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In Reply to: RE: About that mod posted by DHT 4 ME on June 18, 2007 at 15:45:10
It was pretty easy to do after all, like you said, and not time consuming. Thanks for the tip. I owe you for this one.
The result was a better overall sound in a number of ways. The imaging became suddenly more focused. I think there was some sound "turbulence" that was ironed out and the sound just seemed to become more cohesive and uniform or however you might describe it. As a result, more detail was coming through and a more see-through soundstage appeared. It now sounds more like a point source should sound. I was getting more ambience from the back of the hall and other such goodies.
Dynamics were actually a little more tamed, too. It did allow for a few dB more dynamic headroom. This is getting much more satisfactory. As a result of that, I changed a coupling cap in my amp to move the low frequency cutoff down to 300 Hz, 6dB/octave, and then there's another low frequency pole sitting at 220 Hz and another somewhere close by in Bert's crossover. So it's effectively operating somewhere near 300 Hz in a 250 Hz horn. Not the best arrangement, but for overall tone at medium volumes just excellent sounding.
I have measured the frequency response from the mouth of this horn, and it's amazing to me how extended and flat it is on-axis. It's about +/-3 dB from 250 Hz to 20 KHz, at about 110 dB sensitivity all from one point. That's to me an impressive achievement, that kind of flatness and extension over that high a sensitivity from one point of measurement.
Here's a new idea about this horn system. Instead of trying to get all the dynamic headroom I can, maybe it's time to shift gears and soften down the dynamics. To do this I simply change the operating point of my 45 output triode down until it's overloading at just under the spot where the horn stresses. It will be pretty loud still, a little over 100 dB at 1m, but now it will hit a soft clip before it hits a hard one. That might be the better way to go for now. So I need it to overload at 100 mW. How about that? I need no more than 100 mW/ch power for the mids on up. I must be going green saving all that class A power consumption.
Kurt
Follow Ups:
hi Kurt
i am surprised, as i thought Bert had done this modification in the driver. Have you seen wath he has done? Have you found any difficulties, ore is it easy ? Can the driver be damaged in some way ?
Angelo
" am surprised, as i thought Bert had done this modification in the driver. Have you seen wath he has done? Have you found any difficulties, ore is it easy ? Can the driver be damaged in some way ?"
I cannot see anything modded in the driver, but then I have not taken it all apart. I just removed the tweeter section by removing the four hex bolts that hold that in. It's real easy to remove and do it safely. But try to do this with the speakers facing down first so gravity doesn't bite you when the bolts are removed.
The drivers could be damaged if you're a klutz. There is the thin ring membrane around the tweeter's phase plug. I can't see the midrange diaphragm, so I think it is hidden and is only just a ring and not a complete solid circular diaphragm. How else could the tweeter go through the midrange? But I don't really get how this is designed. From what I can see there is simply not as much Sd as a full 4" midrange diaphram would have. Thus I believe it must have to have more excursion to deliver similar SPLs as a solid 4" diaphragm (not a donut hole in the middle). That is the basis of my proposal to try the BMS 4591 and add a supertweeter.
But heck, this new clean sound at medium to medium high levels is pretty cool. That coaxial thing is producing a beautiful soundstage with some pretty tight imaging for a horn. And the instrument timbre is so amazingly lifelike as well and the dynamics uncompressed (keep the volume in sane levels of course). I think this system now kills any electrostatic I've heard, and I've heard one of the best - a SoundLab A1 with an OTL amp driving it. It's actually clearer and more detailed and images better and doesn't compress and the bass is solid. Hey, I'm in world class territory now! I'm serious!
Kurt
Kurt
I agree totally! the images seem to materialize in front of you from clear space.Concerning the mid ring radiator, it is almost the total diameter of the case and the VC is at 4". The radiating surface is like a V section with the VC at the apex of the V. The phase plug is sectoral and is what you see when you look into the holes you plugged. The reason the mod is so effective is because it fixes a relatively big freekin hole in the middle of the phase plug! You can see I was not kidding about the great press I got from fellow audiophiles :)
best wishes
Bob
Great News!
I am glad you did it and are enjoying the clarity and imaging improvements. I also put wool thread in the area near the mid voice coil but I did not take photos and am enjoying my system too much to tear the drivers apart to photo them. The improvement was not as pronounced as the chamber fix. I really enjoy these speakers and the imaging is very focused and unforced.
Glad to have been of help
Bob
Thought I'd give this a go as I had the parts sitting here and half an hour free to do it in.
I used some of those clear silicon/rubber dome feet that come on sticky sheets. They're about 7/16" diameter. With a 17/64" (1/4" would be OK) I drilled into the centre of the flat back - making a round bottom cup out of the pad. THere's a bell like flair right at the top edge of the newly formed cup which was taken off with a mat knife. Then just pressure fitted the cup into the hole and ta dah! The plate sits up where the terminal ends rest in the cups but with just a slight pressure they push the soft silicone onto the hole getting a good seal and reversible for anybody who's feeling nervous about flying into the unknown with epoxy.
The whole thing took about 25 minutes.
Sure sounds different. Everything centred in space between the speakers. Not quite as pretty or ethereal sounding as before but the rough edges at higher volume is definitely smoothed out. Piccolo in Beet's 6th - I was washing dishes in the kitchen and suddenly wondered who could be blowing that high whistle out there.
Thanks Bob !
I would be curious to see how the rubber mod fares against a rigid plug.
Are you planning to do the rigid plug?
Bob
Hah Hah, We can't stop can we `,;^D
My original thought was to make a drill bit with a centre guide to fit the existing hole and cut a shoulder around the perimeter, then make a hard nylon cup with flange to drop in. But not wanting to invest the time without getting at least an approximate taste of the mod I took the quick and easy route.
Another possibility would be a nylon cup washer (used for screw heads) if the right size exists then the hole in the bottom could be filled away from the driver and then just dropped in.
Listening as I write this, I'd swear the mod is breaking in! Whatever it's doing, it sounds good. Focus is much better - more down to earth. Though the highs like the ring of the high e and b strings on a guitar are not quite as pretty.
Or do you have a back-door on your web site that shows your audio stuff?
Nobody here but us chickens.
_________________________
there is a back door / personal folder but I don't have an overall shot of the speakers. there is too much stuff in the living room to get a good overall shot :(
Here is a page with some of my amps . I will take a pic of the speakers soon. I just have to remember to bring home the camera from the store so I can actually do it when I am thinking about it.
Have fun
Bob
in the last picture...
VERY nice work on the Bottlehead build...
Peace,
ME
It's one of mine. An 845 creation w Electraprint iron.
I got one built and the second is still a breadboard. When I started the project I had more space. Then came along the Bottlehead Paramount so I built a hotrodded 300b so I could listen to something. It turns out to be a real sleeper. I am going to convert it to a 2A3 with a shunt regulated output stage.
thanks for the comment.
Bob
we all love to hear about what you tried and liked/disliked.... it is what makes us spin....
and, yeah.. I have no idea how Dan and Joppa sell so much music for so little money.... amazing isn't it?
Peace,
Me
Are you still using the same amp I heard? :)
See you later
D
Now there is an interesting subject! I fixed the mini DHT preamplifier tube problem in the Music Angel and put that in. Then I took the Music Angel to the gallery because it was so darn pretty and in went the Paramount 300b's. I have been playing with the PP 2A3 Webster amps but need to finish that vt25 pre so I can drive the 2a3 amps ( they need 10v input for full power) with a little more authority. Interestingly the Music angel was too soft on the bottom since it drives the passive line level crossover to the 15's and the subs. It sure looks and sounds nice in the gallery though.
The little T amp is very sensitive to power line grundge and tweeks.
When the planets are in alignment it can sound very good.
I wish I had more time and room.
Right now Bottlehead Paramounts win out untill the 2A3 setup is done.It sounds great regardless.
Bob
LOL! The cobblers children...
Look forward to seeing a picture of you speakers.
Nobody here but us chickens.
_________________________
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