Please, @mchambin, you are actually changing the subject here with Pi and T attenuators! A subject I know, and one that should be carefully analysed for correctness.
I am a man who did analog and digital signal processing at Imperial College, London to Postgraduate level, so I ought to know what I am talking about.,
@Galu has already conceded the point to me:
https://www.diyaudio.com/community/threads/celestion-ditton-551.407121/page-2#post-7553209
I did not rub his nose in it. I changed the subject to cone tweeters. It seemed a kindness.
I feel my visual proof that 0^0 = 1 with the x^x function is equally compelling.
I really want to talk about my Brian Cox biography, which is funny as anything, and so far rather good. 🙂
I am a man who did analog and digital signal processing at Imperial College, London to Postgraduate level, so I ought to know what I am talking about.,
@Galu has already conceded the point to me:
https://www.diyaudio.com/community/threads/celestion-ditton-551.407121/page-2#post-7553209
I did not rub his nose in it. I changed the subject to cone tweeters. It seemed a kindness.
I feel my visual proof that 0^0 = 1 with the x^x function is equally compelling.
I really want to talk about my Brian Cox biography, which is funny as anything, and so far rather good. 🙂
Visual: Yes.
However, nothing proven. I presume it is based on some analytic extension, but here I see no definition of this analytic extension. I can make tons of those, simply defining: Take your favorite pensil and scribble beyond the f(0) = 1, into R- or C.
So, what is the source of this impressive visual alleged proof.
Read my lips, @mchambin. The matter of 0^0 = 1 is closed:
https://www.diyaudio.com/community/...enerates-gravity.393908/page-164#post-7562449
To reiterate the telling x^x function:
Let's move on.
https://www.diyaudio.com/community/...enerates-gravity.393908/page-164#post-7562449
To reiterate the telling x^x function:
Let's move on.
And refuse to understand what I am explaining to you. I have enough of this behavior. There is no discussion, you only care about making beleive you are right.
@mchambin, I got the image from Reddit or Physics Stack or something. I can't remember and have cleared my history since.
But the graph is accurate AFAIK.
You might google zero to the power zero to find it. It is more philosophy you are talking than maths, and that is a very bad thing. Just do the maths, not interpretation, as in quantum mechanics!
But right now I must go out. Things to do. People to meet.
Honestly, you are like a dog that won't let go of a bone! 🙄
Laters. Steve.
But the graph is accurate AFAIK.
You might google zero to the power zero to find it. It is more philosophy you are talking than maths, and that is a very bad thing. Just do the maths, not interpretation, as in quantum mechanics!
But right now I must go out. Things to do. People to meet.
Honestly, you are like a dog that won't let go of a bone! 🙄
Laters. Steve.
Thanks, but the discussion revolved (pun intended) around a variable L-pad control used to vary the attenuation of an 8 ohm driver - and not a fixed series and parallel resistor combination.
In the diagram above, the series resistance track on the left has a maximum value of 8 ohm while the parallel resistance track on the right has a maximum value of 120 ohm.
The variable L-pad and driver combination is said to present a "constant" impedance of 8 ohm to the crossover.
One day, I may investigate how the impedance presented to the crossover varies with the angle of rotation of a physical, real world L-pad control. It would be interesting to reveal the exact extent of the departures from the so-called "constant" impedance.
@ Galu
Do we have the law of these pots, or do we suppose linear pot ?
We need the data to derive R1as à function of the angle and R2 as a function of the angle.
With linear pots we will have:
R1 = R10 + A1 x angle
R2 = R20 + A2 x angle
Then the impedance we look for is some mess that involve R1, R2 and the driver impedance.
Do we have the law of these pots, or do we suppose linear pot ?
We need the data to derive R1as à function of the angle and R2 as a function of the angle.
With linear pots we will have:
R1 = R10 + A1 x angle
R2 = R20 + A2 x angle
Then the impedance we look for is some mess that involve R1, R2 and the driver impedance.
I would not mention the word 'pot' in this context. More appropriately, could the law of the two L-pad resistance tracks be logarithmic?
If so, that would mean the centre position of a resistance track is not one half of the total value of its resistance as has been assumed.
However, since the resistance tracks are wirewound, could they be anything other than linear?
EDIT: I would regard the variable L-pad as two linked rheostats.
If so, that would mean the centre position of a resistance track is not one half of the total value of its resistance as has been assumed.
However, since the resistance tracks are wirewound, could they be anything other than linear?
EDIT: I would regard the variable L-pad as two linked rheostats.
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Perry Babin gives a table that shows the values of the series resistance and shunt resistance starting at the maximum level (at the top) and ending with zero volume.
If these values have been measured by experiment, they indicate that the action of the variable L-pad is non-linear (i.e. a 4 ohm Rs would not coincide with a 60 ohm Rp).
P.S. Steve did not comment on these figures after I drew his attention to them.
If these values have been measured by experiment, they indicate that the action of the variable L-pad is non-linear (i.e. a 4 ohm Rs would not coincide with a 60 ohm Rp).
P.S. Steve did not comment on these figures after I drew his attention to them.
| Speaker load | Series resistance | Speaker and shunt in parallel | Shunt value | Load presented to amplifier |
| 8 ohms | 0 ohms | 8 ohms | open | 8 ohms |
| 8 ohms | .5 ohms | 7.5 ohms | 120 ohms | 8 ohms |
| 8 ohms | 2 ohms | 6 ohms | 24 ohms | 8 ohms |
| 8 ohms | 3.5 ohms | 4.5 ohms | 10.29 ohms | 8 ohms |
| 8 ohms | 5 ohms | 3 ohms | 4.8 ohms | 8 ohms |
| 8 ohms | 6.5 ohms | 1.5 ohms | 1.85 ohms | 8 ohms |
| 8 ohms | 8 ohms | 0 ohms | 0 ohms | 8 ohms |
Right, this is two mechanicaly linked rheostats.
Likely they are linear.
It could be non linear only by mean of using a variable winding pitch or a variable resistivity wire.
The table is odd, figures are not consistant.
It is not clear the input impedance is: Rserie + ( Rshunt // Zdriver ).
Likely they are linear.
It could be non linear only by mean of using a variable winding pitch or a variable resistivity wire.
The table is odd, figures are not consistant.
It is not clear the input impedance is: Rserie + ( Rshunt // Zdriver ).
https://www.electronics-tutorials.ws/attenuators/bridged-t-attenuator.html
Actually there isn't much "wrong" with those pages on attenuators that you mentioned earlier. They are just poor examples of where they are used.
I sincerely doubt you quoted these figures to me, young Galu. Perhaps you are suffering from Mental Health and Memory problems?
Anyway, I find this resistance business (in itself) an uninteresting problem.
There are far more pressing issues in the World.
I am still trying to figure out what went on in yesterday's "Intermezzo" movie:
It was great for £5. You got a free cup of tea and a biscuit included. The lovely manageress Ayse was in top form too, and pointed out that the film was only 1 hour and 7 minutes long in a speech. Which is quite an autistic sort of observation IMO.
https://southseacinema.co.uk/
I have to admit I was SMITTEN by Ingrid Bergman in her first screen role. She was extraordinary. I couldn't take my eyes off her. Think "Casablanca" with "Bogie" if she rings no bells with you. And as a high functioning autistic person, I am poor on relationships, even if EXTREMELY gifted in Mathematics.
Best Regards, Steve in Southsea, England.
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Your behaviour is beyond the pale!
You were given two lines of the table and a link to the full table.
Of course I am well aware of that, but we have to treat the speaker as an 8 ohm resistance in order to examine the working of the L-pad.
Besides, I am interested in the use of an L-pad with a tweeter whose impedance may not rise much with frequency above its fundamental resonance frequency.
That's why I had some doubt that the figures had actually been measured by experiment.
As I said earlier, "One day, I may investigate how the impedance presented to the crossover varies with the angle of rotation of a physical, real world L-pad control."
Anyway, let's get this thread back on topic after the diversion of L-pads and Ingrid Bergman movies!
Just before we "Ride off into the Sunset" on this one, as they usually do in B Movie Westerns like "Apache Territory" which I watched recently, I can confirm that I would use a 2.2R (preferred value) series and 22R shunt resistance for 3dB attenuation with an 8 ohm tweeter. But would check my working.
https://soundcertified.com/l-pad-calculator/
Therefore the figures you presented are probably reasonable IMO, though they look calculated. In fact two resistors are the proper definition of an L-Pad. We always spoke of padding down level in the engineering laboratory at STC (Standard Telephones and Cables) when they were fortunate to have me in their employ in the submarine cable division. Everything was 50 ohms there. Even the plugs! And we aimed for 1% accuracy on this, since it mattered to minimise group delay distortion.
I am still keen to find further news of the stricken "Peregrine" moon lander craft. Perhaps you can use your googling skills to get some. It is, at least, about Space. 🙂
https://soundcertified.com/l-pad-calculator/
Therefore the figures you presented are probably reasonable IMO, though they look calculated. In fact two resistors are the proper definition of an L-Pad. We always spoke of padding down level in the engineering laboratory at STC (Standard Telephones and Cables) when they were fortunate to have me in their employ in the submarine cable division. Everything was 50 ohms there. Even the plugs! And we aimed for 1% accuracy on this, since it mattered to minimise group delay distortion.
I am still keen to find further news of the stricken "Peregrine" moon lander craft. Perhaps you can use your googling skills to get some. It is, at least, about Space. 🙂
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