Monday, May 2, 2011

System two - update

Betsy WOW on open baffle

It's been a while I posted any changes to my system. It's because I am working on two other speaker projects, Keele's CBT line array, which is a lot of work, and on Legacy's Whisper look alike. However, one significant change happened in my second system. I replaced vintage Magnavox elliptical midranges/paper cone tweeters with brand new open baffle mids/tweets. I placed two Betsy WOW (Betsy Without Whizzer) and a Selenium horn tweeter in d'Appolito arrangement. The result is seriously good sound, to the point of approaching my main system. I wonder if the same electronics as in main system would be used...one day I will swap the speakers to see. It's not that easy because both systems are biamped. Anyway, here are some pics of the second system after update.





Detail of the left speaker. And from the back.



I highly recommend Betsy WOW speakers for open baffle. They go deep, almost 50Hz, they are reasonably flat in midrange area, they do not have nasty breakup modes typical of real world fullrange drivers, and they are quite efficient. Not in the Lowthers area, but pretty high. Having two per side definitely helps even more. Power handling is good as well, better than Lowthers. Having dedicated tweeter makes top end way better sounding than from fullrange drivers. No matter how puristic the fullrange approach is, the result of well executed dedicated midrange/dedicated tweeter is just better sounding system. Originally I had two Betsy's per side connected equally, as you would normally in d'Appolito 2-way system. However, I prefer the upper midrange to come from one point source, rather than two, so I changed the crossover to 2.5 way, with one Betsy rolling off sooner that other. To me this sounds better. So the top now is 2.5 way, plus the woofer makes this system effectively 3.5 way. I am enjoying these speakers a lot. Highly recommended, but I already said that, didn't I.
Here is how Betsy WOW measures (no tweeter) using Holm Impulse:

It's unbelievably flat from 50Hz to 500Hz, then it has small dip, nothing too bad, then slowly rising fr response with breakup modes not too bad either. With single coil for crossover at about 3KHz, those brakup modes are removed and fr response can smoothly transition to tweeter.

However, to be honest, I have recently had some troubles with Besty I want others using these speakers to know about, here is the whole story from the letter to Paul, the owner of Wild Buro Labs:

Hi Paul,
this is not easy wright, but I have to do it. I was very fond of Betsy WOW for quite a while, but I encountered a problem with my drivers. I bought 4 Betsy WOW from you while back and mounted them on open baffles in MTM configuration with subwoofer. I really liked the sound, efficiency, clarity. However, I encountered the problem, which I am curious to know if you potentially know about it. The problem is that I never blamed the Betsy drivers for it, only this weekend I discovered what the problem was.
Anyway, long story short, here is the problem: with certain recordings, particularly simple ones, with only one intrument in midrange playing, and especially on female vocals, particularly opera high pithced voices I heard buzzing sound. For last half a year I was trying to find a source of this buzz. I never blamed drivers, since inspection always showed free movement, no rubbing of voice coil, the drivers looked good. I removed dust caps and found nothing wrong with voice coils, nothing stuck or loose there. I blamed Behringer ultracurve, thinking its overloading some band, or some pre-amp stage overdriving or similar things. I kept changing preamps and amps, but the problem never went away. I must say with most recordings, especially complex ones, all sounded good. However, the problem got a little worse over last few months, so I investigated deeper. This weekend I used testing cd and with certain mid frequencies on sine wave I heard that buzzing sound. I inspected all stages of electronics with osciloscope, at every stage the sine wave looked great, no sign of overload anywhere. Behringer ultracurve was clearly not to blame. Signal leading to the drivers was clean as a whistle. So electronically all looked great, but with 1 kHz tone I heard buzzing, slightly different level from each speaker, weird. This lead me to discover that at the point on the cone, back side of the cone where lead of multristrand wire is entering small metalic ring, which on the other front side of the cone connects to the voice coil wire, is the source of the buzz! Yes, buzzing sound is comming from that metalic ring or rings on back side of the cone, where those two wires meet. If I touch it gently while the sine wave is playing, it prevents the buzzing! There is something loose inside those rings. It only buzz at certain frequencies. So now I need to find a way to fix the problem.

Thats pretty much the story. I believe there is some lousy connection made which over time loosens and makes buzzing irritating sound.

Paul, have you encounter anything like this with Betsy drivers?

Ed
Since then I fixed the whole problem by aplication of few wood glue drops on each brass ring.