Book shelf speakers for SE tube.

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Even with CNC routing of recessed driver baffles, there can be enough minor variations in nominal thickness of plywood that the face of brace contacting driver magnet needs to be hand measured and cut for each pair.

There's gotta be more than one way to measure / cut these, and since your photos indicate you've already figured that out my technique is probably irrelevant.

I still don't always get them perfect the first time around, and prefer to err on the side of too loose rather than tight, and glue strips of paper or .5mm veneer edge tape to fill the gap.
 
OK,

Last question..lol

The space at the back of the port at the bottom of the box is this lined also? I guess keep the port clear into the box?


Regards
M. Gregg


I don't line the ports, and keep damping material from occluding the internal opening to vent slots. It's a light fit once the box is fully buttoned up, but if needed you can add a little loose wadding later, and even experiment with stuffing the port slots with foam. But you'll probably want to wait for a few hundred hours of playing time on the drivers to finalize those details.
 
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Even with CNC routing of recessed driver baffles, there can be enough minor variations in nominal thickness of plywood that the face of brace contacting driver magnet needs to be hand measured and cut for each pair.

There's gotta be more than one way to measure / cut these, and since your photos indicate you've already figured that out my technique is probably irrelevant.

Don't believe its irrelevant. Anything that stops people struggling like me has got to be good! :)

No CNC, all hand routing - and a few hours of hoping I won't make a mistake. LOL

I never thought of paper / veneer,not much flex in that after a good fit.

Thank's

M. Gregg
 
Regarding the brace driver interface, "why not use a pressure rod." I think GM mentioned it a while back (and others too). A threaded rod from the rear of the speaker box is inserted through a fixed nut (on the inside of the box) and then "pushes" against the rear/magnet of the driver. One could fashion an interface that would contact evenly/completely the rear of the driver magnet.

Or you could pull the driver against the front baffle...

I've glued a thick piece of wood on the rear of the magnet and attached a nut on it and ran the threaded rod through it. You simply adjust the tension by ear, very little tension is needed (but be extremely careful not to break the driver basket). Somehow, adding a bit of mass to the rear of the driver and decoupling it from the front baffle does wonders to the sound, much more solid, precise and real. Perhaps, Mark could incorporate a rear mounting facility on one of his next gen drivers.

The driver baffle interface is often overlooked, but screw tension, screw type, gasket types, bracing maddenningly affect the sound and even more so with full range drivers with light flimsy baskets.
 
Regarding the brace driver interface, "why not use a pressure rod." I think GM mentioned it a while back (and others too). A threaded rod from the rear of the speaker box is inserted through a fixed nut (on the inside of the box) and then "pushes" against the rear/magnet of the driver. One could fashion an interface that would contact evenly/completely the rear of the driver magnet.

Or you could pull the driver against the front baffle...

I've glued a thick piece of wood on the rear of the magnet and attached a nut on it and ran the threaded rod through it. You simply adjust the tension by ear, very little tension is needed (but be extremely careful not to break the driver basket). Somehow, adding a bit of mass to the rear of the driver and decoupling it from the front baffle does wonders to the sound, much more solid, precise and real. Perhaps, Mark could incorporate a rear mounting facility on one of his next gen drivers.

The driver baffle interface is often overlooked, but screw tension, screw type, gasket types, bracing maddenningly affect the sound and even more so with full range drivers with light flimsy baskets.


Well the type of bracing in discussion primarily serves to stiffen the box by connecting several (as many as 4) of the enclosure panels - coupling to the driver is secondary - for which a short wooden spar or arrangement such as you describe would certainly suffice.

Certainly some folks have gone as far to to suspend the entire mass of driver from the magnet itself, and lightly gasket to the front baffle, or even run the driver fully naked. There's even the Lowther type mounting arrangement
An externally hosted image should be here but it was not working when we last tested it.



I wouldn't be surprised if Mark considered engineering such a mechanical connection point into his magnet structures to be an unnecessary expense at best, and potentially damaging at worst.

The latest generation of injection molded baskets and gaskets on Alpairs I've seen aren't anywhere near as "flimsy" or at least as resonant as the stamped metal frames of Fostex FE166/167. The precision cast / machined baskets on Sigma and FX/FA/FW drivers are another matter -
 
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Regarding the brace driver interface, "why not use a pressure rod." I think GM mentioned it a while back (and others too).

Or you could pull the driver against the front baffle.........

I've glued a thick piece of wood on the rear of the magnet and attached a nut on it and ran the threaded rod through it...........adding a bit of mass to the rear of the driver and decoupling it from the front baffle.........

The driver baffle interface is often overlooked, but screw tension, screw type, gasket types, bracing maddenningly affect the sound and even more so with full range drivers with light flimsy baskets.

This was Herb Jeschke's idea AFAIK, it was too obvious for me to think of it. :( I instead made cutouts in bracing and used shims to get the desired loading which of course works on both front and rear mounted drivers with the downside of not having the easy adjustment of the threaded rod.

Hmm, increasing tension between the driver, baffle increases its coupling, doing effectively the same thing as pushing it against it. IOW in either case you're putting everything in tension by spreading the cab apart to better couple the driver to the cab, so one always wants a very rigid cab at least in the driver which usually means adding bracing between the baffle, rear wall.

Note that there can sometimes be enough slop in a threaded joint to ruin its tuning, especially with vented alignments, so sticking blu-tac, silicone caulk or similar around the joint once done is a good plan just in case.

Yeah, it's amazing how much it can affect a 'FR' driver's clarity. Sometimes folks damp the basket, etc. to achieve the same thing, but it reduces electro-mechanical-acoustical efficiency whereas the mass loading via bracing increases it, so out as the extremes of system Q, the former is better for high Q and vice versa.

GM
 

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Certainly some folks have gone as far to to suspend the entire mass of driver from the magnet itself, and lightly gasket to the front baffle...........

Right, the best mount is one that doesn't connect to the box at all as the pioneers of audio concluded and used in early cinema woofer OB 'alpha' installs, but no doubt it was cost considerations that quickly converted them to flange mount when mass production began.

GM
 
If you were putting these speakers on a shelf or work surface,

What would you put under them?

It would depend on how rigid the work surface is. Shelving typically is quite flexible, so it takes considerable damping with the right amount usually being found empirically whereas on a very rigid surface such as a massive workbench that doesn't 'bounce' when a heavy weight is dropped on it, perching them on metal cones pointed end up will suffice.

Note that the speaker should have a metal disc interface for the cones: http://www.parts-express.com/wizard...&WebPage_ID=3&searchFilter=spike+sets&x=0&y=0

GM
 
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More progress,

I have completed the speakers and running them in as per Mark Audio instructions. However I have to keep stopping myself turning them up.LOL

They do sound very good even at very quiet listening levels. The thing that suprised me is I expected a Tinny sound probably because I link metal cones to tweeters! Well they are very mellow and sound stage is very good still at low levels. Bass even though I am trying to keep away from it at the moment seems very deep. I want to turn them up,just got to wait I suppose!

Interesting they seem to run well on the 8 Ohm output. I lined them with a layer of 10mm felt with a 20mm poly fluff on top of the felt. The brace is covered as Dave said on one side with polly fluff.

Picture of the lining before final tidy up!

I tried to get cat 5 cable solid core everything I cut open seemed to be stranded so I used very thin magnet wire (hopfully with a clean surface from the varnish coating). side by side half inch appart on masking tape topped with another layer back to back. Thoughts are paper type base of the tape does not give as much static as other tapes.

I will post a pick of the finished speakers when I bring myself to disconnect them from the amp.LOL ;)

Regards
M. Gregg
 

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I tried to get cat 5 cable solid core everything I cut open seemed to be stranded

I don't think that stranded CAT5 or CAT6 sounds any different from solid. If you are using Ethernet patch cords, they are always stranded for flexibility. Solid core CAT5 can be had at HD or Lowe's by the foot. My local Lowe's has PTFE coated CAT5.

I made a pair of speaker cables out of a Belden 25' CAT6 patch cord using all 8 wires -- solids to solids,stripes to stripes. Other than being a little harder to work with than solid wires, the stranded cables sound exactly the same as the 16ga zip cord I use as a standard.

Bob
 
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This is an old thread,

I said I would post a pic of the finished Alpairs I never did so,

I run them off OTL and they sound great! :D

I can say after run in the bass is very deep sound is very good I would not be without them!

The sound isn't great on this recording its with a mobile phone (dosen't pick the bass up well) they are being driven with an (DIY OTL going through some mods for power increase at the moment)....This is repeat information used in another thread..

6C33C OTL power amp running two heaters on OP tubes.. - YouTube

All the best for the new year.. :)

Thank's to Planet 10 for all the help!


Regards
M. Gregg
 

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