Wednesday, November 30, 2016

Big Horn Speakers For Your Tiny House - 61 milliWatt In - 80dB Out!

The recording is "A Mighty Fortress" at Riverside Church, played by Virgil Fox on the Aeolean-Skinner Organ.



The sound amplification system we are trying out here illustrates how a high-efficiency loudspeaker system requires little electrical power to play at moderate volume levels in a medium-sized room.
Eight volts DC is supplied by a nearly discharged 9V battery.   Supply current is monitored using a Fluke 87 rms reading DVM set on 39.99mA range. 

Although it does not appear in this video, an analog sound level meter registers levels up to 80dB which is loud enough for demonstration purposes in this small room but louder than you would probably listen to normally.

The quiescent power supply current reads 21.44mA.  Peaks of about 29mA occur during this video and the DVM does not over-range.

The difference between 21.44mA and 29mA is 7.59mA.  At 8 Volts, this is 60.72mW.  So, as an approximation to be sure, in my listening room, I can get 80dB peaks with 61 thousandths of a Watt of power supplied above the "quiet" current.

Qualitatively, the "large hall" ambiance is audible almost anywhere in the room.  Loudspeakers like this can provide a convincing illusion of space much larger than your listening room and you don't need much electrical power to run them. You could even be "off grid". This video features a tiny class D stereo audio amplifier, Parts Express Part # 320-604.

Tuesday, May 24, 2016

New Folded Corner Bass Horn New Straight Midrange Horn Super Tweeter

The New Folded Corner Bass Horns and the New Straight Midrange Horns now have a pair of Eminence APT-150 Super Tweeters.  This is a bi-amped system with line-level RC low-pass filters for the bass and RC high-pass filters for the midrange/tweeter.  The midrange and tweeter horns are powered by a Lepai LP-2020A+ amplifier and the folded corner bass horns by a Pioneer SX1280 receiver.  Here are Chester and Lester playing "It's Been A Long Long Time".  The preamplifier is an NAD 3020 Integrated Amplifier with "Y" RCA connectors in the pre-amp outputs.



The audio recording was made using the Tape App running on an iPad Air controlling an iTrack Dock with the high quality Focusrite preamps built in and a matched pair of Behringer C-2 condenser microphones. 

Watching the FFT of this system's response to a white noise track, I find that the smoothness of response vs frequency between 300Hz and 400Hz is improved without the line level low pass filters.  It appears as if the bass horn and woofer together function as a low pass filter.  The high pass filters provide some protection for the midrange and tweeter combination from low frequency energy and do not appear to have a significant effect on the smoothness of response around crossover.

Wednesday, May 4, 2016

New Folded Corner Bass Horns With New Straight Midrange Horns

The New Straight Midrange Horns are now fitted with small two inch drivers originally taken out of Boston Acoustics Unity enclosures.  The back chambers, recycled from the New Folded Corner Midrange Horn, are made from short lengths of PVC pipe.  Here are pictures of the left and right horns.

New Folded Corner Bass And Straight Midrange Horns - Left Channel
New Folded Corner Bass And Straight Midrange Horns - Left Channel


New Folded Corner Bass And Straight Midrange Horns - Right Channel
New Folded Corner Bass And Straight Midrange Horns - Right Channel
I tried making passive crossovers for each channel.  However, the midrange horns are even more efficient than the bass horns and I would have had to pad them down to get a good balance between the bass and midrange.  Instead of padding, I made a couple of line level crossover networks and now the horns are bi-amped.  RC low pass networks for the bass horns and RC high pass networks for the midrange horn allow independent control of the bass and midrange/treble amplifier gains.  Once a balance is achieved, the overall gain adjustment on the preamplifier allows the levels to "track" and stay in balance at any volume level.

Midrange and treble networks are plugged into a Lepai LP-2020A+ Amplifier.

High Pass Networks For Midrange And Treble - Lepai LP-2020A+ Amplifier
High Pass Networks For Midrange And Treble - Lepai LP-2020A+ Amplifier
Bass networks are plugged into the AUX input on a Pioneer SX-1280 receiver.



Low Pass Networks For Bass - Pioneer SX1280 Receiver
Low Pass Networks For Bass - Pioneer SX1280 Receiver
The bi-amp arrangement is also pretty handy when you want to raise or lower bass output relative to midrange and treble.  I have found that the bass level on some recent recordings is way too high so it is great to be able to adjust the bass level without altering phase as a result of the adjustment. 

Thursday, April 28, 2016

Progress On Construction Of The New Straight Midrange Horn

With the large flares of the New Straight Midrange Horn construction essentially completed, I begin construction of the smaller flares of the horns.  Using the same techniques employed on the Sound Transformer Bass Horns, a pair of flanges of the same dimension as the smaller flange on the larger flare are cut out on the table saw.  By beveling the edges of the square opening in the center, I will have the flange interior edge flush with the faired exponential expansion.  Four pairs of ribs are cut at the proper angle on the chop saw.  The ribs will be scribed to the exponential curve using a plywood pattern but only after they are fastened into position between the flanges.  To get the ribs to fit, it is necessary to cut away a bit at the small end of the horn.  Here is one of the horns set up for marking with the pattern.

New Straight Midrange Horn - Throat Flare Progress
New Straight Midrange Horn - Throat Flare Progress
After marking all four of the ribs for the curve as well as numbering the matching parts so they can be reassembled later, the rib curve is cut out on a band saw.


New Straight Midrange Horn - Throat Flare Progress
New Straight Midrange Horn - Throat Flare Progress
The series of small cuts to the line make it easier to "leave the line" without cutting away too much.  Here are the four ribs after cutting the curve.


New Straight Midrange Horn - Throat Flare Progress
New Straight Midrange Horn - Throat Flare Progress
Now, the horns are reassembled so the other two pairs of ribs can be positioned and marked.


New Straight Midrange Horn - Throat Flare Progress
New Straight Midrange Horn - Throat Flare Progress
All eight rub curves are sanded by hand to the line using a sanding block.


New Straight Midrange Horn - Throat Flare Progress
New Straight Midrange Horn - Throat Flare Progress
Here are the horns with all eight sanded ribs fastened in.  The cardboard trapezoid will be used to mark four plywood sides.


New Straight Midrange Horn - Throat Flare Progress
New Straight Midrange Horn - Throat Flare Progress
Here is one of the throat flares set on top of a mouth flare.


New Straight Midrange Horn - Throat Flare Progress
New Straight Midrange Horn - Throat Flare Progress
Tomorrow, I will cut the sides for the throat flare.

Monday, April 25, 2016

Latest Progress On Construction Of New Straight Midrange Horn Pair

Today, I cut out the last four flare sides and custom fit each one into its respective horn.  Following that, I "dry-assembled" the horns several times, refitting here and there, until I got a reasonably good fit for the joints.  After cutting out "throat square" blocks to hold the sides in place, here is what the horns looked like.


New Straight Midrange Horns - Sides Dry-Assembled
New Straight Midrange Horns - Sides Dry-Assembled


New Straight Midrange Horns - Sides Dry-Assembled
New Straight Midrange Horns - Sides Dry-Assembled

With all of the sides marked for proper positioning, I applied adhesive to the joints.  It is necessary to keep the adhesive away from the square blocks so they will come out tomorrow after the glue dries.


New Straight Midrange Horns With Adhesive Applied
New Straight Midrange Horns With Adhesive Applied
It will get quite cold in the barn attic overnight so I have moved the horns inside so the glue can set under more ideal conditions.


New Straight Midrange Horns With Adhesive Curing
New Straight Midrange Horns With Adhesive Curing
Tomorrow, I will start on the smaller portions of the horns.



Sunday, April 24, 2016

Still More Progress On The New Straight Midrange Horn Pair

Because the Lauan plywood is 1/8" thick, I can cut out the horn flare sides with a utility knife.  As in the Sound Transformer Bass Horns, the first two sides for each horn are trapezoids and fairly simple to cut even without a straight edge.  Here is an image of two of the trapezoids ready for fitting.  The only dimension that needs to be trimmed is the length.  Each end of the side needs a beveled edge that I can easy machine with a sanding block.


New Straight Midrange Horn With Two Trapezoids
New Straight Midrange Horn With Two Trapezoids
Here is a horn with trapezoids in position.


New Straight Midrange Horn And Two Trapezoids
New Straight Midrange Horn And Two Trapezoids


New Straight Midrange Horn And Two Trapezoids
New Straight Midrange Horn And Two Trapezoids
The next thing to do is to fit a corrugated cardboard pattern for the other two sides.  Here is the cardboard pattern being fitted by scribing, cutting, and sanding the edges until the pattern fits.


New Straight Midrange Horn - Fitting Cardboard Pattern
New Straight Midrange Horn - Fitting Cardboard Pattern
The cardboard pattern will be used to mark the first side on the Lauan panel.  The first plywood side will be cut slightly larger than the cardboard pattern for a more accurate fit than can be achieved with the cardboard.

More Progress On New Straight Midrange Horn Pair Construction

I cut two smaller square flanges for the smaller end of the horns.  The square hole in each flange is too small to be cut out with the table saw so I used a scroll saw with the shoe set to an angle to match the flare angle.  I made the square hole a little smaller than it needs to be so I can fair it to the horn sides after they are in.


New Straight Midrange Horn With Small Flange
New Straight Midrange Horn With Small Flange


New Straight Midrange Horn With Small Flange
New Straight Midrange Horn With Small Flange
I am playing some music here through the original Sound Transformer Horn Stereo Pair and have to turn the volume way down because I am standing right in front of the horn while attaching the small flange.