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jdlech 19th January 2008 11:58 AM

Replacement Driver
 
I just took possession of a pair of Kenwood LSP 9000 speakers. The second pair of commercial speakers I ever bought were 9000Ds about a quarter century ago, so this is of some sentimental value. I got these for $50 USD + a couple gallons of gas.

I found some pics here
The pics show the same problem that my speakers (as nearly all speakers from that era) has - the surrounds have disintegrated.

I know I could replace the surrounds, but I remember one important detail about these speakers - the woofer was seriously underpowered for the system.

As you can imagine, at this age there are no replacement woofers for these speakers anywhere in the world at any price. And besides, I would just be stuck with underpowered woofers. So, with sentimentality set aside, I'm looking for a suitable replacement. I figured I could either search forever and not get anywhere (or worse) or I could call for help from people who know what they're doing more than I.

Here's what I know:
The box is 108.6 liters minus minimal bracing (I might add some as it does get boomy) and driver displacement.
It seems to be a 10" woofer with a 12" OD measured kittycorner (square frame, . The cutout is 9 1/2"
That's a 15" passive radiator - I assume it matches both box and woofer. Other than that, I really know nothing more about it.

Electrically, I measured the voice coil Re @ 7.40 ohms.
Total system power rating is 400W RMS and advertised as 8 ohms. But in reality, the things could barely manage to handle 200 watts of normal program power due to the weak woofer.
Any replacement does not need to be a square frame so long as it's OD is 12" so it covers up the old mounting holes.;) I have exactly 6 1/8" from the center of the cutout to the edge of the tweeters, but I can also rout the cutout up to 3/4" away from them, so I can go with any round frame driver between 12" to 13 3/4" OD

If there is some tests that would produce more helpful information, let me know. (and tell me how to perform the test). I would really like to get these back up and running.

All the parts for my test jig and cables for my mike should be here today or monday :cheerful:

jdlech 20th January 2008 12:52 PM

29 views, 0 replies, relegated to the 2nd page....

I guess I'm on my own... or did I say something to tick Y'all off?

Do I have B.O.? Bad breath? Too verbose?

I would welcome suggestions, requests for more information, even speculation.

mashaffer 20th January 2008 09:46 PM

Adapting different woofers is a complex process and I suspect that is why you haven't had replies. Start by downloading a modeling program like boxplot and play with it using parameters from various speakers (parts express is very good about providing parameters on their web site).

If it were sealed or even ported it would be fairly easy to model various possible drivers using the volume that you have (or a little less as you can put something in to reduce volume if needed). For a port you would have to adjust port length no doubt.

However a PR is more complicated and I have no experience to help you. If the PR is set up to allow you to add or remove weight however, you should be able to adapt it for any reasonable driver (vas and Q within a range that models well in your cabinet size).

I believe that there is a method for taking the port tuning information from a bass reflex design and deriving the needed tuning of the PR but someone expert in that area will have to help you with that.

Another option for you might be to make it into a sealed enclosure (or one each for the 12 and 15) and use a plate amp or other sub amp to drive the 15 as a built in subwoofer.

Now another problem you are going to have to deal with is that the old crossover will not really be tuned to your new woofer and you will have serious output level mismatches if you do not closely match the original woofer's efficiency. Bi/Tri amping would of course handle that problem handily.

So it comes down to how hard do you want to work and how much money you have to dedicate to this project.

Sorry, I wish it were simple.

mike

jdlech 20th January 2008 11:03 PM

Thanks,
I'm making a schematic of the xover to get a better idea of what I'm working with. And I have both bassbox/xover pro and Speaker Workshop. So I'll be able to take a few measurments of all but the woofer and even test the coil as a passive component. I just need to build the jig and figure out how to do the tests.

I'm hoping that I'll be testing by next weekend.

sreten 21st January 2008 10:53 AM

Hi,

The speaker seems to have midrange and tweeter level controls
so basically you need a high power, high efficiency (presumably),
8 ohm 12" frame paper cone driver that would work in a ~ 100L
vented box.

Fairly reasonable requirements except 4 cuft is a big box for a
vented 12" - but this does not mean there are not suitable
drivers, just that they would usually be used sealed, most
professional 12" drivers are esigned for smaller vented boxes.

I'm no expert on 12" drivers with Vas > 6cuft and the obvious
solution is to repair the surrounds of the current drivers. Such
presumably cast frame drivers are not commonly available.

To get replacements you really need to know the approximate
sensitivity of the driver and the voice coil inductance / ~ size.

High power 12" have large voice coils but may not suit the c/o.
A lot of them Fs is too high and Vas too low.

Assuming PR is tuned to around 35Hz :

http://www.partsexpress.com/pe/showd...number=290-105

models quite well but nowhere near the power handling you want.

http://www.partsexpress.com/pe/showd...number=290-118

Gives oodles more bass with PR tuned (weighted) down to
around 25Hz at the cost of sensitivity.

I chose these drivers as 12" ers suiting a ~ 100L box vented.

Repair and stuffing the boxes with BAF (to increase apparent size,
will not affect damping that much) is likely your best /safest bet.
If bass is boomy adding weight to the PR will reduce boom and increase extension.

:)/sreten.

other suspects :
http://www.madisound.com/catalog/pro...roducts_id=302



jdlech 7th February 2008 09:09 PM

2 Attachment(s)
Thanks for the suggestions; I have an update. I'm attaching an image of the crossover.

It has a 2nd order filter with a 1.5mH coil and a 15uF cap. Fairly simple stuff considering the highpass is feeding 6 tweeters. But that's not my concern.

I'm still waiting on a cable from P/E before I can start doing any driver testing. But with a nonfunctioning woofer, how would one go about testing the impedance of the rest of the system? One driver at a time, or just with the coil hooked up?

gfiandy 7th February 2008 09:31 PM

If you are up for a bit of a challange you could try a 3.5 way design and use the 15 inch as a very low end support driver as the 10inch starts to roll off. This gives you another degree of fredom in the bass design and as you have measurment equipment you should be able to get a fairly sensible result from it. This should enable you to get a very deep response and control the boom as it would be a sealed type enclosure. It would also mean you could use a PA type driver for the 10 inch which would have a higher roll off but much greater output and you can get just about whatever power handling you want. Depending on how much bass you want you could use a PA 15inch but a driver designed for sub duties would probably be more suitable as it would give you much deeper playback.

Regards,
Andrew

jdlech 7th February 2008 09:57 PM

Certainly food for thought. I hadn't considered replacing the PR with an active driver. That would be quite the challenge - probably requiring a whole new xover.

Probably too costly for me ATM, though. And I would certainly need to reinforce the box.

These speakers had plenty of low end already - it was the power handling of the woofer that was weak, IMO. That and they did sound a bit loose for my tastes. I prefered the tighter bass of the vintage Infinity Studio Monitor series over these. But one takes what one is given.

I would probably want to isolate the two drivers if I were to replace the PR. Naw, maybe someday but not any time soon.

Edit: the more I look at the Pioneer A30IR50-51F, the more I like what I see.

jdlech 15th February 2008 11:56 PM

Sorry for necroposting, but I have an update...

I installed the A30IR50-51F. I had to do a bit of unexpected shoehorn modding on the dust cover. I did not take it into account when I made my measurments. It really should have been a 10" and no more.

I like the depth, but the woofer's response extended too much into the midrange and actually competed with the mid driver. I added a 15uF cap in parallel to the woofer. It sounds a lot better now. I toyed with a .56mH coil and a 33uF cap , but it sounds best with just the addition of a 15uF cap.

A little extra bonus is that the bass is a bit tighter than I remembered it. It must have been the original woofer and not because it was a PR system, as I had suspected. Or my memory is a bit out of sorts. :cannotbe:

I remember the "D" model having a "supertweeter" in place of one of the paper cones - basically just a hard dome tweeter that (assumably) extended the highs up to about 20K. But with my aging ears the way they are, I'm not missing much.

Mission Accomplished - I'd show pics but the ex has the camera right now. Needless to say, the new woofer takes up all available baffle real estate.

Thank you sreten.

sreten 19th February 2008 10:54 AM

2 Attachment(s)
Quote:

Originally posted by jdlech
Sorry for necroposting, but I have an update...

I added a 15uF cap in parallel to the woofer. It sounds a lot better now. I toyed with a .56mH coil and a 33uF cap , but it sounds best with just the addition of a 15uF cap.

A little extra bonus is that the bass is a bit tighter than I remembered it. It must have been the original woofer and not because it was a PR system, as I had suspected. Or my memory is a bit out of sorts. :cannotbe:

Thank you sreten.

Hi,

??? the c/o shows 15uF in parallel with the bass driver. You added
another 15uF ?

Tight bass is alignment, not the type of loading. I suspect your PR
is not tuned to below 30Hz which is what you want on paper.
Using PE's measured parameter and 115L to account for the
increase box volume of some acoustic lining of the box :

:)/sreten.


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