Help frequency to dB relationship

In summary, to find the -6dB point for a 24db/oct slope filter with a 0dB@90hz crossover point, you would need to order the resistors and capacitors from Digikey, and resimulate the filter response, based on the published tolerances. If you see any problems, you would need to redesign the filter.
  • #1
frogdogbb
45
0
Hello all, I am having trouble figures out the following filter I am designing. I to use a filter with a 24db/oct slope I want 0dB@90hz. So if I want the knee of the cuttof curve to start at 90Hz how do I find the -6dB point so I can design the crossover, by the way this filter uses -6dB as the crossover point as opposed to the usual -3dB.
Thanks
 
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  • #2
It depends on the topology of your filter. Cheby, Butterworth, etc. Just put a generic form of the candidate polynomials into Mathematica or even Excel, and plot out the frequency response. That will start to show you how close you can get a 0dB flat spot to the -6dB point with each polynomial. It's way different for the different filter topologies. Keep in mind that in the real world, there can be some disadvantages to the sharper edged filters. Quiz question -- what is generally the main disadvangate of the sharper filters...?
 
  • #3
I don't know what is the main disadvantage? Size, added complexity? It is an active filter so componet losses are not really an issue.
 
  • #4
frogdogbb said:
I don't know what is the main disadvantage? Size, added complexity? It is an active filter so componet losses are not really an issue.
Nope. Hint -- you need to order the resistors and capacitors from Digikey to build your filter. Read the datasheets from digikey for the real components, and resimulate the filter response, based on the published tolerances. See any problems?
 
  • #5
frogdogbb said:
Hello all, I am having trouble figures out the following filter I am designing. I to use a filter with a 24db/oct slope I want 0dB@90hz. So if I want the knee of the cuttof curve to start at 90Hz how do I find the -6dB point so I can design the crossover, by the way this filter uses -6dB as the crossover point as opposed to the usual -3dB.
Thanks
BTW, keep in mind that the different topology filters have different characteristics in the passbands and stop bands, as well as different knee sharpness characteristics. The Butterworth is flat and slow, the Cheby is better if you can tolerate some ripple in the passband (not 0dB all across), and the Elliptical is better yet in terms of a sharp knee, if you can tolerate gain ripple in both the passband and stopband.

But the quiz question that I posed above would also factor into your decision for a real world filter (another hint here), especially if you plan on building them in the millions...
 

FAQ: Help frequency to dB relationship

What is the relationship between help frequency and dB?

The relationship between help frequency and dB (decibels) is that as the frequency of a sound increases, the number of decibels also increases. This means that a higher frequency sound will have a higher dB level compared to a lower frequency sound.

How does the human ear perceive different frequencies and dB levels?

The human ear is capable of detecting frequencies ranging from 20 Hz to 20,000 Hz. The higher the frequency, the more sensitive the human ear is to changes in the dB level. This is due to the structure and sensitivity of the hair cells in the inner ear.

What is the unit of measurement for dB?

dB (decibels) is a logarithmic unit of measurement for sound intensity. It is a relative unit that compares the sound level to a standard reference sound level. In the case of sound, the reference level is 0 dB, which is the threshold of human hearing.

What are some common everyday sounds and their corresponding dB levels?

Some common everyday sounds and their corresponding dB levels are: a whisper (30 dB), a normal conversation (60 dB), a vacuum cleaner (70 dB), a car horn (110 dB), and a jet engine (140 dB). It is important to note that prolonged exposure to sounds above 85 dB can cause permanent hearing damage.

How can I measure the dB level of a sound?

A sound level meter is a device that can be used to measure the dB level of a sound. It works by converting sound pressure waves into an electrical signal, which is then displayed as a numerical value on the meter. There are also many smartphone apps available that can measure the dB level of a sound, although they may not be as accurate as a dedicated sound level meter.

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