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Myths & Facts about Loudspeaker Cabinets: Identifying Legitimately High Fidelity Designs

by , October 19, 2011
Contributors: Philip Bamberg
SVS PB13-Ultra Subwoofer

SVS PB13-Ultra Subwoofer

Anytime a product is offered to a consumer, it's bound to be wrapped in marketing to help bolster its appeal and differentiate it from the competition.  Quite often the marketing tactics used by manufacturers contain a hint of truth with embellishment and sometimes simply have no basis in reality at all (otherwise known as “creative” marketing). When it gets to this extreme, you often hear us call such claims "snake oil.”  This is quite popular when dealing with exotic cables but we've also found it a routine practice with loudspeakers and A/V electronics as well.  What makes "creative marketing" dangerous is when it is presented under the guise of science.  This article explores some of the common myths we've uncovered in loudspeakers and discusses how poorly executed decisions can ultimately compromise the quality of the product. 

The reader is also encouraged to check out our prior article of this series:

It’s important to note that identifying truly high fidelity loudspeakers involves controlled listening tests and comprehensive and accurate measurements that correlate with how humans perceive sound.  We will dive into this further in our Audio Measurements & Myths article forthcoming.  Make no mistake however that making a truly great speaker involves truly great parts and design execution.  One cannot expect a 150hp 4-cylinder sedan to beat a super car on a track since it lacks the performance parts and sturdy frame.  The same applies to loudspeakers.  The sum of the parts really does matter as does the engineering behind making all of the parts work together as one unit.

Myth #1:  Internet Direct buying is ALWAYS a better "value" than buying through a Brick and Mortar retail store

Shop OnlineA common perception is that buying from an Internet Direct brand lowers the cost of distribution profit margins, yielding a higher value to you, the consumer.  Over the past 11+ years of reviewing loudspeakers, we at Audioholics have found this is often NOT the case.  In many instances, we've found the build quality and parts usage from an Internet Direct brand vs a traditional Brick & Mortar brand is either on par or worse when directly comparing products in the same price categories.  Ask yourself why anyone would cut their margin on a product when they can justify the price and convince the end user they are getting a better deal simply because they are buying direct and allegedly cutting out the middle man?  While it is possible to get a better deal direct, it is not a foregone conclusion, hence why it's important to look at the quality of parts inside the box.

Smaller companies are always at a competitive disadvantage when it comes to offering value because their purchasing power and therefore negotiating power is less than that older more established company which can place a 10,000 piece order.  This is one of the primary reasons many smaller sized businesses choose to get into the higher end of the market.  While sales are less, margins are higher.   Smaller companies can do some things better, like make decisions more quickly than a big company with a lot of different departments who all want to have their say.  That is a plus for the small guys of course, but only when they have made the right decisions.  That said, larger companies can afford to have elaborate engineering facilities that smaller companies cannot.  That does not guarantee better sounding products – that requires the additional factors of desire, knowledge and competent engineers - but at least there is the potential. Many small loudspeaker companies, even those in the “high end”, lack the facilities to adequately or fully measure their products. This can hardly be considered an advantage, and it helps explain the significant number of overly expensive mediocre sounding “high end” loudspeakers in circulation over the years.

Every company attempts to find a “sweet spot” between the best product they can make, and the least expensive they can profitably sell. Those companies with little or no engineering inevitably go into the bargain basement for products.  Those who know nothing about the products they sell, still know price.  The avenue of least resistance for a small company is usually to pick a niche in the high end, high margin market.  They simply do not have the resources to compete with a much larger, older and well funded company.  That means, if the engineering is top notch, you can and will find a good value.  If not.... move on.

Bottom Line:  First find a speaker system you like the sound and looks of and then work on getting a good price.  Don't blindly assume any company which is large and long established will provide you a better value product. Name recognition may give you warm fuzzies, but is more likely to cost you than to get you the best bang for your buck!  Also remember a poorly designed $600/pair of speakers discounted to $300/pair still doesn’t change the fact that they are poorly designed.

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 #2 :  Premium quality cabinet construction does not require premium materials or workmanship

Cabinet Constructed of PlywoodIt 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. 

Editorial Note by Philip Bamberg
I've always said that the first, and last, problem in manufacturing speakers is making the cabinet.  Materials cost aside, the largest cost remains the high labor hours.  This may be one reason many cabinets from all companies (whether high or low priced) are coming from China. The low labor rate makes the cabinet more affordable if ordered in container quantities.  Whether the speaker is assembled domestically or overseas, more and more cabinets are coming out of China.  However, the Chinese will build whatever designers want, so that does not mean that all Chinese cabinets are inferior. 

Editorial Note by Steve Feinstein
There are, in fact, several grades of MDF in China. There is “good” MDF and “not-so-good” MDF from Asian suppliers. You have to be careful to specify and confirm that you’re getting what you expect. You can get perfectly excellent cabinets from overseas, but it's not automatic.  The same is true of packaging material. Standard box material is sometimes jokingly referred to in the U.S. as "rice paper." You have to specify a multi-layer high-burst-test material to get really good corrugated box material. A manufacturer must be smart and aware of the potential pitfalls.

Bottom Line:  You get what you pay for in terms of quality of craftsmanship and parts. Don’t expect Mercedes performance from a Kia budget.

Myth #3: 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.

Euro Cab   Braced Cab

Tower speakers with no internal bracing (left pic); bookshelf speaker with baffle bracing (right pic)

The left image is from a European speaker costing over $2k/pair and standing 4ft tall.  This box has no internal bracing at all and very mediocre crossover components.  The manufacturer has since then discontinued the product after we did an exposé on the poor design quality, and has made significant improvements on the current versions being sold.  The right image is from a center channel speaker less than 1/2 the size of the tower speaker of the left image.  Notice the baffle bracing.  The poly fill was removed from the cabinet for a clearer image of the bracing.

It all comes down to the mechanical properties of the materials with which the cabinet walls are built, the geometry of the panels and how they are affixed to one another. We discuss this in great detail in:

Editorial Note by Philip Bamberg
Bracing essentially breaks up a larger panel into multiple smaller ones, each with a higher resonant frequency AND lower excursion.  Even if a panel motion is small, its radiating area is still large.  The solution is to reduce its excursion through bracing.  Also, there are many examples of deficient interior brace design i.e. that do not properly “cross-couple” opposing panels.  In other words, the corners have the most support (where they need it the least) while the middle areas have no coupling to the opposing panel.  Adding thickness to panels add weight, which lowers the frequency of resonance.  If the panel increases in stiffness then there is the chance that the panel vibration amplitude will also decrease.  Therefore thicker panels alone do not solve the vibration problem.  Stiffness must also increase, and this is done most effectively with cross-coupled bracing. 

One of the more disturbing trends caused by the notion that the appearance is more important than the speaker sound is the all too common routing (cutting away) of the front baffle board so the front of the speaker frame is flush with the front of the baffle (front board of the cabinet).  Now it should go without saying, the place where structural rigidity is most important is where the woofer screws into the box.  Despite this, for the sake of looks, not performance, the vast majority of cabinet makers think the box in the one place where the need for rigidity is highest; and where the most weight and force exerted on the cabinet are concentrated, at the place the woofer is mounted to the cabinet.  Any motion that is going to occur which results in shaking the cabinet instead of exciting the air, is going to result in at best a coloration in the sound, and at worst, a some loss of output.  To help overcome this, the front baffle must be made thicker so it’s a good idea to verify just how thick not only the cabinet panels are, but more importantly, the front baffle.  Good boxes typically have a thick front baffle.  Thickening the front baffle helps mass load and dampen vibrations coming off the driver basket which in turn reduces its transfer to the rest of the cabinet.  A box made of 3/4" MDF might have a 1" front baffle.  In other words, if one is inclined to route the front panel, one should usually increase the baffle thickness to retain an adequate degree of rigidity to compensate for flush mounting the drivers. Ask for this info when shopping for new speakers if the manufacturer doesn’t provide specifications. 

Editorial Note by Philip Bamberg
Making the front baffle thicker than the other panels may not always be the most effective approach, especially in cases where much of the front baffle may be cut away where the drivers are. That part of the baffle can’t vibrate because it doesn’t exist!  In those cases, my approach is to properly brace the backside of the baffle near the driver cutouts, instead of making it overly thick.  Such a baffle will typically produce the highest pitch of all the cabinet panels during the knuckle-rap test.

If it’s a subwoofer with a high excursion driver, you should expect an even thicker front baffle.  An example of a well engineered cabinet comes to mind with the SVS PB13-Ultra subwoofer we recently reviewed that had 1" side panels and a 2" front baffle and plenty of bracing to increase cabinet rigidity.

Editorial Note by Philip Bamberg
For subwoofers, there is the added problem of supporting the heavy woofer.  Vibration and insufficient support of the driver is not necessarily the primary concern.  It really is more a matter of strength during an accidental drop during shipping.  A thick subwoofer baffle flexes less and has more glue surface to the other panels.  These features put less strain on the cabinet joints.  Very heavy subwoofers need an additional brace that supports the motor itself.  Otherwise high forces (static and dynamic shear and torque forces) develop during a shipping drop. Sometimes the cabinet cracks open, other times the woofer motor or basket parts shear apart.  The supporting brace typically prevents these problems.

Consider mounting a loudspeaker in a box made of simple paper, and imagine how it would sound!  Imagine the paper flapping when you turn on the loudspeaker.  Clearly, the lack of rigidity would make this cabinet sound awful. Any ideal mounting for a loudspeaker would be an infinitely rigid surface.  Only in this way will we insure that the motion of voice coil and cone results in sound, not a volume canceling offset of motion from the cabinet, or the excitation of a panel resonance adding to and coloring the original signal.  Some manufacturer's have actually gone to the trouble of making their cabinets out of marble or granite and even concrete in order to come closest to this ideal.  The idea that making the cabinet better by giving it a lower panel resonance (which means thinner walls) is at best amusing, and at worst, simply a deception. 

Editorial Note by Philip Bamberg
There is improved imaging and low-level detail to be gained from heavy speakers, simply because they “hold still” during high playback levels.  I think there is a point of diminishing returns to this concept, however.  Taken to extreme there is the myth that the best loudspeakers must weigh several hundred pounds. 

The action-reaction of a cabinet moving even slightly tends to degrade imaging accuracy, low-level resolution, and sense of “bloom”.  It is the same effect as compression of the signal to the driver, because the full peak cannot be reached.  Heavy, rigid cabinets on spikes will sound more accurate for any given driver complement. 

Here is an example where three different methods lead to stiff panels with low amplitude and high resonance frequency. 

Method 1 – Cross-coupled interior bracing
The interior braces are shown as blue panels.  In all cases, each brace ties two opposite panels together.  At the brace glue joint itself, the two panels cannot vibrate.  The unsupported panel areas are obviously smaller in size than without bracing, hence any vibration is higher in frequency but much smaller in amplitude.  Notice also how the braces may have a thinner profile in the middle of the cabinet, but the brace’s full edge gets glued to the panel.  This concept is what leads to the D-shape of each brace’s profile. 

Method 2 – Increased panel thickness
In the example subwoofer cabinet, the front panel is double-thickness (1.5” MDF) where the woofer installs.  This is to recess the woofer to give clearance for the grille, plus provide proper and sufficient support for the heavy 10” subwoofer driver.  (Above this board, the front panel is single thickness again, but supported by the large vertical “spine” brace.)  The side panels are dual 3/4" MDF thickness up to about 3/4 of the subwoofer cabinet’s height.  The side panels are the largest of all in the loudspeaker, and they do not have cross-coupled bracing.  

Method 3 – Material intrinsic stiffness
The passive crossover is mounted onto a 1/4” thick aluminum bezel plate, which is then installed into the open window on the back of the monitor cabinet.  Here is an example of a very thin panel (1/4”), but of very stiff material (6061 T6 aluminum). 

Also, while the monitor baffle is 1” thick, it is made from a sandwich of two 1/2" MDF layers.  This is because there are four hardened skins instead of two, and so the baffle material becomes intrinsically stiffer.  The baffle is supported all around its edges by the box, and further stiffened from the two horizontal D-shape braces glued at the webs between the woofers and tweeter. 

 Bamberg Cabinet

Cabinet of Bamberg Series 6 Internal View

Editorial Note by Steve Feinstein
Many speaker enclosures or tweeter decorative faceplates are made out of materials other than MDF or aluminum. A large number of speakers are made from molded plastic or a combination of MDF and molded plastic. Obviously thin-walled ABS plastic (4mm or less) is not the greatest material for suppressing resonances and destructive vibrations, but cosmetics and appearances play such a big role in the mid- and lower-price ranges that looks often take precedence over absolute acoustic performance.

Reality is reality, but there are still common-sense steps that a designer can take to make the best of a given situation. Stiffening ribs help a lot and usually add relatively little to the “tooling costs” that a manufacturer must pay for the plastic molding apparatus. Also, if the developmental budget allows, the plastic material itself can be optimized with hardening agents (like mineral or talc) added to the plastic that makes it less “ringy.” That way, the industrial designer/marketing department can still get their fancy, attractive shape, but the engineer won’t cringe quite as much over the acoustic properties of the enclosure or faceplate.

RBH Sound Status Acoustics Subwoofer Enclosure

RBH Sound Status Acoustics Subwoofer Enclosure - inside look

RBH Sound new cost no object Status Acoustics line of speakers feature a layered acoustically inert enclosure construction.   This method of construction involves bonding multiple layers of materials together and allows the wall thickness of the enclosure to be varied without the limits imposed by more traditional panel construction.  When needed, bracing for the enclosure is integrated into the layered design.  The end result is an enclosure that is extremely acoustically inert. Doing this also allows the manufacturer more ability to shape the cabinet design to their liking.  There are some downsides prohibiting this type of construction for most manufacturers.  It involves a very costly process that uses a lot of materials to produce and it results in a very heavy cabinet which is expensive to ship.

Bottom Line:  Increasing cabinet rigidity is always a good thing.  This can be accomplished by using interior bracing, thicker panels, and/or more dense materials.  If a company tells you using less bracing to lower cabinet resonance is beneficial, recognize that at worst case they simply don't have a good grasp of the mechanics involved; and at worst case are attempting to rationalize their cost cutting methods.  This is especially true for companies that sell direct and offer free shipping with their products.  Adding more bracing complicates and slows the production of the product, and adds more weight to the finished product which means more cost!

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Recent Forum Posts:

MrBoat posts on January 22, 2018 13:43
I just put my hand on them while they are playing at medium to high levels. That pretty much tells all with regard to bracing/damping, not to mention the actual sound of them. As long as it's enough for that particular build. I wouldn't want to condemn speakers for the knock test not showing the build to be overly redundant or.
everettT posts on January 22, 2018 08:43
Beave, post: 1229972, member: 77067
I wouldn't hold up Totem as a great example of cabinet & port design.

https://www.stereophile.com/content/totem-acoustic-signature-one-loudspeaker-measurements
Yup, do the nuckle rap test and it's not great. Aside from the fact I don't like their voicing, subjective, his reference to most manufacturers cabinets assumes he has insight to all manufacturers cabinets
Beave posts on January 21, 2018 15:18
I wouldn't hold up Totem as a great example of cabinet & port design.

https://www.stereophile.com/content/totem-acoustic-signature-one-loudspeaker-measurements
Swerd posts on January 21, 2018 11:32
utubecomment21, post: 1229934, member: 71399
Look into Totem speakers as Vince doesn't believe in stuffing, neither do I. It's for amateurs!
It's a quiet Sunday morning and I actually watched those two videos you attached. The Totem speakers I've heard are pretty good in my opinion. However, neither video ever mentioned the presence or absence of cabinet stuffing. In my opinion, those videos were sales pitches, 17 minutes of sales pitches. They weren't necessarily nonsense, but nonetheless, I'm sorry I watched them.

The speaker did briefly mention coating the inner cabinet surfaces with borosilicate damping. Borosilicate is a 50¢ word for glass, no different than a heat resistant Pyrex glass jar. What's the functional difference between spun glass stuffing or coating the insides of speaker cabinets with borosilicate damping? None! The critical questions are: 1) How much damping material is inside the cabinet? And 2) Is it enough to accomplish the goal of fine tuning the bass response of the woofer and cabinet. Spun glass, borosilicate coating, polyester fiber stuffing, or even fiber made from recycled blue denim all get the job done.

Saying that you don't believe in cabinet stuffing is, at best, misleading. Your Totem speakers do have glass damping material in them. It was applied as a liquid coating. Once dried, it works no different than other types fiber stuffing.
utubecomment21 posts on January 21, 2018 09:57
Well its not subjective, one has two distinct choices. One can either have a well design enclosure, or one can fall the the bilge that the other 99.999999999999999% of manufacturers produce! All the best
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