VTF3 max extension with both ports open?

[unknownshadow]

Hi guys, quick question... I know this has been discussed before but I cannot find it using search. I am wondering what the effect is (or if any damage can be done to the sub) by running the VTF3-MKII with both ports OPEN and setting it to max extension mode, rather than the usual max output mode? Will this allow the sub to dig a little deeper?

I have recently been playing with my dual VTF3's and I have been surprised to find that I seem to prefer running them with both ports open in max output mode. There just doesn't seem to be as much bass when running them in max extension mode, even though they should be digging deeper. I have been playing a bunch of my favorite LFE scenes which dip below 20hz and I am very surprised that max output mode seems to give me more impact.

So I have been curious to try running the subs with both ports open and flipping them to max extension mode to see what would happen. But I don't want to do this unless it is safe. Any info appreciated. Thanks

[Bill Mitchell]

You can find comments about this by searching for "overdamped". See Pete's notes here (http://forum.hsuresearch.com/showpost.php?p=15569&postcount=1), here (http://forum.hsuresearch.com/showpost.php?p=54478&postcount=2), and here (http://forum.hsuresearch.com/showpost.php?p=61254&postcount=8). In particular, he writes:

... On the other hand, never run the subwoofer with both ports open and bass extension switch set to the up position, as the driver can be damaged due to lack of subsonic filtering below the port tuning frequency. ...

Bill

[unknownshadow]

Thanks Bill. I got a reply from Pete via email as well. Looks like I had it backwards. That's why I wanted to be sure and ASK before trying! :)

[unknownshadow]

Although, I'm still not entirely sure what this overdamped response (ie. early rolloff) means?

So here are the possible modes you can run the VT3 in...

A. Both ports open / EQ set to both ports open = Max output above 20hz
B. Both ports open / EQ set to one port plugged = BAD IDEA! Can damage driver
C. One port plugged / EQ set to one port plugged = Max extension below 20hz
D. One port plugged / EQ set to both ports open = Overdamped response

I understand that max extension mode (A) lets the sub dig a little deeper into the subsonic material at the expense of output above 20hz. And I understand that max output mode (C) gives you more output above 20hz while sacrificing how deep the sub will go into the subsonic material. And option (B) is a big no-no!

But what about option (D)? Is that simply a trade-off between (A) and (C)? What am I gaining or losing with option (D)?

[OU812]

by having one port plugged and the EQ set to "max output" is that you'll get more impact than with "max extension/one port plugged" and it gives you more low extension than having "both ports open/max output"

[Bill Mitchell]

... But what about option (D)? Is that simply a trade-off between (A) and (C)? What am I gaining or losing with option (D)?

In overdamped mode, the speaker itself is capable of the Max Extension behavior of (C). But the high pass filter of (A) cuts the low end response below 20-25Hz. This can be useful to control modal room resonances below 20Hz, especially where some other system like Audyssey is boosting the response to try to make it flat. I posted the graph comparing each of these curves in my room (http://forum.hsuresearch.com/showpost.php?p=55017&postcount=32).

Bill