Happy new year, my first post for 2010! I often read in forums (Gearslutz etc) ongoing arguments about polyurethane bass traps (such as ours) versus semi rigid fibreglass. The data below makes for interesting reading. This comparison was performed a few years ago at the Riverbank acoustic laboratory in the US. It compares a large Auralex trap (polyurethane foam) with a semi-rigid fibreglass trap of the same volume, and a flat fibreglass corner design. The polyurethane foam edges out the fibreglass in a close run race!
Cheers James
bank
Due to customer demand the “Staple T” hidden staple gun channel has been added to the popular BA300-90 “SoundBite” broadband acoustic panel. I must admit, when we first started to manufacture the BA300-90 a few months back, I was reminded how tedious it is to install panels which don’t have the staple channel. Putting up the panels for the promo shots wasn’t as easy as usual. Velcro tabs took paint off the walls, glue was messy and a bit too permanant! The “Staple T” was developed five years ago to solve the problem of installing thick section acoustic panels quickly and easily and is unique to SoundAcoustics products.
Controlling drums enough to satisfy neighbours is tough, as drums are loud and neighbours difficult!
Acoustic panels will reduce sound levels within the room, but will only marginally reduce transmitted
sound. Totally covering the windows always brings some improvement (with plywood and insulation),
as does insulation in the ceiling. If it’s a brick house, this may be enough. If it’s weatherboard, the whole
place will still resonate like a big drum.
The best solution is to build a drum booth within the room, which is expensive, but effective.
It’s often interesting to read some of the forums on acoustics (Gearslutz etc.). Some of the comments are informed, and many seem to possibly have an undisclosed agenda. Marketers are well aware of the power of opinions expressed on forums. Acoustic foam (also Auralex, Primacoustic, etc) has it’s fair share of proponents, but also comes in for plenty of criticism. Many state that acoustic foam will not absorb low frequencies, which is not the case. I’m pretty sure this criticism mostly refers to thin acoustic foam like eggshell foam etc. An acoustic foam panel of the correct design, density, composition and thickness is very effective at absorbing low frequencies. Our own SA600-150, (which is 150mm thick) has an absorption co-efficient of .6 (60%) at 100hz and 100% absorption at 200Hz, as demonstrated in the test performed at the certified lab at RMIT. The main alternative to acoustic foam are home made panels using products such as semi-rigid fibreglass or dense polyester panels. The performance of these panels are similar to acoustic foam panels, but again, thickness of the panel is directly related to the low frequency absorption.
Room modes (peaks and dips in frequency response) are directly related to the dimensions of the room. Room mode calculatorThis room mode calculator is helpful to determine where the problem frequencies are in your room. Another method to determine the problem frequencies of a room is to acoustically measure a room with a calibrated mic and software. There are many software programs on the market, and even combined with a budget calibration mic, will provide useful information about the acoustics of your room. The main issue is that rooms with larger peaks and dips (nodes) provide a more challenging starting point than a room with less severe and more dispersed room modes. Rooms that are reasonably flat to begin with require far less acoustic treatment to achieve an accurate listening environment that a “lumpy” room. Also, lower frequency room modes are more difficult to tame. A 50Hz peak is significantly more difficult to control than a 100Hz peak. When facing a losing battle it may be necessary alter the internal dimensions of a room by building additional angled walls, so as to disperse room modes.
I’ve had a bit of break from the blog, so my apologies! We have recently released a new compact panel which I prefer to call an “acoustic block” as it’s pretty chunky. The idea behind this one was to be able to offer a high performance panel at a reasonable price. It offers absorption approaching the SA600-75 broadband panel, as well as looking pretty funky. Being quite a tall panel (90 mm max) it casts a significant acoustic shadow. The value of this in a small footprint panel (300 x 300) is that they can be spaced up to 100 mm apart for increased efficiency. The Soundbite is perfect for treating first reflections in a project studio, listening room or home theatre. They also work well and look great as a ceiling cloud, mounted on MDF. $99 for 12
I recently had a customer ask me whether I thought the Auralex Mopads are worth the money. Wouldn’t any old piece of foam do?
It’s a good question. Essentially the theory is if you decouple the monitors from the supporting furniture it will improve the focus and accuracy of the monitors. I have the Auralex Mopads myself, and they are a well designed products that perform as advertised. I did an experiment with different grades of foam in place of the Mopads to see if they would perform as well. I must say, it does depend on the thickness of foam and the density. It is possible to make your own, but it takes a degree of experimentation.
The one thing Auralex Mopads won’t do is influence the acoustics of your room. If you have significant room modes and low frequency problems, isolation pads will make negligible difference.
A customer requested I modify a BT120/80 bass trap so he could use two of them as an vocal isolation area. The rear of the BT120-80 was covered with 3mm MDF, with some also inserted for extra rigidity. When it’s not in use it can be placed in a corner as a bass trap to help with the mix! This also makes a great wide frequency Gobo. If I get any more requests maybe this could go into production. 
I have to admit it, I’m a gear snob. Not an outrageous snob (if it’s not Neve or Neumann it’s rubbish!) but if it’s chinese I generally consider it to be crap. I’ve had a bit of Behringer gear for non-critical applications and it’s generally fine. But I’ve tried some Chinese microphones and I find them generally pretty harsh and over hyped in the top end. Pretty bad. Recently I decided to add a tube mic to the collection, as a “character mic”. I looked at the Rode NTK (good mic – but I have plenty of Rode mics already) the AKG Solidtube and the CAD M9. After doing the usual forum trawl I thought I might take a punt on the CAD.
Anyway, it arrived yesterday and I eagerly set it up side by side with a Rode NT2-A and ran both channels through the FMR Really NIce Pre. First I recorded some acoustic guitar, and then some vocals. The CAD sounded a pretty nice, better than expected. Not hyped, and with a very similar tonal balance to the Rode, and just a hint of valve “fizz”. And a bit noisier, but not too bad. I can see myself using it fairly regularly. I must just have to re-think my gear snobbery!
(the Melos echo was great!)
