After a great deal of subwoofer testing over the decades I became subwoofer cynical for all of the reasons that you now. There is nothing more frustrating than wanting to get better bassosity in a small to medium size room when the acoustics of all rooms are weird at low frequencies. It is like trying to get an elephant into a bikini bathing suit.

Yet, is understandable that those of us who are dancing to direct heated single-ended triodes are missing the fundamentals of our dance beat, and we all know that single-ended transformer coupled amplifiers are as good at reproducing the lowest register as I am at playing golf. So why ask me to do something I am totally incompetent at? There is just no way, even with regulated power supplies (that create the best low frequency response) to equal the quality of push/pull amplifiers...and it is the price we all gladly pay for our amazing grace midrange.

The conventional speaker wisdom is that by eliminating the low frequencies there will be lower distortion in the midrange and this is true, but it is only a half truth. All tube amplifiers hate low frequency. In the lowest register is where we find that damnable low frequency dip in most dynamic speakers and the highest impedance ratios, i.e. the least uniformity of impedances. While our tube amplifiers are amplifying these low notes the power supply is very modulated and this is modulating the midrange.

By eliminating the Achilles heal, the low frequency signals from your single-ended output transformer, everything else it does, it will do much better. I can think of no other type of tube amplifier that benefits as much from this low frequency filtration...especially if you are not using a regulated power supply. This will translate into more of what you love in the midrange, better transient response and lower distortion and longer tube life, and you can use a much smaller coupling cap if your are using an RC coupled drive circuit, which will also give you more of what you love.

The secret to receiving all of these benefits can be had by all without using a separate electronic crossover...and I do not recommend using the crossover networks in any subwoofer, which is always solid state because you never want a solid state filter feeding your single-ended triode. All you need is one measly little capacitor of the right value in series with your input...which will give you a first order/6db per octave filter.

MR. AUDIO GIZ WHIZ TO THE RESCUE

By now you have read enough rave reviews about the Sunfire subwoofer to know that it has received universal "Gee Whiz how did Bob do that". For apartment dwelling audiomaniac or audiomaniacs with wives who also believe that "Less audio equipment is more" the Sunfire solves many problems. Bob is to be congratulated for proving once again that he is one of America’s most creative audio designers.

During my early years of audio addiction I too was subwoofer crazed and that was a good thing because as I sequed into the New York Audio Labs orthodoxy: Futtermans and Quads, subwoofers were a necessity. To address this we included a switchable first order (one capacitor) low frequency filter in the amplifiers. It cost about $3 worth of parts.

Both OTL and single-ended amplifiers share the same circuit characteristics and so I looked forward to experimenting with the Sunfire subwoofers.

Let me throw in an eccentric twist which has to do with the Sunlight Engineering 308s. Any driver that is ultra-high efficiency will never be able, in a non-horn cabinet, to reproduce the lowest octaves, so when I put the 308s in a "normal" box I knew I was not going to get the low frequency wave front I was able to achieve with the Tannoy horns. Would the Sunfires do the job?

I was experimenting with the Manley Retro push/pull/single/ended 300B amplifiers which produced about ten times as much power as these 108 db efficient drivers needed.

The answer is YES the Sunfires not only did a great job they beat out two other top rated subwoofers we were experimenting with, but I was not happy yet, because once you live with a horn system you want that low frequency magic.

Then I noticed a very large and heavy speaker stand in the corner of the control room at the recording studio where we were making these experiments, and decided to put the Sunfire subwoofer on the stand so that it was about four feet off the floor. Shazam! In all of my years of audiomania I had never tried to get the subwoofer as high as possible because we all know that we get more bass if the subwoofer is on the floor and in the corner...which is what Bob Carver recommends. But I am not searching for more bass, I am searching for integrated wholey bass.

So this is my radical no longer secret advice for using the Sunfire subwoofer: The way to achieve the most natural wholey bass is to get the subwoofer off the floor and as high as possible. Probably the ideal location is half way between the floor and ceiling, but that is impractical.

While there may be a number of other subwoofers that are small enough to get off the floor and onto a stand, I speculate that the bipolar radiation pattern of the Sunfire is also major contributor to its wholey bass quality

My intuition is telling me that by not bouncing off the floors there is less congestion in the room and you will be amazed at what happens when this congestion, that is typical of all subwoofers, disappears, and your single-ended triode will be much happier doing what it does best....the wholey midrange.

That was the good news. The bad news is that you are going to need a very heavy and strong stand because of the enormous energy that the Sunfire produces and you are going to have to firmly attach it with some kind of strapping, and you may have to put some sand bags on the base of the stand...but it is worth it...trust me. If you don’t it will jump around.

It would be a very keen idea for Bob to manufacture such a stand and make it available. The base could be hollow and permit you to fill it with sand.

THE $3 LOW FREQUENCY FILTER

What you need is a very small polypropylene or Teflon capacitor of the right value, which is determined by the input impedance of your amplifier. The designer of your amplifier can give you the value if you tell him the low frequency cut off that you want. I suggest between 80 and 100 cycles, but your experimentation with your system in your room will tell you what is best.

You can make these filters using a Radio Shack metal box and four RCA jacks.

All you have to do is wire the capacitor in series with the signal/hot. If you don’t know how to solder ask one of your audio bros to help you...nothing is simpler.

IT WORKS FOR MINI-MONITORS

I tried the same experiment with three different pairs of B&W mini monitors; at $250, $500 and $1000 per pair, using my 8 watt 300B and got the same excellent results in my small living room. Again the secret is getting the Sunfire off the floor.

All of you who already own the Sunfire subwoofer should pester Bob to make the stand. I know he will respond to your needs.

$20 THE CINDER BLOCK ALTERNATIVE

If you don’t want to spend money on speakers stands and want to build a set of subwoofer speakers stands in about ten minutes, then buy eight cinder blocks and stack them the long way. You will need four on each side. I suggest you paint them or decorate them in some manner. I think brown sounds best. Then all you need is two bungee cords of the right length. You put the bungee cords very lightly around the subwoofers and through the hole in the cinder block and connect the ends. You have now created your basic 100 pound stands which will give the best stability to your subwoofers, but may make your marriage unstable.