This tip is for all you players that use an open back combo amp. This tip comes from a personal experience on a gig. During the soundcheck at a recent gig I noticed that my 5F6-A 4×10 Bassman clone I built sounded a little thin and harsh in the midrange. It also sounded very two dimensional and lacked dynamics. This amp usually sounds nice and thick with plenty of girth and has that juicy tweed tone that goes perfectly with my Tele’s. My rig sounded glorious the night before and after a quick check I knew that there wasn’t anything wrong or broken. It still sounded bad however and I was not going to spend the entire gig with my ears hurting from the harsh non-musical tone.

The only thing I could think of that was different from the previous night’s gig was the placement of the amp onstage. The night before my amp was about 10-12 feet from the back wall of the stage and on this particular night my amp was about 2-1/2 to 3 feet from a wall. The wall was also smooth and painted with gloss paint so it was a reflective surface. What was happening was the sound coming from the back of the amp was bouncing off the wall and combining with the sound coming from the front of the amp. Now we all know (or maybe not) that the sound from the back of an open back combo is out of phase with the sound coming from the front of the amp. This results in a phase cancellation similar in sound to hooking up one speaker with opposite polarity to another in parallel. That’s why I was getting the thin, harsh, very unmusical sound. Had the wall been covered with fabric or carpet or if I had a closed back cabinet this would have never happened.

So now that I figured out what was going on I needed to fix it quickly because we were about 10 minutes before the start of the gig. I needed to deaden the back of the wall directly behind my amp. I took the padded bag for pedalboard and opened it up. My pedalboard bag is about 30 inches by 16 inches. Completely open it then is about 60 inches by 32 inches and the inside is like a sort of velvet material. This is very sound absorbent material and it has 1 inch or so padding. I leaned the open pedalboard bag against the wall behind my amp and instantly my rig was about 85% better!  Most of the reflections were eliminated and the phase cancellation was minimized.

Next time you are a gig with an open back combo and it is close to a reflective wall deaden it with whatever you can get a hold of. Your ears and soul will thank you for it!

300Guitars Shop

My shop is located at 1 Executive Dr Unit L Toms River, NJ 08755 Please feel free to email me if you have any questions or are in need of some tech work.
  • Monday: 10am - 5pm
  • Tuesday: 10am - 5pm
  • Wednesday: Closed
  • Thursday: 10am - 5pm
  • Friday: 10am - 5pm
  • Saturday 10am - 2pm. (I am in every other Saturday).
I am also an Eminence, Mercury Magnetics, Mojo Musical Supply dealer. I do all the tech work myself so you deal directly with me. I am a one man shop and my hours can vary so please contact me to confirm that I will be open. Email me: Call or text me: 848-218-0362 Shipping Info for all repair work: Please ship all repairs to: 1 Executive Dr Unit L Toms River, NJ 08755
I am currently offering all phases of guitar work which includes:
  • Set-ups
  • Fret dressing
  • Re-fretting
  • New hand cut custom bone nuts & saddles
  • Electronics work
And amplifier work which includes:
  • Basic maintenance
  • Bias adjustment
  • Repairs and restorations
  • Modifications
  • And more....
David Nicholas - The 20watt amp is sounding fantastic! Delivered the goods at the gig and I'm finding cool tones all over the place with it. Love the cab w Emenince Tonkerlites too- perfect for my sounds! Makes the 12 string sound like a grand piano!
Peter Lacis - I had an audition for something recently that was all about Led Zeppelin I -- my custom Pennalizer BLEW THE MINDS of the guys I was playing with. They couldn't believe the sounds coming out of that amp. That album was never in my mind when I came up with the that's yet another testament to the amazing work that you do.
Scott Goldberg - I am very satisfied with the set-up, and the fast turn around.  With the "lower" action it feels easier to play.  I will definitely spread the word.