John Curl's Blowtorch preamplifier part III

[scottjoplin]

We have quite a few here that are very knowledgeable in human hearing capabilities, it is important that all discuss.

Yes, but I think there could well be knowledgeable members who don't habitually frequent this thread

 

[PMA]

Late Siegfried Linkwitz has had a nice test files

Toneburst Test Signal CD

called "Toneburst Imaging Test".

A rapid sequence of 22 tonebursts from 12.8 kHz down to 100 Hz can be used to check the spatial stability and focus of the stereo center image as a function of frequency. Each burst consists of 4-cycles of a sinewave with a raised cosine envelope. The sinewaves are at 1/3rd octave frequency intervals. The bursts are separated in time by 50 ms and room reflections can affect the phantom image location. The sequences are repeated 8-times going down and up in frequency.

The burst sweep can also be used to check for the onset of signal clipping as the playback volume is cautiously increased. The peak amplitude of each burst is constant at 0.9 FS.

http://www.linkwitzlab.com/wav/12_8k-100Hz-_4cycle_sweep_spaced_50ms_8x.wav

Anyone can try it and see how acoustically asymmetrical is in fact almost every home listening space.

And also Pink Noise Imaging Tests

http://www.linkwitzlab.com/wav/pink-alternating3.wav

 

[Chris Hornbeck]

Late Siegfried Linkwitz

Oh, no. I hadn't heard. A great one is gone.


Much thanks, as always,
Chris

 

[scottjoplin]

A prime example https://www.diyaudio.com/forums/members/sl08.html

 

[vacuphile]

Yes, unfortunately that lives on.....supposedly there’s a warranty fix but not sure shipping it across country would benefit the rest of the internals.

Swapping out a volume pot surely could be done by a novice or if not a local amp repair shop.....maybe they’d send me one?

If it is bad design and there is DC over the pot, it will come back.

 

[scottjoplin]

http://www.linkwitzlab.com/wav/12_8k-100Hz-_4cycle_sweep_spaced_50ms_8x.wav

That makes a good hearing test on headphones I have HF hearing loss mainly in my left ear where most of my tinnitus is. The image shifts accordingly

 

[gpauk]

But there is a disconnect. A virtual soundstage requires more than just low distortion electronics. It is important to understand what compromises the virtual image.
Without understanding what is needed how does one control it?
Over the years I've tested the stability of both lateralization as well as localization on myself only. And in that process I've had to do a lot of research.

We have quite a few here that are very knowledgeable in human hearing capabilities, it is important that all discuss.
Jn

One potential issue that I came across is testing this sort of thing, admittedly a long time ago - is that even "experts" hear different soundstages from the same source when unsighted and not allowed to speak to each other!
I suspect that the "virtual soundstage" is fairly subjective.

 

[jneutron]

Late Siegfried Linkwitz has had a nice test files

Toneburst Test Signal CD

called "Toneburst Imaging Test".

http://www.linkwitzlab.com/wav/12_8k-100Hz-_4cycle_sweep_spaced_50ms_8x.wav

Anyone can try it and see how acoustically asymmetrical is in fact almost every home listening space.

And also Pink Noise Imaging Tests

http://www.linkwitzlab.com/wav/pink-alternating3.wav

Excellent. Thanks as always.
None of the tests seem designed to text exercise the woofers independently to high displacement while simultaneously testing symmetry. I wonder if anyone has done that? Perhaps a 30 Hzsignal one channe?

One potential issue that I came across is testing this sort of thing, admittedly a long time ago - is that even "experts" hear different soundstages from the same source when unsighted and not allowed to speak to each other!
I suspect that the "virtual soundstage" is fairly subjective.

Which brings to mind, what is the engineer in the studio looking for in the studio system?

Jn

 

[Max Headroom]

85 Mouton Rothschild.

It's good to be the king

 

[mountainman bob]

If it is bad design and there is DC over the pot, it will come back.

Thanks vac,

Are you saying replacing the pot won’t fix the problem?

After speaking to parasound, they said there was a bad batch from alps and will warranty it, either sending me a new one to change myself (void warranty)or I can take it to Gainesville (3 hr drive) to authorized service center.

 

[mountainman bob]

Excellent. Thanks as always.
None of the tests seem designed to text exercise the woofers independently to high displacement while simultaneously testing symmetry. I wonder if anyone has done that? Perhaps a 30 Hzsignal one channe?


Jn

I’ve always heard source location was difficult <100hz
....I find <40hz to be invisible to pinpoint
30hz might be hard?

 

[Tournesol]

Late Siegfried Linkwitz has had a nice test files

Toneburst Test Signal CD

called "Toneburst Imaging Test".

http://www.linkwitzlab.com/wav/12_8k-100Hz-_4cycle_sweep_spaced_50ms_8x.wav

Pationnating. Thanks A LOT PMA. We clearly see a virtual pyramid image emerge from the base to the top while the frequency increase.
It tells a lot about vertical localisation/imaging as well.

 

[jneutron]

I’ve always heard source location was difficult <100hz
....I find <40hz to be invisible to pinpoint
30hz might be hard?

I believe you are correct.

But the point of the 30hz is not to localize 30 hz, but to bring the cone in and out well beyond a 15 to 20 uSec time of flight distance. And only on one cone.

This will test the symmetry of what we can localize as it is possibly modulated by the test signal.

I chose 30hz arbitrarily. If we did something in the 5 to 10 hz range, we wouldn't hear the sound, but the cone would be unloaded and the suspension would be limiting excursion, and we know that is very nonlinear.

At least at 30 hz, there is air mass coupling, so I was thinking it would bring out any magnetic nonlinearities due to the spring loading effect.

jn

 

[Jakob2]

@ Bonsai,

in a typical experiment exploring a hearing threshold of for example a single/pure tone the resulting psychometric function could look like this one:

(Stanley A. Gelfand. Hearing - An Introduction to Psychological and Physiological Acoustics, CRC Press Boca Raton, 6th Ed., 202)

Using the method of constant stimuli, level step size of 1 dB and taking 50 data points at each level. The stimuli range encompass the known or assumed hearing threshold, the different stimuli presented in random order, the participants have to answer if the stimulus was present in the according trial.

 

[Bonsai]

Thanks for that Jakob

 

[gpauk]

Pationnating. Thanks A LOT PMA. We clearly see a virtual pyramid image emerge from the base to the top while the frequency increase.
It tells a lot about vertical localisation/imaging as well.

Really? I don't get that.

 

[scottjoplin]

There's no vertical information in stereo. The suggestions here as to why height may be perceived are as good as any How to Create Width, Height and Depth in a Mix — Pro Audio Files

 

[john curl]

I was also told by Parasound that Alps pots have sometimes become a problem. Unless the problem reoccurs often, I would leave it alone, myself.

 

[PMA]

There's no vertical information in stereo. The suggestions here as to why height may be perceived are as good as any How to Create Width, Height and Depth in a Mix — Pro Audio Files

Vertical info is created by drivers, their directionality pattern, drivers positioning and crossover used.

 

[dreamth]

I was also told by Parasound that Alps pots have sometimes become a problem. Unless the problem reoccurs often, I would leave it alone, myself.

yet a lot less problems than many others...they have countles types of potentiometers...which ones do have problems?
Most of the professional DJ consoles have Alps potentiometers...i think that you know how much used and abused they are and stiill they get to sustain 2 hours live concerts for 100 times in a year. All the car industry is filled with them , literally billions of Alps potentiometers are found everywhere, including medical and high tech equipment.