Introducing Closer Acoustics BLOCKS:
A modular loudspeaker system
Now that Closer Acoustics has been on the market for more than ten years—advocating for the sound of wide-band driver-based loudspeakers and gathering experience and feedback from our customers—I want to introduce a modular system for great sound that can be tuned to different tastes, room acoustics, and amplifier types.
Some members of the family are already well-known, namely OGY and BOBs (Bass Open Baffle) bass modules.
Now it’s time to introduce a new member - OKHO.
The story began with various experiments with open baffle systems. This led to a creation of BOBs, which gave the standard for the enclosure / cabinet or lack of it if you will.
The bass driver was designed for us - to be better adapted to open baffle system.
From the very beginning, however, I envisioned a duo or trio setup featuring the excellent EMS 12” wide-band driver used in our flagship loudspeaker, Vigo.
And now here it is - the OKHO, the central piece of the system. It should be paired with at least one pair of BOBs. To make it possible, and have the OKHO on the level of the ears, I designed another building block - the Blank. It is in fact a voided BOB cabinet. All blocks are of the same size which is very useful.
The basic system you can build is a Blank with a BOB on the second layer and OKHO on the top. If you swap Blank with BOB, and place BOB closer to the floor, the bass will be additionally reinforced by the floor vicinity.
The listener can choose between these two choices depending of the room at disposal and the taste. BOB closer to the wideband driver offers a pinch cleaner sound.
Now if we want even more of the foundation in low end then a second BOB can be added. Here I must to make a clarification I did many times with my one to one customer e-mail exchanges - which are an invaluable experience I cherish a lot. No, second pair of BOBs is not an overkill even in a relatively small room. This is an open baffle so no devastating boominess. Also the second pair of BOBs goal is not to go lower in frequency response but to give a delicate boost in the region from 40 to 200 Hz - providing this way a more reinforced bass foundation. You can feel it right away and more importantly once the second pair is removed from the system an instant feeling of missing emerges.
Having a Blank and two pairs of BOBs with OKHO makes possible another configuration: BLANK - BOB - OKHO - BOB. This changes the way the bass is presented in the room again. Which one is better? I do not know. It depends of the taste and of the behavior in a given room.
This is not mathematics where you know that two plus two equals four. I’ve seen it too often with countless presentations with different customers. One prefers this setup another prefers a bit different. That is not all, you can make BLANK- BOB - BOB - OKHO configuration too. Why or where? In a large room where you have ample space and a distant listening position (say, 4-6 meters), or if you want a nice, even, and full sound in a spacious environment.
All the blocks can be built up starting with the anti-vibration platform equipped with ISO Acoustics GAIA II footers.
The centerpiece is always a wid-band driver based speaker. We are now introducing OKHO, but in our lineup we have the OGY already. The beauty and simplicity of this system is that both can be interchanged. Bass Open Baffles or BOBs are tuned to serve both.
Why? The difference between OGY and OKHO is quite dramatic. The 12” driver 97,5 dB efficient with 34Hz resonant frequency with a whizzer cone installed in a U shaped open baffle vs 4” driver 91 dB efficient with 50Hz resonant frequency in 1 m long tapered transmission line. The big wide band driver is naturally matched to the bass below 200Hz whereas OGY blends so good in the same area because of its enclosure.
The sound differences: OGY, super fast, detailed and analytical, holographic 3D soundstage; OKHO much more relaxed, with a lot more body and flesh in the midrange and lower midrange, great soundstage too.
How it is possible to use them both with the same BOBs in a system with one amplifier given the difference in efficiency? Yes, I had to attenuate the 12” driver. To achieve this, I chose the best speaker resistors available—luckily made in Poland—Pathaudio +/-1% tolerance. (Constant impedance circuit).
If in any case this circuit needed to be by passed then it is possible by sending signal directly to the driver binding posts. In a normal procedure the connection is made by the pure copper binding posts wired to the driver binding post by Cardas 9.5 AWG pure copper wires.
This brings the topic of the BOB MK II. What did we change? Based on the interaction with our customers I decided to eliminate the BOB terminal which kept inside the inductance coil and distributed the signal to individual drivers, by Speakon connector on one side and two or three pairs of bare wires. In the MKii version each BOB has its own inductance coil of an even better grade integrated in the back of the driver, a pair of pure copper binding terminals that can accept spades, banana plugs, or bare wire. The wiring is made of 9.5 AWG pure copper Cardas wire to the driver pole terminals.
To make connection between the BOBs and OHKO or OGY the jumpers are needed. We made a special jumpers from 9.5 AWG pure copper Cardas wires with Cardas pure copper rhodium plated spades.
Also, based on customer suggestions, we added acoustically transparent cloth to the back of the blocks for dust protection.
The Blocks are prevented from sliding by brass pins, hence the holes you can see on the top of the sides.
Selected frequency response graphs
Non anechoic, room 5x6 m, H 3m, 1m distance / 2,83V
all connections parallel
No 1
BOB plus OKHO - Green line vs BOB plus BOB plus OKHO - Red line
No 2
BOB plus OKHO - orange line vs BOB plus OGY - Blue line
No 3
BOB plus OKHO - Orange line vs BOB plus OGY - Blue line vs BOB plus BOB plus OGY - Violet line
Selected impedance chart
BOB plus OKHO - Red Line vs BOB plus BOB plus OKHO - Violet line
Specifications
OKHO
Nominal Impedance - 8 Ohm
Power handling - 40 Watt
BOB
Nominal Impedance - 8 Ohm
Power handling - 100 Watt
OGY
Nominal Impedance - 8 Ohm
Power handling 15 Watt
Efficiency
OKHO - 91 dB
OGY - 91 dB
BOB - 94 dB
Combination (parallel connection)
BOB + OKHO - 4 Ohm
BOB + BOB + OKHO - 2,7 Ohm
BOB + BOB + OGY - 2,7 Ohm
Impedance - lowest point in the impedance 2 BOBs and OKHO - 2,2 Ohm at 85 Hz.
Power handling
General rule for power handling is directly connected to the primary monitor used. So if it is OKHO then max 40 Watts, if OGY 15 Watts.
In both cases whit common sense use it is largely enough even for listening in relatively big rooms ex 65 m2 with BOBs used for bass reinforcement.
Remember, you are always welcome to contact us for any advice.
Jacek Grodecki
