The Curse and Bane of the Rear Port

[bluewizard]

OK, maybe I exaggerated, it's not a curse or a bane, but it is certainly an annoyance.

Why would anyone use a rear port if they didn't have to? Is it just so you can hang out will all the cool speaker designers who are also using rear bass reflex ports?

Here is an example -

http://www.superfi.co.uk/index.cfm/page/moreinfo.cfm/Product_ID/2202

With all that space on the front, why put the port on the back and complicate using the speaker?

I acknowledge there are lots of times when you have no choice, say a typical MTM speaker. There simply isn't room on the front, so you have no choice but to put it on the back.

Yet in a larger tower speaker with plenty of room on the front, why would you put the port on the back?

I don't have a lot of experience with rear ported speakers, but the fact that it is somewhat common for them to come with Bungs to plug the ports, says this is a less than ideal design.

If you have a living room or home cinema room like an auditorium, rear ports and the distance they demand to be from the back wall, aren't a problem. But if you are a normal person living in a normal house, the port causes more misery than good, and is invariably plugged up to resolve timing issues.

So, again, why rear port if you don't have to????

I look at the new Zaph 3.5 design, rear ported, though plenty of room to port in front, and ask Why?

Can anyone enlighten me?

Steve/bluewizard

[ThomasW]

Nothing wrong with putting the port on the back.

Speakers like those you linked to are designed to set 2'-3' out from the wall. So having a rear-firing port isn't a problem.

[benchtester]

I, too, am curious what are the advantages to rear porting?

BTY, there are interesting comments and a graph from Zaph in the middle of his tidbits page under the "front port mounting..." heading. I believe the graph was made during the development of the ZRT speakers.

http://www.zaphaudio.com/tidbits/

[Mike B]

If you are bouncing some higher freq's around the box, bouncing them out the rear can have a mitigating effect.

[jkrutke]

I look at the new Zaph 3.5 design, rear ported, though plenty of room to port in front, and ask Why?

That enclosure was built at a time (a few years ago) when I thought front radiating ports were bad. Why did I think that? Because everyone told me so. Now I know better. At this point, I don't believe anything I read on the internet.

I still put ports on the back sometimes, but it's not important.

On the other hand, putting them on the front seems to be like telling people it's ok to put their speakers right up against the wall. It's not ok. For people who are that tight for space, I have one word for you: headphones.

Let me let you guys in on a little something about midrange "leakage" through a port. Most people have measured front mounted ports nearfield and noted a peak in the response a couple octaves or so above tuning. Some have have just called it midrange leakage, some have called it organ pipe resonance. Both are wrong, at least most of the time I think. It's an artifact of that measurement technique that does not show up for close mic'd rear ports.

The artifact is nothing more than some of the woofer output combining with the port output with the phase wrapping at a certain frequency causing a dip/peak/dip. The port is down in level at that point, but there's still enough there to sum with the woofer's output. The thing is that the artifact is only present that close to to port. Backing up for proper summing will not show it. It's not because the woofer's output is drowning out the peak, it's actually because the peak isn't there at all. The experiment that can show this is simple. Lay your front mounted port speaker on the floor face up, and do the nearfield port measurement. Note peak in port response. Now, take a nice heavy and large board, 4 square feet maybe, and position it between the port and the woofer. If you don't have that, cover the woofer up with a couple dense blankets. Take the nearfield port measurement again. Poof, that peak isn't there anymore, proving the woofer interference artifact. Now you can also note that your port response curve is now very smooth, all the way up to the midrange. Additionally, you can also note: there's less midrange leakage when the port is front mounted, provided you used good damping material. The midrange leakage is now just a noise floor and is generally a bit lower than what is seen on a rear mounted port, simply because the front mounted port does not have a direct path to the woofer cone.

I suppose I should note that this upcoming design I mentioned on my blog has a rear mounted port, but that's only because the cabinets were built 5 years ago, back when I used to believe what I read on the internet.

[bluewizard]

Nothing wrong with putting the port on the back.

Speakers like those you linked to are designed to set 2'-3' out from the wall. So having a rear-firing port isn't a problem.

TWO OR THREE FEET! Like I said, if you live in an auditorium that might be fine. But I think few normal people living in normal homes can have their speakers 3 feet into the living space. Though I do acknowledge you are right.

So, it is not so much of question of what you should do, but what you must do. We must live in the houses we live in. We must deal with the speaker in the space we have, and like so many aspects of audio, that involves compromise. If you live in an auditorium then sweet. And if you don't then ... well, allowable words fail me.

As to the suggestion of headphones, it's pretty hard to throw a party with a pair of headphones. Realistically, that is not an option, except for rare occurrences of very private listening. Also, are you projecting the elitist attitude that if the unwashed masses can't afford a huge house with a large media room, they don't deserve to listen to good music?

Further, I'm not saying it is impossible for rear ports to work. I'm saying, I see it as an unnecessary inconvenience. Placement, for better or worse, is a lot more flexible with front porting. I mean what good is the rear port after all if you have to plug it up?

jkrutke,

If you are indeed the world famous 'Zaph', I wasn't criticizing your design. By all accounts the ZDT3.5 is a first rate speaker, but at the same time, if I ever build a pair, they are going to be modified so I can front port them. Again, given the practical consideration of the average consumers living or listening space; rear ports are a hindrance. Again, what good is the rear port if I have to plug it up?

And the hint that you are likely to have to plug it up come from the manufacturers including a bung plug with the speaker.

You speak about rumored midrange leakage, but isn't that same midrange also leaking out the back port. How does front or rear affect this seeming unrelated aspect?

Certainly, in the ideal space, ideally positioned, rear ports work. But how many consumers have the ideal space and are able to ideally position?

Again, I may have stumbled across a reference or two to front ports being bad, but nothing to tell my why rear ports are good. It seems to me that even under the best of circumstances, it is one big mess of timing problems.

LONG LIVE FRONT PORT! ;x(

Steve/bluewizard

[eyekode]

This is 2-3 feet from the front baffle right? Lets say you have a 20" deep audio rack, not too crazy right? Do you put this flush against the back wall? Nope, you pull it out a few inches. So to get to 2 feet your speakers front will only be 1-2" in front of your audio cabinet. Not too crazy even for small rooms I think...

And these are just guidelines. Move them around until you like the imaging and balance in the lower octaves.

[jkrutke]

Also, are you projecting the elitist attitude that if the unwashed masses can't afford a huge house with a large media room, they don't deserve to listen to good music?

The headphones comment was a bit of a sarcastic joke, sorry. But, I just don't see the refusal to move speakers away from the walls. I have a 12x12 room in my house that I am still able to place the speakers about 2 feet out. With some wall treatments, I'm able to get some shockingly good sound in there, almost as good as my main HT room.

This discussion is less about front ports and more about placing speakers against walls. Wall placement causes huge peaks and valleys in the response curve right in the midrange due to the out of phase rear reflection. The peaks are still there when you move the speakers out from the wall, but they then move lower in frequency where they are less noticeable. If you want to see some response curve samples showing this, let me know. Summary: port location doesn't matter much. Placement in room does matter a lot.

I will say that some of us do get annoyed at how fast a person is willing to make huge sound degrading decisions. Hearing the music with the best sound quality possible is very important to many on this and other forums. Almost all my designs are made for away from wall placement, and it's not because I'm ignoring the real world. I just won't accept anything but the best.

I do understand that some are indeed space challenged, and I think there should be more wall mount optimized designs out there. I'm working on one myself, off and on between other projects. It's got a specific cabinet shape designed to minimize the reflection, something rectangular boxes could never do.

[jkrutke]

By all accounts the ZDT3.5 is a first rate speaker, but at the same time, if I ever build a pair, they are going to be modified so I can front port them.

One more quick comment: If you do the 3 chamber design like I did, there's not much room on the front of the top chamber for a port. You'd have to put it next to the tweeter, which does cause some diffraction artifacts.

Yes, I am the "world famous" Zaph. I have to laugh, because this is such a fringe hobby that none of my friends have ever heard of guys like Linkwitz or D'appolito.

[djg]

Well there's always the sides, top and bottom.

[bluewizard]

The headphones comment was a bit of a sarcastic joke, sorry.

Well, my comment about 'elitist attitudes and unwashed masses' was also intended as a sarcastic joke; just so we are clear.

But, I just don't see the refusal to move speakers away from the walls. I have a 12x12 room in my house that I am still able to place the speakers about 2 feet out. With some wall treatments, I'm able to get some shockingly good sound in there, almost as good as my main HT room.

If is not a refusal to move speakers out from the wall, it is the impracticality for most people of moving them 2 to 3 feet out.

First, I don't think I've ever seen anyone who literally pushes there speaks back against the wall. Roughly a foot out from the back of the cabinet to the wall is common, and that is about where I have mine, but any further out is, from a practical perspective, impossible.

And I assume that is what we are referring to, the distance from the BACK of the cabinet to the wall...correct?

Now consider this, set 12" from the wall, my JBL Stadiums sound crappola with the ports open and fine with the ports plugged. That seems to tell it all. Yes, if I had a big room, it would be far better to move them out and let the ports unload properly, but I think I've see few people with few houses with few room that would allow that.

This discussion is less about front ports and more about placing speakers against walls. Wall placement causes huge peaks and valleys in the response curve right in the midrange due to the out of phase rear reflection. ... Summary: port location doesn't matter much. Placement in room does matter a lot.

Are we talking about general reflected sound or about reflected sound from a rear facing port? Just curious. And how much sound is directly reflected off the back wall above the baffle step?

From a design perspective, the port location doesn't matter. I've seen them in the top and bottom as opposed to the front or back. But from a practical applied perspective, it does matter. I have some 12" 3-way front ported speakers that have never been that particular about placement. But is is very critical with my rear ported JBL's. But practical room considerations say the JBL's go where they go and that is that. The only real and practical solution is to plug the ports. Something I have never ever had to do with my front ported 12" 3-ways.

Now, here is something I will concede, if you are building a DIY speaker, then you can make a reasonable determination if a particular design will work for you. I suspect all those who have build beautiful ZDT3.5 speakers, knew in advance before they sunk $1,000's into it, that they would have room to use it.

But, for commercial consumer speakers, why rear port when it is not necessary? Take the example of the Wharfedale Diamond 9.6, which in the USA run between $600 and $750/pair. That's entry level to most audiophiles. They have plenty of room on the front, why port in the rear other that to be trendy? I suspect many consumers who buy speakers similar to this, get them home, set them up, and go - I paid $600 for crappola like this? It seems a disservice to the consumer and to the manufacturer.

Steve/bluewizard

[servicetech]

Another consideration is the speaker grills restricting airflow from the port. Ideally we wouldn't have to use grills, but as already mentioned many of us share these rooms with family including children.

[bluewizard]

One more quick comment (on the ZDT3.5): If you do the 3 chamber design like I did, there's not much room on the front of the top chamber for a port. You'd have to put it next to the tweeter, which does cause some diffraction artifacts.

Yes, I am the "world famous" Zaph. I have to laugh, because this is such a fringe hobby that none of my friends have ever heard of guys like Linkwitz or D'appolito.

A quick look at your tower cabinet plans shows that the rear port is in the open area below the lowest woofer and above the lower chamber. There is plenty of room on the front for the port, if I am able to assume the plans are drafted to scale.

So, either one big front port, or two carefully places small ports would probably work.

My plan was to move the crossover up out of the lower chamber and into a space/chamber on the back of the cabinet in the mid/tweeter area. Then lower the shelf in the lower chamber to achieve the same internal volume. Lose volume with the new crossover chamber, and gain volume by moving the shelf down. That would certainly give me room for front ports.

Still, it's going to be a LONG LONG time before I have the cash to build a speaker system that sweet.

Just one last comment -

WHOO-HOO! Look everyone, the great and might Zaph is talking to me!
(No really, not being sarcastic this time, I'm honored.)

:E ;x( :E

Steve/bluewizard

[---k---]

Now consider this, set 12" from the wall, my JBL Stadiums sound crappola with the ports open and fine with the ports plugged. That seems to tell it all. Yes, if I had a big room, it would be far better to move them out and let the ports unload properly, but I think I've see few people with few houses with few room that would allow that.
Steve/bluewizard

The problem isn't the ports, it is the baffle step and the overall design. They are designed to be further away from the wall. I think you need to have more experience with rear ported speakers to before you talk in such absolutes.

The reason a few, and it isn't as many as you make it sound like, come with bungs to plug the hole is to change the tunning of a speaker. The PSB Synchro 1's come have three rear ports and come with plugs. I've listened to these at a local dealer. In their smallest room, they sound best with two of the ports plugged. In their bigger demo room, they sound best with all the ports unplugged. This is because the smaller the room, the more the room gain. And this is with 18 inches between the back of the speaker and the wall in both rooms.

Rear ported speakers can sound just fine with only 3 - 4 inches between the rear wall and the port, if the speakers were designed with the correct baffle step to place them at that location. I'm sure the reason your front ported speakers sound great close to the wall is because they were designed to be there. The thing is, most speakers are designed with baffle step to be pulled further away from the wall. And this won't matter whether the speakers are ported or sealed.

[Dennis H]

Now consider this, set 12" from the wall, my JBL Stadiums sound crappola with the ports open and fine with the ports plugged. That seems to tell it all. Yes, if I had a big room, it would be far better to move them out and let the ports unload properly, but I think I've see few people with few houses with few room that would allow that.

Like Ryan said, that's more than enough room for the ports to work properly and it would sound about the same if the ports were on the front. It's got nothing to do with front or rear ports but rather it's the difference between ported and sealed in your specific setup.

[bluewizard]

Like Ryan said, that's more than enough room for the ports to work properly and it would sound about the same if the ports were on the front. It's got nothing to do with front or rear ports but rather it's the difference between ported and sealed in your specific setup.

First, I'm not doubting your expertise. I'm certain you are more knowledgeable and more experienced than I am.

But none the less, I have trouble buy what you are saying. It seems to me to be more of a timing or phase issue between back sound and front sound, a problem that wouldn't likely occur if the port were in front. When I seal the port, it is eliminating the timing and phase conflicts between the front and the too early reflections of the rear sounds.

It would seem that if I moved my speakers out from the wall and away from interfering objects, likely they would smooth out and sound fine. That's actually very difficult in my room.

But if I take your statements to heart, the implications seem to be that the speakers are a bad design, and no amount of arranging or re-arranging is going to change that. Perhaps I misinterpreted.

Ultimately, I'm not necessarily saying rear ports are bad. Only that there is a time and a place for them, and if you don't have to use them, then why do it? It still say there is a huge element of "it's cool" in the decision to use rear ports. Again, from most consumers, it is an unnecessary complication.

Also, just so we are clear, my saying I don't believe it, is NOT the same as saying your are wrong. My opinion does not dictate your reality, so please don't take offense. I'm just trying to learn.

Thanks for all the responses.

Steve/bluewizard

[---k---]

So, do you think all those people who have built the Statements with their mids and the woofers vented out the back are crazy?

[Dennis H]

It seems to me to be more of a timing or phase issue between back sound and front sound, a problem that wouldn't likely occur if the port were in front. When I seal the port, it is eliminating the timing and phase conflicts between the front and the too early reflections of the rear sounds.

If the port is tuned to 30Hz, a wavelength is 37 feet long. A foot or so isn't going to make enough difference in the phase to matter much so that's not the problem.

the implications seem to be that the speakers are a bad design, and no amount of arranging or re-arranging is going to change that.

No, I'm not saying they are a bad design. It's just that with the combination of the room dimensions, where you have them located in the room, and where your chair is located, they sound better with the ports plugged. Nothing wrong with that. If you had them in a bigger room and located farther from the walls, they might sound better with the ports open.

Rooms really mess with the bass response and getting a speaker to work in your room is an art.

[bluewizard]

So, do you think all those people who have built the Statements with their mids and the woofers vented out the back are crazy?

Ultimately, I'm not necessarily saying rear ports are bad. Only that there is a time and a place for them, ...

Perhaps you missed that line.

Steve/bluewizard

[Hdale85]

Sound doesn't exactly come out of the port and that's not what the port is there for. I doubt you would be able to tell any difference at all having the port on the front or the back. Also I know A LOT of audio friends around here and none of them have their speakers closer then 3 feet to the wall from the front baffle. I keep mine about 3 feet from the back. I also think ports on the front are ugly

[benchtester]

Also I know A LOT of audio friends around here and none of them have their speakers closer then 3 feet to the wall from the front baffle.

For a demographic check, how many of your friends have a wife or live-in significant other? Inquiring minds want to know. :W

[Hdale85]

Quite a few actually as do I. My wife doesn't have any issues with anything I do as far as speaker placement. I guess it just depends on how into music and what not that significant other is. Also depends on how ugly your speakers are.

[benchtester]

I'm impressed. :T Any hints on WAF for speakers away from the wall?

crossed postings:

Good points. I'm still working on the WAF aesthetics, the difficult part is the WAF varies with the observer.

[---k---]

Ultimately, I'm not necessarily saying rear ports are bad. Only that there is a time and a place for them, ...

Perhaps you missed that line.

Steve/bluewizard

You know what, I'm offended by your tone. Not just this post, but most of them. I'm not wasting my time further.

[dlr]

Lot's of back and forth here. I don't really like ports and I hate front ports, but I like to re-use/experiment with boxes and most small ones have ports. Too bad, but they appear so often because they're much less expensive than the alternatives (a whole 'nother subject).

Anyway, zaph, I have to disagree in a small way with your conclusion. Your page does address what I see as a too-often significant issue, that being stuffing and the port position on the interior. Most ported systems have a lining and no more. Since the desired tuning determines port length for the diameter used, it may limit choice. Short ports are the worst, I think, but for a specified length, various positions on any given side may alter the tuned response as well as the extraneous frequencies that may exit.

Case in point. I have a Sony box, an SS-K10ED, the smallest in the line of fairly recent ones they sold to be more "high end". It's shaped much like the Insignia box with a small front port. The small midwoofer supplied can't be improved (tweaked) enough for my liking. As an experiment for a 3-way, I put a SS 13m/8640 into the box (surface mount quicky) that I'd measured on my large baffle. The low end had some pretty severe waviness, 300-1K, even though it's a very narrow box. Diffraction I said, so on went significant felt. No real change except for step. All at 1m on axis.

Scratching my head I then thought "internal reflections", but this box has those curvy sides and very narrow back baffle, almost none in fact.

Then I recalled the foam lining not extending all the way down. The smallish box put the port near the narrow back area created by the curved sides. I gave me the impression of actually "channeling" the pressure wave.

Sony didn't make these cheaply. They used good crossover components, the box is not the sliced interior like the Insignia and the foam lining is pretty dense and 1" thick.

Anyway, I stuffed the port with some dense cotton. Voila, waviness gone entirely. The surface mounting wasn't an issue, either. Guess I'll just stuff the box entirely since it's a midrange usage experiment.

To me a port is very much a case-by-case issue with regard to spurious resonances (port self-resonance) and "escaping" frequencies. My take is that all ports should be on the rear unless the box will be on a bookshelf, since the latter is going to have reflection issues anyway.

OT, I need to PM you on the drivers that I got from you. I've looked into the loading and tuning and am inclined NOT to use ports, but PRs due to port length restrictions (and my preference). All loadings/tunings indicate pretty severe mid-bass limitation as well.

Dave

[Curt C]

My personal experiences agree with Dave’s. Depending on the enclosure design, often there are few choices for the port position, and sometimes those choices will result in what I consider significant extraneous acoustic output from the ports.

For examples, look at a few of John Atkinson’s port measurements of vented speakers on Stereophile reviews. Some design's ports have significant output/peaks above the port frequency, some don’t. Presuming John’s measurement regime is consistent; this would indicate that although the pass band of the woofer can have a significant bearing on the effects, in some designs extraneous port output is indeed a reality. Rear/bottom porting in such designs could result in partial absorption of this distortion, compared to front porting.

Since there is no inherent disadvantage, and potential advantages in rear or bottom porting, I consider them preferable to front porting.

C

[Hank]

Perfect reason: rugcrawlers. One of my bud's grandkids was attracted to the front port of one of his speakers, and proceeded to insert a small rubber ball that had to be fished out.
I also think front ports are ugly.

[cjd]

If you front port and don't use a large enough diameter (all too common... IMO ) you can pick up a resonance peak (captured in Unibox and M.King's mathcad worksheets alike) that may be audible to the most nitpicky of listeners, given a front port. The closer we get to a TL or tuned pipe, the less of an issue any of this becomes and I think that Zaph and many others designing where it doesn't matter so much probably approach this without necessarily realizing it (I first noted this when pondering one of my own designs and testing what it should be were I to do a quarter-wave tuned pipe: turns out, I already had - that happened at least twice, then I stopped messing with the mathcad worksheets, which I've lost for now - probably somewhere on my computer).

C

[Jonasz]

I suppose I should note that this upcoming design I mentioned on my blog has a rear mounted port, but that's only because the cabinets were built 5 years ago, back when I used to believe what I read on the internet.

Hmmm... I just read that comment online...

OC everyone knows that boxes sucks and dipole rules... 8)

[A9X]

My experience tallies pretty well with Daves (post 25). However, I avoid ported designs everywhere except for <50Hz ie mainly subs.

[bluewizard]

You know what, I'm offended by your tone. Not just this post, but most of them. I'm not wasting my time further.

Well, if you are offended, then I'm truly sorry, that wasn't my intent. But let's face it, you ask if I thought everyone who used rear ports was crazy, and in my mind that clearly went against everything I have said. And the quote I gave seemed to confirm my position.

There is a time and place for rear ports, and in that time and place, I imagine they work well. But I think far more rear ports are more to do with trends than to do with function or need.

As I said to someone else, my opinion doesn't dictate your reality, so again, I'm puzzled that you are offended. Still, you feel what you feel, and that can't be denied.

I'm simply stating a position, and not even an absolute position. When it is the right time and place to use rear ports, then fine. But again, I think many rear ports occur because of trends and 'cool' factor, when a front port would have served better.

I think my example of the Diamond 9.6 was the perfect example. With all that wide open space on the front of the cabinet, why put the port on the rear? I'm not saying it doesn't work, I'm asking why do it, if you don't have to? Why add, what seems to me to be, an unnecessary complication?

Even the great and mighty Zaph himself, more or less, to a certain extent, confirmed what I am saying.

Again, I'm sorry that you are offended, but I'm not sure I see anything that I said that would be offensive. I'm starting with the statement of a premise, and hoping to learn. But simply telling me I'm wrong, or (massively overstated and exaggerated) saying that rear ports are god's gift to speakers, isn't teaching me much.

Still, your comments were appreciated, and always are. If you feel the need to leave the discussion, then go in peace. But I would much rather you stayed. As always, I learn the most from those who disagree with me.

To summarize my position, I'm not saying never use rear ports. In fact, I've acknowledged situation in which you must use rear ports. What I am saying is, why use them when you don't have to?

Steve/bluewizard

[Hdale85]

Why use a front port when you don't have to? There are probably just as many negatives vs positives for front vs rear ports. And then you don't even mention down firing ports really.

[bluewizard]

Well (he said laughingly) why not put the ports on the top. Seems to be a nice out of the way place. Though the wife (if I had one) would probably want to set a vase on top of it, and uncouth guests would probably think it a good place to throw their cigarette butts.

Sometimes you just can't win.

Steve/bluewizard - who readily admits limited experience (and poverty), which is why he brought the issue up.

[minkuni]

Actually, downfiring ports would arguably be the most practical of the options. Practical as in they are out of sight and reach of those who may not know the reason for the existence of the port (this goes equally for toddlers and partygoers :B ). The speaker might need taller feet than it would have with a front or rear port location, but this is usually a minor adjustment.

I am currently in the finishing stages of my own little speaker and will probably end up putting the port on the rear. My reasons are entirely practical as I have no room left on front baffle and a removable rear panel will simplify port tuning experiments.

I have no practical experience (so far) with downfiring ports other than listening to a set of Audio Pro Black Diamonds at a friends place.

[Curt C]

Well (he said laughingly) why not put the ports on the top. Seems to be a nice out of the way place. Though the wife (if I had one) would probably want to set a vase on top of it, and uncouth guests would probably think it a good place to throw their cigarette butts.

Sometimes you just can't win.

Steve/bluewizard - who readily admits limited experience (and poverty), which is why he brought the issue up.

You want it? You got it! Revel in the mastery of Nelson Pass's "The Legend of EL-PIPE-O" complete with a 'top firing port'. You'd have trouble throwing your butts in there!

el-pipe-o.pdf

I've read through your posts, and I've yet to see where you list the positive attributes of front porting... -Perhaps it was there and I missed it. The only one I can think of is cosmetic: That is, some may actually like the look of a big plastic hole in the front of their enclosure. :rofl:

For the uneducated masses that correlate quantity with quality, this may look like another driver on the front. Seriously: For others, it may just look better to them. We all have our aesthetic predispositions, and that’s jake with me. :T

BTW, Many of us pull our speakers out into the room to obtain the increased soundstage depth which results. for us 'crazies', having the front baffles out a couple/three feet from the front wall, isn't too much of a burden.
arty:

C

[jkrutke]

I also think front ports are ugly.

This is the best reason for rear mounted ports that I've seen so far, and a very valid reason in my opinion.

Even the great and mighty Zaph himself, more or less, to a certain extent, confirmed what I am saying.

If you don't mind, please don't call me great and mighty. I'm just a guy and what I do is hardly rocket science. It makes me a little uncomfortable and it's unfair to others who have contributed in other ways than just a popular web page.

Anyway, zaph, I have to disagree in a small way with your conclusion. Your page does address what I see as a too-often significant issue, that being stuffing and the port position on the interior. Most ported systems have a lining and no more. Since the desired tuning determines port length for the diameter used, it may limit choice. Short ports are the worst, I think, but for a specified length, various positions on any given side may alter the tuned response as well as the extraneous frequencies that may exit.

Hi Dave, Just to be clear, the point I made on my web page under the heading called "Front port mounting" in the Tidbits section is different in meaning to what I mentioned above regarding front mount nearfield port measurement artifacts. I'm not sure if it's the part you disagree with, but I still contend that what many attribute to midrange leakage or organ pipe resonance is actually just a measurement artifact. Midrange leakage and organ pipe resonance are indeed real port issues, but I think what most people see in a front port measurement is improperly attributed to those issues. I may be wrong though. I think it's obvious the subject has not been studied enough.

To all: This is a good discussion, but unfortunately there's a lot of talk and no data. I just fished around in my speaker folder for the tests I did and didn't find what I was looking for. I did these tests years ago using SE version 8 with the question in my mind if a commonly used port summing routine would introduce inaccuracies. About all I can come up with for now is this recent nearfield port measurement



It is a nearfield port measurement from the front mounted port on the ZRT project. It is not as accurate as it could be because it has been polluted by the woofer's response. It has the artifacts I was talking about in it. Note that the port is 16" away from the woofer. The relationship of that 16" wavelength can be seen as the peak at 850 Hz and also as the dip lower in frequency where 180 degrees phase happens. This isn't a worst case situation, because different combinations of port tuning and woofer distance can have more drastic effects.

What I would like to show is that once the front mount port is isolated from the woofer, the midrange leakage (which then looks more like a noise floor) is actually lower than what happens for a normal rear mounted port. The real trick of course is taking the woofer out of the nearfield front mount port measurement. That's where the large board placed between the port and the woofer come in. Nobody ever does this however (myself included) because it's a pain.

If anyone is interested, right now I am in a position to do these tests again. I was contemplating taking this design and moving the port to the front below the woofer and then going through to proper routine to isolate the woofer and show us the real midrange leakage noise floor of both front and back. I think the results would surprise many people who are totally against front port mounting for fear of midrange leakage.

I've yet to see where you list the positive attributes of front porting...

There you have it Curt, at least one positive attribute, though unproven at this point until I come up with some data.

None of this discourages my fight against poor room placement though.

[dlr]

It is a nearfield port measurement from the front mounted port on the ZRT project. It is not as accurate as it could be because it has been polluted by the woofer's response. It has the artifacts I was talking about in it. Note that the port is 16" away from the woofer. The relationship of that 16" wavelength can be seen as the peak at 850 Hz and also as the dip lower in frequency where 180 degrees phase happens. This isn't a worst case situation, because different combinations of port tuning and woofer distance can have more drastic effects.

What I would like to show is that once the front mount port is isolated from the woofer, the midrange leakage (which then looks more like a noise floor) is actually lower than what happens for a normal rear mounted port. The real trick of course is taking the woofer out of the nearfield front mount port measurement. That's where the large board placed between the port and the woofer come in. Nobody ever does this however (myself included) because it's a pain.

On this part I'm in full agreement. The close-mic measurement can be contaminated as you point out. My port issues were evident at 1m, I never tried the close-mic position on it.

None of this discourages my fight against poor room placement though.

My preference has always been for at least 3 feet behind a system, room allowing it. The other preference I've always had is to place speakers on the long wall. The imaging and ambiance always seemed better to me in that configuration.

Dave

[bluewizard]

Bluewizard:
Even the great and mighty Zaph himself, more or less, to a certain extent, confirmed what I am saying.


JKrutke:

If you don't mind, please don't call me great and mighty. I'm just a guy and what I do is hardly rocket science. It makes me a little uncomfortable and it's unfair to others who have contributed in other ways than just a popular web page.

Well, I intended the 'great and might' as well as the other remarks regarding your otherworldly status, to be light hearted. And hope you will take them that way, but it's always wise to know when a joke is over. So, I will respect your wishes and refrain in the future.

But, I do have a bone to pick. You make is sound like you are just some guy knocking around in the garage. I think that is very modest. I'm sure you expend a great deal of time, effort, expense, and engineering to bring these speaker and crossover designs to us. And most generously, you allow us to use them for free.

I think that fairly deserves a degree of admiration, and I'm sure you have the admiration of all those who are familiar with your designs, and for all the valuable speaker test results you so generously provide.

So, please do keep modestly puttering around.


To the issue are hand. I readily admit my inexperience and my lack of money to buy the equipment to do adequate tests. But despite a near consensus against me, I'm having trouble letting go of this being a problem of timing and phase of reflected sound.

Sitting in the exact same position that my 12" DIY speakers were sitting in, I was stunned by how bad the JBL Stadiums sounded. I thought I was getting a deal on $600 speakers. Instead, I regretted the modest $200 I paid for them.

Then I read in one of the forums that someone else had the same reaction, and fixed it by plugging the port. So, I plugged the port and the sound dramatically improved. The speakers are actually pleasant to listen to, though I still prefer my old DIY speakers. But keep in mind that my I've been listening to my old 12" 3-way DIY speakers since 1985. I'm pretty used to them.

I'm having trouble with the idea that this is a speaker design issue beyond being rear ported. The same speaker sitting in the exact same spot is trash with the ports open, and OK with them plugged with some upholstery foam. I'm sorry, again admitting limited experience, but that doesn't sound like baffle step to me.

With the ports open, the JBL's are hopelessly muddy and garbled. It sounds very much like an interference problem, and not simply poorly tuned bass or poorly corrected bass. It seems to be very isolated to the port being in the rear.

I admit, I may be wrong. I may have misread or misinterpreted the whole thing. But, my limited experience doesn't leave me with a good feeling about rear ports. But at the same time, I acknowledge their occasional need and value.

Now someone said, you could place rear ports 3" to 4" from the wall, but I wonder how big those speakers are? I would guess small bookshelf or small MTM with small rear ports could be closer to the wall. But I think the JBL has a 3" flared port.

Again, I'm really asking questions and trying to learn. And the underlying question is why use rear ports if you don't have to? If you have to, then yes, but if you don't have to then why? I know I see an advantage to front ports in that, if nothing else, everything is moving in the same direction. Maybe that is an illusion, but it makes sense to me.

Now I suspect one of the reasons it seems not to matter where the port is placed, is because, regardless of its point of origin, everything below 80hz seems to be coming from everywhere. That's the principle that a single subwoofer works on. But, I'm not convinced that there aren't timing and phase issues with Subs. Yes, intelligently and precisely and optimally placed Subs probably work fine. But I question how many consumers are able to achieve that?

Thanks to all who replied including ---k--- who left in offense. I do regret that. But still, I only own my own feelings. Others must own theirs. I've always valued his opinion in other threads.

Steve/Bluewizard

[Hdale85]

Well Steve there are many many designs on this forum that are free and have had many house and money put into designing them. Also many different designers so what Zaph does isn't really special. Not saying he's not talented he certainly is it's just he happens to have a somewhat well known web page lol.

As for stuffing the ports I would almost guarantee your issues is just the fact that those speakers are ported. When you stuff the ports you are making them sealed and there for changing their tuning. The port on the front or rear doesn't matter. Also if the speaker is not designed properly there may be a chance what your hearing is port noise which if it was on the front would be even worse. A port is not a sub either so I don't think what your saying applies. Your talking about a port like it makes sound. Generally speaking you don't want to hear anything coming out of the port at least in my mind I wouldn't.

[Dennis H]

But despite a near consensus against me, I'm having trouble letting go of this being a problem of timing and phase of reflected sound.

I've always found that it helps to do the math to help knock incorrect mental images out of my sometime thick head. In this case, a 30 Hz wavelength is about 37 feet. Let's say moving the port from the rear to the front would move it 1 foot. The phase shift is 1/37 * 360 degrees = about 10 degrees. Not enough to hear.

If there's a consensus among various listeners with different rooms, that it sounds better with the port plugged, it's just a bad ported design. Plug it and be happy.

Your talking about a port like it makes sound. Generally speaking you don't want to hear anything coming out of the port at least in my mind I wouldn't.

Bass sound does come out of the port to fill in below where the driver rolls off. In a good design, the port rolls off smoothly at 12 dB/octave above and below tuning. In a bad design, you can get all kinds of weird peaking and I suspect Steve's speaker is tuned for the boombox sound.

[Hdale85]

Yeah that's what I'm guessing is the boombox sound. But the way he was making it seem was that a lot more then just the low end fill.

[Dennis H]

Just to be clear, that pic is for a 'good' ported design. Here's a 'boombox' tuning. Note how much higher the port output is, well above the nominal 0dB level of the system.

[bluewizard]

Excellent replies, you've almost got me convinced.

Once again, not against rear ports, I'm just saying why do it if you don't need to? I mean you could put the ports on the top, bottom, or sides, but why do it if you don't need to? Maybe it is just the old codger in me..."You young whippersnappers, we got by using front ports for 100 years, and now you are changing everything".

The speakers in question are not dirt-cheap white-van speakers. Though some may argue the point.

The speakers are JBL Stadium towers with 2x 8" woofers crossed at 300hz, a 4" cone midrange and a 1" dome tweeter crossed at about 4khz (from memory). The speaker retails, per pair, at just over $600. Not that anyone pays retail. For the $200/pr that I paid, they are fine, but I didn't expect $200 speakers, I already had $200 speakers, I expected $600 speakers and was disappointed.

http://jbl.com/home/products/product_detail.aspx?prod=STADIUM&CheckProduct=Y

This speaker also confirms my feelings about cone midranges. Some people think they sound warm and mellow, but I think they sound heavy and dull. I much prefer the lightness and airiness of my horn midrange. But that's another post in itself.

With or without the port plugged, the bass is full, but not excessively peaky, heavy, exaggerated, or one-noted. So, I'm not buying the boombox idea as being literal. Perhaps metaphorically, but not literally.

For the record, the port is flared inside and out, and is 3" in diameter, and 3" long not counting the flares. I suppose I could estimate the cabinet volume, and determine roughly what frequency the cabinet is tuned at.
(External Dims; 40-1/4" x 9-7/8" x 15-3/4" (1022mm x 251mm x 400mm))

Using 2.4 Cu.Ft., with one 3" diameter port, I come up with a port tuning of 39hz (3.012" length).

Oddly, it doesn't seem to be the bass that is muddled with the port open, it is the midrange and general sound quality. That is, with or without the ports doesn't seem to be a bass issue, it seems to be a general sound quality issue. Which is why I'm stuck on this idea of timing and phase.

Once again, thanks to all who took the time to answer my questions.

Steve/bluewizard

[A9X]

I still see no good reason for putting a port on the front at all. If the LF driver is wideband there is potential for rear wave energy above port tuning to radiate and be audible. Mounting the port on the rear or bottom has no effect at LF (as previously stated) and there does not need to be a lot of room behind the speaker for the port to work effectively. Please don't confuse other acoustic placement issues with this.

It seems to me that the JBL you purchased is a far from optimum design and does not work effectively in your room, but this has nothing to do with port placement issues outside of these two considerations.

[bluewizard]

A9X:
"I still see no good reason for putting a port on the front at all."

You see no reason to put it there, but do you actually have a reason for NOT putting it there? (Well aware, that is an odd twist on words.)

As I said above (somewhat humorously) we've been building speaker with front ports with pretty good success for 100 years. Suddenly, in the last 15 years, it doesn't work anymore? That doesn't quite seem right.

Still, I think I've made my point, and am not sure I can really add any more. Mostly, it was just an excuse to vent.

The 'other side' has done a fair job of making its point as well, and have come very close to convincing me.

But, in closing, I can't help wonder how a 100 years of science, success, and history have suddenly become wrong?

It's been a fun, though slightly bumpy, ride.

Steve/bluewizard