Upsetter 110

There are basically two sorts - closed-back and open-backed. Open-backed because they were combos and needed to keep the valves cool and accessible for servicing, closed-back and sealed because that’s how most speakers were made in the 1960s.

The closed-back cabs have narrowing dispersion as frequency increases (a hi-fi speaker uses smaller speakers for higher frequencies to reduce this problem). The open-backed cabs fire sound out of the back as well as the front, so although the dispersion narrows from both front and back in much the same way as the closed-back cab, the sound coming out of the back helps fill the room with mids and highs - but that sound out of the back cancels out most of the lows (due to the inverted phase as the back of the speaker pulls when the front pushes and vice versa). In other words, open-back cabs are easier to hear around the room but the lows are thinner.

From the front it behaves much like a closed or open-backed cab. But the mids and highs coming out of the AVD at the back are amplified and dispersed around the room whilst the lows are inverted to match the lows from the front, giving lots more bottom. Basically you get twice the output of a closed back cab with an identical speaker AND even better dispersion and audibility (and far far greater output) than an open-backed cab

You see it when you look at the back of the cab - it’s the Augmented Vent Diffractor. It’s a unique Patent Pending technology that we started developing back in 2013. At low frequencies it acts as a tuned vent or Helmholtz resonator, improving efficiency, power handling and output. At mid and high frequencies it acts to diffract, disperse and couple the sound with the room for improved audibility and output especially in rooms with poor acoustics.

The increased low frequency output from the AVD may be too much for some guitarists’ tastes - so you can flick this switch and remove lows at the cab. Doing so not only changes the bass response but also increases the power handling of the cab, lowers the distortion due to motor excursion and reduces the load on your amp’s output stage. This can give you two different sweet-spots of optimum speaker overdrive or break-up and two different sweet-spots of power valve overdrive. If your sound is perfect in rehearsal but too dirty at a louder gig then engaging the Lo Cut filer will clean it up.