Phase Canceling Speaker Cab

[DIY Guy]

I think this has become my M.O.

Something excites me and I decide to build one. But it has to be a little different. A little custom.

Johan Segeborn has many great videos on all things guitar.

He got me all hopped up on Fender 410 Bassman's... So I decide to power a new cab with my 2007 Fender Frontman-15.

Only mine's going to be smaller... Hey! Why not overlap the speaker rims!

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Starting with a bunch of 2x6's glued together I route out speaker cavities that are of different depths to acomplish this. I Finish designing the rest of the cab based on a bunch of Jim Lill's cab response discoveries (Another great source) And VIOLA!

MY FIRST 410!

Pleased as pie I stop playing for a while to watch another one of Johan's gems when I discover:

●●●●●●●●●●●●●●●●●●●●
●●●  PHASE~CANCELATION  ●●●
●●●●●●●●●●●●●●●●●●●●

I had no idea about phase cancelation. Never heard of it...but now I have, and it seems logical enough.

This topic mostly comes up in talk about how to record amps and drums with multiple microphones, and usually surrounding the problem of treble loss.

Frequency waves have individual lengths.

The length of a higher frequency is shorter than that of a lower frequency.

If you record the sound coming out of a single speaker using TWO microphones, and place them at different distances from that speaker, you WILL be messing around with Phase Cancelation.

...and if you happen to catch the very peak of one frequency's sine-wave with one mic, and the very bottom of that same frequency's sine wave with the other microphone, THAT FREQUENCY WILL BE MISSING FROM YOUR RECORDING. GONE. SILENCE (Johan Segeborn has a GREAT video demonstrating this).

Not that you'd notice live "In The Room". Just when you stop to play-back what you recorded.

Why am I going on about this in regard to my 410 cab project?

Because I accidentally created
"Live Phase Cancelation" with my speaker baffle design DIDN'T I !!!

I offset the speakers from one another.

So while my ears are in one place, the speakers are in two places!

...by 1/2"...

...but to completely CANCEL a frequency, you need to look at HALF its sine wave length so you are "seeing" both its peak AND its trough...

While 27 KHz does have a 1/2" long sine wave, I need to know what frequency has a 1" long sine wave...

Which frequency is my 1/2" speaker
off-set canceling?

13.5 KHz = 1.0003"

...and I should think OTHER frequencies either side of our "perfectly canceled" frequency would be diminished too, so the range and severity of phase cancelation surrounding 13.5 KHz might be at 1/4 the distance either side of center?

   3/4"   ~    1"    ~   1-1/4"
17.99 KHz ~ 13.5 KHz ~ 10.80 KHz

NOW...what about when your off-set multi-speaker cab is housing dissimilar speaker models? CONE LENGTH?
The RIMS (Bass frequencies) are sitting there at your cab's fixed offset. But the voice coils (Treble frequencies) of different speaker models are closer or further as well!

If I'd known all this before fabrication, I might have designed the baffle for a built-in Phase Cancelation Center Frequency of 10KHz(?) or in other words: 1.35" ÷ 2 = .675" Baffle Offset. Oh well.

There are actually online calculators and charts for this, so I utilized the
"Sound Wavelength Calculator" from www.omnicalculator.com


WHAT DOES THIS ALL LOOK LIKE

Frequency lengths
(Peak to Peak in AIR)
     
Keep in mind that the INVERSION of any sine wave peak occurs at HALF these lengths...

   10 Hz ~ 1350.4"    Infrasound
   20 Hz ~ 675.2"  Audible Frequency
   30 Hz ~ 450.1"
   40 Hz ~ 337.6"
   50 Hz ~ 270.1"    
   60 Hz ~ 225.07"  
   70 Hz ~ 192.9"
   80 Hz ~ 168.8"   START of Guitar
   90 Hz ~ 150.04"
  100 Hz ~ 135.04" Bottom Real guitar
  200 Hz ~ 67.52"
  300 Hz ~ 45.01"
  400 Hz ~ 33.76"
  500 Hz ~ 27.01"
  600 Hz ~ 22.507"
  700 Hz ~ 19.29"
  800 Hz ~ 16.88"
  900 Hz ~ 15.004"
 1000 Hz ~ 13.504"
 2000 Hz ~ 6.752"
 3000 Hz ~ 4.501"
 4000 Hz ~ 3.376"
 5000 Hz ~ 2.701"
 6000 Hz ~ 2.2507"  Top Real Guitar
 7000 Hz ~ 1.929"
 8000 Hz ~ 1.688"
 9000 Hz ~ 1.5004"
10000 Hz ~ 1.3504"    END of Guitar
11000 Hz ~ 1.2276" ● Phase Affected
12000 Hz ~ 1.1253" ● Phase Affected
13000 Hz ~ 1.0388" ● Phase Affected
13500 Hz ~ 1.0003" ● Phase Canceled
14000 Hz ~ 0.9646" ● Phase Affected
15000 Hz ~ 0.9003" ● Phase Affected
16000 Hz ~ 0.844"  ● Phase Affected
17000 Hz ~ 0.7943" ● Phase Affected
18000 Hz ~ 0.7502" ● Phase Affected
19000 Hz ~ 0.7107"    
20000 Hz ~ 0.6752"   Audible Frequency
21000 Hz ~ 0.643"      Ultrasound

So that's been my journey into Phase Cancelation so far...

I hope someone else can benifit from this the way my old skipper would've benifited from understanding the reactions between oxygen and petroleum oil when he sneekilly plumbed an oxygen tank into his dirt-track car's intake manifold.

Camel-Bump hood mod anyone?  lol

Cheers