What would you do with these drivers?

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vinylnvalves
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#31 Re: What would you do with these drivers?

Post by vinylnvalves »

The accelerometers we use at work are quite big, when you compare it to what’s in your phone. But the phone ones won’t be 100g capable. Nokia used to test phones on a 1.8m drop test, as have a friend who did the DYNA analysis for Nokia.

I have seen a couple of different feedback methods, Microphones and LDVT’s the later would need to driver modifications. If you assume pistonic motion only - which I think is applicable for a sub then a stick on graduated scale and a sensor could be another option.
The suggestion is that open baffle subs are best for servo control, as don’t have phase or delay to worry about as much as a sealed one. A bass reflex sub is a definite no no apparently. There was an interesting statement from Earl Geddes, that he has never bothered about Thiel Small parameters, as you don’t need then for “proper” speakers - infinite baffle.

I think my plan is to build a double H frame OB arrangement subwoofer to start with, as my room isnt friendly below 40hz and the dipole should help. I will start with simple contouring of the input signal first via the DSP. Applying current control feedback from the driver into the amp is well beyond my grasp of practical electronics, so motion control feedback is not on the table - although it is interesting and I think could be a big improvement. Apparently the squeezebox boom we used to have had servo controlled bass.
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rowuk
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#32 Re: What would you do with these drivers?

Post by rowuk »

I also believe that Thiele/Small only describes behavior at resonance and is no indicator of sound quality or overall in room performance. It is good for modeling bass response and certainly has contributed to companies building better "real world" drivers.

One would think that with all of the processing power available today, one could get the parameters of each driver and then with feed forward generate the correction signal with no need for feedback. How unpredictable can a simple loudspeaker be?
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Nick
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#33 Re: What would you do with these drivers?

Post by Nick »

How unpredictable can a simple loudspeaker be
I would think just the unknown and variable air temp in the room would break that idea. Same for many other factors. And each driver would need to be instrumented as each will have its own set of parameters, and then the integration with the cabinet and so on. So as you have to instrument it, you may as well use the same sensor for feedback.

Balancing a broom on end on your hand is not that hard, trying to do the same with your eyes closed (no feedback) is altogether harder,
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#34 Re: What would you do with these drivers?

Post by Wolfgang »

This is how it works.

"Direct servo can be thought of as an adaptive equalization system. To be more specific, it performs a transformation on the physical T/S parameters into a set of virtual T/S parameters. By doing so, the amplifier adjusts its output so that the frequency response behaves as if the driver possesses these virtual T/S parameters."

http://www.rythmikaudio.com/DirectServo.html
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rowuk
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#35 Re: What would you do with these drivers?

Post by rowuk »

Nick wrote: Wed Dec 16, 2020 10:37 pm I would think just the unknown and variable air temp in the room would break that idea. Same for many other factors. And each driver would need to be instrumented as each will have its own set of parameters, and then the integration with the cabinet and so on. So as you have to instrument it, you may as well use the same sensor for feedback.

Balancing a broom on end on your hand is not that hard, trying to do the same with your eyes closed (no feedback) is altogether harder,
I remember products from Yamaha with their „active servo“ technology that used negative impedance schemes on the amplifier to extend the bass (no accellerometers or sensors on the woofer). I am not convinced that a subwoofer with feedback has better „quality“ because of the servo. Perhaps more extension - but that also only within mechanical limits. With the room at +- 20dB for the lowest couple of octaves, maybe it is all a moot point?
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Nick
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#36 Re: What would you do with these drivers?

Post by Nick »

that used negative impedance schemes on the amplifier to extend the bass (no accellerometers or sensors on the woofer)
In effect they are using the voice coil as the sensor for the feedback in that case.
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#37 Re: What would you do with these drivers?

Post by steve s »

Are these systems electronic 'band aids' that try and make up for poorly chosen drivers and cabinets?

I remember about 5 years ago at a wam show, going into a room where a couple of guys where going on about their system that had some sort of electronic device to sort the bass, looking back it sounds like of what's being talked about here.

With a room full of people I asked why it still sounded coloured. I was told it was how it should be.!!
I walked to the front and showed them the issue, the cabs where vibrating badly and causing colouration.
But despite that, the underlying sound was no better than average, lacking bass dynamics and detail, (average to me !)
Similar to dsp, which has alot of followers but every system I've heard with it, it seems to take something away from what I think is the goal.
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#38 Re: What would you do with these drivers?

Post by Wolfgang »

I am not convinced that a subwoofer with feedback has better „quality“ because of the servo. Perhaps more extension - but that also only within mechanical limits. With the room at +- 20dB for the lowest couple of octaves, maybe it is all a moot point?
I used an 18" cone Velodyne servo controlled sub for many years. It had a built in DSP (automatic and manual adj.) for the bass with calibrated mic etc. So the whole thing made really sense as the adjusted room response was part of the servo system.The bass was bone dry, not muddy or overpowering higher frequencies but still it was not possible to hear single notes of 40 Hz or lower separated from the rest which the main speakers produced. After all it was a closed sub that simply pressurized the room. It simply added some good amount of wonderful bass-feeling.

The H-frame OB subs with servo control which I am using now are different. They don't "pressurize" the room but it appears that they send short pulses of high pressure (because the drivers fire in opposite directions?) which makes single notes audible as never before. Even if one argues that we cannot hear but anyway only feel air pressure below 30Hz I still say I can follow each single note down to the limit of the subs (14Hz theoretically).Maybe I can feel the pressure and hear the higher octave? But whatever it is, it puts the whole music performance in a completely different context. I don't even have to listen for it with some effort but it simply comes to me automatically.It appears as if the room of the recording can "breathe" which puts every instrument in a new context, the context of the recording session, which wasn't there before. This obviously needs the lower octaves so that it can happen but without over-pressurizing the listening room. No coloration, lightning fast deepest bass. I was very surprised when I realized that my backloaded horns couldn't keep up with these subs regarding speed below 100Hz. The best combination so far that can play as one homogenous system is a combination of an OB with a PM6A with DX4 phase plugs (very small size baffle only down to 500Hz)/Klipsch La Scala bass horns (50-500Hz)/OB servo subs. The La Scala horns produce a very fast pulse-like bass/lower mids which comes pretty close to those subs.
vinylnvalves
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#39 Re: What would you do with these drivers?

Post by vinylnvalves »

Are these H frames subs a commercial offering like the GR Research ones or are they something you designed and built yourself? As any information would be appreciated for when I start making my prototype, in the new year. I haven't yet decided if I go for an H frame or the W frame like in the Linkwitz LX521.
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#40 Re: What would you do with these drivers?

Post by Wolfgang »

H-frame 2.pdf
(81.11 KiB) Downloaded 301 times
The building plans are the GR Research ones.

https://www.audiocircle.com/index.php?topic=127533.0

I didn't use damping sheets but some people think they are necessary.

https://www.google.com/search?client=fi ... ing+sheets
vinylnvalves
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#41 Re: What would you do with these drivers?

Post by vinylnvalves »

Thanks very much. I have looked at the GR OB subs... cost of shipping from the USA put me off :(
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rowuk
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#42 Re: What would you do with these drivers?

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Max N
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#43 Re: What would you do with these drivers?

Post by Max N »

I got an Apple HomePod for Christmas and treated myself to another one. The main use case was to add surround sound and Atmos to our TV in a way which met the threshold WAF.
I have been pleasantly surprised by the sound quality, so I did some research. The woofer uses what seems to be an advanced version of servo control, running on an A8 processor.
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#44 Re: What would you do with these drivers?

Post by steve s »

That's exactly what I hear, and he's spot on that you don't hear the difference until you have something better to compare.
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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rowuk
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#45 Re: What would you do with these drivers?

Post by rowuk »

steve s wrote: Tue Dec 29, 2020 12:04 pm
That's exactly what I hear, and he's spot on that you don't hear the difference until you have something better to compare.
I am not so sure. I have a healthy mistrust of most things “audiophile”. Very often “better” is claimed with bogus proof. I sold Infinity in the years starting with the Quantum Series (watkins woofer) to the IRS Beta and Gamma years. The servo was very convincing as it did give us an extra octave. Funny enough, even although the Infinity had an octave more, the bass of the large JBL systems(L300/4435) (no servo) seemed to go as deep(they did not measure as well). The bass quality was certainly comparable in every respect for my ears.
I do question how to quantify Pauls “better”. Listening habits are created over decades and A/B testing really can not factor those preferences out (if A/B testing could really ever provide any reference for “sound”).
In any case, great drivers sensibly employed can create a very plausible image with or without servo. It is not the gun, rather he or she that pulls the trigger.
Whenever I feel blue, I start breathing again.
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