Arduino-Powered Surround Sound Synthesizer

The Makerspace Eight Speaker Super Surround Sound System(MESSSSS) has been supplying music to the Makerspace for quite a while now, but I identified a problem even before the system was fully installed.  Stereo recordings played back on two speakers are great if you’re in the “sweet spot.” If not, traditional approaches to 5.1 audio improve things, but all rely on there being a single “front of the room.” Unfortunately, it’s not clear which side of the 3000 square foot Makerspace shop is the front, and with four pairs of speakers in the room, even stereo imaging is difficult.

Fortunately, I’ve just completed the Makerspace Eight Speaker Super Surround Sound System’s Enveloping Surround Sound Synthesizer (MESSSSSESSS).  The MESSSSSESSS takes stereo recordings and distributes sound to the eight speakers in an entirely fair and user configurable way, thereby eliminating the need for a “front of the room.” Now listeners can be arbitrary distributed throughout a room, and can even be oriented in random directions, while still receiving an enveloping surround sound experience!

The MESSSSSESSS user interface is somewhat simpler than most surround sound processers, as it consists of only four switches and one knob.  Somewhat inspired by StrobeTV, the simplest mode references questionable quadraphonic recordings, in that the music travels sequentially from speaker to speaker, chasing around the room either clockwise or counterclockwise at a rate selected by the knob. With the flip of a switch, sound emanates from the eight speakers in a random order. Things get considerably less deterministic after flipping the Chaos Switch, adjusting the Chaos Knob, and entering Turbo Mode:  Its best to visit Milwaukee Makerspace to experience the madness for yourself.  I’m legally obligated to recommend first time listeners be seated for the experience.

The MESSSSSESSS is powered entirely by an Arduino Uno’s ATmega328 that was programmed with an Arduino and then plugged into a socket in a small, custom board that I designed and etched at the Makerspace.  The ATmega328 outputs can energize relays that either do or don’t pass the audio signal to the four stereo output jacks.  Care was taken to use diodes to clamp any voltage spikes that may be created as the relays switch, thus preventing damage to the ATmega328 outputs.

As shown by the minimal part count above, using the ATmega328 “off the Arduino” is quite easy:  Just connect pins 1 (The square one), 7 and 20 to 5 volts, and connect pins 8 and 22 to ground.  Then, add a 22uF cap and small bypass cap between power and ground, and a ceramic resonator to pins 19 and 20.  You can even use an old cellphone charger as the power supply.  Boom.  That’s it.  The real benefits of making your own boards are having a well integrated system, and cost, as the Atmel chip is $4.50 while a whole Arduino is $30.  Also visible in the photo are a programming header and the two ribbon cables that route all the signals to and from the board.

A Simple Aux Input For iPod Speaker Systems

The first generation of Bose SoundDocks did not feature an aux input jack, they are only compatible with the 30 pin connector of iPods and iPhones.  Lately, my music player of choice is my Droid Razr, which has 60+ Gb of music on it, even more in the cloud, and no 30 pin connector.  I decided to add an auxiliary input to my SoundDock in the easiest and quickest way possible. I made an adapter cable using half of a $6 iPod extension cable, half of a $1 3.5mm headphone cable, and two necessary resistors.  I can plug this adapter cable directly into any unmodified SoundDock, or any other amplified speaker system that has a 30 pin connector.

It turns out that the SoundDock is smart, and will only power on when it senses 3.3VDC on pin 18 of its input connector.  Luckily, it also outputs 12VDC on pin 19 to recharge the attached iPod’s battery.  To trick the SoundDock into turning on with no iPod attached, I made a voltage divider by soldering a 20 Kohm resistor between the wires connected to pins 18 and 19, and a 4.7 Kohm resistor between the wires connected to pins 18 and 1.  The voltage between pins 18 and 1 was measured to be ~3VDC, which isn’t 3.3VDC, but is sufficient to power up the SoundDock.  I soldered the three pins of the 3.5mm headphone jack to the 30 pin connector’s wires as follows: Ground to pin 1, right audio to pin 3 and left audio to pin 4.  I used 1206 surface mount resistors because they measure only 3.2mm by 1.6mm, a size which fits conveniently under the shrink wrap joining the two cables.  The most time consuming part of this two hour project was identifying which color wires were connected to pins 1,3,4,18 & 19, and determining if the pin on the left of the photo was #1 or #30.

The Critic

This is “The Critic.” It’s the USB accessory version of a red pen: Once armed by rotating the red safety cover up, the device is activated by simply flipping the toggle switch.  When connected to a computer via the convenient USB plug, it will begin to delete text, continually deleting until all the (presumably erroneous) text preceding the curser has vanished. At that point, the safety cover can be lowered, thereby deactivating the device.  The Critic is an indispensable tool for use when the document you’re editing is just so full of errors that your fingers begin to ache from holding down the delete key.  The Critic measures 3″ by 2″ by 2″ tall, and was designed to fit conveniently within arm’s reach, beside your keyboard or mouse.

I was inspired by the open source work of Pete at RasterWeb! and his recent effort to bring “The Button” to a wider audience of busy or non-makers.  He has freely helped tens of people create their own buttons, but is now able to fulfill requests for preassembled units. Among other applications, these USB buttons can be used as the shutter control of  Mac powered Photo booths at public events. These photo booths are powered by Sparkbooth, which can automatically upload the photos to Facebook, Twitter, tumblr or other social media sites.  His buttons emulate a keyboard, and contain an Arduino Teensy (only 0.7″ by 1.2″), which is a USB based AVR microcontroller.  Despite the Teensy cost of $16, I saw an opportunity for cost savings by opening a standard USB keyboard and spending a few minutes to extract and reverse engineer their compact circuit board.  Although this isn’t a solution suitable for even small scale production, it can work for a one-off prototype, like The Critic.

Below are several photos that show the process of opening the keyboard to extract and modify the circuit board.  When the top of the keyboard is removed, a sheet of silicone ‘popples’ is revealed.  These ‘popples’ are the springs under each of the keys.  Under this layer are two sheets of thin plastic, one with conductive ink traces that are (mostly) horizontal, and one with conductive ink traces that are (mostly) vertical.  These layers of traces are separated by a small gap.  When a key is pressed, a protrusion on the bottom of that key’s popple pushes the two layers of plastic together at this location: connecting one of the vertical traces to one of the horizontal traces. These traces are routed to the circuit board via a row of contacts under the front edge:

   

The chip (under the black epoxy potting on the bottom of the board) detects this electrical connection, and outputs the appropriate character over the USB cable.  The keyboard, popples and plastic layers can all be replaced by an external switch and wires soldered directly to the circuit board.  The photo below shows wires (whose free end is to be connected to the switch) soldered to the pads required to output a space bar character.  To output other characters, simply follow the vertical and horizontal traces to the board, and solder wires to those pads instead.

    

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Cacophonator Enters The RPM Challenge!

At Noon today, the Cacophonator decided to enter the RPM Challenge!  This challenge is simple: Compose and record an album entirely during the month of Februrary, be that 10 individual songs or a single 35+ minute track of original material!  After a thirteen second test, Cacophonator was proven to not be up to this challenge as a solo act – It’s just too loud.  Enter Mohoganator: The distortion reducing, level adjusting perfect partner for this challenge.

The Dynamic Duo of Cacophonator and Mohoganator teamed up with Auditionator (I.E. Adobe Audition) to record a session for 10 minutes and 32 seconds at a blazing fast 192kHz sample rate.  This recording was then slowed down to the customary rate of 44.1kHz, thereby expanding the work to its final 45.5 minute length.  Within twenty minutes after the recording was made, Cacophonator had a profile set up on the RPM Challenge site and the piece normalized, saved as a low bit rate mp3 and uploaded.  You’ve read that correctly, in less time than it takes to listen to this piece, it was composed, recorded, processed, mastered and uploaded.  Talk about Non-Causal Audio Delight!  Check out the piece here, by scrolling down to “my player.” This all happened very fast, but Cacophonator still isn’t quite finished – it hasn’t yet mailed a CD to RPM HQ, 10 Vaughan Mall, Suite 201 Portsmouth, NH 03801.  Interested participants still have over 11 days to enter the challenge!

The Tool At Hand

The Milwaukee Art Museum (MAM) and Chipstone Foundation recently invited an international selection of artists to create art objects using only a single tool. Works made using just one tool, be that a saw, glue applicator, pin vise, utility knife, etc are on display at MAM now through March, 2012.  More information about the works in the museum can be found at artbable.org.  Interestingly, the Chipstone Foundation has extended the offer to all Milwaukee area artists, creatives, and makers to enter their own single tool work in a show at Sweet Water Organics on March 17th from 1-5pm. Three works will be selected to join the works already at the Milwaukee Art Museum for the remainder of March.  If you are interested in participating, email Claudia at Chipstone.org as space is limited.

Tool At Hand TableInspired by the Chipstone Foundation’s origins in collecting furniture and decorative arts, and to gain some experience with my chosen tool (Angle grinder with chainsaw cutting disk), I created a small table (and piles of sawdust) in an hour or two yesterday.  After seeing the works at MAM and watching the videos on the website, I realized there are various interpretations for “one” tool,  including “two,” “three,” and “five.”  With this creative numerical spirit, notice that this one tool work has legs attached with wooden dowels inserted into holes made by a second(!) tool: A drill. Don’t worry though, I used the angle grinder to pound in the dowels.

Audiophile Headphones

Sick of thin bass when listening to your favorite music over headphones? Missing that cinematic surround sound experience when you are on the go? Craving the visceral bass impact of live concerts? Trying to get to 11, but your headphones are stalled out at 6.283?  Move over anemic earbuds, there’s a new product in town: BIGheadphones: Bass Impact Gear’s new headphone product, available in two versions: Premium 5.1 (shown below in a user trial) and Mega Premium 7.2 (coming soon).

Reviewers are raging about the unprecedented dynamics, midrange clarity, and sound stage:

“Perhaps it was in the region of articulation and musical dynamics that this system impressed the most.  The dynamic bloom from soft to extremely loud was exquisite, and so clearly delineated that listeners could unravel musical phrases down into the concert hall’s noise floor and below.” The Audio Critic

“BIGheadphones speak with an organic integrity. They are hewn from the living woodendangered old growth Amazonian timber… I wept openly when forced to return the demo model.”– Stereophile

“BIGheadphones make critical listening a joy rather than a strain.  I was flabbergasted by their brilliant pitch certainty.  The midrange sounds were open, clear, and stunningly present. Playback performance like this makes use of the word transparent not only forgivable, but mandatory.” Audiophilia

“The 5.1 has an innate flair for speed and control that is incomparable. The command of bass dynamics moves beyond effortlessness to nonchalance. My eyeballs were vibrating! My hands are still shaking as I write this review.”Sound and Vision

“…the most important innovation in audio reproduction since the permanent magnet.”  –Acta Acustica

“W.O.W.”Bose listening panel

Reviewers agree that BIGheadphones are a huge leap in audio reproduction technology, larger than vacuum tubes, Stroh violins, carbon microphones and Edison cylinders combined.

Relative to planar speakers, typical box speakers are unable to develop the proper surface loudness or intensity typical of large instruments such as the piano.  This audio feat poses no challenge for BIGheadphones. Computationally modeled and optimized by a small and highly trained team of expert acoustical engineers over a period of 13 years, BIGheadphones were inspired by ingeniously thinking “inside the box,” not outside the box.  At the obsolete exterior listening position, a typical loudspeaker rarely generates even a realistic classical music concert level, but inside that same speaker, the sound pressure levels can quite easily exceed the 115 dB of a stadium rock concert. This realization was the BIG breakthrough, but was only the beginning of the struggle pursued by our elite acoustical research team.  Our uberengineers had to break the chains of common design practice to breathe the refreshing mountain air of inside-the-box acoustics, where nearly everything is inverted.

To illustrate, achieving loud bass external to a speaker typically requires the box be a very large size.  However, inside the box, the bass response is naturally flat to the lowest frequencies, and the smaller the box the louder and more impactful it becomes. Further, our astute engineers shrewdly realized that the stop-band and pass-band inside and outside the box are also opposite, as illustrated in the enlightening plot below of the subwoofer section of BIGheadphones. The Blue curve shows the hyposonic level inside, extending well below 10 infrasonic Hz, while the Red curve shows the meager sound pressure level in the more traditional listening position two meters in front of them.  Notice how the passband outside the box begins at 2kHz, whereas the passband inside the box ends at 2 kHz.  How many other speaker systems can boast of a subwoofer response that is flat over more than three orders of magnitude?  Now that’s innovation!  And this is just the customer-average response—the bigger your head the broader the bandwidth that you can brag about to your audiophile friends.

The observant reader has already noticed that this plot shows BIGheadphone’s output level is a mere 142 dB – only 22 dB above the threshold of pain.  Note though that this is with a paltry 1 Watt input – in reality, they are capable of 17 dB higher output with the optional high output amplifier add-on kit, though this reduces the playback time to under 36 hours per charge.  And that’s just the subwoofer!  The industry-leading, consciousness-altering bass response shown above is augmented by five horn loaded, carbon fiber reinforced porcelain dome, 2” diameter neodymium tweeters with single crystal silver edge wound voice coils.  With this critical addition, the frequency response of the BIGheadphones extends from below 10 Hz to 31 kHz and beyond!  Get your BIGheadphone audition today at your local Hi-Fi retailer!  “BIGheadphones, the last audible note in audio reproduction!”

(Not available in France.)

Thanks to the editors at RSW, Inc.

Sonic Vista – An Art Installation

For a few months now, I’ve been acting as an acoustical consultant to Bruce Odland and Sam Auinger on their project “Sonic Vista,” that opened on October 2nd for a 5 year long installation.  Bruce and Sam have been making publicly installed sound art pieces in North America and Europe for over twenty years.  I first heard their work at MassMOCA  in 2006, and met Bruce while he was putting the finishing (soldering) touches on “Harmony in the Age of Noise” at Tufts University in 2008.  Sonic Vista is installed in Frankfurt, Germany on a train & pedestrian bridge connecting two sections of Frankfurt’s greenway, located here.

Sonic Vista is a real-time sound art installation.  It gathers all the airborne noise from the industrial cityscape, filters it acoustically, and plays the resulting harmonious sound back through two giant, brightly colored spherical speakers placed directly over the heads of listeners as they walk along the pedestrian bridge.  Walking along the bridge literally becomes a consciousness raising event as one enters the sonic environment of the piece.  Noise from the cityscape (backhoes, earth movers and jackhammers from the nearby bank construction site, trains, dogs, humans, jets, boats, busses, and other city roar) is captured by two 4” diameter, 18 foot long (B0) and 12 foot long (F#1) tubes, each containing one microphone.  The sound reaching the microphones is naturally filtered by the harmonic overtone series of acoustic modes supported by the long tubes.  These microphone signals travel directly to the speakers, and are not processed with any electronic effects (such as reverb or chorus).  To hear Sonic Vista, follow this link to SoundCloud.  The exact position of the microphone in each tube affects the harmonic balance it detects, as shown by the following plot:

I aided in the design of the 1 meter diameter spherical speakers, first in solving the directivity problem: How can the speakers be designed so that listeners walking along the pedestrian bridge hear a uniform sound pressure level as they walk?  The problem with overhead speakers is that they typically send most of their sound straight downward – so it is much louder directly under them than it is off to the side.  The problem is made more challenging by the wide bandwidth — the lowest note is 60 Hz, and the highest notes are near 3000 Hz.

I’ll skip all the math and acoustics theory, and just state the solution: a 12 inch diameter woofer needs to be positioned behind a 4 inch diameter hole that all the sound must exit through.  This greatly improves the radiation pattern for the highest notes.  The heights and horizontal spacing of the two speakers also play an important role in setting how loud the sound will be when one is in between the two speakers.  Interestingly, I was able to balance these factors and the system as built achieved a pressure that was uniform within a few dB as listeners walk along the bridge underneath the speakers.  The plot below shows the loudness as a function of position along the bridge at the highest and lowest pitches, along with the 35+ dB soundfield variation that would have resulted without this hole to fix the radiation pattern.  The speakers are located at 50m and 64.7m, the two loudest locations along the bridge.

The second problem arose due to the solution of the first:  That the speaker radiates through a 4” diameter, 4″ long port created an undesirable resonance that I correctly predicted through the use of a computational acoustics model.  This resonance was actually eliminated by simply equalizing the speakers electrically.

This front cavity does lead to the loss of almost half of the sound output, but it’s a high sensitivity, 300 Watt maximum input driver, so it is still more than capable of being loud enough.  This is a small price to pay for the tremendous improvement in radiation pattern and listener experience.  To hear Sonic Vista, follow this link to SoundCloud.

Rubens Tube Update!

The Rubens tube I made a while back puts on a fairly impressive show when its speaker is driven with music or a noise box, as was done during the Milwaukee Makerspace Grand Opening.  The story is somewhat different when it is used to display the acoustic standing wave pattern inside the tube.  When a single tone (sine wave) at a resonance frequency of the system is played though the speaker, the heights of the flames map out the sinusoidal shape along the length of the tube. There are two very important variables whose values determine how well this will work.  These are the acoustic pressure in the tube, which is set by the speaker and its input voltage, and the propane gas pressure, which is set by a regulator or the valve on the propane bottle.  Even a professionally made Rubens tube has a relatively small range of these two pressure settings that create a nice sine wave distribution of flame heights.

After running my Rubens tube for a short while, I realized I’d made a few design choices that make the already small range of good operating parameters even smaller.  First, I didn’t actually use a gas regulator, I only used the valve on the propane nozzle.  Note that the propane flow rate is highly affected by the temperature of the nozzle, so the propane tank must be kept in a water-filled bucket to prevent the outlet valve from freezing up.  Just like a gas pressure regulator can be used, so could an acoustic pressure regulator (i.e. a compressor).  This could help prevent the flames from extinguishing during particularly dynamic musical passages.  Alternately, some type of pilot light system could be devised so that the flames automatically relight – perhaps glowing red nichrome wire could be added in a moderately safe way.  I also spaced the fifty 0.043” diameter holes apart by only 0.9 inches.  Having this many holes reduces the amplitude of the resonances, making them more difficult to ‘find’ by simply listening to the amplitude when adjusting the frequency input to the speaker.   Better performance would be achieved by having fewer holes spaced further apart.  Lastly, I’ve used a pipe whose inner diameter is only 2.5 inches.  A larger diameter pipe would further increase the amplitude of the resonances.

I put an electret microphone inside the Rubens tube at the end opposite the speaker, and measured the pressure inside while electrically driving the speaker with pink noise.  I did this with both air and propane inside the tube.  The following graph shows the low amplitude of the tube’s resonances with propane inside — between 4 and 7 dB.

The other interesting bit of data one can find from this graph is the speed of sound in propane.  Knowing the sound speed, one can calculate either the length of pipe needed to have a particular fundamental resonance frequency (n=1) or if a particular speaker has a resonance frequency low enough to excite the fundamental resonance of a particular length Rubens tube.  The resonance frequencies of a tube having uniform cross sectional area and two rigidly closed ends are given by: Fn = nC/(2*L), where n is the nth mode, C is the sound speed, and L is the length of tube.  The Rubens tube doesn’t have two closed ends, it has a paper cone speaker at one end.  It also doesn’t have uniform area – it has a small open volume in front of the speaker.  Both of these will change the “effective” length of the tube.  Don’t worry though, we can use the measured resonance frequencies with air in the tube to calculate the effective length: Leff = nC/(2*Fn).  Knowing C=343 m/s in air, we can use the measured resonances of the first three modes  (144 Hz, 262 Hz and 380 Hz) to find that the (averaged) effective length is 1.28m.  Using this effective length and the lowest three resonance frequencies (108 Hz, 205 Hz, and 300 Hz) with propane in the tube, Fn = nC/(2*Leff) predicts the sound speed to be ~265 m/s.

Makerspace members or any other folks near Milwaukee should feel free to stop by (on Tuesdays or Thursdays evenings) and fire up the Rubens tube.  Just use a small amplifier so you don’t put more than 30 Watts into the 4” speaker!  For some scholarly information about Rubens tubes, check  out the series of articles in the journal “The Physics Teacher:”  M. Iona (14), p325 from 1976; T. Rossing (15), P260 from 1977; R Bauman (15) p448 from 1977; and G. Flicken (17) p306 from 1979.