Ported vs Sealed Part III (possibly Part VII??)

[onplane]

A few weeks back we had a very, very interesting thread titled "Ported vs Sealed" where some terrific information was shared.  Somewhere (and I can't remember where) I mentioned that Velodyne, a highly respected manufacturer of sub-woofers, was still selling "sealed box" units.  In fact, their top of the line units are all sealed boxes!

http://velodyneacoustics.com/subwoofers/digital-drive-plus-series.html/

This got me thinking that there must be a reason for this, so I sent this memo off to Velodyne:

Question: As an audiophile for many years, I have a very simple question. Your top of the line Direct Digital Subwoofers are all sealed boxes. My question is: why sealed boxes?
 
For many years after AR introduced "acoustic suspension", the best speakers were all sealed boxes.  Today with computer aided design, the vast majority of speaker systems are vented/ported. Indeed, you folks market a number of vented subs. So why sealed boxes on your best subs?
 
My guess is distortion. That is, the simpler AS front propagating wave is less prone to distortion than the mixing which has to occur with the vented systems.
 

Today I wanted to share Velodyne's response, because I think it is most interesting:

Your guesses are part of the reasoning. The sealed boxes are also able to be more compact than a ported cabinet would be and these units have a wide range of applications. In truth there is no solid reason for one system to be 100% better than another as far as I am aware. I would not be surprised if later down the line the next model to come out has ported and non-ported options to suit the clients preferences. For the DD line keeping the bulk of the cabinet low was the deciding factor in the model run, but the engineers did get as many advantages out of the system as they could with that choice.

Thank you,
Velodyne Customer Service

 

In short, I guess there is room in the world for diversity of design with no system "100% better than another".

 

Hope you find this interesting ...

Jerry

[Steve F]

I wrote that long article in the thread of S vs. P and I had written an even longer one on these pages way back in 2002 or 2003.

 

The main reason that AS tends to have lower distortion than vented is not because “the simpler AS front propagating wave is less prone to distortion than the mixing which has to occur with the vented systems.”

It’s primarily because an AS woofer depends on the “perfect” motion of compressed/expanding air to supply the restoring force and control the woofer’s motion, whereas a vented woofer must depend on its mechanical parts (surround/spider etc.) to supply its restoring action and control the cone’s motion. Air compresses and expands in a perfectly predictable manner; the same is not true of man-made contrivances.

 

Many of today’s AS systems do not utilize the pure Villchur-type AS system. In his speakers, virtually all of the restoring force was air-derived and his woofers had extraordinarily-low FAR’s. Today’s “sealed” woofers typically have FAR’s as much as 50% higher (say 17Hz to 25Hz) and even in those “sealed” woofers, their mechanical parts are playing a much bigger role than in an AR-1 or AR-3a. I’d be shocked—shocked!—if Velodyne’s 12-inch woofers has an FAR of 17Hz.

 

Remember also, that in a powered subwoofer, all bets are off, off, off, because 1) you can electronically EQ the system for any response you want (within reason) and 2) today’s sophisticated DSP/Distortion detection-prevention circuits can yield lower distortion than in a purely passive system like a 3a.

 

Steve F.

[onplane]

As always, Steve, thanks for your well thought out comments. From both yours and Velodyne's comments it seems clear that acoustic suspension offers some small advantages in the area of distortion.

Now what really surprised me was this comment from Velodyne: "sealed boxes are also able to be more compact than a ported cabinet would be"

Steve, did this surprise you at all?

Regards,
Jerry

[onplane]

After my exchange with Velodyne, I started to wonder what other sub manufacturers think about sealed vs ported. In looking into this, I happened upon this very interesting comparison:

https://www.svsound.com/blogs/svs/75367747-sealed-vs-ported

What I found particularly interesting is SVS's contention that the slower roll off of sealed units (a point Tom has made on a number of occasions) plays a big roll in small to medium size rooms and appears to give sealed a big advantage in that environment. Hope you find this comparison interesting as well ...


Regards,
Jerry