Sean, thanks for the detailed description of your setup. It sounds absolutely fascinating.
I certainly agree about TL being the best way to deal with the back wave if you are going to build a vented design--that is, for all the little I know about it. I was too ignorant and ill-equipped to try designing a TL or even a good reflex in my own first try so I opted for what G.A. Briggs called a distributed port (DP), in his "Cabinet Handbook" from 1955. This is close to an aperiodic--basically you calculated your port area for the bass resonance of the system and divided it up into ten or so slots, damped with felt. Great DIY design, very forgiving, lower Q made it less critical to hit the system resonance right on in the port and box volume calculations. Well below your league.
Reading Briggs' book you got the feeling he was a bit wistful about the infinite baffle. He didn't talk about it much but he liked it. Maybe it was because as a company, Wharfedale could never have sold more than drivers for the design. I bet he would have liked your setup.
I love the variety of enclosure designs. Almost as many as there are for tube amps in Japan. I once saw one for a very short TL ending in a ported box which was said to get great bass out of a 4 or 5-inch paper woofer. |
We're on the same page, Eldartford.
One thing I now remember Bud recently telling me involves the superiority of the TL over the sealed/aperiodic alignment. As many know, the Fried C satellite (often used with D 8" or O 10" subwoofer in the Valhalla system) was originally an aperiodic design, but when they began manfacturing the Model Q, which had also loaded the midrange in a transmission line, their flagship speaker was now inferior to the next model down. It made that much of a difference, as the TL midrange is even more important than a TL woofer.
Obviously, the focus of development switched to bringing the C satellite inline. Thus, the C3L/C4 was born.
It was SO much better that Bud used to demo them at shows and get togethers against the same speaker, aperiodically loaded. He says that people would often get quite overheated, swearing that he must be using different drivers or crossovers in the two speakers. But, he was not. The TL on its own was just very much better. |
Trelja...Not only "to each his own" but "to each kind of music its own". I agree that for heavy duty organ music, and the like, Klipshorns will beat out any electrostatics. And for a solo violin piece, my little B&W monitors are great. |
Cdc2,
As is always the situation, execution of design is at least as important as the design itself.
Good Question! |
I sound like a broken record, but Sean makes a lot of good points.
While I also don't have a lot of experience with aperiodic enclosures, Bud is a big fan of them in certain instances. The transient response is supposedly improved, and the impedance curve is noticeably flattened - resulting in a more "resitive" speaker. Personally, as a tube guy, I don't get so panicked about high impedances (my Atmas love them) it's the low impedances I am more worried about.
The Fried Beta used an aperiodic enclosure, and Bud (who likes sealed boxes, just not as much as a TL) tells me it was the only way to get bass out of the small box. It makes the box size "appear" larger.
While I hope to do a lot of testing in the next 18 months, it would be interesting if we had some more A/B testing going on with between sealed and aperiodic boxes. Off the top of my head, I can't think of why a standard sealed box would be superior. And, you don't need to rely on Dynaudio or ScanSpeak's variovents. A lot of people just use a resin shower drain they get from a home improvement store, and foam or layers of gauze or felt.
Eldartford, as you said, "to each, his own", but I find the bass of electrostatic speakers to be less powerful and extended than a full range loudspeaker. They do have a lot of other niceties, though. |
Tobias: Not all low frequency designs try to eliminate the back wave. There are a few dipolar woofer designs that have achieved critical acclaim for their speed and high levels of in-room linearity. If you doubt this, ask Duke at Audiokinesis for a few references : )
I am using multiple sealed push-pull dipolar woofers in my main system. These are actively crossed with 1000 wpc driving them. Push-Pull lowers distortion and increases speed / self-damping of the drivers. Dipole's reduce in-room standing waves / smooth out in-room response. Sealing & stuffing the chamber between the drivers keeps the impedance down at resonance, producing a lower Q with the associated improvements in power transfer, transient response and "good tone".
As to "while a TL is superior to a sealed box"... those are Joe's words, not mine. Having said that, i will say that TL's are the best way to make use of the backwave from a woofer that i know of without exhibiting the multiple side effects that most vented systems suffer from. Vario-Vents aka Aperiodic's would be the second best vented design. A well designed port with flared inlets and outlets AND a good amount of internal cabinet stuffing would be third. Passive radiators find their way at the rear of the pack as they are the slowest of the bunch in terms of transient response. Having said that, a well designed PR system is probably capable of delivering more overall "bass weight" than any of the designs mentioned here. This has to do with the ability to tune the mass of the drone cone quite low in frequency AND that added mass adding more duration to each note due to overhang / slow transient response. As such, BIG woofers driving multiple BIG passive radiators are the way to go if you want "earthquake bass" in your house for HT use. Just don't expect it to be "tuneful" or "nimble" for use with music.
By the way, not all TL's are "vented". You can terminate a TL in a closed box and cram the end of the tunnel full of damping material to absorb the energy at the end of the line. Like i said, there are a LOT of variations to what is considered a "Transmission Line" and they all have their trade-offs / high-points. Sean
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Trelja...Of course, I jest a bit. Nevertheless I have never heard a ported speaker that I could not recognize, from its sound, as being ported. Although I prefer sealed boxes, and have built my subwoofer systems that way, I have never heard any box speaker that did not exhibit some degree of boxy sound signature. Which brings us to planars. The best speakers I have heard are electrostatic, but Maggies come close, and for practical reasons, that's what I have.
To each his own. |
Infinite Baffle sounds like a cable manufacturer's technical White Paper. :o)
It's also what you get when you set a speaker in a wall, or in a floor like some subwoofers of the fifties. ( Think of the low end from an 18-inch EV hung just under your feet! )
The term means that the driver's back wave is " baffled " as it tries to come round and cancel out the front wave, which is in opposite phase. It's a British term and in England the baffle of a speaker is its front panel. When a speaker is mounted in a wall, the back wave has, for practical purposes, an infinite distance to travel before it can cancel anything out.
Of course all dynamic loudspeaker designs try to either eliminate or control the cancellation effect, which is most serious in the bass. That's why we put drivers in boxes in the first place. |
Let's also not forget that while all Acoustic Suspension speakers (AS) are sealed boxes, not all sealed boxes are AS. When the compliance of the driver exceeds that of the air in the box (i.e. when the box gets larger and larger), this alignment is referred to as an Infinite Baffle (IB). And, the issues which have been raised in this thread regarding the AS speakers are ameliorated. Correct me if I am wrong, but Sean's projects tend to go in this direction - big woofers in big boxes that make big bass.
Again, while a TL is superior to a sealed box, it's really hard to go wrong with a sealed speaker.
Eldartford, there are plenty of excellent sounding ported speakers on the market. Dogmatic comments in audio lead to a lot of instances where the person ends up in the wrong. |
Thanks for the correction, Metralla.
I knew about the spider design ( and the more resilient cone surround ) but I hadn't absorbed the back wave concept. Needed more stuffing, possibly. |
Tobias writes: Sealed box designs need more amplifier power, on the whole, because the cones have to work against the very stiff spring of the air trapped inside the box. Although stiffness is provided by the air in the sealed box, the spider on a driver designed for acoustic suspension is less stiff, and compensates. When Vilchur designed the acoustic suspension speaker he modified the driver spider to provide less spring restoring force on cone excursion because he knew the air in his sealed box would provide some restoring force. The main reason the acoustic suspension speaker needs more amplifier power is the energy of the back wave is totally absorbed by the stuffing (converted to heat). In a reflex design, the out-of-phase back wave energy hits the port and is inverted 180 degrees, and is now in phase with the sound coming off the front of the driver. This extends the bass response, although the eventual rolloff when it does occur is much steeper (typically 12dB per octave as opposed to 6 dB per octave). There are many good speakers using the bass reflex system. Regards, |
Again I sum it up..."Ported speakers make excellent bird houses". |
Is one inherently better than the other?
That question's answer is (IMHO) no. But, they do have real differences and performance tradeoffs, and other tradeoffs.
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Check your local library and they'll usually have a few books on the topic. Weems' (David) might be better for what you need to know: just to get some general insight. The tone of the book is still quite contemporary despite looking 10years outdated. A two week checkout should be enough. Dickason's book isn't bad and more technical in every way that Weems'. Its a good book to have too, but get some momentum through something simpler. The answer to your question is kind of hard to answer in a condensed straightforward manner. |
The straws? cuts down on port noise I've read. Ported speakers are designed to increase bass response of small speakers...a way of outputing the rear wave as energy to combine with the direct sound. I'm not a big fan but do own some of these type speakers...they work as long as you don't over-drive. I'm a planer man myself...which is another set of problems!
Dave |
Although I am not sure Sean meant to suggest that the straw trick for reducing port turbulence or "chuffing" is pure snake oil, I quite agree with him that you need to do some reading. There is much more to this question than you will conceivably get here, and you need a balanced view of your own.
That said, I am just as willing as anyone else to display my ignorance in public.
Any speaker design can result in a pleasing sound or not, depending on how it is implemented. Every design is built around tradeoffs--you win on the roundabouts and you lose on the swings, as the British say. Sealed enclosures have a relatively low resonant 'Q' but the actual resonant frequency will be higher than that of an equal-sized, properly ported box. Sealed box designs need more amplifier power, on the whole, because the cones have to work against the very stiff spring of the air trapped inside the box.
Knew that ? Great stuff. There's more. My supposedly humble opinion is that until you appreciate the tradeoffs involved in any audio design, you don't really appreciate the design. |
Sealed speakers beat ported speakers in the areas of transient response. Because of this, you don't get the port resonances and noise that blurs the sound. And, because of their slower rolloff, produce more deep bass. They are also the easiest, and least costly to design and implement. There aren't really too many drawbacks to a sealed box.
Ported speakers are supposed to be up to 3 dB more sensitive than sealed speakers. In reality, it is not the case. They have a bump in the midbass which many people seem to like, and give the impression of having more bass than they do. While it is difficult to correctly implement a ported speaker correctly, it seems the public does not really care.
Transmission lines have excellent bass response. They have relatively loud deep bass, and can pack a real wallop. They combine the sharpness of attack and decay of a sealed speaker, with the impact of a ported speaker. In my experience they do not have less sensitivity than other designs. |
Sealed speakers are intrinsically faster in transients response so im my opinion are better.Period. |
Too many variables to sum up all of the different design attributes in even several very detailed posts. As such, you really do need to dig into the subject in order to have a better understanding of what is really going on. Take a look at this book about loudspeaker design if you're really interested. Not only is this the most thorough and "relatively easy to understand" book on the subject that i know of, this is the best price that i've found. I will only say that Pepler's comments above are loaded with misconceptions based on the aforementioned design variables. This is not to single out Pepler as i'm sure that he's only trying to share what he knows. Problem is that it is the same rhetoric that has been preached to audiophiles and it is basically wrong and / or a phenomenally small portion of what is a very big picture. Turbulence or friction in a port is not ideal and that is not why they are doing that. They could have achieved similar results by redesigning the port, but that wouldn't look "special" or give them a gimmick to hype. Reading the aforementioned book will allow one to cut through the hype due to becoming an educated consumer. This pretty much allows one to dismiss inferior designs right off the bat without even having to listen to them. Looking at a speaker and picking out the visible design flaws becomes second nature once you understand how they work. Only problem is, once you've attained this knowledge, you'll come to realize that "snake oil" is as much a part of the speaker industry as it is of the cable industry. Sean > |
The Question that every audiophile probably has an opinion about. My feeling is that a well designed speaker is just that. Most designs these days tend to be tuned ports, for what reason I'm not sure, but any sealed speakers I have owned have needed a large amount of power to bring out there best. As I understand a sealed box needs to be quite a bit larger than a vented design to achieve the same bass extention. Larger boxes in general equal poorer sound stage and imaging.
The reason, as I understand it, for the proac speakers having straws stuffed into the port was not to increase bass responce but to increase friction in the port at higher volumes so that the woofer didn't break-up, and yes in much the same way that stuffing a transmition line's horn/port with insulating material. |
