Chronic bass boom? Here’s a new cure

Singaporeans live largely in HDB apartments, which are notorious for bad acoustics. You don’t get to hear many good hi-fi setup in HDB bedrooms where bad acoustics is often the excuse for the bloated, bottom heavy sound. However a recent experience over Chinese New Year during one of the traditional home visit with an audiophile friend change my view.

Arriving there on a warm, humid afternoon I settled down in the cool, cozy typically squarish HDB bedroom, which was now a dedicated listening, room. It was heavily treated with large heavy curtains and two pieces of six feet tall and four feet wide wooden panels which were leaning against the wall besides the Audionote AN-J speakers. Extreme attention was made to isolate the various components on marble slabs and sand trays. The set-up looks promising despite my misgivings. A disc was placed into the Teac CD player after the usual switch on and warm-up period. When the music came on, I heard that familiar HDB bass boom. I just resigned myself to some courteous chatter and comment about the sound. After a few minutes, I walked around the room to have a closer look at the setup. I placed my hand on a violin which was in the room and it was vibrating very strongly to the music. To me, this means that it was of some sonic use in that room soaking up some of the energy which would otherwise contribute further to the boom in the room. I next placed my hand on the wooden panels. They were quiet and thus were of no use in there. On placing my hands on the speakers which were as expected putting out a tremendous amount of acoustic energy , an instinctive thought came to my mind. Why don’t I move the panels that were six inches from the speakers and serving no purpose at all in their present position to touch the speakers. With permission from the host I proceed to do this. The panels started to vibrate energetically and the transformation to the sound was immediate and astounding. The boom disappeared and in its place was a bass that was taut and informative. From the listening position I could feel the bass energy coming through the floor and massaging my bum. It was indeed an unusual sensation. To confirm that this was no illusion my host and I moved the panels back to their original position. The boom returned immediately.

This visit was definitely a fruitful one with a very happy audiophile friend who now has a vastly improved sound system without having to spend a single cent. For myself I discovered a very important principle which can serve as a very powerful tool for the audiophile to improve the performance of his audio setup. After some careful reflection on what had happened during that CNY visit this is what I surmise. The poor, boomy bass was not caused by the room itself. It was coming from the speaker cabinets. When I used the wooden panels to make contact with them, this uncontrolled energy was drawn away from the speakers and conducted to ground. Think of the panels being used as a mechanical ground.

Commercially I can think of no device that does this. There have been many tuning devices purchased by the audiophile to place on his speakers. These devices light or heavy, metal or wood do not in anyway seeks to reduce the heavy vibrations in the speaker cabinets. What they seek to do is to change the resonant character of the speakers and thus change the character of the sound. It is like when you are wearing glasses and you put a tinted lens in front of your regular lens to give it a new colour through which you can view the world. However they do not allow you to see better just differently. What you really need to do is to clean your lens.

There is one product on the audiophile market that attempt to do this and this is the Microscan and now also known as Teknasonics. These devices work on the principle of sympathetic resonance meaning that if two objects having the same resonant frequency are in close proximity to each other and if one of them is struck and starts to vibrate at its resonant frequency, the second object will also begin to vibrate at the same frequency. The second passive object draws energy from the first active object and thus reduced part of its energy. The Microscan/Teknasonics thus work like acoustic sponges to soak up vibration from the speakers. They are among one of the very few audio accessories that actually work. With these devices the sound is cleaner and stays this way at a higher volume. However they have one serious flaw that limit their capability. That is just like sponge they have a limited capacity to soak up energy. Once they hit their saturation point (when you start to play loud) they overload and stop functioning properly and your system like most system will begin to sound noisy with lost of control due to excessive speaker cabinet vibrations. This is why heavy, expensive speakers can play louder before the sound quality starts to break up. However for most of us who own modest speakers which have a tendency to sound noisy, boxy and boomy, there’s still hope and you may not have to spend a single cent. There’s this idea call the mechanical ground.

I will explain how this can be applied effectively to your speakers to allow them to perform at a level that you could never imagine. You will need a basic understanding of this principle first before you lose yourself on your system. Think of the vibrational energy in your speakers as like the heat energy in a transistor. Just for those with absolutely no knowledge of electronics, a transistor is what most tube lovers hate and they would tear their hair out if they find one of these in their beloved tube amplifier. A transistor unlike a valve require a heatsink to stay cool otherwise they would self –destruct. For the heatsink to work it is mounted in direct contact with the transistor to draw away the heat. Think of the Microscan mounted on the speaker. The heatsink mounted this way has a limited capacity to draw away heat. Think of the Microscan saturating. So some transistor amplifier designer chose to mount the transistor with the heatsink onto the chassis thus multiplying the cooling capacity of the heatsink many times. Unfortunately you can’t think of the Microscan being able to do this. This is where the idea of the mechanical ground for vibration control comes in.

In the case of my CNY friend I used the wooden panels as the mechanical ground. One part touches the speakers and the panel being on the floor conducts these vibrations to ground. If you don’t have a wooden panel, anything else that can let vibrations pass through it easily can be used. The shelves from bookshelves, an umbrella, or even a chair can be used, as long the object used is hard. A bolster for example would not be of much use here. You will have to place the mechanical conductor next to the speaker so that part of it touches the speaker and the other end either resting on the floor or touching the wall. Or better still resting against a wooden cabinet or wardrobe which will act like a giant vibration sink. If you are using a heavy wooden shelf, do not rest it too heavily on the speaker otherwise you are changing the speaker’s resonant frequency which I feel should be avoided. If your wife complains how unsightly it looks, you can place these mechanical grounds behind the speakers so that they are out of sight.

I have applied this principle to a pair of Edgarhorns with very good results. These horn speakers have very large wood surfaces that put out a lot of energy during play. These speakers have a wonderful midrange, somewhat reticent highs but I always noticed a strong coloration in the bass region that give them a honking effect in this frequency band. I placed some shelves leaning gently against the sides and back of the speakers. Unfortunately the floor was carpeted so some of the shelves will not ideally grounded but they still work well as a vibration sink. The idea is to draw vibrations away from the speakers. The shelves on the wall sides had better coupling. Even with this non-idea application of the mechanical ground principle, the effect on the performance of the speakers was impressive. Not only did the bass clears up but the entire frequency spectrum and all known parameters that define the performance of a hi-fi system showed improvement. The midband became more palpable and focused. The highs were more extended and shimmers. The soundstage increased in width, depth and height. Every instruments in the soundstage became clearer and decay of transients became more natural and audible. I could not hear any trade-off with regard to this "tweak". I could see one possible danger with this system. It is to do with the tremendous increased in headroom. Before I could not play the speakers to a very loud level before it starts to sound incoherent and messy even though these speakers can play very loud with a sensitivity of 104db/w/m. Now I could crank up the system with my 8 watts 300B single ended amp to its clipping point consistently. That would be at a level of 113 db approximately. It sounded very loud but not noisy. The sound was still clean and coherent. It was only when the neighbours came banging on the door before my listening buddies and I realized how loud it was. There definitely was a danger in damaging our hearing at this kind of level for extended listening. This experience is like driving a high performance car, you do not know how dangerously fast you are going until you look at the speedometer. A lesser car would be screaming for you to slow down with its chassis threatening to break apart from the incessant vibration and the increasing feel of lost of control from not being designed and made for high speed. Thus in hi-fi terms it is possible to bring your modest speakers to a high performance level by paying attention to reducing cabinet vibrations. Even expensive high-end speakers can benefit from some attention paid to this.

Using lay-about objects can work for you. However if you want even better results you may have to put some time and money to build yourself some special vibration sinks cum mechanical ground to maximize the drainage of vibrations away from the speaker cabinets. This can perhaps be the subject of another article.