GM's MLTL with 416-8B

[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

[westend9]

Thanks, GM.
I reassembled a "clicker" as per the schematic you linked to back in a past post in this thread. Results were a very accurate, amplified, click without any boom or veil of the sound.
I will remove insulation in the cabinet when I am able to access the bottom hatches, more readily, when the cabinets are on carpet. I hate to tip them over when situated on a concrete floor, accidental dropping or scratches can be avoided.
I am still enjoying the new TL sound of these and I believe with some minor stuffing tweaks and better matched amplification, it can only get better. Visitors of differing levels of listening experience have all reported with positive compliments, even removing the social-biasing, their reinforcement of a positive experience is approval of the design.

I am comfrotable with the size of these as I have the space and proclivity to not be bothered by large speakers. Others are not so acceptable to their size. Is there an alternative in your MLTL designs to enable a similar alignment? Just curious because the reproduction from the 416b is so enjoyable and others may wish to hear what a TL cabinet can do without having the larger cabinets.

[GM]

You're welcome!

Understood, I've still got five different size commercial plush [super dense] carpet remnants for just such occasions. Turn the big one face down and it makes a great 'towing sled' to drag big/heavy ones around.

Yes, and no. I mean you can shrink the cab's CSA and actually get a more perceived 'tightness'/'snap', but it's because there's much less bass output to balance it out even though it's tuned the same, i.e. has a higher F3, so ideally it would be corner loaded. This is the 'secret' to Pi Speaker's PiAlign, it's an old prosound design routine based on W.E.'s original reflex alignment he resurrected/claimed for his own. For low output impedance systems, the PiAlign is preferred, but for higher output impedance the original is preferred since it de facto requires a [ideally] measured Fs tuning.

Anyway, I've designed/built far more skinny 'tower'/'column' alignments [aka ML-TL, ML-TQWT, ML-horn as well as the various 'Classic' pure TLs] than deep bass capable ones for one reason or another, including Altec loaded, so very familiar with all of them.

Anyway, shrinking yours to be only big enough to mount an 811 on top reduces it to 18.75" o.d. wide x 17.25" deep o.d. or ~7.55 ft^3 net which has much less bass output and due to the smaller net Vb the vent now needs to be 5" long. It's also acoustically too high an aspect ratio, so stuffing density doubles to 0.5 lbs/ft^3 to get a similar response smoothness:

GM