PDA

View Full Version : Rebuilding a 130A/D216/LE20 home brew


QDD
10-21-2009, 02:59 PM
Hi, I am a new member.

Some months ago I purchased two large speakers from a friend. These huge
8.5cubic ft cabinets have the 130A/D216/LE20 drivers. My friend built these
in the early 1970's. I have been adding MDF to the inside surfaces to beef up the stiffness and mass. I had found a nasty resonance at 60Hz, which I am beating down. I'll let you all know the results when complete.

At the moment I am considering changing from the 3 way to a 2 way
design. I have purchased a pair of LE-175's to replace the LE20's which
are a bit weak in the upper octave. I saw a posting with an image of an LE 175 information sheet. The JBL document mentioned that the LE 175 is a perfect match for the 130A, with cross over at 1200Hz. So I am seeking comments from anyone owns or has heard such a system.

Is there any advantage or disadvantage to eliminating the D216?
Seems simple is better, but will I appreciate comments.

Cheers
QDD
grumpy
10-21-2009, 08:14 PM
Does the box have an 80 sq in hole in it? :) :

http://www.lansingheritage.org/images/jbl/plans/1960s-manual/page12.jpg

It would be -simpler- to mimic an existing design with the 130A/175.
I have no idea if you would like it better than a 3-way replacing the LE20
and the challenge of attempting a DIY crossover.

The D216's shouldn't be hard to sell, if that's the direction you wanted to go.
QDD
10-22-2009, 09:14 AM
Does the box have an 80 sq in hole in it? :) :

http://www.lansingheritage.org/images/jbl/plans/1960s-manual/page12.jpg

It would be -simpler- to mimic an existing design with the 130A/175.
I have no idea if you would like it better than a 3-way replacing the LE20
and the challenge of attempting a DIY crossover.
The D216's shouldn't be hard to sell, if that's the direction you wanted to go.

Hello grumpy,

Thx for the response. Good question! the Port is square 8x8 with a 13"
Length. I have looked at several JBL tables as well as doing the Helmholtz
calculation. It seems that the JBL tables are not correct. Interesting that
the page you sent indicates port length is zero. My calculations suggest
6-7". We shall see.

Also some sources suggest that the free resonance of the speaker
should be equal to the enclosure tuned resonance. JBL tables indicate 45Hz
and the 130A is actually 38Hz,... Many questions, it seems there is Art along with the science.

I have done impedance sweeps of the
woofer both in free air and in the enclosure. By that method I have noted
the nasty 60Hz resonance, and determined that the tuning is not correct.

I am planning to design and build the cross over network, when I am happy
with the rebuild. The guide provided at
http://sound.westhost.com/lr-passive.htm
seems straight forward and well thought out.

What I will probably do is include the D216's. The cross over will be external
to the enclosure so I will have the choice of switch between 2 or 3 way design,...
Fun experiment I think. But more work to be sure.

Cheers
grumpy
10-22-2009, 10:28 AM
heh, yes... the table was provided for nostalgia.
Sounds like you're on top of the situation.
Have fun, learn well. Cheers.
QDD
10-22-2009, 10:41 AM
heh, yes... the table was provided for nostalgia.
Sounds like you're on top of the situation.
Have fun, learn well. Cheers.

Grumpy,

I appreciate the table,.... I had not seen that one.
It provides more interesting questions,... and perhaps makes
me more confident with my own calculations since it seems that
Vintage JBL sources disagree. Caution is the rule of the day.

Cheers
QDD