Aviatrix RST MLTL Height question

[joshuass1467]

Hey guys, been awhile.

I have a question regarding the Aviatrix RST MLTL design specifically. The plans call for an outer box height of 44 inches. I read in the design notes that this height was chosen pretty deliberately.

My problem is that I can't build them to 44 inches. Most I can do is 40.

What effect would shortening the box have on the design, given the deliberate selection of 44" as the box height? This assumes that I can keep the box volume and baffle width the same.

[Paul K.]

A couple of things will happen with the shorter box. One, the "line" (the internal height of the cabinet) will be shorter and the 1/4-wavelength resonant frequency of the line will be a bit higher, thereby changing the required dimensions of the port in order to restore the original system tuning frequency. Second, the location of the port relative to the woofer's location may not be ideal in terms of the system response shape, and the only way to determine the optimum location for the port is to use TL modeling software that takes into account not only the volume in the line but its dimensions and locations of woofer and port.
Paul

Hey guys, been awhile.

I have a question regarding the Aviatrix RST MLTL design specifically. The plans call for an outer box height of 44 inches. I read in the design notes that this height was chosen pretty deliberately.

My problem is that I can't build them to 44 inches. Most I can do is 40.

What effect would shortening the box have on the design, given the deliberate selection of 44" as the box height? This assumes that I can keep the box volume and baffle width the same.

[joshuass1467]

Hmm. Alright thanks!

For the time being. I'll have to do the sealed version, unless i can figure out how to calculate the dimensions you mention.

[Paul K.]

Unless you have cabinet modeling software that will take into account what I discussed, along with accurate/appropriate T/S values for the mid-woofers, you won't be able to accurately determine what changes to make. However, reducing the height by 4" is only about a 10% change to the line's length and its 1/4-wavelength resonant frequency, plus if you increase the cabinet depth to re-establish the original cabinet volume, you might be close enough in locating the port as originally designed relative to the bottom of the cabinet, and with the same port dimensions, to not have much, if any, audible differences.
Paul

Hmm. Alright thanks!

For the time being. I'll have to do the sealed version, unless i can figure out how to calculate the dimensions you mention.

[joshuass1467]

Interesting.

Here is what Curt has to say about the design of the cabinet for the AviaTrix MLTL:

While the ML-TL enclosure appears to be a simple vented
floor stander, the enclosure internal height was carefully chosen so
the quarter wave resonance was a bit higher in frequency than the
port. This helped augment the response sag in what would otherwise
have been an extended bass shelf alignment. This resulted in a nice
slow initial roll off below 100 Hz of about 3 dB / octave until shortly
before the f6 at 30 Hz, where it reverts to the expected vented
response roll off of 24 dB per octave.

http://speakerdesignworks.com/AviaTrix_4.html

I'm tempted to give it a try in a simple box for testing purposes. I might have a few other options too:

1. Shift port tube down the front/back cabinet surface to gain back some of the lost TL length (not sure the effects of that here). Could gain about 1-1.5" here.
2. Design allows for a vertically oriented, bottom mounted tube. I could shorten the length of the tube to correct the TL line length. It could go as short as 2 inches.
3. Use thinner material on bottom and top of speaker cabinet.

[Paul K.]

I read what Curt said previously. Anything you do without being able to model their effects first won't necessarily be good (or bad) but you won't know what they actually will be. Moving the port will not effect the TL line length at all because it's simply the internal height of the cabinet. The same applies to changing the port to be down-firing. When locating a port in any ML-TL, it's the location along the line's length of the center of the port's internal entrance that's important regarding the line's length (height) and relative to the TL design center (the center of a single woofer or the center of the tweeter in an MTM).
Paul

Interesting.

Here is what Curt has to say about the design of the cabinet for the AviaTrix MLTL:



http://speakerdesignworks.com/AviaTrix_4.html

I'm tempted to give it a try in a simple box for testing purposes. I might have a few other options too:

1. Shift port tube down the front/back cabinet surface to gain back some of the lost TL length (not sure the effects of that here). Could gain about 1-1.5" here.
2. Design allows for a vertically oriented, bottom mounted tube. I could shorten the length of the tube to correct the TL line length. It could go as short as 2 inches.
3. Use thinner material on bottom and top of speaker cabinet.

[joshuass1467]

I must have misunderstood the important dimension. I thought it was center of tweeter to port center.

Thanks for clarifying this. Knowing this, it basically renders all of my options moot haha.

In conclusion: I have to either measure the effects by building the box with the dimensional changes. Or I model the dimensional changes beforehand.

[djg]

Similar, known designer, great build info.

http://www.divine-audio.com/ochocinco/