SoundPrism speaker systems - beyond record studio-quality

Hidden in the town of Heerhugowaard, located in the province of North Holland, you will find the audio domain of Etienne Heemskerk. Under the brand name ‘SoundPrism’ his fully active loudspeakers are designed and manufactured. The customer has a choice in the appearance, even in the applied electronics and the choice of the subwoofers.



SoundPrism does not aim to sell large quantities of loudspeakers, due to the purpose to deliver customization, full customer satisfaction and true aftercare. Development on a sizable scale, looking for the best solution in cooperation with the customer and subsequently tuning a system is what appeals most to Etienne. A representative system can be auditioned at SoundPrism's location or at one of his dealers.

Probably the most striking component of the SoundPrism Excellent model is an AirBlade tweeter, designed and assembled by hand in the UK at Arya Audio. Due to its complexity only available in small numbers.

SoundPrism AirBlade tweeters

The tweeter reminds me of science fiction scenes where robots or nasty aliens take over the world. Although thoughts like that are very disrespectful given the quality of this AirBlade driver.

In fact, it is an extended development of the Oskar Heil Air Motion Transformer, whereby the high frequencies do not get bundled in the AirBlade, but radiated over a horizontal plane of 180 degrees. Both at the front and at the back of the harmonica-shaped membranes. This technology allows the tweeter to react at a speed that is four times faster than a conventional dome, is at least as transparent as a pure electrostatic driver, but does not have the detrimental beaming that characterises all electrostatics.

The availability of the AirBlade alone limits serial production of the Excellent loudspeakers, because every AirBlade is made to order for SoundPrism. Etienne modifies the AirBlade tweeter in a way that the energy radiated at the back is not attenuated, but utilised in the open baffle principle.

SoundPrism Excellent

The Excellent loudspeaker is an open baffle design, the forward distributed energy is equal to the backward radiated energy, because no enclosure is used, just a baffle, supported by a proper frame that may be visible or kept out of sight completely by extending the baffle panel a little bit. The baffle can be made from wood, composite or stone, finished as desired.

Customisation at SoundPrism really means: "According to the customer's wishes and preferences". In the baffle, under the AirBlade tweeter, a Purifi Pure Sound midrange/woofer is mounted. The AirBlade looks quite special, but the Purifi woofer has a surround that is also different from what we are used to. The woofer is a designed by Purifi engineers, perhaps better known for designing the Purifi Eigentakt class D amplifiers to which I will refer later. The frequency range of the PTT6.5W04-01A woofer as it is officially called, is almost flat from 100Hz to 3,000Hz and turns it into an ideal midrange reproducer for an open baffle. The fact that the woofer is electronically filtered means that phase and timing problems of passive crossovers are avoided. The long excursion of the voice coil and cone allows high sound pressure levels, without distortion due to the special surround.

By electronically controlling the crossover frequency between the woofer and tweeter, the radiating behaviour of the Excellent can be tuned to a specific room and to the customer's preference. By default, the crossover points are set at 120Hz and 2800Hz.

Subwoofers of your choice

For the woofer SoundPrism uses 15-inch Klipsch subwoofers. These Klipsch subs undergo a modification; firstly the electronics are bypassed to alter it into a passive version and secondly the internal damping is modified by SoundPrism. The choice for a commercially available subwoofer makes it easier to customise a speaker system and limits the costs. The customer is free to choose any suitable subwoofer, recommended is a 15-inch for larger spaces, 12 or 10 inches in smaller surroundings. The woofer, like the Purifi unit and the AirBlade, is actively driven by a SoundPrism amplifier after the electronic crossover. Both the open panels and the subs rest on magnetic dampers. These will bring an obvious improvement in the sound field through decoupling. The dampers are Neolevs by TritonAudio, a company from Alkmaar that Etienne often deals with.

Next speciality are the applied electronics. SoundPrism uses a three-channel electronic crossover from Hypex to let the three units each handle the desired frequency range. The filter is adjustable in every way using a personal computer, thereafter the configuration files are loaded into the filter over a USB connection. Every SoundPrism has three customized fixed settings, set with a remote control, to let the customer choose which setting appeals most to him or her. After running in the crossover is tuned at the customer's home and optimised for the chosen settings, to solve for instance acoustic problems in the listening room by means of DSP. Between the crossover and the drivers Purifi Eigentakt class D amplifiers are directly coupled.

Each Eigentakt is powered by a Hypex power supply and mounted in an enclosure as a two-channel amplifier. What remains for the customer is to connect an analogue source with its own volume control to the electronic crossover. This might be of a streamer/DAC with volume control, an analogue preamplifier, an all-in-one with pre-out, or even a setup with only a record player and a phono amplifier with volume control.

Today, SoundPrism uses a streamer with a separate DAC including a volume control. Perhaps worth mentioning is that you can choose any type and any brand of power amplifier after the crossover. From a six channel AV amplifier to six high end mono blocks. Provided that the same type of amplifier drives each channel. Together with TritonAudio SoundPrism is developing a tube preamplifier for the Excellent loudspeakers. However, the release date for the preamp is unknow at printing time.

The SoundPrism Excellent loudspeaker system is offered on the basis of a quotation. A quotation in which the wishes of the customer are included for the design and the subs. A complete system includes the open baffles with Purifi and AirBlade units, two modified Klipsch 15 inch subwoofers, the Hypex active crossover, three complete Purifi Eigentakt stereo power amplifiers, all the cabling, installation, tuning and after two weeks further tuning for customer satisfaction. The price for this complete system and service starts at € 18,000 and only increases when the customer has special wishes that justify an additional price tag.

SoundPrism: Etienne Heemskerk

SoundPrism was not born out of wishful thinking by Etienne Heemskerk. His roots are in the classical music he grew up with and what he still plays on the flute. He has a long-standing reputation in recording soloists, orchestras, choirs and jazz musicians, using an unusual ribbon microphone system of his own design, combined with custom TritonAudio active preamplifiers. He uses for his recordings only two microphones, pointing straight ahead next to each other, exactly the way our ears are positioned. The recordings are saved as digital files and not edited, or as little as possible.

In Etienne's opinion, commercial recordings are too much processed afterwards making the recording unrealistic. Also in his view, often too many microphones are used. This might not be a problem for pop music, but is disastrous for classical music because of timing issues. A natural reverb is impossible to achieve using several microphones, or often a microphone is placed too close to an instrument, voicing the soloist unrealisticly, and detached from the orchestra. A commercial additive gets applied and done is another release. This is not Etienne's way of recording, he always uses his two microphones, nothing else. If there is an imbalance in volume left-right, the conductor is to blame, not the recording nor recording engineer.

Etienne has always been interested in DIY loudspeakers and electronics. At an early stage he realised the advantage of active filtered loudspeakers for perfect rise time behaviour and minimal phase errors. Behringer and Dutch DIY magazine Elektuur's replicated electronic crossovers, class AB amplifiers, Hypex class D amplifiers, Hypex DSP, it's all been tried and used during the development of the Excellent loudspeakers in front of me.

In the past, technology was Etienne’s main focus, nowadays the emphasis at SoundPrism is more and more on enjoying music instead of getting the utmost solution in technology. Etienne sees himself as a builder of custom-made loudspeakers, not as a manufacturer in large quantities. His systems evolve, in such a way that a customer can move along along with the adjustments made. Mainly regarding the crossover software, the optimalisation process for the crossovers and not in upgrading the units mounted on the baffle.

I need to point out that SoundPrism can also be of help for tuning other brand audio and AV systems, for converting passive speakers into active ones, or modifying third party loudspeakers.

Ears wide open

What makes the SoundPrism Excellent model different from all others? It's not just the tweeter and midrange, it's the concept of active drive per unit using a 3-way electronic crossover. The direct coupling of amplifiers to the units, only for the part of the frequency range the unit is optimised for, ensures a clean, direct, fast and undistorted sound without phase errors. Matters all clearly audible.

My first introduction to music on this system, other than background music, is playing music from Dominic Miller. His rippling music is well recorded, although in the long run it might get boring and sleep-inducing, it shows immediately some of the positive aspects of this system. I refer to dynamics, transparency, deep bass and openness.

The bass is extremely controlled, as is shown during the play of "Modul 29-14" by Nik Bärtsch, the heavy beats on a drum and plucking strings of the bass are clearly defined, rich in tone, but without exaggeration. The dimensions of the listening room are well used, the stereo image extends far beyond the physical placing of the speakers, has been enriched with height and depth. The transparency makes the system clear in tone, without any sharpness. The system is indeed direct, fast and dynamic.

The third piece of music that I know well and is in use as reference, needed because both the system and the room are unknown to me, is "The summer we crossed Europe in the rain" by Stacey Kent. I notice a lot of ease, with an emphasis on a solo instrument whenever that is appropriate to the music. Stacey’s voice sounds natural, with a clear “s” where it is expected. The Excellent system does not cover details, nor does it make the music or the vocals more beautiful than they should be. It is certainly not a polished 'plastic fantastic' reproduction. The Excellent active speaker system draws a fine stereo image in which voices are at the right height, not larger than desired or humanly possible.

Stacey was my last track before moving on to music chosen by Etienne. He starts with a song by Father John Misty with his deep, realistic male voice. A powerful band behind the man, when suddenly a tambourine jumps out of nowhere. Convincing in its authenticity, there is a stable image that does not beam too much. Beaming that can be adjusted by shifting the crossover frequency between midrange and tweeter. The intelligibility of what Father John sings is optimal.

Next Nicki Minaj sings "Get on your knees", but she probably doesn't mean to get down to the subwoofers to experience on close range the all-embracing low end that the two Klipsch woofers manage, combined with a deep echo in the virtually created space. The system handles Nicki with aplomb. Infected Mushroom with "Avratz" delivers a lot of melody in the lower notes, more than usually heard with other, mainly smaller speakers. Once again, stereo image is wide spread, completely detached from the loudspeakers. The power of the amplifiers is expressed in strong dynamics, without glorifying or exaggerating the blows. All by Infected Mushroom electronically generated notes stay clear and independent, do not mask each other at any point.

In "My favourite thing" by Youn Sun Nah her voice could be positioned a bit higher, on the Excellent her voice is at the same height as the instrument she is holding in front of her belly. However, she brings a nice intonation into the voice, once again the Excellent speaker system resembles a top electrostatic reproducer, due to the transparency of the AirBlade tweeter and the Purifi midrange driver. It is very admirable how the voice is recreated in the room. It must have taken a lot of effort and a very long time to get to this point. There is a total silence behind Youn, getting her away from the system, with distance to the background and the natural sounding speakers.

She is followed by The Winton Marsalis Septet that made a recording at the Lincoln Center Galas named "United we swing". On it, multi-voice singing can be distinguished voice by voice, with the subtle differences in tone playing an important role. The band is spread out wide behind the singers. A trumpet pulls apart the sound space, percussion is fast, bass drum and bass distinctive. The audience applauds to prove how big the stage and hall really was. Also live is Sting with "Why should I cry for you" from the cd "The Soul cages". Again music passes by very easy and naturally, with a lot of space, a clear echo on all notes and rumbling drums,.

It is striking that the volume hardly needs adjusting, play louder or softer, actually any volume level is correct. This is not often the case, usually every cd has its own preferred volume. One possible reason for this phenomenon is the amount of ease in this system.

Men At Work with "Aquadub" by "Gianmaria Testa" shows that the system is much further controlled than the size of the subwoofers suggest, the subs add to the music without overpowering it. With the electronic crossover they can be turned up easily in sound pressure for the bass freak, but in that case the nicely balanced frequency response is seriously affected. SoundPrism has managed to create a neutral and balanced system, wherein the lack of unrest plays a major part. It resembles in a way the character of a horn transducer, a smooth character with infinite dynamics lacking any form of compression. But without the disadvantages of a horn, such as the sometimes audible crossover from unit to unit, colouring or the limited low end.

Subtle details get out clearly, this is how the special tweeter proves it capabilities. Far more transparent than any high end dome tweeter it even prevents the sometimes hissing character of an AMT. Again in combination with wide dispersion and unlimited dynamics.

SoundPrism's own recordings

So much for the commercially recorded music, time to listen to the recordings of acoustic instruments made by Etienne Heemskerk. Such as saxophones, played by the Artvark Quartet during a jazz festival in Amersfoort. It does not take long to realize how spatially the system performs and how unusual the positioning of the instruments is. You can almost walk right up to the place where the man or woman stood during the recording. Whenever the instrument gets very close to the microphone, the sound is sucked into the speakers, when space is kept between instrument and microphone, a natural ambiance is regained. Close your eyes and the speakers disappear, leaving only the music to enjoy.

Jazz pianist Peter Beets plays with a few others his own compositions in a living room concert. This is the moment I realise that the streamer platform consists only of a Raspberry Pi, a dedicated power supply and a relatively simple DAC. It makes me wonder what extra’s a Lumin, a Naim or an Auralic streamer and DAC would bring? Nevertheless the music sounds realistic, in a natural rough way without being extra polished in the mix. Very direct, excellent microphone placement, percussion that has real power and again I am reminded of a horn speaker.

Classical piano was recorded at the Ruïnekerk (Ruin Church) in Bergen, nearby Heerhugowaard. It remains a difficult instrument to reproduce and once again SoundPrism does not disappoint. The grand piano is not portrayed too big, certainly not too small, has real power and all is in place: strings, hammers, body. Etienne also recorded an organ in another church to test his microphones. The organist addresses all registers at some point. Although it is not always easy to imagine the church size, when long sustained notes slowly fade away you notice in what kind of surrounding the recording took place.

They are all beautiful recordings, very pure, enriched with natural reverb, using only his two microphones. I think that proves Etienne's skill in this process.

For the attentive reader, the loudspeakers are placed approximately one metre from the back wall, with little toe-in, are 2.5 metres apart. In the large SoundPrism room, they are situated in the middle part. No audible problems arise from a skylight in triangle form almost above the speakers.

Craftsmanship and aftercare

It is a bit tricky to describe the SoundPrism Excellent system as a fixed item. The room acoustic behaviour is unknown to me, it is my first introduction to the SoundPrism concept and as mentioned the system can be tuned to the customer's wishes and/or acoustics. Tuned to the desired amount of bass regarding to the size of the subwoofers, tuned in dispersion, tuned to the amplifiers used and so on.

What never does change is the AirBlade tweeter and Purifi midrange/woofer, mounted on an open baffle for a dipole radiation that, thanks to the AirBlade tweeter, will be almost 360 degrees. The pure character and high quality reproduction contained in this system does not change either. Directness, dynamics, transparency, key words with which SoundPrism has succeeded excellently in presenting its signature.

Commercial recordings sound wonderful, the purity of Etienne Heemskerk's own recordings prove once more how realistic his own developed system is. It may be hard for future clients to judge from a photo what the Excellent system will look like in the end, but don't let that put you off. Remember, clients are encouraged to brings forward design ideas. Listen first, then discuss aesthetics and afterwards make up your mind. As always essential in the process of buying an audio system, and the same is true with SoundPrism.

SoundPrism delivers craftsmanship and custom works for the true music lover, in a small, niche market. It remains true to its credo: a sale does not end at the front door, but at the customer's home. Providing aftercare and/or upgrades to satisfied customers is part of the deal for this dedicated company. | Originele Nederlandstalige versie? Klik hier