November 02, 2011 by Audioholics.com
Cabinets Myths & Facts
The purpose of the loudspeaker cabinet is two-fold, to provide a controlled acoustical enclosure for the drivers to operate most efficiently, and to provide a physical structure to hold all of the drivers in place while positioning them optimally for the listener. Let’s explore some of the common myths and facts that distinguish the very best designs.
Myth : Premium quality cabinet construction does not require premium materials or workmanship.
It is often the case that the cabinet costs considerably more than the components it houses. This was not always the case, but as increasing competition drops the prices of the raw loudspeaker drive units, deforestation and the cost of fuel and labor keeps driving up the cost of high quality materials used in speaker cabinets. It is no longer uncommon for a $100 box to be housing $20 worth of components. The continuing emphasis on looks over sound quality reinforces the manufacturers decisions in this regard. Frankly after 25 plus years in the business, I am amazed that this one even has to be raised. It is a fact when using sensitive test gear to measure a woofer’s Theile-Small parameters, we have to hold it with something very rigid and heavy, or else the counter motion of the shaking test fixture will degrade our measurements. How is it then, if the enclosure would have panels resonate at a lower frequency (read more box motion) that this could really be a good thing? Cheap fiberboard will flex more than will a good grade of plywood or MDF. Thicker is better than thinner. The reasons that MDF gets used over plywood is price, not necessarily quality. The joints and gluing of different pieces inside the cabinet is also not something you can tell without poking around inside the box. Taking shortcuts on enclosure construction is a quite typical way manufacturers cut costs. A consumer is not likely to see these shortcuts until after their purchase. The knuckle test, unlike tire kicking (performed at various locations around the cabinet panels), can certainly tell you if the box is rigid from the pitch of the sounds it makes when knocked. Unfortunately, it won’t tell you anything about air leaks or port losses and it’s obviously not an exact science. A scanning laser vibrometer or even an accelerometer is a tool some of the larger more equipped companies can use to better analyze cabinet resonances since it analyzes the pressure fluctuations over the distributed surface where the woofer radiates. It’s important to look at a full battery of measurements at various power levels to see how the loudspeaker behaves. When we do loudspeaker reviews, we typically sweep the speakers with a full bandwidth, long sine wave at high output levels to look for such sonic nasties that can really inhibit product performance. Pay close attention to the measurements section of our reviews as we report these issues when they arise.
Myth: Less cabinet bracing is better because it lowers resonant frequency and audibility
It is argued that if too much bracing is applied, a higher resonant point will result making any cabinet resonances more audible. While it is true that a higher cabinet resonance at a given SPL is going to be more audible (dismissing the possibility that that resonance will ever be over 3.5 kHz) the reality is that the physical coupling of the speaker to the cabinet is going to make frequencies accompanied by higher excursions (read lower frequencies) more problematic and more likely to result in panel excitation than a high Q resonance at a higher frequency. A stiffer cabinet will simply color the sound less. PERIOD. Less glue, less staples, less screws, and/or less bracing and less effort go into a cheaper cabinet making the enterprise more profitable at a given price point. It is a much faster process to throw the cabinet together quickly than to take the time to do it right. The last and final bonus of that approach is the reduction in weight, which is always going to reduce the cost of shipping.
You can read the rest of the article here at Audioholics and check out the forum thread here.
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