PR-15 Tuning Discs

[LE15-Thumper]

I am selling a pair of PR-15's for my dad but he no longer has the extra "tuning discs" or whatever they are called. What can be used in place or are they still available from JBL?
Also, how does one know the correct "weighting" of these
PR-15's ? Giskard, I am looking in your direction

[S.O.Stefansson]

You (or the new owner) can make your own tuning discs from plastic or fiberboard (depending on weight). I think I still have some old JBL documents explaining the use of the discs for tuning the PR15s. I can make copies and mail or fax to you. You can 'pm' your address and/or fax.

Sigurd

[Mr. Widget]

I looked in our library and we don't seem to have the document, but JBL published a brochure describing the use of the PR8, PR10, and PR15. It is Publication OM 23. All three of these passive radiators have removable "tuning" discs.

Using the PR15 with the LE15A
you use 3 discs for a 5.0 to 5.5 cu ft enclosure.
you use 2 discs for a 5.5 to 6.5 cu ft enclosure.
you use 1 disc for a 6.5 to 7.5 cu ft enclosure.
you use no discs for a 7.5 to 8.0 cu ft enclosure.

As Sigurd mentioned the discs can be made of any material as long as they have the correct weight. Years ago I measured a pair that I have for someone in your predicament, but at the moment I am too lazy to dig up the PR15s and disassemble them for the measurement. For a 7.5 to 8.0 cu ft enclosure you also remove the machine screw, washer and lock washer. There is one fiber disc that is glued to the cone and should never be removed. If you are adding the discs you will need the weight of the screw and washers too as it is part of the dynamic weight. As seemingly precise as this is I remember that the different discs I have are not all exactly the same weight.

Since you are just selling these, why not just tell the buyer that they are designed for a 7.5 to 8.0 cu ft enclosure.

Widget

[4313B]

Originally posted by LE15-Thumper
I am selling a pair of PR-15's for my dad but he no longer has the extra "tuning discs" or whatever they are called. What can be used in place or are they still available from JBL?
Also, how does one know the correct "weighting" of these
PR-15's ? Giskard, I am looking in your direction

Sorry but I only have the moving mass specification for the PR15C, not the PR15, so I can't help you with the tuning formula. It's not a showstopper though as anyone with an oscillator and volt meter can tune the volume more accurately. The PR15x metal discs weigh in at ~ 100 grams and the fiberboard discs weigh in at ~ 20 grams.