Having done sound in many hemispherical venues, found they were among the most modal rooms I have encountered.
In one of those domes, a feedback mode just "took off" while having a conversation about 20 feet from the mixer, by the time I ran to the desk to kill the monitors, six JBL 2420 diaphragms had bit the dust, my ears were ringing from the SPL until the next day. In fact, my hearing was so badly affected that while re-equalizing the monitors I did not notice the HF drivers were blown.
Turns out I'd made a gross mistake (an order of magnitude..) in the passive crossovers used for the first time on that gig, it had crossed the HF too low and the 15" too high. An expensive error from trying to "save money" for the client using less amplifiers and no active crossovers and on-stage monitor mix as were usually employed.
The cheerful B-52's had no complaints about the monitors that night, even though they were listening to "full range" EV 15L drivers only.
At any rate, unlike a venue, you can fill your cabinet with damping material if any modal issues require it.
Art
True art!
They will be heavily stuff with Rockwall as the cubes were. But given the sealed chamber of the full range driver almost touches the back of the sphere, the space is well and truly divided and not even into hemispheres given the volume of the woofers, mounting plates etc. The internal surfaces will also be lined with thick wool underlay. I have done a few other spherical builds which required some modifications, but I suspect these will be fine.
Here's some I made from plastic cocktail bowls:
And of course wooden salad bowls...
They will be heavily stuff with Rockwall as the cubes were. But given the sealed chamber of the full range driver almost touches the back of the sphere, the space is well and truly divided and not even into hemispheres given the volume of the woofers, mounting plates etc. The internal surfaces will also be lined with thick wool underlay. I have done a few other spherical builds which required some modifications, but I suspect these will be fine.
Here's some I made from plastic cocktail bowls:
And of course wooden salad bowls...
So having finished my CLD al/MDF/al baffle, it's time to look at the decoupling/damping strategy to minimise energy transmission to the sphere.
First butyl mastic tape to horn, with rubber washers and oversized holes to bolt horn to baffle.
Then a giant sheet of sorbothane for the gasket between baffle and sphere....
First butyl mastic tape to horn, with rubber washers and oversized holes to bolt horn to baffle.
Then a giant sheet of sorbothane for the gasket between baffle and sphere....
Attachments
Then a test fit with the layers- nothing done up and no drivers fitted but gives an idea of the retro look I am aiming for.
These will sit in a dedicated listening room I am building that will be a modern minimalist space.
These will sit in a dedicated listening room I am building that will be a modern minimalist space.
Attachments
Doesn't it seem like a lot of the surface area that might radiate without permission could be on the horn itself? I wonder whether it might make more sense to isolate the woofers from the horn rather than the horn from the sphere. Or maybe both? Or might the tweeter vibrate the horn enough to worry about?
Not saying I know the answers, just throwing in more questions and thoughts to waste your time! 🙂 With compression drivers on horn's throat, I've not really sensed much coupling of vibration to the horn body, maybe because the diaphragm's moving mass is low and doesn't move as far compared to not having it horn loaded. There might be more if the tweeter isn't compression, maybe. Or maybe it's from the high crossover points used, or dumb luck with the wall thickness and materials of the waveguides.
Not saying I know the answers, just throwing in more questions and thoughts to waste your time! 🙂 With compression drivers on horn's throat, I've not really sensed much coupling of vibration to the horn body, maybe because the diaphragm's moving mass is low and doesn't move as far compared to not having it horn loaded. There might be more if the tweeter isn't compression, maybe. Or maybe it's from the high crossover points used, or dumb luck with the wall thickness and materials of the waveguides.
That does look better to me than the eyeball/spanish olive styles from the "inspiration" speakers earlier in the thread. Not that it's my cuppa tea, still, but I wouldn't feel like I'm being watched or am living in a Pixar movie with those. Definitely a 1957-style look.
Good points bwaslo!
Luckily I already mostly know the answers from the previous big box builds - Xbush mark 1.
I made the synergy horn with over sized BB ply rings and about 4-5kg of two part structural body filler. Once the two 8 inch woofers and full range driver with it's enclosure is bolted onto the horn the whole thing weighs about 15kg and is incredibly inert.
I am probably just over engineering to the nth degree here but I would like to better this performance:
Luckily I already mostly know the answers from the previous big box builds - Xbush mark 1.
I made the synergy horn with over sized BB ply rings and about 4-5kg of two part structural body filler. Once the two 8 inch woofers and full range driver with it's enclosure is bolted onto the horn the whole thing weighs about 15kg and is incredibly inert.
I am probably just over engineering to the nth degree here but I would like to better this performance:
Has got me thinking though. I have lots of sorbothane left, so I may try some woofer gaskets too.....
So, finally my button 6mm bolts arrived. So I bolted on the baffle and got measuring....
I am fairly pleased with the distortion - it is the lowest I have ever achieved from 500 up. I didn't think I would manage to beat the massive BB ply boxes with their magnet cradles and sorbothane supports, but it I am overjoyed with the new 'sphere synergy'!
The only thing is the rise in distortion from 200-300 - I have cranked this up higher and I think it is a loose screw holding down one woofer - so I am going to try to chase it down.
Will report back with some polars soon to see if the new enclosure has changed them much.
I am fairly pleased with the distortion - it is the lowest I have ever achieved from 500 up. I didn't think I would manage to beat the massive BB ply boxes with their magnet cradles and sorbothane supports, but it I am overjoyed with the new 'sphere synergy'!
The only thing is the rise in distortion from 200-300 - I have cranked this up higher and I think it is a loose screw holding down one woofer - so I am going to try to chase it down.
Will report back with some polars soon to see if the new enclosure has changed them much.
Attachments
Last edited:
Wow - nice results there. That is excellent above 400Hz. I did not think the little SB65WBAC25 was capable of that low level of distortion. A compression driver tweeter synergy would be envious. 
Nice results indeed! You're well on your way. I'd be inclined to say: modern engineering with sort of a 60's Retro look 🙂. I kinda like it!
So - I had a very late night, last night - from reusing the synergy horns from XBush 1, all the woofer screws had been in and out of their plywood mounting rings more than a dozen times and had actually got quite loose.
So in comes gorilla glue into all the holes, 4 hours to dry. Then both woofers remounted.....and it has paid off:
The 200-300 increase in distortion has gone. Phew.
On to polars next.
So in comes gorilla glue into all the holes, 4 hours to dry. Then both woofers remounted.....and it has paid off:
The 200-300 increase in distortion has gone. Phew.
On to polars next.
Attachments
Tell me about it!
I reckon have about 30 hours into this single enclosure build so far. My second set of aluminum discs is arriving today, so I can push on with the second CLD baffle.
But it take quite some time laying up the additional glass fibre and structural two part filler into the planter.......I just want to get listening!
Glad you fixed it - that's a nice result. A reminder to all of to check for loose screw mounts on our drivers.
I may do that too wesayso! Until this point though, I wasn't happy with the Xbush - too ugly!
I will take some nice pics soon - when finished with the measurements!
Here are some from this morning, now I have the distortion fixed.
I will take some nice pics soon - when finished with the measurements!
Here are some from this morning, now I have the distortion fixed.
Attachments
Last edited:
A quick shot. I need to finish up some cosmetics, but gives an idea of the difference. I think they will look better in my modern retro listening room than they do in my old school study...
Attachments
Last edited:
- Status
- Not open for further replies.