Subwoofer building & voicecoils

[admobass]

How is the stiffness of spiders determined? You can't tell by looks, can you? also adhesive on the coil are to keep the coil from unwinding? and/or to keep the layers of coil from touching each other? thanks in advance.

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[*Ace* 10+ year member]

How is the stiffness of spiders determined? You can't tell by looks, can you? also adhesive on the coil are to keep the coil from unwinding? and/or to keep the layers of coil from touching each other? thanks in advance.

Stiffness I believe is determined by the deflection of the spider with a given mass. This is something you can only get from the manufacturer of the spider I think. But you would have to double check that with someone like Jacob from Sundown, Thilo from TC Sounds, or someone else that has a lot of knowledge on spider design.

The adhesive on a coil keeps the coil attached to the former. And when a subwoofer is "blown", it's actually the adhesive that was overheated and failed most of the time, as oppose to the coil itself. This is why coil's always unravel when blown, because the adhesive keeping it to the former has melted away. The coil is actually capable of tolerating temperatures far above what the adhesive can handle. So power handling is not really coil limited to a point, but more so adhesive limited if that makes sense. But I should say this, even though the coil by itself can handle a lot of power, you will run into issues such as power compression among other things that are for another discussion altogether. Someone correct me if I'm wrong though please.

Your last question I'm the least sure about. I believe the windings on the coil are touching each other, even with the adhesive. What matters is how each individual coil is connected to the next. For instance on a dual 2 ohm voice coil, when the positive end on one coil is connected to the negative end on the other, they are wired in series. When the positive end on one coil is connected to the positive end on the other coil they are wire parallel. In the first example, series, the two 2 ohm voice coils will act as one big single 4 ohm voice coil, and when wired in parallel will act as one big 1 ohm voice coil. If they are not connected to each other, it will simply be two individual 2 ohm voice coils, otherwise known as a dual 2 ohm sub.

 

[admobass]

cool i got adhesive and coil constraints, its seems strange that there isn't an adhesive rated for a higher temp that wouldn't fail. as far as spiders go, a wider diameter spider would give you more xmax, but the motor strength and cone/coil weight would really determine the stiffness and number of spiders?

 

[*Ace* 10+ year member]

cool i got adhesive and coil constraints, its seems strange that there isn't an adhesive rated for a higher temp that wouldn't fail. as far as spiders go, a wider diameter spider would give you more xmax, but the motor strength and cone/coil weight would really determine the stiffness and number of spiders?

Well from what I understand how stiff the spiders are is going to depend on the design goals.

1) How much power is the design meant to handle? If it's 2500 watts rms you're going to want a stiffer spider for mechanical power handling. You don't want your sub ripping it's spiders just from receiving the RMS wattage.

2) What size enclosure do you want the design to excel in? Enclosure size is determined by VAS if I'm not mistaken. The stiffer the spider, the smaller the enclosure needed.

3) Low frequency extension. When you stiffen the spider (and keep everything else the same) you are going to increase the FS of a driver. Now FS isn't everything when it comes to low end extension, but it does play a significant role IMO.

So you will have trade offs. You want your design to work in small enclosures? Well stiffen the suspension, but you are also going to raise FS at the same time and affect your low end. Do you want to fix that and keep more low end and a small enclosure? Well you'll have to add mass to the coil, cone, surround etc. to bring that FS back down but then you are going to sacrifice efficiency in the design.

Efficiency, small enclosure, and low end extension. Pick two and screw the other lol.

 

[ciaonzo 5,000+ posts]

Nice job, *Ace*. Someone has been reading. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Only thing I feel the urge to comment on is the wire for the coil is actually coated and each strand is separate from one another (otherwise you would have issue with achieving a target DCR). That is then dipped and baked.

 

[*Ace* 10+ year member]

Nice job, *Ace*. Someone has been reading. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
Only thing I feel the urge to comment on is the wire for the coil is actually coated and each strand is separate from one another (otherwise you would have issue with achieving a target DCR). That is then dipped and baked.

Ahh thanks for the info on the coil winds being separated. Based off pictures I have seen of coils, the space between each winding must be incredibly small correct? Do you happen to know the usual space between them and the tolerances?

Also could you also visit my other thread about the wire length needed for a given gauge size to acquire a certain impedance? I have yet to get an answer on that one //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif

 

[BlurredVision 10+ year member]

Good stuff ace. I got an edumacation today

 

[ciaonzo 5,000+ posts]

Ahh thanks for the info on the coil winds being separated. Based off pictures I have seen of coils, the space between each winding must be incredibly small correct? Do you happen to know the usual space between them and the tolerances?
Also could you also visit my other thread about the wire length needed for a given gauge size to acquire a certain impedance? I have yet to get an answer on that one //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif

Ideally, there would be zero space between the wires. This can be achieved by using the edgewound process or by using hexagonal wire as Dynaudio and Morel do. A flat wound coil is the next best thing. As far as the other question, not sure. Has to be a calculator for that, I would imagine.

 

[mat3833 10+ year member]

the wire used for coils is the same type of wire used for Stators and Armatures in electric motors. its copper core with an enamel coating to prevent shorts. the enamel is crazy tough, but if you arent careful you can chip it off and cause a short.

Matt

 

[*Ace* 10+ year member]

Ideally, there would be zero space between the wires. This can be achieved by using the edgewound process or by using hexagonal wire as Dynaudio and Morel do. A flat wound coil is the next best thing. As far as the other question, not sure. Has to be a calculator for that, I would imagine.

Ok cool. I'll have to do some more research on the edgewound process and the hexagonal wires, as I'm not to familiar with it at this point. Thanks again //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[*Ace* 10+ year member]

the wire used for coils is the same type of wire used for Stators and Armatures in electric motors. its copper core with an enamel coating to prevent shorts. the enamel is crazy tough, but if you arent careful you can chip it off and cause a short.
Matt

Very good info! Thanks! //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif Perhaps you can answer my question about calculating resistance through a piece of copper wire?

 

[ciaonzo 5,000+ posts]

1) How much power is the design meant to handle? If it's 2500 watts rms you're going to want a stiffer spider for mechanical power handling. You don't want your sub ripping it's spiders just from receiving the RMS wattage.

Nothing wrong with this, I just wanted to add a different perspective. Sometimes a driver may be able to cope with enormous thermal torture but will never need that amount of power to get it to reach Xmax/Xmech or do it's job in the desired enclosure/application. Sometimes it's by design, simply to allow the driver to operate completely free of thermal compression so that dynamic headroom is maximized and always 'on tap'. Many times I will put a driver in a larger enclosure to ensure this behavior. Having gobs of power on tap from an amplifier and having gobs of thermal capacity from a driver, but running both well beneath any of those limitations, gives you explosive dynamics during stressful passages in music...So long as you familiarize yourself with the limitations and you can remain disciplined with the volume (or set level limits accordingly) once you know them. This also assumes the driver will have the mechanical abilities to cope with this setup.
I know that's polar opposite of how many run their equipment but it's food for thought for anyone interested in actually playing music for any sense of accuracy or even realism. Thermal compression is very real and robs you of peak performance.