Experiments with acoustic horns as mobile device amplifiers

Before jumping in I have to make it clear that horns are not amplifiers. If I don't, I'll get a bunch of messages enlightening me. But horns do make sound louder and when paired with cell phones are commonly called "passive amps", and even though that is a misnomer what else should we call them? "Phone horn" doesn't have a nice ring. "Impedance matching device for mobile audio electronics" sounds like the title of a patent application. What's the big deal and what's the difference between an amplifier and a horn? An amplifier adds energy to the system, it makes the speaker vibrate harder, moving more air, and increases sound output. Horns are different, they make speakers louder by making transfer from the relatively dense speaker to the relatively rare atmosphere more efficient. Sound travels easier through dense substances like water and less easy through gasses like air. The horn helps the sound energy transfer from one to the other and the result is louder music. If you'd like to hear a smart person explain it, click HERE.

My first ever "horn" was a piece of PVC pipe with a slot in the middle for my phone and the ends cut at an angle toward the listener. It sat on two feet to prevent it from rolling around. It worked "okay". I don't own it anymore and can't find a picture but you may have seen similar speaker stands, maybe with bamboo.

My second (and real) horn which I'm calling 1.0 is based on a design by Dustin Penner. What Dustin brought to the table is a easy to make flat horn from 3 pieces of wood. I made it smaller and changed the curves slightly but overall the result is impressive.

Horn 1.0

Horn 1.0. Height is approximately 1 inch (25.4mm). It was made in 3 layers. 

Horn 2.0 is based on a folded horn design by MXX on Instructables. This style of horn is usually seen on bass heavy concert speakers and definitely has a warmer but slightly muddier, sound. The downside is this speaker is much more difficult to build than Penner's. 

Horn 2.0

Horn 3.0 is a folded version of v. 1.0. If you are unfamiliar with folded horns, just imagine a trumpet with all it's turns. A horn doesn't need to be straight. 3.0 is much louder than the two previous versions. In my test, it was 12-14 decibels louder than the previous horn designs but the sound is also a bit harsh. To me it sounds like the small transistor radios that were popular in the 60's and 70's. 

Horn 3.0, made in 5 layers and is approximately 1-7/8" tall (47.63mm)

Walnut Trestle Sewing Table

Inspired by an 1840-ish Shaker table originally made in Harvard. I redrew this full scale from a sketch in Shea's "Making Authentic Shaker Furniture" and created full size patterns for the feet and legs. The leg tenons extend all the way through the feet. The feet each have half a mortise which makes construction much simpler. The feet join together and are pinned to the leg. The leg, stretcher, and battens all interlock. The top is attached with screws in elongated slots.

Refurbishing a Delta Homecraft Lathe Headstock

I recently purchased just the headstock for a Delta Homecraft Lathe. Delta sold different models of lathes with this same or very similar headstock from the early 30's until the mid-50's so I don't know when specifically this headstock was sold.

Before and After

I stripped the headstock down completely, cleaned and looked at every part. The Timken tapered roller bearings (1) & (2) are in excellent condition and did not need replacement. The spindle threads had some minor damage which I repaired with a needle file. 

Unfortunately the indexing pin point was damaged sometime in the past but is still usable. 

Since I was down to bare metal I filed the casting seams fairly smooth

And repainted with Rustoleum Dark Machine Grey.

One little mishap during the process, the badge was damaged. 

Now what to do with it? My original plan was to make a bowl lathe / disc sander. I might still do that or might end up reselling it. 

Nova G3 vs. Nova Precision Midi lathe chucks

I've been using a Nova Midi chuck but wanted an upgrade. So when I spied an open box G3 on Amazon Warehouse with 2 sets of jaws for $124 shipped, I bit. The G3 was supposed to be direct threaded for 1x8 threads but instead mine was threaded for 1-1/4x8. No problem, I ring Amazon on the blower (opened a chat with customer service) and told them I would keep it if they gave me credit to buy the proper insert. No problem says Amazon and within 2 days my insert had arrived.

G3 (left) and Precision Midi (right)

The Midi was purchased used and came with 2" and 1" jaws, a woodworm screw, allen keys, and tommy bars for around $50; not a bad deal. The G3 also came with 2" and 1" jaws, a woodworm screw, allen keys, and the wrench doohickey; for a little less than $124. My lathe is still not 100% operational so I haven't turned with the G3 yet so this is not a proper review although I don't believe a review is really necessary. [Update: I have used the G3 a good bit and it performs equal to the Midi although I prefer it since I can scroll the jaws one handed.] The G3 is among the most popular lathe chucks sold and Teknatool makes high quality chucks. What I am doing is comparing size and heft of the two chucks since the G3 looks considerably bigger so you'd expect it to be beefier, but is it?

G3 (left) and Precision Midi (right)

So in about every way, the G3 dwarfs the Midi so you'd expect it to be a heavier duty chuck. But as you can see in the pictures above, the G3 is mostly hollow. Placed on the scale, the G3 weighs in at 55 oz., or 1.56 kg.; the Midi weighs 53 oz. or 1.50 kg. The 2 oz. difference is the G3 has a threaded insert, the Midi is direct threaded for 1x8. They are essentially the same weight.

Precision Midi

Nova G3

One advantage the Midi has over the G3, and it's pretty significant to owners of gap bed lathes, is that being shorter it allows more room for turning platters. The G3 is so long it renders the gap on my Delta 46-111 useless. Of course the main advantage of the G3 and why I wanted to upgrade was that you can open or close the jaws one handed while using the other hand to steady the wood blank or bowl. The Midi chuck requires 3 hands unless your lathe comes with a spindle lock. So was the G3 really an upgrade? It's sounding less and less so, but the G3 also has set screws on the spindle threads so it can be reversed. The Midi has no set screws and if you reversed the lathe it would spin itself right off the spindle.

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Simple Carpenter Bee Trap

My shop has been infested with carpenter bees this year and recently I learned how to make a simple trap. Carpenter bees, or wood bees, like to find little crevices and holes in which they nest. My trap is a simple 2x4 cut off with 1/2" holes drilled to a central chamber that leads to a glass jar. Hopefully the bees will be lured into the wood then crawl toward the light and become trapped. We shall see. I'll post an update in a few weeks whether the trap worked or not.

Rockwell Delta 46-111 Lathe, Part 4: Remote Control Pendent

A long overdue update. The lathe has been repainted, reassembled, the variable speed motor installed, and I've began working on a remote control pendant like those found on Robust or Vicmarc lathes.

current status of the remote

Treadmill motors have a soft start feature so the treadmill must always start at the slowest possible speed, a good safety feature in a treadmill but not desirable in a lathe. Reportedly you can bypass the softstart feature on an mc-60 controller (most common type) by switching the wiper on the potentiometer. Unfortunately I am not using an mc-60 controller and switching any of the potentiometer wires individually does not stop the motor. As time goes on I will experiment with switching multiple wires at once and report back. As it sits now, the speed control works just fine but the little on/off switch does diddly squat. There is a main power switch on the lathe stand for cutting power to everything.

GE PWM speed controller

Dell powerbrick repurposed as a remote control

Switching the center wire to stop/start the motor, an idea that did not work.

Non functioning power toggle and perfectly functioning potentiometer.

Making a saw blade knife

Saw blade knife with padauk handle.

I made this knife from a circular saw blade. There is an internet myth that claims circular saw blades are made from low carbon or mild steel, or just junk steel, nothing could be further from the truth. Saw blades spin at over 3,500 rotations per minute and endure significant stress while cutting wood, the steel must be high quality and very tough. Unfortunately blade makers are not very forth coming with what steel they use and the resulting speculation breeds all sorts of rumor. Many people believe these blades are made of L6, a common tool steel known for it's toughness and impact resistance. A few have sent blades for metallurgical analysis and the results confirm an alloy that is very similar to L6. Still there are a number of people who for whatever reason insist these blades are garbage steel. I'm not a metallurgist and can't say what steel is in any particular saw blade but neither can anyone else who isn't the manufacturer of that blade. What I can say is that many people have made knives from circular saw blades and in testing those knives are very tough and hold an edge well. If you need a disclaimer, here it is: cheap things are cheaply made. I believe that if you use a good quality blade from a respected manufacturer then you're likely to get good steel but this is recycling, there are no guarantees.

Step one was cutting the rough shape from an old Delta saw blade using a 10" cut off wheel in a chop saw. This steel is hardened and cuts very slowly. It is so hard near the tips where the carbide is brazed that I had to break it, even the cut off wheel wouldn't cut it. Usually you will see knives made from annealed (softened) steel which is later hardened then tempered. Since this steel is already hardened and I do not have proper heat treat equipment, I chose to keep the factory heat treat and just be careful to keep the blade cool while cutting and grinding; that meant lots of stopping and waiting.

 

 

The handle material is padauk, a South American hardwood often used for xylophone keys. It is hard and somewhat oily. The red will "bleed" out when the wood is wetted, especially with any kind of solvent. Normally the handle would be attached with pins but this steel is too hard to drill with normal drill bits so I have to rely on epoxy.

The handle scales clamped while the epoxy hardens.

The handle was shaped with disc and spindle sanders, then hand sanded with 120, 150, 220, 320, & 400 grit sandpaper. Sorry, no pics of the sanding.

The finish is shellac and wax. Not an especially good choice for a knife but the padauk is tough wood and would be fine without a finish but the shellac stops the red from bleeding.

Top down shot of the handle.

No trouble with a Roma, fresh from the garden.

See through radishes!