August 13, 2011

Black widow test box measurements and impressions

< Project intro

The measurements were surprising, better than expected based on the sims. 

What is a 6th order bandpass? Think of it as a vented box (the rear chamber and port) that has an acoustic front chamber added. This chamber creates another tuning point that sets the upper bandwidth limit. It filters harmonic distortion as well. 

Nearfield measurements

Red: rear port
Blue: front port

The front port does not have the predicted peak, it is quite flat. I also discovered that I had tuned it too low hence it doesn't reach the 300 Hz target. You can see the front port has surprising extension and the rear port

Electrical crossover filters have been added. 

The box was measured with the box in the middle of the main speakers. Hence there are some modes that haven't been tamed. 

Listening impressions

It's hard to comment too much because, as you can see above, there are some room modes in the response that normally I would have dealt with. The peak around 44 Hz is probably related to the sense of the bass being much more tactile than usual. It's fun and novel for a short burst, but would probably bother me over time because everything takes on a certain "sameness." However, for a thrown together box not fully integrated, all the signs are there that this is going to work well. 

I have a couple of specific goals with this box:
  • cover 40 - 300 Hz using bandpass to increase the efficiency at the top end
  • effectively meet the horn at 300 Hz with the acoustic source close to the horn (achieved with the slot port at the top)
  • reduce the "thermal load" on the subs with music
  • fit inside the large corner bass traps I have planned
So far it appears that this project will work out well. 


  1. Hello Paul,

    Where are you at with this project?
    I would like to try something similar in the 30-300Hz range using a TAD TL1801, to put it closer to the midbass driver and avoid the boost from the floor in the upper part of its range.

    Have you compared this acoutsically filtered version to a normal BR version (slot removed) with eletrical EQ only (with the same target response) ?

  2. I sold the driver as it wasn't suitable to run up high enough to work with a midrange horn. Now using a sealed box with an Eminence Magnum.

    I didn't compare very carefully but tried it with the front chamber, then removed the chamber. The results weren't radically different as I recall.

    My priorities are a little different now, where I prefer to have the box in the corner in a bass trap, with minimum size and a sealed box.


All comments are moderated.