Frequency divider for an audio crossover

[acardianknight]

Hi,
I have built an audio crossover for my project. a 3way crossover using butterworth filters.i have three speakers on which lasers are mounted. the audio signal makes the lasers move. pretty simple the problem i`m facing is i want to drive the crossover using woofers for highs and mids as well as they provide maximum displacement of the diaphragm however the woofers hardly move due to the highs and mids. i wanted to try frequency shifting. i looked up a few chips like 555times and the 4060 but i cant really figure out what to use. I want to reduce the frequency say from 3khz to about 600hz.
please to guide me.

Thank you.

 

[audioguru]

A speaker moves a lot at low audio frequencies. It moves much less at higher frequencies.

A digital frequency divider has a square-wave output but don't you want a linear analog output?
To reduce frequencies you must digitize the analog signal with a high frequency clock and play it back later using a lower frequency clock.

 

[ronsimpson]

This is hard to understand. I think you want to replace the midrange and tweeter with two more woofers, because the woofers move the laser more. That will not work for many reasons. If you want we can go through then one at a time.
Frequency shifting is very complex. Not a LM555 problem.
I do like the idea of lasers on the woofers!

 

[acardianknight]

is there a analog divider? if not, i`m assuming i`ll have to use a a2d converter that would not be built. Frequency shifting is tough? if so is there any alternative to step down the frequencies? woofers need to just move a bit. the laser would make concentric random patterns with the smallest being that of the tweeter laser.

 

[dougy83]

No, analog frequency is theoretically simple - just mix it with a sinewave and you'll create a new frequency spectrum; e.g. if y is the input frequency & x is the mix freq, you get 2 resulting frequencies: x+y & x-y (due to the trig identity: sin(x)sin(y) = 0.5(cos(x-y)-cos(x+y)) ). The problem is that to make it useful, you have to filter out the unwanted frequencies from the initial spectrum before mixing, and you may need to filter again after the mixer. The mixer can be a simple squarewave mixer (will introduce odd harmonics though) using a 555, an inverting amp and a analog MUX selecting between the inverted and noninverted signal at the rate of the mixing frequency.

You could also just sample the signal at some rate using an analog switch and an oscillator - this will create aliasing which will fold the frequency spectrum; the input signal must be filtered before sampling though, so that only the frequencies of interest are folded.

You can alternately use a peak-detector on the bands, which will remove the high frequencies and give you a signal that is the envelope of the peaks in the old signal - not frequency shifting, I know, but you'll get a low frequency signal that the woofer can handle, and it will be based on the mid or high spectrum, which may give you passable result for you light show.

 

[Nigel Goodwin]

is there a analog divider? if not, i`m assuming i`ll have to use a a2d converter that would not be built. Frequency shifting is tough? if so is there any alternative to step down the frequencies? woofers need to just move a bit. the laser would make concentric random patterns with the smallest being that of the tweeter laser.

You've never really explained what you're actually trying to do?.

Presumably it's a sound to light display?.

If so you're going about it completely the wrong way, you can't use the actual mid and high frequencies to 'flash bulbs' or indeed 'move lasers', as the frequencies are much too high - and frequency shifting them, while technically pretty difficult, isn't the solution either.

You simply rectify the signals, and produce a signal that represents the amplitude of the frequencies in question, and use that for control.

 

[audioguru]

I made a "moving tangle of thread" on my oscilloscope screen 40 years ago. Vertical was left channel and horizontal was right channel. Good stereo input made the tangle but mono made an angled straight line.

I have seen the same thing at concerts but the tangle was made with a laser beam. I never thought about how they moved the beam. Maybe a woofer moving a small mirror glued to its cone. I don't think high audio frequencies were used.

 

[Nigel Goodwin]

I made a "moving tangle of thread" on my oscilloscope screen 40 years ago. Vertical was left channel and horizontal was right channel. Good stereo input made the tangle but mono made an angled straight line.

I have seen the same thing at concerts but the tangle was made with a laser beam. I never thought about how they moved the beam. Maybe a woofer moving a small mirror glued to its cone. I don't think high audio frequencies were used.

They use special mirrored deflection units, not just a speaker and a magnet

Interestingly many years ago the UK speaker manufacturer Wharfdale released a range of speakers called 'Laser'. They used laser beams to scan the breakup of the cones during their design, to produce high quality drivers. This was back before lasers used in shows, and they made their own deflection units using their voicecoil and magnet technologies - so bascially a 'speaker' but with no cone, and specially designed to move a tiny low weight mirror ar very high speeds.

 

[irbirb]

I have seen the same thing at concerts but the tangle was made with a laser beam. I never thought about how they moved the beam. Maybe a woofer moving a small mirror glued to its cone. I don't think high audio frequencies were used.

They use special mirrored deflection units, not just a speaker and a magnet

yeah, same as the x/y scope setup. one audio channel for vertical mirror, one for horizontal.

i built a super-trashy one from a couple of old harddrives and a laser-pointer once.
the "swing-arm" voice-coil actuators will act just like audio speakers... you can mount mirrors on them.
when you want higher frequencies, it's going to be easier to move a small optical-mirror than a whole laser unit.

 

[irbirb]

.... but if you have to use woofers with lasers attached,
you might dig through the pdf for this "rOCkTAVE" pedal: **broken link removed**

 

[acardianknight]

A detail of the project..

What I am trying to make is a background illumination light.. The videos on youtube show the mirrors on speakers-laser lights but I have mounted the light directly unto my speaker diaphragm using coil springs. the movement of the speakers moves the laser. making those random pattern on my screen/fog.I am using the small class II lasers found in pens and key chains, so the wt of the laser isn`t a prob. The low frequency woofer(or if any of the woofers are connected to lows or w/o d crossover) move just the way i want them to. I did expect the highs not to move much however they just don`t move at all.. the mids also do not move much either.
As mentioned with Wharfdale`s laser speakers- i have cut out the cone too and using the laser unit removed from d key chain.
@dougy83- I will try the second option of using a analog switch and a oscillator. i am using a crossover, would that not be sufficient instead of another filter for input signal?
could you please elaborate the best approach that i should take, given that i`m not the digital electronics genius kinda guy so i steer away from programming microcontrollers.
though difficult at this point will redesigning of my crossover be of any help?? if yes i will explain the design.

 

[acardianknight]

i am trying to use fast diodes and grounded capacitor to make a peak detector.. please guide me on how to go about it. another option ie the analog switch-should i be using any specific type? keeping in mind that i have to reduce the freq from 1-5 khz to around 500-600Hz what LFO should i use?
Thank you in advance.

 

[audioguru]

Doesn't your laser simply make a straight line when it is moved a little by a woofer?

My oscilloscope had the left channel of stereo move its beam vertically and the right channel to move it horizontally. Since the channels have frequency and phase differences then the beam showed a "moving tangle of thread" or different moving patterns.

 

[irbirb]

Doesn't your laser simply make a straight line when it is moved a little by a woofer?

the spring mount probably make it all wobbly and random.

My oscilloscope had the left channel of stereo move its beam vertically and the right channel to move it horizontally. Since the channels have frequency and phase differences then the beam showed a "moving tangle of thread" or different moving patterns.

like this!
**broken link removed**

 

[acardianknight]

True.. it makes a wobbly pattern and random. there is no x-y axis control as i am using Coil springs from the old big clocks. Thank you.. please to answer my previous query on the freq division and LFO if possible. thank you.

 

[audioguru]

I made a voice encryption circuit that inverted voice frequencies for a wireless speakerphone. High frequencies became low frequencies and low frequencies became high frequencies. It was very linear because when unscrambled with a similar circuit the sound was very clear. It used an MC1496 balanced modulator IC and a switched-capacitor lowpass filter IC. It used a 3.58MHz colour TV crystal and a CD4060 oscillator/divider to make its carrier.

You can do this kind of circuit to make high frequencies become lower frequencies.

 

[dougy83]

@dougy83- I will try the second option of using a analog switch and a oscillator. i am using a crossover, would that not be sufficient instead of another filter for input signal?

A crossover is a filter, but I'm guessing it's only 1st or 2nd order? This may not be a problem for you if you're not too particular about which frequencies are in the the output signal. You can simulate the filter response and calculate the output after teh mixer using a simple spreadsheet.

.. please to answer my previous query on the freq division and LFO if possible. thank you.

If your input signal is, e.g. 3-5kHz, and you use a 4kHz mixing frequency, the resulting frequencies will be between 4+3 to 4+5 and 4-3 to 4-5 (that's 7-9kHz and 0-1kHz). Due to the wrapping of the spectrum around 0Hz, the 0-1kHz is a sum of the shifted 4-5kHz spectrum and the shifted and reversed 3-4kHz spectrum. Refer to my rough sketch (horizontal axis is frequency, vertical is the amplitude of the frequency spectrum).

 

[acardianknight]

Thank you so much. will work on it and let you know about the outcome.

 

[dougy83]

No worries. Here's the spreadsheet to show the filter and mixer outputs. You'll have to enable macros if your security settings are too high. You can view the code through the visual basic toolbar - set design mode & double click on the button