Description

Picture #5 is an old Windows 7 laptop used only for programming the Tact. My basic target curve is ruler flat down to just under 100 Hz where it slopes upward to +5 dB at 25 Hz where it starts it's nosedive. This is a 10th order subsonic filter only possible in the digital domain. This curve gives you the kind of bass sensation you get at a live concert without affecting acoustic instruments. This is also programmed to work in concert with the dynamic loudness compensation which I shall explain shortly. The BBC curve is identical except it has a notch filter centered on 4 kHz at which it is 2.8 dB down. This makes the harshness of some recordings disappear. I can switch to it by remote. Next You can see the subwoofer crossover curves over the basic target curve.  Then there is Dynamic Loudness Compensation. These curves look strangely like the Fletcher-Munson curves. It took over a year to get them just right. The computer hops from one curve to the next as the volume changes. Starting at 0 dB the curves change every 6 dB down to -42 dB. This uses a separate DSP from the other calculations and overlays them. 

Now the measurement curves. Aren't these supposed to be flat? Shouldn't they look the same? Well, they sort of do. Both sides take a nosedive at about 100 Hz. This is entirely because I chose transformers that sacrificed low end for top end. They follow each other up until 2000 Hz where the divergence becomes dramatic. This is all due to the room. There is a window on one side and not the other. There are blinds in place but still the high frequency response remains divergent. Next is the right channel and it's correction filter. The filter also takes into account the crossover. Above 190 Hz they are exact mirror images of each other.
The subwoofer measurements are actually extraordinary. Not only are they very similar but the response variation is at worst +- 5 dB. The response dropping as it heads down to 10 Hz is due entirely to the tight sealed cabinets. If I had made them a little larger the overall curve would have been flatter. Live and learn. Fortunately, the Tact can handle it easily and there is more than enough power to spare. Lastly, the right channel subs and their correction filter. Again, the filter includes the crossover and rumble filter. In the middle they are mirror images. 
The impulse measurements are not easy to understand by screen shot but, the computer arranges delays so that the sound of all speakers get to the listening position exactly at the same time and in phase. The filters assure that the frequency response matches the target curve exactly inclusive of the crossover. Over that is the dynamic loudness compensation which changes with volume. 

Programming target and dynamic loudness curves is actually pretty easy. Next is a picture of the programming function buttons, Add, Delete, Remove. This refers to the little red squares called "corners." If I press the "Move" button I can click on a corner and move it like the next shot. You can add, delete and move corners any way you want. The computer will tell you if you make an illegal move. Thus you have complete control of the frequency response of your system in 1 Hz increments +- 0.1 dB. All computing is done in 48 bit words at very high resolution.
The TacT will store 9 target curves in memory as well as 9 measurements. I can place the microphone anywhere in the room and take a measurement. The Tact will then treat that spot as the listening position and align everything to focus at that spot. I have measurements for my desk and the kitchen table. It is spooky to be way off axis and have a perfect image.
Lastly is the measurement screen. When you press the "Start" button there will be a selected count down, 2 seconds in this example. This gives you enough time to clear the area. The computer then pings each individual speaker 25 times (in this example) and averages the results. This takes 5 minutes to complete. Any extraneous impulse noise like someone putting a coffee cup down, will be averaged out but continuous noise like your AC running will get factored into the measurement so it is very important to have everything in the house turned off. Then Bill Murry drives a dump truck down your street ruining the entire measurement. 

The Sota. What's to complain about? Not much panache I suppose. Newer ones have a wood veneer top which is certainly better looking. I bought this table in 1982. It has never been back to Sota for service. It has been moved from Ohio to Alabama to New Hampshire. I just put a new belt on it. As measured by RPM on my phone. Speed 33.34,  wow and flutter  0.03%, Rumble is far lower than any LP. Pretty good for a 40 year old beater. Please do not message me about the Syrinx. There is already a 3 person waiting list

MS Tool and Woodcraft is me. I make gallery furnisher. I had almost two full sheets of Corian left over from a job. It is almost as heavy as granite but not as hard. It is much stiffer than any plywood or MDF. It is 1/2 inch thick. I was not happy with my second attempt at making subwoofers and it occurred to me that the Corian might make for a great subwoofer enclosure with the added benefit of not having to put a finish on it. Each panel is 1/2" Corian laminated to 1" MDF. The Driver is the 12" DVC Ultimax Dayton. Internal wiring is Kimber Kable. It is epoxied to the inside of the enclosure along its entire length except at the very ends. The driver is siliconed in place. Since it is mounted in the Corian it can be released rather easily. The enclosures without the drive are just shy of 200 lb. To make sure they are spiked to the floor through the carpet I get on top in bare feet and jump up and down. 
The enclosure design is such that the bulk of the mass is positioned behind the driver to neutralize any reactive forces. The panels are as narrow as possible making them as stiff as possible. The driver is positioned as close to the wall and floor as possible. The enclosures should have been about 6 inches longer which would have given me a flatter response curve but give that I have digital equalization it really does not matter. At any rate Model 4 is in the works.

I just had a bone graft from my right hip to my right shoulder. To sooth my misery my wife and daughter got me an automated Lazy Boy recliner and boy is it comfortable. I have taken a new measurement from it but in the reclined position I lose a lot of high end So, now I have to create a target curve for it. A recliner. Is this the modern way of putting you out to pasture? 

Inside the Acoustats are 4 panels. Each one is 46" X 9". To increase dispersion to the front the panels on the left are angled 10 degrees to the panels on the right. This means that on the back side all panels are aimed at the acoustic tile which absorbs all frequencies over 250 Hz. If you look at the crossover curve, the subs still have useful output up to 250 Hz. The computer delays the speakers so that the sound of all the speakers and subs reaches you at the same instant in phase giving the computer the ability to effectively deal with any problem here just by juggling frequency response. 
Dipoles have an hourglass radiation pattern. Line Sources beam vertically. ESLs beam horizontally. No power up, down and to the sides All this means that the only room treatment you need is directly behind the speakers. This is the only early reflection point.  Room control can easily handle the rest. Because the first floor of my house is open concept and the rooms are all staggered I have the Acoustics of your average small Jazz club like the Regatta Bar in Boston. 
I am tempted to add two reverb channels to the system which can be engaged to replicate the acoustics of a larger venue. The size of the venue can be "adjusted" by changing the duration of delay on these channels, the longer the delay the larger the venue. I know this will work already. My shop system is run off a Sonos Connect from the main system. If I leave all the doors open and turn the shop system up the effect is very cool on recordings like Waiting for Columbus. It is awkward because I have no control over the shop's volume or delay from the main system. To do it I will have to get a small DAC with delay capability and volume control, an amp and two small speakers. I was thinking plate speakers I could mount at the back of the room. I would run it off a digital out from the TacT. These channels have the subwoofer crossover and roll off from 125Hz so, I do not need much for speakers and 50 watt/ch would be more than enough. 

From a purist's perspective this system is a complete nightmare and not worth a second look never mind listen. Back in 1978 you would be preaching to the choir. I had an LP12 with an SME 3009 and Denon DL103. I took a Conrad Johnson Preamp and transferred it to a new chassis. All I left was a volume control, a selector switch and a balance control. The power supply was external and it had the power switch. An MC transformer was installed internally.  All the wire was silver. All the solder was silver. All the components were the best of the day. The Speakers were Acoustat Model X's. They had their own amps. As close to a straight wire with gain you could get. So, what the ---- went wrong? Does a Buddhist become a third world terrorist? No, doesn't happen. The Buddist learned 2 things. The room is just as important as the loudspeakers. Conversion between 24/192 to analog and back is totally and completely inaudible and the benefit from being able to work in 24/192 snowballs from there. 

It is not all about the music. That is another subject. It is about making the music sound better.



Read more...

Room Details

Dimensions: 90’ × 16’  X large
Ceiling: 8’


Components Toggle details

    • Acoustat 2+2 (Modified with custom bias supplies and Sowter 1:100 transformers)
    Full range electrostatic loudspeakers modified to run optimally between 100 Hz and 20 kHz on one transformer. This avoids the use of two transformers and a crossover network. Because these speakers are 8 feet tall in an 8 foot room they operate as line sources across their entire range.
    • MS Tool and Woodcraft Model 3 subwoofers
    These are 12 inch Ultimax DVC subwoofer drivers in sealed enclosures. The enclosures are constructed of Corian laminated to MDF both sides. Each enclosure weights just shy of 200 lb without the driver. They are spiked to the floor. The four subwoofers are positioned to form a horizontal line source ending at the side walls. Thus they perform as a line source down to 0 Hz. The drivers are kept as close to the walls as possible.
    • Tact Audio RCS-2.2x Digital
    This is a full function room control preamplifier. It's function will be described with pictures.
    • OPPO BDP 105D
    Pretty sure everyone knows what this is. Because my system doubles as a theater I needed to have something function as a video switcher/Blu Ray player and the OPPO is perfect in this role. It is only used occasionally for music. All my CDs were loaded into a hard drive and are played from there.
    • Audio Research Corp PH3 SE
    With RAM Labs Super Low Noise 6922's, a difficult Phono amp to better. It's only real fault is that it does not have enough gain for cartridges under 0.4 mv.
    • Apple Mini i7 / Channel D Pure Music
    Channel D Pure Music is a music server specifically for Apple computers. It uses iTunes, now "Music" as it's library.
    • Pegasus R2+
    6TB hard drive.
    • Benchmark ADC1-USB
    This digitizes the phono amp to 24/192
    • Sota Sapphire
    With a Syrinx PU3 tonearm and Clearaudio Charisma currently mounted. I purchased this turntable in 1982. Although it has not been used continuously over the years it still owes me nothing. It was recently pressed back into use and all I had to do was put a new belt on it and the wow and flutter dropped to 0.03.
    • Parasound JC-1 MONOBLOCKS
    These drive the Acoustats. You can't see them because they are under the floor
    • QSC Audio PLX 3602
    Two of these. Each subwoofer gets one channel, 1800 watts each. These are commercial two channel Class AB amps with switching power supplies. Damping factor 500. Gain is adjustable. They will drive loads down to 1 ohm without difficulty. They are fan cooled but since they are also under the floor this is no problem.
    • MS Tool and Woodcraft Audio Cables
    Canare Corp high bandwidth shielded wire for all balanced, audio and digital cables. 
    Canare RCAs
    Neutrix Gold SLR's
    Kimber Kable 8VS speaker cable
    Power cords are shielded two conductor plus shield 12 gauge with medical terminals.

Comments 2

128x128
Owner
The fans are to prevent the amps from burning the ceiling. JC1's in high bias mode get darn hot.

mijostyn

128x128
Interesting monoblock setup with the fans! A friend had active Acoustats back in the 80s.

noromance

Displaying all 2 posts