A Blues Harp Player's Guide to Tube Amplifier
Speaker Size and Configuration.

The bigger the speaker, the more air the amp can move. The more speakers, the more air the amp can move. More moving air means more sound. On the flip side of these truths is that the bigger the speaker or the more speakers that there are, the more work the amp has to do to move the speakers. You can't hook up a second speaker to Fender champ and expect to get twice the noise out of it. You might get less sound and you might burn out the output transformer. We hope that the amp designer has given us the best speaker configuration for the amp.

The speaker is a weak link in the path of the sound from your harp to the listener's ears. Using new modern speakers often makes an ordinary amp sound great. If you own a Blues Junior, Crate or Electar 10 then you should consider getting new tubes and a new speaker before dumping the amp. These amps come with cheap speakers and cheaper tubes. You might be surprised at the sound you get.

A. You need a 12-inch speaker if you are going to play without micing the amp. An 8 or a 10-inch speaker is great, but you can't move enough air to compete with the Fender twin that the guitar player is using. You have to mic the small speaker amps.

B. Two 10-inch speakers are better than one 12-inch speaker. Simple math: a 12-inch speaker has an area of 113 square inches. 2-10's have an area of 157 square inches. Not all of the area of a speaker is moving air, but the numbers show the relationship between a twin 10 and a single 12. Twin 8's are better than a 10 and almost as good as a 12. 6-8's are the about the same as 4-10's.

What is the best for a harp amp? I like Twin 8's or a 12 for an amp with 2 6V6's and 4-10's or 6-8's for an amp with 2 6L6 tubes. The 12-inch speakers are way too heavy for me. If I were going to lug all that weight I'd rather have an amp with 6 8-inch speakers than the twin 12.
Here's a simple chart showing how speaker sizes relate.

On the left is a speaker size, 8 to 15-inches. If you go across you'll see that a 15-inch speaker is the same as 3.5 8-inch speakers. You can see that a 10-inch speaker is equivalent to 3 6-inch speakers. These are very rough calculations based only on the area of the speakers and do not take into effect any other factors.

C. Jensen speakers are what you should look for in a vintage amp. Older amps have Rola speakers and a Utah speaker is OK. Modern speakers include Eminence, EV and JBL. If your amp sounds dull or isn't loud enough, but otherwise has a good sound, consider a new Kendrick or Mojotone speaker. There is no advantage to keeping the old speaker except to keep the amp original. Keep the old speaker around and when you sell the amp, put it back in the amp and keep that hot new Kendrick.

If you amp has no-name speakers, look at the size of the magnet. Bigger magnets are indicative of a speaker that can handle more power.