DC or AC FBT for Plasma Speaker Project ? / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

DC or AC FBT for Plasma Speaker Project ?

Move Thread

LAN_403

xsecret

Wed Apr 29 2009, 10:38PM

Registered Member #2100 Joined: Wed Apr 29 2009, 10:01PM
Location:
Posts: 2

Hi everybody,

I'm new here and I want to study some high-voltage projects. Donâ€™t be afraid, I have some knowledge in general electronics and I (often) know what Iâ€™m doing

I will begin with a plasma speaker based on Dr Kilovolt's schematics (SG3525 + better output), but I need an advice about the FBT. I read lots of contradictory descriptions about which (AC or DC) sound better. There is so many HV Guru here, so I wonder what your thought is: Should I use a FBT with a rectifier diode (cheaper) or a pure AC FBT?

Thank you !

PS : If somebody is interested, I will publish the schematics, PCB layout and BOM here when it will be done.

teslacoolguy

Wed Apr 29 2009, 10:48PM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792

Hey, welcome to the forums. TO answer your question, i have built that exact same driver and i only notice slight differences between a ac or dc flyback. With the ac flyback there is a little more amplitude and it has better response to the lower notes.

twist2b

Wed Apr 29 2009, 11:21PM

Registered Member #2086 Joined: Tue Apr 21 2009, 02:33AM
Location:
Posts: 117

i am interested (your ps :P)
Good luck and tell us how you do!!!

The DC voltage, your going to give it the same characteristics of AC anyways (via mosfets, modulated oscillations, etc.), so it should be the same. :)

xsecret

Wed Apr 29 2009, 11:41PM

Registered Member #2100 Joined: Wed Apr 29 2009, 10:01PM
Location:
Posts: 2

teslacoolguy wrote ...

Hey, welcome to the forums. TO answer your question, i have built that exact same driver and i only notice slight differences between a ac or dc flyback. With the ac flyback there is a little more amplitude and it has better response to the lower notes.

Got it. From a technical point of view, an AC FBT should result in much bigger amplitude (two times higher). I thought this would have resulted in a bigger sound difference. Thatâ€™s a good news :D

Dr. H.

Thu Apr 30 2009, 07:42AM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Hi there

I've also built the driver and experimented with different FBTs. The AC one (tested two of them) - gave me much better sound than DC FBTs (thested two of them). So all in all - I vote for a AC.

Cheers

Dr. Dark Current

Thu Apr 30 2009, 07:50AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

It really depends. The AC ones are usually lower voltages so they output higher current, which may be benefical because the arc is hotter. This might work somewhat better for PWM control.
However when using FM control, I haven't noticed much differences. If there is a difference, it is just small.

PS. Use FM, it will give you better sound.

Mattski

Tue May 05 2009, 07:27PM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

How does the FM control work? I have built a pulse width modulated plasma speaker, and it makes intuitive sense to me how it turns into audio in the end.

I would guess how the FM works is you have a carrier tuned to the frequency which gives you the highest output voltage. Then you frequency modulate it with the audio signal, and any deviation above or below that resonance point will reduce the voltage gain, thus producing the audio modulation. Is that a reasonably proper description?

borderline128

Thu May 07 2009, 07:58PM

Registered Member #1531 Joined: Tue Jun 10 2008, 08:37PM
Location:
Posts: 8

Mattski wrote ...

How does the FM control work? I have built a pulse width modulated plasma speaker, and it makes intuitive sense to me how it turns into audio in the end.

I would guess how the FM works is you have a carrier tuned to the frequency which gives you the highest output voltage. Then you frequency modulate it with the audio signal, and any deviation above or below that resonance point will reduce the voltage gain, thus producing the audio modulation. Is that a reasonably proper description?

To my understanding yes. By varying the frequency of the drive signal you inherently vary the amount of power put into the plasma. The temperature of the plasma is directly related to the power and by raising and lowering this one generates temperature changes in the plasma. As the plasma cools down the air around it contracts and vise-versa. This creates pressure waves otherwise known as sound.

EDIT: This brings up and interesting question for me. Perhaps one of the reasons an actual tesla coil is allegedly better for audio modulation (besides the point that they are much higher power) could be that the bandwidth for which a tesla coil will produce a plasma is much narrower and thus a frequency shift should in theory produce a sharper temperature gradient through which the plasma will vary.

Basically, I'm suggesting that the shorter resonance bandwidth of a tesla coil allows for wider temperature variations in the plasma and thus produces a higher magnitude sound wave. Will anyone concur with or dispute this?

Dr. Dark Current

Thu May 07 2009, 09:10PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

The way FM works is that increasing frequency decreases current, because the same voltage over a shorter time results in a lower current through an inductor. This varies the arc current pretty precisely to the frequency, this results in cleaner sound (at least in my experience).

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob