Saturday, December 19, 2015

Latest Find: Pair Of Altec Lansing Corona 893A Acoustic Suspension Loudspeakers

These turned up at the local transfer station.  Someone had left them at the edge of the small covered storage area and they were getting wet from rain blowing in from the East.  This is a quality design from about 1969 with treated cloth surrounds instead of the molded foam ones.  They are finished in the original black walnut.

Pair Of Altec Lansing Corona 893A Acoustic Suspension Loudspeakers
Pair Of Altec Lansing Corona 893A Acoustic Suspension Loudspeakers
Of course, I had to try out the woofers in the Folded Corner Bass Horns.  They worked quite well.  The upper frequency cutoff of these ten inch woofers on this horn appears to be a little over 250Hz.

Altec Lansing Corona 893A Woofer #1
Altec Lansing Corona 893A Woofer #1


Altec Lansing Corona 893A Woofer #2
Altec Lansing Corona 893A Woofer #2
Here is one of the woofers mounted on the New Folded Corner Horn.


New Folded Corner Horn - Altec Lansing Corona 893A 10" Woofer
New Folded Corner Horn - Altec Lansing Corona 893A 10" Woofer
It appears as if any reasonably good woofer works well as a driver for this horn.  Of course, "power handling" is not really a consideration because the music playback is pretty loud at input power levels of less than 1/100th to 1/10th of a Watt.

I now have the KLH CL-3A 12" woofers back in the horns.  The upper frequency cutoff for the KLH 12" woofers is around 350 Hz.  The Altec Lansing 893A pair have been reassembled and cleaned up and are near mint.



Friday, December 18, 2015

New Folded Corner Midrange Horn - Twin Back Chambers

Back chambers for the twin drivers in the New Folded Corner Midrange Horn should help to improve overall performance of the horn.  PVC pipe and 1/8" Masonite form the mounting flange and walls of the back chambers while a disc of mahogany plywood provides a cover.

First, it is necessary to plug all of the holes in the throat flange:


New Folded Midrange Horn - Throat Flange
New Folded Midrange Horn - Throat Flange
 A new flange is cut out of 1/8" Masonite.  Four flat-head wood screws fasten driver, flange, and pvc pipe together.  The assembly is pictured below set upside down on the throat flange.  It is necessary to chamfer the edge of the flange to allow clearance for the driver surround.


New Folded Midrange Horn - Flange-Driver-PVC Pipe Assembly
New Folded Midrange Horn - Flange-Driver-PVC Pipe Assembly
 The assembly is positioned over the throat flange for drilling and countersinking.


New Folded Midrange Horn - In Position For Drilling and Countersinking
New Folded Midrange Horn - In Position For Drilling and Countersinking
 Two 1/16" holes are drilled through the PVC for the driver leads.

New Folded Midrange Horn - Holes for Leads
New Folded Midrange Horn - Holes for Leads
Wires are fed through the holes and ends stripped.

New Folded Midrange Horn - Lead Ends Stripped
New Folded Midrange Horn - Lead Ends Stripped
 The back chamber assembly is now in position and fastened.

New Folded Midrange Horn - Back Chamber Assembly Fastened
New Folded Midrange Horn - Back Chamber Assembly Fastened
 The mahogany plywood disc is provided with black electrical tape as a gasket for a reasonably tight fit in the PVC pipe.

New Folded Midrange Horn - Back Chamber Cover
New Folded Midrange Horn - Back Chamber Cover
The twin driver and back chamber are already installed.  Here is the setup to test impedance as a function of frequency.


It will be interesting to see how the measured impedance vs frequency plot compares with the one predicted in Hornresp.

Sunday, December 6, 2015

New Folded Corner Bass Horn - Installing KLH CL-3A Woofers In Both Horns

During folded bass horn testing so far, I have been using two different eight inch woofers, one by Altec Lansing and one by Boston Acoustics.  Today, I decided to get an idea how the two horns might sound with matching drivers.  The KLH woofers removed from CL-3A acoustic suspension boxes are a good enough match for testing purposes.  I already have matching back chambers cut away from a pair of old Technics boxes.  Here is the right channel getting the 12 inch CL-3A woofer:


New Folded Corner Bass Horn - KLH CL-3A Woofer & Technics Back Chamber
New Folded Corner Bass Horn - KLH CL-3A Woofer & Technics Back Chamber
New Folded Corner Bass Horn - KLH CL-3A Woofer & Technics Back Chamber
New Folded Corner Bass Horn - KLH CL-3A Woofer & Technics Back Chamber

Here is the left channel being set up with an identical woofer and back chamber:


New Folded Corner Bass Horn - KLH CL-3A Woofer & Technics Back Chamber
New Folded Corner Bass Horn - KLH CL-3A Woofer & Technics Back Chamber
I also put an equal amount of polyester fiber fill into both back chambers.  Now for some listening tests!

Thursday, November 19, 2015

New Folded Bass Horn - Testing The Two Found Drivers

Today, I removed the eight inch drivers from the New Folded Corner Horns and set up to measure the Thiele-Small parameters.  The two drivers that I found that worked the best in these horns were removed from subwoofer cabinets, one made by Altec Lansing and the other by Boston Acoustics.  I thought it would be interesting to try these two drivers in the Hornresp simulator but, before I could do that, I needed to measure Thiele-Small for both in order to input the driver parameters for the simulator.

Here is the setup for testing the Altec Lansing eight inch woofer.

New Folded Corner Bass Horn - Altec Lansing Driver Setup
New Folded Corner Bass Horn - Altec Lansing Driver Setup
I used the Lepai 2020A amplifier to drive the speaker under test through a series-connected power resistor.  The power resistor measures 10.0 Ohms on my Fluke 87 volt-ohmmeter.  Sine-wave levels during testing are all under 400mV so a power resistor is probably not necessary.  For a variable-frequency sine wave source, I used a function generator app on the iPad Air.  I also used an old Southwest Technical Products function generator I have had for a long time.  The SWTP one is easier to use to quickly find null points at resonance.  The iPad App allows very precise frequency settings via touch keypad.  I use a freeware program called DPC to calculate the T-S parameters from measurements made with the above setup.

After completing the simulation in Hornresp, it is interesting to find that the two different drivers appear to perform nearly identically in the simulated horns.  However, there are some important differences that we will get into later.

You can listen to how the horns sound at the following blog post:
http://paulsherman.blogspot.com/2015/10/new-folded-bass-horn-more-progress-5.html


Thursday, November 5, 2015

Sound Transformer Plays "Comrade Down" by Eoto

Break-in and testing continues with "Comrade Down" by Eoto.

Sound Transformer With New Bass Drivers - More Testing

Here is a video of Herbie Hancock's "Vein Melter" playing on the Sound Transformer with new bass drivers.  This track has strong bass and percussion, perfect for breaking in the new drivers.  I used Howard Leight hearing protectors during this test because the sound level is quite high.

While shooting the video, I moved around the room to demonstrate how the sound is dispersed by the horns as well as how each individual horn in the system sounds.  Unlike the right channel, the left channel does not yet have a midrange horn so you get to hear how the bass horn sounds driven directly from the speaker output terminals without any crossover.  The right channel horns are connected through a simple L-C network with crossover at about 300Hz.  This video is ten minutes and fourteen seconds long.



If you stay with it long enough, you will see that the power level meters stay between 0.01 Watt and 0.1 Watt.  Even with that small input power, I had to use the Howard Leight hearing protectors.  These horns "throw" the deepest bass out in front and you can clearly hear that in the video every time I position the camera in front of the bass horns.

Wednesday, November 4, 2015

Sound Transformer Gets New Bass Drivers - Preliminary Test Results

A couple of weeks ago, I began to wonder how the Sound Transformer might sound with a set of new twelve inch drivers for the bass horns.  Having read that guitar speakers make great horn speaker drivers, I ordered a pair of guitar speakers from MCM Electronics that looked as if they might work well in this application.  The speakers were really affordable and arrived really quickly.  Here is the new Sound Transformer with MCM guitar speakers playing B. B. King's Bad Case Of Love:



New Folded Bass Horn - More Progress 6

Yesterday, I constructed a couple of corner reflectors for the New Folded Bass Horns.  Each reflector is intended to fit into the room corner and provide a reflective boundary that will change the direction of the sound radiating from the back of the main folded horn assembly and direct it out into the room through the matching pairs of horn flares on each side of the main assembly.  While the assembly is being modified with the addition of the corner reflector, the polyester fill is removed from the back chambers that were used with the original Sound Transformer bass horns and installed in the back chamber for the New Folded Corner Horn driver.

Here are some photos of the corner reflector being set up behind the folded horn assembly for the right channel.

New Folded Corner Bass Horn - Corner Reflector In Place
New Folded Corner Bass Horn - Corner Reflector In Place
Viewed from above, the shape of the twin side horn flares can be seen in the following photo:

New Folded Corner Bass Horn - Corner Reflector In Place
New Folded Corner Bass Horn - Corner Reflector In Place
With the corner reflector in place and the main folded horn unit repositioned to provide the proper dimensions for the side flares, the 4' x 4' plywood sheet is placed over the top of the horn.  As you can see, the plywood also happens to be a yard sale sign we have used several times.

New Folded Corner Bass Horn - 4' x 4' Top Panel In Place
New Folded Corner Bass Horn - 4' x 4' Top Panel In Place
Here is one of the back chambers from the Sound Transformer with KLH driver and polyester fill removed.  The back chamber will serve as a stand for the midrange horn, also from the Sound Transformer, currently being tested with the new folded bass horn.

New Folded Corner Bass Horn - Stand For Midrange And Poly Fill
New Folded Corner Bass Horn - Stand For Midrange And Poly Fill
The back chamber made from part of an old Technics speaker is now stuffed with the polyester fill.
The empty Sound Transformer back chamber is now the stand under the midrange horn.

New Folded Corner Bass Horn - Back Chamber With Poly Fill
New Folded Corner Bass Horn - Back Chamber With Poly Fill
The back chamber is now positioned at the correct height for the eight inch driver presently being used with the folded bass horn.  By the way, this eight inch speaker was removed from a Boston Acoustics Unity subwoofer cabinet.

New Folded Corner Bass Horn - Back Chamber And Eight Inch Driver
New Folded Corner Bass Horn - Back Chamber And Eight Inch Driver
Now the right channel has a corner reflector and polyester fill in the back chamber.  The stack of weights on the small square of plywood are intended to correct a little warping in the "Sale New And Used" cover panel.

New Folded Corner Bass Horn - Corner Reflector And Stuffed Back Chamber
New Folded Corner Bass Horn - Corner Reflector And Stuffed Back Chamber
The same changes have also been made to the left channel folded bass horn.  Now for more listening tests!




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.