Early reflections:

• Off-axis frequency response should in general mimic the on-axis response.
• The far off-axis response should be equally similar. Primary reflections are often between 45 and 90° from the speaker. This will make the speaker stand out from other speakers.
• The speaker should have uni-directional radiation to get rid of front-wall reflections as this causes the most problems. Unlike with side wall, floor or ceiling reflections, the time delay remains practically constant when the listener moves. Therefore it is psycho acoustically far harder for humans to separate reflections and original sound.

Later reflections and reverb:
• These should be smooth and only gradually increase the power response.

Time domain:
• Smooth impulse response with minimal diffraction makes for cleaner more effortless sound. It also helps to keep the frequency response within the listening window more constant.
• Time-aligned drivers for optimum crossover summing.
• Correction of crossover phase distortion with inverted all-pass filter. Minimum-phase behaviour.

• Low distortion drivers.
• Dynamic range, high power handling, oversized amps for non-compressed transients and high S/R ratio.

Room interaction:
• Ray acoustics are the domain of specular or mirror-like reflections and should be considered. Wave acoustics are the domain of room modes like standing waves. The above are related to the Schroeder frequency. Above the Schroeder frequency, the speaker is dominant and works in the ray acoustics domain. Example: a speaking voice has the same character independent of the listener or the speaker location. The voice has the same character in different acoustic environments and is still recognizable and still intelligible. Below the Schroeder frequency, the room and its modes are dominant. This is the domain of wave acoustics. Certain notes dominate and boom, others are too weak. At the transition region, primary reflections and comb filtering play an important role, especially front-wall reflections. Conventional speakers are omni directional in this region.
• DSP room EQ should help match the quantity and extension of the speaker's output to the room's gain and should notch standing waves.
• No DSP filtering above the Schroeder frequency! One must be careful with automatic room-correction systems. More often than not they make things worse. What a measuring microphone picks up is not what two ears and a brain hear.

Direct vs. indirect sound.
• The 8c sounds natural and neutral anywhere in the room. Sit close and listen into the recording - you are there. Sit farther away and hear more indirect sound with perfect timbre because of even dispersion and flat power response for a 'they are here' experience.
• No voicing required. Other loudspeakers usually require voicing. Based on listening to a lot of recordings, the tonal balance of the loudspeaker is changed so that most recordings sound good. Voicing is required to balance differences between direct and off-axis sound. The 8c has very even dispersion. It is the first loudspeaker I ever designed that did not benefit from voicing. The tonal balance is purely based on anechoic measurements.

Cardioid dispersion. The central shape resembles a heart. Most the energy aims at the front, with weaker and weaker output to the sides then rear.

Next to these principles, Dutch & Dutch also consulted the works of the late Roy Allison who designed all of his loudspeakers with their woofers as close as possible to an adjacent room boundary, be it the floor or a wall. A loudspeaker is dominant at middle and high frequencies, the room is dominant at lower frequencies. Problems with discrete reflections arise mostly between 100Hz and 500Hz. Dutch & Dutch tackle that problem area with a cardioid midrange driver to prevent it interacting with the front wall. Yet the same front wall is strategically used to enhance LF response and simultaneously avoids reflections as per Roy Allison. By placing these speakers with their back-firing woofers very close to the front wall, 20-50cm, the wall becomes part of the speaker system. With this setup, the low frequencies get more punch because time-related smearing is avoided.

Design principles are cool but arriving from them at a finished product can be heated. The model 8c—'c' for cardioid—is a fully active yet compact 3-way system. Fully active means built-in amplifiers, here 250w/ea. for the tweeter and mid, 500w for the twin woofers. After ample comparisons, the designers felt that the Danish Pascal Audio S-PRO2 modules were ideal for the job. These are billed as UMAC Class D units with integrated UREC power supplies. Each can deliver 1000 watts in bridged mode; or 2 x 500 watts as Dutch & Dutch use them. Pascal Audio's chief designer has prior history with B&O whilst working on their ICE technology. Background information on the S-PRO2 module can be found here. With power dealt with, DSP was next. The chip of choice, chiefly for its redundancy, is the Analog Devices ADAU1452. This 1.2V 32-bit DSP core can run at up to 294'912MHz and execute up to 6'144 instructions/sample at the standard rate of 48kHz. This fully programmable chip easily handles the present needs but has headroom for more future functionality. Next to the extra storage capacity, high accuracy can perform lossless volume control. For DAC and ADC duties, Dutch & Dutch rely on the TI PCM4104 and PCM4202.