Electronics > Beginners

Tweeter bass blocker

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drussell:
I think the OP is trying to understand some basic filtering concepts. 

What they probably don't realize is that not only can you change where the crossover point is (for example, using a smaller value capacitor in series with the tweeter will raise the frequency at which the filter is effective) but you can also change the slope by creating multi-order filters.

A single capacitor in series with a tweeter, or a single coil in series with a woofer will provide a 6 dB per octave roll-off.

A second order (12 dB / octave) high-pass filter for a tweeter would be built with a slightly different capacitor value in series and then the appropriate coil in shunt across the tweeter.  (You can think of that coil as helping to bleed off the lower frequencies by shunting them around the tweeter voice coil, decreasing the amount of those lower frequencies that actually get into the tweeter voice coil.  This increases the roll-off rate, or slope...)

A second order low-pass would be a coil in series with the woofer and a capacitor across the voice coil to "shunt" some of the higher frequencies that make it through the crossover coil.  etc. etc.

You can keep adding more stages for steeper slopes with the appropriate values.  For example, an 18 dB / octave (third order) tweeter crossover you would go series capacitor to "shunt" coil, to another capacitor, to the tweeter.

It gets a little more interesting when you start to look at the phase relationship at crossover if you don't use "matched" crossover sections with the same slope.  ie. sometimes you will need to reverse the polarity of the tweeter terminals to maintain correct phase at the crossover point if you have an uneven number of orders to orders. 

Good ol' Parts Express has these simple calculators especially to help beginners:

https://www.parts-express.com/crossover-calculators

drussell:

--- Quote from: symbianas on September 26, 2019, 06:46:19 pm ---Tweeter is high quality "logic7", but used and from 2007 year car. Power comes not from dedicated amplifier but from radio itself, so maybe it could be that radio is producing not clear signal?
--- End quote ---

Yes, this is a fundamentally good concept to understand.  As stated above by others, if you are reaching the clipping point, (in any amplifier,) distortion increases DRAMATICALLY as soon as you try to go beyond that.  The sound quality will suffer greatly and the splatter of the harmonics caused by the clipping will be very pronounced, especially in a reasonably good quality tweeter, even with a very steep crossover slope.  (A steeper slope will help protect the tweeter itself under these kinds of conditions, though.)

Kasper:
Might want to measure resistance of the capacitor just to check its not shorted.

symbianas:
So this is video of my test rig:

At start bass is set at -6 so tweeter is ok. As I increase bass to +6 it starts playing bass from tweeter. So I guess the sound gets distorted correct?
The same with increasing sound at some point it starts doing it even if bass is 0.
So there is no way around correct? Radio signal is horrible and I need dedicated amp and better setup?

drussell:

--- Quote from: symbianas on September 28, 2019, 06:29:29 pm ---At start bass is set at -6 so tweeter is ok. As I increase bass to +6 it starts playing bass from tweeter. So I guess the sound gets distorted correct?
The same with increasing sound at some point it starts doing it even if bass is 0.
--- End quote ---

What you are hearing is the higher frequency harmonic components of the bass distorting due to the amplifier clipping. 


--- Quote ---So there is no way around correct?
--- End quote ---

If you want to listen at a level greater than that amplifier will provide at a reasonable level of distortion (ie. before it clips) then you need a more powerful amplifier.  No amount of "filtering the lows" from a distorted signal will remove those high frequency components.  You're not really hearing the bass per se, you're hearing harmonics of the clipping caused by the bass, occurring at the beat of the bassline.

My preferred way of doing this kind of thing is typically with at least two amplifiers and an active crossover, which has many benefits, although cost or simplicity are not one of them.  :)


--- Quote ---Radio signal is horrible and I need dedicated amp and better setup?
--- End quote ---

The radio signal isn't your main problem, running out of amplifier power is.  :)

Ideally you want an amplifier that is powerful enough to drive your loudspeaker drivers to levels higher than you would ever want to go so that you never get any clipping distortion.  While this may be fine in a large PA system with 3000 watt RMS amplifiers feeding speakers that will burn up on more than 1000 watts continuous, letting you still have peak excursions well above what the speakers can handle continuously, that is not always practical in a car.

That's why I tend to use an active crossover on the line level signal, feeding to two separate amplifiers.  That way your mids and highs are still always undistorted as long as you have sufficient amplifier headroom, and the less noticeable bass distortion can run well into clipping, generating 10%, 20%, or even higher levels of distortion before really sounding messy, distorted and smeared.

If you use the same amplifier to drive your bass as your highs, you will notice the distortion as soon as it begins, as you have discovered.  :)

You can imagine how bad it looks on an oscilloscope when you can hear it...  :)

(Although, if you're listening to a sine wave, you can hear as soon as it touches clipping....)

Welcome to the deep rabbit hole of audio electronics!  Happy learning!  :)

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