voice coils: 2, 3, or 4 inch? does it matter??

packrat

Super Member
For years all the big 18" and 15" JBLs had only 4" voice coils, while the Altec 15s had 3", and most other makes had everything in between. EV had some 2.5" and 3" VC woofers (12 and 15, and 18 too?). JBL even put 4" VCs into 12" woofers (like the Fender MI woofers, and some studio monitors) when other makes were using 2" VCs in their 12" woofers. JBL even made an 8 incher with a 3" VC! My understanding is that it was mainly for power handling.

So, I notice that recently (well, within the past 15 years or so..) JBL started making 15" pro woofers with 3" VCs (2035), and going through all the woofers on PartsExpress I see 12, 15, and 18 inch woofers with 2,3,4 inch voice coils.

So, the question is, for in-home use, what's better? I won't be putting 1000W into my speakers all day long so I don't need pro-level power handling. But I would like to achieve a reliable 100dB with low distortion. Is a 4" VC design compromised in some way compared to a 3" VC woofers to get that power handling? Is it possible there are attributes to a smaller VC that are lost in the race to make woofers that can withstand 1000+ watts input? I can think of a lower MMS, and that leads to less magnet (so less weight), but is the sound better because of the 4" coil formers, or is that not an issue?

just thinking out loud here, with questions. google search turns up not much on this, except the improved power handling.

this comes about as I research what it would take to build a 3-way with a 15" or 18" woofer (JBL 2235, 2245, or alternative), a 10" to 12" mid and then CD horn top end - an augmented econo-wave if you like. Yes, I can go with all vintage 30+ year old (and potentailly expensive) JBL parts, but there are also plenty of vintage EV (and Yamaha, Peavy, York, etc) speakers out there too (and the 3" VC JBL woofers too!) for less $$, and then many many new woofers at PE, US-Speakers etc. that cost about the same (or less). :scratch2: one thing I noticed - the cost seems to be related to power handling, but reading spec sheets doesn't say anything about how it will sound.
 
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For years all the big 18" and 15" JBLs had only 4" voice coils, while the Altec 15s had 3", and most other makes had everything in between. EV had some 2.5" and 3" VC woofers (12 and 15, and 18 too?). JBL even put 4" VCs into 12" woofers (like the Fender MI woofers, and some studio monitors) when other makes were using 2" VCs in their 12" woofers. JBL even made an 8 incher with a 3" VC! My understanding is that it was mainly for power handling.

So, I notice that recently (well, within the past 15 years or so..) JBL started making 15" pro woofers with 3" VCs (2035), and going through all the woofers on PartsExpress I see 12, 15, and 18 inch woofers with 2,3,4 inch voice coils.

So, the question is, for in-home use, what's better? I won't be putting 1000W into my speakers all day long so I don't need pro-level power handling. But I would like to achieve a reliable 100dB with low distortion. Is a 4" VC design compromised in some way compared to a 3" VC woofers to get that power handling? Is it possible there are attributes to a smaller VC that are lost in the race to make woofers that can withstand 1000+ watts input? I can think of a lower MMS, and that leads to less magnet (so less weight), but is the sound better because of the 4" coil formers, or is that not an issue?

just thinking out loud here, with questions. google search turns up not much on this, except the improved power handling.

this comes about as I research what it would take to build a 3-way with a 15" or 18" woofer (JBL 2235, 2245, or alternative), a 10" to 12" mid and then CD horn top end - an augmented econo-wave if you like. Yes, I can go with all vintage 30+ year old (and potentailly expensive) JBL parts, but there are also plenty of vintage EV (and Yamaha, Peavy, York, etc) speakers out there too (and the 3" VC JBL woofers too!) for less $$, and then many many new woofers at PE, US-Speakers etc. that cost about the same (or less). :scratch2: one thing I noticed - the cost seems to be related to power handling, but reading spec sheets doesn't say anything about how it will sound.
I had this long winded response, but check this out first...

http://en.wikipedia.org/wiki/Voice_coil
 
Voice coil size not affect sound quality. Some of the finest sounding high end speakers use 1 inch or 1 1/2 inch coils.
 
I remembered an explanation of this and dug it out for you:
education.lenardaudio.com/en/05_speakers_2.html
Voice Coil Diameter. On the same diameter speaker a small voice coil has less control over the cone compared to a large voice coil. With a small voice coil the cone is able to be more resonant compared to the same size cone with a large voice coil. Some small voice coil speakers may appear to be more efficient but this extra efficiency may be only at the one resonant bass note. At frequencies above this resonant bass note the speaker may be less efficient compared to the same cone with a larger voice coil. Cost and performance of speakers increase with voice coil size.

The larger the voice coil the better the control over the cone, and therefore improved damping and linearity. Large voice coils are expensive to make (limit approx 4in 100mm). Assembling the speaker is also more difficult, tolerances taken to greater accuracy. The larger the voice coil diameter - the larger the area of the magnetic gap. To keep the flux density of the magnetic energy (per unit area) in the gap the same (for the speaker to retain the same efficiency) magnet size and therefore mass of the speaker must be increased. The major advantage of larger voice coils is greater power-handling.
 
Thanks for the replies.

It seems that the whole thing is pretty complex and that generalizing isn't a great idea. I've been reading more and there's gap width, depth, VC diameter, winding height, number of layers, and magnetic flux that all play a role in what the speaker will be like. As well as the cone mass, spider, and the dust cap. I guess there can't be a 'generalized' notion about it, except that it does seem to be true that for pro speakers a larger VC seems to be used on the drivers with the higher power handling (especially looking at JBL, Selenium, Eminence etc..), which seems to go back to the issue of cooling the VC with more area.
For a home use speaker, I'm guessing VC diameter is less important because we're not filling a huge arena with sound at 120dB.
 
For a home use speaker, I'm guessing VC diameter is less important because we're not filling a huge arena with sound at 120dB.
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Cooling is less important.

EVM-15B used a 2-1/2 inch VC and was in production for years. They enjoyed the same relative acoustic output, power handling, and sensitivity as bass drivers from their competitors sporting 3 and 4 inch voice coils.
 
EVM-15B used a 2-1/2 inch VC and was in production for years. They enjoyed the same relative acoustic output, power handling, and sensitivity as bass drivers from their competitors sporting 3 and 4 inch voice coils.

EV had technical articles touting the advantages (as they saw it) of their 2.5" coils over the larger ones but I'm damned if I remember what those were.
 
Wouldn't a larger vc have greater mass and therefore exhibit greater inertia; requiring more force accelerate (speed up and slow down)?
 
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