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Getting just enough

Paul's Posts — 21 June 2012

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Getting just enough

In the late 1970′s I began experimenting with planar loudspeakers: first with Magnepans and later with electrostatic loudspeakers – specifically the Acoustat 2+2 which happened to be tall enough to qualify as a line source.  If you’ve never heard an electrostatic loudspeaker then you’ve missed out on an amazing experience – albeit one that is very limited – that of a window-like quality of “you are there” midrange.

We used to joke that with an electrostat you had to have your head held in a vise to enjoy the benefits – so narrow the sweet spot of these products.  But when you were in the zone they could be rather amazing – so light is their diaphragm that their transient response is nearly instantaneous.  They had other faults and benefits as well, chief amongst them was a lack of dynamic range and bass.  It was to this latter quality I address this post.

After acquiring the 2+2 pair I quickly became unhappy with their limited dynamics and low end and was ready to sell them and move on when by chance I happened to be standing next to the panels when they were playing.  I noticed that standing next to the speaker there seemed to be an enormous amount of bass present that apparently wasn’t being projected into the room.  Instead, the flimsy wooden panels were themselves wobbling to the bass and hence little of that energy was being transferred into the room.

The solution seemed obvious: brace the panels so they didn’t move and the air in the room did instead.  To do this I built a bracing system out of 2×4′s and screwed it into the panels – a good solution but ugly and much to the horror of my ever loving and forgiving wife Terri – as these were in the family living room.  I lived with the improved results for some time but eventually hated the look of this contraption as well and dismantled it.

I decided it might be worth while to augment the bass instead – with a subwoofer – of which at the time there weren’t too many of any quality.  I happened to have a low cost M&K sub hanging around and added this to the right side of the system – the right side being the correct side always when a single sub is chosen because of where the bass instruments reside in an orchestra.

I spent the day moving the sub around turning the volume up and down and could never quite get the thing to integrate with the panels – until at one point in my adjustments I nailed it.  It integrated perfectly!  True, in this setting there wasn’t much bass but dang if it didn’t integrate seamlessly with the panels.

It was when I went to the rear of the sub to write down the volume setting that I noticed I had actually set it to zero.  No wonder it integrated so seamlessly.

I put the 2+2′s up for sale the next day.

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About Author

Paul McGowan

Paul McGowan is the CEO and co-founder of PS Audio Inc. a Boulder Colorado design and manufacturing company of high-end audio products and services. McGowan has been designing and building high-end products for nearly 40 years. Hobbies include skiing, music, hiking, artisan bread baking, kick boxing and cooking. He lives in Boulder Colorado with his wife Terri and his 4 sons.

(6) Readers Comments

  1. Soundminded

    June 21, 2012 at 3:13 am

    The first electrostatic speakers I ever heard were KLH Model 9. Electrostatic speakers have always had a special niche in the minds and hearts of many audiophiles. Many consider the Quad ESL 57 or ESL 63 the best loudspeaker system ever offered. The first Infinity speaker I’m aware of was the Servo-Statik 1 and later 1A which consisted of a pair of 2 way electrostatic panels meant to be bi-amplified and a single servo sub-woofer with its own servo amplifier. This was in fact the first sub-woofer I ever saw or heard of. A modern exponent of electrostatic speakers is Martin Logan.

    Unlike dynamic loudspeakers which are actually linear eletromagnetic motors, electrostatic speakers rely on the repulsion and attraction of capacitor plates charged with a high voltage DC bias from a power supply. Their large sound radiating area compensates for their limited travel capability to produce acceptably loud sound, they are in effect the equivalent of a large surface array in their radiating pattern. This and not their supposedly low harmonic distortion is what I ascribe their characteristic sound to. Integrating them into rooms presents difficulty and they have other problems besides limited dynamic range. As dipoles they need to be placed some distance from a wall behind them to allow their rear radiation room to propagate and bounce. Their high frequencies often beam over a narrow angle explaining their limited “sweet spot.” This is often compensated for by adding a line array of ribbon tweeters. Their bass is notoriously weak which is why dynamic subwoofers are often added. Large, expensive, they seem an impractical solution for a home sound system but many accept those limitations and like them. Personally I’ve never thought of them as something I’d want to own. I’d prefer to build and experiment with a large multiway surface array of dynamic drivers. I always thought it would be interesting to compare the results to see how close I could come.

    If I’d been confronted with the flexing problem of the TNT’s wooden frame, I think I’d have stiffened it by screwing lengths of L ur U channel aluminum to it. Light, strong (pacticaly unbendable), paintable, inexpensive, it would not have offered much visual impact and should have worked.

    The last electrostatic loudspeaker I heard was ML Summit ($10,000) five years ago in a system consisting of a Krell power amplifier and McIntosh preamp and CD player. The recording was the dealer’s, a performance of a violin and piano I wasn’t familiar with but I do know what these instruments sound like. I heard five serious FR errors, a number even I was surprised at.

    The one contribution Floyd Toole gave us that seems to me of real value was his experimental results demonstrating that for most rooms uniform bass response can be obtained by placing four subwoofers in it, one in each corner. An alternative is to place them on the middle of each of the four walls. A single subwoofer can result in serious difficulties. Surprisingly, few audiophiles ever seem to incorporate this finding into their own sound systems. Two pairs of side firing 12″ subwoofers on the short wall in my main sound systems results in deep bass that varies within the room often from strong to overwhelming. This can be as objectionable in its own way as not enough bass. Equalization and two levels of switchable low cut filtering helps. Another two speaker sound system a a room half the size suffers a similar shortcoming in uniformity within the room. The more capable the speakers are of producing deep bass, the more evident the problem becomes. Perhaps I should try a dose of my own medicine.

  2. Ed S

    June 21, 2012 at 9:35 am

    I owned the 2+2s for a couple years too and basically confirm your experience. But still, on voices and midrange, they were as pure as anything made today. I’m glad I had those 8′ monoliths, which everyone though were room dividers!

  3. June 21, 2012 at 1:42 pm

    I used both the 2+2′s and the Monitor 3′s for quite some time. The panels do go flat to below 30Hz. If you couldn’t get good bass out of them there are two possibilities, one is that you’ve got them in the wrong location in the room (or simply a bad room). The other possibility is that your amps did not enjoy the load they saw through the Acoustat transformer interfaces.

    I got around this second problem by driving the panels with highly modified versions of the original Acoustat OTL servo-charge amps (no interfaces needed). With those amps the Acoustats were among the best sounding systems I’ve ever used. I remember once throwing in a Paradigm Servo 15 subwoofer but as I recall it did very little work and didn’t contribute much to the overall presentation.

    But the Acoustats could actually rattle things if you had them set up right . Their bass was fast, articulate and full. I will say that the wider panels did have a bit more apparent midbass… so although the 2+2′s went a little lower than the 3′s, the 3′s had a little more plump to the bass. Some of my friends were actually using Acoustat 6′s with the tube servo-amps and they really put out some impressive bass (although you needed a large room for them).

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