daleh

[Y]

I have 82’ Khorns and I like how the sound with my DIY SE45 amp. My room is only 10’6”x16’6” though. I had to modify the upper x-over to get rid of some overlap in the 4k-6K range and use a 5k:8 ohm output transformer. The power band of this amp is goes is a little down at 4 ohms and 16 ohms with this transformer. A sign wave at 1kHz will put out 105db from one speaker without clipping and sweeping 20-20k will not clip at this input level. Of course the spl varies +/- quite a bit through the range like with any other amp. I want to try a 300b amp next.[H]

I’m not sure if mine is an x-100 or x-101 but I found the best grounding point to be the top of the pre tower. It’s located behind the left side of the face plate and has two tubes mounted horizontally. There is an exposed grounding wire connected to these two tube sockets and I used closest screw to this point to ground my TT. Your unit may not be the same as mine though. Also, if you haven’t done so, try reversing the power plug in the outlet or a different outlet if available.

I don’t know if these use the same drivers as my 82’ khorns but I found too much overlap in the 4k to 6k range with the stock values of the AA crossover. I ended up crossing the tweeter higher more like the AK and using the bridge cap trick to make the slope steeper and kill the 3.3k resonance of the tweeter at the same time. Rolling the squawker off lower as suggested would probably be better if you have the older one that’s not soldered on.

One more picture if I may. This is with a 4th order high pass on the tweeter. 2uF>125uH>4uF>900uH. The interaction has been further reduced and the 1/24 octave resolution still looks pretty bad. Smoothing to 1/3 octave resolution doesn’t look bad at all other than the high frequency peak, it’s within +/- 1db through the crossover region. This is an order of magnitude better than the stock values which had the tweeter and midrange overlapping at full strength from 4 kHz to 6 kHz. The proof is in the sound though so I’ll have to see if I like it better. Now I have to wind another 900uH coil for the other side.

Thanks for the tip, I’ll check it out. The squawker has no low pass on it that I can see but it rolls off quite nicely at 6 kHz as seen on the graph above. I’m sure everybody knows this but if you click on the graph it is much easier to see. Here’s another. The lower trace is continuous pink noise at 90db SPL and the top is a quick sweep that is supposed to eliminate room interactions. The speaker is pulled out from the corner and the mic is about 3’ from the tweeter.

Here’s a shot of the measurement I took. There is still a lot of interaction with the area just under the 6 kHz crossover point but no where near the stock configuration. I’m thinking of trying a 4th order high pass to see if I can get it a little cleaner. I don’t see a model# on the tweeter but it has a square brownish magnet. The test rig is DBX measurement mic> M-Audio 610>TruRta.

The measurements were done with a microphone on axis at about 4’. The 55s are V’s with the soldered connections, not sure about the tweeters, maybe I’ll drag them out and look later. They have square magnets though. The DCR of the mids was 11.5 ohms and the tweets were 6.5 ohms. I didn’t measure ith actual impedances of the drivers because I was too lazy.[] The AA crossovers were bone stock when I got them and in good shape. I re-capped them when I got them with some type of metal film or foil caps I had. I matched them to factory specs with a Sencore LC101. The reduced output of the tweeters was discovered while measuring with the microphone and also showed up in the modeling software. Interestingly the response curve of the tweeter looked really good except for the reduced output. I didn’t use a dummy load for the measurements and that could affect the measurements some. There must be some reason for the lower output with the bigger coil and higher crossover point but I’m not sure what it is. The response curve of the entire system was much flatter throughout the area of the 6 kHz crossover point after the modification. I noticed the peak around the upper crossover point when I first set them up but I just left them like that until now. The peak was not really annoying but it sounds a lot smoother now. There was also a pretty severe impedance dip at 5 kHz that I saw with my scope and my little amp (SET45). I could only get 100db measured output at the crossover point before there was distortion on the scope. I swaped the output transformers from 3k:8 to 5k:8 since then (my last speakers were 16 ohm Altec VOT). I’ll have to measure again and see if this impedance dip has been reduced.

Hello all. I’m new to the forum and I picked up some ‘82 Khorns last summer. I’ve been pretty happy with the sound except for a little bump around 5 kHz and a room mode around 125 Hz. These have the AA networks in them and I re-caped them early on for and got a little more clarity in the highs. I put some makeshift bass traps in the room which is way too small at 10’6x16’ with the speakers on the short wall. Unfortunately the long wall is impossible due to layout. The bass bump is manageable though by moving the listening position out of the standing wave. So the reason I’m posting here is the stock crossover had the tweeter rolling off under 4 kHz instead of 6 kHz. I determined this by measuring the on axis response with the squawker disconnected. So I plugged the parameters into a crossover calculator program and came up with about 2.7uF>130uH>8.1uF for the high pass section. My coil measured 270uH so I played around with a modeling program and adjusted the cap values to give me the 6 kHz crossover point I figured I needed. I swapped the new cap values into the circuit and the crossover point measured perfect. What I failed to notice was the tweeter level was now 10db to low, on the model and the speaker. There was no way to model the crossover a 6 kHz with that coil without lowering the overall output of the tweeter. I had some cheap magnet wire from Radioshack laying around so I wound some 130uH coils and used the calculator values and everything is good now. So the obvious question is are my speakers unique in this problem or is it well known by all you Khorn veterans. Maybe the crossover was designed for 16 ohm tweeters. Mine measured 6.5 ohms DCR so I would guess they are 8 ohms nominal. Or, maybe I’m missing something and all that geeky tweaking was a waste of time. So far they sound cleaner and better balanced in the highs to me.