I just finished building a pair of Pensil 12s with Alpair 12P drivers and today I installed the drivers after running them in for about 100 hours playing a classical music radio station at low volume. I stuffed the cabinets and closed the backs and hooked them up to my 300B amp and one cabinet sounded excellent (if a bit toppy) and the other sounded just horrible, as though the driver is damaged. It sounds badly distorted, as though the cone is ripped or coming apart. I opened the back to see if some of the stuffing was contacting the back of the speaker cone, but it looks fine.
This is my first real speaker building project (I've built a few open baffle speakers, but nothing like this), and I don't know how to diagnose the problem. I built the cabinets using the Pensil 12 plans on the Planet10 site and I made holey braces for them. When I installed it, the magnet of the driver in question wasn't quite touching the brace behind it, and I added a couple of strips of sandpaper to fill the gap, so I don't think the driver is being deformed by the brace.
I glued 1/4" thick wool felt to the walls around the driver, but not on the front wall itself.
I built both cabinets as identically as I could. There's nothing about the bad sounding cabinet that makes it different from the other one.
Here are some photos:
The wool felt
The driver installed
The stuffing
The cone of the unhappy driver, which looks fine to my (untrained) eye
I have so little experience building speakers that I don't know what the problem might be. Of course, I'm wondering if I simply got a defective driver (bought them from Madisound), but I thought I'd ask here before deciding I didn't inadvertently cause the problem.
This is my first real speaker building project (I've built a few open baffle speakers, but nothing like this), and I don't know how to diagnose the problem. I built the cabinets using the Pensil 12 plans on the Planet10 site and I made holey braces for them. When I installed it, the magnet of the driver in question wasn't quite touching the brace behind it, and I added a couple of strips of sandpaper to fill the gap, so I don't think the driver is being deformed by the brace.
I glued 1/4" thick wool felt to the walls around the driver, but not on the front wall itself.
I built both cabinets as identically as I could. There's nothing about the bad sounding cabinet that makes it different from the other one.
Here are some photos:
The wool felt
The driver installed
The stuffing
The cone of the unhappy driver, which looks fine to my (untrained) eye
I have so little experience building speakers that I don't know what the problem might be. Of course, I'm wondering if I simply got a defective driver (bought them from Madisound), but I thought I'd ask here before deciding I didn't inadvertently cause the problem.
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The best way to check for a bad driver is to swap it between the cabinets.
Of course, you've already swapped the entire speaker systems between the L and R sides to rule out the rest of the stereo system, right?
Of course, you've already swapped the entire speaker systems between the L and R sides to rule out the rest of the stereo system, right?
Double check all the connections. Swap the channels to make sure it's not the connection to the amp. Check the distorted driver's connections (on the frame), and check it with a multimeter if you have one. I just checked one of mine, and it measures bang on 8 ohms.
If you can confirm it's a driver issue, maybe Madisound will exchange it if they have any left in stock.
jeff
If you can confirm it's a driver issue, maybe Madisound will exchange it if they have any left in stock.
jeff
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Yes, I swapped channels to rule out something else in my system, and the distortion followed the speaker.
I'll swap the drivers between cabinets and report back.
But I just thought of something else: I soldered the connections at the driver end and one connection on one of the drivers (I don't know which one) got a second round of solder because I didn't think I used enough the first time. Could such extra heat from my soldering iron cause the distortion I'm hearing? We're talking an extra 5 seconds of heat a minute or two after the first 5 seconds of heat.
I'll swap the drivers between cabinets and report back.
But I just thought of something else: I soldered the connections at the driver end and one connection on one of the drivers (I don't know which one) got a second round of solder because I didn't think I used enough the first time. Could such extra heat from my soldering iron cause the distortion I'm hearing? We're talking an extra 5 seconds of heat a minute or two after the first 5 seconds of heat.
Just make sure there is continuity thru the connection to the tinsel leads that go to the voice coils.
jeff
Well, it's the cabinet, not the driver. I swapped drivers between cabinets and the distortion stayed with the one cabinet rather than following the driver. I measured both drivers and they each had continuity from solder connections to voice coils and each driver measures 7.2Ω resistance.
I'll take another long look at the "bad" cabinet tomorrow. I checked the connections on the binding post end and they seemed OK, but I'll resolder them just in case. Maybe it's as simple as that. I did use cheapo terminal pins that fought me when I soldered them to the internal speaker wires.
I get the impression that you all think the issue is an electrical connection rather than the build of the cabinet itself. Correct?
I'll take another long look at the "bad" cabinet tomorrow. I checked the connections on the binding post end and they seemed OK, but I'll resolder them just in case. Maybe it's as simple as that. I did use cheapo terminal pins that fought me when I soldered them to the internal speaker wires.
I get the impression that you all think the issue is an electrical connection rather than the build of the cabinet itself. Correct?
Yeah it just sounds like a bad connection. My Super Pensils have standard issue plastic terminal cups. Like these but with plastic hex nuts: https://www.parts-express.com/Round-Speaker-Terminal-2-15-16-Gold-Binding-Post-260-283?quantity=1 Why not install those while you're working on the cabs.
jeff
Check the surface if it is a little crooked where you screw the driver to the box. If the element is warped in any way, it can be exactly as you wrote.
That was it, LeifB60! I unscrewed the driver and sure enough it rocked a little against the rebate (is that the term?) I'd routed in the cabinet for it. The rebate surface itself was flat, however. I think the problem was the way I had arranged the speaker wire; it must have been getting in the way somehow and throwing off how the driver was seating. Once I found a different path for the speaker wires and reinstalled the driver, the distortion was gone. A telltale sign was how much easier it was to install the screws once I'd rerouted the speaker wires.
Thank you all for your help. I couldn't have tracked down the problem without it.
Thank you all for your help. I couldn't have tracked down the problem without it.
