How can you achieve good room acoustics in your home studio? What are the most common mistakes? And what do you have to consider when planning your acoustics? Room acoustics expert Kevin Kleinschmidt answers these and other questions in Synthesizer Magazine.
SynMag: Hello Kevin! Would you like to briefly introduce yourself to our readers? What did you study, what is your role at HOFA – and how are you personally connected to music (perhaps even synthesizers)?
Kevin: I have been with HOFA-Akustik for five years and am responsible for product development, room planning and more complex customer projects. After training as an electrician and further training as a state-certified technician, I worked in industrial and building technology for many years.
My first influential involvement with music was with electronic music in my youth. Since I was twelve, I have been very interested in unusual sounds and melodies – Jean-Michel Jarre, Kraftwerk and Berlin and Frankfurt techno and made a lot of music along these lines in my youth and early adulthood. I was always most fascinated by powerful, distorted sounds, which is why a few years later I completely changed my interests and turned to metal. Having played drums in bands for 23 years, I eventually found my way into audio production and, fortunately, came to study audio production with a focus on room acoustics. I still really enjoy making synthesizer background tracks for rock and metal songs, but unfortunately not as often as I’d like.
In summary, I can combine my broad range of training and interests quite well when it comes to room acoustics, and I think I can familiarize myself well with projects and contribute all this to the team at HOFA Acoustics.
SynMag: What does HOFA-Akustik offer? And for whom? Is there a specific group of people who use your services?
Kevin: A relevant group are users and operators of recording studios, e.g. home studios and professional studios. However, the line between ‘home’ and ‘professional’ is blurred. This group includes anyone who wants to make recordings and mixes with good sound quality or simply wants to listen to music and sound with as much detail as possible. The situation is similar for rehearsal rooms, live venues, hi-fi rooms, home theaters, living rooms, etc., for which we offer suitable room acoustics solutions. And there are also rooms of commercial customers, such as offices, conference rooms, restaurants, nurseries, classrooms, etc. In these fields, the awareness of good room acoustics is growing rapidly, and our expertise ensures optimal sound in these spaces as well.
For recording studios and all the other rooms mentioned, we offer various product groups that can also be combined.
Sound-absorbing solutions for reducing sound energy in the room, sound-dispersing solutions for sonic quality and sound-insulating curtains for improving acoustic separation between rooms and areas.
SynMag: What are the most common misconceptions (in terms of room acoustics) that customers approach you with?
Kevin: You can’t really call them misconceptions. Once you’ve made the decision to do something about good acoustics, the biggest misconception has already been corrected. But if you’re not familiar with acoustics, false expectations can quickly arise. For example, the size of the room and the scope of the acoustic measures must match. On the other hand, even after a large investment in room acoustics, the sound may still not be ‘perfect’. Good room acoustics are created by many small steps taken in the right order and in the right direction. And that’s where we at HOFA-Akustik can help with our professional and targeted advice and products.
Misconceptions could include things like ‘light acoustic curtains’. Anything that is supposed to provide effective sound insulation must be heavy and thick, i.e. it must have the right mass. Unfortunately, there are also many half-truths and untruths floating around: lots of carpet helps a lot, or any glass surface is bad for the sound in the room, or loudspeakers must not be placed directly against the wall…
You always have to consider everything in relation to the other planned room acoustic measures in the room. Not to mention all kinds of esoteric gimmicks at exorbitant prices. We feel much more comfortable on the side of science, so that we can show a budget-friendly, plannable goal.
SynMag: What mistakes are commonly made in the acoustic treatment of rooms? And what are the biggest challenges?
Kevin: Many mistakes made by room users are usually made before the acoustic treatment. Speakers and listening positions are sometimes not determined according to acoustically recommended aspects, but rather based on the rest of the furnishings (studio) or according to the best appearance (hi-fi), which can result in very distorted sound in the bass range at the listening position, for example. Even though bass absorbers can help here, a well-planned listening position is just as valuable. The issue of room furnishings is similar. Sometimes a room is so cluttered that no alternative speaker and listening positions can be tried out. Or there may be pieces of furniture that absolutely have to be placed where it would actually be important to install or set up acoustic modules, e.g. to reduce very destructive first reflections. This requires compromises at the expense of the room sound.
Another common mistake before acoustic treatment of rooms is placing carpet all over the room.
The reverberation in the high frequency range is then already ‘dead’, even though there is not a single acoustically relevant and highly recommended absorber in the room. There is also a mistake in the use of sound-absorbing material that should be avoided at all costs: different wall designs on the left and right. For example, there is a window on the right in front of which a curtain is hung, while the wall on the left remains untreated. This distorts the mono and stereo image even more than it was in the untreated room. Therefore, always design the room as symmetrically as possible on the left and right, unless you know exactly what you are doing.
The biggest challenges on the way to good room acoustics are in the bass and low midrange. This is where the greatest distortions in sound always occur at the listening position, and the trick is to take the many small steps in the right direction that we mentioned earlier. Without professional help, it is difficult to achieve significant improvements here. In our acoustic measurement and planning PRO service, we address many aspects that help to improve the sound in addition to bass absorbers, e.g. the positioning of loudspeakers and the listening position.
The additional use of a subwoofer may also be advisable, even if the speakers can actually reproduce everything you had hoped for. The adjustment options on speakers and subwoofers should be used, and electronic aids such as EQs, etc. can also bring about further small improvements.
SynMag: Are there limits to what is feasible, and where do they lie?
Kevin: Almost anything is feasible. It just depends on your willingness to experiment, the time you have available and your budget. We have yet to encounter a square concrete basement with a ceiling height of 2.15 metres where we have not ultimately been able to enable professional productions to be made. In most cases, it is not the limits of what is feasible that determine the outcome, but rather the limits of what is reasonable. Sometimes, concluding ‘Okay, it’s not perfect, but I can work with it’ is also a good psychological conclusion to a room acoustic design. You can then concentrate on the actual audio work in the room and determine the necessary technical aids such as analysers, headphones, etc. No room out there is perfect. You can familiarise yourself well with most acoustically treated, but not perfect, sound conditions.
SynMag: Speaking of the limits of what is feasible, what about sound insulation? That’s usually very difficult, isn’t it?
Kevin: Yes, this topic is actually one of the trickiest in the field of acoustics. In home or project studios, where major structural measures are often not possible, you have to live with and work with the compromises that a room entails. Whether it’s the neighbour’s chickens or street noise that can interfere with vocal recordings or mixing work, we are happy to advise you and discuss what our soundproof curtains can do in each situation. Even if external noise cannot be completely prevented, good soundproofing can still provide a noticeable improvement. Heavy, well-positioned acoustic curtains with an insulating layer can be very effective – in addition to their sound-absorbing properties. It is always worth taking a close look at the windows and doors. There is often potential for improvement of several dB here if something is wrong with the mechanical settings or seals.
SynMag: What are the most important standard values in a recording studio that you take into account when optimising a room, and can you please explain them briefly? And what are the solutions for bringing these values into a recommended range?
Kevin: Reverberation time (mid and high frequencies): The sum of all sound reflections in the room. It is often referred to as RT60 (reverberation time), where 60 stands for 60 dB. The reverberation time is the time it takes for the sound field in the room to become 60 dB quieter than the signal coming from the loudspeaker. In studio control rooms, the aim is to achieve values between 0.1 and 0.3 seconds, depending on the size of the room and the exact type of use.
Only then can you hear and evaluate what is being played through the loudspeakers with precision.
Here, absorbers are clearly the method of choice for bringing the room sound into such good ranges: absorber modules, wall and ceiling panels, acoustic curtains, etc. In recording rooms, i.e. where drums or violins need to sound lively, the reverberation time can be between 0.5 and 1.0 seconds, depending on the size of the room and the sound quality. Absorbers and diffusors are suitable for achieving a good balance between reverberation time and sound quality. With our interchangeable frames, the room sound can also be easily and flexibly adjusted, for example by simply removing a few absorbers and inserting a few diffusors.
Decay time (bass and low midrange): Here, there is no sum of sound reflections; rather, resonances dominate the sound image, which are pronounced between the sound-reflective surfaces of the room – known as room modes or standing waves. These resonances sometimes take more than a second to decay. Of course, this makes it impossible to listen to and assess the bass range accurately, as dynamics and transparency are lacking. The best solution here is to install bass absorbers in the room corners.
Due to the volume required for this, the bass range often has a slightly longer decay than the midrange or treble. If you have achieved a reverberation time of 0.4 or 0.5 seconds in very low bass frequencies, you have already come a long way.
However, room modes cause even more problems: each of the many resonance frequencies in the room causes loud and quiet spots that are fixed in the room. And, depending on the frequency, these can also occur at different locations in the room. Every spot in the room sounds different in the bass range. That’s why good advice, starting with the position of the loudspeakers and the listening position, is so important as one of the first steps on the way to good room acoustics. Bass absorbers in front of sound-reflecting surfaces in the room can also be very helpful here.
First reflections: These are the sound reflections that are first reflected from the nearby surfaces of the room and reach the listening position. This happens within a few milliseconds after the direct signal from the loudspeakers reaches the listening position. If left unattenuated, these first reflections cause strong comb filter effects, distorted mono and stereo images, and washed-out transients. The target values here are to ensure that all early reflections arrive at the listening position at least 20 dB quieter than the direct signal within the first 30 milliseconds. Absorbers, acoustic sails or acoustic curtains are suitable for this purpose, as are diffusors or bass absorbers.
Frequency response at the listening position: This refers to how the mixture of direct sound from my loudspeakers and the acoustic ‘fingerprint’ of the room, consisting of reverberation, early reflections and room modes, sounds at my listening position. The sound of the room should be suppressed as much as possible using acoustic modules. However, we still need a certain amount of room sound in order to feel comfortable in the room. On the other hand, room acoustic treatments also have budget and space limitations. This means that in every room, there will be a certain amount of ‘ripple’ in the frequency curve of the loudspeakers, which will be noticeable at the listening position. Here, too, there are target values. In professional studios, it should definitely be better than +/-6 dB. If you achieve values better than +/-10 dB, you have usually already done a lot to achieve this in the room. +/-10 dB here means that, for example, 55 Hz is 10 dB below the average volume of all frequencies and 110 dB is 10 dB louder than the average.
SynMag: How does a consultation work in practice?
Kevin: The easiest way is for the user of the room to send us photos and measurements of the room and briefly describe their sound goal, i.e. what they want to do with the room later for audio work (and in what quality). Ideally, a budget has already been set, but you can also take it as it comes and first see what the expert recommends. Optimisation can then be carried out step by step, depending on the budget. Before, during and after the planning stage, we are in close contact with our customers and offer telephone or video calls so that we can tailor the planning precisely to the room user’s wishes. However, consulting can take many forms. From a short phone call, where it becomes clear what is recommended, to 3D modelling of the acoustic measures, to measurement and detailed on-site consultation.
You can contact us for a personal consultation either by email or phone, or by booking one of our room planning services. All of this can be found on our website.
SynMag: Who needs an acoustically optimised room and for whom would a few simple measures suffice?
Kevin: Anyone who wants to hear properly or to be heard should consider the issue of room acoustics. From online meetings in your home office, where you are difficult to understand because your modern building is made entirely of concrete and glass, to all kinds of audio work, to office workers, teachers or waiters who, after eight hours – to exaggerate slightly – need an hour’s walk in the woods to let the noise in their ears subside.
For rooms where the main concern is to calm the sound field and not to achieve precise recording studio sound, a brief consultation followed by simple and often inexpensive measures is usually sufficient. However, wherever there are many sound targets to be met, e.g. in a recording studio, more time should be allowed for optimisation that is as complete as possible. It doesn’t have to be more budget, but in a recording studio it is more complex, and that brings us back to the many small steps in the right direction.
The interview was conducted by David Kurz, editor-in-chief of Synthesizer Magazine (SynMag).
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