4642a driver replacement

[Jon Dent]

Can you still run 'Voyagers'?

Nope, KDM expired. Lionsgate never gives you any extra time outside of your booking window. Gravitas Ventures, on the other hand, gave us a near six month window on 'Our Friend'. Different strokes I guess...

Marcel, it was definitely coming from the sub. It's at ear level behind the screen and I was standing right in front of it.

Marco, the sub was indeed very close to the screen. Can't say whether that was the sound, but I did push it back a bit before putting the screen up.

I should explain how I'm testing this. We don't have a frequency generator, but we do have a 7.1 'showoff' trailer that I created for the theater that has some pretty strong content in the LFE, including a bass drop from 70Hz to around 35Hz that needed some decent limiting to avoid clipping the channel. When the noise was present, it was very audible with this trailer in several places. Since yesterday I've played the exact same trailer multiple times (both before and after a regular showing to make sure the amp was nice and warm) at the same volume with no issues at all. The only difference is the amp is one 'tick' lower on the volume dial.

[Carsten Kurz]

When our subs blew a few years ago, it was audible at higher levels, but also clearly visible on the cones. At our site, however, it is much easier to inspect the speakers visually, I just need to go behind the screen, there is enough space.

A few years ago when we transitioned to digital we found we had a number of JBL surround LF drivers blown. This was not visible on the cone, their voice coils had developed bubbles. They were not burnt-through, but the bubbles would make them stick in the gap at low levels. Most of the time, they would simply not play, only at very high surround levels with low frequencies they would cause 'some noise' (rarely in 35mm days). The remaining good surrounds made up for this deficit to an amazing extent. So we never learned when the actual issue occured. Could have been months or years before

A sine sweep is a very good tool to test speakers, but also plain room/outfit resonances that are not a speaker defect.

I am not sure though about the proper sweep levels over the whole spectrum that are 'healthy' for the system, especially for the HF drivers, so, it's probably a good idea to stop the sweep at 6000-8000Hz.

[Jon Dent]

When our subs blew a few years ago, it was audible at higher levels, but also clearly visible on the cones. At our site, however, it is much easier to inspect the speakers visually, I just need to go behind the screen, there is enough space.

Before our renovation you could easily get behind the screen. Now there's maybe two feet of clearance between the screen and back wall and the old access is gone, so the only way to get to the speakers is to take up at least part of the screen.