[Rusty Jefferson]

First, GG, the ability of a person to detect absolute polarity is the Wood Effect, I can't remember his first name......

It's Charles Wood.
Clark Johnsen's book.
http://www.amazon.com/Wood-Effect-Unaccounted-Contributor-Confusion/dp/0929383001

......Oh, and I actually did read the first four entire paragraphs of the Wikipedia article on transmission lines.  I consider that penance for all sins, both of commission and omission, for my previous 64 years and for any sins in my future.....

Guilty (for sharing the link, not writing it)  .  I was looking for an easy way to show TL speakers aren't out of phase between the woofer and backwave, as the OP was assuming.

[daves]

Rusty, the wave doesn't start out out of phase, but the extra travel distance certainly adds a time delay - the calculations prove it.

[Scott F.]

Clark Johnsen's book.
http://www.amazon.com/Wood-Effect-Unaccounted-Contributor-Confusion/dp/0929383001

Hey Francis, Clark and I are old friends (in fact I need to call him one of these days). I've got a copy of his book. It's a quick read and you'd find it interesting as it deals with absolute phase.

You also might be interested to know he's a big mono guy. We've had several lengthy conversations about 78s 

[G Georgopoulos]

I think Francis should ask Duke LeJeune of AudioKinesis Loudspeakers this question
he has drivers shooting at the back wall of the speaker at the ceiling etc

cheers...

[Rusty Jefferson]

Rusty, the wave doesn't start out out of phase, but the extra travel distance certainly adds a time delay - the calculations prove it.

Dave, No doubt there's time delay, however the OP's question was:

If you have a speaker with normal drivers, but it has either a port or transmission-line opening at the bottom (let's say either are forward-firing to keep things simple), wouldn't this mean that the information coming out of the port is out of phase with what is coming directly from the drivers up above?.......

And I responded no, not necessarily out of phase, but he might be hearing time domain issues.  He then stated:

...... To my ears a speaker with a port, or with a transmission-line opening, just plain sounds out of phase. Maybe only slightly, but I am sure I hear it. Or am I hearing something else? ........

Not sure just what this means.  I'm reasonably confident he's not hearing "phase" issues from the transmission line/port but probably time delay issues.  Because there are no transients at those lowest frequencies, I'd be surprised if he could hear whether the sound from the TL/port was in phase or not.  Most of us would notice a "system out of phase" with transients from say a piano, trumpet, or guitar, or even from the pluck of a bass string but not from frequencies coming from the TL/port.

Again, some speakers have low frequency woofers intentionally wired out of phase from mid woofers and tweeters to achieve smoother response (and less bloat) at the crossover point. Few would notice the fact the LF woofer is out of phase.

[Baumli]

Dear folks,

I am vastly grateful for the work--and I know it is this--which many people have put into all this. Dave's calculations I am already familiar with, but it was nice seeing everything set forth so elegantly. And Dave's summation is absolutely on target: the problem is in the physics. Also, I would add, the problem is getting the physics to translate into well-reproduced music in a mechanical medium. Many modifications can be made to this mechanical medium, many variations tried, but still--one is dealing with a mechanical medium--sound waves going through air, a mechanical instrument called a microphone for picking up that mechanical transmission of sound waves, electronic wizardry to reproduce all of it, and then a mechanical medium at the end of this electronic chain called speakers. Not to mention your eardrums. Mechanics is messy. In a very old issue of "Stereophile" I once read that if the temperature of a room is 70 degrees and the humidity is at 50, if you then raise the temperature to 80 degrees and the humidity to 80, there will be required no less than five times as much power from your system to reproduce music at the same SPL. I don't know if this is accurate or not, but that's what was claimed, and in my early rock-'n-roll days as a musician, I ran into absolutely huge variables like this especially in outdoor concerts. Scott Faller and I discussed the issue of phase by phone, and we both concluded that whatever comes out of that port or transmission line opening, even if it is musically pleasing, is nevertheless a mess as far as being mathematically streamlined or linear.

The real question here is whether what you hear can indeed be pleasurable. An analogy applies to perfect pitch. Many people think perfect pitch is just that--perfect. Well; it isn't. I have perfect pitch, and I can vouch for its imperfections. A person with perfect pitch can get confused. For example, you might have perfect pitch when you start tuning, but then someone turns on the jukebox, and your sense of pitch just goes to mush. Or, as is often pointed out, even people with perfect pitch can't hear the note "B" no matter how good they are with other notes. I can't. I can come close, but I'm not right on. The result is that many musicians talk about "absolute pitch" which means, basically, that you don't get confused and that you can hear a "B." In this distinction, the conductor Koussevitsky had perfect pitch, but his perfect pitch wasn't absolute. Toscanini's was. Mine is perfect; it isn't absolute.

But here is where the issue of "pleasurable" comes in. I have noted to many people that having perfect pitch is both a blessing and a curse. It sure helps you play better, most of the time, but it can drive you crazy listening to music when you hear an instrument off pitch, or worse, it is an irritant when playing with musicians who can't hear that they are out of tune. If perfect pitch can be a curse, then I wonder if absolute pitch would be even worse. Toscanini was a great conductor, but not among the very best. And I've often wondered if his sense of perfect pitch to some degree prevented his becoming a better conductor. If you're standing up there in front of an orchestra and you wince at everything you hear that is wrong--and, you hear much more that is wrong than most conductors would, well, this would make for difficulty.

And just to keep things accurate in this discussion: I never said I could hear a phase shift of one millisecond. I said I could hear it if it was "more" than one millisecond. In the afternoon I spent with Harry Pearson, neither Frank Doris nor I could hear one millisecond. But when it got to about 1.5 milliseconds, we could. Harry couldn't hear a difference unless it was at least 3 milliseconds. We were dealing with subwoofer information--180 Hz. and down, all through a Muse Model 18 (I think that's what it was called--it had two down-firing 10-inch drivers). But this brings us back to the issue of pleasure. Phase shift is something I can hear better than most people. (There are other things I can't hear as well as most people.) But because I can hear it, I am always on an odyssey to minimize (sic) issues of phase and time delay. My system is far from perfect in this sense, and given that we are dealing not only with the pristine worlds of math and physics, but also with the cluttered world of mechanics, then I can't hope for perfection. I can only try to avoid what I know can be a problem for me.

It's important here to keep in mind that experiencing pleasure means putting up with a lot that is inconvenient. Maybe it even means preferring a great deal that is artifactual. For example, I am surprised at how many people actually prefer speakers that have a great deal of first- and second-order harmonic distortion. But I can understand why they do. All that extra bass makes for a thick, involving presentation. Run raggae through a system such as mine which has virtually no such distortion, and the music can sound lean and un-involving. Run the same piece through a different system with a good deal of first- and second-order harmonic distortion, and it sounds pleasing, involving, and ... well, it sounds like raggae.

I am going to keep in mind the many tendrils of this discussion, and one day sit down with a speaker manufacturer who understands the theory, and ask a lot of questions. Maybe I'll even pay that person if I am sure he can answer my questions. This is only fair. People pay me to translate Latin and French; people with different knowledge bases have a right to be compensated for their time too.

Thank you again to everyone. I am still on a quest, but more aware than ever of how deficient I am with theory. I think I don't even quite understand all the differences between time-delay and being out-of-phase. But I do know what pleases me, and I know that there is a great deal which bothers me. The trick is to thread your way through the difficulties and end up with pleasurable, even impressive, music reproduction. And, not least, by the time you get there, have enough energy left to enjoy that music.

Speaking of which, I've got a new version of the "Exsultate, jubilate" I've not yet heard. So if you'll excuse me ... .

Thanking you again,

Francis Baumli 

[JohnH12]

Francis

I talked about this with a few other amateur and pro designers this weekend.  The port is a bit easier to discuss than a horn.

The port is an operating device similar to the driver.  The back wave off the driver is the impulse that drives the port sound. The port sound is determined by the box, port size, dampening, and driver. There are equations and programs that model the port response.

The port location and tuning frequency have an effect, but generally the port response is in phase with the front of the cone until port tuning frequency then it shift to out of phase. The port response rolls off at -12 dB per octave where the driver’s response rolls off at -12 dB per octave.  The combined response rolls of at -24 dB per octave.  This is easy to see when comparing sealed and ported speaker designs.

There are issues with the internal cabinet back wave sound leaking out of the port as well as this sound radiating through the cone.  The port size and shape also create tube resonances and air noise to be dealt with. These anomalies are captured in the driver measurements.

For back loaded horns we can model the back wave, plus horn, plus front wave in programs like David McBean’s Horn Response.

Hope this helps somewhat.  Please send a PM if you would like to discuss further or need to see the measurements.   

John

[jibzilla]

OP have you thought about headphones? There is a headphone meet this year at jds labs again on April 30th. I will be bringing a metrum pavane/mjolnir kgsshv(full size)/ sr-007mk1 plus lots of other cool schtuff.

I was about to say what daves said in that you can't really get around the speed of sound. I was thinking shortening the distance it travels might cure your woes. You have mach 2 ears.

[Baumli]

Dear jibzilla,

Thank you for the invitation, but I can not attend. On that very day I shall be at my 50th-year high school graduation reunion.

But I do wish I could have heard your cans. Headphones do indeed help solve the time lag, but then there is that sense of the image coming from both sides of the head and not (quite) from in front of you. And there also is the problem that no headphones have ever satisfied me. I'm told that the two best headphones out there now are the Beyerdynamic Tesla (Series 2) and the McIntosh. That's about $1300 or $2000 depending on how rash you are that day. I haven't yet heard either of them. I've heard the Audeze (too heavy, but wonderful), but I haven't heard the much-praised Oppo, or the Abyss--which goes for nearly six grand!

Maybe another time?

Thank you for the observations.

All the best,

Francis Baumli

[jibzilla]

Anytime. If you or anyone else want to hear them I'm free most Sunday's. My personal recommendations are the 3 headphones that I own, which are Sennheiser hd800, Audeze Lcd-X, and Stax sr-007mk1(71XXX). I live right across the JB bridge in Columbia IL. Literally 5 maybe 10 minutes tops from the bridge. A personal listen is always better than a meet. Meets are more for schmoozing.

I do enjoy speakers as well. I have some Adam a7x's and sub8

[daves]

So that is why you won't make the five minute drive across the bridge...

[DaveC113]

Couple things... as far as sensitivity to phase if you're judging that by placing subwoofers operating up to 180 Hz then yes, most anyone is going to be very sensitive to that. Most people have integration issues with subs running above 80 Hz and after that placement gets more and more critical, but I have head a sub that was "invisible" running at 120 Hz. To me sub frequencies are 50 Hz or less. This isn't nearly the same thing as listening to a full range speaker though...

IME very few people are sensitive to the phase shift/group delay in a well designed BR/TL cab, which is generally at very low frequencies. However, it's possible to correct for this using DSP so if you want to hear what a bass cab sounds like with and without correction that's not hard to do.

Ultimately, unless you have a very special sensitivity there are far more important things to worry about. But that's why there's a million different speaker designs... everyone has different preferences.

[G Georgopoulos]

Couple things... as far as sensitivity to phase if you're judging that by placing subwoofers operating up to 180 Hz then yes, most anyone is going to be very sensitive to that. Most people have integration issues with subs running above 80 Hz and after that placement gets more and more critical, but I have head a sub that was "invisible" running at 120 Hz. To me sub frequencies are 50 Hz or less. This isn't nearly the same thing as listening to a full range speaker though...

IME very few people are sensitive to the phase shift/group delay in a well designed BR/TL cab, which is generally at very low frequencies. However, it's possible to correct for this using DSP so if you want to hear what a bass cab sounds like with and without correction that's not hard to do.

Ultimately, unless you have a very special sensitivity there are far more important things to worry about. But that's why there's a million different speaker designs... everyone has different preferences.

 

[jibzilla]

So that is why you won't make the five minute drive across the bridge...

Well the nice thing about a headphone setup is I can bring it to your place easily and I have about as big and bulky headphone setup you can get. If you have a source it makes it even easier but the kgsshv is xlr only. My new ecp dsha-4 is both xlr and rca but about a month off from receiving. My peak/volcano amp is rca only.

I would not have brought it up if the stax did not have perfect bass. I know stats are not really known for bass but this headphone is different and I have tried out quite a few stats at this point. The headphone itself is not perfect. A bit intimate soundstage, especially compared to the hd800, but the bass is literally perfect. I can not think of any way to improve it and it is the best I have heard both speaker and headphone wise, talking many times the price ($1500).