Wednesday, October 28, 2015

New Folded Bass Horn - More Progress On Second Horn 5

The second folded bass horn main assembly is essentially complete at least for preliminary testing. I have just posted a video recorded using a digital camera with a measurement microphone for a higher quality audio track than is attainable with the microphones built into the camera. The microphone is plugged into a Focusrite iTrack Dock. Set your headphone volume so the audio plays quietly at the beginning of the video because the volume gets louder when the microphone is closer to the horns later in the video.



This is Affordable Audio at it's best.

Wednesday, October 21, 2015

New Folded Bass Horn - More Progress On Second Horn 4

Before cutting out the cover for the fold between the first and second chambers, four braces are cut to stabilize the midpoint of the edges of the panels.  The braces also function as spacers to correct any warping or bowing of panels.  Here is an image of the braces taken while the glue is drying.

Braces With Glue Drying
Braces With Glue Drying
 After the glue dries, the cover is cut out and drilled and countersunk for fasteners.  The cover is made from 5/8" plywood instead of 1/2" plywood so it will be stiffer.  The next step will be to fasten the cover with screws but without glue to make it possible to get the assembly apart later on if necessary.  I plan to use speaker gasket material on the joints to prevent pressure leakage.

Cover Ready To Be Fastened To Assembly
Cover Ready To Be Fastened To Assembly
The second folded corner bass horn is a lot easier to build than the first because I am simply copying the first one.  On the first one, I did not know the dimensions of the parts until I began to assemble them and was able to measure the partial assembly to get correct dimensions for cutting panels.


Tuesday, October 20, 2015

New Folded Bass Horn - More Progress On Second Horn 3

The next step is to cut out a matching pair of rectangular panels to form the sides of the third chamber.  But first, it is necessary to fit the second chamber side extensions.  Using a handsaw, the edges of the cover on the first chamber are cut away to provide a landing for the second chamber side extensions.

Trimming First Chamber Side Edges
Trimming First Chamber Side Edges
Next, one of the extensions is fitted in place while fastener holes are drilled.

Second Chamber Side Extensions
Second Chamber Side Extensions
With the extension fastened in place, the first side for the third chamber can be held in place with clamps while drilling and countersinking for fasteners.

Side For Third Chamber Clamped In Place
Side For Third Chamber Clamped In Place
 It is important to get each of the side panels centered so that the twin halves of the third chamber will be of equal dimensions.   After one side panel is fastened, the alignment of the second side panel can be checked with a square.
Third Chamber Side Panels Aligned
Third Chamber Side Panels Aligned
 With the third chamber side panels glued and fastened, it is possible to install the covers for the third chamber.  No glue is used for this step, only fasteners.

Third Chamber Covers Fastened But Not Glued
Third Chamber Covers Fastened But Not Glued

New Folded Bass Horn - More Progress On Second Horn 2

The next step is to cut four more panels that will enclose the dustpan assembly and cover the first channel of the bass horn and will become the bottom panels of the second channel.  Here is the assembly with one cover (one trapezoid and one rectangle) fastened on and glue drying:

First Channel - One Trapezoid And One Rectangle Attached
First Channel - One Trapezoid And One Rectangle Attached
 Here is the trapezoid fastened to the opposite matching first channel:


First Channel - Second Trapezoid Attached
First Channel - Second Trapezoid Attached
 Here is the assembly with both halves of the first channel covered and glue drying:

First Channel - Both Sides Covered
First Channel - Both Sides Covered
Next, four more trapezoids are cut to form the sides of the second channels.  The smaller of the trapezoids is "keyed" to fit over the edge of the first channel side.  The small rectangular cutout "key" helps to maintain symmetry during assembly.

Second Channel - Two Panels Setup For Drilling For Fasteners
Second Channel - Two Panels Setup For Drilling For Fasteners
After marking and carefully drilling and countersinking for fasteners, the second channel sides are fastened on.


Second Channel Sides Aligned And Fastened
Second Channel Sides Aligned And Fastened
Here is another view with both second channel sides fastened and glue drying:

Second Channel Sides Glued And Fastened
Second Channel Sides Glued And Fastened
The next step will be to cover the matching pair of second channels.

Thursday, October 15, 2015

New Folded Bass Horn - More Progress On Second Horn

The rain stopped the next day, so I set up outside again.  First, I set up the clamp for a cross cut to separate the matching pair of trapezoids.

Cross Cut To Separate The Matching Trapezoids
Cross Cut To Separate The Matching Trapezoids
 This is just after making the cut.

Cross Cut To Separate The Matching Trapezoids
Cross Cut To Separate The Matching Trapezoids
 Here, I am preparing to attach two pairs of matched trapezoids to the central panel.  Earlier, I had made an extra one of these central panels as a pattern while I was cutting out panels for the first folded bass horn.

Attaching Trapezoids To Central Panel
Attaching Trapezoids To Central Panel
 To make sure that the countersunk holes are centered in the center plywood lamination, I use an awl to mark hole centers before boring the holes into the center panel edge.  I pre-drill all of the countersunk holes in the side panels on a drill press to make sure they are perpendicular.  I use the pre-drilled sides as a pattern to center the awl while marking the center lamination.

Marking Hole Centers In Center Lamination With Awl
Marking Hole Centers In Center Lamination With Awl
It is important to center the trapezoids on the center panel and maintain symmetry as correctly as possible to avoid starting with a slightly warped assembly.  This assembly is similar to a dustpan that, instead of collecting anything, is instead designed to distribute sound from the square shape of the horn throat to the rectangular shape at the opposite end.  In addition to the shape change, the cross-sectional area increases to follow a linear interpolation of an exponential expansion.

Dustpan Assembly - Both Sides Glued And Screwed
Dustpan Assembly - Both Sides Glued And Screwed


Dustpan Assembly - Both Sides Glued And Screwed
Dustpan Assembly - Both Sides Glued And Screwed
As you can see, the trapezoids are in the same plane so it would appear to be possible to cut each side from a single strip of plywood and avoid a butt seam.  I chose the simpler cutting process of separate trapezoids because it allows side cuts to be shared thereby saving plywood.  Tomorrow, I will attach four more panels that will enclose the dustpan passage and provide the sides for the returning passage.



New Folded Bass Horn - Progress On The Second One

A few days ago, I purchased two 4' x 8' sheets of ULB grade 1/2 inch plywood and began to cut out the panels for a second folded bass horn to match the first one.  I selected one of the ULB plywood sheets and set up the straight edge for a rip cut.


Clamping Straight Edge For First Rip Cut
Clamping Straight Edge For First Rip Cut
With the straight edge clamped in place, I made one straight cut for a strip of plywood from which to make several panels of the same width.
After The First Rip Cut
After The First Rip Cut
 The second rip cut from the remainder of the plywood sheet will not extend for the whole length of the sheet, so I stop cutting when I have enough length.

Second Rip Cut Completed
Second Rip Cut Completed
I set a four-foot straight edge at a right angle to the rip cut in order to guide the saw while I remove a strip of the correct length.


Third Cut At A Right Angle To The Rip Cuts
Third Cut At A Right Angle To The Rip Cuts
Because the circular saw leaves a curved cut, I complete the cuts with a scroll saw with a reciprocating blade.
Completing The Cuts With Scroll Saw
Completing The Cuts With Scroll Saw
There is enough plywood in the remainder of the sheet to begin to cut out some of the smallest panels for the throat region of the horn.  Using the square as a straight edge, I prepare for the first cut for the side of one of these trapezoidal panels.


Beginning To Cut The Smallest Trapezoidal Panels
Beginning To Cut The Smallest Trapezoidal Panels
 Here is the second cut completed for the first trapezoid.

First Trapezoid With Both Sides Cut
First Trapezoid With Both Sides Cut
 I saved panel material by "reusing" the side cut for the adjacent trapezoid and made a third cut completing the sides for a matching pair of small trapezoids.

Sides Cut A Matching Pair Of Small Trapezoids
Sides Cut A Matching Pair Of Small Trapezoids
As you can see in the above photo, it started to rain so I had to stop working and move everything inside out of the weather.

Saturday, October 10, 2015

New Folded Bass Horn - Some Tracks Played Back

Here are some LP tracks recorded using the iPad Air and iTrack Dock by Focusrite:

Motown Records MT621 - The Supremes - Where Did Our Love Go
The Supremes - Where Did Our Love Go

Mercury MG 20591 - The Platters - More Encore of Golden Hits
The Platters - Harbor Lights

Capitol T-1503 - Plas Johnson - In The Mood For The Blues
Plas Johnson - Tanya

Columbia CL 2512 - Dave Brubeck - Time In
Dave Brubeck - Lost Waltz

Trip Jazz TLP - 5518 - The Jazz Giants Vol 2 - Reeds
Count Basie - Afternoon With Basie-ite

Warner Brothers BS 2721 History of the Grateful Dead Vol 1 - Bear's Choice
Grateful Dead - Black Peter (Acoustic from Bear's Choice)

The iTrack Dock and Tape App are a great combination.  I cannot say enough in praise of Focusrite as a supplier.  For example, when my iPad Air upgraded to iOS 9, Tape would no longer start.  Within a week after I discovered this, I emailed Focusrite and within hours, they released the next version of Tape that corrects this problem.  As a result, I was able to record the above tracks with the excellent Focusrite system.

Wednesday, October 7, 2015

Foot Drum Using Recycled Bose 901 Driver From CTS

This project originated when our band, The Horseshoe Crabs, realized that we would like to have a bass drum.  After a little internet research, I found that several people have made foot drums from fruit crates or other wood boxes with microphones built into them.  I already had eighteen four inch CTS drivers that I removed from a pair of Bose 901 speakers I found at the local transfer station several years ago.  The 901 wood cabinets were in very poor condition and the drivers were the only thing worth saving.  I built a wood box with 3/4 inch pine wood for the bottom and sides and a 1/4 inch plywood top.  I mounted one of the 901 speakers inside the box.  The box is sealed like an "acoustic suspension" speaker.  I plugged the speaker into an amplifier input and found that the drum worked but the pitch was too high to sound like a bass drum.  However, after epoxying a large steel washer to the speaker cone, I was able to lower the resonance of the system into the "bass drum" range.  Here is the foot drum viewed from the bottom:


Foot Drum
Foot Drum
Recently, I decided to add a handle and paint the sides.  I did not paint the top and bottom so as not to interfere with the sound.  Here is a picture taken while the black paint was drying:


Foot Drum - New Paint
Foot Drum - New Paint
Here is the foot drum with the handle installed.
 
Foot Drum - Handle Installed
Foot Drum - Handle Installed
I must say a few words in praise of the quality of the four inch CTS speaker driver found in the Bose 901.  This foot drum has been in use for about four years now.  I have seventeen more of the CTS speakers from the 901 and I always knew I would be able to replace the foot drum speaker in the event that it succumbed to the beat imposed upon it during gigs.  However, the speaker is still working fine.  Kudos to Bose for sourcing such a robust little woofer.  The foot drum sounds great too!


New Folded Bass Horn - Back Chamber From Recycled Technics SB 2745 Speaker

I have been putting off building a back chamber for the new folded bass horn.  I was recycling a pair of Technics SB 2745 speakers, removing the drivers and other hardware, when I realized that the dimensions of the particle board cabinet might be ideal for a back chamber for the new folded bass horn.  All I had to do is cut about 11 1/4 inches from the length dimension on the table saw.  Then I cut out a rectangle of 1/2 inch plywood to fit into the open end.  Here is the "Technics" back chamber installed over the eight inch driver on the new folded bass horn:


There is already a round cutout for a twelve-inch driver in the Technics box.  The box will work for any diameter bass driver up to 15 inches.  In the picture above, the modified Technics back chamber is resting on a couple of two inch maple blocks to raise it to a height centering it on the horn throat and driver.

One observation regarding the back chamber is that, apparently as a result of the high efficiency of this folded bass horn, very low power levels and cone excursions produce very loud sound levels in the room.  As a result of this high efficiency, there are extremely low back pressures in the back chamber at normal listening levels.

Sunday, October 4, 2015

New Folded Bass Horn - Testing Two More Drivers

Here is a CAMM, formerly Near, 6 1/2" woofer installed on the folded bass horn with back chamber cover removed:


New Folded Bass Horn - Near 6 1/2" Woofer
New Folded Bass Horn - Near 6 1/2" Woofer
And here is a vintage Rola 15 inch woofer taken from a Leslie organ speaker cabinet found in an open-top dumpster. With the 15 inch woofer attached, you can get an idea of the relatively small scale of this folded horn when you consider the horn length is about eleven feet!  Also consider that the corner placement theoretically multiplies the measured ten square foot mouth area of this horn by a factor of eight for a total mouth area of eighty square feet!

New Folded Bass Horn - Rola 15 Inch Woofer From Leslie Cabinet
New Folded Bass Horn - Rola 15 Inch Woofer From Leslie Cabinet
Both the little Near and the large Rola speakers sound great on the new folded bass horn.  However, the eight inch woofer I normally use for testing this appears to be much more efficient than either the Near or the Rola.

Saturday, October 3, 2015

Eight More Realistic Minimus 7 and Optimus Pro 7 Speakers!

More Radio Shack Minimus 7 and Optimus Pro 7 Speakers turned up at the local transfer station a couple of days ago.  It is ironic that I keep finding tiny loudspeakers now that I have developed the very large Sound Transformer and the somewhat smaller but still quite large New Folded Bass Horn.  These little speakers do sound quite good, especially if you put them on the floor up against a wall.  This most recent batch was pretty dusty, but they cleaned up pretty well.  Here is a photo of the find:


Realistic Optimus Pro 7 Minimus 7 Speakers - Four Pair!
Realistic Optimus Pro 7 Minimus 7 Speakers - Four Pair!

Friday, October 2, 2015

New Folded Bass Horn - Current Setup

Here is a photo of the new folded bass horn with a four foot by four foot plywood panel set over the top to enclose the final flares at both sides of the horn.  The corner midrange horn is set over the top with the Magnavox horn tweeter.  In the foreground, you can see a pair of 68uF nonpolar capacitors and a large induction coil temporarily wired as a series crossover so I can listen to music through this and do more testing.  This is a "bare-bones" setup.  The whole thing could be made more attractive by constructing a large curved shelf or bench in place of the plywood panel.  The bass driver will eventually be inside a back chamber and not visible.


New Folded Bass Horn Setup With Crossover, Midrange Horn, and Tweeter
New Folded Bass Horn Setup With Crossover, Midrange Horn, and Tweeter