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Pioneer HPM-900 Refresh

mrichmond3d

mrichmond3d

New Member
First post here but thought you guys might like to see some speakers I'm working on. I found a set of Pioneer HPM-900s on Wallapop or one of the other new classified apps (c'list has gotten so expensive for vintage gear near NYC). They were only $75 but were in fairly rough shape. Both 12s need new foam one of the 12" graphite cones was badly cracked and one of the cabinet had moisture damage where the seams on the bottom edges expanded. After repairing the crack with superglue, I moved them into my main system to test them.

My current speakers are Allison CD-8 with a Spec-1 pre and Spec-4 power amp. I've been generally happy with the Allisons but have always wanted to try some JBL L100s or 4311s but when these HPM-900s popped up, they fit the bill. The Allisons have much more dispersion but the Pioneers seem to have the edge in range, articulation and power handling. My main complaint on the Pioneers is that I feel like I'm hearing resonant frequencies of the box. After listening to them for a few days, I've decided that they make the cut and are going to replace the Allisons. Also, after A/B testing the speaker with the superglued driver vs the undamaged I can hear no difference and it's not falling apart when I give it plenty of power.

Now the issue is cosmetics. Not being a fan of the vinyl wrap, I've decided to veneer them in real walnut and add an internal cross brace.View media item 6222
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I used a heat gun to help remove the original vinyl. It wasn't too difficult to remove. The last photo is the brace that I'm installing inside the cabinet. I'm going near the middle of the cabinet above the woofer but below the port. In this position, the sides have a resonant frequency approximately the same as the bottom and top. It's a much higher pitch; hopefully outside the range of most vocals. I'm going with a piece of solid walnut approximately 3/4" x 1 1/4" to minimize amount of internal volume that I'll lose.
 
It looks like you're planning on screwing in from the outside to install the brace. Might I suggest that you anchor them internally instead? If the screws ever loosen, they'll poke right through your veneer.
 
The brace is done - I screwed through the sides but also glued and there's a layer of bondo on top of the screws between the veneer so I doubt they will ever back out. Plus I don't have a reduction in volume from installing cleats to mount them to.

I'm using Walnut PSA backed (pressure sensitive adhesive) veneer. I've never used it before but it's great. No fumes from contact adhesive and goes on very flat. It took a lot of filling and sanding those bottom edges. The joints were still air tight, just ugly. Filled the big cracks with Bondo then sanded it back to a sharp corner. I think this speaker is stronger than it was originally now!

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Excellent. I really like that PSA veneer, too. I used a hand file like this one on the edges with great results.

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Very nice idea and a nice sounding speaker from Pioneer. Will be interested in your final results. Any plan to upgrade crossover?

I would have been tempted to add a brace in the side to side direction to or simply glue battens to the inside to stiffen the sides. Probably could add enough stuffing or fiberglass to compensate for the loss in volume. If cross brace you could always cut it out but I would wager you some tasty brews you would not want to.
 
The crossovers are working fine but I'm going to replace all the caps with 1% tolerance Daytons. I think that'll be a worthwhile upgrade while I have them out. I was a little surprised when I saw the woofer runs full-range on these but they sounded great to me when I was testing so I'm not going to mess with the design.
 
Zonker92 said:
Excellent. I really like that PSA veneer, too. I used a hand file like this one on the edges with great results.

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I trimmed the edges of the veneer flush with a razor blade and then sanded it smooth. The blade worked better taking multiple passes with very light pressure. I got a little tear-out when I used more pressure.
 
I forgot to mention that the lower back of one cabinet was so swollen from moisture damage that I had to shave it all down with a sure-form. After that, I leveled it with a thin layer of bondo.
 
Wow looking great! I had some HPM 900 and thought they were very enjoyable. I'm sure those new caps make a nice improvement. Keep us updated! ☺
 
The next step is to either re-cover the grills or build new ones and figure out stands. I have an 11 month old daughter and I worry about her little hands on the graphite cones. I'm thinking about maybe building a wood framed grill or at the very least adding some reinforcement bars in the original in front of the woofer. I wish these had a metal mesh over the woofer like Yamaha NS-1000s. Maybe I could fit a stock metal mesh 12" grill. Anyone have experience here or have other thoughts?
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You could try looking for a grille designed for car stereo woofers, but due to the aluminum flange, I doubt you'll find anything that looks even remotely stock. You might also have an issue of them pushing into the grille cloth if they protrude too much.
 
swechsler said:
You could try looking for a grille designed for car stereo woofers, but due to the aluminum flange, I doubt you'll find anything that looks even remotely stock. You might also have an issue of them pushing into the grille cloth if they protrude too much.
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Yeah, that or a PA type cover. I was thinking these perhaps: http://www.parts-express.com/12-waffle-type-black-steel-speaker-grill-with-rubber-edge--260-374
I'm pretty sure there's plenty of clearance under the fabric grills. Hope I can use the speaker mounting screws for the bracket so they're completely reversible.

Listening to them now with an Adcom GFA-1 and they sound great! I'd accidentally installed one set of terminals backwards but quickly hear they were out of phase. So far, they're very articulate and not as bass heavy as I'd expected.
 
I love my 900's, they've been in the family since new, they are a great speaker, and even better loud.
 
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