August 13, 2011

Black widow prototype - 6th order bandpass

Before building the final version of my black widow active woofers, I decided to build a test version. I didn't fully trust the WinISD simulation of band pass boxes as it seems buggy and incomplete. This box was built, tested and then enjoyed in the one day. Many thanks to Antripodean who helped with building the box.

The box is 550mm wide x 580 deep x 620 high. The top of the box behind is about 900mm or seated ear level and you can see the 6" waveguide with foam in it at the top of the shot. The test box is similar in size to a 2 draw filing cabinet.

1. Testing driver parameters with the Dayton Woofer Tester 3

I did a quick test to make sure the parameters were close enough to the model.

Peavey Black Widow 18" (specs from Peavey in brackets)

fs: 39 Hz (36)
re: 6.5 (5.8)
Qts: 0.43 (0.37)
Le: 2.94 (2.07)

2. Simulation in WinISD

As you can see, there is a substantial difference in parameters, so I checked the simulation to see if it meant a different design. The two were quite close.

You can see a big peak from the front chamber port. This means WinISD thinks the port is too efficient, ie tuned too high for it's size, or the volume too large for the tuning point, or both. Reduce the front chamber size and you get a big dip in between the two humps. My plan was to EQ out the peak carefully, then yielding a flatter response than otherwise possible. However, the test box revealed that WinISD didn't really predict things too well.

3. Building the prototype

This is a simple unbraced box with an estimated net volume of 124L (12L for the front) with a shelf port for each. You can see the front chamber which is not much bigger than the driver:

The front chamber can be removed easily.

There isn't too much you can show when building a very simple box like this. Bunnings were out of 18mm MDF so this was built with 16mm. Not too much different, but given that this is a big unbraced undamped box, it rings like a hollow el cheapo boombox. It often can be a surprise how much you can get away with ...

Surprisingly I didn't quite manage to build the whole thing with one sheet. I had to add some particleboard flooring on the front chamber. Being a timber hoarder does have advantages.

Continue to measurements and listening impressions >


  1. hi Paul,

    this looks interesting.. i was wanting to build 2 subs with black widow drivers, but ended up buying 2 Beyma 15 ND/W at a clearance sale.
    Would like to have a passive x over/ roll off around 90Hz.. DO you think its a realistic aim?

  2. Alex, I wouldn't even try. Far better to go active, for many reasons. Beyond reasons like choice of amplification, damping factor, issues of bafflestep and matching sensitivity, you also have a need to be able to make adjustments until you get the bass balance just right. Some of that has to be done by ear, but the passive method is inherently inflexible and fixed.

    1. thanks Paul, apologies for my late response. I gues am trying to avoid the many "attachements". My goal is to build something to support my 2 powered Peavey Impulse 10's. I aim to drive the Beymas with a Crown K2. Was thinkin rather than dragging 2 subs, i could maybe build an isobaric. Have you built any?

  3. In that case you halve the box size but decrease the efficiency. I'm not a big fan of isobarik because it's an expensive way to throw away efficiency to get a smaller box.


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