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New member Username: KeplerPost Number: 1 Registered: Oct-18 | Hi Guys this is my first post on this forum. I can see many positive reviews for slot ported speakers especially in terms of positioning. Good example are Wharfedale diamonds 225 for which whathifi even recommends to place the speakers closer to the rear wall. Many people including me are having issues when it comes to place the speakers at least 40 inches from the wall. So, my question here is. Are there any disadvantages using slot ported speakers? If no, why would not every manufacturer use the same design? |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 18582 Registered: May-04 | . It would get pretty boring if everyone looked the same and did the same. Manufacturers are always looking for an advantage so anything that is uncommon can be seen as a selling point. Yet, for everything you gain in one design, you trade off for anther positive value by accepting that design. If you gain one thing, you will surely give up another - and possibly another on top of that. Very few rules of audio do not follow the simple proposition of give and get. The larger question IMO is, why even do ported systems if ported systems cause a "struggle" with room placement? This is absolutely a case of everyone doing the same thing over and over and not thinking beyond what everyone else is doing. It is a case of everyone accepting the same problem and probably most buyers don't even know why they are accepting a faulty design. If they did, if it were explained to them, then possibly they would demand better answers for their audio dollars. This is "me too-ism" taken to the extreme. This is, undoubtedly, one of the dumbest "fads" in speaker design I have seen in over 50 years of audio. If you go "retro", back to the heydays of American loudspeakers, the most prevalent design of, say, the late 1950's thru the mid 1990's would have been an acoustic suspension system. A sealed enclosure has no port and, therefore, it has no specific concern for placement close to a barrier wall due to reflected pressure waves exiting a port. An acoustic suspension system is an "infinite baffle" system with bass extension that is more usable in room, octave for octave, than for any vented/ported system. The basic laws of physics dictate that any infinite baffle rolls out at -12dB per octave while every vented system rolls out at -24dB per octave. You lose bass extension twice as fast for the system that causes more problems! I'm open to anyone who wants to try to explain the common sense behind that thinking which is so dominant in today's audio systems. Back in the 1970's, Advent proved the worth of a lowly 15 watt amplifier running into a sealed enclosure loudspeaker. Yet you would have a very difficult time finding any acoustic suspension loudspeaker on the market today. It makes no sense to me that vented speaker designers struggle with how to deal with room reflections due to port placement when the simplest and most logical answer is to simply eliminate the port. I see no logical reason for not building acoustic suspension loudspeakers again. I see absolutely no logic in continuing to build the same type of speaker enclosure that causes the same type of problems in the most rooms. . |
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New member Username: KeplerPost Number: 2 Registered: Oct-18 | Thank you for your time. I guess we should email Andrew Jones to ask the same |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 18583 Registered: May-04 | . I'd be interested in his answer. Jones is no dummy and he has worked for companies that turned out nothing but acoustic suspension systems for decades. Probably the most famous system associated with KEF (long before Jones worked for them) is the LS3/5a, which was a small sealed system. But, back then KEF's sounded like British speakers. Once they switched to ported systems, they all began sounding like American JBL's. I've never received what I consider to be a satisfactory answer to the question of why designers continue to build problematic systems. Or systems that avoid "this" problem but introduce a much larger problem (or problems) by "solving" the issue of where to place a port. "So, my question here is. Are there any disadvantages using slot ported speakers? If no, why would not every manufacturer use the same design?" In the bigger picture, there's no difference between a slot or a round port or a group of smaller ports of any given shape. The tuning of the system is pretty much first and foremost just a function of port volume in cubic inches. Placement in the enclosure and port shape (plus length) is important for best performance but the effect of building a more "sellable speaker (because I can guarantee you all the reps for Wharfedale are telling the salespeople to start by pushing the difference in the Wharfedale's port) can easily outweigh the value of a better design when the product is selling in the mass market price range. In the end, a designer's job is to create a sellable product. Lots of really great ideas have been lost in audio because they weren't easily sellable. For most listeners, it won't make any difference in how the port is shaped or where it fires the backwave of the woofer. The tuning of the system is not so dependent on the shape or the location of the port unless you are doing more "serious" listening to more serious music. If you are a casual listener who doesn't sit and just listen to a recorded performance and just concentrate on the value of the instruments' character without any distractions, then you won't notice the difference between a simple vented system and, say, a transmission line system or a passive radiator. The less sellable aspect of those two designs are their size vs a simple vented system. Lots of people want speakers that don't take up visual space. Either a TL or a passive radiator will need to be at least 1/3 larger but will, IMO, give far more accurate bass performance. But a salesperson has to explain that to a customer and not that many customers are interested enough to care. So people keep buying the same old stuff because the designers are told they need to turn out the same old stuff. So, yes, an answer from someone like Jones would be interesting. The difference gets into the details of how the bass instruments "sound". If your priorities go to timbre of an instrument, rhythmic momentum and a bass sound that doesn't add its own snorting and chuffing sounds to the music, the small differences matter. If you "listen to music" while you read your emails or send texts, then you aren't paying sufficient amounts of attention to notice details like the sound of a port. How the details matter is an issue of where your priorities lay. I can give more details but, as I've said, there are some simple solutions that start with every manufacturer not starting with the same sheet of paper. . |
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Gold Member Username: MagfanUSA Post Number: 3505 Registered: Oct-07 | When dealing with Ported speakers, I think the Front port has a few more placement options than a speaker with a Rear port. Obstruction of such rear ports is ALWAYS a problem. I've seen recommendations for 'putting a sock in it' but I'm not totally on board with that, either. You change the 'tune' and design intent by obstructing the port. My fairly large sub, is Double ported. And doesn't produce any of the artifacts to which Jan refers. At least at the modest (except for dinosaur movies) levels to which I'm prone. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 18584 Registered: May-04 | . "I've seen recommendations for 'putting a sock in it' but I'm not totally on board with that, either. You change the 'tune' and design intent by obstructing the port." That's the idea of blocking the port, to change the tuning of the system. How useful it is depends on the system and the listener. The first speaker system I know of that offered a set of foam plugs for the ports was the Marantz Imperial 7 back in the late '70's. It was a very typical vented boom box without the plugs and it became a thuddy POS with them. But that was before speaker placement suggested not putting one speaker behind the sofa and the other in the diagonal corner. Adding resistance to the port can create an aperiodic loading to the system; http://diyaudioprojects.com/Technical/Aperiodic/ Such a system design can be beneficial if the low frequency driver is meant to accompany the port design. It does, when properly achieved, lower the twin impedance peaks of a typical vented cabinet and when done well with the right driver it can offer one reasonably small peak more similar to an acoustic suspension/infinite baffle system. It is essentially a leaky sealed enclosure. Under the best of circumstances, aperiodic loading tends to offer a fairly well damped system often approaching a "critically damped" system. That's not a sound that sells well in the demo room but performs well in most cases for the serious listener, particularly with typical tube amps with a low damping factor. Under less than ideal circumstances, it's just a gimmick IMO. The low frequency driver design must be intended for aperidoic loading or else the system goes to sh!t. Most contemporary systems which offer a plug are really just saying they know their buyers aren't very critical listeners and aren't that concerned about the actual performance of the speaker vs the convenience of speaker location. It's like buying a bacon cheddar cheeseburger and onion rings in a Chinese restaurant. "Obstruction of such rear ports is ALWAYS a problem." How is it ALWAYS a problem? The pressure wave escapes and does what that makes it a problem? . |
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Gold Member Username: MagfanUSA Post Number: 3506 Registered: Oct-07 | The general rule is that space constrained persons are not well served by rear ported speakers which are a little more space consuming than front. Setup, of course, rules and maybe a speaker is too boomy or has other bass problems when either near rear boundary or corner loaded....or 'other'. It is the Obstruction of the rear wave and the bounce back creating problems. Again, the general rule would dictate giving the port some 'breathing room'. My sub not only has a pair of ports but came with a single plug. AND the plate amp has a switch intended for 'maximum extention' or 'maximum output'. Switch one way, plug installed. The other switch position intended for No Plugs. I do NOT know what electronic changes occur by flipping the switch. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 18585 Registered: May-04 | . "The general rule is that space constrained persons are not well served by rear ported speakers which are a little more space consuming than front." That's what I'm asking, why are rear ported speakers supposedly "a little more space consuming than front" ported speakers? Why is this a "general rule"? Who made it so? For what reason are rear ported systems considered "space consuming"? I can see no rule of physics which predicts poor results that apply only to rear ported systems. As I've frequently mentioned, I'm not an engineer nor am I a designer. But I understand the physics of speaker placement and boundary reinforcement rather well I think. I can find no logical reason to ostracize rear ported systems, due only to the fact they are rear ported, relative to placement. "Setup, of course, rules and maybe a speaker is too boomy or has other bass problems when either near rear boundary or corner loaded....or 'other'." Don't know what you have in mind by "other". Nor do I know what "other bass problems" (double "others"? Is a double other similar to a double negative in that the two others tend to cancel each other- and the other other - and thus create no other?) would exist due to the placement of the rear ported system relative to a boundary. "Boom" is a function of the bass alignment of the system, which, in that case, is inflexible and not a variable which can be altered due to the distance away from boundary walls. "Boomy" bass reinforcement of any loudspeaker is related to its proximity to boundaries. The closer the speaker is located to a (large, solid) boundary, whether the speaker system is vented, infinite baffle or baffleless, the more bass is perceived at the listening position due to the omni-directional nature of long low frequency pressure waves and the subsequent reflections which either reinforce or cancel the forward going waves. Acoustic cancellation occurs due to the omni-directional nature of bass waves. It results in comb filtering of the in room bass response. It is not related only to the location of the port on the enclosure. So the issue of room boundary reinforcement is not one that is relative to only rear ported speaker systems. Correct? "It is the Obstruction of the rear wave and the bounce back creating problems. Again, the general rule would dictate giving the port some 'breathing room'. " "Breathing room", eh? How much? That's what I'm asking. How much "breathing room" is required for a generic rear ported system? And, why? You are not "obstructing" the port unless you are physically obstructing the port. You obstruct the port by placing some device into or over the port which actually blocks the port from functioning as a port. Simply placing the speaker enclosure 2" from the rear wall does not "obstruct" the port. "My sub not only has a pair of ports but came with a single plug. AND the plate amp has a switch intended for 'maximum extention' or 'maximum output'. Switch one way, plug installed. The other switch position intended for No Plugs. I do NOT know what electronic changes occur by flipping the switch." That's not relative to the discussion. If the manufacturer/retailer of the system supplies a device which physically creates a non-vented system, that doesn't then mean anything to the placement of a vented system. I'm asking about the widely held belief that rear ported speaker systems are some how bad when they are placed in close proximity to a boundary. Why is that a commonly held belief? The port is not obstructed. Not even partially. Boundary re-inforcement occurs as predicted by the laws of physics, which are the same (relative to boundaries) for any type of enclosure or non-enclosure. If the speaker system (or subwoofer) is capable of 40Hz reproduction, the bass pressure wave is roughly 28' in length. And it tends towards omni-directional dispersion into the room. If the speaker system is placed within a few inches of a boundary, what difference does that make to a 28' pressure wave only if the speaker is rear ported? What rule, or rules, of physics am I missing that predicts such behavior only for rear ported systems? Why has the perception gained strength among consumers that it is a no-no to place a rear ported system within, according to the op, 40" of the nearest boundary? There are a good many downfiring subwoofers which place the driver, and likely the port also, within a few inches of the floor - which is an extremely large, and typically very solid, boundary in virtually any domestic situation? If the driver is producing pressure waves, or the port is releasing pressure waves, why does placement close to a boundary affect "speakers" but not subwoofers? I'm just trying to figure out why this supposed rule exists. There doesn't seem to be a rational explanation for it, merely a "common belief" (a selling point for front ported speakers?) that it is true. How did it get started? Why does it persist? As I asked above, leo, "The pressure wave escapes and does what that makes it a problem?" Create extraneous noises perhaps? But aren't extraneous noises simply inherent in any simple bass reflex/vented system? So, what makes rear ported systems such bad joo-joo? . |
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Gold Member Username: MagfanUSA Post Number: 3507 Registered: Oct-07 | Jan, Asking why a rear ported speaker needs more room clearly shows you aren't a designer or engineer. The Port needs to work into at least a little 'clear air'. Were the speaker to be placed parallel and close to the wall, the backwave also interferes with proper propogation of the ports output. I'm not talking feet here, but for most small speaker with a port, 6" to a 1' should do. Toe in of the speaker might help the distance requirement. The sound reinforcement from near 'boundries' is subjective, but IMO, speakers loaded into corners can get boomy, while elevating a speaker moved away from the corner will maybe relieve you of some extra bass, were you to think that's a problem. My brother was having a problem and I told him to elevate his speakers a foot or more and I also told him to expect somewhat less bass, maybe 8 feet away at his listening position. He called back to ask how I knew that. Downfiring subs are DESIGNED to work into such a boundary. If measured as designed THAN elevated up a foot from the floor, you'd measure differences. Maybe better or maybe not.....and than it'd get subjective. Could rear ported speakers be designed to work into a wall? Yes and no. You'd almost have to specify a range of distances to get correct loading. It's perhaps easier to simply move the speaker away from too close to such a wall. Nothing at ALL wrong with rear ported. Even my panels produce a strong (as strong as front wave) backwave since they are symmetrical. But too close to the wall starts into problem range. Various rules of thumb NOT having anything to do with bass dictate a minimum distance of 5' as a good working start. Again, NOT parallel with said wall / boundry. I've seen recommendations for the wall distance being the Port Diameter. 2" port? 2" from wall. Opinions vary. I suspect the idea got started when doing setup, people LISTENED to the speaker in question and realized that a little distance helped. |
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Gold Member Username: MagfanUSA Post Number: 3508 Registered: Oct-07 | http://www.soundstage.com/revequip/polk_lsi9.htm Do cut/paste for this 'link'. read down for description of features. Interesting idea from polk. Back 'plate' provides spacing to rear wall. Plate has cone facing IN to port to deflect sound. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 18590 Registered: May-04 | . And that response shows you are even less of a designer or engineer. It's your typical say nothing response, leo, with something about your system thrown in, as always. "Were the speaker to be placed parallel and close to the wall, the backwave also interferes with proper propogation of the ports output." That's the basic assumption. I'm asking how that became an accepted truth. " ... the backwave also interferes with proper propogation of the ports output" says nothing. It's gobbledegook! What backwave? The backwave from the driver? That's what the port is releasing. So how does the backwave interfere with "proper propogation" of the port? What is "proper propogation" of the port in the first place? The port doesn't "propogate" anything. Look up the definition of "propogate". The port is the vent or pipe which allows the backwave of the driver to escape the enclosure. Pipes don't propogate anything, they simply release their contents. The port is fixed and non-changing. It can't propogate anything. The pressure wave may "propogate" by spreading its wavelength into a 28 or 35 foot peak to peak pressure front. But the port can only release what is inside the enclosure and there are no 35' long pressure waves inside a 12" x 13" x 8" speaker enclosure. The "port's output"? What is that? It is constrained by the size of the port. Will a 35' wave develop from the output of a 2" port. Yes, but your response does not explain why or why not. It is a pressure wave, leo. It will do what the laws of physics say it will do. If you believe the placement close to a boundary interferes with the laws of physics, feel free to explain how it does so rather than just state more nonsense gobbledegook. "I'm not talking feet here, but for most small speaker with a port, 6" to a 1' should do." And, how did you arrive at your somewhat nebulous distances? Because you go on to contradict yourself later in this post. If we are trying to "propogate" a 35' wave front, how does the distance away from the boundary of 6' to 1" determine success? Which of the two is more successful? Why? "The sound reinforcement from near 'boundries' is subjective... " "Sound reinforcement from near boundaries"? What the hell is that?! If you are talking about the boundary reinforcement of low frequency, long wavelengths, then it is not subjective. It's simply wrong to suggest it is. It is a provable law of physics which determines the effect. It is easily proven in about thirty seconds. Take whatever digital device you use for music storage/streaming and listen to it outside. Come inside and place the device on the floor or a large table. Sounds different? That's due to boundary reinforcement. Proven! Not subjective. Personally, I'm surprised your brother can hear lightning and see thunder. And, yes, we discussed this before, no need to duplicate. "Downfiring subs are DESIGNED to work into such a boundary." How are they "designed to work into a boundary"? What has the designer done that makes them any less susceptible to boundary effects than a typical rear ported speaker? Don't just give me more gobbledegook, leo. Explain. The driver and port are designed in what way that makes then unique to extremely close placement near a boundary? "If measured as designed THAN elevated up a foot from the floor, you'd measure differences. " leo, you and I can both read what you said about your brother's speakers. You told your brother to elevate his speakers and expect less bass (which is technically incorrect but I'm not arguing that point). Now you tell me that if the downfiring sub is elevated the measurement will change. Of course it will change, leo. You are "measuring" a change in the boundary reinforcement effect. Stop giving me gobbledegook and doublespeak. "Maybe better or maybe not.....and than it'd get subjective." No, leo, it would not get subjective and it's not "maybe". Boundary reinforcement of bass pressure waves is not "maybe", it is a rule of physics as old as physics. The Greeks knew about the effect and they described the rules which create the effect. They didn't tack a "maybe" on the end of their equation. "Could rear ported speakers be designed to work into a wall? Yes and no." LOL! Yes and no! We've sunk to the level where alternative facts exist to explain longstanding laws of physics!!! There are laws of physics which dictate the boundary effect, it is an easily demonstrated effect and one of the first anyone interested in audio will learn. The rules are not subjective nor are they "Maybe". They are not "yes and no" or "yes or no". You're simply spinning your wheels and saying nothing real. "You'd almost have to specify a range of distances to get correct loading." OK, if that's what you believe, how do you arrive at the "range of distances to get correct loading." How broad is your range? 6" to 1'? Or, more? Or, less? How do you arrive at "correct loading"? What is "correct loading'? Does it change with the speaker driver? Or, with the enclosure? Or, with the bass frequency? Or, with the port? More gobbledegook, leo. "Nothing at ALL wrong with rear ported." Well, actually that's not really true. As vented speakers represent a trade off of values, depending on your priorities, there are several things "wrong" with rear ported speakers. But I'm asking specifically about the belief they cannot be located easily when placed in close proximity to a boundary surface. "I've seen recommendations for the wall distance being the Port Diameter. 2" port? 2" from wall." That is the most common "rule" I can arrive at. Which does nothing to say the rear ported speaker cannot be located within a few inches of a boundary wall and still perform respectably. 2" port = 2" from the boundary has what to do with your "proper propogation of the port's output"? Explain what is happening at 2" distance that entails "proper propogation"? It is not opinion, it is provable science. I may not be an engineer but I can engage in empirical observation and, after repeated examples of similar results, draw a rational conclusion. "I suspect the idea got started when doing setup, people LISTENED to the speaker in question and realized that a little distance helped." Helped in what way? Your words are still gobbledegook, leo. What problem did they experience and what changed when the speakers were repositioned? Not gobbledegook say nothing words, leo. Not doublespeak. Not "Maybe". I'm asking for answers and not just more silliness that says you don't know but that's what you've heard. . |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 18591 Registered: May-04 | . OK, here's my take away from the Polk ... uh, ... "review". Polk wants to design a speaker with a rear port. Or, it appears they want to design a speaker with both front and rear ports but they also want to keep the physical dimensions of the enclosure as compact as possible to facilitate sales to customers with size constraints - which, when you are selling HT systems, is almost everyone. Polk understands rear ported speakers can get knocked in the showroom by an uneducated or somewhat less than truthful salesperson who opines to the customer that front ports are better than rear ports for some stupid reason they aren't really sure of and can't explain but they know they have been told to hit on the front port of the one rep's speakers. There really is no physical reason a vented enclosure cannot be placed close to a boundary wall into which the port will fire - if we are only discussing port placement. But the front ported thing and the compact enclosure thing are at odds with one another. The larger the port on the front baffle, the larger the entire enclosure is likely to be. One selling point contradicts the other. And, since most people don't play their system with the speaker grills off, most people don't care where the port is located but they do care about whether that speaker fits in a certain location due to its physical dimensions or its ability to occupy physical or visual space. So ... Polk knows they must place a port on the rear of the enclosure to achieve their desired bass tuning if they are restrained by enclosure volume and driver dimensions. But they will possibly lose sales due to the "common wisdom" that says the user can't place a rear ported speaker close to a boundary, which often means inside a cabinet or on a shelf in the "entertainment center" which holds the audio equipment for their HT system. Thinking hard and consulting the marketing department, they decide to simply place a fixed plate a few inches distance away from the mouth of the rear port which says to the buyer the speaker has been "designed" for placement close to a boundary. The plate, of course, is nothing more than a spacer which prevents the user from jamming the speaker enclosure hard up against the wall. This ensures the port has sufficient inches in which to release the internal pressure wave without excessive chuffing and puffing noises acompanying the loudest bass sounds reproduced by the speaker system. The rest of the story about the cone dispersing the wave exiting the port is pure Polk BS sales story because the pressure wave exiting the port is, according to the laws of physics, going to "disperse" and become a 35' pressure wave within the room with or without the cone. They could have put a dead chicken in the mouth of the port and just told people the same story, as the cone really does nothing. It's doesn't serve as a waveguide or a horn. It just is because Polk needed a story to tell the salespeople to tell their customers. The designers can live with the idea and the marketing department is excited to have another new BS story to tell that sets them apart from the competition. The sales reps are satisfied because they get to tell the sales staff the story and how it justifies the additional cost despite the fact the cone is simply a bunch of old parts that came back for warranty repair and the plate cost them $0.05 to add to the speaker. No one is expected to notice the rest of the Polk line also has rear ports but lacks a spacer plate. If some one asks, they can just say it's all because Polk is so smart they figured it out for you. Pure Polk! . |
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New member Username: KeplerPost Number: 3 Registered: Oct-18 | Guys you lost me, the question was simple - Pros and Cons of slot ported speakers. Please calm down |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 18592 Registered: May-04 | . "Slot ported speakers" says nothing that represents either a pro or a con. In the big picture scheme of things, ports are ports. They are there to facilitate the release of the rear wave of the bass driver(s) from inside the enclosure. As I stated in my op to this thread, there are pros and cons to building a vented enclosure and there are numerous types of vented enclosures to design with. Once again, in the simplest concept you can only say a vented enclosure is not an infinite baffle system. An infinite baffle is any system in which the rear firing wave of a driver cannot wrap around the baffle. In any system other than an infinite baffle (of which an acoustic suspension system/sealed enclosure is a type), the backwave from the driver is allowed to exit the enclosure. In so doing, due to the length of the bass waves, they act in an omni-directional dispersion pattern. Basically, this means the rear wave has the ability, due to its size and its dispersion characteristics, to wrap around the enclosure and continue into the room. It's the presence of both forward going and rearward going bass pressure waves and the wrapping around that causes the initial peaks and nulls from a vented system. In other words, if the rear wave is dispersed into the room in an omni-directional pattern, there are certain waves which will meet the front going wave coming at the listener directly from the driver. Also realize, in practical use the room acts as a secondary enclosure to the system and sound waves are reflected back and forth inside the room which further accounts for peaks and nulls in response as the combining waves meet in the room. Basically, a rear going wave cancels a front going wave and a front going wave doubles the value of another front going wave. The result is called "comb filtering". That's the basic idea and pros/cons of a vented system for this discussion, the enclosure is not constraining the rear wave from the driver. A vented system in its most basic form has output from the driver only to a certain frequency. Beneath that frequency the port is tuned to create the lowest frequencies and most of the bass extension from a vented system is created by the port itself as it "tunes" the resonant frequency of the enclosure. Sort of like blowing air into a Coke bottle. The larger the volume of the enclosure, the lower the bass extension. The larger the port, the lower and louder the exiting air will be as it creates "bass". Until that is the port becomes so large it can no longer act to tune the enclosure. Try blowing air across a pickle jar and see what you get. But that's it. Those are more or less the rules for a vented system. The enclosure volume and the total port volume determine the bass extension and the bass tuning of a vented enclosure. From the Stereophile measurements of a Polk speaker with a vented (tuned) enclosure; "Though 3dB of the apparent peak in the LSi7's upper-bass output is in fact an artifact of the nearfield measurement technique (which assumes a hemispherical acoustic environment for the radiators), the rest is real, correlating with BJR feeling the speaker to have some "midbass thickness." Speaker designers will very often go for this kind of reflex alignment to give the listener the impression that a small speaker goes deeper in the bass than it actually does. However, my experience has been that getting this right is quite tricky, and whether the excess upper-bass energy will be perceived as power and extension (good) or boom and thickness (bad) will also depend on the speaker's upper-frequency balance." https://www.stereophile.com/content/polk-audio-lsi7-loudspeaker-measurements So, before you drift off thinking I'm still not answering your question, the port is only a port. The shape of the port is of minimal difference. What counts is the total port volume in cubic inches and, to some extent, it's placement on the enclosure surface relative to the high and low pressure areas inside the enclosure created by the backwave of the driver. One issue with ports is they make noises. When the system is tasked with turning out high SPL's and low bass frequencies, the port noises become more evident. This is where port shape can make a difference in that flaring the port's entrance and exit can reduce the wind noises created by the port. Various designers have taken that idea further and have applied specific techniques to further reduce the noise. B&W introduced the dimpled port and their story was the golf ball's dimples allow it to fly further by reducing drag. "Drag" can also be read as turbulence. Turbulence is what creates noise in a Coke bottle or an HVAC vent. So we run into another case of pros and cons in that the port should excite turbulence in order to reduce noise but not too much turbulence or the port itself becomes noisy again. Therefore, you should be able to see that a "slot ported speaker" says nothing that sets it apart from any other vented system. If the slot is simply a vent in the enclosure shape that is unlike a round pipe, then the rules apply which say the total vent volume is what's important to tuning the enclosure. Then the slot simply becomes another story for the sales staff to tell which is meant to "sell" a certain speaker over another. If there is a specific and scientific design to the vent and it is, say, rounded inside and out to reduce vent noise, then that's another story but not one that merely saying "slot ported speaker" describes. Marketing drives most designs in the mid-price ranges and the marketing department counts on selling to a fairly low information consumer. So that's your answer, nothing particularly unusual or exotic about vents shaped like slots. If that's the only thing the speaker has going for it, it's no better, or no worse, on the face of it than any other vented system in the shop. . |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 18593 Registered: May-04 | . This is a case where Wikipedia gives a fairly decent and fairly complete overview of a vented (bass reflex) speaker system; https://en.wikipedia.org/wiki/Bass_reflex . |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 18596 Registered: May-04 | . "The first speaker system I know of that offered a set of foam plugs for the ports was the Marantz Imperial 7 back in the late '70's. It was a very typical vented boom box without the plugs and it became a thuddy POS with them." "I see no logical reason for not building acoustic suspension loudspeakers again." https://www.audioholics.com/loudspeaker-design/loudspeakers-when-is-good-enough- enough-part-1 If you've read the Wikipedia article on vented loudspeakers, you can see the author here ignores many of the finer details of time and phase inconsistencies in vented boxes along with their inherent trade offs in the areas of transient response and rate of bass roll out. Somewhat typical of Audioholics, which IMO is far too numbers on a sheet of paper oriented for my tastes. It is a possibly interesting article none the less given the references to speakers which have been mentioned in this thread. . |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 18598 Registered: May-04 | . Going back to the op, the Wharfedales that were mentioned as slot ported seem to have a single port on the bottom of the speaker. The port fires downward though it fires into what appears to be a bottom plate that looks to be no more than 3/4" from the bottom of the enclosure. Now, looking at the measured frequency response of the system, I can't imagine the port is no more than 3/4" in measurement at any point. That would seem to indicate Wharfedale feels it's OK to have a vent firing into a barrier which is extremely close to the vent's mouth, just as Polk does. I could never find any substantiating data on the 2" port = 2" distance from the barrier wall, just wisened old hands claiming that was the rule of thumb. Given the design of the Polk and the Wharfedale, I think that may also be just another old wives tale. So, ... If a port can fire into a barrier that is within an inch of the mouth of the vent, it would be interesting to hear Wharfedale explain how their slot port makes a difference vs a more typical port placed on the rear of the enclosure. What difference are they claiming? . |
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New member Username: KeplerPost Number: 4 Registered: Oct-18 | Thanks Vigne, At the end it all comes to marketing strategy, nothing less nothing more. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 18599 Registered: May-04 | . Yes and no is, I think, the best response. Most designers are in a group rather than designing on their own. They work for large international companies rather than starting their own cottage industry business. That certainly reduces their input into any design. As I mentioned, the primary task for a designer is to create a sellable product. Companies such as Wharfedale are international with production off shored to other international companies. Millions of dollars ride on any one design, even more when it represents a single product within a line of products. As the Audioholics article suggests, what sells inspires imitators and marketing plays a large role in public perception. https://www.youtube.com/watch?v=cwkzNclZR4s https://www.nytimes.com/2006/01/09/business/media/fake-products-and-the-movies-t hat-loved-them.html Very, very few designers are so fortunate to be the next Henry Kloss, the founder of Advent. Beginning with Acoustic Research (AR) and the world's first acoustic suspension loudspeaker, he started his first company with a college professor fresh out of MIT. Their designs were founded in science and a love of music. Moving on to KLH, Kloss was in the company of other brilliant designers who marketed what they thought up with a vision toward creating systems of electronics that would encompass all aspects of home music reproduction. A little over ten years into his career as an audio designer, Kloss was on his third speaker company by the time he began Advent with no marketing department to tell him what they wanted. Kloss actually created Advent to sell speakers which would finance his interest in full line home entertainment systems. He brought to market the world's first "widescreen" (72" diagonal) projection television, the Advent Novabeam;https://www.google.com/search?q=advent+novabeam&rlz=1CAACAY_enUS754US756&oq=adve nt+novabeam+&aqs=chrome..69i57.11625j0j1&sourceid=chrome&ie=UTF-8 Kloss never stopped thinking like a visionary and looking like a stereotypical, liberal, university tenured professor. To paraphrase my favorite quote from Kloss, "Of course it's research. If we knew what we were doing, it wouldn't be research." Times were different and cottage industry consumer audio companies were flourishing under the leadership of one strong thinker and a small team of equals. Audio was yet to become an industry as opposed to a hobby. Not to sound too much like an old timer, the VietNam war changed America's concept of home entertainment. The returning GI's had access to an incredible array of electronics from Japan sold in the PX at ridiculously low prices. Transistors were changing the look and sound of reproduced music and large, heavy, transformer coupled tube amplifiers were experiencing a falling out of favor low point. The very first Quadraphonic "surround sound" system I ever listened through came from a PX. In the late '60's, America was beginning to see the first wave of Japanese audio products capable of undercutting the quality and the price of long standing American lines. Many of the established and well known US manufacturers did not survive that first wave, let alone the second and third. By the time the war ended, the audio industries were changing in ways that made sales numbers often far more important than quality. From there the marketing people, fresh out of the universities with degrees in their hand, transformed much of how America did business. While many companies resisted, it was become more and more clear, they couldn't survive selling only on their home turf and marketing was to hit the ground running. Audio was becoming a matter of big money. From there, I can think of no better tale of how consumer audio grew up than that of DaytonWright; https://www.google.com/search?q=dayton+wright+audio&rlz=1CAACAY_enUS754US756&oq= dayton+wright+audio&aqs=chrome..69i57.4881j0j1&sourceid=chrome&ie=UTF-8 America was "the market" for everyone else. Companies such as B&W and Wharfedale began aiming their products directly at the US markets with designs the marketing department deemed "Americanized". The first high end audio store I worked in back in 1975 carried only a few lines of speakers. They were all American designed and built products. Everything we had wouldn't fill one aisle of speakers in today's big box stores. I can say general quality has improved in today's products, almost to the point of blandness and me-too-ism. With internet on line sales just a touch away, searching for the truly designer driven audio products has become far more difficult than it was when I first began selling. I always made the distinction between active listening and background music with each of my clients. Most buyers don't know the sound of live music and don't care for anything other than something that jumps out at them in the showroom. Audio reviews have reverted to the tried and true reporting rather than reviewing and all end with, "I was impressed by the Lirpa PLX-1B and feel it is competitive in its price range." If you listen to music while you're doing something else, then that's background music. You need a commodity, not a design. If you're not paying attention to the performance and the music is not the reason you buy a high quality system, the marketing people have hundreds of products to choose from, each as good as the other. If your wish is to own something rather special, you'll probably have to get out of the big box, mass market lines. They are out there but you'll have to work more and read less BS reviews to find them. IMO you'll also need a reference for music that comes from experience with live music being performed in front of you in a real world venue. You might want to read the B&W vs Monitor Audio thread for more insight into loudspeaker design. . |