GM's MLTL with 416-8B

[airboss]

Very interesting project, and beautiful workmanship. I never did see a link to the original plan? Or maybe there isn't one.

Two thoughts, both incompletely informed perhaps. The result of idle midnight thinking.

Sealing openable joints: I've thought of using ordinary Crouse Hinds (or other manufacturer.) duct seal (sometimes called Elephant Poop amongst other things) My thinking has been to run it thorough my old hand crank pasta machine with the linguini blade installed after thickness rolling. The stuff is good forever in some pretty tough industrial settings but provision would need to be made with a "pry" lip attached to the removable piece. Or maybe a screw thread against a hard spot on the support cleats to break the seal. It's pretty sticky. Drivers can be attached to the baffle using these: http://www.mcmaster.com/#threaded-inserts/=bzcrce Drill the mounting holes so they don't go through the baffle, or (if they do) back them with a piece of 1/8th ply, glued in place with some of GM's magic poly glue. Actual leaks through the driver suspension (if bad enough) might require re-doping the surround. Weber speaker might sell some speaker dope; I dunno.

Second. I've heard some good things about R-13/R/18 for internal sonic resistance and have seen it settle over time to the bottom of the box. My thinking has been to loosely tack bird netting (the black UV resistant kind) over the bats to try and hold them in place. I've heard that packing the stuffing too tight will require a larger box for the same results as loose filling but it may be worth a try.

[westend9]

I think it's track 18, 19 and 20 (I'm not really sure) There you can hear all Hz from 10Hz and up. The best is that you can hear almost NO or less volume peaks in the frequency's.

I'm not an expert, but when I look to the enclosure, the briefcase vent looks not too big.
So I think when you have some problems with the LF, you can tune the vent, to make the vent deeper. I would start with a vent from around 6 cm deep (make a 4 cm. deep wood frame from plywood, and put that wood frame on the inside around the vent. In the test phase you can clamp it temporary with a clamp. (during the tests you can adjust the frame by cutting it smaller and find out what works best in your situation) Succes!

I was thinking forward to doing that very thing, temporarily adding a plywood vent extension. At this time, my ears tell me it is not necesary. I believe the designer hit the ball on the fat of the bat, it is going over the fence!

Increasing vent length lowers F3, Fb, so for all but VLF special effects and some pipe organ symphonies, tuning lower would normally only be called for if the bass was too 'boomy' which can occur with corner loading. For more bass/mid-bass 'presence' [tonal balance] then, either a larger vent that raises F3, Fb and/or some baffle step compensation [BSC] is called for which is usually the case if the speakers are well away from any wall, corner boundaries. Of course, fiddling with these or any other fine tuning adjustments should only be done once installed in-room.

As for tuning by ear, it's better than nothing, but due to the way we perceive sound it's a crapshoot unless one has perfect pitch good enough to tune a piano and why I got in the habit of getting young women to help since men tend to do better down low while women do much better through the HF, so between the two, a decent balance can normally be struck and I'm guessing why I didn't have a clue what all SAF, WAF, etc. meant/implied when I got on-line.

GM

My thoughts, too, GM, wait until I have everyting in situ. I'd sure like to have some measurement devices, at this point. I may get to a local place that stocks all of it and just plunk down the funds.

Very interesting project, and beautiful workmanship. I never did see a link to the original plan? Or maybe there isn't one.

Two thoughts, both incompletely informed perhaps. The result of idle midnight thinking.

Sealing openable joints: I've thought of using ordinary Crouse Hinds (or other manufacturer.) duct seal (sometimes called Elephant Poop amongst other things) My thinking has been to run it thorough my old hand crank pasta machine with the linguini blade installed after thickness rolling. The stuff is good forever in some pretty tough industrial settings but provision would need to be made with a "pry" lip attached to the removable piece. Or maybe a screw thread against a hard spot on the support cleats to break the seal. It's pretty sticky. Drivers can be attached to the baffle using these: http://www.mcmaster.com/#threaded-inserts/=bzcrce Drill the mounting holes so they don't go through the baffle, or (if they do) back them with a piece of 1/8th ply, glued in place with some of GM's magic poly glue. Actual leaks through the driver suspension (if bad enough) might require re-doping the surround. Weber speaker might sell some speaker dope; I dunno.

Second. I've heard some good things about R-13/R/18 for internal sonic resistance and have seen it settle over time to the bottom of the box. My thinking has been to loosely tack bird netting (the black UV resistant kind) over the bats to try and hold them in place. I've heard that packing the stuffing too tight will require a larger box for the same results as loose filling but it may be worth a try.

I've used duct seal to seal woofers to the cab, the Large Advebts had this as a stock sealant. I epoxied the T-nut fasteners into the inside of the baffle. I wouldn't think any air can travel through the filled T-nut. I passed through the heating/cooling section of a local lumber super-store, recently, and saw a woven filter containment material. It is close to what you have descibed, a loose weave. The purpose of the material is to hold spun filter elements when someone has to build a filter from scratch. I may remove some of the R-13 before the cabs are moved out of the shop and the additional netting sounds like a prudent idea.

I'm enjoying the heck out of these!

[GM]

Depends on the quality of the hardware, I've had them leak enough around the threads to ruin a ducted port's tuning, so some form of thread sealant is required to ensure a good seal.

Don't recall ever having any sealing problems between the baffle and t-nut, but then I've always deep seated them by either using washers and a large 'c' clamp or pulling them in with a bolt or using a proper press when available. Just whacking them in with a hammer as I've seen many DIYers do doesn't tend to seat them well, so they typically way over torque the screw to seat them well enough to keep them from falling out when removing the driver and why over time they have become a fastener to be avoided now that threaded inserts have become reasonably priced.

Right, short of needing a high enough stuffing density to require filling the whole cab which requires the back of the driver[s] and any other exposed components to be covered with cheesecloth or similar, anytime stuffing [loose fiberglass batting, polyfil or similar] is used it should always be contained in a suspended cheesecloth or similar 'bag'. This is more effective, ergo requires less stuffing than when lining the walls with it and of course de facto protects any driver[s]/components well enough.

Yes, like all things there's a point of diminishing returns and if too dense a stuffing is used, then it goes from acoustically increasing the cab's effective acoustic volume [Vb], raising F3/lowering Fb and begins decreasing it, raising F3, Fb: http://web.archive.org/web/200210070...ces/fiberfill/

GM

[westend9]

GM, I'll certainly add some pipe dope to the machine screws that fasten the woofer to the baffle. That is easy and prudent. I have the T-nuts epoxied into the holes that accept them and I sized the holes to be a very tight fit. I'm not going to lose any sleep over air getting around the body of the T-nut.

I'm still on the fence about removing stuffing or leaving everything as-is. Since I haven't contained the fiberglass, yet, now would be the time to play with that. My reading on stuffing yielded that fiberglass is superior to fiberfill due to the length of fibers. Lambs wool being superior to both, again, because of length of the fibers. Am I on the right track about that?

Since these cabs are so big and I met some resistance from Her Majesty about placement in the "Throne Room", I've placated the situation by taking on a trim job around three windows in the Palace. These windows are directly behind where I plan to locate the speakers so I am now a little bit of time away from final placement. Not too much of a dissapointment because we have a pretty nice shop system going.

[GM]

Correct about the stuffing. Again, assuming you're not trying to damp down a seriously under-damped alignment [you're not], then the 'name of the game' is to have just enough stuffing for the driver to make a sharp 'click', though if you have keen/experienced enough hearing, a well recorded kick drum or even bass guitar will suffice. The best way of course is do an impulse response test or so goes conventional wisdom...........

I forget what you did now, but a number of the larger Altec MLTLs where I got feedback didn't bother with any testing other than known music and wound up pulling out much of what I recommended based on actual testing, with usually just a pad covering most of the top, one side beside the driver and one behind it on the back cover, ~the same way Altec did with some of their designs.

One man with a 515B in ~27 ft^3 MLTL IIRC and driven with a matching impedance amp ripped it all out before he was happy. Apparently the amp's ~DF = 1 combined with the cab's 'ringing' matched up well enough to 'color' the signal at the listening position just the right amount to inject the 'richness' of a live event that the recording studio process filters out, especially those on CD.

So if yours is lined all the way to the bottom, I'd just remove all of it below the halfway point and if more needs to be removed, cut off the tops and sides of what's left before trying to thin it out since this will somewhat destroy its structural/damping integrity.

Just so long as those windows have some nice heavy drapes you can pull shut to damp all those reflections.

GM

[westend9]

I have the cabinet covered on the back side down 16" from the top, as are the sides. The top is also covered, all of this with 3 1/2" fiberglass R13, density 1 lb./cu.ft. (as nearly as I can surmise from the sources I've read).
I am driving the 416b with a JBL/UREI 6290, 300w.@8 ohms, damping rated at +200. The response is very good, it's definitely digging low but I think I can get it a little more lively than I have it by removing some stuffing.

For some reason I abandoned the toggle "clicker" device. I'll try that out tonight. Drapes are sure to be hung, along with some type of shade. Her Highness has a thing about daylight in the Palace.

[GM]

Hmm, knowing how R19 performs, it's interesting that it doesn't sound hollow with it just down to the bottom of the driver. Then again, the sim shows a near critically damped alignment with no damping, something I don't normally look at, so consider just pulling it all out and suspending strips of it diagonally across the top and either anchored or weighted at its bottom. This will damp both planes with a much reduced stuffing density and if it still doesn't sound 'boomy', then try something even more acoustically transparent.

I've got a sneaking suspicion that just some on the top to quell the TL's harmonics and loosely covering the back of the driver with coarse muslin or cheesecloth/insulation like was once common with I.B. installs may suffice, so you may want to try this after removing it from the sides/back [fig. 5b]: http://www.lansingheritage.org/image...ign/page08.jpg

As for Her Highness's lighting preferences, I'm not touching that one with a '10 ft pole'!

GM