I understand overporting to be when the "optimum" or indicated length of the port is exceeded in order to extend the low end of the box.
Correct?
Symptons of overporting? Low power handling. Too much bass. Soft & flabby bass. Excessive cone movement.
Correct?
Just trying to clarify. Any thoughts appreciated.
Thanks in advance.
Correct?
Symptons of overporting? Low power handling. Too much bass. Soft & flabby bass. Excessive cone movement.
Correct?
Just trying to clarify. Any thoughts appreciated.
Thanks in advance.
If you exceed the optimum length of your port, it means you are tuning lower than optimum. Depending on how much extra length you are adding, you should have a fairly thin bass, unless you want to give it a special boost in the lower octave or so. You will extend the bass downward, because reflex boxes really don't work too well when driven below Fs, IF you give it that extra boost. Otherwise, your bass will sound thin.
Yes, absolutely.
The "hump" will be a bit flabby, but then if you are building a PA or party type speakers, often that sound corresponds to what you want the bass guitar to sound like.
Tune your speakers too high, and you get a higher F3 but a hump in the bass. Depending on how big the hump is, some listeners might prefer that sound.
The "hump" will be a bit flabby, but then if you are building a PA or party type speakers, often that sound corresponds to what you want the bass guitar to sound like.
Tune your speakers too high, and you get a higher F3 but a hump in the bass. Depending on how big the hump is, some listeners might prefer that sound.
Member
Joined 2003
Overporting is a vague, misleading term. In all honesty you can almost never have enough port, although you can definitely have too little. "Mistuning" is a more accurate word.
EBS is much more than just a "big port", and it does not cause flabby bass unless the driver cannot handle the lower tuning and is distorting..
EBS is much more than just a "big port", and it does not cause flabby bass unless the driver cannot handle the lower tuning and is distorting..
I am not sure of the proper english terminology, in Swedish, the term for what you describe is "sub-tuning" (in direct translation).
It is not very well defined what the tuning is below, however. In some cases it is when it is below a maximally flat design. In other cases it is when the port is tuned lower than the free air resonance of the driver.
Anyway, lowering the port resonance makes the response slope towards lower frequencies, but also pushes the cutoff knee towars lower frequencies. In other words, the bass gets deeper but weaker.
"Sub-tuning" may be a way to compensate for the room gain, which typically introduces a boost of low frequencies (below ~100 Hz). Too many loudspeakers today are IMO designed to play in free space, even though they are used in rooms.
It is not very well defined what the tuning is below, however. In some cases it is when it is below a maximally flat design. In other cases it is when the port is tuned lower than the free air resonance of the driver.
Anyway, lowering the port resonance makes the response slope towards lower frequencies, but also pushes the cutoff knee towars lower frequencies. In other words, the bass gets deeper but weaker.
"Sub-tuning" may be a way to compensate for the room gain, which typically introduces a boost of low frequencies (below ~100 Hz). Too many loudspeakers today are IMO designed to play in free space, even though they are used in rooms.
Mos:
Below is a graph of the same driver-ACI SV12, in two enclosures.
The red is a flat response, in a box 8.2 cu ft and tuned to 18 Hz.
The blue is in a box half that size-4.1 cu ft, and tuned to half an octave higher-25 Hz.
This setup has been suggested by David Weems in his book Designing, Building, Testing Loudspeakers. He recommended for a hobbyist-not so much someone after super hifi, but a good, serviceable way to put a woofer in a smaller box. You get a 2.3 dB hump in the half-size box.
The sound isn't bad, and some people like that slightly fat bass sound. I think this illustrates the principle.
Below is a graph of the same driver-ACI SV12, in two enclosures.
The red is a flat response, in a box 8.2 cu ft and tuned to 18 Hz.
The blue is in a box half that size-4.1 cu ft, and tuned to half an octave higher-25 Hz.
This setup has been suggested by David Weems in his book Designing, Building, Testing Loudspeakers. He recommended for a hobbyist-not so much someone after super hifi, but a good, serviceable way to put a woofer in a smaller box. You get a 2.3 dB hump in the half-size box.
The sound isn't bad, and some people like that slightly fat bass sound. I think this illustrates the principle.
Attachments
Here is a better idea of what is being discussed. The driver used in this sim is a Dayton RS Series 15" HO Sub. FS on this driver is 21hz.
White Line: Max Flat Response, 3.55 ft^3 tuned to 22hz
Yellow Line: EBS -3db, 7.1 ft^3 tuned to 16.35 hz
Magenta Line: EBS -6db, 8.3 ft^3 tuned to 12.76 hz
As you can see the bass in the EBS alignments start rolling off earlier however extend the bass lower at the expense of spl higher up. So that would give you your "weaker" bass because the EBS -3 alignment is a full 3db down at 30hz where the flat response alignment is just starting to drop off at 30hz. However, at 17hz where the EBS alignment starts to roll of it's shelf the max flat is almost 8.5db down.
AS in all things speaker related it is a compromise. Extend the bass lower, or keep the power up for a sharper rolloff higher.
White Line: Max Flat Response, 3.55 ft^3 tuned to 22hz
Yellow Line: EBS -3db, 7.1 ft^3 tuned to 16.35 hz
Magenta Line: EBS -6db, 8.3 ft^3 tuned to 12.76 hz
As you can see the bass in the EBS alignments start rolling off earlier however extend the bass lower at the expense of spl higher up. So that would give you your "weaker" bass because the EBS -3 alignment is a full 3db down at 30hz where the flat response alignment is just starting to drop off at 30hz. However, at 17hz where the EBS alignment starts to roll of it's shelf the max flat is almost 8.5db down.
AS in all things speaker related it is a compromise. Extend the bass lower, or keep the power up for a sharper rolloff higher.
Attachments
Olay,just to illustrate this even more, I am taking elambert's example of the Dayton RS Series 15" HO sub, putting it in a 3.5 cu ft box, using a 4" diameter port, and giving the response for three different port lengths. For all three curves, the box is 3.5 cu ft and the port diameter is 4 inches. The tuning frequency is in parentheses.
Green-7 in long port, (31 Hz)
Red-16.67 in long port, (22 Hz)
Blue-38 in long port, (15.4 Hz)
Red, of course, is the optimal tuning, green is one half octave above optimal tuning, and blue is one half octave below optimal tuning.
I hope this illustrates what happens when you vary the length of a port.
Green-7 in long port, (31 Hz)
Red-16.67 in long port, (22 Hz)
Blue-38 in long port, (15.4 Hz)
Red, of course, is the optimal tuning, green is one half octave above optimal tuning, and blue is one half octave below optimal tuning.
I hope this illustrates what happens when you vary the length of a port.
Attachments
I remember a concept I was taught in school. That of "area under the curve". For a given set of conditions, the area under the curve will remain constant. That generally holds true for the tuning of bass response. As you push the resonant frequency lower, the response for some higher frequqency must drop in order to provide the energy for those lower frequencies.
I notice something as I try more simulations. Pushing the resonant frequency lower and lower will cause the "droop" seen in elambert's red and blue traces to increase. The trace becomes non-linear...
Svante, I support your observations and you hint at something I want to understand better: my listening room's gain. I don't know what a plot of it's response would look like. I read that speakers and the room they are in make a system.
Back to "Overporting".... I'd never heard the term. Could it be referring to the non-linearity that comes from a poor match between speakers and room?
I notice something as I try more simulations. Pushing the resonant frequency lower and lower will cause the "droop" seen in elambert's red and blue traces to increase. The trace becomes non-linear...
Svante, I support your observations and you hint at something I want to understand better: my listening room's gain. I don't know what a plot of it's response would look like. I read that speakers and the room they are in make a system.
Back to "Overporting".... I'd never heard the term. Could it be referring to the non-linearity that comes from a poor match between speakers and room?
Ed:
"Area under the curve remains constant" is a good way to put it. As you move the tuning frequency higher, you add amplitude to the frequencies above Fb, and reduce amplitude for frequencies below it.
In fact, using that analogy, you can include a Closed Box in it, by simply regarding a Closed Box as a Ported Box with an Fb so low it falls into the negligible area. Fact is, as you move Fb, (the tuning frequency), lower and lower under the driver's Fs, you will hit a point where the response of the Ported Box is virtually identical to a Closed Box. However, as you move the Fb from that negligible area up toward the driver's Fs, you see the amplitudes change.
As far as taking rooms into account, some years when I got Audio Magazine, almost all the high end ported system had drooping responses similar to the Blue curve in the graph above, and those from elambert. It was explained that this was to take room gain into account, to yield a flat curve.
Personally, since your perception of deep bass falls off rapidly under 60 Hz or so, I would prefer to have the bass flat and have the room emphasize the lower frequencies. I have often felt the "I tuned it lower to make the curve flat with room gain" gambit was really a sneaky way of saying, "If I made the curve actually flat, I would have to make the cabinet twice the volume, and I didn't want to do that".
"Area under the curve remains constant" is a good way to put it. As you move the tuning frequency higher, you add amplitude to the frequencies above Fb, and reduce amplitude for frequencies below it.
In fact, using that analogy, you can include a Closed Box in it, by simply regarding a Closed Box as a Ported Box with an Fb so low it falls into the negligible area. Fact is, as you move Fb, (the tuning frequency), lower and lower under the driver's Fs, you will hit a point where the response of the Ported Box is virtually identical to a Closed Box. However, as you move the Fb from that negligible area up toward the driver's Fs, you see the amplitudes change.
As far as taking rooms into account, some years when I got Audio Magazine, almost all the high end ported system had drooping responses similar to the Blue curve in the graph above, and those from elambert. It was explained that this was to take room gain into account, to yield a flat curve.
Personally, since your perception of deep bass falls off rapidly under 60 Hz or so, I would prefer to have the bass flat and have the room emphasize the lower frequencies. I have often felt the "I tuned it lower to make the curve flat with room gain" gambit was really a sneaky way of saying, "If I made the curve actually flat, I would have to make the cabinet twice the volume, and I didn't want to do that".
kelticwizard said:
Well, considering the sensitivity of the ear is just plain wrong, at least if the music is reproduced at the same level it was recorded. If we did that, every loudspeaker should have a dip in the 3-5 kHz region, since the ear is most sensitive there. If we are aiming at reproducing sound, of course the sound should have the same spectral content as the original. The ear will have the same sensitivity regardless of if we listen to the original sound or the reproduced sound.
But, regarding the question of whether the entire room gain should be compensated for, there are arguments against that, actually. There is a Swedish Guru that has thought quite a bit about this, and I think he is right in many aspects. In short he sees the room as a "theatre box" where three of the walls, the floor and ceiling correspond to the same surfaces of the room. The wall behind the speakers, however, should be removed, perceptually. The room should "open up" towards an imaginary "scene". This means that the reflections from the back wall should be compensated for, and one of the effects of adding this wall to the theatre box is a boost of ~10 dB at 20 Hz, starting at 100 Hz. Now, this is less than what the room gives if we were to measure the response of the entire room, and the reminder is what would have been perceived if the room had been the theatre box.
I find this line of thinking rather appealing. When we enter a room, the brain learns what bass boost to expect, and if that bass boost is not there (ie if we have compensated for it) the bass level sounds too weak. But if we want the wall behind the speakers to "disappear", we have to compensate for the difference between the room and the theatre box.
Finally, one thing that complicates this is that recording studios must have implemented this in their monitoring order to produce CDs that play well in theatre box compensated speakers. In my limited experience, and from what I hear in CDs, the situation is far from standardized. Of course the sound engineer adjusts the bass level such that it sounds good in his studio. So, in order to get the sound right, at home, we should use the same compensation as they do in studios. From this perspective, it is a pity that studios are not standardized...
Have a look at these equal loudness contours. There is a dip in the 3-5 kHz region, meaning that the ear is most sensitive there.
http://www.sengpielaudio.com/Fletcher-MunsonIsNotRobinson-Dadson.pdf
http://www.sengpielaudio.com/Fletcher-MunsonIsNotRobinson-Dadson.pdf
richie00boy said:
I would disagree with that. That's the highest octave on the piano-you know, the keys that go plink plink plink when you play them. I definitely think that is the high range.
I think the idea that the midrange begins above 1,000 Hz comes from the fact that loudspeaker manufacturers find it easier to make small cone drivers than large ones, so they take a 4 inch, tell you to cross it in at 1,000 Hz, and thus the idea that the midrange starts somewhere around 1,000 is born.
The way I look at it, middle A on the piano is 440 Hz, (at least for now-people used to have fistfights over this, lol). And middle A, in music, is unquestionably considered the middle. So the midrange would have to start at least an octave below that-220 Hz. And it would have to extend at least an octave above that-880 Hz. Rounding out the numbers, 200 to 800 is the midrange, or at least the middle of the midrange.
I think this view is corroborated by the following experiment. Play your favorite music, whether on computer or your home system. Taking an equalizer-whether online or home, if you have one-raise the two octaves which corresponds closest to 200 - 800 Hz all the way up. Like the 250 - 500 Hz sliders, whatever comes closest to a 200 - 800 Hz boost. Note how much louder the "guts" of the music sounds.
Now take any other two octaves-50 through 200, or 1000 through 4,000, etc. and raise them up. Remember to take two octaves at a time. The ones above 1,000 Hz will be piercing when you raise them, but notice how the "guts"of the music is largely unaffected.
I think your listening tests will confirm that most of the music is centered in the 200 through 800 Hz range. In fact, if I had a terrible system and was forced to listen to only two octaves, with all the rest being suppressed by 12 dB or so, I know I would get the most enjoyment out of hearing 200 through 800 Hz.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.