Kairos

[Bob in St. Louis]

Indeed Charles, indeed. 

[jimbones]

Yes, that might work!

I think UPS could destroy it, but then they could probably destroy the steel bolt idea too if they dropped it just right.

These coils are probably 15 pounds each, 5.5" round, 2" thick. They really should be built into a separate XO box, blocked in with wood on all sides. But that would make the box too big or make the internal volume too small. Probably already eating into the designed volume too much.

Thanks Bob!

Bob,
I'll bet that IS eating into the designed internal volume. Having sufficient stuffing makes the box appear "larger" so tune accordingly.

Jim

[richidoo]

I'll bet that IS eating into the designed internal volume. Having sufficient stuffing makes the box appear "larger" so tune accordingly.

You are right Jim, the large coil is eating into the volume. But I compensated for that by omitting the reflex port on Jeff Bagby's recommendation. Due to the very low driver resonant freq. the bass FR is excellent without port, and omitting the port makes better bass transient response.

I also used a different bracing scheme which should use less volume than the original design. But there were some braces that didn't fit after crossover parts were installed, so I'll need to make some side to side cross braces. I can feel the box sides moving on low notes. I'm pretty sure that's where my low midrange problem lies.

Woofer upper range sounds a bit reticent compared to the tweeter at crossover freq, so I think I have a bit too much stuffing in there, as the stuffing only acts on the woofer, not the tweeter. Bass is well damped and very clean. By removing some stuffing I hope to free up the woofer to play high range with more detail and a touch louder to better match the tweeter, while retaining the clean bass I have now with maybe a little more loudness. A bit looser ("warmer") bass is a fair price to achieve good M/T matching. You are right that acoustic damping is a very critical factor! Too much or too little can ruin the recipe.

[richidoo]

I got all of the planned mods done:

Replaced Dayton brass speaker binding posts (used as wire clamps to banana plug) with pure copper Electratubes. No threads in signal path, soldered connections. The cabinet holes are sealed up now too.

Installed 5 new braces in each speaker. 3 corner braces from the sides to the baffle and 2 side to side cross braces in each cab. Max unbraced span is now <3". Knock test is pretty solid.

Replaced steel bolts, washers and nuts for holding down the coils with nylon bolts and zinc threaded inserts.

I also tightened down the tweeter screws which had come a little loose after only 50 hours of playing. That's a 1" long #8 sheet metal screws in 1.5" baltic birch! I was surprised to find them a little loose.

Overall it sounds more present, and purer treble. Imaging is much improved, but still not as expected.

Despite the new bracing there is not much change in the bass, it still sounds too thick and blurred. which is strange. So I guess it did not have anything to do with the box vibrations. Could be internal box reflections, the reflected waves pushing on the back of the cone. So maybe I need more stuffing. I read that FG stuffing is much more efficient sound absorber than dacron pillow fluff, so I'll change to FG and fill it up. I can pull some out to find the sweet spot.

That's all for now...

[Bob in St. Louis]

Have you seen the shredded denim material that's pressed into "sheets"?
I don't know much about it, but it was recently talked about on AC in the GR Research area.
Looks like neat stuff.

Bob

[richidoo]

Ya I have a lot of that stuff - 12 pieces of 2'x8'x4" thick!   It is great for bass traps. Bryan once said it absorbs better than OC703. I was thinking of using it but it sheds a lot of dust, so I'll need to screen it off with fabric to keep the dust out of the drivers, but FG sheds too.

I will check out the GR thread. Thanks Bob!

[Bob in St. Louis]

You'll never find the thread, as it was buried in a thread about an up-and-coming new driver. It wasn't specifically about absorption.
>>>>> Check here <<<<<


But yea, four inches thick would be hard to deal with for use lining the inside of a small speaker. The stuff in that thread is thinner than a large coin.

On a side note, it sounds like you had some serious plans if you bought that much. You could insulate the attic of a small house. haha

Hope that helps ya Rich. 
Bob

[richidoo]

I bought that stuff a long time ago to build an anechoic listening chamber. It's floppy so it needs a wooden shell to hold it up. Someday I'll get back to that.

I do want to stuff these speakers full as an experiment. I have the sides partially lined with dacron mat now but it's not enough. The denim fill should be enough to kill the bass freqs and tighten the bass, if the problem is caused by reflections.

[richidoo]

Thanks for finding that link Bob.

I have some 1" thick denim sheet, but it is too powerful for something like a full range driver. I was looking all over for 1/2" felt to line the horns of that last big speaker I built but I couldn't find any in this country. So I ended up using not very absorbent felt pad intended to be put under a big rug. Good to see it available now.

I also saw that Home Depot now sells the denim insulation in small rolls 16"x48"x2". That would be pretty handy for stuffing speakers.
http://www.homedepot.com/p/t/202710055

[Bob in St. Louis]

Good deal Rich, sounds like you're hooked up.

[richidoo]

I think the foggy bottom is caused by my recently acquired oldie Oppo CD player. I've been listening to LP, radio today and not heard it.

Listening now to 1960s Christmas carols with male baritone singers using the Sonos analog out and not hearing it.

That's my Christmas present!

[richidoo]

The bass problem was definitely the CD player.

I'm just using the Sonos zone player now, sans DAC, and that's better than the Oppo. What a relief!

I'll get the DAC back in a day or two, that should be another big jump.

[rollo]

  Ah Ha ! Could this be  some proof that the arguement of speaker first as oppossed to source end first in our systems is coming through !
   It appears the bass was OK but the source limited such. The Ol garbage in garbage out theory. Interesting.
   


charles

[richidoo]

Listened to these in Carlman's system today. A revelation. They really sound fantastic. Incredible coherence from 100Hz up. The ample power of the McIntosh amp really made them come alive, as did his great DAC. Sol has modded the Belles preamp and the Mac amp, making the system really improved since my last listen. The Kairos speakers sounded very refined, very detailed, and very musical, especially after we put in a -2dB shelf on the tweeter, which I will do with resistor mod. Neither of us like flat FR, although the tweeter is not objectionable even when flat.

Frustratingly the bass thickness tone did rear its head again, so maybe it is in the speakers. I'll ask Mr Bagby for some advice.

Some ideas came to mind:
Increase the Qts to dry out the bass, increase control. It is currently Q .69 sealed. That should be good enough, but maybe not for the very low bass. Lower Q will make LF even louder, so I don't know if it will help or hurt.

Try a ported box. If the large excursion while playing LF is the cause of the distortion then a ported box would limit woofer excursion at LF.  But the price is group delay, I don't really like ported speakers.

Leave it as is and just high pass it high enough to avoid the problem, put a sub under it. We tried hi passing the speaker with foobar EQ. It seemed to help a lot, but even up higher with female vocal low notes there was still some feeling of it. Weird.   If I can fix this these will be super awesome.

We both agreed that while they play pretty low, it would be nice to have the bottom octave for impact, and to allow overall louder SPL for rock and symphonies. Relieved of low bass they can play very loud without feeling strained.

I was looking at plate amps tonight. Ryhtmik servo system looks like a good choice, or a Digimoda 2 way computerized plate with built in DSP, but I don't really want ICE amps on the mid/highs. Any happy Rythmik users here? Sealed stereo GR 12s is what I'm thinking.

[richidoo]

I tried putting a small 18ga steel lam coil of same value on the woofer in place of the 10ga air core to see if that had any effect on the LF distortion, no change, other than loss of dynamics and fine detail.

I'm starting to think that it is actually the cabinet wall vibration from internal pressure. I can still feel very slight vibration on all the walls, so if I can feel it then I can hear it. They really should be totally inert at this level of performance. Cab vibe was my first suspicion, that's really what it sounds like, and there's really no other possible explanation. High detail drivers demand very quiet  boxes. I had similar problems with boxes for the Feastrex drivers until I went to open baffle.

Not sure what materials to use though. Can't find or afford the phenolic materials that Wilson uses, nor could i cut it if I could get it.  I need to keep the exterior baffle width at 9", but that allows sidewalls up to 2" thick if I redesign for internal volume. Maybe 1/4" steel plate laminated to wood? Panzerholz wood product is supposed to be the ideal speaker making material - extremely stiff and extremely damped. There is a dealer in NC. Or maybe LOTS and LOTS more bracing (B&W Matrix style) inside a wood box. How about 2" thick foam/wood sandwich? Or the old standby: 3 layers of MDF on the sides and 4 layers on the baffle.

Many companies build very inert bookshelf speakers. It can't be rocket science?

Lenahan uses steel plates glued into high density engineered wood material.