marcb515 Posted October 18, 2005 Share Posted October 18, 2005 and why are some rear ported? In looking at center channel speakers I noticed that some are not ported, some are front ported, and some are rear ported. I wouldn't think a speaker that small would need to be ported, but if anything I would think front ported would be the best? Sorry if this is a silly question, just trying to learn some. Quote Link to comment Share on other sites More sharing options...
Petrol Posted October 18, 2005 Share Posted October 18, 2005 and why are some rear ported? In looking at center channel speakers I noticed that some are not ported, some are front ported, and some are rear ported. I wouldn't think a speaker that small would need to be ported, but if anything I would think front ported would be the best? Sorry if this is a silly question, just trying to learn some. Ah, my guess is that they are ported for slighly deeper Bass reproduction... the front ports are more forgiving of book shelf and direct wall mounting Quote Link to comment Share on other sites More sharing options...
dragonfyr Posted October 18, 2005 Share Posted October 18, 2005 Porting is a form of 'adjusting' the acoustical (air) load on a transducer. There are many differing enclosure alignments (designs), each having various strengths and weaknesses. So typically what you encounter is a compromise designed to minimize the disadvantages while maximizing the advantages within a given set of restrictions and goals, namely: bandwidth, efficiency and enclosure size. With a vented box, there are two primary variables: the volume of the enclosure and the tuning frequency of the enclosure. Generally you need a larger enclosure for a vented enclosure then for a sealed enclosure. Vented enclosures also typically exhibit greater phase shift, group delay (the derivative of the phase - or the rate of change of phase), a more complex impedance and transducer excursion response. Mid-range frequency leakage emanating from the rear of the transducer that exits from the vent is another issue that must be minimized as it will interfere with the sound emanating from the front of the transducer. The orientation of the port can be for aesthetic reasons, space reasons (as in minimizing the size of the baffle), and in attempting to compensate for MF signal radiation. Rear placement affects the ability to place the speaker close to a reflecting surface minimizing its ability to leverage coupling advantages. For a given transducer the advantages include an extended low frequency response and greater efficiency in a smaller enclosure then that offered by a sealed enclosure. Quote Link to comment Share on other sites More sharing options...
hwatkins Posted October 18, 2005 Share Posted October 18, 2005 ditto for what was said above - the condensed version is: Center channel speakers are generally spaced constrained for most folk's homes and for the mass market the smaller boxes need to have help in extending the bass response to create a better match for the voicing that is to appear to be coming from the screen. The position of ports (if for all other intents and purposes the box is well designed) is of no consequence on the speaker perfrormance unless there is an obstruction (wall) near the face of the port. Otherwise, many speakers (regardless of size) are ported as a tuning exercise to produce reliable and specific responses. Quote Link to comment Share on other sites More sharing options...
TBrennan Posted October 18, 2005 Share Posted October 18, 2005 "For a given transducer the advantages include an extended low frequency response and greater efficiency in a smaller enclosure then a that offered by a sealed enclosure. " Not quite. Vented doesn't give you more efficiency with a given transducer but allows you to use a more efficient transducer for the given combination of box size and F3, efficiency being set by the driver itself. You kind'a have it backwards. Quote Link to comment Share on other sites More sharing options...
dragonfyr Posted October 18, 2005 Share Posted October 18, 2005 "For a given transducer the advantages include an extended low frequency response and greater efficiency in a smaller enclosure then a that offered by a sealed enclosure. " Not quite. Vented doesn't give you more efficiency with a given transducer but allows you to use a more efficient transducer for the given combination of box size and F3, efficiency being set by the driver itself. You kind'a have it backwards. Sensitivity is determined by the transducer. Efficiency - the ability to convert electrical energy into sound energy for a given amount of input power is greater for a vented enclosure then for a sealed enclosure. Quote Link to comment Share on other sites More sharing options...
TBrennan Posted October 18, 2005 Share Posted October 18, 2005 "Efficiency - the ability to convert electrical energy into sound energy for a given amount of input power is greater for a vented enclosure then for a sealed enclosure. " Only in the area of the lowered F3 and that's already covered by the notion of the lowered F3 with the vented box. Otherwise the vented box is doing nothing to give the driver more output. Even so the total amount of low frequency output "below the curve" is pretty much the same for vented and sealed, the vented has a lower F3 but a faster roll-off. You can't get something for nothing. Quote Link to comment Share on other sites More sharing options...
dragonfyr Posted October 18, 2005 Share Posted October 18, 2005 For the purposes of this post, the basic characteristics were synopsized in one sentence. Any descriptions here are gross simplifications and I can cite any number of specific exceptions for any generalization. The synopsis was the 5 cent tour, If you desire more comprehensive and rigorous analysis, PM me for my very reasonable rates! A vented enclosure offers greater efficiency then a sealed enclosure. Period. I am not going to waste time debating relative efficiencies between acoustic suspension and reflex loaded enclosures. And as enclosure tuning has little to do with the HF response while addressing the LF response characteristics, saying that it only makes a difference in the LF region with a lower F3 begs the obvious! And if all other aspects are equal (as you so obviously point out!) and there is an increase in the LF response, the net efficiency increases!! This makes even the SET and cable debates look attractive as a viable waste of time. If you wish to explore granularities of enclosure design, various orders of tuning and transducer topologies, etc., may I simply point you to Benson, and you can debate with his reference and I will defer to whatever he 'says'. After all, that is where I head for answers anyway, so simply cut to the chase and go to the source! And to address a few other topics that seem to come up now and then on the site regarding ports... At frequencies well above the vent tuning frequency, the acoustic output is from the front radiation of the woofer. But for a narrow bandpass near the tuned frequency, the acoustic output is the sum of the vent and direct radiated energy, assuming that these sources are in phase. Thus, the distance of the listener to the two sources is the critical factor. Thus they can be located anywhere within 1/4 wavelength of the driver. But before you start to worry, as the wavelength of a 100 Hz tone is ~ 10 feet long, and enclosure tunings are typically less then that, this limitation is typically not of prime concern as long as the listening position exhibits no more than 2.5 feet of difference between the transducer and port! Additionally, larger diameter vents tend to be quieter then small vents. Oh, and to add one or two more things as regards the ports - yes, ports can extend out of the box instead of into the box,although internal enclosure volumes will need to be accounted for and an outward protruding vent looks weird and is a bit unwieldy! In my opinion, while rear or side facing vents are perfectly acceptable and present no real issues (provided design limitations are observed) and also offer the advantage of reducing the audibility of the mid frequency distortion, their restrictions on spatial loading (corner placement, wall placement, etc.) are important to me. Small amounts of port flaring does tend to reduce additional noise when the velocity of the volume of air in the port reaches ~5% of the speed of sound. In other words, none of these issues generally present a major limiting issue in vented enclosure design! Disclaimer: The above is not intended to serve as a substitution for comprehensive design procedure and anyone who wishes to pursue the actual design of loudspeaker enclosures is hereby directed to (among other reference texts): Theory and Design of Loudspeaker Enclosures by J.E. Benson Quote Link to comment Share on other sites More sharing options...
TBrennan Posted October 18, 2005 Share Posted October 18, 2005 Sophistry and many words to confuse the issue. Basic system efficiency is set by the driver not the box, the box cannot make a driver more efficient over more than a small bandwidth near F3. Venting allows a more efficient driver, it doesn't make a driver more efficient as you originally stated. You should just admit you've the wrong notion here, don't feel bad, I used to think it myself, you know, back in the 70s when Ray Newman was first writing articles on T/S theory. Quote Link to comment Share on other sites More sharing options...
dragonfyr Posted October 18, 2005 Share Posted October 18, 2005 Basic system efficiency is set by the driver not the box, the box cannot make a driver more efficient over more than a small bandwidth near F3. Venting allows a more efficient driver, it doesn't make a driver more efficient as you originally stated. You should just admit you've the wrong notion here, don't feel bad, I used to think it myself, you know, back in the 70s when Ray Newman was first writing articles on T/S theory. ----------------------------------------------------- Discover the respective meanings of sensitivity and efficiency! And I never said it "make(s) the driver more efficient!" as YOU INCORRECTLY state! It makes the vented system more efficient then the sealed system!! Personally, I don't use sealed drivers or ported drivers!!! I utilize sealed enclosures and ported enclosures to augment transducers! Words do mean things! Unfortunately some less then others! Lets follow this nonsense that has nothing to do with the original intent of the post! "the box cannot make a driver more efficient over more than a small bandwidth near F3." But you maintain that the topology of the enclosure has NO effect upon system efficiency! Nonsense! The converse of your statement means that there is a potential increase in output at the lower end of the frequency bandpass for a given input! Thus, all other things being equal, the amount of returned acoustical output is greater given a proper tuning of the enclosure. Should I repeat this again! So you heard it here folks! 1) As "system efficiency is set by the driver not the box", there is absolutely no point in messing with all the combinations or permutations involved in system and enclosure design. Thus, according to this lunacy, the various tunings do not result in additional acoustic output at the lower extensions of the frequency bandpass! 2) " the box cannot make a driver more efficient over more than a small bandwidth near F3." Oops! this minor exception is the critical issue! But I am focused on systems, and not a particular driver. Make up your mind. And if you want to debate, debate a point that I am making, not some fantasy that you have created! Efficiency is a ration of the output to the input. And a greater output for a given input, equals greater efficiency. And as the box makes a small difference in the focused area of interest by increasing the output near F3, the vented enclosure is more efficient. As Neville Thiele published his "Loudspeakers in Vented Boxes in 1961 in the Proceedings of the IRE in Australia (reprinted in the AES Jrnl in 1971), Richard Small published his dissertation on direct radiating loudspeakers in 1972, and Benson, the examiner for Small's PhD thesis, originally published his works in Amalgamated Wireless Australasis Technical Review in 1968, 1971 and 1972 and these were published in 1993 by SynAudCon (ISBN 0-9638929-0-8). Benson's works supplant and go far beyond what Thiele and Small presented. In fact, Benson's work: "is a classic, and even more detailed and comprehensive than Thiele and Small's loudspeaker papers as published in the "AES Journal" (if you can believe that!). He goes into an exhaustive analysis of the infinite baffle, closed box, damped vented box, passive radiator vented box, and the acoustic resistance controlled systems. The papers are very instructive and a 'must read' for anyone seriously interested in low frequency cabinet design. It includes the only complete mathematical model and formula that includes all of the previously mentioned systems that I know of! it includes both analysis and synthesis of all of the systems, including innumerable design tables, charts and graphs. The color graphs and tables are stunning! I highly recommend it!" Oh, that's not my opinion (although I do share it!), that is the opinion of Don B. Keele in the work's preface! May I suggest reading the original works, as evidently something has become confused in the interpretation! Perhaps you shouldn't have stopped reading and continued to read the source material itself and not simply about it. And now I suspect that it is time for the few who maintain that T/S, et. al., are nonsense to show up! But before this happens, I'm out of here! This ranks up there with one of the most asinine tangents in a while! I am done with this BS! Isn't it nice when the discussions digress into such superfluous BS? Have fun! Quote Link to comment Share on other sites More sharing options...
TBrennan Posted October 18, 2005 Share Posted October 18, 2005 Now you're trying to wriggle by claiming that increased efficiency and lowered F3 are the same thing. They're not. You said that for a GIVEN DRIVER venting increases efficiency. It doesn't. It gives lowered F3 or smaller box for the same F3. Now were you a Greek Philosopher you could argue that in a sense lowered F3 is an increase of efficiency but that's not the accepted usuage of the word so you're playing semantics. Plus your definition of increased efficiency fails to deal with the total amount of low frequency energy of sealed and vented systems and the different rolloff slopes of each and may not be increased efficiency at all by your own definition. Quote Link to comment Share on other sites More sharing options...
DrWho Posted October 18, 2005 Share Posted October 18, 2005 Well the textbooks claim that a vented enclosure increases the efficiency of the driver... The textbooks also mention that the nominal system sensitivity is the same...yet the actual sensitivty of the system changes (which is why eminence doesn't list nominal sensitivities for their drivers, but rather frequency dependent sensitivites). You can think of efficiency as the area under the transport function curve ignoring anything below -20dB (where masking is officially achieved). Ironically, the optimal sealed and ported transport functions for the heresy K-22E cross at -20dB @ 23Hz, so there's that whole eye shaped curve where the ported version is more efficient. I usually see this point happening around -12dB, but even in that case the area under the ported curve will still be greater. Nevertheless, the system efficiency is clearly greater for the ported K-22E. To keep this practical please by all means list drivers that you feel this is not the case... Do we need to bust out the thermodynamic definition for efficiency? (which is actually where this particular speaker science comes from) Quote Link to comment Share on other sites More sharing options...
dragonfyr Posted October 18, 2005 Share Posted October 18, 2005 For a given driver, the difference in placing it in a sealed enclosure and placing it in a tuned vented enclosure is an increase in the LF response near F3! A bass reflex enclosure is more efficient then the corresponding acostic suspension enclosure! And the response does too address rolloff and slopes and ALL the radiated acoustic energy! It contributes to it!!! Enough of your Martian acoustics! Quote Link to comment Share on other sites More sharing options...
dragonfyr Posted October 18, 2005 Share Posted October 18, 2005 Doc, thanks, but don't even try![] I can cite a dozen references that say the same thing, and now the poor gentleman who dared ask a simple question is convinced of nothing more then the fact that asking the question - heck ANY question on this site - is a mistake! But its nice to be able to identify the wackos. Maybe if we passed out signs we could have some warning and avoid them! Quote Link to comment Share on other sites More sharing options...
TBrennan Posted October 18, 2005 Share Posted October 18, 2005 More mere assertions. Fact is you don't react well when someone calls you on your self-important, long-winded and humorless pedantry. Explain the mechanism by which a given driver in a system would be more efficient at 2F3 in a vented rather than a sealed system. Quote Link to comment Share on other sites More sharing options...
dragonfyr Posted October 18, 2005 Share Posted October 18, 2005 So you are still hallucinating that the driver becomes more efficient!???? I maintain that the system including the enclosure becomes more efficient.Of course so does every other source!Rant on.....Kisses big boy! Quote Link to comment Share on other sites More sharing options...
TBrennan Posted October 18, 2005 Share Posted October 18, 2005 You've changed your argument in midstream. First you said for a given driver you can have more efficiency AND deeper bass, implying an increase in overall driver efficiency (for only by increasing driver efficiency can widerange system efficiency be increased) then you redefine deeper bass and increased efficiency to be the same thing. Which it is in a very narrow sense perhaps but not in the wide sense you implied, especially as you said this efficiency came as an addition to lower bass, not as part and parcel of it. Quote Link to comment Share on other sites More sharing options...
DrWho Posted October 18, 2005 Share Posted October 18, 2005 orange = ported K-22E yellow = sealed K-22E I figured a picture would be a good way to show what's happening with the frequency response. Afterall, the question was concerning the implementation of ports. As far as the efficiency thing goes....there is more acoustical output from the ported cabinet in the lower frequencies. Since the same power output from the amplifier results in more net acoustical output from the ported design, the ported design is therefore more efficient. This is the definition of efficiency in its simplest most basic form. Quote Link to comment Share on other sites More sharing options...
dragonfyr Posted October 18, 2005 Share Posted October 18, 2005 nope... ...you are all over the place.Only one characteristic has been consistently addressed - the efficiency of a vented/ported enclosure - the system! And this manifests itself in the form of increased LF extension response of the system!. You are the only one preoccupied with the insane notion that an enclosure changes the electro-mechanical characteristics of a driver! Throughout the driver has been assumed to be a static variable - a given - a constant - and not subject to adjustment! ONLY the enclosure has been addressed as a variable along with the resulting response and the total system. As the focus was on ported systems, with sealed systems referenced as a point of comparison. As I was not about to enter into multivariant analysis in a non-mathematical format! But this is too complicated for some folks to understand.And just when it doesn't seem possible, the story gets even loonier!What is this nonsensical "efficiency came as an addition to lower bass, not as part and parcel of it." So now "efficiency" is a separate 'thing'? a quantity"? It's a quality or characterisitc of the system!Sorry, but you have become a parody of yourself!So, let me officially excuse myself from this parody! And you are left to play with yourself.... Have fun...BTW, I certainly hope the original poster got the information/answers he was desiring. If you haven't, please PM me and I will try to find out any other info you may need - or feel free to post. Good luck!As far as everything thereafter, well... Quote Link to comment Share on other sites More sharing options...
Seadog Posted October 18, 2005 Share Posted October 18, 2005 So, should I start drilling holes in my Heresys?? [*-)] Quote Link to comment Share on other sites More sharing options...
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