonable choice.
For now I keep the silk choice: less siblance.
May be in the future Be is a winning choice, I need to make some listening tests after the pandemic.

 

[bigjacko]

Diamond is the winner but at a sky high price.
Aluminum is to avoid (parasitic resonance).
Then only Be and silk are reasonable choice.
For now I keep the silk choice: less siblance.
May be in the future Be is a winning choice, I need to make some listening tests after the pandemic.

How do you come up with diamond is the winner? I thought Be is the best material. Also what is parasitic resonance and why it only happen to aluminum?

 

[ctrl]

(This is not my specialty, so I apologize in advance for any inaccuracies)

Do you know why the silk dome is the only one that does not behave like an ideal dome?

This behavior is precisely the "specialty" of a silk dome. Due to the low stiffness of the dome material (compared to, for example, Be), "controlled" dome resonances (dome modes) occur in the human hearing range. Thus, below the human frequency limit, the silk dome does not show ideal piston-like stroke movement, which lead to a characteristic radiation pattern.

In this way, silk domes prevent severe breakup resonances as they often occur in materials with high stiffness. When using 1'' domes, however, these severe breakups occur above the human hearing range.
So the T25A-6 shows a very pronounced breakup resonance only at about 31kHz (which is pretty good, since with other 1'' Al-domes this often occurs already between 22-27kHz).

When dome modes (resonances) oscillate in phase, there is an increase in sound pressure in the direction of radiation:

In the opposite case, of dome modes oscillating in inverse phase, there are cancellations:

Source link

The different physical parameters (such as stiffness, material sound velocity, specific weight,...) lead to different radiation characteristics of the tweeters, which in turn explains the tonal differences.

 

[Mashcky]

Is there a consensus on the audibility of aluminum dome resonances and ringing? The AluMg dome breakup looks to be well beyond 20khz, though the peaks do appear visibly in the odd harmonics at lower frequencies (though still quite low overall). I'm considering both the AluMg and Beryllium in three-way project but can't decide if a little better measured Beryllium performance is worth it or even audible.

 

[andreasmaaan]

Is there a consensus on the audibility of aluminum dome resonances and ringing? The AluMg dome breakup looks to be well beyond 20khz, though the peaks do appear visibly in the odd harmonics at lower frequencies (though still quite low overall). I'm considering both the AluMg and Beryllium in three-way project but can't decide if a little better measured Beryllium performance is worth it or even audible.

Personally, depending on application, my pick of those two would be the Alu diaphragm. Because it has a varied thickness/mass, wide directivity is maintained out to a higher frequency than in the case of the Be dome.

Yes, there are some small bumps in the HD spectrum corresponding to the break-up peak, but as you say, these are well below the fundamental. I would expect them to be less audible, if at all, than the improved off-axis response of the Alu dome.

 

[valerianf]

The listening test of the Be version is very clear about sibilants:
"otherwise there may appear problems with a sharp transmission of sibilant sounds "
On that point, Be is better than aluminium but not as good as silk.