Category Archives: Acoustics

Home Theater with Insane Subwoofer

Posted on by KevinB

After the mediocre commercial successes of some of my previous audio products, I decided to pursue a project that has absolutely no commercial potential.  Although my Automated Gmail Assistant had a 0.1% view to purchase rate, they definitely delighted their new owners!   On the other hand, my novel audio surround sound processor, audio-visual processor and audiophile headphones did not produce any revenue, despite being manufactured in an exclusive edition of one each.  Not to be discouraged, the goal of this project was to expand on the core idea behind the aforementioned audiophile headphones, but to overcome the main two drawbacks of using headphones:  1) Many people find that headphones are too uncomfortable and impractical for long term listening. And 2) most headphones lack the concert-like visceral bass impact, which is that feeling of the kick drum shaking your chest that only rock and roll shows could provide.

BIG_HMMMMMM2

Simply put, the Humorously Maniacal Milwaukee Makerspace Multimedia Machine (HMMMMMM) is a personal sized movie theater, with 5.16 surround sound.  That’s right, this theater is like a conventional 5.1 home theater, but with 15 extra subwoofers to delight the senses. While the bass in a live concert can be felt in your chest, the bass in the HMMMMMM can be felt in your soul(!).  In addition altering listener’s consciousness, the HMMMMMM will soon be used to screen our yet-to-be-filmed Milwaukee Makerspace orientation video as an integral part of our onboarding process for all new members. The HMMMMMM measures about 7 feet long and about 4 feet wide.  An eager movie-goer can simply climb up the integral stairs (shown on the left) and jump in through the 27” diameter escape hatch in the top of the HMMMMMM. Despite its crazy appearance, the HMMMMMM offers a surprisingly comfortable reclining position, much like that of a lazy-boy.  Check out this photo of the HMMMMMM under construction for a better idea of the ergonomic internal layout: There is a pillow for one’s head, and ones feet extend to the right.  The 27” display is mounted to the angled portion on the top surface, about 24” from the viewer.  Eventually, two 24″ monitors will expand the visual experience into the periphery.

The_Incomplete_HMMMMMM4

The audio portion of the HMMMMMM is a 5.16 system.  The high frequencies are played by 5 uninteresting Swan/HiVi speakers that are arranged in a properly boring 5 channel surround configuration.  The more exciting portion of the audio system is the subwoofer – well, the 16 (Sixteen) 10″ high efficiency subwoofers that provide that TrueBass™ sensation the masses crave.  Its clear from the use of 16 subwoofers that one object of the HMMMMMM was to create an audio system that plays low bass.  Playback of really low bass typically requires an extremely large speaker box, and still notes as low as 20 Hz are rarely audible.  However, inside any speaker box the bass response is naturally flat to much lower (subsonic) pitches.  For more on the sound pressure level inside and outside speaker boxes, check out this link.  The graph below is a measurement of the SPL or sound pressure level (how loud it is) versus frequency (pitch) at the listener’s ears in the HMMMMMM.

SPL_in_HMMMMMM

The graph shows that with a sine wave input, the SPL inside the HMMMMMM is 148.6dB at 40 Hz.  That means the acoustic pressure on the 27” diameter escape hatch is 45 pounds.  Excellent.  Note that earplugs in addition to earmuff style hearing protectors are mandatory to safely experience the TrueBass™.   To understand this strict hearing protection requirement, lets compare the sound pressure level inside the HMMMMMM to other audio systems that may be more familiar.  Note that the loudness of these other audio systems are not visible in the graph above, because essentially all other audio systems (including yours) are inferior.  Adjusting the margins of the graph a bit produces the following graph:

SPL_of_many_systemsThe plot shows how loud typical audio systems are, and how low they play.  For example, cellphone speakers play only a bit below 1khz, and are ~90 dB if they’re 40cm from you.  When a Jambox-type bluetooth speaker is about 60cm from you, it plays ~10 dB louder, and another 1.5 octaves lower, to 200 Hz.  Typical bookshelf speakers can get another 5 dB louder if you’re 1.5 meters from them, but only play down another octave to 100 Hz.  OEM installed car stereos are a big improvement, but they’re still not in the same league as the HMMMMMM.  Yes, the IASCA record holding car is louder than this, but it plays only from 50 Hz to 60 Hz, which isn’t even really bass.

Note that the difference in loudness between a cellphone and a car is 20 dB, while the HMMMMMM is 30 dB louder than a high-performing car stereo.  Also note that the frequency range of a piano, with its 88 keys, is about the same as a bookshelf speaker – a bit over 7 octaves.  Surprisingly, the subwoofer portion of the HMMMMMM has a 6 octave bandwidth, but it plays the 6 octaves you’ve never heard before!  The HMMMMMM plays 6 octaves below what your bookshelf speaker or Jambox calls bass. The HMMMMMM has a +/- 6 dB passband extending down to 2 Hz, with the output at 1 Hz being nearly still above the 120 dB “threshold of pain.”

Disclaimers: For safety, the big 2000 Watt amplifier that drives the HMMMMMM to its full potential is not available when the author is not present.  Ironically, the author has taught 75-100 people, the eager early HMMMMMM listeners, how to properly insert earplugs, meaning that the HMMMMMM is actually a learning tool for hearing safety! Finally, the author has some hesitancy in having the HMMMMMM reproduce recordings with 5 Hz content at 140 dB, because typical hearing protection has little effect at these unnaturally low frequencies.

PS:  Please don’t hesitate to contact me if you’d like to help with the video scripting, filming or editing.

Arduino-Powered Surround Sound Synthesizer

Posted on by KevinB

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.

Cacophonator Enters The RPM Challenge!

Posted on by KevinB

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!

Audiophile Headphones

Posted on by KevinB

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 wood—endangered 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

Posted on by KevinB

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.