Volume of the model 19 enclosure

[martyh45]

I have been trying to calculate the internal volume of the Model 19. Based on the drawings at Jeff Markwart?s site (http://home.earthlink.net/~jmarkwart/id13.html) and a couple of questions have come up. The gross volume I calculate is approximately 5.40 feet but I am not sure what volume to subtract for the 811 horn and driver. I remember seeing a link to a sheet of displacements of Altec components at this site but can?t find it in the archives. Can someone help me find that again?

Also, I tried to simulate the enclosure in WinIsd but the results didn?t seem to match the performance of the 19 in real life. Is there a free or inexpensive program that can model slot loaded cabinets?
Thanks,
Marty

[GM]

Greets!

One of us miscalculated in a big way since I came up with ~9.427333209 ft^3 net. I don't recall ever seeing a FR plot, so don't know how close I simmed it.

I assume you mean this one: http://www.lansingheritage.org/image...ure/page04.jpg

WRT WinISD, it's not known for accurate vent calcs and it can't sim the effect of the vent location WRT the driver, which can make an audible difference. MJK's MathCad sheets are the only ones I'm familiar with that will do this, though they can't sim a slot, only round vents. Even then, for programming simplicity he assumes that both the driver and vent output is at the same point on the baffle, so its vent harmonic accuracy declines with increasing frequency. Regardless, the M19's vent doesn't have a high enough aspect ratio to really affect the response enough to matter.

GM

[martyh45]

Hi GM,

?One of us miscalculated in a big way since I came up with ~9.427333209 ft^3?

Yeah, that would be me???as usual
9.4' looks allot better in WinIsd too. I have been thinking about getting a copy of MathCad but have been hesitant to take the plunge. Are the worksheets easy to use?

Marty

[martyh45]

And thanks for the link GM, that was the one I was looking for.
Marty

[GM]

Greets!

You're welcome!

The worksheets (WS) are 'plug n' play, they just look daunting because it's not formatted into a user friendly looking GUI. I only have the old freeware versions which only auto calcs Qts, so not sure whether any more fields, such as BL, are auto calc'd now that he rents them. Basically, you input the driver's specs and any other options the sheets now allow, such as series resistance, and the box design info by highlighting it and typing in new info, then it will auto calc as you scroll down through the WS.

FWIW, even though I have a licenced copy of MC 2001 PRO and XP PRO I've had mixed results (errors/crashes) doing it this way and the 'refresh' command has never worked in either 98 SE or XP PRO, so I unclicked the 'auto calc' in the 'math' window of all my masters and just hit F9 when I want it to re-calc. FYI, MJK has used them all and says to avoid MC12 like the plague.

Anyway, I highly recommend them and any Qs you may have about using them can be answered by users on the DIYaudio forums and I assume some here too. I'm pretty computer/software/math challenged and even I could figure out how to redesign some of the unlocked input fields using MC's tutorial/math Wizard. One of these days I want to learn how to use its basic drafting program to make drawings like MJK does, though I'm not sure if it's part of the package with all MC releases.

GM