open and closed backs

[bill67]

Why do some amps have backs on them and others are open,what different s does it make in sound?

[twanger]

Lots of opinions on this one. In general a closed back will increase bass response of your speakers. An open back allows bass response to "fade into the background" which gives an effect of allowing more mid treble. A semi-open back cab seeks to achieve a better balance between open & closed back. This effect is mechanical and a matter of physics and will therefore work with whatever speakers you choose to use in your cabinet. The trick is to find what works best for you to achieve the sound/tone that you're looking for.

 

Things to google to help you understand this further are:

impedance

reactance

Thiele/Small parameters

 

And remember that speakers for use in a guitar cabinet are not really designed to be linear like you would use in home stereo cabinets, studio monitors or better PA cabinets.

[Dave]

Open back cabinets in my past were generally lacking in bass response. I favored closed back cabs, generally populated with 4x12" speakers. My recent purchase of a Peavey Vypyr Tube 60 changed my opinion on open backed cabs. I has tight, well defined lows, and a great mix of tones reflected off the wall from the open back. Granted, when you walk around to the back and listen at volume, there's a mid range peak. I think that mixes well with the sound coming from the front to balance the overall sound.

 

Most tube amps are open back or at least have an open upper section to let the heat out and cool air in.

 

My Peavey is a tube amp with a DSP front end that, I think, has a lot to do with the overall sound in spite of the fact the back is open. You can tune the cab with DSP to provide full range sound by balancing the EQ with active circuitry.