I have a set of JBL L60T speakers that are in need of a surround
replacement. I know that I can replace the surrounds with rubber
instead of foam, but I am interested in changing the drivers
altogether. The internal dimensions of the cabinet are about 1.6 cubic
feet, which makes it difficult to find really good replacements. The
other issue is that the overall efficiency of the cabinets are about
89 db. I would like to increase this moderately but realize that by
doing so, I am also modifying the function of the crossover networks.
Can anyone recommend which route I should take with replacement??

Thanks in advance...

Brad wrote:

I have a set of JBL L60T speakers that are in need of a surround
replacement. I know that I can replace the surrounds with rubber
instead of foam,

There could be minor parameter issues, but it appears to be the wiser
solution.

but I am interested in changing the drivers
altogether.

What is it that you want to obtain?

The internal dimensions of the cabinet are about 1.6 cubic
feet, which makes it difficult to find really good replacements.

I don't see a problemk, appears to be a very reasonable volume for a
probable 8" unit.

The other issue is that the overall efficiency of the cabinets
are about 89 db. I would like to increase this moderately

Simply said you can't unless you also increase box volume, more LF
efficiency generally as a simple guideline necessitates a larger box.

but realize that by doing so, I am also modifying the function
of the crossover networks.

That is - almost - the least worry. Cabinet tuning could be a larger
worry, it is already a "concern" when using a non-standard front
suspension, but the front suspension is not likely to alter a units
properties all that much, this based on gp knowhow gained from Duelunds
unit rebuilds in the 1970-ties.

Can anyone recommend which route I should take with replacement??

Use original spareparts, you loudspeakers will then be ebayable, ebay
them, get something else that solves whatever it is you want solved.

If you want to use a different bass unit, then the best avenue is to
start with designing a proper box for it and DO maintain the box width,
it is a parameter in the cross-over design for acoustic reasons. Build a
smaller box for the original "top-units", whatever they are, and do
maintain distance to side of box as well as to top of box, both are also
likely to be parameters in the original cross-over.

There are two possible outcomes: the upper range frequency response and
the induction of the voice coil of the new unit will be similar enough
to the original unit for the sound to be acceptable or not.

Both are compensated for in the current cross-over. If it is a 3-way
then the frequency response issues may be so well correlated with unit
size that the compensations fit. The cross-over may be designed so that
a simple tweaking of a capacitor and resistor in parallel with the unit
is all that is required, or it may be computer optimized to use the
least amount of components for lowest manufacturing costs, in which case
it is untweakable.

Thanks in advance...

Yes, you can also try simply inserting another bass unit. Bass reflex
tuning will be incorrect, the simple solution is to close the port. No
matter the units mid-band efficiency rating you will loose bass range
efficiency or at best maintain it, it will not increase, not even if you
find a unit with a rated 6 dB higher efficiency.


Kind regards

Peter Larsen

--
*******************************************
* My site is at: http://www.muyiovatki.dk *
*******************************************

Peter,

Thanks for the technical advice. I guess my primary concerns for this
post were pertaining to cabinet volume and driver specs, having built
cabinets for speakers in the past. At this point, the most probable
solution is to replace the surrounds and get a little more time out of
these speakers.

Was it you that recommended getting some Tannoys in the other forum??
I've thought of getting new speakers in the past, but it's kind of
like selecting a mate for life...while they look and sound pretty good
at the store, you get them home and you find out about those little
things that irritate you. I used to work in the audio industry, so
buying decisions are few and far between. Srarting medical school has
not helped either due to the lack of time spent actively listening.

I'll figure it out, but thanks for the insight.

Brad

Peter Larsen wrote in message ...
Brad wrote:

I have a set of JBL L60T speakers that are in need of a surround
replacement. I know that I can replace the surrounds with rubber
instead of foam,

There could be minor parameter issues, but it appears to be the wiser
solution.

but I am interested in changing the drivers
altogether.

What is it that you want to obtain?

The internal dimensions of the cabinet are about 1.6 cubic
feet, which makes it difficult to find really good replacements.

I don't see a problemk, appears to be a very reasonable volume for a
probable 8" unit.

The other issue is that the overall efficiency of the cabinets
are about 89 db. I would like to increase this moderately

Simply said you can't unless you also increase box volume, more LF
efficiency generally as a simple guideline necessitates a larger box.

but realize that by doing so, I am also modifying the function
of the crossover networks.

That is - almost - the least worry. Cabinet tuning could be a larger
worry, it is already a "concern" when using a non-standard front
suspension, but the front suspension is not likely to alter a units
properties all that much, this based on gp knowhow gained from Duelunds
unit rebuilds in the 1970-ties.

Can anyone recommend which route I should take with replacement??

Use original spareparts, you loudspeakers will then be ebayable, ebay
them, get something else that solves whatever it is you want solved.

If you want to use a different bass unit, then the best avenue is to
start with designing a proper box for it and DO maintain the box width,
it is a parameter in the cross-over design for acoustic reasons. Build a
smaller box for the original "top-units", whatever they are, and do
maintain distance to side of box as well as to top of box, both are also
likely to be parameters in the original cross-over.

There are two possible outcomes: the upper range frequency response and
the induction of the voice coil of the new unit will be similar enough
to the original unit for the sound to be acceptable or not.

Both are compensated for in the current cross-over. If it is a 3-way
then the frequency response issues may be so well correlated with unit
size that the compensations fit. The cross-over may be designed so that
a simple tweaking of a capacitor and resistor in parallel with the unit
is all that is required, or it may be computer optimized to use the
least amount of components for lowest manufacturing costs, in which case
it is untweakable.

Thanks in advance...

Yes, you can also try simply inserting another bass unit. Bass reflex
tuning will be incorrect, the simple solution is to close the port. No
matter the units mid-band efficiency rating you will loose bass range
efficiency or at best maintain it, it will not increase, not even if you
find a unit with a rated 6 dB higher efficiency.


Kind regards

Peter Larsen

Brad wrote:

Thanks for the technical advice. I guess my primary concerns for
this post were pertaining to cabinet volume and driver specs,
having built cabinets for speakers in the past. At this point,
the most probable solution is to replace the surrounds and get
a little more time out of these speakers.

Yes.

Was it you that recommended getting some Tannoys
in the other forum??

In some context I may have. Context matters and there is also a budget
context.

My default recommendation is to give KEF Cresta, preferably the
smallest, an audition. I haven't heard that specific model, but it has a
real treble unit instead of the de la mode item consisting of a cutout
from a cola can and a nice price range. I got myself a pair of KEF Coda
(first version, T27 and B200) and they have remained in the household
ever since, and do a very good job since supplemented with a pair of ATC
9" subs. I lament failing to get me a pair of KEF Q15.2's while they
made them, I heard the pair in a shop but it just was not in the budget.
This just to point out that the KEF coax stuff is most charming and
works well in a room. YMMV.

Brad


Kind regards

Peter Larsen

--
*******************************************
* My site is at: http://www.muyiovatki.dk *
*******************************************