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Karlsonator 8 with BG20
Karlsonator 8 with BG20
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Old 26th March 2018, 04:16 PM   #1
Thomasbien is offline Thomasbien  United States
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Default Karlsonator 8 with BG20

A while back I found the Karlsonator discussions here and decided to give it a go for a set of shop speakers with the 8" Visaton BG20 spearkers. Many thanks to the guys who have put so much into this design!

Attached are some pics from the build as well as the completed speakers. The baffle is caulked to seal it to the sides. The back is attached with screws and has a weatherstrip for sealing.

I lined the area behind the driver with felt carpet pad (bottom, sides, back, and back of baffle). The stub is moderately stuffed with Polyfil. I installed craft felt on the back of the apertures from the bottom to about 11" up. I should get some pictures of this to add.

The speakers are built and playing, but I'm having significant issue with the high frequency response being much too harsh. They are quite fatiguing to listen to, which is a problem in the shop where they are always on while I'm working and usually at high volume. I know the BG20's have a rising response, but I thought the Karlsonator design would suppress this.

Using the Audio Tool app on my phone, but without a calibrated mic, I've taken measurements that confirm the rising response. The two screenshots included were taken with speakers on the wall, playing white noise, phone held about 12" away and on center with driver. One picture is with apertures installed and one without. Apertures installed has the step at 1kHz and lower average SPL.

Any ideas on what to do to tame the highs and make them enjoyable in the woodshop? I think a filter is going to be needed. I had hoped to avoid, but if that's what it takes so be it. (And... I will be driving past Parts Express this weekend.)
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Old 26th March 2018, 04:24 PM   #2
Thomasbien is offline Thomasbien  United States
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Found a couple pics of felt. Can get additional.
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File Type: jpg 20180313_194329.jpg (235.8 KB, 108 views)
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Old 26th March 2018, 04:41 PM   #3
xrk971 is offline xrk971  United States
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Karlsonator 8 with BG20
Nice build! Very pretty.
Those are actually very good frequency response measurements. You just need to add a baffle step filter. Try 1mH and 6.8R (10W) in parallel between amp +ve and driver input. Adjust the R value to taste. If too dull, decrease R a little by paralleling a 47R or 22R. Or drop to 5R or 4.7R. If still too bright try 10R.
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Old 26th March 2018, 04:54 PM   #4
Lingwendil is offline Lingwendil  United States
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Karlsonator 8 with BG20
Those look great!

Did you go by the karlsonator "8" original plans without modifications? I've been wanting to do a bigger set of K's and the price on those drivers is pretty nice.

If you want an easier to adjust/tweak baffle step at line level, the one Rod Elliot outlines here. works best in a buffer sandwich, but works well at the input to a preamp if it has a moderate to high input impedance.
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Old 26th March 2018, 06:45 PM   #5
IG81 is offline IG81  Canada
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Nice Karlsonators! While the smaller - mainly foamcore -variants have surged in popularity in the last years, it's still good to see a "full-size" all-wood build.

I've had Philips 9710 in my DIY K12 and if anything, they have an even worse elevated HF response, but it sounded fine to me. I think taming the 3kHz-8kHz plateau of the BG20 might make them sound better to you. BSC, basically a shelf filter, would help, but it would also reduce the output above 8kHz, which you may then find lacking. A wide low-Q notch might be better in this case IMO.
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Old 26th March 2018, 07:48 PM   #6
freddi is offline freddi  United States
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Karlsonator 8 with BG20
in addition to a filter - it might help a bit to take a piece of Dacron long enough to wrap between the whizzer and the main cone - a reversible tweek -- (those look Fabulous !)

Last edited by freddi; 26th March 2018 at 07:51 PM.
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Old 27th March 2018, 01:43 AM   #7
Thomasbien is offline Thomasbien  United States
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Thanks for the comments and suggestions. These were built to the Karlsonator8 plans. Only change was to make the sides extend a half inch past the back so I could hide a French cleat on the back. This makes them easy to hang on a mating cleat screwed to the wall. Comes in handy as they are not light.

I will try the Dacron idea. I found details of this mod some time ago but forgot about it.

BSC vs notch filter is interesting. I did find a couple references to notch filters for these drivers, though not in K type enclosures:

0.68 F, 0.8 mH, 22 Ω in this one:
DIY Visaton BG 20 Single Driver Full Range Speakers

0.47 uF; 12 Ohm; 0.82 mH in this one (German):
Lautsprecher Partybox
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Old 27th March 2018, 01:51 AM   #8
Thomasbien is offline Thomasbien  United States
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French cleat details... 45 degree bevel on both cleats. Screw one cleat to wall, into a stud, and as long as it's level the speaker will be level. Because sides, top and bottom of enclosure extend 1/2" past the back, both cleats are hidden when speaker is hung on wall.
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Old 27th March 2018, 01:02 PM   #9
IG81 is offline IG81  Canada
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I like the addition of French cleats, good thinking!

That first notch filter (0.68 F, 0.8 mH, 22 Ω) should help, I just hope it does not attenuate the 10kHz+ area too much for your taste.
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Old 30th March 2018, 09:16 PM   #10
Thomasbien is offline Thomasbien  United States
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I picked up components for a parallel notch filter with a couple extra resistors to experiment with attenuation level. Trials upcoming.
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