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As Dr. Toole said, generally a few inches will do the trick, and a foot is generally more than enough. The actual minimum distance varies widely with the speaker, though.

It's actually not too hard to hear the effects of this. Get to the listening position and get someone else to hold something flat and rigid to serve as a "wall" (a small piece of plywood or a clipboard or something). Play something with a lot of content near the port tuning frequency, turn up the volume so the speaker is working hard, and have the other person gradually move the "wall" closer to the port. When it gets close enough to the port the airflow will be affected and it'll change the response of the speaker—this is usually quite audible, and it's kind of a fun exercise. Some speakers you can hear it quite clearly even 6-7" away from the speaker, and for some speakers you won't hear much of anything change until the "wall" is almost in contact with the speaker.
That does sound like an interesting exercise. I will have to try it sometime.

I wonder why many "audiophiles" insist that rear-ported speakers need a huge amount of space behind them to sound good, sometimes several feet. I guess maybe moving the speakers around changes the interactions with the room and they attribute those changes to the distance between the wall and the rear port.
 

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What do you think of the Rnonlin metric? That does look to predict subjective ratings.

"Predicting the Perceived Quality of Nonlinearly Distorted Music and Speech Signals"
Tan, Chin-Tuan; Moore, Brian C. J.; Zacharov, Nick; Mattila, Ville-Veikko
JAES 2004
As I point out in my book, there is a new generation of metrics based on a stronger psychoacoustic foundation than the traditional ones. This is one of them, and time will tell if it catches on. I recall that their test impairments were fairly substantial, as is reasonable in early phases of model development, and that room reflections were not considered. Masking is a dominant factor deciding what can and cannot be heard, so room reflections matter, as does the complexity of the program.

There are some very smart people involved, and I wish them good luck in generalizing the method. The industry needs something better than we have at the moment.
 

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I wonder why many "audiophiles" insist that rear-ported speakers need a huge amount of space behind them to sound good, sometimes several feet.
Beyond altering port tuning, the distance to the wall will affect the amount of bass reinforcement and the frequencies of reinforcement/cancellation. Many "audiophiles" don't use EQ so they have no way to compensate for it/smooth it out. Even without EQ it can be instructive to take measurements when placing speakers to see what different distances do to the response.


It's also said that placement farther from a wall helps to provide a deeper soundstage. I don't know of a scientific way to measure that or if any study has been done into how much it matters after "fixing" the bass with EQ. That would be interesting. Virtually all anecdotal accounts I've ever seen were from people not using EQ, so they're basically testing speakers with radically different bass responses when making the assessment.
 

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Beyond altering port tuning, the distance to the wall will affect the amount of bass reinforcement and the frequencies of reinforcement/cancellation. Many "audiophiles" don't use EQ so they have no way to compensate for it/smooth it out. Even without EQ it can be instructive to take measurements when placing speakers to see what different distances do to the response.


It's also said that placement farther from a wall helps to provide a deeper soundstage. I don't know of a scientific way to measure that or if any study has been done into how much it matters after "fixing" the bass with EQ. That would be interesting. Virtually all anecdotal accounts I've ever seen were from people not using EQ, so they're basically testing speakers with radically different bass responses when making the assessment.
I too have heard many opinions about soundstage "depth" and physical distance from the rear wall. Methinks much of it is related to sighted evaluations and overactive imaginations. In any "blind" tests I ever did it was not so simple, and absolutely not consistent across a variety of recordings - most of the soundstage "imaging" information is in the recordings. That said, there may be truth to the notion if one is using omni- or bi-directional loudspeakers.
 

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I too have heard many opinions about soundstage "depth" and physical distance from the rear wall. Methinks much of it is related to sighted evaluations and overactive imaginations. In any "blind" tests I ever did it was not so simple, and absolutely not consistent across a variety of recordings - most of the soundstage "imaging" information is in the recordings. That said, there may be truth to the notion if one is using omni- or bi-directional loudspeakers.
I've seen this said several times in this thread... that soundstage and imaging information is in the recording. I have no doubt that, if the imaging information doesn't exist in the recording, it can't, (and shouldn't) exist in the playback. Yet, IME, when imaging and soundstage information does exist in a recording, different speakers portray that imaging information quite differently. Some will sound like all the "images" are emanating directly from the speakers, i.e., like the speakers are the actual sound sources. Others will sound like the soundstage is huge, but the placement of individual instruments is vague and imprecise. Others still, will have "pinpoint" imaging of individual instruments, groups of instruments, and voices. In those systems, the soundstage is usually more compressed.



Sounds that are recorded in "dual-mono" will portray sonic "images" that sound as if they are originating from a point directly between the two speakers, (given the pre-conditions that the speakers are equidistant to the listener, level-matched and that the listener is precisely located at the central listening position.) If those conditions are met, the central image can be an uncanny point source... or it can be an excessively wide and imprecise image that sounds like the singers mouth is 10 feet wide... and this distinction is very much dependent on the speaker system.



In all these instances, when the exact same material is reproduced on different speakers, the SPEAKERS portray the imaging differently. I have listened to dozens, maybe hundreds, of speaker system in my 65 years of life and they all image differently. When I want to evaluate the imaging capabilities of a system, I will use one specific recording to do so, Chant, by FourPlay.






The very first note is a powerful strike of a floor tom. The apparent "size" of the note tells a lot about the imaging. Then there is a left to right pan of a set of bells. On some systems they "jump" from the left side to the right side. On other systems they smoothly pan between the speakers, as if the percussionist is swiping the bells from left to right. And on some other systems, the bells don't pan at all, the whole string of bells just "exists" in the front of the room. There are vocals and multiple other instruments that take up space in the recording, and their apparent "images" can be precisely located or imprecisely indistinct, depending on the speaker system involved.



In any event, IME, there is way more to it than just having the information available in the recording, and the speaker system is the primary determinant of the quality of the imaging, (when the information exists.)



Craig
 

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and the speaker system is the primary determinant of the quality of the imaging, (when the information exists.)
I would agree with that only if you're including the room and speaker setup within it as part of the "system." I always remember something Dennis Erskine once said--"with 2 channel stereo, your room is your surround processor" or something to that effect.
 

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When people complain about front-ported speakers, the complaint is usually about leakage and phase cancellation. I know that the bigger Primus bookshelf speakers had some phase stuff going on at around 700Hz. I assume that sort of stuff is lessened with a rear port.
Given the wavelengths involved and the dimensions of most home loudspeakers, it is hard to think that where the port is placed on the cabinet will have much effect.
 

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I've seen this said several times in this thread... that soundstage and imaging information is in the recording. I have no doubt that, if the imaging information doesn't exist in the recording, it can't, (and shouldn't) exist in the playback. Yet, IME, when imaging and soundstage information does exist in a recording, different speakers portray that imaging information quite differently. Some will sound like all the "images" are emanating directly from the speakers, i.e., like the speakers are the actual sound sources. Others will sound like the soundstage is huge, but the placement of individual instruments is vague and imprecise. Others still, will have "pinpoint" imaging of individual instruments, groups of instruments, and voices. In those systems, the soundstage is usually more compressed.

Sounds that are recorded in "dual-mono" will portray sonic "images" that sound as if they are originating from a point directly between the two speakers, (given the pre-conditions that the speakers are equidistant to the listener, level-matched and that the listener is precisely located at the central listening position.) If those conditions are met, the central image can be an uncanny point source... or it can be an excessively wide and imprecise image that sounds like the singers mouth is 10 feet wide... and this distinction is very much dependent on the speaker system.

In all these instances, when the exact same material is reproduced on different speakers, the SPEAKERS portray the imaging differently. I have listened to dozens, maybe hundreds, of speaker system in my 65 years of life and they all image differently. When I want to evaluate the imaging capabilities of a system, I will use one specific recording to do so, Chant, by FourPlay.

https://youtu.be/xYZ5qriC7M8

The very first note is a powerful strike of a floor tom. The apparent "size" of the note tells a lot about the imaging. Then there is a left to right pan of a set of bells. On some systems they "jump" from the left side to the right side. On other systems they smoothly pan between the speakers, as if the percussionist is swiping the bells from left to right. And on some other systems, the bells don't pan at all, the whole string of bells just "exists" in the front of the room. There are vocals and multiple other instruments that take up space in the recording, and their apparent "images" can be precisely located or imprecisely indistinct, depending on the speaker system involved.

In any event, IME, there is way more to it than just having the information available in the recording, and the speaker system is the primary determinant of the quality of the imaging, (when the information exists.)

Craig
Thanks Craig. I've got a real busy day today after screwing off all last week, and you just saved me a big bunch of typing. This has been my major point in the 3 1/2 years I've been on this forum and for my 60+ years as a hobbyist.

THANK YOU!

Edit: and what's really nice is that you can have almost the entire Northridge Mafia chasing you down the street instead of me for a change. So again, thank you.
 

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Given the wavelengths involved and the dimensions of most home loudspeakers, it is hard to think that where the port is placed on the cabinet will have much effect.
It seems like a lot of ports have their output centered around their (low) tuning frequency, but then also have an output peak much higher, e.g., the Primus 6.5" bookshelf speaker makes some noise around 700Hz:

https://www.stereophile.com/content/infinity-primus-p162-loudspeaker-measurements

While that peak doesn't seem to make much difference in the overall frequency response on that page, here are anechoic measurements of the speaker that show some presumably-related weirdness around 700Hz:

https://www.soundstagenetwork.com/measurements/speakers/infinity_primus_p162/

I'm not sure what causes this higher-frequency output from the port but it seems to be fairly common, and it also seems fairly common for it to affect the overall frequency response of front-ported speakers, to varying degrees.

Ports seem kind of like magic to me and I don't really understand them. Looking at the close-mic measurement of the Infinity port, it seems to be producing ~2 octaves worth of sound at clearly-audible levels (-10 dB or above) that would be completely out of phase with the desired signal. That sounds pretty awful to me, and you'd really rather have that stuff coming out the back and hopefully be absorbed by the room somewhat, vs. coming out the front. I think there's probably something I must not be understanding about ports though.

But either way, I notice that not very many speaker designers choose to have front ports even though they would make placement easier. (No requirement to be X inches away from a wall.) So I assume there must be a reason for that, acoustically-speaking?
 

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Thanks Craig. I've got a real busy day today after screwing off all last week, and you just saved me a big bunch of typing. This has been my major point in the 3 1/2 years I've been on this forum and for my 60+ years as a hobbyist.

THANK YOU!

Edit: and what's really nice is that you can have almost the entire Northridge Mafia chasing you down the street instead of me for a change. So again, thank you.
Huh? Your point has been that different speakers produce different imaging and soundstage? Has anybody disagreed with you about this?
 

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It seems like a lot of ports have their output centered around their (low) tuning frequency, but then also have an output peak much higher, e.g., the Primus 6.5" bookshelf speaker makes some noise around 700Hz:



https://www.stereophile.com/content/infinity-primus-p162-loudspeaker-measurements



While that peak doesn't seem to make much difference in the overall frequency response on that page, here are anechoic measurements of the speaker that show some presumably-related weirdness around 700Hz:



https://www.soundstagenetwork.com/measurements/speakers/infinity_primus_p162/



I'm not sure what causes this higher-frequency output from the port but it seems to be fairly common, and it also seems fairly common for it to affect the overall frequency response of front-ported speakers, to varying degrees.



Ports seem kind of like magic to me and I don't really understand them. Looking at the close-mic measurement of the Infinity port, it seems to be producing ~2 octaves worth of sound at clearly-audible levels (-10 dB or above) that would be completely out of phase with the desired signal. That sounds pretty awful to me, and you'd really rather have that stuff coming out the back and hopefully be absorbed by the room somewhat, vs. coming out the front. I think there's probably something I must not be understanding about ports though.



But either way, I notice that not very many speaker designers choose to have front ports even though they would make placement easier. (No requirement to be X inches away from a wall.) So I assume there must be a reason for that, acoustically-speaking?

Port... Resonance...?
 

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I assume that rear ported is better than front in general. Presumably that's why all (?) of Harman's speakers are rear-ported now.

Revel Perform3 floor standers and JBL M2 are all front ported, seems like they haven't necessarily gone away from that design.
 
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Yeah, there are plenty of front-ported speakers out there that don't exhibit those sort of problems. If you have a nasty port resonance I'm not sure how much having it come out of the back is going to help. I consider use/placement a much bigger consideration--for on wall, in wall, baffle wall, etc, you'll probably have an easier time with a front ported speaker.
 

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I've seen this said several times in this thread... that soundstage and imaging information is in the recording. I have no doubt that, if the imaging information doesn't exist in the recording, it can't, (and shouldn't) exist in the playback. Yet, IME, when imaging and soundstage information does exist in a recording, different speakers portray that imaging information quite differently. Some will sound like all the "images" are emanating directly from the speakers, i.e., like the speakers are the actual sound sources. Others will sound like the soundstage is huge, but the placement of individual instruments is vague and imprecise. Others still, will have "pinpoint" imaging of individual instruments, groups of instruments, and voices. In those systems, the soundstage is usually more compressed.

Sounds that are recorded in "dual-mono" will portray sonic "images" that sound as if they are originating from a point directly between the two speakers, (given the pre-conditions that the speakers are equidistant to the listener, level-matched and that the listener is precisely located at the central listening position.) If those conditions are met, the central image can be an uncanny point source... or it can be an excessively wide and imprecise image that sounds like the singers mouth is 10 feet wide... and this distinction is very much dependent on the speaker system.

In all these instances, when the exact same material is reproduced on different speakers, the SPEAKERS portray the imaging differently. I have listened to dozens, maybe hundreds, of speaker system in my 65 years of life and they all image differently. When I want to evaluate the imaging capabilities of a system, I will use one specific recording to do so, Chant, by FourPlay.

https://youtu.be/xYZ5qriC7M8

The very first note is a powerful strike of a floor tom. The apparent "size" of the note tells a lot about the imaging. Then there is a left to right pan of a set of bells. On some systems they "jump" from the left side to the right side. On other systems they smoothly pan between the speakers, as if the percussionist is swiping the bells from left to right. And on some other systems, the bells don't pan at all, the whole string of bells just "exists" in the front of the room. There are vocals and multiple other instruments that take up space in the recording, and their apparent "images" can be precisely located or imprecisely indistinct, depending on the speaker system involved.

In any event, IME, there is way more to it than just having the information available in the recording, and the speaker system is the primary determinant of the quality of the imaging, (when the information exists.)

Craig
Craig,

I got a chance to listen on one system. Nice recording with nice soundstage. However, most of that one images within the boundary of the speakers. You might want give this one a try and 'see' where the bari, alto and soprano sax are This one even works on my desktop speakers so you'd think it would 'work' on just about anything. Plus, the three dimensionality is uncanny.

 

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Huh? Your point has been that different speakers produce different imaging and soundstage? Has anybody disagreed with you about this?
Not in this thread.
 

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It seems like a lot of ports have their output centered around their (low) tuning frequency, but then also have an output peak much higher, e.g., the Primus 6.5" bookshelf speaker makes some noise around 700Hz:

https://www.stereophile.com/content/infinity-primus-p162-loudspeaker-measurements

While that peak doesn't seem to make much difference in the overall frequency response on that page, here are anechoic measurements of the speaker that show some presumably-related weirdness around 700Hz:

https://www.soundstagenetwork.com/measurements/speakers/infinity_primus_p162/

I'm not sure what causes this higher-frequency output from the port but it seems to be fairly common, and it also seems fairly common for it to affect the overall frequency response of front-ported speakers, to varying degrees.

Ports seem kind of like magic to me and I don't really understand them. Looking at the close-mic measurement of the Infinity port, it seems to be producing ~2 octaves worth of sound at clearly-audible levels (-10 dB or above) that would be completely out of phase with the desired signal. That sounds pretty awful to me, and you'd really rather have that stuff coming out the back and hopefully be absorbed by the room somewhat, vs. coming out the front. I think there's probably something I must not be understanding about ports though.

But either way, I notice that not very many speaker designers choose to have front ports even though they would make placement easier. (No requirement to be X inches away from a wall.) So I assume there must be a reason for that, acoustically-speaking?
Kevin Voecks pointed out to me that the port becomes irrelevant if you are using subs and crossing over at 80 Hz.
If it's a 40 or 50 Hz tune, yeah. But if it's a 70Hz tune, it's still going to be near max output with only an 80 Hz crossover. But you're right, you can consider most ported speakers to be like large internal volume sealed speakers when using subs, from what I understand.
 

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If your speakers cant image properly, yes you will have an imaging problem. It can also be the amps fault too. I have listened to plenty of amps that kill the soundstage and phantom imaging (comparing on the same speakers.) in my experience amps do have different imaging. I am at the point that I want to start a thread “ How to choose an amp: what the science says’ to establish what qualities and specs a good amp needs to properly reproduce stereo imaging with no variance.
 
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