so Bruce Thigpen and his crew at Eminent Technology have been working on and off with several research instituitions on several applications of his sub-sonic TRW woofers, and none of them for audio/entertainment.
University of Hawaii used the TRW as a mobile earthquake sonics generator – in effect an earthquake in a box used to test the sensitivity of their remote earthquake sensors. Attached is a PDF of their findings, which states that the TRW generated subsonic waves could be ‘felt’ more than 3 miles away!
You ready for one or two of these in your theatre?
seen here in the AES exhibit demo Oct 2008, with and without illumination by a green laser (100mW)
A visit to the TRW demo just happened to have a 100mW laser and he beamed the laser into the fan blades during the demo. This had the unexpected effect of showing the amplitude of fan blade deflection as the beam would go from a spot to a line the length of roughly maximum blade deflection. If we could take that beam length and clock it out against a time axis, we’d reproduce the input signal perfectly.
now for a couple of YouTube videos made during the same AES demo. Notice the laser modulating it’s reflection against the moving fan blades.
at the AES show (http://www.aes.org/events/125/). I worked the booth for a few hours on Friday, helping them out since I am local and Eminent Technology is in Florida. They have a demo room outside the main convention center and a booth in aisle 1500 of the show floor.
Bruce Thigpen and crew are at room 8051 of the San Francisco Marriott (right across from the Moscone West convention center building) … demos all day today 10-6 and tomorrow 10-4. Some great content including a Titan Rocket launch… you will walk out woozy!
In other news, I learned that the TRW woofer has been installed in three commercial venues now:
1) a theme park up in Oregon where it simulates the sound effects of the Titan rocket launch referred to above.
2) Theme park in Niagara falls, where the TRWs simulate the thunder down under the falls…
3) the famous cathedral down in Wall Street. The pipe organ was ruined by the dust cloud of the Twin Towers demise. So they installed a keyboard organ with a signal fed to the TRWs to simulate the largest of the conventional pipes. They said they achieved 110dB in the middle of the cathedral with two units. Using the belltower as the back compression area… interesting.
I am about to pull the trigger on a Integra 9.9 pre/pro to replace the Lexicon MC12B… the specs say that the analog bandwidth starts from 5Hz on this unit, so it should be fine for driving the TRWs. And I have been hearing good things about it from installers here in the Bay area. If it turns out to sound poor, I will just sell it on eBay and go try the Denon AVP next.
I sold off my Lexicon MC12B, which had great low freq response for the TRWs. Why? Because it’s completely incapable of supporting the latest audio codecs. The new MC12B-HD supports HDMI audio in, which gives you support for 7.1 channels of MPCM from the BluRay player. Except the Lexicon MC12B-HD still only support 5.1 thru MPCM! Lexicon is really behind the curve for state of the art home theatre audio performance.
SO now it’s time to upgrade… I am looking at either the Denon AVP, or the Integra 9.9. The latter is about 40% the street cost of the Denon, at least. It says it goes down to 5Hz, which is good for the TRWs. The Integra is 7.1 out, which is not as much as the Lexicon or the Denon, but I can make it work.
I use the Lake Contour EQ to take the single LFE/Subwoofer out, and split it to the 3 subwoofer bands I require. 30-80Hz for the Wilson Watchdogs, 20-30 Hz for the Wilson XS and 0-20Hz for the TRWs.
I will probably get the Integra, and if I don’t like the sound, I will eBay it off and get the Denon. However, it looks like the Integra is still not available. So we’re in a waiting period here, while audio vendors catch up to high performance audio codec support with full 7.1 or more decoding.
Been quite a while since I posted here, well, I’ve been enjoying the room!
For various reasons, I had been tweaking the room settings, and the room’s bass performance had drifted off of optimal. Bruce Thigpen was stopping by the SF Bay area anyway, so I invited him over to retune the room.
By the way, if you haven’t seen the TRW in action, here’s a YouTube clip of our first testing of it (there’s alot of high freq noise that in the final installation is filtered out by the insulated manifold to the room):
In addition to checking and adjusting EQ to obtain a flat frequency response curve, we decided to also get at another very important tuning exercise – timing. Why timing? I had visited another media room in the area, and was impressed by how great his movie experience was with much less subwoofer output than mine. Listening to Master and Commander’s cannon shots, I immediately came to understand why. I heard a room with speakers and subwoofers aligned in the time domain as well as the frequency domain.
Meaning? Well, you want the low frequency sound effects to arrive at your ear around the same time as the mid-low and mid frequency sound effects. The combination of all these frequencies together create a much more realistic and emotion evoking sound effect. In real life, these sound effects are generated from a point source, and the sound pressure waves expand at one single wave front, I suspect, and so time alignment of the various frequencies happens naturally. [or is group delay a phenomenon as well in nature?]
In a media room, especially mine, where sound processing for the woofers go thru an extra signal processing chain, in this case the Lake EQ/crossover (see earlier post), the woofer signal can be delayed relative to the mid to high frequency sounds that are not going thru the Lake. We took a stab at what these processing delays might be, and we subjectively felt we improved the sound, but a more technical measurement of a room impulse response would give us more accuracy. We left this to a future tuning exercise. We really cannot conclude at this time that the Lake processing delay was perceptible or not.
Looking at the room’s frequency response, turning back to the frequency domain, we did see that the TRW’s were putting out too much bass. Yes, too much bass. How can there be too much bass you might ask, especially since I went to all the pain to add more and more subwoofers to the room. Turns out that large SPL of <20Hz were masking out the ear’s perception of 20-100Hz, where alot of sound effect (that I’m interested in) exists. So in the end, we tuned down the TRW output, yet resulting in a far more pleasing and emotional sound effect experience.
I use the word ’emotional’ several times, because the best movie sound effects are those that put the chill up your spine, or raise your hair on your arm or back of the neck. We’ve had plenty of those experiences when things are right in our media room. But just get things slightly out of tune, and it can be loud and clean, yet not emotional. Maybe realism is the key factor creating emotion, the sense of actually being inside the movie, versus watching it from the other side of the screen.
Shown here is the final room response, at the seating position… ignore above 80Hz, since the mains and center channel were not producing the pink noise signal, hence only the subs were pumping out the sound.
a Bay Area Audio Society meeting is coming up this weekend at my place in the SF Bay Area. Bruce Thigpen is flying out to do some press interviews and demo’s, as well as explain to the audience our installation and run some tests/measurements to update this blog.
We’ll also be doing a blind listening test designed to elicit peoples response to below 20Hz sounds. We’re going to try to address the popular conception that all frequencies below 20Hz are inaudible, or ineffectual, and so why bother reproducing?
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:
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.
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!
Rotary Subwoofer Install Blog 