The different projects


I added a 4.7ohm serial resistor and a 3.2 ohm paralell  resisor and remeasured with both phases tried out.
The orange one is the the response with the Seas H86 tweeter in the right phase. Reversing (blue) is far inferior and the brown line with no tweeter.  The response as measured on axis from the tweeter at about 75 cm distance shows a decent respsonse. Flat to 10 kHz and a falloff above that without any nasty peaks. Padded down by 10 dB the tweeters are well protected from abuse.

I also tried adding a zobel filter to the woofer to see if it changed the filter resoponse but it is more or less the same so I will not add one. Time to wrap up this one by finding some screws and assemble the speakers, and move on to the next project.


First tweeter trial
I padded down the Seas tweeter by 5-6 dB and tried both phases and none is that good
The black trace is without tweeter. I am surprised at the lift in the top end of the midrange dome. The red trace is with the tweeter in phase with the midrange and the combined output is way to high. The blue were they work out is better in the overall level but the dip at 5 kHz is bad. The measurements are bit rough so I will try to increase the attenuation to 10 dB and see how that pans out. If that does not work out I will try some other tricks with phase tracking around the crossover frequency.

The H86 is not the best of tweeters but  I have four of them and they fit perfect in the cutout for the original tweeter. The Philips tweeters looks like obvious replacement as the rebate does not match with the diameter, so I try to tweek the Seas before falling back on the Phillips, and make some more stringent measurements.

The bass
The drivers are mounted with the boxes filled up with bonded acetate fiber, I do not like to work with fiberglass. The system now have a Q of close to 45 Hz and a Q of  about 1.1. A very good candidate for capacitor coupled closes box. Simply inverting the phase gave good integration with the midrange. Frequency response is on axis of midrange driver at a distance of 75 cm so the room has effect on the response below 400 Hz or so. A nearfield measurment of the  bassdriver show response down to 50 Hz as expected the low pass is a bit earlier than expected. I will make a Zobel filter and see how that affect the interaction between the crossover and the driver. The drivers intrinsic response is flat to 3000 Hz.
The black line is with the driver in phase and the other two is the two loudspeakers. Very good matching.

The Tweeter
Both tweeters are blown, I have some vintage H86 Seas tweeters that are a drop in replacement for the drivers as far as cutouts are concerned. Frequency wise it is far from a drop in replacement. The output is about 10 dB to high. The proper replacement is a seas 19mm metal dome but I will try my hand at the vintage drivers first. If they are padded down 8-10 dB they ought to be very well protected from further misshaps. To bad about the tweeters.


 Progress report
Today I have coated the gray cones of the Seas 21TV-EW woofers with three layers of Visaton LTS-50 speaker compound. Not that the cones need damping, the do not, but the allmost black semiglossy color fits better than the matte gray cone color in original. The drivers had been glued to the old boxes with some white glue. Scraping of that stuff has also removed some of the black color of the chassies so that has been painted. I also need to find some more black screws.

Tomorrow I plan to play around with the Zobel and phase to get a decent match with the midrange driver. Then I will also try to measure the individual drivers. I do not dare to desolder the crossover from the drivers after ruining one ScanSpeak tweeter. Lastly I will add more fiber filling to the cabinets until I reach the lowest resonance frequency and lowest Q. And then I am done with the first pair of those speakers.

Then I might return to my open baffle project Sleipnir...
Kirksaeter Monitor 121
I was asked to try resurect a some loudspeakers. Made in West Germany dates them pretty well.

The familiar foam rot had set in but the midrange and tweeter appeard to be in good condition.
The woofers were open circuit and a dissection suggested that the voice coil had been wobbling around (scrape marks on the bobbin) and causing a break in the coil.

The woofer is a Seas but the model is hard to make out, the sticker printing is really faded

The boxes are well made sturdy and filled with some fiber glass at the back and top. With a high Q driver some improvement can be had by adding more fiber glass or other damping material.

The crossover seems to be quite resonable, probably a mix of 6 and 12 dB filters.

The impedance curve is taxing. Here I had a Seas 8 Ohm woofer replacing the orignal woofer.  The impedance is below 3 Ohm from 150 to 400 Hz the range where music has it's highest power demands. At 6 kHz the impedance dips to 1 Ohm! That is really low but the energy content in music is much lower there so the demands should not be that bad.

With some more damping material added I hope to lower the Qt below 1.0 and the Fr down in the 45 Hz range. The integration between the woofer and midrange might be tricky but I will try to keep the original crossover and use just a Zobel filter and phase switches to get the work done.