Hi there,
I know a lot about car audio, but I am completely new to building planars. I would like to build a SQ competition car using mainly, if not exclusively, planar magnetics.
Can you think of anything that I should take into account for my development process, that might not play a big role for home audio, but for a car interior?
Things like temperature fluctuation, humidity, UV, vibrations..
The car in question is a Toyota MR2 SW20. It has a very small interior, similar to a single cab pickup. It also has T-tops, which means it's basically glass all around, so it heats up very quickly in the summer.
I live in Germany, temperature here fluctuates between -15° C and 40° C (5° F and 105° F), inside the car that would probably be -10° C to 70° C (15° F to 160° F), some sources even state up to 80° C (175° F).
Could that already cause a noteworthy degree of material expansion/shrinkage? Considering mylar would shrink with heat, while metal would expand (including the aluminum layer).
I also read that neodymium magnets can permanently lose magnetic strength above 80° C (175° F).
Does humidity matter?
What about UV?
Then there's vibrations and shaking from driving. Would you expect that to cause premature delamination? Any way to avoid that?
And lastly, since cabin gain will likely already set in slightly above 100 Hz, there will be a lot of pressurization.
Could that cause distortion? Since a mylar diaphragm is so lightweight and they will be monopoles? The Mms of a typical dynamic (car audio) midrange driver or silk dome tweeter can easily be 50-100 times that of a mylar/aluminum planar..
Any hints are well appreciated.
If there's any interest I can also share more information about what exactly I'm planning to build.
Happy listening!
I know a lot about car audio, but I am completely new to building planars. I would like to build a SQ competition car using mainly, if not exclusively, planar magnetics.
Can you think of anything that I should take into account for my development process, that might not play a big role for home audio, but for a car interior?
Things like temperature fluctuation, humidity, UV, vibrations..
The car in question is a Toyota MR2 SW20. It has a very small interior, similar to a single cab pickup. It also has T-tops, which means it's basically glass all around, so it heats up very quickly in the summer.
I live in Germany, temperature here fluctuates between -15° C and 40° C (5° F and 105° F), inside the car that would probably be -10° C to 70° C (15° F to 160° F), some sources even state up to 80° C (175° F).
Could that already cause a noteworthy degree of material expansion/shrinkage? Considering mylar would shrink with heat, while metal would expand (including the aluminum layer).
I also read that neodymium magnets can permanently lose magnetic strength above 80° C (175° F).
Does humidity matter?
What about UV?
Then there's vibrations and shaking from driving. Would you expect that to cause premature delamination? Any way to avoid that?
And lastly, since cabin gain will likely already set in slightly above 100 Hz, there will be a lot of pressurization.
Could that cause distortion? Since a mylar diaphragm is so lightweight and they will be monopoles? The Mms of a typical dynamic (car audio) midrange driver or silk dome tweeter can easily be 50-100 times that of a mylar/aluminum planar..
Any hints are well appreciated.
If there's any interest I can also share more information about what exactly I'm planning to build.
Happy listening!
I've measured 170 °F on a car dash under similar conditions. So yes, it's something to consider in your design. Careful selection of adhesives and materials is often required in a car that's not going to spend the vast majority of its life in a garage.
If you are planning to have a lot of bass in the car, acoustic coupling to the diaphragm can be an issue. The bass moves the diaphragm, which may or may not be a problem depending on the spacing you are using, how/where the planar is mounted, etc. My experience with this was with electrostatics in a car that likely used much smaller spacing than you will (and probably had much more SPL capability than you intend). It's something to be aware of though.
Power density and Mylar will also be an issue in a car, unless you want to use a large planar. Thigpen (Eminent Technology) and Bohlender Graebener patents talk about this:
US 6,104,825 - [summary] greater than 1 watt per square inch causes expansion problems with Mylar membranes (loss of tension and increased distortion, bowing from thermal expansion rate mismatch)
https://patents.justia.com/patent/20020191808
"another area of needed advancement in single ended planar-magnetic transducers is that of improving the diaphragm 21 to achieve greater thermal change and heat tolerance, high dimensional stability, and low distortion. A common diaphragm material in prior single-ended planar-magnetic loudspeakers has been polyester thin films, also known under the trademarked name Mylar . A limitation of such single-ended planar-magnetic loudspeakers has been reliability due to thermal problems both with the adhesives used to attach the conductive regions 26 to the diaphragm 21, and with thermal limits of stability of the diaphragm 21 itself."
If you are planning to have a lot of bass in the car, acoustic coupling to the diaphragm can be an issue. The bass moves the diaphragm, which may or may not be a problem depending on the spacing you are using, how/where the planar is mounted, etc. My experience with this was with electrostatics in a car that likely used much smaller spacing than you will (and probably had much more SPL capability than you intend). It's something to be aware of though.
Mylar expands with temperature up to a certain point, then starts to shrink with temperatures above that. Can't remember the exact temperature off the top of my head, but my recollection is that you're in the expanding with temperature zone in a car.
Power density and Mylar will also be an issue in a car, unless you want to use a large planar. Thigpen (Eminent Technology) and Bohlender Graebener patents talk about this:
US 6,104,825 - [summary] greater than 1 watt per square inch causes expansion problems with Mylar membranes (loss of tension and increased distortion, bowing from thermal expansion rate mismatch)
https://patents.justia.com/patent/20020191808
"another area of needed advancement in single ended planar-magnetic transducers is that of improving the diaphragm 21 to achieve greater thermal change and heat tolerance, high dimensional stability, and low distortion. A common diaphragm material in prior single-ended planar-magnetic loudspeakers has been polyester thin films, also known under the trademarked name Mylar . A limitation of such single-ended planar-magnetic loudspeakers has been reliability due to thermal problems both with the adhesives used to attach the conductive regions 26 to the diaphragm 21, and with thermal limits of stability of the diaphragm 21 itself."
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Kapton is about the only material you can use that can handle the heat inside of a car in the summertime, I thought about making such driver myself, ESL's for cars back in 2003-5 or so and Kapton was the only thing I could find at the time and still to this day, that may work for such an application.
It does not shrink or weld with temp and Must Be mechanically mounted and stretched mechanically in order too put any tension on the diaphragm at all, this much I have tested, since then it has been one of those projects put way back on the back burner.
jer
It does not shrink or weld with temp and Must Be mechanically mounted and stretched mechanically in order too put any tension on the diaphragm at all, this much I have tested, since then it has been one of those projects put way back on the back burner.
jer
I really appreciate your advice!
I agree that neither Mylar, nor Kapton are ideal.
PEN, also referred to as Teonex®, seems to be the best compromise.
This is also the material used for the planar magnetics designed by Harman for various car models. There's a thread about those already as well.
Ever since I found out about them, I have been less invested in my research on making my own planars from scratch, as they're roughly the size I was aiming for anyway, at least for my A-pillars. They're probably better than whatever I could build myself and I don't think you can buy any 2 Ohm planars off the shelf.
Once I make some progress testing those inside of my car and I like the results, I might consider making a pair of larger midbass panels for my door cards or footwells. They would need to cover ~100-500 Hz, can be push-pull and benefit from a sealed enclosure or infinite baffle as well as cabin gain.
I realize that that's very silly and I don't expect it to work, or only at very limited volume. It's just an interesting concept, an all-planar car audio system.
I could even fit close to 1 m² of planar on the rear firewall behind the seats as a subwoofer, but why bother if stereo front subwoofers in infinite baffle are plausible.
It looks like AMTs are the flavor of the month right now in competitive car audio. I'm sure that planars have more potential because they can reach lower.
I agree that neither Mylar, nor Kapton are ideal.
PEN, also referred to as Teonex®, seems to be the best compromise.
This is also the material used for the planar magnetics designed by Harman for various car models. There's a thread about those already as well.
Ever since I found out about them, I have been less invested in my research on making my own planars from scratch, as they're roughly the size I was aiming for anyway, at least for my A-pillars. They're probably better than whatever I could build myself and I don't think you can buy any 2 Ohm planars off the shelf.
Once I make some progress testing those inside of my car and I like the results, I might consider making a pair of larger midbass panels for my door cards or footwells. They would need to cover ~100-500 Hz, can be push-pull and benefit from a sealed enclosure or infinite baffle as well as cabin gain.
I realize that that's very silly and I don't expect it to work, or only at very limited volume. It's just an interesting concept, an all-planar car audio system.
I could even fit close to 1 m² of planar on the rear firewall behind the seats as a subwoofer, but why bother if stereo front subwoofers in infinite baffle are plausible.
It looks like AMTs are the flavor of the month right now in competitive car audio. I'm sure that planars have more potential because they can reach lower.
Maybe BOPP film https://www.eraudio.com.au/index.php?option=com_content&view=article&id=13&Itemid=123
Bernt
Bernt
The original cellofan was cellulose-acetat (see "cell" in this name). This is a hydrophylic material. My grandmother's kitchen foil.
The BOPP is very strechable, viscous material, good internal damping but limited thermal and mechanical "strongness": this causes the risk of voice coil delamination.