The modification of the mid-bass dual 18" cabinets in the middle of each channel's array was completed at 2:00am this morning. Part of the design goal was to allow both drivers to share a common space. This has the effect of lowering Fc, while maintaining the benefit of mutual coupling to the vent. The dual vents in this modified design are much longer and tuned much lower than the single large vent in the old design. I was quite amazed that I achieved an Fc of 20Hz in such a small box! It actually goes substantially below that, which is a bonus I didn't plan on.
The new design is working out well, extending the low frequency response by another octave without losing much, if anything, on the upper end. While I was in the process of doing these modifications, I decided to replace the E-V 18B drivers that had been inhabiting these cabinets with the four Altec 3184 drivers, temporarily, until the Bassmaxx ZR-18s arrive later this month. (I got an e-mail from my supplier and he should have the four drivers ready in about a week for delivery to me.) The Altec drivers are a big improvement over the early E-V drivers, with a 50% longer Xmax and higher compliance. As such, with these modifications, the former mid-bass cabinets are now contributing copious quantities of sub-bass to the overall system output. I was listening to a Crystal Clear direct-to-disc recording of the Atlanta Symphony Orchestra performing at the Cathedral of Christ the King at Atlanta, Georgia, a number of organ and brass ensemble-oriented pieces. This recording has a nice balance on the low end and amazingly clean organ pedal sound, with occasional use of the 32' principal, rendering generous quantities of very pure 16Hz. The air is extra-strong with these low tones and the sensation is very overpowering--makes one get nauseous and weak in the knees. Everything that has any --even the tiniest --quantity of sub-20Hz energy in it is now very readily felt. Despite that extra sensitivity on the extreme low end, it doesn't color or add anything to the middle range. Piano stills sounds like a piano. But, oh, those organ pedals and close-miked kick drums!
The modification has eliminated the impedance rise at 20Hz, which means that real power is being used to produce that sound. This has resulted in circuit breakers tripping on the main power panel, more often than ever. In fact, the power sag problem is becoming a real annoyance. Line voltage is now dropping well below 100 volts on a leg, at the amp racks. Playing back a 16Hz organ pedal tone presents a continuous drain on the mains that internal capacitors cannot maintain for long. After the first 300mS, the energy built up in the capacitors is expended and the remaining power must come from the line. And our lights go dim, computers that are not on UPS backup reboot themselves and our headroom is drastically reduced from what it should be. I'm of a mind to just buy some 4awg copper cable, an outlet and just make a temporary high current feeder and string it across the ceiling until I can do something about the internal wiring. Our electric oven, stove and clothes dryer don't pull the line voltage down this much. When I installed the studio wiring in 1983, I never anticipated that Bass Pig would grow to use this much electric power! With the Bassmaxx ZR-18s coming soon, and their practically limitless power handling capacity, the need for more mains juice becomes more massive than ever.
I spent last night rewiring the breaker panels on the amplifier racks to maximize current capacity of the wiring and allocation of breakers/loads. In addition, I strung a temporarily 8AWG copy cable, doubled up, from the main breaker panel to the rack.
This had mixed results. The rack breakers don't tend to trip so easily now, and there is less voltage drop along the double 8AWG cables, but the line is still sagging badly--this time, at the breaker panel. Since there is about 200' of 3/0 wire between me and the nearest pole pig (utility power transformer), I may just have to live with this situation. I could put step-up transformers on the line input for each amplifier individually, however that only make the sag percentage worse. We have only 116vac on each leg here, not the 244vac that locals downtown have. Somewhat odd though, since there is a transformer near the end of my driveway. One would think that I should have 122vac per rail of the split-phase 200A service, but that simply is not so. I'll have to have a talk with the local utility about this some day.
But in the meantime, the modifications to the middle section of former mid-bass cabinets into low bass cabinets has continued to show its benefits during listening tests today. The system is effortlessly producing huge quantities of subsonic bass, which feels different than the usual bass, in that it affects breathing, produces the sensation of being lifted off the floor, and is just downright scary. I have also noticed that it's having an effect on my hearing. It's hard to imagine one's self going deaf from 16-20Hz signals, but the fact is, I noticed yesterday that my hearing is 'strange' with high distortion and a sort of resonant peak to it, noticeable when someone is speaking, or when I'm speaking. I used to think you had to be listening to screaming guitar solos to get ringing and other symptoms, but having achieved new SPLs at and below 20Hz, I am finding out that the ears can have a hard time with frequencies outside their pass band.
Affects on humans aside, the system sounds and feels great, despite my awareness that I cannot obtain enough electrical power to allow it to achieve its full potential. The output at 16Hz has increased by several orders of magnitude. It's cleaner than ever. Just gobs and gobs of undistorted 16Hz. And I'm not done yet. At this point, even the most insane bass freak would say "enough already", but the Pig has set in motion a plan, and when implemented, will push things beyond the absurd into the truly bizarre range, with the installation of the Bassmaxx ZR-18 drivers later this month. Perhaps my next investment should be a 450kW CAT diesel generator.
I decided to make some frequency response measurements, using the CEL 241/1 sound level meter, which has the benefit of a Flat setting for the meter frequency response. In this mode, the meter is flat down to 5Hz.
To make this measurement, I selected a preset on the DCX2496, which I created for pure crossover network with no EQ, limiters, time delays, etc. I disengaged any high pass filters elsewhere in the system.
I wanted to find out what "Destroyer", the former midbass dual 18" woofer system (that started life as a folded W horn believe it or not!) was doing with the modification to the cabinet design for lower vent tuning. I was quite surprised to see that I had surpassed my goal and achieved a -3dB point of 16Hz!
Even more amazing was the "Earthquake" double 18 system, with its extended vent length and subsonic tuning. It achieved -1dB at 16Hz. In fact, it's output at 100Hz and at 16Hz with the same electrical voltage across the input was identical. There was a broad 2dB hump from 85Hz to 30Hz, which accounts for the +/- 1dB.
I also did a room response measurement at the preferred listener position, 8' from the array. With room gain, the response was up 4dB at 16Hz! This was with no electrical boost--truly flat bass response, acoustically-achieved.
This discovery clearly proved to me that I no longer needed any electrical EQ compensation to flatten out the low end. No wonder the organ pedal tones were shaking the house off the foundation!
This discovery will ease the electrical power consumption issues considerably.
As I was listening at relatively high volume levels on several occasions, I noted some not readily explainable phenomena pertaining to hearing and temporal perception.
I was listening to Tomo Sakurai's "Adventure Life" the other day at very high volume levels. This tune has all its bass notes between 17Hz and 19Hz. And there was a lot of it in the air. Well as the bass ramped up in the early part of the song, the tempo seemed to be slowing down. At normal listening levels, this phenomena is not noticed--the tempo in the song is maintained. But during the high volume playback, it seemed to slow down as the bass got overpowering. It seems as if my perception of time was speeding up, making the tempo of the music appear to slow down. Previously, I used to think such distortions of time were only possible with drugs. I'll have to research this effect more.
The other effect that I've noticed frequently is easier to explain. During moderately high volume playback, if I take out my earplugs, the pitch of the music drops by about a semitone. I'm guessing this is an effect caused by the ear drum itself moving further and slowing down just a bit. But it's definitely a curious effect. Plug the ears, the pitch rises a little, unplug them, the pitch falls. Interesting stuff.
COUNTING THE DAYS
As payment has been sent to the custom woofer folks, shipment is only a day or so away, and early next week are expected to arrive, four specially-built weapons of mass vibration--eighteen-inch drivers that were built to my specifications. I've waited four long months for this day, and it's almost hard to imagine that it's happening only a week from now. These drivers were tested under the most grueling signal levels and power levels, and they are, for all practical intents, indestructible. In fact, two of these in each end subwoofer "Earthquake" cabinet will have a 6,000-watt RMS power handling and about 18,000 watts short term power handling. A mere Hafler, even ruggedized to produce more than its rated power, will be a pittance of drive power for these monsters. I'm looking at some used QSC Powerlight 6.0s as a possible choice to more fully utilize the CGN drivers. Of course, I still have to solve the challenge of getting enough AC electrical service to the building in order to power the existing amplifiers to their full potential!
I have some sad news: Sunfire Corporation, Bob Carver's brainchild, is no more. It seems that the company was bought out by a (possibly Chinese) firm which has no future plans for continuation. I was reading some discussion on the announcement at the Carver Audio web site. Gone is the service companies, as OEM parts have been removed from circulation by the new owners. This is a worrisome situation for Carver owners like myself. While not as much a concern for me, as I can do most repairs myself, the inability to obtain any custom specialized parts would be a serious problem. However, some research I did on my own revealed that Carver Audio Repair has taken over the repair end of things since March 31st.
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