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Project HPM-60's... Need advice

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dwintx

New Member
Well, they weren't supposed to be projects, but the evils of ebay have touched me. At least they were cheap. Anyway, I get these 60's, which were supposed to be original and in great condition. I pull off the covers and they look totally wrong. I have had a set of HPM-100's since the 70's, so you can probably guess, I got the early versions that didn't have the cast aluminum baskets like the 100's. Didn't even know there were different versions till I searched and found the posts here.

It still wouldn't be a problem but one woofer is not original and the other's foam is disentegrating. That one is original but when I first saw them I thought both woofers had been replaced cause I thought all HPM's had the cloth surrounds/cast baskets. So I went back on evilbay and got a pair of cast-basket HPM-60 woofers (this was still before I found the early/late posts here) to replace them. Can you see the comedy of errors going on here? They're in really good shape but the cast baskets are bigger than the hole in the early cabs so they won't fit without some messaging.

So now I have two cabs and four woofers, one Taiwanese no-name with a semi-clear cone, one early original with disentigrating foam and two really nice cast-basket late ones. So what do I do? Should I work the cabs and put the later model woofers in there? Are they compatible? Should I fix the foam on the early original and look for another early one? I'm afraid that might be hard to find. Or should I sell the whole mess, take my hit and start over?

I can't believe I didn't ask for pics with the covers off. :sigh: My other hobby is rebuilding classic cars and I'm so careful buying stuff for them, but I'm just getting back into this vintage stereo equipment. Live and learn.
 
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sell the cast basket woofers to get money back ,foam original woofer keep it wait for another woofer here or on epray to finish speakers listen to your 100,s enjoy
 
Thanks for the response, care to elaborate why you would do that? Sound, originality, compatability? If it's just cost, I'm not really worried about that, I didn't spend much for any of it.
 
Oh man, now you're going way above my head. Why might I need to modify the x/o's, how would I know I need to, and how is it done? I can rebuild a Mopar 440, but it scares me to take the cover off a receiver.

Okay, it's not that bad, I cleaned all the pots on my MCS 3125. Gotta remove half it's guts to get to 'em. :)
 
i too was confronted with the same problem a year ago i have two pairs of hpm 60,s for the same reason as you do bad foam woofer, bought cast frame for replacements same problem waited two weeks foam woofer shows up on ebay buy it place it in speaker one week later at local S.A other 60,s show up needing new woofers because someones child thought woofers made nice play toys i was told. just my karma put other speakers in there i also still have pair of hpm -500 speakers WOOFERS 10 inch done in paper cones with foam surrounds by gordon W. our resident speaker god i believe the 500,s are a good fit in the hpm 40-60 speaker maybe another direction to look at
 
i believe there was a thread a while back with the differences beetween the two hpm 60,s electronically and apperance wise it might have been a casuality of the change over which would be bad thing very informative (do a search)
 
It's been said by those who have both styles, that sonically, they are nearly identical. My experience with my two pairs of HPM-40's confirms this. My point is, that both styles of woofers are probably about the same from a technical viewpoint and may be interchangable. I say stick the cast framed ones in there and find out, assuming you don't have to alter the baffle to the point of not being able to go back. Just my opinion, of course. - Mark
 
The woofer specs are different so it won't be a direct drop in, the ports are different and crossover modification will be necessary. In the HPM-60 Series I, like yours, the port is nearly twice as long and has a 90° bend to it, which interestingly should have a bit of felt at the bend. The Series II is, accordingly, short, straight, and fairly shallow.

As to the crossovers, the Series I had a crossover point of 1.2 kHz on the woofer whilst with the Series II it was bumped up to 1.9 kHz. Not that this is of any particular concern, it may hint at other associated changes to account for the woofer differences.

- JP
 
I don't really understand ports. Is that the tube that I see inside the cab? What does it do, just vent air? Does the woofer have to be matched to the port somehow?
 
dwintx,

Those Series I woofers come up on ebay quite often and go very cheap. Usually all the other drivers are offered at the same time too...go for about 10$ a pair.

I wouldn't mess with fitting the cast woofers in. Sounds like enough differences to make it dicey as to what you would end up with soundwise, and unless you know what you're doing with xover shite......man, forget it.

Foam the good one, be patient, and you'll get the old woogers soon. Then your set will be original (the gold cone is sweet looking too and matches the mid).

That long 90 degree tube is a tuning port for for the bass response, and goes down behind the woofer to collect the waves.

PM me with your email and I can send you lots of cool helpful info :thmbsp:
 
dwintx said:
I don't really understand ports. Is that the tube that I see inside the cab? What does it do, just vent air? Does the woofer have to be matched to the port somehow?
Click to expand...
The tube you see is the port I speak of.

I found a quick and simple description of what a port essentially does here.

From: Jim Chaverel

I've always wondered how the ports in a speaker cabinet work. Also, how do they design them or decide how many to use?

Jim, the purpose of the port is to replace the bass that is lost from the main speaker as its effeciency drops off at lower frequencies. As mentioned in an earlier Q&A answer, in order to reproduce strong bass, we either need a larger speaker, more movement of the cone, or both. Since the bass output of the speaker is determined by both the movement of the cone and the size of the speaker, you can see why the bass drops off quite rapidly as the frequency goes down. OK, on to the design of the port. What we do is size the speaker cabinet and the port so that the port will resonate at the frequency below the resonant frequency of the speaker where the speaker output power or loudness drops to half. So, we are taking the energy (in airflow) from the back of the speaker cone, since it moves just as much as the front side, and blowing it into the port. This is no different than blowing across the top of a coke bottle. The idea then, is that this 'free energy' is put to use by replacing the sound that is decreasing from the speaker. Of course, nothing's free or perfect. Since the port is only tuned to one specific frequency, it has a resonant frequency where it works best and provides the most help to the main speaker. A problem associated with ports is due to the fact that we are blowing air through the port. The result is wind noise due to the tumbling of the air through the port. Designers refer to this as port viscosity. What it means is that the walls of the port are a different resistance to the air movement as the air in the middle of the port. So, tumbling of the air occurs. One way to cure this is to use multiple ports to split up the airflow and divide it among the ports. Many designers of multi-speaker cabinets use one port for each speaker. Some use as many as four ports for a large base woofer.
Click to expand...

Basically, the port is tuned to the way the woofer behaves (parameters) and how the volume of the cabinet effects it. By trading out for different woofers, you're changing the tuning of this port and risking poor quality sound.

- JP
 
I have a spectacular idea, mount the wooger with the magnet sticking out, then you will not have to modify the cab (the grill maybe), the internal volume will increase meaning you will not need to modify the port tube or crossover (as it will all be new parameters anyway) and your dispersion with be better.

:D

No, I'm not smoking anything but I should be huh :smoke:

- OK, back to all that tech-talk Blah Blah Blah stuff :boring:
 
Besides.....how could you Frankenspeaker that pretty face ?? :nono:
 

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Well that's the first pic of a series 1 I've seen and I to would not have realized they
were that different either. All the drivers except the HPM look different, humm!

I wonder which set sounds better and mybe even more accurate?
 
Kegger,

I've attached some pics of the internals for the Series I.

FYI.

You may see some interesting differences. I like the long bent port tube....looks like someone was trying something out there. Neat support column in the middle, and wonder what that big baffle brace is doing :scratch2:

Are those xover caps good ones ? or tend to degrade ?
 

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well it looks like they put more engineering and "some" better parts in the series one.

As yes those look to be poly caps "better and last longer" instead of electros as used
in the 60's I have and 100's I've seen.

Not to mention the tuning of the port and the bracing that the others don't have.
 
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Cool.

The Series I is probably more rare. I've seen a lot parted out. Seems like people want to pull these apart rather than restore. Not as sexy as the Series II I guess.
 
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