Wednesday, April 29, 2015

Two Bass Channels For STEREO

Today, I finished up the first two lengths of the second bass horn and installed an eight inch bass driver.  Here are some photos of the work progress so far.

Four ribs are fastened to the larger flange.

Sound Transformer Second Bass Horn - Four Ribs Attached
Sound Transformer Second Bass Horn - Four Ribs Attached
 Then, the smaller flange is attached to the rib ends.


Sound Transformer Second Bass Horn - Smaller Flange Attached
Sound Transformer Second Bass Horn - Smaller Flange Attached
The other four ribs are fastened in.


Sound Transformer Second Bass Horn - Other Four Ribs Attached
Sound Transformer Second Bass Horn - Other Four Ribs Attached
After fastening two opposing trapezoids, a piece of corrugated cardboard is used to make a pattern for the curved sides.

Sound Transformer Second Bass Horn - Fitting The Cardboard Pattern
Sound Transformer Second Bass Horn - Fitting The Cardboard Pattern

The only tools required to fit the pattern edges to the curved trapezoids are a utility knife and a length of 50 grit sandpaper cut from a sander roll.


Sound Transformer Second Bass Horn - Tools For The Cardboard Pattern
Sound Transformer Second Bass Horn - Tools For The Cardboard Pattern
 For the first part of the second bass horn already completed, I used a scroll saw to cut out the sides.  This time, for the second part of the horn, I used a fine-toothed handsaw and it worked pretty well.


Sound Transformer Second Bass Horn - Handsaw For Cutting Panel
Sound Transformer Second Bass Horn - Handsaw For Cutting Panel
 Here is the mid section part of the second bass horn with three sides attached and the fourth one being fitted.  I cut them a little larger than the cardboard pattern.


Sound Transformer Second Bass Horn - Fitting The Fourth Side
Sound Transformer Second Bass Horn - Fitting The Fourth Side
Jumping ahead a little, here are the first two sections bolted together and ready for the eight inch driver installation.

Sound Transformer Second Bass Horn - First Two Sections Bolted Together
Sound Transformer Second Bass Horn - First Two Sections Bolted Together

Here are the two nearly identical stereo pair set up for listening tests.  They will be more identical after I build the third throat section for the second bass horn.  The second bass horn uses different panel stock than the first one.


Sound Transformer STEREO Version Ready For Listening Testing
Sound Transformer STEREO Version Ready For Listening Testing
It is 6:30PM and I don't have a lot of time to try this out right now.  Before closing up shop today, I did manage to listen to a little of Beatles' Yesterday and Today, Dire Straits' Brothers In Arms, and The Notorious Byrd Brothers.  I also listened to a vintage promotional stereo LP of big band music made by University Sound a long time ago.  This is all amazing sounding stuff played through this system.  I plan more testing tomorrow.

Monday, April 13, 2015

The Latest Sound Transformer Setup For STEREO

I moved everything around today in the barn attic to get the big bass horn out of the direct sunlight coming in the skylight.  It actually got up to 75 degrees F today in the barn attic.

Here is the latest arrangement for listening tests:


Sound Transformer - Latest STEREO Listening Test
Sound Transformer - Latest STEREO Listening Test
Here is a picture of part of a shipping crate I retrieved from the construction waste pile at a local transfer station a number of years ago:


Handle With Care This End Up Please Victor His Master's Voice
Handle With Care This End Up Please Victor His Master's Voice

More Progress On The Corner Midrange Horn

Here is one of the side flares in position.


Corner Midrange Horn - One Side Flare In Position
Corner Midrange Horn - One Side Flare In Position
With the first flare nearly fitted, I used it to mark the other three flares to save some time.  After further fitting of all four sides, I was able to mount them all to the corner.


Corner Midrange Horn - All Four Side Flares Fastened In
Corner Midrange Horn - All Four Side Flares Fastened In
It helps that the paneling is somewhat flexible.  By measuring the width of the core flare, it was possible to improve the fit and symmetry of the mating side flare edges.  Finally, I could insert the core flare into the space between the side flair pairs.  Here is a picture of the horn on its side:

Corner Midrange Horn - With Core Flares In Place
Corner Midrange Horn - With Core Flares In Place

Here are pictures of each side of the horn:


Corner Midrange Horn - Right Side
Corner Midrange Horn - Right Side


Corner Midrange Horn - Left Side
Corner Midrange Horn - Left Side

I used coarse sandpaper to remove the last of the edges that were still pushing too hard into the central core.  Here is a strip of sandpaper removing material from the edge of the side flare to improve the fit.  It helps that the paneling is flexible enough to distort enough so you can see where to remove more from the edge.



Here is a picture looking into the vertical shaft in the corner where the pair of throat horns will be located:


Corner Midrange Horn - Looking Into The Vertical Shaft For The Throat Horns
Corner Midrange Horn - Looking Into The Vertical Shaft For The Throat Horns
The next step will be to construct and fit the throat flares.

Sunday, April 12, 2015

Midrange Corner Horn Progress

Here is the corner with ribs attached to the walls for bending and holding the side flares.


Corner With Side Flare Ribs Attached
Corner With Side Flare Ribs Attached
I added two more core braces to the Midrange corner horn core.  Now the sides of the core conform to the correct curve.  Here is a view of the core with four braces:


Core Flare With Four Braces In Approximate Position In Corner
Core Flare With Four Braces In Approximate Position In Corner
With the core flare positioned, it is possible to begin to cut out a template for one of the side flare halves.  Here is a piece of corrugated cardboard set adjacent to the lower right side flare for fitting.

Preparing To Mark And Cut A Side Flare Template
Preparing To Mark And Cut A Side Flare Template
After Marking And Cutting The Template To Fit The Side Flare
After Marking And Cutting The Template To Fit The Side Flare
Side Flare Template Nearly Cut To Fit Side Flare
Side Flare Template Nearly Cut To Fit Side Flare
At this point, I began to check the fit of the template in the other four side flare positions.  While the template is still a little too large to fit, I will be using it to mark and cut four side flares from the Masonite paneling.

Saturday, April 11, 2015

Getting More Efficiency From A Midrange Horn Using A Corner

The two or three midrange horns I have made work pretty well but they are not as efficient as the bass horns.  It is likely that the small, inexpensive speakers I have been using for midrange drivers are not particularly efficient.  To compensate for this, I decided to try loading a midrange horn with a corner to get the magnification frequently employed by placing bass speakers in room corners.  This required a design that fits into a room corner.  I designed a straight square horn with a cutoff of about 290Hz.  At least on paper, I split the outer eleven inches of horn length in two halves, with each half against a wall of the corner.

To begin fabricating this, I cut out three squares of wafer-board and glued the three together to form a corner.  I have had the wafer-board scraps for about 10 years so it is great that I finally found a use for them.    Here is the corner with two templates:

Wafer-Board Corner For Midrange Horn With Two Templates
Wafer-Board Corner For Midrange Horn With Two Templates
I made the corner a little larger than the horn.  Using the bilaterally symmetrical flare template on the left, I marked and cut two ribs from 7/8" board scraps that I retrieved from a "free wood" dumpster at a local lumber yard a couple of days ago.  I always check this dumpster whenever I purchase anything at this lumber yard.

Here is what the central core of the horn looks like in its approximate position in the assembly:


Midrange Central Core In Approximate Position In Corner
Midrange Central Core In Approximate Position In Corner
Here is the corner turned on one of its sides with a side flare template in position:


Side Flare Template In Position On Corner Side Wall
Side Flare Template In Position On Corner Side Wall
Here is another view looking onto one of the "Wall Half-Horns":

Another View Of One Side Wall Half-Horn Close Up
Another View Of One Side Wall Half-Horn Close Up

After cutting eight side flare ribs, I will be ready to attach them to the corner side walls and bend the panels for the side flares that will join the corner side wall with the central core flare pictured above.

At least in theory, I should be able to fit the throat portion of the horn in two vertical halves set into the vertex of the corner.  This would be my first horn with two drivers.

Friday, April 10, 2015

Progress on the Second Bass Horn for the Sound Transformer

The first two sides are trapezoids because they do not need curved sides.  After the opposing trapezoids are fitted and fastened, the second pair of sides needs to have the edges machined into the curve to match the bent trapezoids.  A compass is handy to scribe the edge of the panel after it has been positioned parallel with the planes of the plywood flanges.  In the following photo, some material has already been machined from the throat end of the work piece.

Second Bass Horn - Fitting A Side Panel - A
Second Bass Horn - Fitting A Side Panel - A
Second Bass Horn - Fitting A Side Panel - B
Second Bass Horn - Fitting A Side Panel - B

Second Bass Horn - Fitting A Side Panel - C
Second Bass Horn - Fitting A Side Panel - C
The tools needed for this are a scroll saw and a small block plane.

Scroll Saw and Block Plane for Fitting Bass Horn Side Panel
Scroll Saw and Block Plane for Fitting Bass Horn Side Panel
You can use the first one as a template to mark the second for cutting.  If you make it a little bigger than the first one, you can shave it down fairly quickly for a custom fit.  After you mark for the second side, you can fasten the first one into the horn.

Fastening the Third Side into the Bass Horn
Fastening the Third Side into the Bass Horn
Here is the Bass Horn with all four sides attached.


Second Bass Horn With All Four Sides Attached
Second Bass Horn With All Four Sides Attached

Second Bass Horn With All Four Sides Attached
Second Bass Horn With All Four Sides Attached
To stiffen the panel edge, the cleats are necessary especially to hold the corners in place


Second Bass Horn With All Four Sides Attached And Cleats
Second Bass Horn With All Four Sides Attached And Cleats
With the panel edges secured, you can now apply adhesive to the panel corner joints.  I removed the white finish along the landing for the glue joint with coarse emery cloth.  Then I applied a bead of vinyl-based adhesive to all four joints.


Second Bass Horn - Adhesive Applied to Corner
Second Bass Horn - Adhesive Applied to Corner

Second Bass Horn - Adhesive Applied to Corner
Second Bass Horn - Adhesive Applied to Corner
I used a vinyl-based adhesive instead of PL-200 to give the joints a little flexibility for when the wood shrinks or swells with moisture content.  On the first horn, I found hairline cracks adjacent to some glue joints.  Apparently, this happened because the PL-200 is quite inflexible after it sets.  To fix the cracked glue joints, I applied a second bead of the vinyl-based glue over it.  So far, cracks have not reappeared in the first Bass Horn.

Tomorrow, I will cleat the side edges at the smaller end of the Second Bass Horn.

Saturday, April 4, 2015

Some History - The Merry Barn

In the 1950s and 1960s, Howie Davidson operated a dance hall in "The Merry Barn".  Several years ago, a friend called me up to say he had inherited Howie's sound system for the dance hall.  Howie also had a Califone portable sound system that he would take with him to "record hops" at local high schools.  This is when I acquired the GE S-1201D loudspeaker I first connected to the first two sections of the Sound Transformer.  At the Merry Barn, Howie had several of the GE S-1201D speakers in open back plywood boxes suspended from barn beams around the perimeter of the dance hall.  On each of the plywood baffle fronts was a decal portraying a couple of young people square dancing.


Decal Of Square Dancing On Speaker Baffle
Decal Of Square Dancing On Speaker Baffle

Decal Of Square Dancing On Speaker Baffle
Decal Of Square Dancing On Speaker Baffle
My classmates and I used to attend record hops hosted by Howie at Lincoln Academy and at the Merry Barn.  Howie would play 45 RPM records of all of the hits popular at the time.  I remember being particularly impressed with the Merry Barn sound system and the Califone portable, with Hilton Turntable, that Howie would play at the school gymnasium.


Califone Portable Speakers
Califone Portable Speakers


Califone Portable Speakers
Califone Portable Speakers

The Second Bass Horn For The Sound Transformer

Throughout the winter, I have been building the ribs for a second Sound Transformer bass horn.  At first, I thought about constructing a pair of redesigned bass horns based on what I learned building the first one.  However, after trying several different bass drivers on the original Sound Transformer, I settled on building another one identical to the first.  There are some minor differences in the way the second one is constructed, however.

A couple of days ago, I made three more ribs for a total of eight for the largest portion of the bass horn, the mouth flare.  Then I purchased a new sheet of AC plywood, 19/32" thick.  When I built the first one, I was not sure how it would work out so I used old pieces of plywood and paneling found at the dump.  The recycled plywood pieces were warped.  I had to reinforce the plywood flanges with pine cleats to try to correct the warping.  Parts of the plywood were damaged and could not be used. The second time around, I decided to use new plywood for the flanges.  The first two flanges I cut for the mouth flare are perfectly flat so I don't think I'll need the pine cleats.  As a result of having no cleats, I was able to use shorter sheetrock screws to fasten the ribs to the flanges.  Here is the mouth flare assembled.

Second Sound Transformer Bass Horn Mouth Flare Flanges And Ribs
Second Sound Transformer Bass Horn Mouth Flare Flanges And Ribs
Here is another view of the mouth flare that shows the curve of the ribs.


Sound Transformer Mouth Flare Showing Rib Curves
Sound Transformer Mouth Flare Showing Rib Curves
I have moved the ribs a little closer together to provide more room for the edges of the paneling at the smaller end.  The following picture illustrates why that will help.


More Clearance Between Rib Ends To Secure The Trapezoidal Side Edges
More Clearance Between Rib Ends To Secure The Trapezoidal Side Edges
The yard stick is about the same thickness as the paneling.  On the first Sound Transformer, I had the rib ends of adjacent sides in contact with each other so there was no overlap for the joint between the trapezoids and the curved sides.  The overlap provides a landing for glue applied later on.

For paneling, I selected a Masonite board with hard finish on one side.  The thickness is about 5/32".  Here is the panel with a yard stick as a straight edge clamped for marking out the trapezoid.


Marking The Trapezoid On The Masonite Panel With A Yard Stick
Marking The Trapezoid On The Masonite Panel With A Yard Stick
Tomorrow, weather permitting, I plan to cut out a couple of trapezoids for the first two sides of the Sound Transformer.


The Latest Find - A Pair of Radio Shack Minimus 7 Loudspeakers

While at the local dump last week, I happened to notice a pair of what appeared to be small black boxes that had been left atop an old clothes dryer next to the open-top dumpster for metals.  Upon closer examination, these turned out to be a pair of the very excellent Radio Shack Minimus 7 speakers.  These are black-painted cast aluminum and are marked "made in Japan" on a label on the back.  Whoever had discarded them there had apparently stopped short of heaving them into the metal dumpster.  Here are a couple of photos.


Radio Shack Minimus 7 Loudspeakers
Radio Shack Minimus 7 Loudspeakers


Radio Shack Minimus 7 Loudspeakers
Radio Shack Minimus 7 Loudspeakers

It is ironic that I should find these while I am working on such a large sound system, the Sound Transformer.  It would be fun to try an "A-B" comparison.

The Sound Transformer STEREO Setup Gets Atlas HR-3 Tweeters

Today, I removed the Atlas HR-3 Tweeters from the Party Speakers to see how they would sound with the Sound Transformer STEREO setup.  They sounded fantastic.  Here is what the right and left sides of the STEREO setup look like now.

Sound Transformer Midrange and Atlas HR-3 Horn Tweeter - Right
Sound Transformer Midrange and Atlas HR-3 Horn Tweeter - Right


Sound Transformer Midrange and Atlas HR-3 Horn Tweeter - Left
Sound Transformer Midrange and Atlas HR-3 Horn Tweeter - Left

I need to do some listening tests on the HR-3 version.