RMC
04-06-2017, 07:43 PM
Hi guys,
Recently comparing 15" woofers in JBL's Tables of T/S parameters issued 2008/2012, to see changes before/after converted from Alnico to Ferrite. A number of cases didn't seem to make sense or are wrong. Members/guests here often rely on JBL Tables for optimal speaker design. Using somewhat inaccurate tables could lead to more approximate design...
So, I took a sample of popular 15" drivers to see effect on T/S parameters after conversion (2225/2235 excluded since were issued as "H" versions with Ferrite magnets). The following drivers show many variations in T/S tables when converted which makes sense: 2220A/H, K/E-130, K/E-140 and K/E-145.
The drivers here appear suspicious cases in T/S tables since nothing changed: 2205A/H, 2215A/H and 2231A/H, even if incomplete driver data sheets before/after show minor difference. Table numbers of one version copied on other version, except for probable typo error on "Flux" number of 2215H...
BTW, conversion of 12" drivers apparently follows same pattern: 2202A to "H" did result in changes to T/S, as well for K/E 120. However, 2203A/H T/S para. look like "copy and paste" job between the two versions...
Finally, I have a computer printout from JBL for a box design given to me early 80's stating the 2205 (A or H ?) has an Xmax of 0.14 in.(3.56mm) contrary to JBL's number in 2008/2012 T/S tables of 2.54 mm (0.10 in.) for A/H versions. This would mean, on Xmax, equal to E-130 (lead guitar); In my book its more equivalent to E-140 (3.56mm, bass guitar). 1 mm makes a difference in bass output capability in speaker design software.
WHY SOME WOOFERS APPEAR AS WINNERS AND OTHERS AS LOSERS UPON CONVERSION IS BEYOND ME... Specially in view of JBL's commitment in data sheets: "JBL continually engages in research related to product improvement. ... but will always equal or exceed the original design specifications..."
I have spec sheets for JBL drivers mentioned here, but they don't answer the questions raised by T/S tables for drivers launched prior to 1982 (year JBL appears to have started giving T/S in driver data sheets). Now I'm trying to find other data sources than the above, credible numbers for some drivers prior 1982. I' ve looked on this site but didn't find the info needed to attempt a correction on some drivers' parameters.
DO YOU HAVE DATA (e.g. GISKARD/TECHBOT on 2216-7 Eng. Design Specs) for 2205H, 2215H, 2231H and/or 2203H, Design Engineer's data (test results) on prototype/initial production unit before giving OK/release for production, as you have already shared on this site (Thanks!) for numerous other more recent drivers.
If info not all available, I could still calculate some, e.g. Xmax with reliable numbers of Voice coil length and Height of Gap, using formula: VC length minus Gap height, then divide by 2 = Xmax, right? Earl K or Subwoof may have given on this site (Thanks!) some Gap numbers for drivers if I remember correctly...
Could be other drivers too with inaccurate T/S in tables. If you're a fan of older drivers (prior 1982, you can't check table data VS data sheet), think about reliability of numbers seen. Particularly, if the driver you're looking at for a project has the exact same T/S parameters in the tables before and after conversion...
Even if it was probably a hectic period, It's unlikely JBL converted drivers and didn't bother testing them for parameters outcome/compliance with design specs. Some showed very minor differences but were still mentioned. So, difficult to buy "not enough to mention"... Why not publish others' revised figures ?
Richard
Recently comparing 15" woofers in JBL's Tables of T/S parameters issued 2008/2012, to see changes before/after converted from Alnico to Ferrite. A number of cases didn't seem to make sense or are wrong. Members/guests here often rely on JBL Tables for optimal speaker design. Using somewhat inaccurate tables could lead to more approximate design...
So, I took a sample of popular 15" drivers to see effect on T/S parameters after conversion (2225/2235 excluded since were issued as "H" versions with Ferrite magnets). The following drivers show many variations in T/S tables when converted which makes sense: 2220A/H, K/E-130, K/E-140 and K/E-145.
The drivers here appear suspicious cases in T/S tables since nothing changed: 2205A/H, 2215A/H and 2231A/H, even if incomplete driver data sheets before/after show minor difference. Table numbers of one version copied on other version, except for probable typo error on "Flux" number of 2215H...
BTW, conversion of 12" drivers apparently follows same pattern: 2202A to "H" did result in changes to T/S, as well for K/E 120. However, 2203A/H T/S para. look like "copy and paste" job between the two versions...
Finally, I have a computer printout from JBL for a box design given to me early 80's stating the 2205 (A or H ?) has an Xmax of 0.14 in.(3.56mm) contrary to JBL's number in 2008/2012 T/S tables of 2.54 mm (0.10 in.) for A/H versions. This would mean, on Xmax, equal to E-130 (lead guitar); In my book its more equivalent to E-140 (3.56mm, bass guitar). 1 mm makes a difference in bass output capability in speaker design software.
WHY SOME WOOFERS APPEAR AS WINNERS AND OTHERS AS LOSERS UPON CONVERSION IS BEYOND ME... Specially in view of JBL's commitment in data sheets: "JBL continually engages in research related to product improvement. ... but will always equal or exceed the original design specifications..."
I have spec sheets for JBL drivers mentioned here, but they don't answer the questions raised by T/S tables for drivers launched prior to 1982 (year JBL appears to have started giving T/S in driver data sheets). Now I'm trying to find other data sources than the above, credible numbers for some drivers prior 1982. I' ve looked on this site but didn't find the info needed to attempt a correction on some drivers' parameters.
DO YOU HAVE DATA (e.g. GISKARD/TECHBOT on 2216-7 Eng. Design Specs) for 2205H, 2215H, 2231H and/or 2203H, Design Engineer's data (test results) on prototype/initial production unit before giving OK/release for production, as you have already shared on this site (Thanks!) for numerous other more recent drivers.
If info not all available, I could still calculate some, e.g. Xmax with reliable numbers of Voice coil length and Height of Gap, using formula: VC length minus Gap height, then divide by 2 = Xmax, right? Earl K or Subwoof may have given on this site (Thanks!) some Gap numbers for drivers if I remember correctly...
Could be other drivers too with inaccurate T/S in tables. If you're a fan of older drivers (prior 1982, you can't check table data VS data sheet), think about reliability of numbers seen. Particularly, if the driver you're looking at for a project has the exact same T/S parameters in the tables before and after conversion...
Even if it was probably a hectic period, It's unlikely JBL converted drivers and didn't bother testing them for parameters outcome/compliance with design specs. Some showed very minor differences but were still mentioned. So, difficult to buy "not enough to mention"... Why not publish others' revised figures ?
Richard