Rotary Subwoofer Install Blog

October 1, 2006

Rotary Subwoofer early conclusions

Filed under: Uncategorized — bassment @ 9:54 pm

After a full day of watching movies, examining real time spectrum plots, calibrating mics, soundcards, and more, we came up with the optimal solution for deploying the TRW technology.

Thanks to a tip from Ilkka at hometheatershack.com, we learned what we had wanted to test for ourselves, which was that the L and R main channels have significant sub-bass content. And that the LFE does not get all the sub 20Hz content. There were several movie clips that did not show up sub 20Hz on the LFE, but did show up later when we had the crossover configured as I am about to describe. This is very important for those who have a separate LFE and subwoofer channel to understand and test for.
Recall that I have one Wilson XS driven by a 2400 Crown K2 amp, and two Wilson Watchdogs with their integrated 400W amp and eq, and now the twin rotary subwoofers, aka the TRWs.

We tried various combinations of the TRWs with either or both of the XS and the Dogs. The Dogs and TRWs provided an absolutely anemic experience at the movies. Clearly 20Hz+ is as vitally important as sub 20Hz. You must have both in balance, otherwise it just sounds wrong.

The XS and the TRW’s didn’t quite satisfy either… there was still something missing… slam, concussion, violence, in the movie clips. Concussion needs both sub 20Hz AND 40-80Hz, that much we learned from extensive testing today.

But how to put all four subwoofers together into an integrated and pleasing subwoofer solution? Clearly the TRW’s own 0-20Hz. Clearly the XS is better at 18-30Hz than the Dogs, and the Dogs, well, let them have from 30-80Hz. Which means we need one sophisticated crossover to handle all of this, and a crossover that can EQ and handle down to zero Hz, AND with low distortion.

Enter the best EQ on the planet… the Lake Contour. Two inputs, 6 outputs.

Here is what we did. We used the stereo Sub setting crossed at 100Hz, and turned off LFE on the Lexicon… doing so mixes the LFE with the Sub L and Sub R. The Lexicon automatically takes all the sub 100Hz in the L and R channel and, along with the LFE, shoves it into the L and R subwoofer channels, respectively.

We take the Stereo L and R sub outputs from the Lexicon and XLR them into the Lake Contour.
The Lake Contour can mix the two inputs together, so that’s what we do.. inside the Lake the L and R are mono’d. This mixing of stereo to mono was necessary so that the XS and the TRWs could get the mix of both L and R subwoofer bass… this was the only way to do it with the Contour, that I could see.
Now, we separate the mono signal internal to the Lake, and carve out the following 4 outputs:
1. TRW’s at 0-30Hz
2. Wilson XS at 20-40Hz
3. qty 2 Wilson WD’s, at 40-80Hz.

This provided a bass output that was so crisp, clean and violent, that we simply had to tone down by 3dB the two Lake inputs while watching WOTW. The lightening, the alien machine foot steps, everything was threatening to liquify the room and the body. Again, I have to say, I was, for the first time ever, cringing at the anticipation of the next infrasonic blast heading our way… finally, I can say the goal of ultimate bass has been achieved.

There is no room to improve from here. Distortion and SPL ouput have simultaenously been optimized to an extreme level. Where we can improve is on fan self noise. My room is extremely quiet, and when the movie is perfectly silent, you can hear what amounts to a normal air conditioner type of air noise.

Bruce is quite confident we can knock that all the way down to inaudible, it’s just that we simply ran out of time… they are flying back tomorrow AM after 14 days non stop here. They will be back in 4-6 weeks doing their next install in the SF Bay area.

The solution to knocking the self noise down is more fiberglass and turning the fan speed down a bit. We have so much available headroom we can easily make up for the resulting output loss with more volume.

This week I will post pics of simultaenous spectrum graphs alongside the movie running, so you can get an idea of the calibrated SPL levels we are reaching in the room.

Bottom line is that one really needs three subwoofer technologies to fully exploit the film sound opportunity. The TRW for 0-20Hz, a large multi 15 or 18″ driver subwoofer(s) for 18-30Hz, and several smaller subs 15-18″ that are tuned for output in the 40-80Hz region. With the right crossover and sound processor, one can achieve levels of bass that will absolutely frighten the most diehard bass fan.

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