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Old 3rd January 2011, 11:06 AM   #21
markusA is offline markusA  Sweden
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Thanks, I guess that means it might at least be worth a try.
I doubt I'll be throwing any rock concerts in my living room any time soon.

So... 1.1mm d/s test run.
Panel size: 1650x250mm
Active diaphragm size: 1600x200mm
Extra vertical spacer from top to bottom monted at the center line (100mm).
What width should I choose for the spacer?
Tapes are available in 25mm and 19mm Width. (I got 19mm already and I'll be buying 25mm). Splitting them in half I can get 12.5mm and 9.5mm widths. (Splitting them might include some irregularities?)
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Old 3rd January 2011, 01:41 PM   #22
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Quote:
Originally Posted by markusA View Post
Thanks, I guess that means it might at least be worth a try.
I doubt I'll be throwing any rock concerts in my living room any time soon.

So... 1.1mm d/s test run.
Panel size: 1650x250mm
Active diaphragm size: 1600x200mm
Extra vertical spacer from top to bottom monted at the center line (100mm).
What width should I choose for the spacer?
Tapes are available in 25mm and 19mm Width. (I got 19mm already and I'll be buying 25mm). Splitting them in half I can get 12.5mm and 9.5mm widths. (Splitting them might include some irregularities?)

Since you reference a vertical center spacer, I assume you will be building a flat panel.
My slightly wider flat panel (30.5cm) uses 19mm on the edges and two 9.5mm vertical support spacers. Since your panel will have only one vertical support spacer, I would use 19mm on the edges and 12.5mm for the vertical center spacer.

Last edited by CharlieM; 3rd January 2011 at 01:45 PM.
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Old 3rd January 2011, 02:17 PM   #23
markusA is offline markusA  Sweden
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You're absolutely correct Charlie.
It'll be a flat panel. I might be crazy but there's got to be a limit to my madness. It's my first panel and flat seams to be the easiest route.
I think I'll try heat shinking as well to get the diaphragm tension up, unless there a good reason not to?

If I go for 19mm at the edges I'll drop the 25mm tape all togeather and in that case it'll either be 19mm or 9.5mm center spacer for obvious reasons.
Maybe 19mm edges is the way to go?
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Old 3rd January 2011, 03:35 PM   #24
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Hi,

1.1mm is good for a maximum SPL-value of 110dB@4m for f>200Hz with my small panel.
Sounds sufficient eyyh? Gives any bass a good run for the money.

jauu
Calvin
Have you measured that loudness from one of your panels (at what distance and room??) or is that the theoretical excursion that is needed for 110dB at 200 Hz?
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Old 3rd January 2011, 10:00 PM   #25
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Quote:
Originally Posted by markusA View Post
You're absolutely correct Charlie.

I think I'll try heat shinking as well to get the diaphragm tension up, unless there a good reason not to?

If I go for 19mm at the edges I'll drop the 25mm tape all togeather and in that case it'll either be 19mm or 9.5mm center spacer for obvious reasons.
Maybe 19mm edges is the way to go?
Either tensioning method would work. I've not tried heat-shrinking myself but many builders prefer it. You can get much higher tension mechanically and higher tension is preferable when using very high bias voltage (over 2.5kv, let's say) with close d/s. On the other hand, heat shrinking is easy and fast and the lower tension gives a lower resonant frequency and that's a good thing too (we want the resonance at least low enough to fall below the crossover frequency). Again, either method works and each has its tradeoffs-- so it's a matter of personal preference and matching the results to the application.

19mm tape is sufficient to secure the diaphragm to the stator and leaves more active radiating area on the panel. I think 9.5mm would be fine for the center support spacer if your stators are pretty flat. Otherwise, I would go with the wider 12.5 mm to better stick and hold the stators parallel.
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Old 4th January 2011, 08:02 AM   #26
Calvin is online now Calvin  Germany
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Hi,

Markus, you may rethink the vertical dimension of Your panel.
The increased height increases the capacitance of the panel without beeing of good use, because SPL-wise you don´t gain when the height exceeds 1m-1.3m. The higher the panel the farther away comes the transistion from nearfield to diffuse field conditions (which gives the point of highest SPL).
This also means that as long as You listen in nearield You hardly will get the impression of a realistic soundstaging, but rather the impresssion of listening to a oversized headphone. If You want to listen in a seat as well as in standing position just raise a smaller panel in mounting height.
A flat panel forms laser-beamlike highs. Already small variations in head position lead to varying sonic character. Curved panels are a bit more forgiving. Think about additional bracing of the panel to increase stiffness.
Flat panels will easily rattle and resonate.
You won´t gain high dynamics if You tension the membrane just thermally. Tension mechanically and add a heat treatment after.
The higher the tension the more fixating area you need. 19mm could be sufficient for thermal treatment , but I doubt that it would withstand mechanical tensioning for long. I´d opt for 30mm for high tension.
The segmenting spacers may be silicon dots with a flat panel. This leaves the most active area left. With curved panels -or generally if using strip shaped spacers- use the smallest width (6mm for 3M). Some Tapes may be a pain to be cut by hand. Rather use 2 or 3 different widths instead.

The cited 110dB@4m is a real value measured by Prof. A. Goertz in the anechoic room of Aachen University using MonkeyForest and freshly calibrated Bruel&Kjär Mic-capsules. The measurement was repeated to confirm the values. Signal voltage calculated to an equivalent power of 50W into 8Ohms.

jauu
Calvin
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Old 4th January 2011, 08:29 AM   #27
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I would second Calvin's advice on using mechanical tensioning. Heat tensioning can only provide so much tension, and it's more difficult to control. Personally I used heat after gluing one stator just to even out some small wrinkles. Just be careful to keep moving the hot air source around without pausing, to avoid burning holes in the film. Mylar has exceptional mechanical properties (it will eat scissors for breakfast ) but heat is its enemy.
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Old 4th January 2011, 09:54 AM   #28
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Make a small panel and just DO IT. Can you now see that some important issues can be best resolved by experiment not engineering contemplation?

Being a biker has immeasurably improved the strategic balance in my life between contemplation and action. Started when I was a grad student. 50 years ago.
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Old 4th January 2011, 11:37 AM   #29
markusA is offline markusA  Sweden
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*Drawing a deep breath*
Calvin, you rock my world and I guess it's back to the drawing board once again.
I can work with a smaller panel, especially if there's no real downsides to it?
Mechanical tension! I guess I'll have to build myself a jig?
Curved panels? Since it looks like I'll be building a jig anyway I might just go all out if it's worth the extra work?

Let's lay out the ground rules then, shall we?
  • What curvature should I choose? (20 degrees or what?)
  • Will I need to roll the stators before hand? Or will it be enough to just bolt them to the fixture?
  • Going for curved stators, am I right in assuming horizontal spacers is the way to go?
  • The perf metal comes in 1000x2000mm sheets, practical matters put the absolute maximum width at 250mm (possibly somewhat less due to cut away scraps). What are my target dimensions? 1300x250mm total panel area? (1250x200mm radiating area minus horizontal spacers?)
  • How important is it to line up the holes in the front/rear stators?

It might look complicated when I line up the questions like that but in my head it's a fairly straight forward process as long as I get the details figured out.
I have a fair understanding of the crafts involved and the underlying material science.

bentoronto> I've worked as a mechanic myself and know that theory seldom mimics the real world. I try to minimise the "fixing it on location" kind of problems before hand. I know there'll always be stuff to correct but you can try keeping it to a minimum.

Last edited by markusA; 4th January 2011 at 11:40 AM.
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Old 14th January 2011, 11:29 AM   #30
jeneses is offline jeneses  United Kingdom
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Hi Markus,
I have just finished my first panels following Charlie's blog and they sound fantastic.
Thanks Charlie!
At my first attempt I used 1.1mm 3M VHB tape and heatgun for tensioning the mylar (instead using Charlie's jig). Soon I realised that I can not get even tension because of the size of the panel and the diamater of the heatgun, and it is very easy to melt holes. However I finished the panels, hooked up and they worked but I couldn't get good sound level because coupling and arcing. After several hours of listening and testing I got to the final conclusion I need to rebuild my panels using high mechanical tension and thicker spacing. So I did and now I am happy with the result. Very happy.
I also used the licron spray but the spary cap is such a rubish I find it impossible to make an even coat so after a thin spay I used a brush to spread it.
If I would start again I would go to a shop to get my perforated shets cut by them and get it rolled flat because the evenness is everithing. Wichever process you chose make sure you can repeat it at least one more time to get equally sounding panels.
So I would go for high mechaninal tension, shop cut and rolled metal and powder coating. All worth it.
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