jbl d123 16 ohm cabinet duct size [Archive]

rudy sesztak

08-07-2009, 02:22 PM

http://www.lansingheritage.org/images/jbl/plans/1975-kit-plans/page09.jpg

vintage driver: vintage plans :D
Thanks for chart on duct sizes. I've seen 2 charts for my d123.
my d123 is 16ohm with a fs of 40. later d123's were 8 ohm with
a fs of 45. I don't know which chart is for my d123. I've owned
over 20 different tweeters. The jbl 077 is the ultimate!!

speakerdave

08-07-2009, 06:08 PM

Thanks for chart on duct sizes. I've seen 2 charts for my d123.
my d123 is 16ohm with a fs of 40. later d123's were 8 ohm with
a fs of 45. I don't know which chart is for my d123. I've owned
over 20 different tweeters. The jbl 077 is the ultimate!!

The voice coils for the "16 ohm" and the "8 ohm" versions are the same, according to our and JBL's very own Harvey Gerst. I've measured some of both and this was borne out as regards DCR. Harvey says JBL rated the D123 at 16 ohms because they sounded better connected to the 16 ohm taps of the tube amps of that day. In a later era people were mostly using solid state amps and wanted 8 ohm speakers, and JBL accommodated them. By the way, Harvey also says that the designer of the driver preferred it in about 4 cu ft.

Use the chart grumpy linked--it was created by JBL based on their own knowledge of their own drivers, I assume. Or, get WT2, test your specific drivers, and plug the values you get into BaseBoxPRO.

I wouldn't use the D123 and the 077 with nothing in between. Earache! The 077 loses sound quality rapidly going below about 10k, and the minimum is rated at something like 6500. The metal dome on the D123 will resonate at about 7000 HZ, and it is recommended you cross out of that driver by 3500 at most. Even the full range aficionados recommend a zoebel to take that out. If you want to make a 2-way, find Zilch's work on that at AudioKarma. Save the 077's for a three- or four-way.