Allen mid-range speaker dope

[tschnuckel]

This mid-range seems to work OK, but why would someone have put dope all over the cone like this? I don't think this is the original HC10 from when the organ was installed, because it isn't labeled Main or with a Green dot like the Flue channel speaker. It has always been serviced by Allen. I don't know if you can tell, but it looks like it is caulked to the cabinet. Also seems odd to me. Is this some sort of fix or was it done for tone?

This the same driver, just different angle/lighting.

[toodles]

Using silicone sealant to install a speaker is pretty common for amateur builders as it provides an airtight seal--a good thing. Manufacturers don't usually do it during production because it takes some time, is labor intensive, and takes time to cure. Maybe a service technician did it.

Dope all over the midrange might have been somebody's idea of an improvement, but it changes the character of the speaker and is a bad idea. Maybe a technician did it for a reason--these don't look like any Allen mid range units I have seen.

[tschnuckel]

Are the Mids of a Presence Projector speaker the same as the Mids on an HC10? Or what is a close replacement? I've always thought this organ channel sounded off from other Allen's I've played.

[jbird604]

The mid on the HC-10 was a sealed-back unit, so not the same as on a presence projector at all. About all I can tell you for sure is that it was an 8 ohm driver. Early HC-10 cabinets had a 6.5" Wilder midrange.

Allen was seemingly sort of "experimenting" with drivers when the HC-10 was in production. I seem to recall that several different midrange units were used in various iterations of the HC-10. That ugly thing in your pic might in fact be one of the units they tried out for a while, complete with doping. The crossover design for HC-10 kept changing too, but the mid probably needs to have decent output down to 300 Hz just to be safe. Not necessarily flat down that low, but able to take some signal that low, thus a pretty hefty speaker is needed.

Keep in mind that this was Allen's very first stab at a "hi-fi" speaker, all previous designs being open-back boxes with uncontrolled frequency ranges more or less built by "wishful thinking." The HC-10 was a good first effort, but soon was replaced by the HC-12, a much more carefully thought-out design.

You might remove the mid from the cabinet and see what it looks like in the rear. And remove one of the "better" ones from another HC-10 in the organ. Then you can search various internet speaker drive suppliers to see if you can find a similar unit. That may be a crazy way to replace a driver, but the original is almost surely not available any more, and you may only need to find a good quality modern midrange that will fit the hole and match up with the screws, if possible.

I used to get by with a cheap Pyle midrange to replace the excellent Peerless mids in the HC-12 and HC-15, but I don't do that any more, now convinced that it is better to re-foam the originals. Unfortunately, you don't have that option with this ragged old driver.

[toodles]

Be aware that it is always an option to use an open back midrange or a smallish full range speaker (4 inches through 5+ inches) and fabricate a sub enclosure for the midrange. This may necessitate some modification to the speaker cabinet to acommodate the change.

Note, too, that Parts Express has a couple of 2 inch dome midrange units with sealed backs: RS52AN-8 and RS52FN-8, aluminum and fabric domes, respectively. Probably these should be crossed over at 800 Hz--I don't know the crossover frequency of the HC-10. Both are about $40 each.

[jbird604]

toodles, the HC-10 crossover was revised several times over the brief period of production, as Allen apparently struggled with getting the sound they wanted, while also trying several different midrange drivers.

Looking at the various versions of the crossover on the Allen site, it appears that the most common one had the crossover something like this:

The input to the mid goes through either a 30 mfd or 15 mfd cap, then shunted to ground with a 5 mH coil (or in some versions a 2.5 mH, or no coil at all). Next it went through a coil of either 0.6 mH or 1.2 mH, then shunted to ground through a cap varying from 7.5 mfd to 30 mfd. In some designs, the midrange is IN phase with the woofer, in others, it is OUT of phase! Honestly, it appears they NEVER settled on the best design, just seemed to be flailing around.

So it seems that the crossover point to the mid MIGHT be about 500 Hz, more or less, best I can correlate these components with my crossover calculator. Other than the Peerless mids used in the HC-15, I don't really know of anything that quite fills the bill.

In the past I've order a larger version of the Pyle midrange that fits a 6" hole. Here it is on Amazon:

https://www.amazon.com/Pyle-PDMR6-6-.../dp/B0013CC2SW

If the poster's HC-10 had the original 6.5" Wilder midrange, this one might work. What do you think?

[toodles]

Because of the interaction of the high pass section and low pass section of a mid-range crossover, it's hard to simply calculate the band pass frequencies. It's easiest to evaluate the low pass section for the woofer and high pass section for the tweeter, and then "assume"--and we all know where assuming can lead--that the midrange section is intended to be a band pass between the woofer and tweeter sections.

As to a suitable replacement for the Wilder midranges--a look at the back of the Wilder unit would tell a lot. If it has a deep sub-enclosure, like the Peerless, then it probably has a low Q (something about 1 or lower) and could be used pretty close to its resonant frequency. The Q of the speaker (Qts, specifically) is the gain of the speaker at its resonant frequency--20 times the log of the Qts gives the gain in dB. Most of the sealed back midrange units I see today have a very small sub-enclosure volume and thus have a very high Q, so it's best to set the crossover several octaves above resonance--like 3 or 4 depending upon the Qts.

[jbird604]

The Wilder midrange didn't have a deep back-chamber like the Peerless units do. It looked more or less just like those Pyle drivers I linked to above.

The woofer of the HC-10 was crossed over much like the woofer of the HC-12. The signal first goes through a 5 mH coil, then shunted to ground with a 30 mfd cap. Going by the calculator I use, that produces a 500 Hz second-order crossover, though the cap is actually bigger than it should be for that frequency. They must have wanted to attenuate the upper portion of the woofer's output. Who knows?

But anyway, that more or less confirms what I assumed from looking at the midrange bandpass filter. The crossover point was likely intended to be at 500 Hz at a 12 dB/oct slope.

Those Pyle drivers are advertised as having a response down to 200 Hz, but of course we all know how much stock to place in advertised frequency ranges, particularly from Pyle.

It's just really hard to find drivers for these old Allen cabinets, and in truth they never sounded all that great anyway.

[tschnuckel]

This the speaker with all the dope on it that must have been replaced. The crossover is 911-0141-1.

I haven't done an internet search yet .... it's next.

[tschnuckel]

This the mid as supplied from Allen. I didn't take a pic of the enclosure length, but was its length was pretty equal to the diameter. Crossover is 911-0141 (no dash number)

On a plus side, both HC10s and the B20 sub have the woofer without the foam surround. It has the accordion folds like on an HC12 or 15.

[tschnuckel]

Well tonight I replaced the tweeter in the cabinet with the non-Allen mid. It made a huge difference.

I know nothing about speaker building. I notice non-sealed mid drivers have better freq response than the sealed. Seems the problem is getting a sealed down past the 500Hz for the crossover without moving to a 6" driver. Can I use an non-sealed in a isolation cup or what ever it's called like the CTS and Phillips speakers above? Are those types of things readily available and I just don't know what to search for? Maybe since it works, it's not worth the hassle.

[jbird604]

I don't know if you can buy the back-chamber, but if you can find a stiff plastic cup or bowl of some kind that fits around the back of the driver, you could epoxy it in place (with a bit of loose fiber-fill inside) and accomplish the purpose. Anything to shield the rear of the midrange cone from the pressure inside the box ought to do the trick. Run the wires out through a small hole in the cup and seal around it with caulkling or epoxy.

The problem with using a non-sealed midrange in a sealed cabinet like the HC-10 is that the woofer is using the box as it's "air spring" in order to keep the cone from flapping wildly on lower frequencies. In other words, the woofer cone is VERY loosely suspended and needs the compressed air in the box to keep from ripping itself apart on the lowest notes. This compression effect causes the air pressure inside the box to fluctuate widely as the woofer cone moves in and out.

The changing air pressure is not a healthy thing for the little midrange cone to endure. Of course the midrange cone is fairly stiff and suspended quite rigidly, compared to the woofer. But it could still suffer damage by being pushed around (forced to move in and out at the cyclical rate of the low notes being played by the woofer). This undesired cone movement may also produce "intermodulation distortion" in the midrange tones (a warbling effect as the midrange tones are modulated mechanically by the low frequencies). IM distortion is considered very unpleasant to the ear at relatively low levels, so it could really spoil the sound.

All that said, it might not always be a serious problem. If the woofer cone has already been replaced and happens to be a stiffer paper or accordion-surround cone instead of the original foam or rubber, and if this particular HC-10 happens not to be on the channel that carries pedal stops, and if the midrange cone is quite stiff, it may work just fine. If it sounds good to you, and if the midrange cone doesn't seem to be flexing dangerously as the organ is played, then you might safely leave it alone.

Don't quote me on that, as it is heresy in the speaker design world! And in the interest of honesty and full disclosure, I can think of at least one case where I myself used an open-back midrange speaker to replace a closed-back mid in an Allen organ cabinet, and that was 10 years ago. It sounded just fine and has continued to work without problems. So ...

[toodles]

You've discovered why the loss of the Peerless and Pioneer midrange units with deep cups is such a loss--no one is making such midrange units these days and they were never very common. But that deep cup is what it takes to make a midrange with a decent low end response, even down to around 250 Hz.

If I had to replace something like this, I would indeed use an open back midrange or small full range driver and fabricate a small subenclosure. PVC or ABS sewer pipe is good for such things--heavy cardboard tubes such as those used for carpet or vinyl flooring is also a suitable material. You can fab a rear cap out of plywood or particle board.

Routers with a trammel point or Jasper Jig are very useful (almost a necessity) to make backs and adapter plates. Silicone sealant is good for sealing things.