Actually, with the caveat that they are limited to +20 dB transients, some of the best produced music today are movie soundtracks.

Yes, good classical is pretty awesome, but organ symphonies will test the mettle of all but extreme sound systems and find them wanting, especially if you want to go ~ 'live'.

Accuracy/smooth are 'floating targets' since folks don't all hear exactly alike, have different frames of reference, etc., and if you fall back on measured 'perfection' to level the playing field, most folks find them too 'sterile' sounding. For instance, all expo horns are 'colored' (distorted), so anything but accurate and the 511/811 conical/expo CD horns are much more so no matter how much you tweak them, yet many folks consider them 'accurate/smooth' enough without any tweaks. Then there's the woofer and XO to consider..........

So the good news is that you can technically improve what you have and the bad news is that you can't make them 'right' and might not like them once you're done. Still, as you know you're starting at a high enough level that few do much tweaking, so major leaps will require mass quantities of $$ and ultimately, space.

Note that unless you have room to toe them in, a horn super tweeter will be required to get enough off axis HF power response. This, or make horizontally slanted front baffles like the late NHT 3.3 tower system: http://www.stereophile.com/loudspeakerreviews/1293nht/

GM

• NHT 3.3

So let's assume 21" wide and 42" tall for a mass loaded transmission line. I've done some reading on design and used the calculators here:
http://diyaudiocorner.tripod.com/formula.htm
to try to get a feel for dimensions of ported and sealed enclosures, but TL design looks quite a bit more complicated. Would you give me a starting point/idea?

The living room arrangement won't have enough room to toe in, and slanted baffles are beyond my woodworking skills for now. I'll look into supertweeters. As it is, I've found the Heathkits mostly satisfying to listen to; maybe the supertweeters can wait.

OK, build this, preferably using either 19 mm 13 ply Baltic Birch, Appleply, or marine grade (only if you can find guaranteed no-void though) plywood (all dims inside): H = 40.5", W/D = 19.5", add a full width 811 horn mounting recess similar to the link's 800 Hz VoTT except just make its height big enough to fit the horn flange (~8.75"), and due to the narrow cab it will be necessary to notch out the sides; driver cutout down 17.88" from the top, and for initial tuning, a 5" dia. plastic pipe x 4" long ~5" from the bottom. Assuming a low output impedance amp, this should tune it down in the high 20s and perform similar to sealed except with a bit of extra gain. Shortening the tube to the 0.75" minimum should yield a ~T/S max flat alignment (max BW half space gain) once the horn is properly shelved, so none of this takes into account the LF wall/room gain. If the 4" pipe is too 'boomy', then either add more internal damping as required or just seal it off.

For proper vent action, a good seal is essential, so I recommend using high grade neoprene gasket material in lieu of the typical cheap foam weatherstripping.

WRT general construction, I recommend mounting the driver to a separate removable baffle like the 846B has rather than a rear access cover/removable back, then run top and bottom front to back braces. Since most of the cab's pressure is vertical, brace the panels using ~1.5" wide plywood strips glued on edge and vertically offset in a golden ratio, so centered at ~19.5*0.618 = ~12.06", just don't extend the braces all the way to the top and bottom of the panel since this causes a vibration 'hot spot'. Just to make sure there's no horizontal modes of note, randomly add some strips tying the vertical strips together. Install a HF driver support cross brace and line the notch (no need to contour it to the driver's diameter) with neoprene or similar. For gluing, FWIW I prefer caulk tube loaded construction adhesive, adding a few scrap wood glue blocks along its length, then when it sets I add a second bead along the joint just in case there's any pinholes, though many folks are satisfied with cheap caulk's sealing attributes.

WRT damping, Altec's recommendation of covering the top, one side, and back should work fine for sealed or vented, though I recommend adding a second full depth 'panel' louped around the horn to create a damping chamber. FWIW I normally used 1" thick acoustic fiberglass. Bottom line, it'a very room/personal preference dependent since some folks like more or less depending on how 'lively' they like their box sound. The space between the top/bottom of the horn 'lips' and the recess's walls along with the horn flange/baffle sides will need to be lined with either 1" acoustic fiberglass or similar.

........and if you're interested enough to delve into TL/MLTL design, then start here:

http://www.quarter-wave.com/

http://www.geocities.com/rbrines1/ .......though some of his conclusions are a bit too narrow minded IMO since like most things it's not what you have, but how you use it that usually counts most.

Anyway, looking forward to your thoughts on its performance/final tuning choice and whether you think it was worth the extra $$/effort.

GM

• p. 23

When you list placements of woofer and port, do you mean XYZ inches from the edge of the cabinet to the middle of the circle?

For the stiffening strips, this is how I read it:
Each panel (two sides, front and back) has a single 1.5" wide strip glued at ~12.06" (.06"? ) from the edge. The strip does not extend all the way from top to bottom (any suggestions on how far or is it cook's choice?). There are several randomly placed horizontal 'rings' that tie all four vertical strips to each other. The top and bottom each have a brace or two extending from front to back.

This one sentence still puzzles me after many readings:
"Shortening the tube to the 0.75" minimum should yield a ~T/S max flat alignment (max BW half space gain) once the horn is properly shelved, so none of this takes into account the LF wall/room gain." I understand that the room will affect the LF, but how does that relate to the first part of the sentence?

I plan to build three cabinets - the first from rough plywood to get a better idea of how to do it twice properly with nice the 13 ply Birch stuff. If you have patience for more questions, I have a number of woodworking posers for you.

As to whether I will "think it was worth the extra $$/effort," it damn well will be after I go through the palaver of building the cabinets! Just these will be quite a challenge for me, I'll save TL for another time.

GM, thank you for your many posts and patience. I'm looking forward to enjoying building these and doing some listening.

You're welcome!

Right, inside dims.

0.06" = ~1/16", but the (~) means more or less, so if you're not a perfectionist, then round it off.

'Cook's choice'. I'm sure there's some math to calc an ideal distance, but I'm no structural engineer. I forgot to add that as long as the brace spans at least ~70.7 % of the distance it works for me.

Horizontal 'rings'?

The top/bottom front to rear braces are above/below the driver. What you're trying to accomplish is to provide the driver with a rigid 'platform' to allow it to work as mechanically efficiently as practical. The 'tie' braces between the vertical bracing can be more of the plywood scrap strips. For these to work their best they should intersect, creating an 'X' brace.

A T/S max flat alignment means that the system's half space F3 is as low as it can go. Since the horn is much more efficient than the woofer, it must be shelved (attenuated) to sound tonally balanced. When placed near a wall or corner it can sound too 'boomy' to some due to the extra acoustic gain, while others prefer it since it means less HF shelving. I just gave you a vent size and length range of adjustment that I think is flexible enough for you to find one that works for ya'll.

GM