When recording, we record voltage of the microphone.
When playback, we should use voltage drive. At least, make more sense to me.
I think that would only be true if the microphone and the loudspeaker were exact opposites to each other, with exactly the same - but opposite - transfer functions. That is not the case.
Jan
When playback, we should use voltage drive. At least, make more sense to me.
I think that would only be true if the microphone and the loudspeaker were exact opposites to each other, with exactly the same - but opposite - transfer functions. That is not the case.
Jan
That's nonsense, it's enough if you reproduce the original acoustic event. There's nothing that is misunderstood here.
But the point was that because a mic is a voltage-output transducer, that therefor you should drive the speaker also with voltage. That conclusion is not tenable.
Jan
The sound image in the brain is similar to the visual image. Associated with training and previous life experiences. The TV also gives a 2D picture, but before it was black and white
Last edited:
Correct. Voltage source acts as a short for external excitation. If there is no external excitation than voltage or current source if equalized for the same there is no difference between them(i don't talk about non linear distortion). For open baffle speakers external excitation is so small that could be said that it is of zero influence. But External excitation is big when the sound waves inside the cabinet reflect back from the same driver or other drivers in same enclosure.
So voltage drive tries to fight back and is trying not to let the back wave of the driver escape the box through the drivers cone. Like a closed window. And with current drive there is nothing done to stop the internal box sound waves to escape the box through the cone. Like open window.
But how much this effect translates to linear and non-linear distortions i don't know. Depends on the speaker box design. Should be measured and listened. I think i will add this into my TO DO list.
I agree with the internal reflections in the box getting out as '2nd hand sound', so to say, through the cone.
But don't forget the inertia of the moving system, voice coil, cone, surround. It's a moving mass, and once it is set in motion, when you take away the drive signal, it doesn't stop right there, it starts a decreasing back-and-forth based on its natural resonance frequency and gradually comes to a standstill.
Unless you short the connections, then the moving system generates a current through that short (or the voltage source) which takes energy from the system and stops it much faster. That's the whole idea about damping: take energy from the system so it no longer moves on its own.
I know that Bruno Putzeys of Kii and Purifi fame uses a combination of voltage and current drive in the low frequency area of the Kii but has drivers specially developed or modified for it. I don't know the details.
And your idea of voltage drive at driver resonance and current drive above it (as I understand) seems very sensible; voltage drive damping where you need it, and current drive for low distortion elsewhere.
Jan
But don't forget the inertia of the moving system, voice coil, cone, surround. It's a moving mass, and once it is set in motion, when you take away the drive signal, it doesn't stop right there, it starts a decreasing back-and-forth based on its natural resonance frequency and gradually comes to a standstill.
Unless you short the connections, then the moving system generates a current through that short (or the voltage source) which takes energy from the system and stops it much faster. That's the whole idea about damping: take energy from the system so it no longer moves on its own.
I know that Bruno Putzeys of Kii and Purifi fame uses a combination of voltage and current drive in the low frequency area of the Kii but has drivers specially developed or modified for it. I don't know the details.
And your idea of voltage drive at driver resonance and current drive above it (as I understand) seems very sensible; voltage drive damping where you need it, and current drive for low distortion elsewhere.
Jan
Last edited:
Everything has an impedance. There can not exist a current without a voltage, except perhaps for practical purposes in a superconductor. The impedance includes mass and compliance, inductance and capacitance which cause resonances and variations in frequency response. Many microphones and speakers are not "impedance matched" in order to improve frequency response. Usually that means underloading/buffering because most microphones and speakers are electrodynamic. Transformers perform best when driven by a low impedance and damper loaded to prevent self resonance at high frequencies.
The different kinds of damping, ways to lower the Q of the resonance. The good, the bad and the ugly.
Acoustical (changing the enclosure)
* Acoustic damping material
* Bigger volume enclosure: Infinite baffle or Aperiodic enclosure
* Length enclosure tuned to resonance, Transmission line: Closed or Open
* No enclosure: Open baffle or No baffle
Mechanical (changing the driver)
* Higher loss suspension: Surround and/or Spider
* Selecting lower Q drivers
* Redesigning drivers with lower Q
Hydraulic (to avoid)
* Ferro-fluids (gives modulated noise)
Electromagnetic (to avoid)
* Eddy current (gives modulated noise): By using non-conducting voice coil former (harder to find in tweeters)
* Resistive (gives modulated noise, destroys the -voltage- input signal, reacts on velocity in stead of acceleration, thus too late, and needs voltage-drive): By using high output impedance amplifiers
Electronic (the most easy and most precise and fastest ones)
* Passive
* Active (even better): ASP or DSP
* Notch filter: Adjusting Q
* Linkwitz transformer (the most interesting): Adjusting Q and f
My system
* Stereo two way loudspeakers with acoustic suspension and damping material
* Four channel current-drive amplifier (Zo ≈ 1400 ohm)
* Active crossovers with Linkwitz transformers to alter the curves of the drivers to be combined
High Q drivers
Drivers with a high Qms are no problem at all, as long as the resonance frequency is rather stable (the higher the Q the more the need for a stable f). In several years I didn’t measure a change in resonance frequency in the drivers that I use.
Last edited:
Biggest damping of primary resonance is with output impedance as near to zero as possible. High impedance is like disconnecting the voice-coil and letting the cone flap in the wind.
As for "Resistive (gives modulated noise, destroys the -voltage- input signal, reacts on velocity in stead of acceleration, thus too late, and needs voltage-drive): By using high output impedance amplifiers". Eh???
The limitation I see to equalization is that you will never manage to exactly cover the poles of the loudspeaker with the zeros of the equalizer, so there will be some original-Q resonance left at a much reduced level. Apparently this effect is in practice so small it doesn't bother Jerry at all.
With ESL it is F = qE
I hope you don't mind if I add something:
When you understand F = Bl x i, you stop using voltage-drive with electrodynamic speakers.
When you understand F = qE, you stop dreaming about current-drive with electrostatic speakers.
In an electrostatic speaker there is a thin charged diaphragm in the middle of two stators. The diaphragm is charged with a high voltage source, but not directly. There is a big resistance that protects the diaphragm and also helps keeping the electric charge constant. That charged diaphragm represents q which is the electric charge. The perforated stator plates are there to create a homogenous electric field E, which is directly proportional to signal voltage. Sound pressure and force F are also directly proportional. In the near field the sound pressure follows quite exactly the voltage signal that was brought to stators.
I hope you don't mind if I add something:
When you understand F = Bl x i, you stop using voltage-drive with electrodynamic speakers.
When you understand F = qE, you stop dreaming about current-drive with electrostatic speakers.
In an electrostatic speaker there is a thin charged diaphragm in the middle of two stators. The diaphragm is charged with a high voltage source, but not directly. There is a big resistance that protects the diaphragm and also helps keeping the electric charge constant. That charged diaphragm represents q which is the electric charge. The perforated stator plates are there to create a homogenous electric field E, which is directly proportional to signal voltage. Sound pressure and force F are also directly proportional. In the near field the sound pressure follows quite exactly the voltage signal that was brought to stators.
True, but you usually don't listen to an electrostatic loudspeaker in the near field, it's either the far field or something in between. Electrostatic headphones ideally have to be driven with a frequency-independent voltage to get a flat frequency response.
This is all about frequency response that could be equalized anyhow, I don't know if there is any measurable difference in distortion between current and voltage drive for an ESL, like there is for electrodynamic speakers. Without diaphragm, the stators would be a quite linear capacitor, but then there wouldn't be any sound anyway.
This is all about frequency response that could be equalized anyhow, I don't know if there is any measurable difference in distortion between current and voltage drive for an ESL, like there is for electrodynamic speakers. Without diaphragm, the stators would be a quite linear capacitor, but then there wouldn't be any sound anyway.
ACE-Bass Loudandproud musik med n?rvaro
"F is that force that to be brought forth of the amplifier's ut-spänning U and Ru is the amplifier's utresistans.
We can here see that apart from the true moderation Rm exists an additional “electrical” moderation. Normalt is the amplifier's utresistans Ru~0, but through doing the barrel organ or negative can one to give the total moderation a rather arbitrary value. This is old well-known technology that in certain case has been used early."
Last edited:
http://user.faktiskt.io/RogerGustav...Pro - Subwoofer attivo con Ace-Bass B2-40.pdf
Bottom right corner of the diagram ...
Bottom right corner of the diagram ...
Last edited: