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Multi-Way Conventional loudspeakers with crossovers

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Old 8th June 2016, 01:39 AM   #31
bwaslo is offline bwaslo  United States
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Quote:
Originally Posted by AllenB View Post
How do you test a spider? I suppose I'd be adding a little mass at a couple of symmetric locations part way out or damping it with my fingers. Surround maybe the same.
As it is out of the woofer's used passband, and as it turns out not to be the cause of the mysterious HD2 peak, it doesn't matter what it is now (for this design at least).
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Old 8th June 2016, 01:55 AM   #32
bwaslo is offline bwaslo  United States
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OK, the secret of a wasted afternoon is now to be revealed.

It's something in the crossover. An ERSE solid-core inductor, to be exact.

When I took a pair of pliers and squeezed its laminations together, the distortion product went away -- completely. Even with the woofers disconnected, it appears that the inductor was able to impress enough 2nd harmonic onto the system (through a longish speaker cable back to the amplifier) to show up on the analyzer plot.

Here's the current schematic --
Click the image to open in full size.

If I had been smart enough to use stuff in my own simulator program, I would have discovered that:
1) With the woofers connected, the current through L1 peaks at ~450Hz.
2) With the woofers disconnected, the current peak moves down to ... 350Hz. And also the system impedance dips below an ohm... oops, rookie move, can't just remove the driver and assume the crossover won't suck current.

So, next move is to either clamp the laminations with something, or get some different inductors (2mH, not a small inductor or something I have a lot of around), put the speaker and crossover back together and make sure there aren't any new surprise distortion peaks.

to be continued....
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Last edited by bwaslo; 8th June 2016 at 01:58 AM.
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Old 8th June 2016, 02:05 AM   #33
xrk971 is online now xrk971  United States
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Great detective work. You heard about my frustrations with months of a wierd 50Hz bass peak that turned out to be a hidden SRS sound processor?
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Old 8th June 2016, 02:11 AM   #34
bwaslo is offline bwaslo  United States
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Any ideas on how to fashion a non-ferrous clamp on the inductor laminations? Or maybe dip the whole thing in lacquer?

The alternative is to go with one of their "Super Q" inductors (for near 3x the price). Probably should replace L4, too. Too much inductance needed to go with an air core coil -- by that time, an active crossover starts to look really good.

BTW, it occurs to me that this little adventure shows that there may be something to "bi-wiring". Probably if the mid and woofer circuits weren't sharing the same milliohms cable resistance drop, the inductor distortion wouldn't have been able to get into the other drivers....
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Old 8th June 2016, 02:15 AM   #35
bwaslo is offline bwaslo  United States
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Originally Posted by xrk971 View Post
Great detective work. You heard about my frustrations with months of a wierd 50Hz bass peak that turned out to be a hidden SRS sound processor?
Pretty poor detective work, actually. Should have been more methodical, would've saved time.

I'm wondering whether a secret SRS might be what messed up my "near the wall" measurements earlier. I was playing test tones through a TV system and media player then because I was too lazy to drag my other stuff upstairs! Pretty sure the TV has SRS, would they have been dumb enough to have it affect the line outputs as well? (The EQ and balance controls don't affect the line outputs though, so I just assumed...)
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Old 8th June 2016, 04:29 AM   #36
bolserst is offline bolserst  United States
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Originally Posted by bwaslo View Post
Any ideas on how to fashion a non-ferrous clamp on the inductor laminations? Or maybe dip the whole thing in lacquer?
I have had luck quieting noisy inductors with a tightly stretched wrapping of PVC electrical tape around the core.
Of course, the best solution is dipping in wax or varnish.

Thanks for sharing this unexpected source of distortion...something new to keep an eye out for.
It reminded me of the surprisingly detrimental effect a single twist tie can have on an air core inductor.
Distortion in MTM build
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Old 8th June 2016, 06:19 AM   #37
bwaslo is offline bwaslo  United States
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Hmm. I was just thinking about trying plastic cable wire ties to snug all the laminations together (I like the price, hope it works). Tomorrow..

Varnish seems like it should be good, but I think it might be difficult to get it to go between the laminations -- I think I read that high end transformer makers apply varnish in vacuum to pull the air out. Maybe I'll get some varnish and do both varnish dip and cable ties, can't hurt.
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Last edited by bwaslo; 8th June 2016 at 06:39 AM. Reason: CABLE TIES, not tie-wraps....
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Old 8th June 2016, 06:38 AM   #38
bwaslo is offline bwaslo  United States
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Originally Posted by bolserst View Post
It reminded me of the surprisingly detrimental effect a single twist tie can have on an air core inductor.
Distortion in MTM build
Thanks for that link, I hadn't seen that! Makes sense.

So, if you want 3rd harmonic distortion, use a wire twist-tie around the core. If you want 2nd harmonic, have the laminations be slack.

Maybe this can be the next audiiophile tweak -- think I can get ;philes to buy $100 per pack audiophile cable tie clamps to put around the cores in their speaker crossovers?
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Old 8th June 2016, 09:30 AM   #39
wesayso is offline wesayso  Netherlands
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Originally Posted by bwaslo View Post
Maybe this can be the next audiiophile tweak -- think I can get ;philes to buy $100 per pack audiophile cable tie clamps to put around the cores in their speaker crossovers?
If you translate this to their usual language you just might
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Old 8th June 2016, 04:08 PM   #40
bolserst is offline bolserst  United States
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Originally Posted by bwaslo View Post
..Varnish seems like it should be good, but I think it might be difficult to get it to go between the laminations -- I think I read that high end transformer makers apply varnish in vacuum to pull the air out.
Yeah, the wax and varnish used is low viscosity so it will wick up in between the laminations.
Vacuum is used if you need absolutely all air pockets removed; a must for HV applications.

Hmmmm....I wonder if some thin CA glue would work for bonding the laminations together thru wicking action?
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