Saturday, March 28, 2015

The Sound Transformer Gets A Bass Driver With Two Voice Coils - STEREO

By replacing the bass driver with an Altec Lansing bass driver from a computer sound system subwoofer, it is now possible to hear stereo recordings by combining the bass signals from the left and right crossover networks in a single bass driver.  Here is the back chamber held on with stretch rubber cords.

Sound Transformer Back Chamber
Sound Transformer Back Chamber
With the back chamber removed, you can see the KLH 12-inch driver used in the original design for this bass horn.

Sound Transformer With Back Chamber Removed
Sound Transformer With Back Chamber Removed
With the KLH driver removed, you can see the horn throat.


Sound Transformer With Back Chamber Removed
Sound Transformer With Back Chamber Removed
Finally, here is the Altec Lansing 8-inch driver installed.


Sound Transformer With Altec Lansing 8-Inch Driver Installed
Sound Transformer With Altec Lansing 8-Inch Driver Installed
This is a much smaller bass driver but seems to be an even better match for the bass horn.  The stereo is quite good, even though I have no tweeter for the left channel.  Here is what the stereo setup looks like.

Sound Transformer Now In Stereo
Sound Transformer Now In Stereo
I still plan to make two bass horns.  Probably, I will make two more identical horns using the one pictured here as a mold former.

The smaller, 8-inch driver appears to be superior to the larger 12-inch driver for a number of reasons.  With the 12-inch driver, the low frequency falls off abruptly below about 45Hz.  There is also a sharp notch at between 72Hz and 80Hz depending upon microphone placement and/or horn placement in the room.  While listening to low frequency sine waves, I discovered that there is quite a bit of nonlinearity in the 12-inch woofer revealed by harmonics clearly audible at low frequencies below cutoff.  With the 8-inch woofer installed, I get useful output down to about 35Hz with much less harmonic distortion.  There is also less of a peak around cutoff frequency.  I believe the moving mass is lighter in the smaller driver.  In addition, the smaller cone is likely to be moving more as a unit than the large cone is able to especially with the horn load.  The bass is cleaner overall from the 8-inch driver while loaded by this horn.

It helps a lot that the Altec Lansing driver has dual voice coils because, at least above 400Hz, we can get an idea how this system will sound in stereo.

Tuesday, March 24, 2015

An Early Project: A 1/3 Scale Klipschorn

In about 1973, I built a one-third scale model of a Klipschorn.  I did not have plans, so I just guessed about dimensions.  I bought a five-inch speaker for it.  The Masonite cover over the speaker access opening was sealed with rubber cut from an old tire inner-tube.


One-Third Scale Model of "Klipschorn"
One-Third Scale Model of "Klipschorn"
Here is a photo with the speaker removed:



One-Third Scale Model of "Klipschorn"
One-Third Scale Model of "Klipschorn"
 
The second driver, mounted on a Masonite baffle, is a subwoofer removed from a Cambridge Soundworks computer sound system.  This did not work as well as the original speaker.  Here is another view of the model showing the opening into the back chamber where the speaker is mounted.


One-Third Scale Model of "Klipschorn"
One-Third Scale Model of "Klipschorn"
Here are some close-ups of the speaker back chamber showing the slot at the throat of the folded horn.


One-Third Scale Model of "Klipschorn" Back Chamber
One-Third Scale Model of "Klipschorn" Back Chamber


One-Third Scale Model of "Klipschorn" Back Chamber
One-Third Scale Model of "Klipschorn" Back Chamber
Like the full-scale original, this is made to be positioned in the corner of a room to take advantage of wall and floor reflections.  It is made of 1/4 inch plywood and glued and fastened with wire brads.

Monday, March 16, 2015

The Story on the Background Image - The EL84

People might be wondering where the EL84 electron tube image came from.  Years ago, I had a Dynaco SCA-35 and an HH Scott 299B Integrated Tube Stereo Amplifier. Each of these had four electron tubes similar to the EL84 in the output stages.  Here is a picture of the Scott 299B with the tubes on.


H H Scott 299B Integrated Amplifier With Tubes Lit
H H Scott 299B Integrated Amplifier With Tubes Lit

Here is the Dynaco SCA-35.  It looks as if I had it playing mp3 files recorded to a CD spinning on the player in the foreground.


Dynaco SCA-35 Integrated Amplifier
Dynaco SCA-35 Integrated Amplifier


These amplifiers sounded so good, that I went to great lengths to "memorialize" that electron tube by building a three-dimensional model in TrueSpace4.  This was quite a project because I did not have any training and had to learn this program on my own.  At any rate, I built the model of the tube within this program and saved several "output" images of it.  Years later, I got the original version of TrueSpace4 to work on a vintage XP desktop given to me by a good friend and managed to find the original working files I used to develop the model that I had saved on a backup disk.  I was able to input the model and adjust rotation and perspective and lighting to get higher resolution output images.  More on that later.

The image from which the background on this web page is generated is a copy of one of the original images I had saved of the tube model from several years ago.  It would be interesting to make a scene in TrueSpace4 of a complete classic tube amplifier in operation with all filaments glowing.

Saturday, March 14, 2015

Garrrard Model RC88 Record Changer

Here is the Garrard Record Changer that is like the one I had in 1957.


Garrard Model RC88 Record Changer With Viking Label
Garrard Model RC88 Record Changer With Viking Label
The one I have now is part of a Viking floor console record player.  Here are more images.

Viking Amplifier in Floor Console Record Player
Viking Amplifier in Floor Console Record Player


Garrard Model RC88 Record Changer
Garrard Model RC88 Record Changer


Garrard Model RC88 Record Changer
Garrard Model RC88 Record Changer

Tuesday, March 10, 2015

The Sound Transformer Plays Some Music: Recorded With A Sony Measurement Microphone

I am getting materials together to make a second Sound Transformer system for stereo.  In the meantime, I have been enjoying listening to Monaural LP records through the single Sound Transformer and recording with a Sony measurement quality microphone set about two and one half to three feet away from the midrange and treble horns.


Sony measurement microphone about 2 1/2' to 3' away from the midrange and treble horns
Sony measurement microphone about 2 1/2' to 3' away from the midrange and treble horns
Here are links to some music recorded in this way.  The Berlioz and Haydn are fairly long pieces.  The Gershwins are relatively short.

Hector Berlioz - Romeo and Juliet Opus 17 Part 1
George Gershwin - Rhapsody in Blue - played on dual harps
George Gershwin - Summertime - played on dual harps
Franz Joseph Haydn - Cello Concerto in D Major

Here are more shorter pieces.

Chet Atkins - Little Rock Getaway
Kaiwaza - Hawaiian Holiday
Lester Young - Upright Organ Blues (This one has loud trumpet near the beginning.)

Sunday, March 8, 2015

The Sound Transformer Plays A Little Jazz and Country Music

Now that we have the Sound Transformer looking a little more presentable, here is a short (one minute) video of some jazz playing through the system.



This is from a monaural vinyl LP that I have here.  The sound is really quite good.  It is not necessary to turn up the volume to hear every instrument.  However, it is possible to raise the volume considerably without any increase in distortion.  I tried this while wearing Howard Leight T3 hearing protectors.

Here is some Country Music.  The video is a little less than 2 1/2 minutes long.



This is from another vinyl LP that I have here.  It is remarkable how faithfully some of these monaural LP records were recorded.

The Sound Transformer Gets Wheels and Some Sprucing Up

Today, I attached some large caster wheels to the underside of the bass horn to make it easier to move it around.  Here is what the wheels look like:


Sound Transformer On Wheels
Sound Transformer On Wheels
The wheels are set near the center of gravity to make it easier to maneuver the Sound Transformer.  This was a huge improvement especially for changing the bass driver and back chamber, for example.

I also attached the KLH crossover and some 12 Gauge wire to the speaker terminals.


KLH Crossover With 12 Gauge Wires Attached
KLH Crossover With 12 Gauge Wires Attached
This PVC-jacketed power cord has an extra conductor that might be useful later on for bi-amping.  This recycled power cord is 50 feet long.  I made a pair of them from a 100 foot cord found at the transfer station (dump).

Finally, I made a baffle to hold the midrange and tweeter horns.  I discovered that this is necessary, now that I can "wheel" this thing around, to prevent the smaller things from falling off.


Midrange and Tweeter Horns Secured to Baffle
Midrange and Tweeter Horns Secured to Baffle


Midrange and Tweeter Horns Secured to Baffle
Midrange and Tweeter Horns Secured to Baffle
Now that this is beginning to look "presentable", I will post a couple of videos.

Friday, March 6, 2015

Electric Bass Practice Rig for NS Design WAV Bass with Fender Bronco 40

Here is my setup for practicing on the WAV Bass by NS Design.  As similarly described in the previous post, My First Record Player, A New Back Chamber, and Electric Bass Practice Setup, the NS WAV bass is connected into the Fender Bronco 40 amplifier input jack.  The Bronco's headphone jack is connected to the Lepai 2020A digital amplifier with Sound Transformer connected to the output of one channel.  You can play your backing tracks through the Bronco's Aux input where the stereo is mixed into one channel for monaural playback through the Sound Transformer.  Here is what the setup looks like:

Practice Setup: NS Design WAV Bass, Fender Bronco 40, and Sound Transformer
Practice Setup: NS Design WAV Bass, Fender Bronco 40, and Sound Transformer
Playing the bass while fully immersed in the sound coming from the horns is a pretty exciting experience.  This amplification setup appears to be a perfect match for the clean and powerful piezo signal from the WAV bass.  Playing through the Sound Transformer, you can get clean, loud, seemingly effortless sound from this instrument.  The Sound Transformer does not appear to favor or understate particular musical notes no matter what position you are playing on the fingerboard.   The Bronco amplifier lets you try several different classic bass amplifiers.

Here is another view of the Sound Transformer:

Sound Transformer Showing 2" Dust Cap on the Woofer in the Bass Horn
Sound Transformer Showing 2" Dust Cap on the Woofer in the Bass Horn

Thursday, March 5, 2015

My First Record Player, New Back Chamber, and Electric Bass Practice Setup

My first record player was made possible by equipment given to me by a kind uncle in about 1957 or 1958.  I found myself in possession of a Thordarson amplifier and a Garrard record changer.  I have been searching the internet for quite a while for an image of one of these.  In the last couple of days, one turned up.  Here is what my 6V6 push-pull amplifier looked like although the one in this picture appears to be a slightly different model than the one I had.


Thordarson Amplifier with 6V6 Push-Pull Output and Walnut Cabinet
Thordarson Amplifier with 6V6 Push-Pull Output and Walnut Cabinet

There are small incandescent lamps in each of the chrome or nickel plated globes at the top.  I connected a 4 x 6 speaker removed from a radio to the speaker output terminals.  The Garrard record changer pickup wires I connected to the phono input terminals.  This setup sounded really great and my favorite record to play on it was Beethoven's Fifth Symphony.

Here is an advertisement for the Thordarson walnut amplifier series in Thordarson catalog 400C.

Thordarson Catalog 400C Advertisement for Amplifier with Walnut Cabinet
Thordarson Catalog 400C Advertisement for Amplifier with Walnut Cabinet
As far as I can tell, the amplifier pictured in this advertisement is the model I had.  I have not yet been able to find one of these to "recreate" my original sound system.  I do have a Garrard record changer almost exactly like the one I had then.  It is part of a Viking floor console record player which is itself a very fine system.  I will post more on that later.

On the current project, the Sound Transformer, I just recently constructed a back chamber of the same volume as the volume that seemed to work best in the Hornresp simulator.  This optimal back chamber volume seems to have removed the last of the slight "boom" in the bass horn.  I set up a Fender Bronco 40 bass amplifier by connecting the headphone jack to the Lepai 2020A input.  The Bronco 40 Aux input, used for backing tracks from an iPod for example, combines left and right stereo channels into a single monaural signal.  I then plugged a Fender Precision bass with '62 Re-Issue pickup into the instrument input and played along with the iPod for an hour or so.  I believe this may be the ultimate "practice" setup.  You are fully immersed in the sound of the bass and the "backing tracks" sound very realistic.  More on this later.

Sunday, March 1, 2015

Time Alignment Experiments on the Sound Transformer and The Inspiration

Yesterday, I recorded a series of twelve-second audio tracks of square waves tuned to musical notes in the chromatic scale and played them through the Sound Transformer system while monitoring with a microphone/preamp/oscilloscope placed in front of the horns about three feet away.  The square-wave "test" is regarded as the most discriminating, but perhaps the least applicable generally, because, although it appears to reveal resonance and incoherence in the loudspeaker, the test setup itself, i.e., placing a microphone at a single point in a room at an arbitrary distance from the speaker under test, is encumbered with a load of inconsistencies. (By the way, Japanese investigators have devised a way of testing loudspeaker/room systems that involves placing a matrix of many microphones.)

With the bass and midrange/treble horn mouth ends in the same plane, I could not really see or hear any advantage to adding delay to the midrange/treble signal to achieve "time-alignment".  Therefore, it appears as if nothing is lost by mounting the whole huge speaker flush with an interior or exterior wall in a building, for example.

Last night I processed several music tracks by mixing from stereo to mono, and remixing a stereo track with the bass horn right channel low-pass filtered and the midrange/treble left channel high-pass filtered.  I had processed the square-wave tracks in the same way in order to "split" the bass and midrange/treble information so as to be able to introduce a relative delay in the midrange/treble. This processing simulates a "bi-amped" setup with active crossover.

I hope to listen to these tracks sometime today.

Here is the inspiration for the Sound Transformer Project.  Below is a photo of the horn-loaded Theater Loudspeaker designed by Albert L Thuras and Edward C Wente and reported in the March, 1934, edition of the Bell Labs Record Vol 12, No 7.


Theater Loudspeaker by Albert L Thuras and Edward C Wente
Theater Loudspeaker by Albert L Thuras and Edward C Wente
In 1971 or 1972, I got a look at these speakers in the basement of the Seeley W. Mudd building at Columbia University.  By the way, the metal diaphragm pictured in the lower right is 20 inches in diameter.  The attached voice coil is 8 inches in diameter.  As a result of this experience, I have always thought it would be interesting to build a horn-loaded loudspeaker to hear how it might sound.  I will post more regarding the history of my own interest in sound reproduction later.