Speaker cabinet construction..

Albert Von Schweikert has written an interesting paper on low-distortion speaker cabinet construction. It can be seen at the VSA Audio Circle:


Some pretty cool ways to control resonances. Enjoy.
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Interesting. This is a well known problem. It is why speaker quality can in effect be somewhat correlated to weight and the knuckle rap test. The heavier in general the better. Thin walls (like Harbeth) will have more coloration than heavy damped designs.

What is not mentioned is that these efforts may be negated in large part due to significant audible distortion from ports on speakers. Since VSA relies heavily on ports in any of its designs it is odd that this aspect is not mentioned in the article (ports can ring well up into the midrange).

Cabinet distortion can also be attenuated through soffitt mounting provided the speaker is properly decoupled from the wall, bracing and several inches of rubber/fibreglass and extra thick multiple layers of heavy MDF (not pine) may also be needed (a concrete or brick wall being ideal)
Indeed...once they decide on ported design, no matter how much effort they put elsewhere, the result will likely be less than ideal...
Ports are of use dont toss the babie out with the bath water. But for smaller rooms and close seating. A sealed design will be far less colored and easyer to place. Poor designed loudspeaker cabinets can add much coloration to sound, smearing image since tweeters midrange etc is vibrating on baffle, causes bloom in bass notes since cab walls become a driver, plus reduction in low bass responce. Vibration on cabinets can be controled so vibrations do not cause problems. Seems many loudspeakers go more for WAF then performance and cabinet material choice show this.
thanks for posting a very interesting article.
All the VSA speakers are ported, either front or rear, and employ a tunable transmission line woofer cabinet. The speakers can be tuned to the room by adding dacron filling to or subtracting from the port tube. The speaker can effectively become a sealed enclosure by filling the tube totally. This will tighten the bass but will likewise reduce the amount of bass. What you choose to do depends on your room acoustics.
Few understand that a transmission line IS NOT simply a vented enclosure, and that a properly designed TL can afford some of the lowest distortion bass available. The transmission line speaker was first described and patented in the 1960's. In a classic transmission line, the sound wave from the back of the woofer is channeled down a long pathway filled with a fibrous bundle of wool or bonded dacron, as in mine. This material is packed in deminishing density towards the end of the line, and turns the acoustic energy into thermal energy. In a properly tuned line, only very low frequencies exit the end of the transmission line and extend the low frequency response one half octave below the fundamental resonance of the driver.

In a transmission line enclosure, the back wave of the woofer does not bounce off an interior wall and radiate back into the room through the woofer's cone as in sealed or ported enclosures. These multiple echoes color the sound and can only be eliminated in a transmission line enclosure(IF there is to be an enclosure at all).

There is no pressure in a transmission line to excite strong enclosure resonances. In a sealed or ported box, enclosure resonances can usually only be controlled, not eliminated as in a properly designed transmission line enclosure.

In toto, a well executed TL's extended low frequency response, lack of multiple echoes from the inside of the box, and elimination of wall resonance will result in a very low distortion, fast and extended low frequency system.
Seems many loudspeakers go more for WAF then performance and cabinet material choice show this.

Absolutely. That is fundamentally what the majority of audiophiles plonking down $5K on a showpiece really want. Most are not aware of the colorations and many prefer teh colored sound (what they are used to hearing and expectations are everything)

Ports are of use dont toss the babie out with the bath water.

For sure ports have their merits especially large ones tuned very low can add little coloration, however, if you want to get fanatical about coloration simply take a look at the ort response from prototypical small port bass assisted design speakers from most Stereophile measurement plots and you will often find what is audible port output (distortion above 1%) up as far as the lower midrange.

In the context of extreme measures to reduce cabinet distortion it makes sense to talk about ports also....so WHY does the article ignore this? IMHO, since none of the discussion is breaking much new ground, it seems to be a very selective discussion clearly intended to be marketing material couched as science and technology.

That's quite a conclusion you've jumped to. Am I sensing a history with VSA? I think it's fair to say that a paper regarding cabinet resonances can be written without the inclusion of porting. That's a different can of worms altogether. Albert Von Schweikert is a very successful speaker designer/manufacturer and I for one thank him for taking the time to explain cabinet resonances in technical terms. Don't be surprised if you see the occasional technical paper from the likes of Dave Wilson or Alon Wolf, "couched as science" or not. Don't forget, these gentlemen must sell what they design and manufacture. If they choose to write a tech paper explaining why their particular design may be better than that of the next guy, then more power to them.
It goes 'round and 'round and it all boils down to how to market a speaker?
Trust your ears, what Bell Labs discovered many decades ago, and take all the white papers out there and line your birdcages with them.
Again, trust your ears and not what someone is telling you you're hearing.
I think this is a mischaracterization of ported designs. There was a time that I was a sealed enclosure snob, and dismissed all ported designs as "boomy one-note bass." But over time the designers learned how to properly damp a ported enclosure, and today there are many ported designs that have stunningly clear, fast, articulate bass. Everything from Wilson comes to mind.

The Stereophile measurements sections of their speaker reviews display a measured cumulative spectral decay plot, derived by attaching an accelerometer to a speaker enclosure's side panel. As you can see, speakers that have enclosures specifically designed for resonance control are very low in panel resonances, whether sealed or ported. Examples include B&W 802D (matrix enclosure, ported), Magico V3 (baltic birch and aluminum baffle, sealed), WilsonSofia (Wilson proprietary mat'ls, ported), and YG Anat Reference II (aluminum, sealed).

The B&W, Wilson, and YG are incredibly inert, and at least two of them are ported. The Magico is sealed, but a little more resonant. The YG cabinet has no internal stuffing; yet cab vibrations are nearly unmeasurable.
There is absolutely no doubt to the fact that this is a marketing/PR piece. It is a very poor PR effort however, with little integrity. To open this piece with a blatant slam to his competitors (in no way veiled) was a very poor choice on the part of Mr. Von Schweikert. I have no doubt that the paper is based on genuine R&D (“science”) and that the resulting tactical implementation is effective. I would also like to believe that one not need spend ridiculous amounts of money on exotic cabinet materials and that this approach by VS does provide a cost effective solution. Furthermore, my comments are not intended as a slam to VS speakers but to the lack of integrity taken in publishing a public article with such demeaning reference to the competition – sounds more like politics.
I just had a discussion about "white papers" with my wife. In her case, it was white papers in the nursing profession.

In my experience (and I was a career technical writer for three decades), white papers are propaganda with scholarly affectations. They are not, nor are they intended to be, objective. They are there to sell a point of view. In the case of audio, computer, and most technology-based products, it's to sell the vendor's design theory (especially if it's been patented) as superior to the competition, with an air of academia.

That doesn't mean the presentation is dishonest or untrue, but it is highly selective in the facts and subjective in the point of view.
After I finish reading white papers...they are used in an envirnoment more sutable for their purposes.
Not sure this can truly be considered a white paper as it was originally penned on parchment.

I missed your reply until today. You make a good point. Actually I have no axe to grind with VSA but, as you point out, perhaps I am overly distrustful of most technical claims made by audio manufacturers...especially given that most designers concentrate on aesthetics first and foremost.

Being a retired EE and putzing around with this hobby for over 40 years, no one is more skeptical than I am....trust me...so believe me when I tell you that Albert Von Schweikert, the "mad scientist", would NEVER put form above function. All you need to do is look at some of his previous speaker designs....zero WAF. His current designs are aesthetically pleasing to be sure but I wouldn't bet huge sums of money that he had a lot to do with the VSA aesthetics evolution. All the VSA speakers make great music regardless of price point, and tend to outperform speakers costing magnitudes more. That's my story and I'm sticking with it... :-)
All the VSA speakers make great music regardless of price point, and tend to outperform speakers costing magnitudes more

Agreed - they are indeed exceptional value and that is their main strength.