Fostex RP9 swapmeet find. Need info!

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Howdy. Todd here.
I was at a swapmeet, and saw a pair of speakers that were in individual shipping boxes, and one speaker with no shipping box that was smashed up and missing woofer. I noticed that the speakers were Fostex, and had ribbon tweeters and ribbon mid-ranges!
The lady wanted 15 dollars for each one. I didn't want to unwrap the plastic and mess with them. They seemed to have a funky little 3-way crossover box with them (simple 1st order?) which said "for rp-7 or rp-9". It looked to be missing parts, so I just moved on.
Well, I had already been stewing on some speaker projects and lurking on this (and other) audio/DIY websites. I decided to go back today with a double A battery to test the drivers. I opened up the boxes, and took the speakers out completely. I plugged in the crossover network to speaker wire harness (pictures show proprietary Molex style plugs for the crossover and speakers). Then I touched the battery to the crossover input and only the mid-range worked. The woofers did not work, as their surrounds are trashed and coils may have been blown. I then disconnected the crossover network and tested each speaker at the Molex plug. The mid-range and tweeter sounded good to me :) I was happy that the broken third speaker was there, as the grille was trashed and I could see the mid-range and tweeter up close. The grilles are glued on, and I have to rip them off to take out woofers :(
They are now in my possession. I just took some pictures to share with people and see if ANYONE has ANY info on these. I don't know where to get specs for the ribbon units, or the speakers as a whole. They seem somewhat old (80's?) and I cannot find a single iota of information on the interwebz. I also had to tear grilles off, as they are glued on. I took one picture with grille on so you can see what it looks like.
I have strong basic knowledge of speaker design. I have custom built more subwoofer boxes than I can count, including 4th order bandpass, many sealed, and few ported. I have built simple passive crossover networks (2-way, different orders). I have built speakers from well designed kits with entry level speakers.
I was thinking these drivers could be used for a fun project. Alas, I have limited experience with ribbons, and also no specs to start with. :( No testing equipment at all.
I am in SoCal LA area, so if anyone has some cool ideas for me to start with as far as making custom enclosure, and maybe a quality crossover network... I would greatly appreciate it.
This is my first post, so sorry it's sooooo long. But I enjoy telling stories, and you can never have too much info :D

Well.. Here are some photos.
By the way, the crossover says 4ohm, and the woofer says 4ohm...

If the photos do not work, it is because I could not find a test forum on this website for checking to see if I am doing it right. I am new to this site, but not to forums in general :D :p


An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

The back of the cabinet has threaded bolt holes. I have no clue what this would bolt to! Can't put it on a solid wall, as you would not have access to nuts! Maybe it was put on a board, then in wall as infinite baffle? I don't see any felt or type of sealer for woofer baffle where it might attach to a box. They barely stand on thier own, so they are most definitely not OB speakers :D The panel appears to be made of some composite. The woofer has decent basket and magnet. Woofer on one of these is not good, as some dork pushed thier fingers in from behind. Surrounds are totally trashed as expected. I have no intentions of fixing the woofers, or using original panel with new woofer. This will be a "from scratch" project to help me learn more about crossovers, and different baffle options :)

Since the crossover is 4 ohm, I was considering using an 8" Infinity Beta series car woofer I have, and put it in a small sealed enclosure. Make a panel for the mid and tweeter drivers, and place on top of box to see what happens. This crossover network looks very small. Like something you would get with a cheap set of car audio components :D I am going to open them up... Don't need the cover, anyhow. If anyone needs to see a picture of crossover, I will take a picture.

Thanks for your time. I appreciate it. Any input or ideas are welcomed. I am hoping I did not waste 30 bucks on these :( I will experiment with them tonight and tomorrow.

One of the woofers looks as if it can be fixed. The other woofer has crack in the edge of cone due to swap meet people fiddling with it :D The woofers seem to be rigid, yet very light. Possibly carbon fiber, or some composite interwoven material. You can see light through the cones, they look like little dots where the light goes through. They have what appears to be a cast aluminum basket. My Infinity Beta woofers are high quality, and these look to be a step up! The magnet is huge, and has what looks like a 3 inch voicecoil, or bigger! But not worth fixing, in my opinion... Not with one woofer being cracked.
I leaned my Infinity Beta 8 woofers against panel and hooked it up to crossover. Due to no direct contact with baffle (almost 3/4 of an inch gap due to basket mounting plate being different shape), and the woofer being designed for a sealed cabinet, there is NO mid-bass as I expected. But with my sub crossover cranked as high as it will go, it is making it easier to tolerate the sound. When I have the money to buy wood, I will make a small cabinet (.2 cubic feet for flat response, .4 for enhanced response) for the woofers. I am not accustomed to the sound of the ribbons, but it seems so detailed it would be worth messing around with.
I just got a pair of Boston Acoustics VR20's for 100 bucks on craigslist, and they sound ok for the money. I don't like the tweeters (never liked Boston tweets). The ribbon tweet and midrange on the Fostex sounds very detailed, yet a little overbearing due to no cabinet or woofer... Yet I still like the sound a lot better than the Boston!!!! Just need to find the right woofer and cabinet style to go along with this. Time to learn more stuff!!!!

I took the cross-over apart, and it is very small. The coils look pathetic and the caps are tiny :D But they seem to work ok for a typical 1st order...

Thanks for the info, as those tweeters do look similar. Although the tweeters on this unit do not have a rounded metal plate.
Found some pictures online of similar designs.

This first picture shown below is of the Fostek rp-1001 which seems to use same ribbon mid-range and tweeter combination as the RP-9 set that I have. There was another higher model with larger ribbon elements which I decided not to post.

The second and third pictures are of VMPS speakers that seem to be using the same size and possibly same make of tweeter and midrange. I put pictures of both styles to see what options I had for woofer styles and mounting.

The last 2 pictures I am too lazy to look up where I got them. But I do like the idea of a ribbon with a wave guide.

Still have not found any specific information on the older Fostex speakers. But this is a step in the right direction on figuring out what to build for my next project using these drivers... I won't know what to do with them until I know what I have. I have never owned anything with a ribbon on it. :D

I am using this thread to collect info on this model of speaker, and similar designs for the most part. I will start another thread when I figure out what questions to form regarding actual design options as I start working on the "project".

If anyone has seen speakers using similar driver set ups, please post pictures and details. The more information the better.



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I was taking a closer look at the warranty card. I was initially confused by the questions they wanted filled out. They were asking the owner filling out card if they were in a car club, and what brand CAR stereo they owned. What? :D That is when the light went on in my head. No wonder it has such and odd design. It is for inside a vehicle. Like a pimped out shag wagon or something :D
I read the other side of warranty card, and it did mention the warranty only covered the product if it was "professionally" installed in the VEHICLE. Well, wha'dya know!
So, I guess this was some fancy car audio product!!! Very interesting indeed. I tested the two ribbon units, and they are 8 ohms. The woofer was 8 ohm, and the crossover said 4 ohms as well.
I still intend to dismantle this thing and make home stereo speakers with the ribbon drivers in a dipole configuration....
Should this be moved to car audio forum (maybe someone will find this old design interesting?), even though I am going to dismantle the unit? I can always start a different thread in a home audio speaker forum when I am ready to start designing the HOME speaker version of this :D
Thanks... Todd
Hi to you all!!! I'm from Italy and this is my 1st message on this beautiful forum.
I have both the loudspeakers (the midrange and the tweeter) mounted on the
speaker of the 1st post.
The midrange is a FS-41RP and here you are the picture of the 1 that I have
An externally hosted image should be here but it was not working when we last tested it.

The tweeter is a FT-12RP and here you are the picture too
An externally hosted image should be here but it was not working when we last tested it.
Thank you for helping with the part number of the tweeter. I could not find it anywhere on the net, including any pictures. Your first post was appreciated greatly for the help! :D
You said that you had the speaker like I showed in my first post. Where did you buy the speaker? Do you know if it was used in a car stereo application?
Also, I have a suspicion that this tweeter may be the same unit that is used in the Ft7rp, but my tweeter has no enclosure or mount. This is only a guess, as the tweeter I have matches no other smaller tweeter by Fostex that I can find a picture of online. Almost every home speaker made Fostex or other speaker manufacturers uses the FT7-RP tweeter in thier designs, some used with the FS21-RP. Being that this speaker I have is for car and has limited depth due to grille, maybe they dismantled the FT7-RP tweeter driver from it's mounting faceplate to make it fit?
You say that the tweeter you posted is called the ft12-rp but I can find no info in all my searches on the internet. As a matter of fact, your picture is only other picture I have seen of that particular tweeter! I have found limited info on many other tweeter models and mid-range models like the FS41,FS21 and FT7 in the rp series.
Are you going to make something with those drivers? If so, be sure to make a thread!


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These units (couple of Fostex RP9) borns for car audio use.
In italy the price in the firsts 90's years was $ 6.000,00 circa and ideal mounting on back panel.
Excellent sound and very low distortion, isodynamic technology, dipole function (mid and tw).
The kings of car speakers.
I think better listening use in home.
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Nice to see an old RP-9. Its an old CarAudiosystem from Fostex, equipped with a FW220 Woofer, a FS21RP midrange and a RP7 Tweeter. They were launched in the mid of the 80ties and were the NO.1 of the CarAudio scene for a long time. I have heard them several time, a friend runs a ACR (former Fostexdistributor for Germany) Store and he has it installed inside his 7 BMW, together with a pair of 18 inch Woofers in the trunk! The front was equipped with some Boston stuff and driven by Alpine Electronics. That was a fun system, and one of the rare cars that are not only loud. It was incredible loud but it also sounds great! Really a pleasure to hear music in it!
These units (couple of Fostex RP9) borns for car audio use.
In italy the price in the firsts 90's years was $ 6.000,00 circa and ideal mounting on back panel.
Excellent sound and very low distortion, isodynamic technology, dipole function (mid and tw).
The kings of car speakers.
I think better listening use in home.
Sorry, a wrong notice: in the past in italy price was $ 3.000,00 circa.
That was Lira, not Euro.. :tongue:
Too bad the woofer surrounds went bad, and one cone was damaged. Not worth fixing due to rarity. But now that i have measuring equipment and am learning more about PCD7, I hope to build something with them in the near future. I also have a seos12 waveguides with dna360 compression drivers to compare them to.
This is a direct replacement for your bass mid driver Fostex FW 220 by ACR (discontinued).
Volt BM220.8

You can use the same crossover (is it available/not broken?!).
As I was saying, they are very similar and if I find a better one (driver in production) I will post.

The drivers are very similar but as you know (and between good drivers also) it's difficult or expensive, or impossible like in this case, to find a very high sensitivity driver that matches the Fostex because those are generally the most sensitivity in the world "aux pair" with TAD's and others.

So, this Volt driver has about 07.dB lower from the expected with the Fostex speaker. Try to experiment and if it misses something and you need that extra sound swap the inductor* in the woofer section of the filter (if it has one) with one with the same mH but lower DCR.

If not and if you are going to use another woofer make it (driver) flat in frequency to ~2K0/2K2Hz and Re 6.6 Ohms. You can always use a pair or 4 woofers but use the same impedance for the crossover and try to get ~91.0 dB/W/m (or up, that has to do with system Q/crossover/alignement and is possible to calibrate/simulate when designing new speakers). If not you will have to make a new crossover. :D

*)This is an example:

2.0 mH air core Jantzen from Parts Express = $11.00 each = 0.80 ohms DCR
2.0 mH iron core Erse from Parts Express = $ 7.49 each = 0.26 ohms DCR
The Loudspeaker Crossover Part II: Capacitor & Inductor Issues | Audioholics
I have the original crossover parts. They sounded ok with a sealed 8" 4 ohm woofer I had laying around. I had never heard an open baffle speaker before, and it was quite eye opening. The woofers have about 90 db of sensitivity. They are designed for sealed enclosures and don't put out much below 80. But with a sub they sounded awesome. I may build a baffle to set on top of my Cerwin Vega speaker boxes and see what it sounds like.
I spent my last bit of extra money on some seos wave guides with dna360 1" compression driver. Still playing with those.
If I had money, I would have built something already.
When i first got the fostex speakers, i downloaded tons of stuff on the acr line that used the same midrange and tweeter. So i have cabinet volume and crossover info to work with.
I was considering trying an mtm. The lower crossover point might open my woofer selection a little.

I do plan on trying open baffle and sealed enclosure. It requires a 14 liter cabinet.
I am getting a little more knowledgeable on ob speakers. I measured the midrange on it's own, on a basic baffle, and kind of half assed baffle sitting on a .3 cu ft enclosure. Looked good from 750 to about 2.5k
Need to find the tweeters so i can test them and get the le so i can put them all in pcd.
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I dug through my stuff, and found the tweeters.
After measuring them on holmimpulse, I am not happy with what I see.
The distortion is plotted as well on the graph.
One tweeter has some issues. Not sure what it is. I did see that one of the magnets has a crack in it, but it has not moved and is where it should be. Since the tweeters are so different from each other, I may just take one apart just to see what is up. I don't plan on using it now, anyways.
I definitely can't afford new fostex ribbon tweeters right now.
I can buy these in the future: The Madisound Speaker Store (fostex ribbon tweet)

Or look at other less expensive tweeters. My hearing is crap above 7k on my right ear, anyways.
I may consider looking to see if there is a replacement diaphragm available.

The good news, is that the frequency response for the midrange is where it should be, and both are completely identical. Absolutely no variance between the two.
I bought them for the midranges, anyways. So not a total loss.


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