Wednesday, May 31, 2006

What's that guitar?

Someone recently asked about the guitar shown on the Contact page of the Crowley and Tripp website.

It is a Hofner Verithin. I'm not sure of the date but I estimate it was from 1962, which is the year "All Night Long" was made. I bought the Verithin from Tom Allman about 25 years ago. This one has a tremelo tailpiece, and is missing the original raised pickguard. That bridge isn't original. When I first got it, the tremelo spring was missing, so I replaced it with a valve spring from a chocolate Triumph GT6+, which fit perfectly. I had two GT6s, and if you know those cars, you are familiar with the valve springs since GT6 valves needed to be adjusted about once every month.

Notice the knobs. These are the original knobs, but with our logo in the center. The action is a little hard. Not high, but a bit hard. I have it strung with heavy bottoms, light tops. It stays in tune and it plays well.

1962 was a productive year.

Tuesday, May 30, 2006

Jazz Age Classic with Patrick McGoohan

A plug for one of my favorite films of the early 60's, which stars Patrick McGoohan (Danger Man, The Prisoner, Braveheart) as a conniving drummer with a plan to take over the band.

This film barely ran in the US. The interracial marriage and not-so-implicit sex themes were just too much for the time: American audiences ultimately failed to recognize the genius of this modernized version of Shakespeare's "Othello".

But the film, and its incredible soundtrack, proved popular in Australia and New Zealand, which is where I managed to find original lobby cards, an original poster, and some good quality vinyl of the soundtrack with tunes by Mingus and Brubeck, who also appear in the film. Well worth the postage.

I told you it was one of my favorites.

Fisher double wide version and power supply - world's first phantom powered ribbon mics

Shown here is the double version. I haven't seen the inside of this one yet. This has to be one of the rarest production ribbon mics - not something you would read about in ribbon microphone reviews!

5:03pm: Micha informs me that the ribbon is not double width, but it is a two ribbon arrangement, sandwiched for higher output. This is interesting since we just isolated the ribbon motor on the single ribbon mic, below, connected it with a Crowley and Tripp ribbon microphone transformer, and it produced a very healthy output! Also, the response of the mic is pretty similar without the amplifier, so that amp is fairly flat.

Actually, RCA labs and Harry Olsen made a number of amplified ribbon microphones almost as soon as the first ribbon mics were made, in the 1930s. These amplified ribbon microphones used multiple tubes located in the housing, which was quite large by today's standards.

Fisher phantom powered ribbon mic - World's First Phantom Powered Ribbon Microphone

Here's an end-on and a side view of the Fisher mic prior to reribboning. The width of the ribbon is too wide relative to the gap, and is skewed.

Adjusting the tension via the support rods is tricky and the more you pull up the closer the ribbon edge is to the gap. Fisher made and sold a number of these microphones, some which were prized by David Hancock and passed on to Micha Schattner. The supply voltage is 48VDC and this one was made around 1975.

Sunday, May 28, 2006

About ebay

If you do want to buy our mics through ebay, you can do so safely. Our seller name is
We are the only US seller of our mics on ebay. You may see legally listed product from outside the US, like from England. KMR Audio of the UK does this.
We take paypal and credit cards and will not demand money orders, we actually have product here, and we provide the full warranty no matter how you buy from us. Make sure the seller has the product in hand. There are scams out there.
researchlabz = good

Thursday, May 25, 2006

World's firstt phantom powered ribbon microphone

Boston based recordist, engineer, music critic, and generally interesting person Micha Schattner (WGBH, WBUR, BAS, NPR and many others) stopped by the lab with his ultra rare Cambridge Microphone ribbon mics which he uses quite often. Cambridge Microphone was created by inventor Charles P Fisher in the late 1960's and his innovations, which include the tapered pole piece arrangement and tapered adjustable ribbon, resulted in US Patent 3,435,143. These were built in the mid 70's and used a +48VDC supply.

By the way, where the heck is Charles P Fisher? Anybody know?

It is quite unusual in design, and has a transformer coupled amplifier/emitter follower powered by a split 15V external supply. All of the electronics except the supply are in the body of the mic.

The mic in the picture has a stretched ribbon, which is common in all aluminum ribbon microphones. We're going to replace this ribbon, make some measurements, and get the mic back in service this week.

Monday, May 22, 2006

Special Guest at Soundwave Research

Last week we had a special guest: Greg Calotta, on the right, came up from NJ to check out our gear and make sure we are up to snuff.

Here he auditions the Crowley and Tripp Studio Vocalist and Proscenium mics hosted by Chris Regan on the left. In the Background is a Naked Eye and way in the background you can see Des at the microscope.

Sunday, May 21, 2006

South Beach Mules in Disguise

Mules are test devices (microphones, BMWs, Ducatis) that have been intentionally disguised so as not to reveal the final released design any earlier than needed.

A couple of people said they liked the mules. I refer to these designs as "South Beach". The three mules here have been used for ribbon motor development and for field testing. This is different from so-called "beta" testing. "Beta" usually means the product is actually released, but it allows the manufacturer to pull the product and change it in case it sucks.

On one hand, the customer becomes the guinea pig, but on the other, the customer gets to have first crack at something new.

If you are an early adopter, get the beta, but if you're a pioneer, get a mule!

Friday, May 19, 2006

Results! Proscenium vs "The Tube"

OK we caught up at the last moment of the day, and managed to measure the response of the acoustically loaded tube vs the Proscenium mic. The loaded acoustic tube was adjusted according to Olsen and according to the design used in the 77DX acoustic labyrinth. I don't have the polar plot set up yet, but the frequency response results are encouraging, to say the least. Look at how closely the response tracks the reference mic. Not bad. Of course, the average efficiency is down, more than 12 dB, and I see a strong bass response in The Tube, but we know how to fix both of thise things easily..

By the way

Proscenium is the RED curve
The Tube is the BLUE one

You knew that.

Have a nice weekend.

A little delay, but for good reason

A customer contacted us and wanted an SPLx type Custom curve device included with his shipment, so we dropped everything and tailored the curve to the "V1" position on an RCA 77DX. (of course!)
Anyway you can see the relative, (Not NORMALIZED) bass curves of a Studio Vocalist in stock form (green) and a custom Studio Vocalist (SPLx) (red). I emphasize that this is raw data, not normalized, obtained in direct A-B (two side by side mics looking at the same source) mode.

I will get back to the acoustic tube next week as everything is ready, but it will have to wait.

AES Paris starts tomorrow....stop in and see our mics.

Thursday, May 18, 2006

Acoustic Tube vs figure 8 Ribbon Microphones

Today we are making the measurements of the Acoustic Tube model (also referred to as the redirect tube in some places) shown below, against the figure 8 Proscenium reference microphone. I decided to use the Proscenium and not the 77DX as the reference. The reasons for this are:

1. We have a large number of Proscenium mic data sets
2. The SD of the measurements is known for the Proscenium
3. The figure 8 pattern of the 77DX in figure 8 mode has a "squint" that makes that pattern slightly asymmetrical.
4. Our test fixtures fit the Proscenium more closely, which reduces one measurement variable.
5. We know the precise acoustic Z of the materials around the ribbon motor in the Proscenium.

OK, the tests are being done now. We are putting a brand new ribbon in the test object today to make sure that everything is to spec before we begin.

Saturday, May 13, 2006

Crowley and Tripp Proscenium Comparison

This week I will get comparison plots of the side by side acoustic tube test object and the reference Proscenium mic which has already been measured vs the 77DX in figure 8 mode, You can see that if you scroll down.

That way we can look at what happens when the "rear" lobe is redirected into an acoustic load. I'm not going to be a curvemeister about it, though. How it sounds is more important than what the curve looks like.

Friday, May 12, 2006

Acoustic Tube

The acoustic tube (I also refer to it as the redirect tube) is a vertical plated brass tube brazed into the pole pieces in the 77DX. The radius of the tube OD fits the inside radius of the pole pieces and confines a small area of air behind the ribbon, which is only about an inch long. The top of the tube is closed, and the bottom of the tube is positioned above the entrance hole in of the Acoustic Labyrinth.

The acoustic tube has two slots cut into it: One is at the entrance, just behind the ribbon, and the other rear slot is on the opposite side of the ribbon, toward the rear. The rear slot is milled to have a flat surface on which the shutter rests and rotates.

The shot above shows a modeled acoustic tube and ribbon motor assembly used to characterize the geometry and acoustic Z of the basic 77DX design. One apparent shortcoming of the 77DX is reflection from the back of the shutter loading the adjacent ribbon. Here we have placed the ribbon about 2X the distance from the back of the tube, added an acoustic matching network, and tuned the acoustic load until the response is fiarly flat looking at a distant broadband source.

Thursday, May 11, 2006

Shutter Mechanics

The drawing of the shutter mechanism shows how a thin phosphor bronze spring 5, applies pressure to the shutter plate. Turning the adjustment screw positions little indented spots in the sleeve, 4, that line up with pips on the spring. It works, but is not exactly a positive or precise mechanism, and it can be broken with too much spinning, so watch out.

Saturday, May 06, 2006

Hosstraders/Hopkinton NH

This weekend is the Hosstraders Hamfest held twice a year in the Hopkinton, NH fairgrounds. The weather is perfect.

Here's what I have purchased:

4 deluxe HD hospital type casters with brakes. Big ones.
40 TDK cup cores and bobbins. About 1" diameter, material unknown.
4 five-pin XLR panel mount. Never used.
4 five-pin XLR plugs . Never used.
1 2304 loop yagi for WIFI. Been up in the air, looks fine. Will replace the 915 Loop Yagi on the tower. Perhaps I should put a USB powered WIFI card right at the antenna and save the coax loss.

1 really cool, new in the box, "Noonie" transistor radio, multicolored dots, very pyschedelic!

Thursday, May 04, 2006

The Shutter Cam

Here is the famous metal shutter cam shown taped onto the 77DX motor unit. The shutter tension arm and shutter adjustment screw are not shown here, so you can view the squarish shaped hole in the cam, and get a good sense of its shape. This position of the cam corresponds to the figure 8 pattern, in other words, wide open. The small ribbon can be seen through the redirect tube (more on that later) and the screen. By varying the angle of the shutter, one can vary the size of the rear opening of the redirect tube, which is positioned tightly into the pole pieces and adjacent to the ribbon, with no air gap.

Tuesday, May 02, 2006


What is IVUS?

IVUS stands for IntraVascular Ultrasound. IVUS is a catheter-based acoustic imaging method that uses a tiny transducer that scans the inside of a blood vessel to map the vessel wall, show plaque (hardened arterial blockages) and to guide therapies such as drug coated stents. An IVUS transducer is like a very high frequency microphone/speaker arrangent.

Link to other IVUS and 3VUS work at Soundwave Research Laboratories.

Here is an IVUS image of a diseased left femoral artery. This shot actually is a Polaroid image taken from a CRT. Remember CRTs? Remember Polaroid?

Mon travail en IVUS: Hopital Cardiovasculaire et Pneumologique/Hospices Civils de Lyon pendant envers 1990

Robert J Crowley

View of the R&D bench

If R&D is going on, there has to be clutter. This is the scene here in our R&D section of the lab, where A-B testing is done, and where comparisons are made against various microphones.

On the left is the Proscenium, and on the right, the subject 77DX. Both are placed a specific distance from the RCA speaker. If you zoom in, you might be able to see the many reference mics lined up in the background, including other Proscenium, Soundstage Image and Studio Vocalist instruments, among several mic boxes, and an EV driver in the background used for first octave testing.

Now that consumers commonly have audio systems with good response in the 10-100 CPS range, musicians, instrument makers, producers, broadcasters etc. need to be aware of that First Octave. CPS is back. Hertz deserves his name on measurements of electromagnetic wave energy, not soundwaves. I nominate Chladni. "...reponse up to 8 KiloChladnis" might not work out so welll, but Chladnis Per Second does.

Monday, May 01, 2006

Comparison: 77DX vs Proscenium

Doesn't this look like an old Polacolor print? I used to enjoy doing Polacolor
transfer prints using Polaroid peelaway film onto cloth, rice paper, and wood.
See how close the Proscenium curve comes to Herb Singleton's Measurements.

Here is a comparison spectrogram of the 77DX vs the Proscenium ribbon mic. The Proscenium has only a figure 8 pattern, and the 77DX was set to figure 8 (open shutter) and with the reactor switched OUT.

The horizontal lines are at 10 dB intervals. The software used is Visual Analyser version 7.0 which can be downloaded for free, somewhere. I like it because it is well suited to R&D use.

The Blue curve is the Proscenium.

The Red curve is the 77DX.

Both microphones are excited by a single white noise source placed equidistant to each. No attempt is made to normalize the source transducer, which is a cheap RCA-branded two transducer affair that I got on sale. It has its own kinks that you can observe, as they tend to show up on each channel.

The frequency range shown is log, Zero Hz to 20,000 Hz. I know it is hard to see and I have to find a way to save these as a jpeg in the future. We are going to need them.