I don't think apologies are necessary here, its more than fairly important - in my experience its vital.
I'm not quite clear here - certainly this is true if the mixing or intermodulation is merely a multiplying function. But when its intermodulation with a highly non-linear transfer function such as with rectification, it must appear somewhere in the audio band as I hear it.
So I'm keen to find a mechanism which results in the sound of sibilance on female vocals as my first port of call. None of your three mini-examples seems to fit the subjective data, so I'll keep on truckin'
I don't think apologies are necessary here, its more than fairly important - in my experience its vital.
I'm not quite clear here - certainly this is true if the mixing or intermodulation is merely a multiplying function. But when its intermodulation with a highly non-linear transfer function such as with rectification, it must appear somewhere in the audio band as I hear it.
So I'm keen to find a mechanism which results in the sound of sibilance on female vocals as my first port of call. None of your three mini-examples seems to fit the subjective data, so I'll keep on truckin'
I think the "examples", or something like them, might actually fit your subjective data. It would be extremely difficult to know, because it's extremely difficult to imagine the myriad effects that could result from stray rectified RF/DC appearing in the wrong places in a complex transistor circuit, especially when considering all of the possible RF signals. My examples only barely hinted at the practically-infinitely-many strange subtle-to-not-so-subtle effects that RF could induce, in complex semiconductor circuits
And note that it would not have to form an audible signal at the point of rectification, to produce an audible effect. Just changing the DC biasing of transistor circuits could be audible, for example.
Another possibility that's maybe even more mind-boggling is that there could be some high-frequency instability in a particular amplifier design, which produces its own RF bursts or waveforms that are more or less in sync with some aspect of the audio signal, with the resulting RF then affecting the system in the ways that were hinted-at in my examples. Imagine an audio signal then causing time-varying RF and "self-modulating" the DC biasing in some of the transistor circuits in a chipamp. Or maybe it could be as simple as having a time-varying DC offset going to the speakers. But who knows? It's way too complex to guess at, I'm guessing.
DF is named on the perception that speakers, like all inductive motors, can turn into generators. The generated energy will lead to uncontrolled behaviour, if not absorbed. The lower the source impedance, the more effective is the absorption and the better the damping of the speaker's uncontrolled movements.
DF = Zload/Zsource. It is NOT Zload/(Rload+Zsource).
We can assume that Zsource is more or less constant across the audio range, while Zload is not. Since Zsource and Zload form a voltage divider the frequency response at the speaker terminals is therefore a scale model of the speaker impedance. The lower the DF, the smaller the scaling. In other words an amplifier with high DF will lead to a more linear frequency response than one with a low DF.
Considering that a speaker's impedance usually has one or more peaks in the bass region due to driver and/or port resonant frequencies, an amplifier with a lower DF will lead to higher peaks in the frequency response in just that range.
Add to that the improved damping of reactive energy, which also appears mostly around the resonances.
While DF may not be the only reason for perceived differences in bass response, it certainly has some influence.
It is easy to decide, whether DF is worth worrying about. Put a resistor in series to the speaker, a switch to bridge it and listen to the influence the lower DF due to the added resistor has on the sound.
I would like to add one item to gootee's must excellent post about RF noise.
Modern RF digital communication systems transmit data in packets. That is the transmitter (cell-phone or wi-fi, etc.) turns on sends some date then turns off. The on/off repetition rate is often in the audio range. This rapid bias-point shift is the noise that you hear.
Modern RF digital communication systems transmit data in packets. That is the transmitter (cell-phone or wi-fi, etc.) turns on sends some date then turns off. The on/off repetition rate is often in the audio range. This rapid bias-point shift is the noise that you hear.
Ah! Good catch! There's some 577 microsecond repetition rate in cell phones, if I recall correctly. That translates to a frequency of 1 / .000577 = 1733 Hz. And I think there are other "nested" periodic bursts within the 577 us frames, possibly giving some higher audio frequencies too. And I imagine there are similar phenomena from other types of digital devices.
Thanks everyone for your excellent explanations! It is clear now that RF noise is a BAD THING.
Now, the big question is: what kind of shielding could prevent RF noise from getting into the listening room?
I suppose it would have to be some kind of Faraday cage? But with such high frequency signals, it would have to be practically solid with no openings in order to catch them?
It is clear now that RF noise is a BAD THING.Now, the big question is: what kind of shielding could prevent RF noise from getting into the listening room?
I suppose it would have to be some kind of Faraday cage? But with such high frequency signals, it would have to be practically solid with no openings in order to catch them?
You "could" shield the whole room, and low-pass filter all cables/wires going into and out of the room. The grounded Faraday cage itelf could have openings as large as window screens have, or perhaps larger if you don't have too many millimeter-wave radars around.
But typically you just shield each signal cable and piece of equipment, and low-pass filter each of the points of entry into each piece of susceptible equipment. It's mostly covered in chapter 7 at the link I gave.
One thing that a lot of DIY amplifier designers and builders don't do, that I think they should, is put low-pass RF filters on their amplifier inputs. I went over low-pass RF input filters in almost-embarrassing detail at http://www.diyaudio.com/forums/pass-labs/169382-f5-how-reduce-bandwidth-response.html#post2231859 .
And the outputs need to be RF-filtered also, since unshielded speaker wires will be big RF antennas.
DC power inputs usually already get some low-pass filtering due to their impedance combined with bypass capacitors. But separate power supply boxes might be more of a problem (not sure).
Cheers,
Tom
But typically you just shield each signal cable and piece of equipment, and low-pass filter each of the points of entry into each piece of susceptible equipment. It's mostly covered in chapter 7 at the link I gave.
One thing that a lot of DIY amplifier designers and builders don't do, that I think they should, is put low-pass RF filters on their amplifier inputs. I went over low-pass RF input filters in almost-embarrassing detail at http://www.diyaudio.com/forums/pass-labs/169382-f5-how-reduce-bandwidth-response.html#post2231859 .
And the outputs need to be RF-filtered also, since unshielded speaker wires will be big RF antennas.
DC power inputs usually already get some low-pass filtering due to their impedance combined with bypass capacitors. But separate power supply boxes might be more of a problem (not sure).
Cheers,
Tom
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A long time ago (1965) when I worked at an antenna company. They built a Faraday Cage room on the factory floor. Picture a wood framed two car garage, but instead of plywood or sheet rock walls, the room was finished with copper window screen material. One layer on the inside and one on the outside, all soldered together. The doorway gaskets were rather complicated.
I knew a guy who owned a wood-products manufacturing company. Some of the things they made included the wood parts of drums (snares, tom-toms, bass, etc) and things like cello bodies, which they made by using many sheets of thin veneer with glue between them. The glue was cured "instantly" by irradiating it with RF. They were located in southwestern Indiana. One day, the FCC came to their door and told them that they were interfering with ship to shore communications off of Cape Cod! They enclosed the glue-curing room with metal window screen and solved the problem.
I visited the Thomson (formerly RCA) research and development buildings in Indianapolis, a few years ago. They had many INCREDIBLY-NICE shielded rooms. They were in the middle of a building, in a unit that was two or three stories tall, but were electrically and mechanically isolated from the rest of the building, and had a separate foundation, down to bedrock. Each one was like a large vault. Very impressive. They also had some much larger merely-shielded rooms, for long term testing of equipment. Some of those were also environmental test chambers. Cool place!
sure. But please re-read more carefully what I have written. As I said, the (amplifier) "DF" as defined is basically only a "strange" way of expressing the (amplifier) output impedance. It really has NO direct relationship with "effective" speaker damping.
The load (as well as wiring/connections, but let forget about that for the moment) add dissipative elements (resistance) to the mix on their own. This resistances are effectively in series with the amplifier output impedance and pose a hard limit to the maximum "effective" damping which is achievable (for a given speaker).
For the same reason, there is a point of "diminishing return" for the amplifier output impedance ("DF") effectiveness in damping the speaker. Once the amplifier output impedance is ~ an order of magnitude smaller than the speaker (+wiring) resistances, further decreasing the amplifier output impedance does not significantly increase speaker (electro-mechanical) damping any more.
(as shown, even if you could put a perfect -ideal- short circuit across a loudspeaker, you would NOT get significantly better damping, let alone a "perfect" -infinite- one).
In practice this added resistance is rather high - usually at least an order of magnitude higher than the common output impedances of most SS amps.
Got that?
yes, that is the "DF" as defined.
again, please re-read what I have written. I was not trying to calculate the "amplifier DF" (as shown on amp. spec sheets), but rather trying to show the real, effective damping factor achieved for a given amplifier+speaker combination.
I was still using the same formula, "Zload/Zsource".
BUT what you call "Rload", is effectively in series with "Zsource". Thus it MUST be added to it if you want to get a meaningful result.
That's WHY the DF as is usually defined and expressed is a meaningless number (well, not completely meaningless, but misleading: as said, it is ONLY a measure of the module of the amplifier output impedance at some unspecified frequency).
Wrong! the amplifier output impedance does vary with frequency! (and it is NOT a pure resistance, either).
again, you forget the other resistances in the circuit. Which are effectively in series with the amplifier output impedance and limits the maximum effective damping!
To get exactly what you'd like, you'd need an amplifier with a NEGATIVE output impedance to overcome the other resistances in the circuit!
Speaking about resonances, that's exactly what this is all about. Again, if the speakers were not resonant, by definition there would be no damping to speak of.
What the amplifier output impedance do is altering the "Q" of these (electro-mechanical) resonant systems (that is, the speaker).
But then again, voice coil resistance, cross-over resistance, ecc, pose an upper limit to your ability to control that "Q" using the amplifier output impedance (unless you resort to use negative impedance).
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In my experience this filtering has to be done in conjunction with the correct grounding of the signal input, which few people seem to follow. Putting a passive RC right at the input can just couple the noise on the input ground direct to the first stage LTP otherwise, potentially making matters worse
Ok, my wireless phone "base" and my ADSL were both connected to the same power extension lead as my HiFi gear, and were in pretty close proximity to it. I have now run a telephone extension cable under the carpets and moved them both away to a room across the house.
And guess what - it really made a difference. It's hard to describe what has actually changed, because it's something I feel more than actually hear. The most noticeable difference is, surprisingly, when there is silence - previously, even during pauses there was this sense of strain, anxiety in the air, busyness (I know it sound silly, but that's how I felt it). Now the room just becomes still, like an old library.
As for the sound, it used to have certain clinical, ruthless quality to it - this is now gone, and it sounds a bit like old paper now (not literally - it's just what springs to my mind when I try to describe it). It certainly sounds a lot more analogue, although it also seems to lack certain clarity (hence the old paper analogy). It's not that there is less detail than there used to be - it's just more readily perceivable that the sound is not perfect. Although on the other hand, it is a very inoffensive imperfection - it reminds me of my '79 NAD 3030 amp.
Overall, especially considering how cheap a 20m telephone extension cable was, it was well worth doing. And to think last week I was almost ready to sell my Marantz CD player, because I thought it was responsible for that harsh, clinical edge to the sound! I'm still intending to upgrade it at some point (I want to get myself one of them Sony's ESD-series machines based on TDA1541) - but I can certainly live with my Marantz for a while longer now!
And guess what - it really made a difference. It's hard to describe what has actually changed, because it's something I feel more than actually hear. The most noticeable difference is, surprisingly, when there is silence - previously, even during pauses there was this sense of strain, anxiety in the air, busyness (I know it sound silly, but that's how I felt it). Now the room just becomes still, like an old library.
As for the sound, it used to have certain clinical, ruthless quality to it - this is now gone, and it sounds a bit like old paper now (not literally - it's just what springs to my mind when I try to describe it). It certainly sounds a lot more analogue, although it also seems to lack certain clarity (hence the old paper analogy). It's not that there is less detail than there used to be - it's just more readily perceivable that the sound is not perfect. Although on the other hand, it is a very inoffensive imperfection - it reminds me of my '79 NAD 3030 amp.
Overall, especially considering how cheap a 20m telephone extension cable was, it was well worth doing. And to think last week I was almost ready to sell my Marantz CD player, because I thought it was responsible for that harsh, clinical edge to the sound! I'm still intending to upgrade it at some point (I want to get myself one of them Sony's ESD-series machines based on TDA1541) - but I can certainly live with my Marantz for a while longer now!
Hi bra,
Please also post in English as well. This site uses English as the default language. If you're going to post in Polish, that's okay as long as you also repeat the post in English.
Please edit your post above adding English, or post again in both languages and we will delete your Polish only post.
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