The cosmetic choice of having all new drivers on the visible face of the manifold was a mistake. There was far too much vibration through the lack of reaction force cancellation. I have now fitted the older drivers in opposition in the lower part of the manifold. The upper four places are now taken up by the newer drivers. It proved almost impossible to tell them apart at a glance anyway.
A quick fire up proved that my car audio bass tracks CD could be played at 115dB(C) + read from the Galaxy SPL meter without any sign of cone movement or rattling of the enclosure door.
I had used the opportunity to remove all the drivers and open up the driver fixing holes slightly to improve T-nut grip. Then caulked the inside edges of the box with black acrylic stuff before refitting the drivers. The latter exercise was great fun as the release trigger on the cartridge gun kept sticking so hard I could not release it! The stuff was everywhere before I had finished! Fortunately it was water washable and invisible against the black finish of the box.
It didn't take long to put everything back together and rewire in series-parallel sets per channel again. A few minutes adjusting filters slightly on the BFD smoothed everything out nicely. The violet line is the new (provisional) 4 + 4 + BFD curve.Bass is prodigious on Franck's organ works despite backing off the EP2500 even further to 12 o'clock. ('24' on the big Behringer's twin control dials) Bass quality is stunning. Timbre is even further exposed with a harder edge, more character and colossal weight. The great pipes seem even taller.
Felix Hell's "Organ sensation" Track 6: Liszt Prelude on Bach is great fun but lacks the unique character of the French organ on the Franck CD. There is weight aplenty but the pipes do not speak with the nasal authority and sometimes malevolent roar of the St Eustache organ in Paris. The Franck work seems to have as many different voices as it has great pipes. Increasing the volume on The Felix Hell CD works wonders though.
I have been listening a great deal to the new IB in between tidying up around the large hole in the wall. I lined the triangular inner face of the wall with 3/4" plywood to beef it up a little. Hopefully the plywood will help to carry the remaining reaction loads into the roof structure where the great structural mass can resist vibration. I have been looking at potential wooden mouldings to finish off the edge of the manifold mouth. There is never enough air movement to warrant a neat radius but it still needs something to fill the rebate where the manifold stops and the wall surface begins.
It is surprising how the bass varies as I wander around the room. This is to be expected as one moves from node to anti-node along the considerable wavelengths involved. My computer desk was always a bass hotspot before but this seems to have reduced in favour of the stereo hot seat. The detail in the deep bass is much more obvious when I sit there and listen attentively.
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