Open- or Closed-Back Cabs for Blues Harp?

You may have noticed that I have a propensity to test conventional ideas. When I decided I needed a speaker cab I went with a closed –back design, while almost all harp players seem to prefer an open back cab when using separate cabs and heads.

I liked the way some closed-back cabs sounded with guitar: Dark and THUMP! I wanted to try that with harp, so I ordered a 2x10 closed back cab from Avatar, thinking I could saw off part of the back panel to convert to a semi open-back configuration if it didn’t work out.

All those cool old tube combination amps harp players use are semi open-back for two reasons: Efficiency and air circulation. Open-back cabs can sound louder than closed unvented cabs, and those tubes get HOT and need airflow.

I’ve played the closed back cab for several months and like the low end, but to my ear it sounded kind of muddy, so I finally got around to removing the back panel and running it across a table saw, cutting off the bottom seven inches.

Now it sounds great! As expected, the cab instantly sounded more lively and open; more musically nuanced, more dynamic. I drove it with my Masco ME-18, which is kind of a darker-sounding harp amp, and also with a Fender Pro Junior and a Fender Champ. They all sounded good, particularly the Champ.

I miss the deep grind I could get with the closed cab when bending a 2-hole draw reed with a tight cup on a lower-tuned harp, but the open cab is more versatile and efficient. So, there are good reasons why some wisdom becomes conventional. Semi open-back cabs sound better.

But if I change my mind I can always put that bottom panel back on the cab and get deep and dark again…

TEST NOTES: The drivers in the cab as I write this are a Weber Sig 10 alnico with smooth cone and a Jensen Mod 10 ceramic. I have a Weber Beam Blocker on the Jensen.