Curved Small Thor Redux

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Well, I lied when I said I had finished crossover design mods! After living with the speakers for about a year now, I felt the mid to upper bass could be better, and the treble was still too bright on some sources.

A good friend brought over his KEF LS50s for a comparo, and it was quite revealing. The Thors were clearer and more transparent overall, but also much brighter. The little KEFs also had that mid-bass punch I felt was missing vs. the much larger Thors.

So I contacted the ever helpful Jim Mitchell once again, and he suggested going to 12 AWG chokes in the bass section, and perhaps lower the 1.2 mH choke to 1.1 or 1.0. And for the treble, raise the 2.7 ohm resistor further.

I ordered a pair of 0.75 mH 12 AWG chokes (not able to readily find 0.70mH 12 AWG versions). I had a pair of 1.0mH 12 AWG foil chokes from a previous project on hand, as well as 3R0 and 3R3 resistors to try in the tweeter circuit.

Using the AudioTools RTA app and the little Parts Express calibrated mic on my iPad, as well as listening to various tracks, I experimented with the following options:

1) unwinding the 0.75 chokes to a value of 0.70,
2) rewinding back to 0.75mH,
3) raising the tweeter resistor to 3R0 and 3R3.

For my speakers in my room, I found the 0.75mH and 1.0mH chokes restored the missing bass, and the 3R3 resistor tamed the overly bright treble, smoothing out female vocals in the process.

Jim very kindly sent me some simulation plots to show what the changes in the crossover design looked like. The 1st image contains the overall system plots, the 2nd shows the difference my changes made to the original. The difference plot shows a 1db boost in the mid-upper bass, with ~ 0.75 db cut in the treble.

My AudioTools RTA 'in room' measurement plots are very close to the differences seen in Jim's plots, even the wiggles in the difference output plot were visible.

A 1 to 0.75 db shift may not seem like much, but the differences are clearly audible. I'm much happier with the overall sound of the speakers at this point.

The other discovery I made along the way was that the speakers sounded oh so much better running off the 8ohm taps rather than the 4 ohm taps on my Audio Research power amp. Much smoother overall presentation with that simple change.

But being an ever restless speaker builder, I'm gearing up to start another project, one which should advance my system to another level. Just as I've always loved the Sonus Faber design concepts which inspired this Thor build, I've also admired the Wilson Audio Watt/Puppy & Alexia designs. I'm honing in on Troels Gravensen's ATS-4 as my likely project.

It was interesting showing pics of the Alexia to my family. Both my wife and son thought the Alexia was really ugly, while I really like the form follows function of the design. People also believe the speakers are a lot larger than they actually are, and that seems to be partly appeased when shown some dimensions. But they still think they are ugly. So the woodworker in me sees that as yet another challenge.
 

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inductor

I am building thor with your cross over drawing.
I am having hard time to find 0.37mH 20AWG.
When I google it, I only can see 0.37mH 18AWG(currently all sold out) and
0.35mH 20AWG.


Can you share where did you get the 0.37mH 20 AWG?
or Is it okay to use 0.35mH 20AWG?
 
Chunki, .35mH should be ok, but you may be better off buying the next biggest size (.40mH?) and unwinding some until you reach .37mH. A decent LCR meter is no more expensive than a lot of larger inductors these days, or see if you can borrow one if you don't think you'll need it again.

BTW, I just recently found this thread after looking for ways to fix my Odin speakers, and am building a set of small Thors with the crossovers above in post #41. Looking forward to hearing the improvement.
 
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