Avatar SB112 - port tuning too high?

[gimmeagig]

I just took the plug out and I'm not going to mess with it anymore. I like the way it sounds and I guess that's all that matters.
I did notice looking into the port that there is only one very thin piece of felt on the back wall and it covers only the left half of it and I'm not sure how high up it goes.
My Bag End S15 XD cabs are completely lined with felt and it's really thick stuff.
The Avatar was really inexpensive and maybe it's what you give up when you buy something less expensive. Or the skimpy felt padding might be one of the magical mojo ingredients why this cheap little cabinet sounds so good.....
I don't know.

 

[will33]

Fully lining it with some quilt batting/mattress pad or other will smooth it out a bit and clear up some midrange. Maybe keep the big bottom but help some other stuff??? ya never know...again totally reversible.

 

[will33]

I have stock Emi. deltaliteII 12"er's and Avatar versions and I wouldn't put either of them in that high of tuning, but then again, your ears aren't mine and vice versa. If it works, it works. Not trying to bend your ear too much.

 

[1958Bassman]

I recently bought a pair of Avatar SB112s. I decided to calculate the stock port tuning and came up with these measurements:

Ports: 7.5"W x 2"H x 7"D x 2
Internal dimensions of cab: 15.5"W x 22.5"H x 12.75"D = 4446.6 cubic inches or 72.9 liters.

Guesstimating a net internal volume of 68 liters, the port tuning is around 56 Hz. Modeling a stock DeltaliteII 2512 (since I don't have the parameters for Avatar's longer x-max variant) shows a 3 decibel hump at 80 Hz. But more worrisome is the risk of fartage and blown woofers since I play a 5-er and don't have a steep high-pass filter to protect the drivers below the tuning frequency.

I've plugged rectangular ports before using tightly fitting carpet covered plywood rectangles. If I plug one of the two ports, the tuning frequency drops to about 40 Hz and airspeed in the remaining port is still acceptable at mach .11. I'm inclined to plug one of the ports to eliminate the 80 Hz hump and more importantly, to protect the woofer.

Am I missing anything? Why would the port be tuned so high in the first place?

If you don't have the parameters, there's not much point in modelling this cab, is there?

Are you using WinISD? Re-check the parameters, or get the right ones. Is that driver similar to the Shiva? If it is, WinISD has the Shiva in the database and when I tried it, the Ft came in at 23.5Hz with very flat response. The -3dB was also 23.5Hz.

 

[bobcruz]

If you don't have the parameters, there's not much point in modelling this cab, is there?

Lack of accurate parameters is a drag, I'll admit, but that's rarely stopped me in the past. No guts, no glory!

Are you using WinISD? Re-check the parameters, or get the right ones. Is that driver similar to the Shiva? If it is, WinISD has the Shiva in the database and when I tried it, the Ft came in at 23.5Hz with very flat response. The -3dB was also 23.5Hz.

Hmm, not sure but they don't look similar to me....

 

[Crockettnj]

...With one port plugged, tuning is 41 Hz. To get down to 41 Hz with two ports, the ports would have to be much longer than the available space, and that's more difficult to implement and not reversible, ...

You are already thinking... think outside the box. Literally. The port can extend outside of the box so long as its connected and structurally sound.

With a little creativity you could certainly fabricate an external port extension to play around with dual ports tuned to where you want.

A little more creativity you could make it temporary.

If for no other reason than to try it out and see how you like the tuning difference.

ALso, it'd give you something to play with while learning to measure the port tuning freq (to confirm your calculations.

If I were interested in tinkering and had the time, its what I'd do.

.02


EDIT: i didnt read the rest of the thread, and didnt see that your cabs actually look great and arent older (ugly) boxes. port shelf extensions out fo the cab would look like monkey butt. cratch my suggestion.

 

[Crockettnj]

Alright, here are the pix. [/IMG]

BTW the wheat grill looks great.

 

[bobcruz]

BTW the wheat grill looks great.

Thanks. During the summer I plan to measure the actual port tuning using the "sugar test" to compare to the calculated tuning, so "stay tuned."

 

[bobcruz]

Subtracting the port area brings my guesstimate down to 64 liters net and the port tuning at that volume is about 58 Hz. With one port plugged, tuning is 41 Hz. To get down to 41 Hz with two ports, the ports would have to be much longer than the available space, and that's more difficult to implement and not reversible, so I'll roll with a port plug for now and I can always pop it out if I get port noise. Thanks to all who posted!

...During the summer I plan to measure the actual port tuning using the "sugar test" to compare to the calculated tuning, so "stay tuned."

The "sugar test" (actually used a grain of rice) is done and the cab is tuned to 38 Hz with one port plugged. That's likely to be too low for some users but I like it and will keep the plug in place. I didn't want to pull the plug and test the tuning of the unmodified cabinet so I'll leave that to someone else. If the same ratio of calculated to actual tuning applies to the unmodifed cab, then it would be tuned to about 54 Hz rather than 58 Hz.

FYI, I used Audacity to generate 30 second sine waves, amplified by an Alesis RA150 power amp, no high pass filtering.