Saturday, February 11, 2012

Tweak #1a you can do on almost any speaker

Saturday mornings are clm in our household. I can be reasonably assured that only the sound of the grandfather clock will disrupt the sweet sounds streaming from my old Bozaks. Mozart first thing in the morning - what more could one ask for?

So back to audiophilia. Let's start with speakers and a little remembered article I read in the Journal of the Audio Engineering Society (JAES) back in the 1980s. The JAES is the pinnacle of electronic publications and if one is published there, those contrubuting engineers have pretty much "made it to the top," at least as recognized by their peers.

A well known loudspeaker company discovered that minute vibrations occurred in the baskets of their drivers as the piston moved back and forth. Lasers had just been drafted into measurement techniques and polishing the basked and watching the reflections with sensitive optical detectors easily showed when and how such vibrations occurred. Such vibrations, once resonance is reached, contribute to the distortion generated in the speaker itself. Hmmmm...very interesting. So as the piston moved back and forth, faster and faster, there were certain resonances occuring that sympathetically exaggerated or diminished the sound coming from an otherwise perfectly linear diaphragm.

This company tried many, many different methods to eliminate this artificial contribution to distortion by changing the thickness of the frame, going to exotic metallic compositions, using cast instead of stamped frames, but although in theory everything they tried SHOULD HAVE WORKED, the measurements showed only MARGINAL IMPROVEMENTS.

What they had discovered was any loudspeaker they played was literally gyrating on the baffle board regardless of the style or type. After numerous failed attempts at eliminating the problem, someone looked at it from a different perspective - a different point of view (sound familiar?). I will tell you what was finally figured out that caused these undesired resonances at the end of this article but see if you can come up with your own idea in the meantime.

Now to me, this was a ground breaking discovery and one that I thought would be immediately adapted by every loudspeaker manufacturer in the world.  However, it pretty much went unnoticed in the audio industry (maybe audio engineers are too busy listening to marketing tell them what to design rather than reading how others solved problems, who knows).

I was working on the model 24 speaker at the time, a floor standing 3-way 12", and decided to try what it is they discovered. I applied the trick to the woofers and could not believe my ears. although the change was at first subtle, once I knew what to listen for I could hear its effects. The sound at first was interpreted as being quieter, that is less loud, and as a result the change was initially undesirable. But I persisted and allowed my saddened ears to adjust from what I was "used to" to what I now heard.

There is much that can be said for maturity and patience when raising children or learning to play an instrument or whatever. When it comes to my stereo, patience sometimes is not one of my strong points and I tend to let my personal acoustic biases get in the way. Instead of asking myself "does it sound more real?" I was asking myself "does it sound better?", and which is the better question to ask of the two? You decide this as an audiophile.

After a short time, a period of adjustment let's say, I began to hear things that I had not noticed before. Yes, the overall sound seemed a bit less loud but what arose from the background were inner details the speakers were always capable of reproducing but never given the chance because of these resonances. Resonance in box designs is a well understood issue today but resonances in speaker drivers not so much. It is a mystery to me why everyone does not embrace this simple solution. It may be that the ego is involved and lord knows that audiophiles and audio engineers especially have some of the biggest egos on the planet. But for whatever reason, here is what was discovered and it takes no ego to at least try this trick. Here we go:
  1. Remove the speaker grill and count how many screws there are holding the driver to the baffle board
  2. If there are more than three, there are too many. Remove all screws except for three resulting in as close to an equilaterl triangle pattern as possible (or Y-shaped pattern with say one screw on the top and two on the bottom)
  3. Replace the grill and turn on some music to which you are intimately familiar.
  4. See if you can hear a difference.
Remember that not all things are immediately obvious so be patient and listen carefully. Play a variety of music and notice what it is that you may hear.

Yes, the trick is a three-screw mount. How many points does it take to define a single plane? Three. This is the theory behind how basket resonances are better controlled in mounting a speaker to a baffle board.  In the model 24, there were eight holes in the woofer basket and so I put in eight screws to hold the woofer in place. What I did is what anyone in the industry assumed at the time and that is "more s better." Well, in this case, less is better and something that runs contrary to generally accepted designs. Below is a picture of what I did to my Bozak B-209A midrange driver to transform a four-hole mount to a three-hole mount (I drilled a new hole midway between the top two holes).

You can now understand why I was appalled - and I still am today. You can see who has read this old JAES article by looking at a speaker and who has not; it's as simple as that. Regardless of what the marketing group has developed to proudly proclaim the benefits of a new design, the fact is this: if there are more than three screws holding a driver to a baffle board, resulting resonances in the driver frame itself will color the sound, period.

The good news is that in some cases you can try this tweak without voiding warranties or compromising designs. Take off your speaker grills and try this for yourself, remember that you can always "back it out," so to speak if you do not like what you hear. Know that there may be tiny holes through the baffle board to the inside of the box as a result of removing these screws that should be plugged up if you decide to leave the screws out after your evaluation. A dab of Silicon Caulk should do the trick nicely.

Wait...there's more. Next time I will tell you about the second half of this trick.

Yours for higher fidelity,
Philip Rastocny

I do not use ads in this blog to help support my efforts. If you like what you are reading, please remember to reciprocate, My newest title is called Where, oh Where did the Star of Bethlehem Go? It’s an astronomer’s look at what this celestial object may have been, who the "Wise Men" were, and where they came from. Written in an investigative journalism style, it targets one star that has never been considered before and builds a solid case for its candidacy.

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