So, my dad gave me a pair of HPM 1500 he bought while overseas but they have been kept in his attic in the midwest for the last 25+years. The foam on them was already messed up before that but the cones aren’t looking too good either. I’m going to try and refoam and hope for the best, but worst case I will need to replace them and I can’t get oem replacement parts. I was hoping to get some recommendations on 15" drivers for my worst case scenario. As always I appreciate the help.
Have you contacted Pioneer?
If you could get the TS parameters for the driver it would make finding a substitute a little easier.
Not sure what else is needed. And am starting to think I might be in over my head lol. I should probably mention that my knowledge is very limited when it comes to audio. I have not contacted pioneer.
I came across that spec sheet as well, but it does not specify the TS parameters of the driver.
The following should give you a good idea of what TS is and why it matters, but essentially the design of the speaker from the box and port sizes to the selection drivers is all math.
That said, replacing the driver with something significantly different will change everything about it’s sound signature.
Yeah, I started reading up on TS a bit after your first post. And it makes sense why those parameters are needed to get close to the same or the same sound when replacing the driver. I’m not sure exactly where to start looking for those answers unfortunately. thanks again for your help.
/e
It also seems like most people buy a driver and then build the box around it, and I’m trying to do the opposite.
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Which means the chance of getting a similar driver are quite good. 
Sorry I meant in general, unfortunately not for what I’m looking for. I’m hoping the foam replacement will be enough but I doubt it