Monday, September 21, 2009

Speaker filter

Original Post (September 2009)

Here are some pictures of my DIY speaker filter inspired by several threads on Audioasylum.

Very much like the Combak Enacom or the Walker High Definition Links, these are R-C networks or zobel networks that are applied in parallel across the speaker or the amplifer if you prefer (although they usually work better across speakers).

They will filter out ultrasonic garbage that happens to be in your system and their efficacy across the band depends on the value of capacitor and resistor that you use.

Why this project ? More out of necessity rather than vanity. The Alpha-Core Goertz speaker cables I use have much higher capacitance than average, enough to upset some amplifiers into oscillation. I thought I heard my AG1 speaker cables induce a hazy grain on the top end of my Hypex amplifier the other day. Maybe it was my imagination, but it was frightening enough to get this project up pronto. Zobel networks, besides their filtering effect also stabilises amplifiers.

Since this is a prototype project, I left this quite simple with a 10 nF and 1 nF cap, each in series with a 10 Ohm resistor.

It was really a surprise how much difference this simple device makes. There is a distinct clearing up of the sound, especially in the focus and articulation of the midrange. Vocals in particular sharpen in image size and the texture of the human voice becomes easily discernible. High frequency hash and the mess that happens when the recording mix becomes too heavy are cleaned up substantially by this.

Try it ! Its cheap, effective and really works.

Revisting the speaker filter - 4 years later (October 2013)

After a fair amount of experimentation using terminal blocks and spare capacitors, I made a second version of the speaker filter.

First off, the choice of capacitor is critical. The typical audiophile plastic foil capacitor does not work well here. I tried using a suitable value Multicap RTX and Vishay MKP 1837 but the results were underwhelming. Please stick to parts suitable for high frequency application like suppression caps, ceramic or silvered mica caps.

Secondly, it pays to utilise the other high quality parts and techniques recommended on Audioasylum, such as solid silver wire leads, and shielding the box - they really do make a difference. I am not sure whether the resistors make much difference, but I used 1% PRP resistors as recommended.

This filter sounds even clearer and more resolving that the initial set made. Soundstaging is particularly wide, and imaging is absolutely pinpoint. Go for this version if you can.

My audio buddy TC made a version using 3 stacks, i.e. 10 nF, 1nF and 0.1 nF but found it too dark. He removed the 0.1 nF capacitor and liked it a lot better.


Tianci said...

Give those audiophile brand filters a run for their money :)

Rui Umbelino said...
This comment has been removed by the author.
Rui Umbelino said...


Do you still use this filter?

Using a 0.01uF of Mundorf or Auricap should give better results...


Eric said...

There seems to be a lack of consensus on this matter.

Some feel that caps suited for high frequency application like silvered mica, or suppression caps would work best. The other school of thought believes that boutique polypropylene caps would work best.

My filter was made using Rifa and Wima mains suppression metallized paper caps.

If I have some time, I will try a basic filter using boutique caps and resistors and will report back.

Rui Umbelino said...

Since this is already the music signal, maybe is better to use a good capacitor...
Even in AC we have better results with boutique caps, so...

Let us know your results with a better cap. ;)


Rui Umbelino said...


Do you already have some results?


Eric said...

Rui, I've procured a 0.01 uF Multicap RTX and 10 ohm PRP resistors. It's running in now. I've also got the Vishay Roederstein MKP1837 (which is very popular as a bypass cap). Will report back in a week or so.

Eric said...


It's a no go for boutique caps. The Multicap RTX sounds inferior to mains suppression caps or a Cornell Dubilier silvered mica cap. Maybe I'll try running in the RTX some more.

Rui Umbelino said...

Thanks for your try... ;)