I am currently looking for some inexpensive subwoofers for double duty in a mobile application as well as maybe serving as HT subs.
Anyway, I came across this for an NVX 15" subwoofer but have also seen this for other brands (Skar Audio is another with EVL series subs)
Why are some of the specs (Q values, Vas, Fs) so different for dual 2-ohm compared to dual 4-ohm models? I guess some of the Qts, Qes, stuff would make sense, but why Qms, Fs and Vas? I thought Qms was more of a mechanical spec, not electrical. Are some manufacturers intentionally messing with some of the mechanical parts in order to achieve something different with the different impedance VCs? I just highly doubt they would put that much effort in changing out mechanical parts in such low budget drivers
https://cdn.shopify.com/s/files/1/0646/2577/0712/files/mn_VCW15v3.pdf?v=1679586953
Anyway, I came across this for an NVX 15" subwoofer but have also seen this for other brands (Skar Audio is another with EVL series subs)
Why are some of the specs (Q values, Vas, Fs) so different for dual 2-ohm compared to dual 4-ohm models? I guess some of the Qts, Qes, stuff would make sense, but why Qms, Fs and Vas? I thought Qms was more of a mechanical spec, not electrical. Are some manufacturers intentionally messing with some of the mechanical parts in order to achieve something different with the different impedance VCs? I just highly doubt they would put that much effort in changing out mechanical parts in such low budget drivers
https://cdn.shopify.com/s/files/1/0646/2577/0712/files/mn_VCW15v3.pdf?v=1679586953
I kind of figured I would get a response like this, and I appreciate it and will look those links over.
However, on some of the other drivers that are offered in dual 2- and 4-ohm versions, the parameters can actually be quite similar, and I'm not sure why. See the below.
https://cdn.shopify.com/s/files/1/0655/3550/8703/files/Hawk_Subwoofer.pdf?v=1682346116
I guess maybe after I read through the links it will make sense.
However, on some of the other drivers that are offered in dual 2- and 4-ohm versions, the parameters can actually be quite similar, and I'm not sure why. See the below.
https://cdn.shopify.com/s/files/1/0655/3550/8703/files/Hawk_Subwoofer.pdf?v=1682346116
I guess maybe after I read through the links it will make sense.
Hope so, not much good at synopsizing it, assuming it can be done good enough and still answer your Qs without further Q&A.
The voice coil is the elephant in the room. You can not build a voice coil of 4 or 8 ohms with exact the same mechanical properties. There will be at least a difference in wire mass, or even in winding length, winding thickness or whatever.
I figured that might be part of it. Now that makes me wonder how VC's are built to be 2,4,8 or even 16-ohm? I have some tiny 4" drivers that are 16-ohm.
It can be done - but there will always result some different T/S parameters.
What bucks bunny said.
I design and build my own voice coils so am painfully aware of compromises and limitations.
In principle you use different diameter wire, different turns count, different winding length depending on desired outcome, all affect each other, BUT there are 2 BIG problems:
a) dcr/impedance varies inversely to the CUBE of wire diameter 😲, so a small variation in diameter causes a HUGE effect.
b) VC mass varies inversely proportional to square root of impedance (a 2 ohm coil is heavier than a 4 ohm one, everything else being the same)
This obviously affects TS parameters.
So "nothing is linear/directly proportional", "everything affects everything else", and to make matters worse:
c) you can NOT get wire in "any" diameter you want (unless you order 5 tons each size so they custom draw it for you) so you must pick from their regular production.
US-Brazil and many others use the AWG scale or a similar one, with an exponential series of diameters, here in Argentina and in most Metric Countries (think Germany) thin wire diameter varies in 0.1 or 0.5 mm steps , getting the exact size you want Isa lottery or plain impossible, so you use closest one ... which often is not close enough by any means (remember the cube inverse law).
In practice, voice coils are whatever winder can do and not exactly what speaker designer specified.
Real World 🤷🏻
JMFahey -- amazing description, thanks so much for the detailed response. I was not aware of those inverse cube and square root relationships. I'm sure that can account for some relatively significant variations in VC's from batch to batch in speaker building.
Be aware that you always want
2-layer winding
same coil diameter
same winding length
same gap width
And you will realize that there cannot be a simple solution for arbitrary impedance
2-layer winding
same coil diameter
same winding length
same gap width
And you will realize that there cannot be a simple solution for arbitrary impedance