Passive Radiator in the L220 speakers and the tuning discs

[billiam62]

I am working on a project pair that I picked up in a thrift shop. I have refoamed drivers and replaced some of the capacitors for now. I listened to both speakers today and I thought they sounded really good. I have a question about the tuning discs on the passive. When I purchased the speakers, they had two. I am just assuming that is how it came from the factory. What determines how many discs should be there? What can I use as a substitute if more are needed?

[macaroonie]

From a previous post by Mr Widget in 2004 .... might help you some

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.

[Odd]

More about Passive Radiator.

65607

[billiam62]

The L220 that I have uses the LE14H. The passive radiator (PR15D) and woofer have its own chamber as the tweeter and mid are sealed off from it. Does anyone know how big the lower chamber is? I would highly doubt that it is over 5 cubic feet.

[billiam62]

The L220 that I have uses the LE14H. The passive radiator (PR15D) and woofer have its own chamber as the tweeter and mid are sealed off from it. Does anyone know how big the lower chamber is? I would highly doubt that it is over 5 cubic feet.

If my calculations are right, I would estimate the internal volume of the lower chamber to be 3.4 cubic feet not counting braces.