Acoustat (1+1) + (1+1) = 2+2 with one pair 121B interfaces - diyAudio
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Old 13th February 2015, 12:17 AM   #1
Spiegs is offline Spiegs  United States
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Default Acoustat (1+1) + (1+1) = 2+2 with one pair 121B interfaces

Acoustat Query:

I have an opportunity to acquire (locally, I know it's amazing), another pair of 1+1's.
I am considering marrying them to my current and wonderfully restored/updated 1+1's that I acquired last summer. The only concern I have had to date with the 1+1's are occasional bass passages that will cause a static pop, even at low volumes. Folks in the know say this was a shortcoming with the 1+1 design. Perhaps true.

There was a conversation about adding panels to convert to a 2+2 to eradicate this condition.

So the question is if I buy another pair of 1+1's and mechanically marry them to the first pair wiring included (less the new pair's interfaces), and modify the bass wiring in the original 121-B interface to the orange pole (if I recall correctly), will this yield a better performing assembly? Will I have bass without subsonic passage static pops. Will the frequency spec be as per a 2+2 at 28-20K Hz @115 db or as per the 1+1 at 30-28K Hz @110 db?
Will the assemblage image as well as the 1+1's?
Will they image better?
Will they sound better, i.e. sound-stage etc.
The sound room measures 17x24x12h, so I have the space to suit a 2+2.

Please advise on all.
Many thanks,

Spiegs
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Old 16th February 2015, 01:28 PM   #2
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Quote:
Originally Posted by Spiegs View Post
Acoustat Query:

I have an opportunity to acquire (locally, I know it's amazing), another pair of 1+1's.
I am considering marrying them to my current and wonderfully restored/updated 1+1's that I acquired last summer. The only concern I have had to date with the 1+1's are occasional bass passages that will cause a static pop, even at low volumes. Folks in the know say this was a shortcoming with the 1+1 design. Perhaps true.

There was a conversation about adding panels to convert to a 2+2 to eradicate this condition.

So the question is if I buy another pair of 1+1's and mechanically marry them to the first pair wiring included (less the new pair's interfaces), and modify the bass wiring in the original 121-B interface to the orange pole (if I recall correctly), will this yield a better performing assembly? Will I have bass without subsonic passage static pops. Will the frequency spec be as per a 2+2 at 28-20K Hz @115 db or as per the 1+1 at 30-28K Hz @110 db?
Will the assemblage image as well as the 1+1's?
Will they image better?
Will they sound better, i.e. sound-stage etc.
The sound room measures 17x24x12h, so I have the space to suit a 2+2.

Please advise on all.
Many thanks,

Spiegs
This conversion is certainly possible, and would provide a step up to the most popular model in the Acoustat line. Bass response and dynamic capacity will be improved, but you will NOT completely eliminate the occasional crackle or pop on bass transients. But it will happen less often.

Imaging will be slightly decreased, but it will still be excellent. This was always a compromise with Acoustat's MK121 series: narrow models like the Model 1 and 1+1 had the best imaging but very limited bass capability, whereas wider models like the 3, 4 and 2+2 had greatly increased bass capacity but less precise imaging. This is a consequence of driving all panel area full range. This trade-off between models was largely addressed with Spectra's variable-area technology, where all models have nearly identical imaging characteristics, but with increasing bass response and dynamic capacity as the number of panels increases.

In regards to frequency response, you WILL have a Model 2+2, not something 'like' it, so your creation will have the same specs as a factory-built 2+2. By the way, the transformer tap should be adjusted from RED (for the 1+1) to YELLOW for the 4-panel 2+2. The ORANGE tap is intended for 3-panel systems. Other than the selection of the bass tap, there is no difference between the MK-121 used for the 1+1 or 2+2.
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Old 24th February 2015, 05:22 PM   #3
Spiegs is offline Spiegs  United States
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Hello Andy,
Thank you so much for your kind reply and I saw your posted note on the FB Acoustat Group too.
You saw that I did acquire the additional pair (for a song!).
I had another query about doing a quasi dry run running two 1+1's simultaneously (all four interfaces) via Siamese speaker wire split to each interface respectively. It seems to work! I was wondering if there was anything detrimental to the system (amp, preamp, interfaces) by doing this. I can clearly hear the difference between the non serviced interfaces and the interfaces that Roy worked on for me. Roy's are light airy, transparent and with greater range as compared to the newly acquired units, which sound dull comparatively.
So that was my first concern, split audio cable wiring.

Secondly, when committing to the conversion to a 2+2, my plan is to mechanically fasten the 1+1 frames together to unitize them.
I plan on a straight array, not unless someone tells me that a splayed array avoids a noise cancelling effect that occurs in a straight array configuration . If it's only a sound dispersion issue I will go straight array. If splayed is required what is the center axis angle to each panel, in degrees. Please advise.

I am also concerned about the best way to wire the new one plus one panels into the modded interfaces (Roy's). I want to do it right the first time to the best possible spec. What is the best (sounding) method to wire these over to Roy's interfaces. What gauge/type of wire is recommended and what process of attaching, i.e. solder wire leads from one to another or should I mechanically fasten plate connectors and solder those accordingly? Should the interface wires be connected to each other and have a midpoint tap that runs to the poles of Roy's interfaces, like a Siamese Y?

What do folks do about the base? As I don't have 2+2's I need to make a base. What were the working dimensions of the 2+2's bases? Is there a schematic layout somewhere? T-nuts will have to be installed from below to catch the interfaces. I can wing it, but if there are dimensions that I can follow that work, that would be helpful.

And as I will likely try to sell the non-modded interfaces, will I need to compensate for the loss of ballast weight back there so the speakers are properly balanced on their based and not susceptible to falling over. What is recommended here?
Thanks for your advice in advance.
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Old 24th February 2015, 06:56 PM   #4
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Quote:
Originally Posted by Spiegs View Post
Hello Andy,
Thank you so much for your kind reply and I saw your posted note on the FB Acoustat Group too.
You saw that I did acquire the additional pair (for a song!).
I had another query about doing a quasi dry run running two 1+1's simultaneously (all four interfaces) via Siamese speaker wire split to each interface respectively. It seems to work! I was wondering if there was anything detrimental to the system (amp, preamp, interfaces) by doing this. I can clearly hear the difference between the non serviced interfaces and the interfaces that Roy worked on for me. Roy's are light airy, transparent and with greater range as compared to the newly acquired units, which sound dull comparatively.
So that was my first concern, split audio cable wiring.

Secondly, when committing to the conversion to a 2+2, my plan is to mechanically fasten the 1+1 frames together to unitize them.
I plan on a straight array, not unless someone tells me that a splayed array avoids a noise cancelling effect that occurs in a straight array configuration . If it's only a sound dispersion issue I will go straight array. If splayed is required what is the center axis angle to each panel, in degrees. Please advise.

I am also concerned about the best way to wire the new one plus one panels into the modded interfaces (Roy's). I want to do it right the first time to the best possible spec. What is the best (sounding) method to wire these over to Roy's interfaces. What gauge/type of wire is recommended and what process of attaching, i.e. solder wire leads from one to another or should I mechanically fasten plate connectors and solder those accordingly? Should the interface wires be connected to each other and have a midpoint tap that runs to the poles of Roy's interfaces, like a Siamese Y?

What do folks do about the base? As I don't have 2+2's I need to make a base. What were the working dimensions of the 2+2's bases? Is there a schematic layout somewhere? T-nuts will have to be installed from below to catch the interfaces. I can wing it, but if there are dimensions that I can follow that work, that would be helpful.

And as I will likely try to sell the non-modded interfaces, will I need to compensate for the loss of ballast weight back there so the speakers are properly balanced on their based and not susceptible to falling over. What is recommended here?
Thanks for your advice in advance.
Driving two interfaces in parallel is generally not recommended, as it puts a real strain on the amplifier. But, the detrimental effects will depend on how loud you attempt to play, and the ability of your amplifier to drive low impedance and dissipate heat. There shouldn't be any harm done to the interfaces or to any other component.

I wish I could give you a more compelling explanation of why you should 1) build a new frame so that the side-by-side panels are as close to each other as possible, and 2) there should be a slight angle between the panels. Perhaps 20 years ago I could have explained it better. Suffice to say that every Acoustat speaker ever produced (except Spectras) had an angle between panels. That alone should be enough reason, but perhaps someone else can help me with the explanation, and also help me remember whether the angle is 6 or 9 degrees. I think it was 9 degrees on some of the earlier speakers, but was reduced to 6 degrees for the 2+2.

The wiring is straightforward, with all bias wires connected to the red interface terminal, all rear stator wires connected to the blue terminal, and all front stator wires connected to the white terminal. If you build a frame as I recommend, then you should already have enough wire length for each panel's wires to go directly to the interface. If not, use wire rated for a minimum of 10-kV to extend the wires. A small gauge is fine: the original wires are 24 GA.

The new base should be constructed in the same fashion as the 1+1 base, only larger. There are no published drawings that I am aware of. I would recommend adding an inch or two to the front and rear edges, and make the width as large as necessary to accommodate the frame width. The same interface was used on the 2+2, so 'ballast weight' will be the same as a stock unit.
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Old 24th February 2015, 07:32 PM   #5
Spiegs is offline Spiegs  United States
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Thanks Andy,

Thanks for the wiring info. I will digest on the frame suggestion, the jury is still out on the splayed panel design.
I think the panels will image better when aligned and not splayed.
Perhaps other Acoustat folks could chime in here and advise.

Spiegs
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