please help me devise a modest chladni setup

[mqbernardo]

OK... after 2 ruined woofers i think i better ask for help! so i have my PC connected to my HI FI amp (a TEAC A-H300mkII, which says 85 W amp) which are connected to a Pioneer TS-G1321i car woofer (which says 200 Watts Maximum Output /35 Watts Nominal Output). links here: http://www.amazon.co.uk/Pioneer-TS-G132 ... B006NU551A and http://www.ebay.co.uk/itm/TEAC-A-H300mk ... 1c34fd1846

as you´ve may have figured out this is all rather obscure to me (my speakers have always been active or have been part of the HIFI package, so i never had to match them) and i can´t quite see why i have ruined 2 perfectly sound woofers. i guess impedance mismatch would be improbable, but someone should know better. the fact is one of the speakers turned into smoke on my hands.... i wasn´t using too much gain, i think... at least i could here a friend speaking

so, basically, any fresh ideas for a proper, functioning chladni setup? should i buy different columns?

thanks in advance,
Miguel.

[Trevor Gore]

Hi Miguel,

Once upon a time it was easy to figure out what components would go with what because the power handling was always given in Watts RMS. These days, there's "music power", "peak power" nominal power" etc. etc..

Anyway, having checked the specs of your gear, the amp outputs 45 Watts RMS per channel (at 6 ohms, which is unusual. 4 or 8 are more common. I guess they're just saying that you can use either 4 or 8 ohm speakers). The speakers will handle 35 Watts RMS per channel, so you do have enough grunt in your amp to blow your speakers if you drive them at high volume for too long.

The amp has a frequency response down to 5Hz, which is inaudible, so it also matters what you're using to drive the amp. If there is a DC offset on the amp output, or there are low frequency signals (noise) generated by your signal generator that you can't even hear, you may be putting a lot more power through your speakers than you might think.

The amp in my Chladni system only puts out 15 Watts RMS, which I find is plenty. I use a 4 inch (100mm) speaker, mounted in a baffle, pics here. I think the speaker is rated at 25Watt RMS. Hearing protection is definitely needed. With the smaller speaker you can hold it over an antinode to get better coupling whereas with a larger speaker you can cover anitnodes of two phases and not get any coupling.

Without a lot more electronics gear than you're likely to have, you're unlikley to be able to do much by way of diagnostics. So I'd say get another (smaller) speaker, with as much power handling as is economical, mount it in a baffle and try again.

P.S. I notice on Martin 's (Kiwigeo) pics of his set-up, he looks like he has a capacitor mounted in series with the speaker. If that is what it actually is, it's not a bad idea, as it would protect your speaker from DC signals that you wouldn't hear. Perhaps we'll get a comment from Martin.

[mqbernardo]

Thanks trevor. I might buy a new more powerful and smaller speaker when i find one (or maybe i´ll just order it online), but going again at it i found i maybe was using too much gain? turning the volume lower i could still excite the lower modes and managed to find 3 before the woofer turned too hot. it also helps if you know what you´re looking for and try to excite the antinode region, as i´ve learned from you. here´s an example (crappy phone pic):

[kiwigeo]

Miguel,

How is your top supported?

[kiwigeo]

P.S. I notice on Martin 's (Kiwigeo) pics of his set-up, he looks like he has a capacitor mounted in series with the speaker. If that is what it actually is, it's not a bad idea, as it would protect your speaker from DC signals that you wouldn't hear. Perhaps we'll get a comment from Martin.

My speaker is a car stereo speaker and its got two coaxial tweeters mounted in the woofer. The capacitor would be a crude crossover to split the signal between the main woofer and the tweeters. I got my speaker from Jaycar in NZ but it would be something like this one available from Jaycar Australia: http://www.jaycar.com.au/productView.as ... TID=1027#4

[mqbernardo]

Miguel,

How is your top supported?

Hi Martin,

The top is supported with pyramidal foam blocks , a la Al Carruth and i try to put the tip of these under the node lines.
I cut the blocks from an acoustic foam panel like this one: http://www.thomann.de/gb/the_takustik_s ... schaum.htm.

all the best,
Miguel.

[jeffhigh]

Looks like you have a bare speaker Miguel. Because of phase cancellation that cuts down on the efficiency dramatically compared to having it mounted in a box or other form of baffle and therefore means you have to drive it harder.

[mqbernardo]

thanks Jeff, i might do that... now were´s that paint can?

[klooker]

Quick question:

What are all of you using for a signal generator?

Thanks,
Kevin Looker

[Trevor Gore]

Hi Kevin,

Welcome to the south side.

I'm using 70's era analogue combination sig gen, power supply, amplifier. A bit of a dinosaur, but very useful.

Martin uses the Bradley combination sig gen/amp, from Don Bradley in CA.

There seems to be no analogue inexpensive sig gen or kit currently available in the Aus market. There may be something in the USA.

If push comes to shove, there's always the digital sig gen in Visual Analyser, which works fine, but is not very user friendly. If you use a Mac, there this one.

[klooker]

Thanks Trevor.

I just picked up this off of Ebay.

Freq-Gen.jpg (68.03 KiB) Viewed 32893 times

It lists a 600 Ohm output impedance. Does anyone know if I can run this directly into my hi-fi preamp or will I need to somehow change the impedance.

Thanks,
Kevin Looker

[Trevor Gore]

That looks great, but don't expect the analogue meter to be particularly accurate. However, the frequency meter on VA or a phone app. should sort that.

It should work fine into the aux input of almost any audio amp.

[charangohabsburg]

Hi Kevin,

What Trevor said.

I have a very similar tone generator (also 600 Ohm output impedance) and combine it with a frequency counter:

I (sometimes) use this inexpensive (about 10$ IIRC) frequency counter, but it is quite quirky because when changing the frequency on the tone generator dial it will display most of the time between 0.5 and 1.5 off, but when I switch the FC off and on again it always is spot on.

How do I know it is off? Well, I also bought another FC with which I can compare. It is a tiny bit of overkill, but I got it for a reasonable price (there are also new, Chinese ones around for about 100$ I think).
Hidden in the box behind the TG:

2013_D70_7667-a.jpg (59.99 KiB) Viewed 32883 times

... and connected:

It is much nicer to work with the big frequency counter connected, but the inexpensive one does also a fairly good job.

[klooker]

Thanks guys.

I knew the needle pointer wasn't going to be accurate but didn't know there were cheap frequency counters available. I think I'll buy one which will be a easier than recording tones and analyzing.

Kevin Looker

[charangohabsburg]

For me recording a tap tone is easier and much quicker than setting up the whole Chladni pattern thing. I only use Chladni patterns when I am in doubt which peak is which. The two methods complement each other.

Here's a link to an eBay offer of the frequency counter I've built in. I recommend to combine it with a toggle switch in order to get accurate readings (see my former post).

[mqbernardo]

right now i´m using an ipc signal generator, like this one: http://www.chescientific.com/edu/product_140.aspx

thought i´d have to hook it up to an amp but (at least for the lower modes) the signal is apparently strong enough. i use app on my phone to reality check the frequency values (most of the times this one: https://play.google.com/store/apps/deta ... s.fm&hl=en ).


all the best,
Miguel.

[Craig Bumgarner]

Miguel,

Where did you buy the IPC signal generator?

Craig

[DarwinStrings]

I had a little trouble with my first attempt at tea leaf reading, two burnt speakers. I am now sorted out though as I bought another $20 4" bass speaker and a $30 18w rms amp from Jaycar and everything is working as it should using the VA tone generator.

tea companzlf.jpg (63.28 KiB) Viewed 32751 times

Jim

[mqbernardo]

Miguel,

Where did you buy the IPC signal generator?

Craig

Hi Craig! Nice hearing from you.

I got it from ebay, it was the cheapest available at the moment. They turn out from time to time. I don´t remember the seller´s name but Markus has kindly provided me with a link to his own source. These are more expensive, but the offer is reliable and they come calibrated: http://www.ebay.com/sch/lutz-volk*nachr ... pg=&_from= (they are also delightfully vintage-geeky, if you´re into that)

Although i guess you could find something similar in the US and save ob shipping/customs.

All the best,
Miguel.


P.S. - have you been giving the world any new gypsy guitars lately? are you still focused on Castellucias?

[Craig Bumgarner]

Chladni newbie here. Any idea how many decibels one needs to crank out to make Chladni patterns?

I ask because I'm generating tones on a computer, sending them out to one channel of a 2x40 watt amp and an 8 ohm 4" speaker rated for 40 watts. Volume on the sound card and amp are maxed. At 229hz, I measure 98dB 6" from the speaker, my ears hurt, but my tea leaves just sit there. From tapping, 229hz is where I would expect the main monopole peak resonance. I tried a couple hz either side of this, nada.