Rotary Subwoofer Install Blog

October 19, 2006

Distortion figures coming

Filed under: Uncategorized — bassment @ 9:22 am

I also took THD measurements while running the output test below. Will post later this week.

It’s still amazing that Bruce’s homemade mic (from Radio Shack parts) responds so well down to 1Hz.

October 18, 2006

How does backvent space affect front vent output?

Filed under: Uncategorized — bassment @ 5:56 pm

Early on in the design phase, we fretted about the rear volume space, and how it might affect output. Clearly I would not be able to vent outside to the infinite volume there. Neighbors would burn my house down.

Clearly I only had the following spaces to back vent to:
– garage above media room, about 1.2x the volume of the media room, or the front side vent. This garage volume would be accessed by a 7-8 sq ft opening in the media room bath ceiling, which was next to one of the fans. So the opening cross section is quite small, but it’s all we had. Hence our concern.
– office and bathroom volumes were also directly available as back vents, via the ceiling grills shown below. Recall that the twin TRW’s are sitting up above the ceiling of the media room bath and office rooms, which are both adjacent to to the media room, separated by a heavy IAC STC55 door.

I wanted to see what I was missing by not venting to the outdoors, and also, if I left the garage door open, would that make any productive difference. So I ran three tests:

1) normal configuration, garage doors closed, garage windows closed, media room office door to stairwell closed.
2) media room office door open. This connects the office to the outdoor stairwell, about a good a vent as the TRW’s are ever likely to get.
3) normal but with the garage twin door open. I thought this might make a difference, because in normal config, the garage doors slap around quite a bit when the TRW’s are pumping. Hence, the hypothesis went, if I opened the doors, maybe more venting would increase the output.

SO here are the results:

output spl.jpg

Clearly, the output is helped in one frequency range by more infinite baffling in the rear, and hurt in the other band. So it’s a toss up. Hopefully Bruce will come in here and comment on what he thinks is going on.

By the way, the SPL readings above were using Spectral Pro software, with a calibrated mic and the software calibrated SPL-wise using an RS meter at higher frequencies. I trust the SPL level calibration makes sense down to DC. I did record RS digital SPL meter measurements alongside with the above Spectral Pro readings, and the RS meter just pretty much indicated 75-80dB between 3 and 18Hz, no matter what the Spectral Pro had to say. So it seems to me that the RS meter is sort of useless below 20Hz.

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Something strange, but fortuitous

Filed under: Uncategorized — bassment @ 12:25 am

The backside of the TRW’s vent into the office and bath,  which are two rooms just outside of the media room, separated by a IAC STC55 door.  The TRW also vents into the garage up above, thanks to an HVAC chase we opened up from the media room bath connecting to the garage floor. As explained in previous posts.

There is a third venting option very close to the TRWs… just below those grates you see below in the previous post, there is a regular sized door opening to the outdoor stairwell to the media room office. You’d expect that by opening that door, that output in the media room would rise… given that the TRW design likes as much back volume as you can give it. Ideally, Bruce wanted to vent the backside into the great outdoors, but we nixed that when the neighbors in the next block over starting wondering what (un)natural phenomenon was haunting their house by slowly shaking their walls.

Maybe not. Because opening that stairwell door causes 10Hz, for example, SPLs to drop by 3dB. Somehow, constraining the backside volume, as we did with trepidation that output would suffer, instead turned into a stroke of luck and actually gave us 3dB of gain.  Hey, I’m not about to complain!

October 12, 2006

Pics of various venting points

Filed under: Uncategorized — bassment @ 12:33 pm

garage vent… inside that cavity, looking down, is another 7-8sq ft opening into the area behind the dual TRW install. So air pressure waves, in addition to venting into the bath/office outside the media room, also vents into the garage, albeit through a bit of a chokepoint. Trust me, there is lots of air pressure making it’s way through that opening into the garage… how can I tell? The garage doors slap around like pieces of cardboard.

the larger of the vents in the office and media room.

different angle, yes, I know, the paint didn’t quite match… it came out of the same can!
The flash bulb convicted me of faulty work here… but you’d be hard pressed to notice it in person.

the front side vent in the media room… again that damn flash bulb hints at what is normally unseed, i.e.
the insulation behind the foam grill. Hey, in person, this stuff all looks halfway professional!


Eqpt rack… red switch starts the twin turbines… the Lake EQ can be seen just below the DVHS. Bruce’s custom turbine amp below the HTPC.

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October 11, 2006

ultimate Haunted House

Filed under: Uncategorized — bassment @ 4:39 pm

This just in from Bruce…a haunted house ( in Tallahassee is using a TRW to create wierd and scary sensations for their c lients… apparently it’s a scream. Check out the video below… look at the door carefully…

Haunted House shaken by TRW’s

TRW chilling the Haunted House

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How to EQ and Crossover Five Subwoofers?

Filed under: Uncategorized — bassment @ 11:37 am

start with this:

Lake Contour EQ/crossover

this puppy has two XLR inputs, presumably from your subwoofer left and right outs (though you could also feed it subwoofer and LFE out, whatever, it can work from two inputs or one input and create almost anything you want).

Anyway, Bruce loaned me this puppy for evaluation (he is a dealer for Lake), and I am in love with the accuracy and capability of this EQ. After using pro audio junk like Ashley’s, I really appreciate a well done DSP based EQ/crossover.
So, this Lake takes in my subwoofer left and right out, sum’s them into a mono signal (at my request), and then splits out 4 signals for the two fans, the XS, and the left and right Watchdogs.

You can adjust the crossover points, filter shape, add EQ up and down anywhere, add phase adjustments, delay time, etc… really a very powerful unit.
Their new flagship EQ (about $5k)  has extremely low THD…  the unit I am looking foward to buying for myself.

October 10, 2006

TRW impact on movies… here are numbers

Filed under: Uncategorized — bassment @ 11:14 pm

I’ve taken some spectral analysis during some movie sequences suspected to have low bass content.
These snaps are of a peak hold FFT during the scene… so you are seeing the maximum SPL levels reached between 0 and 90 Hz for the 2-3 minute clips of interest. I believe Bruce and I calibrated this mic when he was here, so the SPLs should be somewhat accurate, but I’ll do the cal again soon, just to make sure.


this is HHGTTG (dts5.1), when the earth is demo’d. Notice that we’ve almost reached 115dB at 10Hz. Cool.

I need to post another snap of what happens without the TRW’s.

m and c cannon scene dts5.1 w TRW.GIF

this is Master and Commander (dts5.1), with all 5 subs woofing away. Pretty cool to listen to.

Nearly 110dB SPL across 1-5Hz.

m and c cannon scene dts5.1 no TRW.GIF

Now for the same scene in M and C without the TRW’s. The crossovers are set so that the XS is responsible for the performance around 20Hz.
You can see that it does pretty respectably down to 18Hz at 100dB or so… not bad at all!
My sentiments at this moment are to first calibrate the mic once again, and endeavor to make sure that these SPL readings are in fact accurate. Because if they are, I want to see 110-120dB SPL peaks being reached instead of 100-110.
I think. I am not sure… 120dB might just rattle the room apart as I’ve noted before… but 115 seems doable without drywall crumbling to dust.

I have put some fiberglass just behind the grill covering the TRW’s manifold … this has reduced fan self noise, but perhaps whacked a few dB off output. I have the following courses of action, again, assuming the mic is calibrated:
1) increase amplifier output… right now I am at 12 o’clock on the dial.
2) I could try opening the garage door or window up above… that provides more venting back space
3) I could try opening the media room office door…that would provide ultimate venting.
4) combination of 1 and 2or3.

I’ll check with Bruce as well… he got a clean 120dB out of the system with pure tones…I need to acquire that software and see if I can duplicate our earlier outputs.

Tomorrow I will post some pics of the finished install areas. I am no finish carpenter, but I did a decent job on the grills for which I copied Winstons original design.

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October 2, 2006

Crossover challenge

Filed under: Uncategorized — bassment @ 5:57 am

Just to be clear in the post below, what I ultimately wanted to do with all four subs was have the following happen:

1) Left Watchdog get all the 30-80Hz of all left channel signals, mains/surrounds/subwoofer

2) Right Watchdog get same, for all the right channel signals

3) XS to get mono 20-30Hz

4) TRW to get mono 0-20Hz

Unfortunately, the Lake, although extremely capable, did not allow us to set a given output to be any mixture of inputs. You can have any output assigned any filter, but they all share the same input mix. Which meant for my application that I had to go mono to all the four subs above.

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, 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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