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Old 7th September 2012, 12:30 PM   #7121
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Thanks DVV .
gpapga . Thanks also for Callas in Paris 1958 . Not Citroen DS for the arrival ! The commentary was very like the BBC which helped .

This link is a recording that was made just made in time . The lady always wanted to perform this piece . Her teacher was doubtful she would ever succeed having discovered her ability later in life than many ( 16 ? ) . In many ways wrong , in important ways how it should be done ( from the heart ) . Oh how I wish the Telefunken engineers had done it .

https://www.youtube.com/watch?v=p77JoONFX8U
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Old 7th September 2012, 01:31 PM   #7122
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A slight branch-line here . Did anyone ever try an infrasonic sub woofer ? I am told it works very well . My friend made them from solenoids with digital delay to the main speaker .This was tuned by ear to suit the dance venue . He said it added colour and size to music .

File:Graham Holliman Velocity-Coupled Infra Bass speaker design.jpg - Wikipedia, the free encyclopedia

My father when I was young was obsessed by a low frequency noise which he heard late at night . He thought it might be lorries filling with fuel at the garage 1 kM away . He would walk out at night to see what it was . I read recently about some people hearing the sound of gas being pumped . On the farm next to our house was a little cabin . When asking it was galvanic protection for a very big gas main . Dad was right and he was highly sensitive to subsonic's . I went to Didcot power station . The resonant frequency of one its chimneys is 5 Hz . The guide said people liked standing in area . I did although I could not say why . It felt great although nothing obvious was happening .
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Old 10th September 2012, 12:52 AM   #7123
tvrgeek is offline tvrgeek  United States
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infrasonics cause a headache.
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Old 10th September 2012, 07:30 AM   #7124
dvv is offline dvv  Serbia
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Quote:
Originally Posted by tvrgeek View Post
infrasonics cause a headache.
Play 16 Hz loud enough and you'll be standing guard in the toilet for a few hours at least. At least, that's what happened to a friend of mine when I got the "bright" idea to play that prank on him in an anechoic room. I never forgave myself that display of collosal stupidity and arrogance.
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Old 10th September 2012, 07:55 AM   #7125
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Interesting and logical about subsonic's and danger. My experience in the big chimney was good ( 5Hz ) . I was told that buildings which parapsychologist check often have subsonic noise . Now there will be a divide on that as to how and why . Personally I think it is just noise . This brings me to a point .

I am more interested in sounds and noise than most people . That is like saying a veterinarian is more interested in animals than most . Hardly surprising . It makes what I say next more believable . Simply put I was in my car one day when I jumped and THEN heard a car backfire . The time delay was small yet noticeable . I was told our fascinating for sound is related to man having lived in the forests of this world . Imaging which we love in music is about locating sounds . The other ability is transients which make us prepare to run . The spatial music was bird song .

I would imagine if we studied real music ( not amplified ) we would find much more subsonic's than we would imagine .

https://www.youtube.com/watch?v=XWEp...eature=related
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Old 10th September 2012, 08:35 AM   #7126
dvv is offline dvv  Serbia
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Subsonics are sometimes found where we do not expect them.

Not too long ago, I was fooling around with a Technics 570 digital tuner. Quite by accident (or was it?), I looked at my left loudspeaker box and noticed some quite extraordinary cone excurision actvity. On the surface of it, I heard nothing, yet that cone was pumping air from the, er, airwaves. Eventually I did actually hear a low down THUD.

Somewhat perplexed, I dug up the Technics User Manual and went straight to the specifications page, where indeed I found that the frequency response was quoted as: "20-15,000 Hz +/- 0.5 dB, 5-18,000 Hz +0.5, -3 dB". 5 Hz? Where the heck was it coming from?

Then I noticed I had the subsonic only when the radio show host was talking, i.e. using the studio microphone.

Lastly, I pushed the "Subsonic filter" switch on the preamp (Luxman C-03) and the cone movement was greatly reduced, now down to hardly noticeable, meaning I hd to get near and look hard to notice any real movement.

All this left me perplexed. First of all, I have no idea how that subsonic got through the airwaves all the way to me. I would never have thought that was possible, yet I saw it myself. Obviously, this hapened in the studio, and I cannot remember ever seeing any microphone for a radio studio with a response down to 20 Hz, let alone lower. Then again, I haven't exactly been researching the subjcet.

I was also surprised by the frequency response of the tuner - the specs are usually given for the 20-15,000 Hz range, so it never really occured to me that it's possible for the tuner to go much lower than 20 Hz, probably in an attempt to avoid phase funnies if using a sharp cut-off filter. Or something.

Lastly, I wondered if other users had even noticed it. Never mind if they actually saw the cone make large excursions as I did, perhaps their speakers didn't go as low as mine (-3 dB at 38 Hz), yet the very presence of it would load their bass drivers trying to reproduce something they couldn't.

Is that even legal?
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Old 10th September 2012, 09:08 AM   #7127
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This is a very good subject to study . It seems to me we should never ask a conventional speaker to do it . Digital delay is appropriate to get it right .

I suspect all timing on all speakers could be better . It is not about reproducing exactly what was there . This is about making it sound right as best we can ( tunable ) .

When I was 28 ( half my age now ) I was asked to help an old Jesuit priest with some digital electronics . He was far above me and I suspect only wanted to say hello . He showed me how the tone colour of the organ was due to subsonic timing . Remember this guy understood electronics . He called it hetrodyning . Thus if we get the hetrodynes as good as we can some magic starts to happen ( openness and dynamics , no extra power required ) . Just as inappropriate subsonic's can suggests ghosts , not having any suggests no tone colour and robs transients . One of my major criticisms of valve amplifiers is no real sub bass . I built one that had it . I was great ( when it worked ) . Some say that 5Hz - 3 dB total is the goal .
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Old 10th September 2012, 12:28 PM   #7128
DF96 is offline DF96  England
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Really low frequencies on FM broadcasts are theoretically possible (FM goes down to DC) but in practice certainly were unlikely as FM transmitters often used a phase modulation method which has a built-in high-pass action. Newer transmitters probably use digital techniques so DC may be possible in practice nowadays.

FM detectors usually go down to DC, so it is only coupling caps which limit LF.

Older 'analogue' FM tuners could have a response peak in the subsonic region due to poor design of the AFC loop. A 'digital' FM tuner might not need AFC so this peak should not occur.

Although you noticed that the LF seemed to be associated with speech, it might partly arise from multipath propagation. Multipath creates signal distortion, so the LF could be IM.
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Old 10th September 2012, 02:18 PM   #7129
dvv is offline dvv  Serbia
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Quote:
Originally Posted by DF96 View Post
Really low frequencies on FM broadcasts are theoretically possible (FM goes down to DC) but in practice certainly were unlikely as FM transmitters often used a phase modulation method which has a built-in high-pass action. Newer transmitters probably use digital techniques so DC may be possible in practice nowadays.

FM detectors usually go down to DC, so it is only coupling caps which limit LF.

Older 'analogue' FM tuners could have a response peak in the subsonic region due to poor design of the AFC loop. A 'digital' FM tuner might not need AFC so this peak should not occur.

Although you noticed that the LF seemed to be associated with speech, it might partly arise from multipath propagation. Multipath creates signal distortion, so the LF could be IM.
Not so, I checked the multipath levels, they were way below any dangerous level.

Also, I noticed the subsonic signal was on the left channel only, nothing on the right.

Mind you, it's not really a problem because I can always switch on the subsonic filter on the preamp.

Also, nothing like that ever happens on the ReVox B760 digital synthesis tuner, nor on the Marantz 6000 digital tuner, nor on the Sony 3950 analog tuner. I tried them all on the same day. So it's only the Technics. That tuner has not been refreshes since its purchase, some 15 or 16 years ago. Perhaps one of its decoupling caps has given up the ghost?
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Old 10th September 2012, 02:38 PM   #7130
DF96 is offline DF96  England
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Could be a coupling cap, or a resistor, or a bad solder joint. The association with speech could be an example of our brain's need to find patterns even when there isn't one. As it was just on the left channel it must be in or after the stereo decoder.

In your original post you said 'left', but as you didn't say 'not right' I assumed it was on both channels but you have only happened to notice it on left.
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