Hi All,
I thought i'd document my current project, a hybrid centre speaker for my home theatre system. I'm currently building the above to compliment better my current left & right fronts, which are a no-baffle fullrange complimented with a TL sub and a horn loaded ribbon tweeter. The current centre is an old wharfdale devondale 3 lying on it's side. The wharfdale is great, but i think i can do better.
I'd decided on an open baffle mid (pioneer DSS9 midrange i'd had sitting about for years) and horn loaded ribbon (another pioneer unit), vertical layout, with a 12" bass on each side. I'm not yet convinced about sealed/open benefits of the bass drivers, though with a Qt of about 0.5, i could go either way, i'll cross that bridge later. Anyway, onto the mid and tweeter. Flush mounted onto a piece of hardwood, 1:1.61 offset, fired up REW and pulled out a linkwitz style mic and measured the midrange.
Oh dear. Listening, there was a distinctly gritty sound. Something was rattling around in the magnet gap. Undeterred, i unscrewed the 3 magnet fixing screws with polygrips, the old glue presented no issue and pop, off came the huge magnet.
Yep, crap in the gap. After a blow out with the compressor a good scrape with a bit of blunt stainless (from a windscreen wiper) then a final tweezering out, the gap was empty. The voice coil appeared to be edge wound, silver coloured (plated?) and wound on paper. The cone, vapour deposited coated titanium. Quite a bit of effort gone into this driver, worth saving.
Back together, re-aligned and re-measured and voila!
Now to deal with those nasty breakup modes...
I thought i'd document my current project, a hybrid centre speaker for my home theatre system. I'm currently building the above to compliment better my current left & right fronts, which are a no-baffle fullrange complimented with a TL sub and a horn loaded ribbon tweeter. The current centre is an old wharfdale devondale 3 lying on it's side. The wharfdale is great, but i think i can do better.
I'd decided on an open baffle mid (pioneer DSS9 midrange i'd had sitting about for years) and horn loaded ribbon (another pioneer unit), vertical layout, with a 12" bass on each side. I'm not yet convinced about sealed/open benefits of the bass drivers, though with a Qt of about 0.5, i could go either way, i'll cross that bridge later. Anyway, onto the mid and tweeter. Flush mounted onto a piece of hardwood, 1:1.61 offset, fired up REW and pulled out a linkwitz style mic and measured the midrange.
Oh dear. Listening, there was a distinctly gritty sound. Something was rattling around in the magnet gap. Undeterred, i unscrewed the 3 magnet fixing screws with polygrips, the old glue presented no issue and pop, off came the huge magnet.
Yep, crap in the gap. After a blow out with the compressor a good scrape with a bit of blunt stainless (from a windscreen wiper) then a final tweezering out, the gap was empty. The voice coil appeared to be edge wound, silver coloured (plated?) and wound on paper. The cone, vapour deposited coated titanium. Quite a bit of effort gone into this driver, worth saving.
Back together, re-aligned and re-measured and voila!
Now to deal with those nasty breakup modes...
...
I started by putting some blutak blobs on the cone edge, simple mass damping.
This showed me that the 9kHz breakup mode from the cone, the 14kHz ringing being from the main dome.
Once i'd worked out how to effectively damp the main dome, i shifted that blutak to the back
and carried on experimenting with cone damping. I was convinced i could to better than just some blobs on the edge.
To cut a long story and many many measurements short, this is what i ended up with.
measuring like this
I dubbed the pattern, the Egyptian hieroglyph, finding out later it was the glyph meaning to walk. Cool.
now onto the crossover...
I started by putting some blutak blobs on the cone edge, simple mass damping.
This showed me that the 9kHz breakup mode from the cone, the 14kHz ringing being from the main dome.
Once i'd worked out how to effectively damp the main dome, i shifted that blutak to the back
and carried on experimenting with cone damping. I was convinced i could to better than just some blobs on the edge.
To cut a long story and many many measurements short, this is what i ended up with.
measuring like this
I dubbed the pattern, the Egyptian hieroglyph, finding out later it was the glyph meaning to walk. Cool.
now onto the crossover...
Interesting. You turned that little peak at 5.5K into a little dip at 5.5K. What's going on there? Maybe it won't matter much with the tweeter. There is a lot of energy from voice constants circa 5-6K so the change should be rather audible. Is it?
Good work on the magnet clean.
Good work on the magnet clean.
I've not put anything other than sine waves through it so far. Something funky is happening at 5.5kHz with the distortion plots too. I'd guess some sort of cancellation. <shrug>. It could be the mike, not calibrated.