Hello Speakerplans Community,

since some time I am owner of 8 Martin audio F2B Subs. They are the kickfills of our Soundsystem and work together with 16x WSX an 8x Martin Mach MS1262.

As a lot of you know it can be really hard to find spare L1540/ATC PA100-375BASS 15“ drivers for the F2B. They are also really shallow so it is nearly impossible to find a more modern and robust Driver for this speaker. Also heat is a limiting factor in this enclosure.

As I read in the forums a lot of people are searching for option to use a more modern driver in this cabinet until now only option was to make the chamber a little bit higher which is a pain in the ass to manufacture.

While searching for a new driver my good friend corell (also in this forum) advised me to use the B&C 15FW76 16 OHM as it suits this cabinet really well regarding TS Parameters. Additionally this driver is avaiable also in rare impedance of 16 OHM which allows to amplify all 16 Drivers with 4 OHM per channel on a strong 4 Channel Amp.

Happily this Drivers Magnet diameter is exactly 200mm which brought me to an idea.

In the Photos attached you can also see Pictures of what I am describing now.

In Germany they use for Wastewater so called KG-Pipes they are orange pipes sealed towards each other with a LipSeal. My Idea was to put this seal around the magnet so the magnet is flush with the outside of the cabinet and the pressure chamber still 100% airtight.

This not only gives the opportunity to use a much more efficient driver it also Improves cooling more than every Heatsink or aluminium plate in the backchamber because the Back of the Magnet touches the cool Air and also the hot Air inside the pole Hole can transfered to the outside. Powercompression should be reduced a lot with this modification.

The Mod Consists of 3 Parts that have to be manufactured and one 1,20€ Sealing Ring.

The Sealing can be bought in every hardware store in Germany I dont know if this sealing can be bought easy in other countrys too.

I manufactured all the parts in our Workshop from some scrap pieces.

If people are interested I can also share all the drawings of the Parts which I can make from the CAD-Files I made

Parts:

1.Woodring with Bolt Circle and M6 Drive-In Nuts

2.Lid of the backchamber with recessed Boltcircle and driver cutout.

3. 6mm Aluminium Ring with the same bolt circle like the previous parts.

4. KG-pipe Sealing ring

5. B&C 15FW76 16OHM

6. 8x M6x35 countersunk screw 

I produced one Prototype already for one of my two Halfcut F2B and it worked flawlessly Backchamber is totally airtight and there are no sounds at all coming out of the Pole Hole. It also sounds really nice. And is easy to mount in the speaker.

As it took me quite some time manufacturing the Metal ring on the lathe and milling machine, I am going to let these rings be Lasercut. For the Prototype i made the ring out of 3mm thick steel in the Future this part will be lasered out of 5mm thick Aluminium.

As this is getting cheaper if I order more of these Parts I would really appreciate if people that want to make the same Mod to their F2Bs and need the Parts tell me and I can order the Parts here in germany and ship them to the person. I will make 16 of this rings in the next future. If you need this Part write me a PM and I will try to help.

The wood Parts are produced on our CNC machine. Which we use to mill speakerparts.

I needed to manufacture one Special-Tool for finding the Center of the Driver on the backchamber Lid. This centerpoint was then drilled to 8mm to use it as reference point on the CNC so the milling is exactly on the right point without having inaccuracys of length measurements.

After cutting out the parts the Woodring needs to be glued to the inner part of the lid for centering the wood ring I just mounted the parts together with glue and tightened the screws. Alternatively you can also just put for screws to put the two woodparts together.

As this was the prototype I did not put the handles but The original handles will be mounted recessed in the Lid again with this Mod. Adam Hall 34001 handles were originally used for F2B and they are really comfortable for carrying this heavy speaker.

The middle of the Driver is 4mm higher than the surface of the Speaker. To prevent it from being scratched while transportation and to ensure a certain distance for hot Air to dissapear between the cabinets when stacked next to each other I will also mount on the side some wood bars which will also help to protect the paint from being scratched when the cabinets is pushed over the floor of a truck or a trailer.

I want to make some Outdoor measurments of Frequency response with my friend corell when I am finished with the second Backchamber and want to compare it 1:1 with the F2B equipped with the original L1540 Driver. So this mod can be judged regarding measurments. I will keep you updated in this Thread if people are Interested.

I am open to share any Files and Ideas of this project to give something back to this community and maybe help someone.

Best

Martin

ToDos:

-Put Wood Bars on this Side of the Cabinet as feet to protect back of the Driver

-implement the the original handles in the Lid

-frequency Response Measurments comparing it to original Driver L1540

-if needed Drawings with Dimensions of the Parts for people to do the same Mod

-build this Mod for all my 7 F2Bs and 2 half F2bs

PS: I have 13 fully working original Martin Audio L1540 Drivers and would be open to give them if someone is interested and want to have them write me a PM!!! 

Tool for finding and marking the Center of the Speaker on the Lid (Sheet metal with bolt pattern of L1540 Driver and a spike mounted in the middle for marking the wood)

Metalring for compression of the seal

The Woodring cut on the CNC

Milling work on the Lid the center part of the circular Milling is taken out

Assembly of the 3 Parts

Lid mounted without Sealing inserted

Lid mounted with the sealing firmly pressed inside the gap (Sealing needs to be inserted in the right direction with the tip of the Lip facing down)

Near view of the Sealing 

Metalring mounted and screws tightened to additionally compress the Seal around 1mm.

Modification finished

Front view of the halfcut F2B showing that the Driver is nearly flush with the outside and the middle of the Driver Sticking out 4mm.

Some more F2Bs waiting for new Driver