 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
71.161.237.126
In Reply to: RE: Why are ported designs ubiquitous? posted by peter on December 22, 2009 at 18:19:36
All in good fun.
No, as far as I know, I am not "protecting" anyone. What makes people say such things? Have you tried reading what I write?
I have mentioned the theoretical and in some ways practical superiority of sealed boxes many times over the past five years, which is about the time I woke up to the fact that most audiophiles had only been exposed to ported designs. I attach a link to my overview of the subject.
In addition, I have quite recently gone out of my way to praise sealed box designs from Aerial (5B) and ATC (SCM 11). And JA's measurements have validated my subjective reactions.
The overview was a sidebar to my review of a $40,000 sealed box design, that perhaps would have cost half as much as a ported design.
Nobody here but us chickens, I guess.
To attempt to answer your final question, I think it is more likely that the commercial motivation is that a ported enclosure can be roughly half the size of a sealed enclosure with the same subjective bass output. Whether you call it room friendliness or spouse acceptance factor, it is a very real sales factor and cost factor, everything from the packing boxes to storage space.
In the early 1980s, Duntech Sovereigns (from Mr. Dunlavy's former company) were the #1 speaker in NYC mastering rooms. They are now no longer imported into the US. Weight, bulk, and cost, not 3 dB more efficiency, which is kind of a non-issue in an age of digital amplifiers, explain that, IMHO.
JM
Follow Ups:
You surprise me, John.
I spent some time evaluating the Sovereigns about 25 years ago, in consideration of buying them. To me, they were remarkable in many respects, but they consistently made violins into violas, as if adding a chest register.
Might have been the room, I suppose, but in the event I kept (and still use) my Spendor BC3s which sound more mid-range neutral. Not much chance of boomy bass with those bass-reflex speakers, mind.
Jeremy
Pardon me while I put on my "manufacturer" hat. Here are three arguments in favor of a vented box:
First, in a two-way design, the woofer's performance in the region of the crossover frequency is of paramount importance. If we're going to ask a cone woofer to go up fairly high (I take 12" woofers up to 1.5 kHz ballpark), the cone better be light and the motor strong. Now it just so happens that woofers with light cones and strong motors generally do not give adequate bass extension in a sealed box (not even my 12's). So if we don't want to add subs, a vented box is called for.
Second, for years I assumed that a sealed box had better midrange than a vented box, but a couple of years ago decided to find out for sure. I build two test speakers, one ported and one sealed, but otherwise identical. I then conducted a blind listening test, instructing the listener to focus only on the vocals. In every trial the listener preferred the vented box. I have since learned how to make a sealed box that is comparable to a good vented box in midrange clarity, but it's more expensive to do than a plain old vented box.
Third, seldom is the acoustic environment in a room exactly right for a given speaker in the bass region. With a vented box and a bit of ingenuity and/or courage, it is possible for the end user to change the shape of the speaker's bass response curve and improve the in-room response.
Just for the record, it's been years since I read John Dunlavy's critique of vented boxes but my recollection is that he chose a rather boomy vented box alignment to compare with, and unfairly characterized all vented boxes based on this example. Likewise, I could chose a Qtc = 2.0 sealed box and thus make sealed boxes look bad.
All that being said, I use both sealed and vented enclosures in my own designs. Depends on the specific application.
Duke
Me being a dealer makes you leery?? It gets worse... I'm a manufacturer too.
Ultimately a closed box(welldesigned, of course) has better control of overhandg than a vented one. But I do think most of vented boxes are made to sell to unsophisticated listeners and are conciously made a bit boomy. That isn't nedded. A bessel function reflex design is quite well controled and definitely no one note. My speakers are so designed. Then agai they were also designed to have the port stuffed(for rooms where the reflex design which went into the low 20s would boom). And the bass is more articulate that way.
There is one more factor. Reflex is king in sales. So the speaker manufacturers design most woofers for that application. A woofer needs to be designed for one application or the other idealy.
I'll add one other point. I asked the TAD speaker designer why he chose a reflex loading since he could have drivers designed for him to his specs. He said he could easily go about 10 Hz lower with a reflex and down to the point where the closed box went the reflex was just as good quality wise but with the extra extension. He's a great designer so I have to respect his opinion but I'm honestly not convinced(given my more limited exposure).
Thanks for posting, hahax.
I agree with your observation that most vented-box speakers are made to impress the uneducated, especially if the audition is a short one.
While it's true that a sealed box has better time-domain behavior, I'm not convinced that's of audible significance in and of itself. Group delay on the order of what we find in a good vented system hasn't been shown to be audibly significant on music in blind listening tests, whereas frequency response definitely is audible. I think the subjective differences between sealed and vented enclosures are primarily a function of the in-room frequency response, and in general the rolloff characteristics of a sealed box are a better match for "room gain" due to boundary reinforcement in most rooms. But it is possible to tune a vented box to mimic the rolloff characteristics of a low-Q sealed box (or maybe an even shallower rolloff) and in that case it sounds tight and fast. I don't recall what sort of slope a Bessel tuning has, but from your description I'd bet it's on the gentle side.
I'm doing some prosound work, and if one knows in advance the bandwidth of the signal the speaker is going to see, an appropriate choice of tuning frequency can significantly increase the excursion-limited power handling in comparison with a sealed box.
I presume the conversation you describe was with Andrew Jones of TAD. If I had a storefront, I'd want to carry his speakers... whether they're vented or sealed or stuffed with fresh cow pies, they sound great.
Me being a dealer makes you leery?? It gets worse... I'm a manufacturer too.
"But it is possible to tune a vented box to mimic the rolloff characteristics of a low-Q sealed box (or maybe an even shallower rolloff) and in that case it sounds tight and fast."
True, but this is so rarely done and in the end kind of defeats the purpose of what the vented systems supposed advantages are. A sealed box is MUCH easier to design AND execute correctly (there is a lot of forgiveness in the dimensions and still get quite close to the right result).
Other than one or two vented speaker systems I have heard none that compare to a well designed sealed box bass system or large flat panel for that matter. Remember the NHT 3.3? It had a 12 inch sealed woofer system and gave prdigious tight deep bass...one of the all-time greats in that category. NHT's SW3 was using the same woofer and was a world class sub.
Bessel function is minimum time delay. In a closed box a bessel function is a Qtc 0f 0.577.
Yes it was Andrew Jones and my impression is he's one of the elite speaker engineers(I said engineer rather than designer because I believe he measures as much or more than he listens so his biases are minimized).
"I agree with your observation that most vented-box speakers are made to impress the uneducated, especially if the audition is a short one."
That is a subjective statement based on prejudice if I ever saw one. Companies like PSB, Paradigm, Energy use NRC's facilities along with true DBT listening tests to get the sound they are looking for. There are countless many other speake companies who use anoechic chambers as well to tune their speakers to achieve the flatest response possible. Far more impacting to a way a speaker osunds than ports are crossovers. So before dumping on the ports as the cause of the problem, look at the cross over used.
I was talking about speakers not aimed at the audiophile market. For example, Best Buy moves far more speakers than brick-and-mortar stores carrying the likes of Paradigm. Their target audience isn't audiophiles, but rather "the uneducated". And boom-n-sizzle is more likely to impress in a 30-second audition.
Me being a dealer makes you leery?? It gets worse... I'm a manufacturer too.
While I prefer a big sealed box (something like 30 square foot is close enough to being infinite for smaller drivers) it is not a black or white choice.
A normal size bassreflex system can i.e. be tuned to 35-41 Hertz and thereby reduce the cone movement a lot. This will reduce distortion compared to a same size sealed box.
Secondly the port does give a more open sound in many systems.
I normally design loudspeakers including a foam plug, so that the owner can convert the bass reflex box to a sealed box.
Converting a sealed box to a bass reflex would require drilling holes by the owner:-)
Merry Christmas !
I assume you choose the volume of the box so when sealed the Qtc is a tight one and the F3 is reasonably low. Just closing a port may not work.
I was fortunate. The designer of my woofers took all these factors into account. I ended up with the closed format because of superior control. But I ended up with an F3 of 33 Hz rather than 23 Hz which isn't too important except for deep organ notes and low frequency room affects(if they're on the software) and a few other times.
Thanks, Ole!
I like your idea of being able to convert the box from ported to sealed, that makes the speaker usable out in the room or up against the wall.
Duke
Me being a dealer makes you leery?? It gets worse... I'm a manufacturer too.
Nobody has mentioned the Nestorovic woofer system. It's not as well known as it should be.
If you are unfamiliar, it's a hybrid of the sealed and vented designs using two electrically overdamped/mechanically underdamped woofers, typically one larger thatn the other (i.e.: one 10-inch, one 12-inch). The system operates in a sealed enclosure with both woofers operating essentially in parralel, down to a point where the larger woofer is attenuated (between 50-100Hz) so it begins to act like a passive radiator. It won a patent in th late '70's, I believe it's expired.
Great system. Some of Nestorivic Labs' speakers were very well regarded and even won some A and B Stereophile ratings (don't recall which models got specific ratings). I personally own a pair of Model 3's, very similar to the Speakerlab S30 (a late 70's kit speaker), and you would not believe the depth and control that this 1.7 cubic ft enclosure is capable of.
Paul Johnston "The LoudSpeaker Guy"
Owner and Chief Loudspeaker Biologist
Kent, WA USA
www.theloudspeakerstore.com
My uniform experience over 50 years with sealed box speakers is that they have two unacceptable characteristics: They sound muffled-very little if and only if they are expensive(near and above $5k) and they lose a good bit of the music as they are turned down.At low levels they've lost a lot.
Post a Followup:
| FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
||||||||||||||
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
