Thursday, January 28, 2016

The 1965 New York World's Fair - DuPont "Wonderful World Of Chemistry" Show

One of my inspirations growing up was experiencing the New York World's Fair in 1965.  The one show I remember most is the DuPont "Wonderful World Of Chemistry".  It was at this performance that I first heard a really high-quality and high-power music amplification system.  Up until that time, movie theater sound was about the best I had heard.  When the music started playing, featuring brass instruments and heavy percussion and bass, at first I thought there must be a jazz orchestra somewhere "behind the scenes".   However, there was also a chorus and spoken dialogue and the sound seemed to be coming from different directions from one moment to the next.  So I knew it had to be a recording playing back through a really powerful and "live sounding" multi-channel sound system.  Fortunately, a recording of this event can be found at archive.org.

Up until this experience, I had for a long time been interested in listening to recorded sound but I never realized that recorded sound could sound as real as this.

There is more information including links to tape recordings of the event made by Ray Dashner and Bradd Schiffman.



A Stereo Sound Transformer Setup Using GE S-1201D Speakers

A while ago, I posted about the Merry Barn, operated by Howie Davidson, and record hops Howie would host at what was the Old Gym at Lincoln Academy, in Newcastle, Maine.  I decided to try out a stereo pair of the old GE S-1201D speakers on the sound transformer.  Here is an image of the old Califone portable speaker cabinets that clipped together for transport.  You can see Howie's clothesline that provided a handy carrying handle for easy transport.


Califone Portable Speakers Clipped Together
Califone Portable Speakers Clipped Together
If you unclip the two halves, you have two open-baffle boxes, each with a long lamp cord for connecting to an amplifier.



Califone Portable Speakers With Open Baffles
Califone Portable Speakers With Open Baffles
Here are the two GE S-1201D speakers removed from the baffles and ready for installation into the sound transformer:




Pair Of GE 1201A Speakers
Pair Of GE S-1201D Speakers
And here is the stereo sound transformer with the GE S-1201D speakers installed.  The amplifier is an old Pioneer SX-4 receiver.


Stereo Sound Transformer With GE1201A Speakers
Stereo Sound Transformer With GE1201A Speakers
Here is a vintage setup if there ever was one:  speakers from the 1950s and a pair of bass horns based on 100-year-old technology.




Tuesday, January 12, 2016

New Folded Corner Bass Horn: Why? It Is An Acoustic Amplifier!

Why would anyone need a bass horn?  Why not just drive the speaker directly with lots of electric power?  Simply put, the horn provides considerable gain so you can use a much smaller electrical amplifier.  Another way of putting it is that you can have a smaller electronic power amplifier because you already have a pretty large acoustic power amplifier.  The result of having this acoustic amplifier is that the speaker driver does not have to work nearly as hard while horn-loaded.  The benefit of not working so hard (as a direct radiator would have to do) is that you get cleaner, louder, more undistorted bass than you can ever get with the same driver as a direct radiator.

To get a comfortable listening level in my small listening room, I have found that all that is required is a power input of 100 microWatts.  In fact, Hornresp predicts a one-meter sound level of 70dB at 0.0234 Volts (23.4 mV) rms input.  This does indeed correspond to a power input of only 0.0001 Watt, or 100 microwatt.

In addition to working amazingly well at the microwatt level at home, it appears as if the acoustic amplifier that this horn is would work well anywhere you might need very high levels of clean, undistorted sound.  For example, the combination of the New Folded Bass Horn with Tymphany FSL-1225R02-08 driver would work especially well in a large room or outside where the average power input level could be quite a bit higher than it can in my small listening room.  For example, at the specified voice coil dc resistance of 5.5 Ohms, only 2.34 Volts rms is required to draw one Watt from the amplifier.  However, Hornresp predicts a one meter sound level of 110dB from 35Hz to 400Hz at one Watt input.  As you might imagine, a one-meter 110dB sound level would be way too loud in the home environment.

How much gain does the New Folded Corner Bass Horn provide?  Here is a way to find out.  Tymphany rates the sensitivity of the FSL-1225R02-08 at 96.3dB at one Watt input at one meter as a direct radiator.  Loaded with the New Folded Corner Bass Horn, the average one Watt one meter sensitivity predicted by Hornresp is 110dB.  At the very least, this amounts to a 13.7dB gain over the same speaker as a direct radiator.  It is more than that as well because the 13.7dB horn gain applies over a bandwidth of 35Hz to 400Hz while the non-horn-loaded rating of the manufacturer applies over a bandwidth that probably does not extend down to 35Hz or even close.

The horn gain of 13.7dB allows you to get the same acoustic sound level from an amplifier power only 4.27% as much as you would need to get the same sound level from the same speaker as a direct radiator.  This is the same as saying that the horn multiplies the electric power put to the speaker driver by a factor of about 23.4!  So, if you have a 5W amplifier and you factor in the horn gain, you will actually have a 117.2 Watt amplifier!  At even higher sound levels, to get a system amplification including bass horn gain of 1000 Watts, you will only need 42.66 Watts from your electronic power amplifier!

Note:  According to the manufacturer, the FSL-1225R02-08 has a 150Watt power handling rating.  Here is a table of predicted one-meter sound level versus power input for the New Folded Corner Horn combined with the FSL-1225R02-08:

Input
Input
One Meter
[Volt]
[Watt]
[dB]
0.0234 0.0001 70.0
0.0740 0.0010 80.0
0.2340 0.0100 90.0
0.7400 0.0996 100.0
2.3400 0.9956 110.0
7.3997 9.9556 120.0
23.4000 99.5564 130.0

Predicted sound levels are extremely high even at modest amplifier power input levels.  It would be interesting to set a pair of these horns up outside and try them out at an input of as much as one Watt :)

Note:  The bass is overwhelmingly loud and clear through a stereo pair of these horns.  Until you hear it yourself, you will just have to take my word for it :)

Latest Find - Pair Of Cambridge Soundworks Model Six Loudspeakers

I found these only after they had already been in an open-top dumpster for several days during which time we had quite a bit of rainfall.  As a result, they are in poor condition but still salvageable.  It appears as if the woofer surrounds were already worn out before the rain.  Here are images of the crossovers showing ice around the terminals.

If you look carefully at the first photo, you will see the ice in the recess around the terminals :)


Pair Of Cambridge Soundworks Model Six Loudspeakers
Pair Of Cambridge Soundworks Model Six Loudspeakers


Pair Of Cambridge Soundworks Model Six Loudspeakers
Pair Of Cambridge Soundworks Model Six Loudspeakers
After a little research, I found that the crossovers were designed to cross over at 2000Hz so these might be perfect for midrange/treble horn crossovers.

I am letting the cabinets dry out now that all of the drivers and polyester stuffing is out.  A good thing is that the cabinet interiors are dry.  All of the water damage including swelling of MDF panel joints at corners appears to be confined to the exterior.

Saturday, January 9, 2016

New Folded Corner Bass Horn - New Driver Testing

A couple of days ago, a Tymphany model FSL 1225R02-08 guitar speaker I ordered from Parts Express arrived.  Here is an image showing the Tymphany next to the New Folded Corner Bass Horn throat.


New Folded Corner Bass Horn - Tymphany Speaker
New Folded Corner Bass Horn - Tymphany Speaker
I mounted the new speaker, right out of the box, to the horn, then placed the back chamber over it and sent some white noise to it to get an idea of the frequency response.  I got the following plot using an FFT app running on the iPad.


New Folded Corner Bass Horn - Tymphany Speaker
New Folded Corner Bass Horn - Tymphany Speaker
You can see that the response is not particularly flat in the bass region, or anywhere else for that matter :)  By way of comparison, here is an image of the plot of the New Folded Corner Bass Horn with KLH CL-3A woofer installed.


New Folded Corner Bass Horn - KLH Woofer From CL-3A
New Folded Corner Bass Horn - KLH Woofer From CL-3A
This one is not so "flat" either but I think the KLH plot looks better in the bass region.  Well, what is happening here is the new Tymphany speaker has not been "broken in" yet.

Today, I set up to measure the free-air resonance of the Tymphany right out of the box new.  I used a signal input level within my accustomed listening level, about 0.001 Watt, and recorded a resonant frequency of 83.6Hz.  Well, the Tymphany specification for this is 59.1Hz but that is on a speaker that has been broken in.  I set up a sine wave signal source at about 9V rms at 30Hz and let it run to the speaker for 2 1/2 hours.  After that, I checked the resonance again and got 67.7Hz.  After another 2 1/2 hours, the resonance is down to 59.6Hz when measured at my accustomed maximum listening level of about 0.001 Watt.  Putting a little more power to it with 3.122 Volt rms across the speaker and 57.3 milliamperes rms running through the voice coil, I get a resonance of 56.3Hz.

This is a great example of how important it is to break a new speaker in.  It is the only way you will get close to the manufacturer's specification.  This is particularly important if your speaker is horn-loaded.  If the most power I ever put into this speaker were only 0.001 Watt, it would probably never reach rated specification, at least with regard to free-air resonance.

Thursday, January 7, 2016

Latest Find - Pair Of Vintage Air-Suspension Speakers - Made In Japan

I could not find any images of these online so I am posting some photos I just took of a pair of Air-Suspension Speakers I saved from a dumpster day before yesterday.  Both of these had been heaved over the side and into a large open-top container.  One survived the impact pretty well with minor dents in the cabinet.  The other was already held together with fiber-reinforced packing tape and essentially came apart on impact.  I glued and clamped the taped one keeping the tape in place to maintain alignment of the joints.


Pair Of Vintage Air-Suspension Speakers - Made In Japan
Pair Of Vintage Air-Suspension Speakers - Made In Japan
For clamps, I used rubber stretch-cords.  While this one was apart, I discovered that the drivers in these vintage speakers have woven surrounds instead of molded foam.  I have not been able to find an image of the logo in the lower right corner online so here is a close-up of that.


Pair Of Vintage Air-Suspension Speakers - Made In Japan
Pair Of Vintage Air-Suspension Speakers - Made In Japan
Here are the binding posts on the back panel.




Pair Of Vintage Air-Suspension Speakers - Made In Japan
Pair Of Vintage Air-Suspension Speakers - Made In Japan
There are three drivers in each speaker.  The crossover consists of two nonpolar capacitors.  I might try the midrange driver in a new midrange horn design at some point.


Pair Of Vintage Air-Suspension Speakers - Made In Japan
Pair Of Vintage Air-Suspension Speakers - Made In Japan


After I unclamped the speaker yesterday, I connected both of these to a Lepai 2020A amplifier and listened to several tracks while I was processing several photos taken on a recent trip.  These sound pretty good for the size.  They have a very clean sound and undistorted bass.

There is a little damage around the edges but not too much.


Pair Of Vintage Air-Suspension Speakers - Made In Japan
Pair Of Vintage Air-Suspension Speakers - Made In Japan


Pair Of Vintage Air-Suspension Speakers - Made In Japan
Pair Of Vintage Air-Suspension Speakers - Made In Japan
Here is the setup for listening tests.  When there is deep bass in the source, it comes through cleanly and undistorted but at a lower relative level than the New Folded Bass Horn output in the bass region.

Pair Of Vintage Air-Suspension Speakers - Made In Japan
Pair Of Vintage Air-Suspension Speakers - Made In Japan