Article by Bill Gaw
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Welcome to another meeting of Audiolics Anonymous, our support group for the insatiably TWEAKED. Today, I want to discuss my latest home built project- a pair of subwoofers. I know. I already have two VMPS Audio large subs, each of which has a 15 and 12 inch driver and 12 inch passive, and two HSU Research 7 foot tall 12 inch units. So in my 17x28x14 foot listening room I have plenty of bass, but I have always disliked it. It tends to be deep and strong, but flabby. At first I blamed it on my room, tried all sorts of fixes, and nothing improved the sound. The HSU units are ported and the VMPS units use the passive driver, and both types of enclosures, while extending the bottom end, tend to loosen up the bass produced. Each had a Q of about 0.9, and, after sitting directly in front of the tympani in orchestras, I prefer tight bass with a Q of about 0.5. I had looked at several powered subs, but couldn't believe their prices. Enter my friend, Kwami Ofori
Asante. He had had a pair of subs built for him by a "speaker expert" who worked for a well-known speaker manufacturer from the Boston area, using a NHT 12 inch sub driver each . He didn't like the sound of them in his room, and decided to dump them on me.
When I first hooked them up, I had to agree, they sounded just as flabby as my units. And, unhappily I made a boo-boo. I was driving them with my Crown Macro Reference amps, and like an idiot, disconnected the preamp to amp interconnect while the amp was on. Both units made a great guttural sound, the drivers pushed out to their limits, the voice coils left the gaps, slammed back down, and refused to return. So much for $300 worth of drivers. When I called NHT for a possible
re-cone, shock number two occurred- they don't do it. They claim that all of these drivers are built to tight specs, and they won't
re-cone them. But they would be very happy to sell me new ones.
Being the tweaker that I am, I removed the drivers to look inside the cabinets. Each was 2x2 1/2x4 feet outside dimensions, with double thick walls of 1 inch MDF and good internal bracing. Thus they were worth saving. Internal dimensions gave 9 cubic feet of volume. This seemed a little high for a 12 inch driver, so I went up to the NHT web site, and found that this driver prefers 2.7 to 3 cubic feet of space. So the supposed expert who built this cabinet was off by a factor of three in the volume. Thus the flabbiness of the bass. What to do? Why, buy 8 more drivers of course, at $150 a piece, four for each cabinet, two in front and two in back, hooked up series-parallel, thus giving the same 6 ohm impedance of one driver, with four times the output, 1/4 of the distortion of one driver, and 1/4 the risk of destroying a driver the next time I did something stupid. Also, by adding more fiberglass stuffing, I was able to bring the Q of the system down to 0.5.
How do they sound? Deep, tight, and mind blowing. Flat to about 22 Hz, with at least 112 dB output, at which point I backed off due to heart palpitations and a felling that involuntary defecation was about to occur. Drawback? There was too much bass in the 40-50 Hz. crossover range. I sat there for a couple of days trying to decide what to do with this- rebuild my crossovers, move these behemoths around the room, power them down and lose the sub bass, etc.
Epiphany Number 1. It dawned on me that I had extended the output of my bass horns below 50 Hz. by using Golden Flute bass extenders. This mated them well with the VMPS units, but was obviously too much in the crossover area with the faster NHT drivers. So I removed them. Immediately the 40-50 Hz hump went away, giving the tightest deepest bass I have heard in my room. Interestingly, the lower mid range opened up. I guess the Golden Flutes had affected the upper end output of the bass horns in the 200-350 Hz. range.
Thus, several things were learned from this experiment. First, for the tightest bass, use sealed enclosures, just make them big. Two, never trust even supposed experts, including yours truly. Do your own research, and tweak, tweak, tweak. Third, each change in a system may affect completely separate and seemingly non-connected pieces of equipment. So if the experiment doesn't do what you want, see if a change in the rest of the system will help. Fourth, never refuse a gift. Fifth, it takes a lot of driver and a huge cabinet to produce truly good bass. There are no shortcuts or substitutes without in some way damaging the final product. There's no substitute for a full Concert Grand.
Last Saturday, I got a chance to show off my system to two persons who are definitely high end nuts; Steve Klein, owner of
Sounds of Silence, of Nashua New Hampshire, and his associate, Art Katsikas. Steve has been into high end audio for many years, and, as with many of us, got bit with the tweaking bug. His bugaboo was trying to decrease distortion associated with vibration transmitted to equipment from the shelving they sat on. As can be seen in my column on this topic, CHAPTER 2, Unwanted Acoustic Vibration
Chapter2), this problem probably produces more distortion to the signal than anything short of a mistracking cartridge. Steve's fix was to begin using and then selling the
Vibraplane, a very heavy air loaded isolation platform originally developed to isolate electron microscopes from environmental vibrations. This product was such a success, that Steve then became a distributor for other super high end products, now including the
Beauhorn, Kondo-san products, Simon Yorke turntables, Crown Jewel cartridges, etc. Art's part time job is as the set-up man for Steve. And boy, do both of them have great ears. They brought along several records that were breathtaking in their closeness to live acoustic sound. Happily, one of them, a violin solo album by Ricardo Ricci, was left behind, and, hopefully, forgotten.
Anyway, the reason for their coming over was to demo a new amp he was thinking of selling to see how it would sound on my horns, and, I have a hunch hoping to see if they could interest me in a pair. The amps are constructed as either single ended monoblocks or stereo on one chassis, made by Jeff Korniff Designs, and use, believe it or not, the 70 year old TYPE 45 output tube, with a whopping 1-2 watts of brute force power. They use tube rectification, and a 6SN7 driver tube, and transformers that look suspiciously like they were produced by my friend Jack
Eliano, of ELECTRAPRINT AUDIO from Las Vegas,
The stereo model that they brought had a silver metal chassis and average run of the mill parts, and thus the outcome of our listening was a surprise. At least from 300 Hz up, where I used them on my Edgar round horns, they really kicked butt. Compared to my 2A3 based home built Bottlehead amps, they presented a slightly deeper and wider sound stage, with possibly a tad more information coming through. They were also a tad sweeter, with maybe a slightly rolled off top end, but then they could be flat and my amps could be causing a rise. They were also about 6 dB less sensitive. Anyway, they really sounded great in that range, and Steve says that on his Lowther based
Beauhorns, which he also sells, they kick ass down to at least 40 Hz. I can believe that, as I am familiar with Jack Eliano's transformers, which are built to give deep tight bass. Considering that the parts quality otherwise was not up to high end standards, I can imagine how they'll sound when tweaked. One thing about single ended amps: each part makes a tremendous difference. And happily, Steve is willing to have these things constructed to your specs, for a price of course. While the base price has not been set yet, it will probably be in the $3000 range for the monoblocks and $2300 for a stereo chassis. That's $1000 per watt. But oh what a watt.
Epiphany number 2. It amazes me, that the further I go back in audio antiquity with tubes, the cleaner and more beautiful the sound becomes. The 45 is two generations back from the 2A3, which is two generations back from the 300B, which is a generation back from 845 and 211 tubes. Is it the simplicity of the tube design, the quality of hand workmanship that went into these things, or the easily controlled low wattage that causes this? I don't know. All I can say is that now I understand what some of our older brethren love about this tube. Unhappily, unlike other ancient tubes, the construction of which has been resurrected, the 45 hasn't been made for 50 years. Doc Bottlehead, on his bulletin
BBS), has suggested the possibility of a company doing a run of these tubes, but who knows whether it will come to fruition, and how the new tubes would sound. So there might be a little worry from the purchaser of this amp, whether there would be tubes available when the ones supplied with the amps give up. All I can say is that when driven conservatively, they will probably last ten or more years. That brings the cost of the amps down to $100/watt/year. And who of us tweakers has an amp now that we've had for that long? And there are 45 tubes out there which have been run in equipment for much longer than that. So don't fear the obsolescence of these amps. And remember, single ended amps are made to be tweaked, and with parts changes, other tubes could be substituted. A tweaker's dream.
Was the amp that much better than mine that I would make a switch. Nope. There's still that pride of ownership in something self-made that keeps me from the switch. On the other hand, for those who don't feel comfortable building their own, this amp is a great one to own if you have the right speakers for it- at least 100dB/watt efficient. I have recommended it to my friend
Kwami, he who gave me the subs, who has also bought a pair of Beauhorns from Steve, so hopefully I'm right in my judgment.
Oh, how did they like my system. They were pretty tight lipped, but they didn't ask me to shut it off. And they stayed for four hours. And this was in the middle of the day, when the system only sounds so-so. Also, the subwoofers were at the destroyed stage, so I was just using my bass horns with Golden Flute extenders, which made them flat to about 35 Hz.
Well that's it for this month. Sorry it's so short, but I'm off to the Consumer Electronics Show in a couple of days, where I hope to spot some goodies to take up my spare time for the New Year. Please look for our same day write-ups at
www.enjoythemusic.com/ces2001. Good listening.