On Thursday, September 18, 2014 8:22:22 AM UTC-7, krasw wrote:
On Thursday, 18 September 2014 17:44:54 UTC+3, Richard wrote:

On Thursday, September 18, 2014 6:28:40 AM UTC-7, krasw wrote:



On Wednesday, 17 September 2014 23:01:31 UTC+3, wrote:







Routing CAN cable and pressure lines there from instrument panel was quite a job but it ISU works flawlessly. I also changed radio and variometer speakers to ones with magnet-shielded driver (you would be amazed how much better your radio and variometer sound with proper driver/speaker instead of those made with chinese 5c parts).































krasw































Please provide make and model numbers of the magnet-shielded speakers you used with your Butterly vario.















The speaker driver is Tangband W2-800SJ, installed in palm-size plastic box from local DIY-electronics store. I just drilled lots of holes to the cover of the box and pop-riveted the driver flush on the back side of it. I soldered a shielded pair cable to driver and routed it straight to BF wiring connector. I did similar speaker for the radio. My variometer speaker is over my left shoulder, and radio speaker over my right shoulder, behind my back. It's important to put the speaker close to your ears, and not bury it inside instrument panel or behind back rest.







Be careful about the speakers connected. I believe the Butterfly varios are supplied with 8 ohm speakers and the Tangband is a 4 Ohm speaker.







The short of it do not connect a 4 Ohm speaker to an 8 Ohm amplifier.







What are ohms, anyway?



Short answer: The ohm is the unit of measure for impedance, which is the property of a speaker that restricts the flow of electrical current through it. Typical speakers have impedance ratings of 4 ohms, 8 ohms or 16 ohms. The impedance of a speaker is a physical property that (ideally) does not change value, although from an engineering standpoint, there are many complex characteristics that make up speaker impedance For this reason, the rating of a speaker is called its 'nominal' value, which pretty much means "in name only". For the average audio user, the nominal impedance is the dominant characteristic and for the purposes of this discussion, we will use the nominal value of the speaker's impedance.







Why are ohms important?



Two reasons:



(1) If you connect your amplifier to the wrong speaker impedance, you risk damaging the amp. In solid state amps, if the speaker impedance is too low, the amplifier will tend to overheat and more power is used up in the amplifier than is delivered to the speaker. Too many speakers on a solid state amp can burn up the power output section.



(2) The amplifier will deliver maximum power (volume) to the speaker when the speaker impedance matches (is equal to) the internal impedance (called the OUTPUT IMPEDANCE) of the amplifier. Too low an impedance will result in weak output and poor tone. If the speaker impedance is higher than that of the amplifier, its power output will again be less than it is capable of.







Understanding Ohms and Impedance:



In order to understand the reasons for the rules for speaker connection, we need a bit of electrical theory. You probably had this as a lesson in high school at some point, but were more interested in other things at the time. In order to relate it to something you are more familiar with, let's consider the ordinary garden hose. Print this off and go outside, hook up the hose (no nozzle) and turn on the water. Pretty soon, water should start flowing out the end of the hose. This flow of water through the hose is similar to electric current, which is usually described as the flow of electrons through the wire and is measured in Amperes.







Now put your thumb over the end of the hose and try to stop the flow of water. Feel the pressure? This pressure is similar to Voltage. It is the force of electricity that pushes the electrons through the wire. Notice that if you succeed in plugging the water flow, (no current) the pressure is still there. This is like an amplifier with no speakers attached, or an AC outlet with nothing plugged in. Voltage is present, but there is no current flow.







Finally, move your thumb a bit to allow some water to spray. By varying the position of your thumb, you can control how much water comes out of the hose. Your thumb is restricting the flow of water. In an electrical circuit, things that restrict or control the flow of current are said to impede current flow, and are described as having impedance. In a hose, we use a nozzle to restrict the flow. In an electrical circuit, the device that uses electrical energy and has impedance is called the LOAD.







It should be apparent by now that there is a relationship between pressure (voltage), flow (current) and restriction (impedance). Since voltage or pressure is what moves the current, increasing the voltage pressure should increase the current, assuming the impedance doesn't change. Decreasing the voltage should decrease the current. On the other hand, increasing the impedance restricting the flow of current will cause the current to decrease, like turning the nozzle toward OFF. Lowering the impedance is like opening the nozzle to allow more flow. This relationship was analyzed by a fellow by the name of George Simon Ohm a long time ago, and he identified a simple formula that is extremely important in electricity and electronics which bears his name: Ohm's Law.







Richard



www.craggyaero.com



I have been building speakers with complex crossover networks and multiple drivers for decades. Even single wideband driver has real-world impedance that goes from couple of ohms to 20-30 ohms at speech-band, and nominal impedance still might be either 4, 6 or 8 ohms. The impedance also depends on the enclosure you put the driver BTW.



Solid-state audio amp in modern radio or variometer has output impedance of 0.0-something. It means that damping factor is usually close to 100. These amps drive Tangband (or any other similar) driver with complete ease. The simple fact that you put the speaker close to ears means that you can turn the volume down by 10 dB, meaning that your amp has to work only 10% of the original power. This is far more important than nominal impedance. 4 ohms versus 8 ohms impedance means only that driver draws twice the amount of current but needs only half of the voltage. I need maybe couple of % of variometer amp output in normal volume, drawing enough current to make amp distort means that you can listen to my radio from other side of the airfield.



Of course it is good idea to be careful, but I honestly did some research of the expensive Becker etc. speaker-boxes, and the drivers and whole construction of these is complete joke. Same with chinese toy-speakers delivered with expensive variometers.

Krasw,

Here is what Air Avionics (the designer and manufacture of the Butterfly Vario) says when I asked the question about using a 4 Ohm speaker.

What happens if you use a 4 Ohm speaker? Will this damage the amplifier?

It will shut down in case of overheating. Should not be an issue.

Richard
www.craggyaero.com