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openglcg

Bandwidth principles applied to subwoofers

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So I did some experimenting today to see how the basic bandwidth principles of digital communications can apply to accurate bass reproduction.

 

Here's the basic concept: Take a basic sign wave and pulse it on and off with another signwave via amplitude modulation. You will get something that is the equivalent of two signwaves centered around the original waves frequency. The faster you want to pulse the wave accurately, the wider the two components have to be in terms of frequency. This is why we use bandwidth as a term for describing the number of pulses that can be transmitted digitally each second.

 

  -There's a picture of this in the attached sub bandwidth.jpg-

 

So I decided to try producing an example of this limitation digitally. I used an oscillator and a 24db/oct high pass filter to simulate a woofers roll off.

  -I attached a sample of this as "sub bandwidth.mp3" and a picture of the two wave forms as "wave forms.jpg"-

The rolled off version is first and the unfiltered version is second in the audio. The unfiltered version is first and the rolled off version is second in the picture.

The rolled off version was boosted in volume to make it easier to hear the true difference between the rolled off version and the not rolled off version without the change in volume. I tried to place it within the frequency range of most subs (~37-61hz) so more people could listen to it.

 

Its pretty easy to hear and see that the pulsing is not as strong in the filtered version.

 

So there could be an advantage to having low frequency extension beyond just hearing solid low frequencies.

 

The question is how much? I tried with my apartment sub (quietly) using its own roll off and could hear what i thought was the same effect. Its hard to tell because i cannot quickly switch off and on its roll off and get a pair of normalized samples to listen too. I also have no good mic to use for this experiment. But it seems to me, according to this experiment, that it does play somewhat of a roll although probably not as exaggerated as in the example.

post-3648-0-61967900-1445129361_thumb.jpg

sub bandwidth.mp3

post-3648-0-05675300-1445129364_thumb.jpg

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..

So there could be an advantage to having low frequency extension beyond just hearing solid low frequencies.

 

The question is how much?

..

 

High-pass filtering at 10Hz is audible.

 

This is caused by time-domain ringing due to the filter.

Higher cut-off is more audible, and when you approach 20hz there will be audible loss of weight and low frequencies, in addition to the ringing effect.

 

This has been confirmed in a controlled test I did recently, using transient wide bandwidth test signals.

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So I did some experimenting today to see how the basic bandwidth principles of digital communications can apply to accurate bass reproduction.

 

Here's the basic concept: Take a basic sign wave and pulse it on and off with another signwave via amplitude modulation. You will get something that is the equivalent of two signwaves centered around the original waves frequency. The faster you want to pulse the wave accurately, the wider the two components have to be in terms of frequency. This is why we use bandwidth as a term for describing the number of pulses that can be transmitted digitally each second.

 

  -There's a picture of this in the attached sub bandwidth.jpg-

 

So I decided to try producing an example of this limitation digitally. I used an oscillator and a 24db/oct high pass filter to simulate a woofers roll off.

  -I attached a sample of this as "sub bandwidth.mp3" and a picture of the two wave forms as "wave forms.jpg"-

The rolled off version is first and the unfiltered version is second in the audio. The unfiltered version is first and the rolled off version is second in the picture.

The rolled off version was boosted in volume to make it easier to hear the true difference between the rolled off version and the not rolled off version without the change in volume. I tried to place it within the frequency range of most subs (~37-61hz) so more people could listen to it.

 

Its pretty easy to hear and see that the pulsing is not as strong in the filtered version.

 

So there could be an advantage to having low frequency extension beyond just hearing solid low frequencies.

 

The question is how much? I tried with my apartment sub (quietly) using its own roll off and could hear what i thought was the same effect. Its hard to tell because i cannot quickly switch off and on its roll off and get a pair of normalized samples to listen too. I also have no good mic to use for this experiment. But it seems to me, according to this experiment, that it does play somewhat of a roll although probably not as exaggerated as in the example.

 

Thanks for doing the experiment and posting the results. Without getting into the inductive discussion of bandwidth (which I used to have hosted on my web page from Dan Wiggins at Adire) it's nice to see your data and conclusion which prove again that larger bandwidth systems have better overall performance...especially down on the bottom end.   B)

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