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Stereo Sub-Woofers

Posted by Bold Eagle on December 29, 2016 at 09:41:28:
I wanted a little more deep bass in my den system, so I hatched a plot to build up a pair of sub-woofers using stuff I had lying around. First, I had a pair of old JBL L-110 cabinets. Next, there was a pair of 250 Watt Parts-Express plate amps from maybe 10 years ago. And third, there were a pair of Eclipse W1038R 10" woofers. The woofers had once been installed in the JBL cabinets, so the threaded inserts were still there for mounting the woofers.

The L-110 cabinets were ported, so I closed the ports with wood plugs. Then opened the mid-range sub-enclosures, and capped the midrange opening. The cabinets were 100% filled with Acousti-stuf, as I wanted a true Acoustic Suspension set up.

The plate amps were mounted to 4" deep open back frames and mounted to the back of the cabinets using small angle brackets, and the output leads from the plate amps were terminated in gold banana plugs and plugged into the 5 way binding posts on the back of the cabinet. The plate amp covers the cabinets input jacks.

OK, that gave me a matched pair of sub-woofers. They were placed in the front room corners with the front of the cabinets facing a wall with a 2" spacing. The air trapped between the front of the cabinet and the wall adds mass to the cone and lowers the resonant frequency of the system by a few more Hz. The subs are driven off the output of my Adcom GFA-545 II with a separate set of cables going to the right high level input on each plate amp. The low pass filter on each sub is set to about 50 Hz.

The main speakers are a pair of Advent cabinets on 15" stands and fitted with a SEAS 27TBFC/G tweeter and a SEAS A26RE woofer.

I'm a big fan of using stereo subs rather than a single sub fed with a summed L+R signal. Years ago, I had the opportunity to compare stereo subs vs summed L+R through the same two subs. The summed signal seemed to have less information - something was missing in the summed signal. I think this is due to cancellation of out-of phase data from the L & R channels.

Stereo subs, as opposed to a single mono sub have an advantage in power handling, lower distortion, and no pulling the image to one side or the other. I also find it a lot easier to set up a pair of subs each located near the main speakers than a single mono sub. I also find stereo subs don't need a steep low pas filter. These amps use a second order filter which is easier to blend with the main speakers, which are run full range.

Bottom line - How does it sound? I'm finding deep bass in recordings where I didn't know there was any. Overall balance is better and recordings with room ambience give a more natural sound. It's easy to overdo the level with sub-woofers, so I started with a low level and gradually increased the level. Depending on the recording, I'm now at the point of having a little too much bass on some albums, and a bit too little on others; but most sound well balanced. Deeper male voices don't sound "chesty", thanks to the low setting of the low pass filter.

The project was months in the planning before I decided to pull the trigger on it. Over the next couple of weeks there will be some fine tuning of the plate amp settings (level, phase, and low pass frequency) and some tidying up of details. But mostly, I'm done and pretty happy with the results.

And my "unused" pile of stuff is now considerably smaller.

Jerry