Russells DIY Hemholtz Resonator - Page 2 - AVS Forum
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post #31 of 35 Old 01-21-2010, 11:20 AM - Thread Starter
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Churches were the rock events of the Middle Ages and thus had pipe organs with 16 foot pipes and Centuries before that the Roman Senators when speaking had a need for clarity and echo reduction.

But what to do in a stone building filled with echoes and no Dacron invented yet?

One solution was placeing clay pots in the walls and carefully filling those pots with ash to obtain the frequency to reduce echoes and improve Senators oratories and centuries later the oratories of church priests.

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post #32 of 35 Old 01-21-2010, 11:32 AM
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Quote:
Originally Posted by lennon_68 View Post

How does one determine the bandwidth that a helmholtz resonator will be effective in? Is it similar to the bandwidth at which a port adds output in a ported speaker model?

As I said, I'm not clear on whether these work by antiphase resonance or resonance+damping.

If the latter, Q will be a lot lower than for a ported box.

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Originally Posted by Lonely Raven View Post

In the acoustics books I'm reading, they talk about being able to expand the Q slightly by using some material over the opening or in the neck of port to broaden the bandwidth.

As far as I can tell, the common notion of spreading out the effect over freq by increasing damping/increasing BW is false.

BW is increased by its mathematical definition, but it works only by lowering the amplitude of the peak, not by increasing amplitude over a wider band.

It's just that more energy is removed at the resonant freq than any other freq.

I tried but failed to find a graph of amplitude ratio vs freq vs damping online, which would make this obvious.

[edit]

Here we go; http://en.wikipedia.org/wiki/Vibration

Scroll down about halfway to the section titled "Forced vibration with damping".

The first of the two graphs show Amplitude Ratio (Q) vs. freq; each curve is for a different value of damping.

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post #33 of 35 Old 01-21-2010, 03:25 PM
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In the acoustics books I'm reading, they talk about being able to expand the Q slightly by using some material over the opening or in the neck of port to broaden the bandwidth. I guess the story is that the Roman Amphitheaters used large clay pots with ash in them to tune to specific frequencies, and then wool in the necks of the clay pots/jars to broaden the bandwidth.
I don't recall where I read that, but I'll see if I can find the reference and post a link in this thread.

Hi Raven,
That is correct you can Get A little wider Bandwidth but compared to Broad band Bass traps The Q is still very narrow thus the need for A few HelmHoltz perferably placed in the High pressure zones...

Cheers..
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post #34 of 35 Old 01-21-2010, 06:07 PM
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Quote:
Originally Posted by Lonely Raven View Post

In the acoustics books I'm reading, they talk about being able to expand the Q slightly by using some material over the opening or in the neck of port to broaden the bandwidth. I guess the story is that the Roman Amphitheaters used large clay pots with ash in them to tune to specific frequencies, and then wool in the necks of the clay pots/jars to broaden the bandwidth.

I don't recall where I read that, but I'll see if I can find the reference and post a link in this thread.

IIRC, the "clay pot" reference is from the Master Handbook of Acoustics.

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post #35 of 35 Old 01-23-2010, 12:54 PM - Thread Starter
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Originally Posted by mobius View Post

IIRC, the "clay pot" reference is from the Master Handbook of Acoustics.

I was wondering when some one was going to notice that as I expected the QRD mention was a dead giveaway but instead someone noticed the claypot.

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