low frequency tone generator

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Tommy volts
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low frequency tone generator

Post by Tommy volts » Mon Jun 30, 2003 8:44 am

The audio frequency of low A on a piano is 27.5 Hz.<p>When I use my function generator to send a 27.5 Hz audio signal to a speaker, the speaker just clicks in and out at that frequency. It isn't until I increase to a higher frequency that the speaker starts to produce a "tone".<p>Two Questions:<p>1. What does a low frequency audio tone generator (like a synthisizer) do that my sine wave generator doesn't?<p>2. Is there a kit available for a low frequency audio tone generator?. I would like to generate the lower tones of a piano/organ (25 Hz or so).

I would appreciate any replies, this has puzzled me for a while now.<p>Thank you

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Re: low frequency tone generator

Post by hlreed » Mon Jun 30, 2003 8:52 am

On a piano you are hearing overtones of 27.5
To produce 27.5 Hertz with a speaker, you need a large speaker enclosure and a large room.
Harold L. Reed
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Chris Smith
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Re: low frequency tone generator

Post by Chris Smith » Mon Jun 30, 2003 11:52 am

You don’t have enough power to drive the speaker, at that low frequency. At higher frequencies less power is required, [impedance] and so what you need is a audio power amp. They come in chip form from a few watts to dozens of watts and the external circuits are minimum. The tone generator out put goes into the input of the amp, [and may need to be balanced?] the amp drives the proper impedance to the speaker. <p>A LM 386 or TDA 2002 should do?

Dean Huster
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Re: low frequency tone generator

Post by Dean Huster » Mon Jun 30, 2003 2:17 pm

If all your speaker is doing is clicking "in and out" at that low of a frequency, I'd bet a dollar to a donut that you're feeding it a square wave rather than a sine wave. All it'll do is "tick".<p>Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).


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Re: low frequency tone generator

Post by russlk » Mon Jun 30, 2003 7:37 pm

The audio amp you are using probably does not have a response that extends below 60 Hz due to coupling capacitors and an intentional design to reduce hum.

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Re: low frequency tone generator

Post by analogee » Mon Jun 30, 2003 7:45 pm

And let's not forget that your ear is MUCH less sensitive to 27 Hz than midband (500 Hz - 5 kHz or so) frequencies. Something like 60 dB less sensitive. So, for you to hear a 27 Hz tone, it will have to be a LOT louder than a 1 kHz tone.<p>Do a search on "Fletcher-Munson curves" if interested in learning more on this. For example:<p>Link to Fletcher-Munson Equal Loudness Contours explanation<p>Regards,
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Re: low frequency tone generator

Post by Joseph » Wed Jul 02, 2003 3:45 am

Also, your speaker probably has poor response that low. Therefore, it may only respond to the higher harmonics of a square wave input.

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