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In Reply to: RE: You local dudes have completely run out of ammo. So sad. Maybe take up macrame. posted by Geoffkait on May 07, 2025 at 05:43:49
Actually in more than a sound produced by an unobserved tree falling in a forest sort of way, your right.
No doubt that sound is the minute and alternating variation of static atmospheric pressure within the range we can detect.
Goggle "ripple tank simulator" and play with sound, light is positive pressure, dark is negative pressure.
That pressure change the source produced is altered slightly by your head too, the time of arrival to each ear and the changes your outer ear impose (pinna responses) which allow one to help "hear" the height of a source.
However, it isn't what we think of as sound until we hear it.
To do that, the pressure moves a small piston (ear drum) which drives a tiny mechanical amplifier / impedance transformer that connects to the snail shaped coil of hair cells that turn the sensation into an electrical signal (electrons) that our brain, through a life time of hearing learning, is able to interpret and triangulate the direction up and down and if close enough, the distance to the source with just two ear holes :-).
The back side of the "microphone" piston has a small air volume and there is a tiny port (like a vented box speaker) ending in your throat that is a "high pass" filter so we don't "hear" the kinds of pressure changes weather causes.
So while it starts with air pressure, it kind of ends with electrons going through bio-wires to the Head phantom image processor unit (wow it sounds like she is right there).
That is what creates the 3d image we perceive and that's electrons too.
While i live on the outside of this process, i can say it looks to me like some very significant thought went into this inside part.
Rainy day thoughts
Follow Ups:
I'm actually trying to have a discussion about the *audio signal* in the audio system but not the acoustic waves, only the electronics and cables and power cords. So, what is the audio signal? See my original multiple choice challenge. I thought your as a speaker maker would have the answer immediately. What makes the speaker produce sound in other words.
How a woofer works would be the simplest thing to describe but even at that parts of it are not that obvious, but is appropriate for propeller talk.
Radiation
The acoustic radiation load on the radiator is actually quite small and it changes with frequency because the wavelength changes with frequency and so the radiator is effectively getting larger (compared to the wavelength) as the frequency climbs.
A woofer cone is tiny compared with bass wavelength BUT higher up, at a point they refer to as K=1, the radiator is about 1 wavelength in circumference and that point and above increasing radiation load with F stops.
I use horns at work often because one can look at it sorta like coupling the tiny driver to the radiation load of the big end .
How to make the velocity roll off to make a flat response woofer?
In order for the woofer to have flat response above the low end, the motion Velocity of the radiator has to fall off to offset that increasing efficiency below K=1
The motor does this;
The "wire in a magnetic gap" VC motor produces a force proportional to current and this is called BL and one way to look at this is Newtons of force per amp of current. The greater the force per AMP, the greater the Voltage it produces proportional to it's velocity if you move it and these two go hand in hand. The Voltage the motor produces if moved is also called Back EMF which some think is bad but in reality is only the inseparable counterpart of the force per amp property.
Our input signal is a Voltage that represents the acoustic pressure in the signal.
The motor has another part to it, the resistance of the wire its wound with and electrically equivalent it's in series with the motor / between the source and motor.
IF you blocked the woofers motion, you would see this series resistance and this resistance limits how much current flows when blocked with a given voltage input.
It turns it into a constant current = constant force vs frequency device with no motion.
Constant force means the motor is in the constant acceleration mode instead of velocity. Un blocked it is moving the mass of the motor and cone still constant acceleration and flat response.
One hard to picture fact is that one can glue a heavy lead ring to the woofer voice coil former and while it changes / lowers the sensitivity and low corner IT DOES NOT effect the high frequency response shape or corner.
The cones motion is constrained by the suspension and cabinet air stiffness at the low end, while the moving mass constrains the Velocity at the top end.
If you examine the impedance curve you see at box resonance that the two reactive things (mass as a parallel capacitor and a parallel inductor as the compliance) are equal but opposite and cancel out and the peak in the impedance curve represents the very slight radiation load and mechanical losses. On either side of the peak, the falling impedance eventually reach the wire resistance (except at the high end where the smaller series inductance of the wire comes into play)
IF you make the motor have the right strength for the box and driver stuff, you get flat response down to the low knee (Fb) which then rolls off at -12dB/oct. A woofer motor that is not strong enough produces a bump at the low end, a motor that is too strong has a rolled off (over damped) low corner.
This applies to the simple end of a sealed box woofers response where it's easier to describe.
I read your comments carefully but it's still unclear what you think the "audio signal" is in the audio wires and cables and speakers. What it is that makes the speakers produce music? If we were discussing what makes a light bulb turn ON and OFF that is a different but analogous question, right? Voltage and current are calculated values, so I prefer a more simplistic straightforward approach to defining what the "audio signal" actually is. Voltage abd current are calculated from what? That might help with the answer.
Edits: 05/11/25 05/11/25
Music could be the signal or noise or what ever but what the signal is supposed to be or starts as is a Voltage / time representation of the acoustic pressure from a microphone.
From there and through every stage of electronics, it is a Voltage signal and that's a key thing, it is NOT a power signal and is why an ideal amplifier puts out x in = X Voltage out independent of an open circuit load or low impedance.
The simple case woofer, the cone only moves and produces sound if there is a force applied. While the audio or test signal is Voltage referenced, the motor produces force proportional to the current in the wire and the direction according to polarity.
If this was an electrostatic speaker, the force is electrostatic and so is proportional to Voltage itself and a step-up transformer is usually used to supply the higher drive V they need.
Voltage is a characteristic of the signal, but it's not the signal - it's the power or strength of the signal. And the same for current, voltage and current are both calculated quantities. Have you looked at the magnetic b or electric e fields?
I would disagree, starting at the microphone, it proportionally turns pressure into a Voltage representation of that pressure. While sound power is the sum of pressure and velocity, it is pressure our ears detect.
Every stage of the electronic chain, amplifies or modifies the Voltage signal and the gain is in dB Voltage ref. The final stage, the audio power amplifier is also normally a Voltage amplifier with X dB of Voltage gain and has an output impedance (damping factor) that is a small fraction of the load impedance so that the Voltage does not depend on or change with different output impedances.
The sealed box woofer i described is meant to be Voltage driven however, if one examines the load impedance, one sees that although the response to the input Voltage may also be flat (ideally), the power delivered due to the impedance changes a GREAT DEAL from the impedance peak at the low corner to the hf roll off to Rmin. The output is ideally flat compared to the input Voltage, the power delivered to do this changes a lot.
Yes, B is a key element, the BL in a driver spec is the force per amp i mentioned it can also be stated the Magnetic field strength in Tesla (B) in the gap and the (L) length of wire in that gap in meters.
Here is a way to picture what happens inside a woofer, examine a DC motor.
So you have a simple pm dc motor, it has a DC resistance of say 1 Ohm and has no load on it.
You have a battery and a switch connected and can monitor current and motor speed.
The instant you close the switch, the motor is not moving and so, has no back emf. As a load it looks like 1 Ohm and so with say a 12V battery, 12 amps of current will flow through the winding.
That current produces a force that starts the motor moving. As soon as the motor moves and accelerates, it produces a Voltage and this Voltage cancels out some of the input voltage so the current flowing is less and the rate of acceleration slows. This continues until the motor stops accelerating and is at "top speed" for that Voltage. Now the motor back emf is nearly equal to 12V and the only current flowing is the small amount needed to overcome the rotating static friction and windage friction inside the motor.
When you put a load on the motor, it slows but then the back emf V falls which then increases the current flowing and the force the motor is producing fighting the reduction in speed.
As I stated I'm only interested in the "audio signal" in the playback system, excluding acoustic waves in the room. As I also commented current and voltage are both characteristics of the signal but not the signal. Therefore, the signal the audio signal must be something else. Hint, it's all about the electrons.
I'm actually trying to have a discussion about the *audio signal* in the audio system but not the acoustic waves, only the electronics and cables and power cords. So, what is the audio signal? See my original multiple choice challenge. I thought your as a speaker maker would have the answer immediately.
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