Open-Back and Closed-Back Speaker Cabs
As an amp builder I often get asked about the sonic difference between open-backed and closed back speaker cabs and which is better? It is clearly a matter for debate. Some players insist and that only one type or another is good or that Marshall amps need close backed design or Fender’s need open backs. So what’s the lowdown? The truth is that both designs have applications and pro and cons.
Open-backed cabs are exactly what the name suggests: speaker cabinet with an open back. The open back cab means that sound is dispersed through both the back and front of the speaker. In general open-backed cabs have a room filling quality and sound open and natural. The high end has lots of presence and the low end is moderate. One issue that comes up with open backed cabs is that the sound dispersion can change based on how far from a wall the cabinet is placed so there is an element of inconsistency from room to room with the cab. One strategy that could be employed would be the use of a plexi glass that could be stood at the rear of the cab at the distance of choice.
What amps have them?
Pretty much any tube combo amp will be open-backed simply because the tubes need air to cool. They are also common as extension cabs.
Closed-backed cabs have more low end punch than a open-backed cab. The highs are rolled off a bit giving them less presence. This is why many amps that are designed for them have circuits that promote brighter sound. The other quality they have is they are more more directional. Since the sound only comes out of the front of the cab the volume can be earth shattering standing directly in front of it but hard to hear if you stand to the side of the cab.
One major design issue is that a cab needs to be deep enough to sound natural. Many cabs are not deep enough and for that reason do not sound very good. Remember large manufactures are more concerned with material costs and shipping costs than sound. Because the air is trapped inside the cones movement is restricted--this tends roll off certain frequencies and reduce volume slightly. This leads to a cab sounding "boxy". With a closed back cab bigger is better!
It should be noted that some companies use padding on the inside of their cabs. This makes the cab behave as though it is bigger by absorbing the back-waves off the speaker. Sometimes add such a material to a cab can enhance the sound but it all a matter of taste.
So which is better:
That mostly depends on you! Both have applications. You really have to try both to know but if you read the descriptions I’m betting you already have an idea of which you will gravitate toward. Also different amp will work differently with one type of cab or another.