Review: Grimm Audio SB1 Subwoofer – Oh Lord, give me an SB1…

Review: Grimm Audio SB1 Subwoofer obviously provides further added value for the LS1 systems which will be available for € 11,500 (per pair)

Grimm Audio recently introduced the Grimm Audio SB1 subwoofer. It took a while before those woofers were available here. Almost all reviewers who visited this subwoofer did not want to return such a set. A new set has therefore been built especially for this review.

Subwoofers are usually bulky devices. It is often difficult to talk a set of floorstanders into the living room. Anyone who takes up the challenge will encounter considerable resistance from different perspectives. Sometimes the consideration is to receive her, provided with a limitless credit card, for an hour of shopping at the jeweler. That’s a bit of a swallow, but you’ve dragged in those two 18-inches. The SB1 is also of a smaller size.

It’s all about harmonics

Why are subwoofers so important, or rather the reproduction of frequencies from 16 Hz? This is because 80% of all floorstanders and monitors do not provide a substantial bass below 40 Hz and therefore miss something that is important for the reproduction of music. Aside from modern active processor-controlled reproducers that usually can. Music is made up of fundamentals and harmonics. They form a natural connection with each other and ensure that music sounds real, realistic and natural. It is still difficult to get good bass reproduction from speakers of limited dimensions. The industry has of course found many solutions for this. Bass reflexes, labyrinths, passive radiators and other constructions. With varying degrees of success. Very often it is reproducers that are banging,

Adjusting is an art

So you can add those important fundamentals by providing a system with one or more subwoofers. Unfortunately, that’s not a free lunch either. It is extremely difficult to choose two smaller loudspeakers, the suitable subwoofer(s) and then to properly adjust and place such a system. It is true that with the arrival of processors from Trinnov, Lyngdorf and others, this has become more accessible, but a lot of knowledge and experience is still required. A job for roughly five dealers in the low countries who can handle such complexity. However, your author strongly believes that audio systems should not be built by consumers, but by that handful of super dealers.


Servo control, feedback or feedback, known to many from the Philips Motional Feedback loudspeakers, is also a way to get deeper and better lows. Historians will have to determine whether the industry has always consciously kept us from this elegant solution. Building a bass reflex is a quick and super cheap way to throw speakers with a bit of bass into the market. Building a servo requires knowledge that not too many manufacturers have and of course a bit of extra investment. Perhaps just a bit more expensive than building a bass reflex. Philips did come up with Motional Feedback systems. There are also subwoofers on the market with a servo system. The earlier Genesis 1 and Infinity IRS also had servo control. The basic principle of servo control is simple. An accelerometer is mounted on the cone. It tracks its acceleration and compares it with the input signal. The moment the movements of the cone deviate from the input signal, a correction follows. The comment on that is that you are always late with that response. That would be at the expense of sound quality. But, that’s a myth. What is required for a properly functioning feedback system is sufficient loop gain, sufficient open loop bandwidth and sufficient phase margin. Given the ridiculously low frequencies that a sub handles, it takes ‘seas of time’ for a feedback system to function properly. In fact, there is so much time available that the sensor signal can be digitized, processed and then converted back to analog to drive the actual amplifier. Some will see all those techniques as a compromise. But, basically every audio product is a compromise. It always consists of a series of choices related to performance, design requirements, costs, technical capabilities, impossibilities and production facilities. However, a long experience with layer systems has shown that the application of servo control has enormous advantages for the sound quality. You usually always have a better sound. The Infinity IRS1B also had servo control, but not based on an accelerometer on the woofer’s cone. It is in fact possible to derive a ‘speed signal’ from the voltage and current that runs through the voice coil of the woofer. The acceleration can then be derived by means of differentiation. It is a cheaper alternative, with the disadvantage that the noise level increases, because the noise is also differentiated. The Infinity IRS1B had six large woofers per side, but the feedback was done through a single woofer on each side. What that woofer then did was considered representative of the other woofers in the housing. In theory that can go well. That counter-coupling went wrong here a long time ago. It turned into coupling. In addition to the gigantic acoustic energy, which caused a mega boom in the listening room at the time, the cones flew around and the servo went up in smoke. It took several months before the undersigned had repaired everything. Grimm uses analog piezoelectric sensors as an accelerometer on the cone. That sounds less advanced than using modern MEMS accelerometers with integrated AD conversion, but the latter are totally unusable due to distortion and bandwidth limitations. At Grimm, of course, they don’t know all MEMS either, but noise is often the limiting factor. However, while the servo electronics used to be built analog, the SB1 has servo control in the digital domain, with corresponding advantages.

Grimm Audio SB1

The SB1 is an extremely compact subwoofer (358 x 340 x 213 mm), based on a Dayton bass driver. On board are a 700 Watt class-d amplifier, a DSP and the servo electronics that work entirely in the digital domain (Digital Motional Feedback). The SB1 has an analog balanced input, which can be switched in two positions. The DSP (digital sound processor) is an essential link in the feedback circuit, resulting in a flat frequency curve and optimal impulse response. Thus, both the frequency behavior and the time behavior are according to the textbook. The total Q is 0.5. The dsp (digital sound processor) controls the frequency curve. This means that in a so-called dead room, the SB1 shows an almost straight line as an acoustic output, starting far below 20 Hz (17 Hz). The part of the dsp that controls the servo has super low latency. This means that the servo adjusts very quickly if there are deviations. If the latency were too high, the feedback loop would not be stable either.

Purely sound, these techniques also provide extremely low distortion in the low range (up to 30 dB less distortion compared to traditional bass systems). It is important that the bass does not ‘thicken’, as with many other subwoofers and loudspeaker systems. In principle, this thickening is caused by delay effects in layer systems. They are created by the ever-present fundamental resonance of the bass drivers. Also, the linear range is from 17 Hz. Servo control in a closed case also by definition means that the layer goes deeper than what you would expect given the content of a layer system. The frequency response of closed systems is in any case more linear than of other layer principles. However, the advantages of the SB1 have everything to do with the fact that the feedback is controlled in the digital domain.

Target groups for the Grimm Audio SB1

An important target group consists of the users of the Grimm LS1 systems. Basically this is an active two-way system with the option to add a subwoofer. An active three-way reproducer is then created. The SB1 connects to the LS1 via an analog balanced connection. The switch of the Grimm Audio SB1 is then set to ‘LS1’. The LS1 has its own DSP on board. In the digital domain, this builds up a phase-corrected Linkwitz Riley crossover. Because of that phase correction, a 3-way LS1 (including the SB1) has a latency of approximately 40ms. The purpose of the dsp (filtering and time correction) in the LS1 is that the system, whether deployed as a two-way or three-way (with SB1) connected, has an acoustic output in a dead space that is close to a straight line.

Readers will appreciate that any loudspeaker that has a linear frequency response in a dead space will not have that in a regular listening room. The acoustic properties, the properties of the loudspeaker and its placement make the frequency curve more erratic. If you want to make the LS1, or any other loudspeaker for that matter, sound good, you have to look for good acoustics, pay attention to the placement of the system and, in the case of a three-way system, have a very small influence on the loudspeaker because the crossover of the LS1 for certain settings is accessible via the firmware. In fact mainly limited to delay correction and level control if the SB1 is not on the intended foot of the LS1.

Second and third important target group

The switch already mentioned, with which the SB1 can be ‘switched’ to the LS1, also has a ‘third party mode’. This means that the SB1 can also be used in other systems. What you get is a subwoofer with again an analog balanced input, with a range of 17-500 Hz, but without the usual adjustment options of the well-known standard subwoofers. This simply means that a consumer who wants to create a stereo setup with one or two subwoofers must use an active crossover/dsp in the form of a Lyngdorf or a Trinnov. You can of course buy a cheap low-pass filter in China, but there are many drawbacks. There are also active crossovers available in the market with many adjustment options and high quality. An example is the affordable K231 Stereo 3-Way Active Crossover from Sublimeacoustic and some consumers may still have an Accuphase DF-55 (with built-in DSP) or Audio Research EC-22. With DSPs like Trinnov and Lyngdorf you can not only make the ideal filtering and time settings for the system, but of course you also have room correction. So you can give the system a frequency response that is as linear as possible, but electronic room correction is not a magic bullet with which it is possible to get a super sound from poorly placed speakers in problematic acoustics. The third group of consumers are owners of home cinema systems with an AV processor with a subwoofer output. Modern AV receivers often have a DSP and room correction on board to control subwoofers in a good way. Grimm is not planning to come up with a smart dsp/filter box for the SB1 for the time being. Eelco rightly noted that the company’s development resources are not infinite and there are simply priorities regarding the projects that are chosen.


The intention was to build a stereo system. Two speakers, equipped with two SB1 subwoofers. Connected with the Grimm SQM cabling. Neutral and transparent cables for a consumer-friendly price, where it is almost unthinkable to find a ‘better’ cable. Somewhere in the warehouse of the listening room are still a number of elderly Luxman A-2003 tube crossovers and crossovers from JBL, Nakamichi and Krell, among others. The disadvantage of these devices is that the filter type to be selected and the crossover frequency must be hardwired onto plug-in cards. So you will not do that so quickly for a test of a few weeks. But, maybe if a permanent system were put in with those SB1’s. A separate dsp and comparable dsp’s that are part of professional studio mixing tables have therefore been chosen. Such devices provide enormous flexibility in settings, you can immediately apply room correction and you can see everything on a screen and draw any corrections. Because the acoustics of listening room 2 are of very high quality, that room correction does not have much to do. It is therefore about the dots on the i. In any case, what is needed is at least an RTA (real time analyser). However, there are now many measuring systems, whether or not computer-based, to visualize things such as time, energy and frequency. It is also possible to look at a fractional-octave analysis, the power spectrum and a transient analysis. Findings come from all those measurements and they are here during the test, if relevant, converted to settings for the dsp. With measurements and dsp’s you can of course go wild, but the ultimate intention is that a very good integration is created between the subwoofers and the main monitors. You may therefore not perceive subwoofers as a separate part of the whole. Ultimately, of course, all factors that you can measure and adjust are important. Recent experiences with L-Acoustics’ Syva system (speakers, DSP and amplifiers) have also highlighted the importance of transient analysis. When you play a Steinway Model-D, every keystroke has some kind of intrinsic power and energy behind it. That has nothing to do with playing ‘hard’. It was particularly noticeable while playing trptk’s Canto Interno. The grand piano, played by Justyna Maj, revealed tremendous physical energy. As a result, this recording also sounded eerily lifelike. The funny thing is that those sonic characteristics are just part of the recording. However, if you run this drive on some systems, those properties are often less noticeable. As a result, Canto Interno sounded less lifelike and realistic on some systems than on other systems. Ergo, what is simply registered and part of the recording, does not appear on all audio systems. In order to be able to perceive those recording qualities, the audio system must therefore have certain qualities, but it is best to tinker with specific settings in filters and DSPs. In any case, after two days of measuring and drawing curves with the DSP, the system provided a listenable starting point. It should be noted that the author is in no way pretending that the system was performing at its maximum. A temporary system is built for each review. That goes away after two weeks. It is therefore a snapshot, but as representative as possible of what components can do. However, it is conceivable that if you were to build a permanent system for yourself in the living room, some extra attention would be paid to tuning and setup.


There is, of course, no greater pleasure than listening to a full range system. Although you can do pretty nice things with a mini monitor, the concept is of course laughable. You start listening to music, knowing that you are missing a large part of the fundamentals. Sounds like looking at color photos where one of the basic colors is missing. Let’s just conclude that this misery with loudspeakers is caused by technical limitations that used to be almost insoluble and by a kind of law that dictates the maximum dimensions of loudspeakers in a living environment. But, with the two SB1s used here, there is a full range system that deploys from 17 Hz. There is of course a lot of material available with some deeper layer content. Think of the somewhat rarer CDs by Klaus Schulze and Pete Namlock (The Dark Side Of The Moog) or the tone in Bjork’s Hyper-Ballad. It is of course not necessary to look for all kinds of music with very low tones. The fact that the fundamentals are part of the reproduction at the right strength makes the music sound more lively and real, but also that the tone of instruments, which is determined by the proportions between the harmonics, sounds more natural. Most consumers can still faultlessly indicate whether a real guitar is sounding or one that is reproduced by an audio system. It’s also important to know that few musical instruments, other than the synthesizer, naturally produce very low tones. Basically the church organ, grand piano, double bass, cello and bass guitar. Many consumers think that the ‘low’ in modern dance music has something to do with bass. Those ‘lows’ are usually frequencies from 50 Hz and have little to do with bass reproduction. However, a subwoofer does not only contribute to the reproduction of super low tones. Many floorstanders and mini-monitors already drop off slowly from 80 Hz. A subwoofer can therefore reproduce the range of roughly 40-80 Hz with the correct strength. To tempt the gods started with Listz’s Prelude & Fugue on Bach, performed by Felix Hell. It is striking how much gigantic and palpable power the SB1s can operate with. For some reason, closed layer systems are always able to deliver physical pressure as well. What the SB1s are doing here is masterful. You can of course be impressed by the enormous amount of acoustic energy that is just launched, but of course the quality is what counts. Well, no thickening when the frequencies drop and no fuzziness, smearing and loss of tonality. There is absolutely no whipping undefined smoke of sound. On lesser systems, such a church organ often turns into something vague, where all kinds of tones intertwine and form a mess. Such a church organ naturally produces ‘steady tones’. Other music with pleasant bass, which rolls like a wave in the surf with enormous energy and power over the carpet of the listening room, is Psychedelic Brunch Pt-II from Klaus Schulze’s The Dark Side Of The Moog vol.5, the beautiful and super low tone that is occasionally audible in Wende’s Au Suivant, the great intro to Céline Dion’s Encore un Soir and Save the Best for Last by Vanessa Williams. That last track is an all time favourite. As a teenager, your author had built a servo system based on huge 18-inch JBL drivers. The servo electronics were in Elektor at the time. If you had dragged the hottie from the seventh grade into your boy’s cave, you could score reasonably well with such a track. However, percussive sounds also pose a challenge to the definition and ‘speed’ of the bass reproduction. You should not actually use the term ‘speed’. However, it basically means that a woofer follows the offered music signal as accurately as possible. If a tone stops, then the woofer should not continue to swing for a while. That also determines whether attacks on a bass guitar sound realistic and defined instead of getting bogged down in a kind of fading slurry of sound. Listening to Marcus Miller (Cousin John) it must be concluded that the SB1s show that very tight and defined. The SB1s also sound neutral. That makes sense, because the housings are so compact that there is little that can resonate and color. So small compared to the wavelength. The sound remains tight, but certainly not ‘underdamped’ or ‘overdamped’. This has to do with the Q of the system. With overdamped it all sounds too pointy and tight. At underdamped sloppy and vague. In that respect they have done a good job at Grimm. Listening to Marcus Miller (Cousin John) it must be concluded that the SB1s show that very tight and defined. The SB1s also sound neutral. That makes sense, because the housings are so compact that there is little that can resonate and color. So small compared to the wavelength. The sound remains tight, but certainly not ‘underdamped’ or ‘overdamped’. This has to do with the Q of the system. With overdamped it all sounds too pointy and tight. At underdamped sloppy and vague. In that respect they have done a good job at Grimm. Listening to Marcus Miller (Cousin John) it must be concluded that the SB1s show that very tight and defined. The SB1s also sound neutral. That makes sense, because the housings are so compact that there is little that can resonate and color. So small compared to the wavelength. The sound remains tight, but certainly not ‘underdamped’ or ‘overdamped’. This has to do with the Q of the system. With overdamped it all sounds too pointy and tight. At underdamped sloppy and vague. In that respect they have done a good job at Grimm. but certainly not ‘underdamped’ or ‘overdamped’. This has to do with the Q of the system. With overdamped it all sounds too pointy and tight. At underdamped sloppy and vague. In that respect they have done a good job at Grimm. but certainly not ‘underdamped’ or ‘overdamped’. This has to do with the Q of the system. With overdamped it all sounds too pointy and tight. At underdamped sloppy and vague. In that respect they have done a good job at Grimm.

Grimm Audio SB1 – Epilogue

The SB1 obviously provides further added value for the LS1 systems. The Grimm Audio SB1’s huge credit to the consumer who wants an audio system with a single or dual subwoofer, or to someone with a home theater, is the very compact size of the Grimm Audio SB1. A little power amp is bigger. In addition, the impressive range from 17 Hz and the pure quality of the reproduction. Of course, much larger diameter subwoofers will go the extra mile in terms of quietness and authority. But above all, the SB1s fit into a real world scenario. In today’s time, hi-fi should be as compact as possible and not be a disturbing factor in the living environment. There is then no more useful and elegant solution than placing the SB1. With well-chosen mini-monitors or a small, high-quality floorstander, there is a real full-range system. It is also a kind of ‘secret tip’. Anyone who can really build audio systems knows that very impressive systems can be built with relatively small floorstanders or monitors, supplemented with a powerful subwoofer or subwoofers. That really goes further than what can be achieved with many floorstanders. Oh Lord, give me an SB1…


Grimm Audio SB1 € 11,500 (per pair)