Pioneer HPM40 rebuild/repair/mod?

I've owned a pair of HPM40s that i got for basically free at a yard sale several years back and have thoroughly enjoyed them, both as a casual listening speaker and a secondary pair of studio monitors, i know people have very mixed opinions on these but i personally like them, at least. However they've suffered some hardship in the sense that one of the tweeters basically fell apart, the dustcap and cone on the other is slowly crumbling away, plus they're pretty fugly, so i've been considering a replacement. I'm decently well versed in the field of audio electronics but i must admit i know very little about speakers. So, essentially i want to switch out the tweeters, currently looking at some silk domes from the likes of Dayton and Monacor that should cover the same range with ease, but have different "recommended" XOver points from what the Pioneer service manual specifies, which is 4kHz on the low end, 10k for the "super tweeter", while the considered replacements range from 2k-2.5k. Is it even worth considering just dropping in the new tweeters and seeing how it pans out or is this generally a no-no? Would i have to reconfigure the crossover with new passives, or maybe build a whole new one? Apologies if this comes off as a dumb question, again i'm clueless :)
 
There are two versions of the tweeter fitted to the HPM-40, but that "copy" tweeter is said to replace either.

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Since you are in Sweden you may like to consider the Scanspeak D2606/922000 Discovery range dome tweeter(€54).

https://www.soundimports.eu/en/scan-speak-d2606-922000.html

It has the required impedance of 6 ohm (not as common as 4 or 8 ohm) as well as the necessary high sensitivity.

However it has a smaller face plate diameter of 104 mm (compared to Pioneer's 120 mm) that may require you to fashion an adaptor ring.

Any other questions, please ask.
 
Since you are in Sweden you may like to consider the Scanspeak D2606/922000 Discovery range dome tweeter(€54).

https://www.soundimports.eu/en/scan-speak-d2606-922000.html

It has the required impedance of 6 ohm (not as common as 4 or 8 ohm) as well as the necessary high sensitivity.

However it has a smaller face plate diameter of 104 mm (compared to Pioneer's 120 mm) that may require you to fashion an adaptor ring.

Any other questions, please ask.
Since this is a very budget-conscious endeavor, one of my first contenders was this model from Dayton, the impedance matches and admittedly I also really like the look of it ;) Do you have any specific idea regarding the necessary sensitivity? I haven't been able to find and detailed specification but maybe i haven't looked in the right places.
 
A dome, i think, would not be as suitable as the cone tweeter.

dave
Interesting, would you mind elaborating on how these behave differently and perhaps what alterations would have to be done to accommodate? Decent quality domes seem a whole lot easier to come across than the cone variety these days. I did also have a minor concern regarding alignment, the factory first gen tweeter portrudes a fair amount from the face of the speaker, many commercially available domes seem to be considerably recessed, would this have a negative effect on the phase correlation between the drivers, and if so would it be advisable to compensate accordingly? Or is it small potatoes? Thanks!
 
Do you have any specific idea regarding the necessary sensitivity?

The necessary sensitivity is that of the "copy" tweeter which is vaguely stated as "90 dB".

Dave (planet10) is a speaker designer so would naturally want to tweak the crossover to suit an alternative tweeter as well as to pay regard to the different dispersion pattern of a dome tweeter compared to a cone tweeter.

However, it would appear that you would be more than happy if you simply got your yard sale speakers up and running at minimal cost.

In that case the Dayton tweeter is worth a punt with its low cost, impedance of 6 ohm and sensitivity of 89.9 dB/1m/2.83V.
 
However, it would appear that you would be more than happy if you simply got your yard sale speakers up and running at minimal cost.
Pretty much, that said I'm hoping to maximize how good i get them sounding in whilst spending as little money as reasonably possible 😅 I think i'm gonna go for it and get some measurements and work my way from there, I do have ome of the original tweeters that i can run some comparisons with after we all
 
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The first generation HPM-40 dates from 1976-79, so it may be worth renewing the 4.7 uF capacitor in the tweeter filter if, as I suspect, it is an NP electrolytic type.

Since you expressed some uncertainty regarding "different XOver points" in your introductory post, I'll add the following:

The tweeter rolls in at 4,000 Hz as dictated by its high pass filter and its response then extends upwards in frequency until it "runs out of steam".

The super tweeter "piggybacks" on the tweeter filter to provide support to the tweeter above 10,000 Hz. It simply provides some "icing on the cake", provided the super tweeter is still working well that is.
 
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Good call, thanks for the insight, i'll give the cheaper tweeters a shot and see how they turn out and compare with the one factory tweeter i have, will definitely recap the xover board if it does turn out to be NP Electrolytic, i haven't dug out the stuffing to check, it does appear , i will post updates and if it turns out nice i'll look into fashioning some sort of nice looking adapter plate, fingers crossed
 
Further improvements could be had by redoing the box as well.
Hey Dave, would you mind elaborating on this? What can be improved with the box, i've been reading that additional/different absorbent stuffing can help "clean up" the low end although i haven't had any major issue with it personally, any other pointers/thoughts?
You’d likely have to fiddle the XO for that.
Also this, in which way do domes play differently and what way can i account for this in eventual alterations to the network?
 
Yes, it looks cool and that's enough!

Best leave the super tweeter alone as, due to its unusual construction, it can be damaged by removal and refitting.

See post #19 here: https://audiokarma.org/forums/index...ribbon-tweeters-on-a-pioneer-hpm-1100.890836/

If you want to check if it is working, place one end of the cardboard tube from a kitchen roll at the tweeter and place your ear at the other end.

This helps to isolate the output of the super tweeter from the output of the other drivers.