Simple Model 19 plans available

[GM]

Greets!

Indeed there is!

Yes, in theory there's only one vent to the room air assuming there's no leaks anywhere, but due to the reduced area cutout and spacer between the upper and lower cab Vbs, this constitutes a ducted port between the two and this alignment is normally called a double bass reflex (DBR) wherein this extra chamber/duct forms a second resonant acoustic circuit that in this case is tuned to higher frequencies, though below this tuning the driver just 'feels' the extra volume (Vb). My earlier comment was addressing the difference in tuning due to this duct being much longer than Marty's 3/4" thick one, which will tune it even higher than the M19's.

Once the horn is installed though, the ratio of chamber Vb to duct Vb may not be enough to matter, I haven't crunched any numbers or ever seen a hi-res FR plot, so as I noted, this is all theoretical at this point, I just wanted to point out a potential reason why they may not sound ~identical.

WRT reflex vents Vs ducted ports, yes they have more tuning flexibility if desired, but they damp the driver better, which affects quite a wide BW in a BR, so for a given amount of internal insulation/damping material, the ducted port will sound a bit 'tighter' than a simple cutout, ergo you typically need less of it with a ducted port.

GM

[GM]

Originally posted by martyh45:
Hi GM,
Thanks for the inpu. It should be a simple matter to add the port to the interior. I am thinking a 2-3/4? extension around the cutout in the horn shelf should be close but I am not sure if it would be better to make it a bit longer so that the volume inside the port matches the original or to keep the length and entrance exit areas equal. What do you think?
Thanks,
M

<font size="2" face="Verdana, Helvetica, sans-serif">Greets!

You're welcome!

Yes, you can add it, but then it's big enough that the Vb will have to be added back in the form of a slightly longer lower cab. Well, best to mimic the original and fill the voids with sterile sand, kitty litter, or similar if you're trying to preserve as much of the M19 cab's 'tone' as practical.

Really though, as I've noted on a number of occasions, I'm no fan of the M19 because it's a marketing design with too many compromises. The few folks that have built my taller, simple one box tower (aka MLTL) alignments don't plan on going back AFAIK, but they are much more 'accurate' reproducers than Altec's 'West Coast' tuning, though the towers can be tuned this way by moving the vent closer to the driver.

GM

[sekess]

Hi GM,

Are plans available for your MLTL cabinets? From what you say, it sound more like what I'm after.

Thanks,
Steve

[Jim Butler]

Concerning the M 19's spacer between the top and bottom...I completely dismantled a pair of 19's a few years ago and reassembled the top/spacer/bottom elements by screwing,glueing ,and caulking. The ones from the factory were completely unsealed (you could see daylight between the joints). Amazing difference in bass response, being much tighter. This seems to support the theory of the internal duct having an audible effect.

I too am curious about the MLTL cab design dims. I'm always looking (hoping) for deeper, tighter base extension.

[gamalot]

Here Steve, Hope this helps.

Gary

[GM]

Greets!

Thanks for sharing! That said, the vent duct length between the two resonant cavities is considerably shorter, so in theory it won't sound the same, but I don't have time now to sim them to see if it's enough to be obvious.

Then again, factor in that I don't recall the couple I saw apart having any gasketing between the various components to effectively seal the two chambers enough for either vent to work according to theory, it could be a moot point depending on whether or not all the components are effectively sealed to the cab.

GM

[intotubes]

Wow, thats awesome martyh45! Thanks a lot. That's what I've been lookng for. Thanks for sharing.

GM, please upload your plans if you are able and it's not a proprietary design. I would love to see it.

Man, I love this board.

[martyh45]

Based on GM?s comments, I?ve revised the plans to lengthen the internal duct. They can be found at http://www.filecrunch.com/file/1e3 The internal volume is just slightly larger than the original Altec plans. You can add a 14? x 20-1/2? piece of 3/4? scrap screwed and glued to the center of the bottom to get the volume within a quarter of a cubic inch of the original. You don?t need to register to get the plans, just stare at their screen for awhile until the download button activates. Thanks to all for your comments.
Marty
Link to plans

[GM]

Originally posted by intotubes:
GM, please upload your plans if you are able and it's not a proprietary design. I would love to see it.

<font size="2" face="Verdana, Helvetica, sans-serif">Greets!

Right now I'm up to my eyeballs in little projects I volunteered for and some personal stuff I've put off as long as I can, so I'll start a new thread as soon as I can with its details if I still have them.

Regardless, I don't do drawings, but Marty has graciously volunteered to do them and some others of my design, so hopefully, over time a small library of TL/MLTL designs for different drivers will become available, starting with one for him that will probably work for some others also.

GM

[Jim Butler]

GM and Marty: mighty generous of you both.
If and when you can get to uploading plans, I have a request:

Your large vented cabinet designs for a 411 subwoofer.

Thanks again.