3 way without inductor?

ShaneF

Member
2015-12-02 4:42 pm
I was introduced to a person recently who -to my understanding- had created a way to generate a 3 way loudspeaker without the use of induction coils. According to him, his project was realized by only using multiple capacitors... and by multiple, I mean many, many, many capacitors,

He told me that he was able to achieve his goal through a lot of multi-amplified and digitally-processed bi and triampification which, of course makes perfect sense, when filtered through some rather exotic signal processing.

I was quite confused by what he presented to me. If he is using several amplifiers, and it is digitally processed, this makes perfect sense to me. There is nothing new here. It is akin to an electronic crossover. Hardly earth-shattering and new, conceptually. But, I am still confused by what he was speaking about.

Capacitance and no inductance.
 
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Just a multi-way active speaker with dsp control for xo etc.
Minidsp is very popular https://www.minidsp.com/applications/digital-crossovers/stereo-34way-xover
three-way-plus-sub.png
 

AllenB

Moderator
Paid Member
2008-10-18 11:31 am
The thread title reminded me of a phase I went through building passive crossovers without using capacitors.

Inductors are not terribly practical, nor essential in electronic filters such as a line level crossover. The fact that your friend specifically mentions them suggests to me that he is making use of the analogue variety of active filter.
 

Ron E

Member
2002-06-27 10:41 pm
USA, MN
You can make a passive lowpass filter with a capacitor and a highpass with an inductor (both opposite from how it is normally done) but either involves a series resistor and some insertion loss. I suppose you could set yourself a challenge to make a capacitor only passive filter, but it likely wouldn't be practical, IMO.

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/filcap2.html
https://en.wikipedia.org/wiki/RL_circuit

Active filters generally use only caps.

There are many cheap 3 ways that only have series caps on the midrange and tweeter ;)
 

infinia

Member
2005-05-15 9:51 am
SoCal
It can be done passively.. it's all about driver selection
yes this was (is) done all the time, seen em on Yamaha low end 3way speakers. their mids are pretty sweet!
can usually spot the concave dust caps to limit high end on-axis response in mids and woofs. Special papers and doping helps cone break-up too IMO It's all about limiting the upper end response to "pistonic" motion , so the on-axis to off-axis response tracks well.
it'd be a disaster with fancy metal cones and pole pieces
 
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If you're padding down a mid/tweeter by use of a series resistor or L-pad, placing a parallel capacitor will achieve a 1st order low pass. It's just an RC filter instead of RL or LC/RLC.

The downside is that the impedance drops at frequency increases, and it's difficult to implement an electrical 2nd order lowpass filter without inductors (RC cascaded with another RC) unless you need to pad down the mid/tweeter a lot (10dB+), or you live with presenting an unusually low impedance to the amplifier. Using RC high passes most of the time is not practical as the capacitor will have to deal with heavy currents from low frequency content, neither the amplifier, capacitor or resistor will be happy about that.

In low cost commercial speakers using RC filters where appropriate is a valid technique to reduce cost (inductors are expensive, capacitors are cheap), especially to get 'another order for almost free' in a filter design. A 1st order lowpass may also be enough if the driver already has a steep acoustic roll-off. It's pretty dumb to try to use it to avoid inductors completely though.
 
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