• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Tweeter front plate design

ctrl

Major Contributor
Forum Donor
Joined
Jan 24, 2020
Messages
1,640
Likes
6,288
Location
.de, DE, DEU
Have you ever wondered why the tweeter front plate design is somehow the same and yet different and if these small differences matter at all? Some tweeter front plate are just flat, some have something like tiny little wave-guides or "lenses" integrated,...
1688472384555.png
1688472396379.png
1688472408131.png
1691747056761.png


I would like to try, to show here with a few simple simulations, what certain changes of the tweeter front plate cause. For this purpose we simulate an ideal 1'' tweeter with about 700Hz resonant frequency fs.

1) Flat front plate
Let's start with the tweeter dome on an infinite baffle. So the tweeter front plate is simply a flat plate.
First the sketch (lateral cutaway drawing of the tweeter dome), then the frequency responses from 0° to 80° (in 10° steps) on infinite baffle (IB) of the dome on a flat front plate and then those normalized to on-axis frequency response:
1688472558754.png 1688472581012.png 1688472596820.png


2) Front plate with 3mm step
Next we introduce a 3mm high step (I use the term "step" because it looks like a step in the lateral cutaway drawing of the tweeter dome), one could also say the tweeter has 3mm off-set/recess to the front plate. It is a tiny wave-guide which on-axis contributes to an increase of the SPL of the high frequencies and at the same time makes the radiation less wide.
1688473329624.png 1688473354694.png 1688473388292.png


3) Front plate with 2mm + 1mm steps
Instead of just a big 3mm step, we round the corner a bit. The diameter of the tiny WG remains unchanged.
The radiation becomes minimally narrower, but more uniform above 15kHz.
1688473971184.png 1688474857709.png 1688474877763.png
Something like this is what most tweeters have.


4) Front plate with 2mm + 1mm + 2mm steps
Let's add another step, creating a small wave-guide with 40mm diameter. In the 2-9kHz the on-axis SPL has increased. The radiation becomes a bit narrower.
1688474000736.png 1688475078944.png 1688475128334.png


5) Front plate with 2mm + 1mm + 2mm + 3mm steps
The next step with a height of 3mm and a diameter of 70mm provides a wave-guide that most would recognize as such.
1688474037173.png 1688475146798.png 1688475172843.png

If we now compare the normalized frequency responses of the tweeter with flat front plate with our 70mm WG, for example, at 80° radiation angle the frequency responses at 4kHz are offset by 2.5dB SPL.
1688479135120.png
The less wide dispersion in the frequency range 2-4kHz usually makes the transition to the woofer more even. However, there are other effects such as edge diffraction that are not discussed here.

6) Front plate with 2mm + 1mm + 2mm + 3mm steps and reflector
If you now want to straighten the on-axis frequency response up to almost 20kHz, you can add a reflector at the expense of radiation - this would look like a washer when viewed from above.
1688474213272.png 1688475188814.png 1688475201946.png

If we now compare the frequency responses (deg0-80 in 10° steps) of the tweeter with flat front plate and the tweeter with the 70mm wave-guide with just 8mm height and reflector on IB, the differences are dramatic (same color, same angle):
1688480192312.png



To see the impact of each change in direct comparison, here is the FR as a series:

1) Flat front plate
2) Front plate with 3mm step
3) Front plate with 2mm + 1mm steps
4) Front plate with 2mm + 1mm + 2mm steps
5) Front plate with 2mm + 1mm + 2mm + 3mm steps
6) Front plate with 2mm + 1mm + 2mm + 3mm steps and reflector
1688472581012.png1688473354694.png1688474857709.png1688475078944.png1688475146798.png1688475188814.png

7) Front plate with "small lip" around the tweeter dome
See post#12 for more details.

8) Tweeter flush mounted but with gap around face plate?
See post#19 for more details.
 
Last edited:
OP
C

ctrl

Major Contributor
Forum Donor
Joined
Jan 24, 2020
Messages
1,640
Likes
6,288
Location
.de, DE, DEU
Hope it could be shed some light on why manufacturers use different front plate designs, even though the size of the tweeter dome is identical.
By the design of the front plate, the sound character of a tweeter can be influenced significantly - see below. Every little edge, every protruding screw has an impact.

Here are a few summary comparisons of the effects.

First, let's look at the effect on the on-axis frequency response:
1688491507439.png


Next, we compare the 60° frequency response when normalized to on-axis frequency response to see how the radiation changes (using the 60° FR as an example):
1688491568296.png



What happens if the tweeter is not flush mounted with the baffle?
The typical tweeter has a front plate diameter of 104mm and front plate thickness of 3-5mm.

Let's compare a simple tweeter with two small steps, one flush mounted and one not - plate thickness only 3mm:
1688492086995.png 1688492100761.png
1688492144075.png 1688492185698.png
Small difference, big impact, just like when you run your hand over the rotating flush mounted saw blade or whether it protrudes 3mm ;)
 
Last edited:
OP
C

ctrl

Major Contributor
Forum Donor
Joined
Jan 24, 2020
Messages
1,640
Likes
6,288
Location
.de, DE, DEU
Very nice. I can run a shape optimisation on a similar setup to find the best curvature for some given targets.
That sounds very exciting. So you would try to find a "short waveguide" for, say a 1'' tweeter, which corresponds to a given radiation pattern with shape optimization? What parameters would you need for this?
 

617

Major Contributor
Forum Donor
Joined
Mar 18, 2019
Messages
2,465
Likes
5,446
Location
Somerville, MA
This is amazing. The focal study is especially interesting.

Curious what a simulation of the wide dished SS revelator flange would look like.
 
OP
C

ctrl

Major Contributor
Forum Donor
Joined
Jan 24, 2020
Messages
1,640
Likes
6,288
Location
.de, DE, DEU
Curious what a simulation of the wide dished SS revelator flange would look like.

If you mean this SS tweeter, don't expect too much.
Have used the tweeter in the process of the Directiva r2 design simulations and the results were not satisfactory in terms of even radiation.

For a uniform radiation the tweeter should radiate narrowly in the range of the typical edge diffraction (to counteract the radiation widening by edge diffraction), which is partly fulfilled in the range 2-4kHz, but above that the radiation widens a bit and then becomes very narrow.
Manufacturer measurement:
1691705029895.png

Directiva r2 simulation with SS D2905/990000
1691706097425.png 1691706115879.png

Simulation result up to 10kHz first FR deg0-180, then normalized to on-axis FR and normalized contour plot:
1691706385312.png 1691706402549.png 1691706476944.png

The results are not very bad, but not SOTA either. Because it is a treated textile dome (very early damped breakup versus ideal tweeter in simulation), the real radiation might look a bit better though.
Anyway the radiation of the Seas DXT tweeter is more uniform, therefore it was also used in the r2.

Scan Speak should have hired @René - Acculution.com to shape optimize the heck out of it ;)
 
  • Like
Reactions: 617

mv8

New Member
Joined
May 15, 2022
Messages
3
Likes
3
Location
Poland
Have used the tweeter in the process of the Directiva r2 design simulations and the results were not satisfactory in terms of even radiation.
I own a Seas DXT as well as a Scan Speak d2905-990000 and in my opinion the DXT is a much worse tweeter than the SS. The DXT has a much higher level of distortion and a narrower usable frequency response. These speakers sound completely different. DXT with a proper front end in terms of diffraction performs very well in measurements, but its sound will still be worse than SS.

I did measurements of the SS in a wide baffle, with a large radius rounded edge, and they came out very well. The SS narrows the radiation in at around 10 kHz, but I don't consider this a big problem.

Personally, I would choose an SS in a non-optimal enclosure for diffraction than a DXT in an excellent enclosure for diffraction without a second thought.
 

Attachments

  • DSC_2682.JPG
    DSC_2682.JPG
    175.8 KB · Views: 94
  • ss wide.png
    ss wide.png
    143.8 KB · Views: 94

neRok

Senior Member
Joined
Oct 7, 2022
Messages
307
Likes
178
Location
Australia
What happens if the tweeter is not flush mounted with the baffle?
The typical tweeter has a front plate diameter of 104mm and front plate thickness of 3-5mm.

Let's compare a simple tweeter with two small steps, one flush mounted and one not - plate thickness only 3mm:
1688492086995.png 1688492100761.png
1688492144075.png 1688492185698.png
What happens if the tweeter is flush mounted, but the recess it sits in isn't perfect. Eg there is a 1mm gap all around? Or the recess has a chamfer? If the gap was a problem, would filling it in with silicone or something be a solution?
 

René - Acculution.com

Senior Member
Technical Expert
Joined
May 1, 2021
Messages
428
Likes
1,317
That sounds very exciting. So you would try to find a "short waveguide" for, say a 1'' tweeter, which corresponds to a given radiation pattern with shape optimization? What parameters would you need for this?
Really just some starting geometry. I would have to decide whether or not the depth the tweeter sits at compared to the baffle should vary also, but the targets are actually the most difficult part as they are easy to express in words but not so mathematically. I will keep this in mind, currently to most going on.
 
OP
C

ctrl

Major Contributor
Forum Donor
Joined
Jan 24, 2020
Messages
1,640
Likes
6,288
Location
.de, DE, DEU
Front plate with "small lip" around the tweeter dome

What about these kinds of "waveguides"?
Nerdy question ;)
Let's take a look at what the manufacturer had in mind when designing the tweeter with a front plate like a lip augmentation from a plastic surgeon.
1691739018086.png

Let's start with the third tweeter front plate design from the initial post for comparison. Again a 1'' dome tweeter with fs=700Hz.
The parameters for the simulation (resolution, distribution of the simulation points,...) I tried to choose identically to the initial post. But I didn't write them down, so small deviations can occur.

1) Front plate with 2mm + 1mm steps

First the sketch (lateral cutaway drawing of the tweeter dome with surround and front plate),
then the frequency responses from 0° to 90° (in 10° steps) on infinite baffle (IB)
and then those normalized to on-axis frequency response
The same applies to all other simulations:
1691736989674.png 1691740527788.png 1691740544663.png
As we already know, this small measure raises the on-axis FR significantly above 3kHz and leads to a flat response.

2) Front plate with 3mm + 1mm steps
In the next step we increase the first step by 1mm to 3mm.
1691737027559.png 1691742354862.png 1691742372873.png
This results in a slight on-axis hump between 4-10kHz and a slightly narrowed radiation above 5kHz.

3) Front plate with 3mm + 1mm - 1mm steps
Now we do our "lip surgeon" and form a small lip around the dome.
1691737046431.png 1691742626876.png 1691743114872.png
Wow, this again results in a flat on-axis FR and much wider radiation above 2-3kHz - even wider in radiation than the front plate simulation 1).
The only downer is the resonance at 15kHz. The simulation often exaggerates the consequences a bit with pointy/tapered shapes - nevertheless, it's not pretty.

4) Front plate with 3mm + 1mm + 1mm - 1mm steps
Our "lip surgery" went wrong in 3) somehow and cause a resonance, it seems no one likes pointed lips. So we make our lip around the tweeter a little rounder:
1691738147186.png 1691745210986.png 1691745240124.png
Problem solved. Now we have all the advantages of 3) without the resonance at 15kHz.

Now one could get the idea and ask, what advantages did all the effort bring us, if version 1) is already almost perfect?
To answer this, we compare deg0 and deg60 FR from both versions 1) and 4) - normal FR and normalized FR:
1691745755399.png 1691746307796.png
Our "lip surgery" gave us a little more SPL above 5kHz on axis and a little wider radiation in the 3-12kHz range.
 
Last edited:
OP
C

ctrl

Major Contributor
Forum Donor
Joined
Jan 24, 2020
Messages
1,640
Likes
6,288
Location
.de, DE, DEU
I did measurements of the SS in a wide baffle, with a large radius rounded edge, and they came out very well. The SS narrows the radiation in at around 10 kHz, but I don't consider this a big problem.

Personally, I would choose an SS in a non-optimal enclosure for diffraction than a DXT in an excellent enclosure for diffraction without a second thought.

Because of the low harmonic distortion, high power handling and possible low crossover frequency, the D2905/990000 was considered.

Since the goal with the Directivia r2 is to achieve SOTA radiation at a low overall price, preference was given to the Seas DXT over the D2905/990000, which is 2.5 times as expensive, but with slightly inferior radiation. The directivity of the Seas DXT front plate ("short WG", Seas marketing calls it "DXT lens") is more uniform.

Directiva r2 tweeter full hor and ver measured responses, CTA-2034A and hor normalized contour plot:
1691748885166.png

The simulations for the D2905/990000 tweeter have shown an unsteady directivity above 5-6kHz, as your measurements also show.
Simulation (only to 10kHz) Directiva r2 with D2905/990000 full hor and ver responses, CTA-2034A and hor normalized contour plot:
1691750177777.png

No problem if you came to a different conclusion ;)
 

PKAudio

Member
Joined
Mar 25, 2021
Messages
48
Likes
78
I own a Seas DXT as well as a Scan Speak d2905-990000 and in my opinion the DXT is a much worse tweeter than the SS. The DXT has a much higher level of distortion and a narrower usable frequency response. These speakers sound completely different. DXT with a proper front end in terms of diffraction performs very well in measurements, but its sound will still be worse than SS.

I did measurements of the SS in a wide baffle, with a large radius rounded edge, and they came out very well. The SS narrows the radiation in at around 10 kHz, but I don't consider this a big problem.

Personally, I would choose an SS in a non-optimal enclosure for diffraction than a DXT in an excellent enclosure for diffraction without a second thought.
Exactly my experience from listening and working with a lot of tweeters (really many, from cheap tweeters to Bliesma Be, Mundorf AMT). DXT measures great in optimized faceted baffle and the reasons it was chosen for Directiva are obvious.
 
  • Like
Reactions: mv8

holdingpants01

Addicted to Fun and Learning
Forum Donor
Joined
Mar 18, 2023
Messages
738
Likes
1,176
extremely interesting thread with zero use for me and I love it, thank you
 

mv8

New Member
Joined
May 15, 2022
Messages
3
Likes
3
Location
Poland
Some time ago I built small monitors, in which I paid special attention to offaxis characteristics. The tweeter is a cheap Dayton from WG.
In my opinion, it looks very good, but unfortunately it in no way equals the sound of Scan speak in an ordinary shoebox-shaped enclosure.

I pay very close attention to the offaxis characteristics in every project I do, but I don't think their absolute accuracy makes a very big difference in sound. I still think that the most important thing in a design is to use high-quality speakers, because they have the biggest impact on the sound.

If someone is looking for exactly the sound that Scan Speak offers, they won't find it in the DXT in any enclosure, even an ideal one, unfortunately :)
 

Attachments

  • dayton wg.png
    dayton wg.png
    139 KB · Views: 113
  • DSC_3855.JPG
    DSC_3855.JPG
    187.7 KB · Views: 108

617

Major Contributor
Forum Donor
Joined
Mar 18, 2019
Messages
2,465
Likes
5,446
Location
Somerville, MA
If you mean this SS tweeter, don't expect too much.
Have used the tweeter in the process of the Directiva r2 design simulations and the results were not satisfactory in terms of even radiation.

For a uniform radiation the tweeter should radiate narrowly in the range of the typical edge diffraction (to counteract the radiation widening by edge diffraction), which is partly fulfilled in the range 2-4kHz, but above that the radiation widens a bit and then becomes very narrow.
Manufacturer measurement:
View attachment 304960

Directiva r2 simulation with SS D2905/990000
View attachment 304965 View attachment 304966

Simulation result up to 10kHz first FR deg0-180, then normalized to on-axis FR and normalized contour plot:
View attachment 304968 View attachment 304969 View attachment 304970

The results are not very bad, but not SOTA either. Because it is a treated textile dome (very early damped breakup versus ideal tweeter in simulation), the real radiation might look a bit better though.
Anyway the radiation of the Seas DXT tweeter is more uniform, therefore it was also used in the r2.

Scan Speak should have hired @René - Acculution.com to shape optimize the heck out of it ;)
Rene was probably 12 years old when that tweeter was designed!
In general I agree, it's curious how few tweeters with decent sized waveguides are available. Your study shows that even a moderate waveguide in a ~150mm faceplate can make a big impact in a conventional design.
 
OP
C

ctrl

Major Contributor
Forum Donor
Joined
Jan 24, 2020
Messages
1,640
Likes
6,288
Location
.de, DE, DEU
Tweeter flush mounted but with gap around face plate?

What happens if the tweeter is flush mounted, but the recess it sits in isn't perfect. Eg there is a 1mm gap all around? Or the recess has a chamfer? If the gap was a problem, would filling it in with silicone or something be a solution?
If gaps are present and not too narrow, I always stuff them with black foam or black sealing tape (or black cardboard) - this allows the tweeter to be removed again without any problems.

What happens if the tweeter is flush mounted or mounted with a 1mm or 2mm gap?

As always first the sketch of all three cases:
flush mounted no gap,
a gap of 1mm and
a gap of 2mm around the tweeter.
1691757996375.png 1691758012636.png 1691758031076.png
then the 0°-90° FR (10° steps)
1691758352055.png 1691758369607.png 1691758381582.png
and last but not least the comparison of the 0°, 30° and 60° FR of the tweeter with 1mm, 2 mm and without gap
1691758891392.png

The simulation software usually depicts the effects a little more dramatically than they are in reality (it is rare that a gap is exactly 1mm wide all around, the corners are perfectly right-angled all around,...).
Therefore a gap of 1mm or less is IMO still acceptable (perfectionists also fill 1mm gaps ;)), but with 2mm and more you should probably fill the gap if possible (this could already have minimal tonal effects).

Update: These are of course very academic considerations, the easiest way is to seal the gaps with easily removable tape, take an on-axis measurement and then compare it to the one without tape.
 
Last edited:

badspeakerdesigner

Active Member
Joined
Jan 12, 2023
Messages
274
Likes
447
Some time ago I built small monitors, in which I paid special attention to offaxis characteristics. The tweeter is a cheap Dayton from WG.
In my opinion, it looks very good, but unfortunately it in no way equals the sound of Scan speak in an ordinary shoebox-shaped enclosure.

I pay very close attention to the offaxis characteristics in every project I do, but I don't think their absolute accuracy makes a very big difference in sound. I still think that the most important thing in a design is to use high-quality speakers, because they have the biggest impact on the sound.

If someone is looking for exactly the sound that Scan Speak offers, they won't find it in the DXT in any enclosure, even an ideal one, unfortunately :)

Well now, I was about to build something just like this, almost a cheaper DXT mon if you will, but it's good to hear some feedback on the idea. Guess I will pass.

I'd be curious to see what sims say about a pretty deep loaded tweeter like the Peerless D27. That things dome is below the faceplate and the sides are basically vertical walls with a very small round over.
 
Top Bottom