Background
In the ULF thread and @coolrda 's Vibsensor thread, we've been discussing how different sub designs (sealed, ported, horn, etc.) can produce different tactile responses. When placed nearfield, these differences become more pronounced. Our focus has been largely from a ULF tactile response (TR) standpoint.
One of the theories is that ported produces more TR than sealed around the tune. I first demonstrated this in the ULF thread in this post:
Ported vs Sealed in my room
Recently, others have also done similar tests, but used a far more accurate measuring system with VibSensor:
@derrickdj1 example
His martysub is tuned to 20hz, and you can see in the above (scales were adjusted on images so that you can directly compare) that 20hz is much higher compare to his sealed Marty (plugged vents).
@MKtheater example
MK ported his IB setup, putting him at around a 7hz tune. You can see from the above how much the 10hz TR changed, even when he was running his sealed setup much hotter.
Within the spoiler below, I put together a much more detailed analysis of MK's example above:
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If we assume that around the port tune there is more Tactile Response, then you could apply the same approach for LF frequencies, and more specifically mid-bass frequencies.
The reason I created this thread was to try out an MBM nearfield in support of this theory.
Based on the above, it appears that this mid-bass "chest slam" or "shortness of breath" effect is in the 50-100hz range.
I know HSU has an MBM offering and it's tuned to 50hz. But the problem with that design IMO is that the driver is downfiring. In order to get max Tactile Response, the driver and port should be facing the main LP. I've heard great things about the HSU though, I just think there might be a better solution.
I searched google, and really couldn't find anyone else that makes MBMs....BUT, if you think about it, an MBM is just a high tuned sub. Most PA subs have high tunes as they are geared toward music. With that being said, this opens up a lot more possibilities!
For my HT, I don't have a lot of space behind my seats as I already have two FV15HPs behind me as well as a second row.
So I do have size restrictions as well when thinking about this sub...it pretty much has to be no bigger (and preferably smaller) than the FV15HP...
So I found this $299 gem:
Behringer B1200D-PRO
Specs
It doesn't specify tune, but the FR is 60hz to 130hz. The frequency range is 45hz to 180hz (-10), although I'm not sure what that means...
It's only a 12in driver, but it claims to push 122db at 1m. This will be placed nearfield, so I'm not really concerned about it keeping up.
Also, I'm really doing it to see if it can be an improvement...I'm not currently lacking in mid-bass today by any means (2 FTW21s, 2 FV15HPs nearfield, Fusion 12 LCR, and Volt 10 for surrounds).
Thoughts? Any other subs or MBMs come to mind? Is this a solve for max mid-bass slam?
Testing Update 6-1-16: FV15HP vs 1200D
Subs:
Rythmik FV15HP - 15in Driver w/12hz tune
Behringer 1200D - 12in Driver, w/65hz tune
Distance:
10.5in behind the Main Listening Position
Content:
47hz Sine Wave
Level:
88db
Measuring tool:
LG G5 running VibSensor 2.0.0
Each sub was placed in the exact same location, and each was calibrated to 88db. I placed the LG G5 at the MLP and ran the tests.
The results are in....
As you can see, the 1200D has almost 2X the PSD and acceleration as the FV15HP at the same frequency and the same SPL.
Additionally, I don't believe this is at the tune of the 1200D. If VS was able to measure around 55hz, I believe the difference would be even larger...
Conclusion:
VibSensor does not lie...no subjectivity, just the data. Another example that "at or around port tune", there is more TR in the nearfield because of the increased Sound Intensity.
The below graph (data points extracted from hornresp) show that the ported box produced much more PVL (10 TIMES more) compared to sealed around tune . And it looks as though the elevated PVL continues to about an octave over the sealed.
Given this, it's no wonder why all the examples above demonstrate that ported subs are more tactile around tune.
There's a lot of good discussion with regards to the near field and its benefits. I wanted to take a moment and define it based on what I've researched. Caveat: I'm an enthusiast not a scientist.
I originally talked about the nearfield almost 4 years ago in this post.
I will try and summarize it below and use the ISO 12001 definition of near field:
First defining Sound Intensity:
Sound Intensity (SIL) = pressure (SPL) * particle velocity (PVL)
Sound intensity has a direction as particle velocity is a vector quantity. This means it has a magnitude and direction. Pressure is a scalar quantity and has a magnitude, but no direction.
Sound Energy is a form of energy associated with the vibration of matter.
Sound Intensity is sound energy per unit time per unit area.
Sound Intensity is how we 'feel' sound on our bodies.
While bass waves are said to be omnidirectional (meaning we cannot locate the sound with our ears), the intensity of those waves are directional. This means we can feel where the waves are coming from in the right conditions. (e.g. Feel a NF sub with the driver pointed directly at your LP and then turn it 180 degrees away and see if you can feel the difference; the answer is yes.).
Now, on to Sound Fields...
Sound travels through various Sound Fields.
What does this all mean in practice...
The majority of sub frequencies in our HT's exist in the near field. This means that just understanding SPL is not enough to understand Intensity, or how we 'feel' sound.
Sound intensity is dependent on distance. The closer to the source, the more intensity you will have. It is also directional.
In the Very Near Field, the physics starts to enter fluid dynamics and starts to behave differently than the near field. It is said that this has high levels of PVL in this field relative to SPL.
To optimize (have the highest levels) Intensity:
Sources:
https://www.bksv.com/media/doc/br0476.pdf
http://www.who.int/occupational_health/publications/noise1.pdf
http://www.microflown.com/files/media/library/books/microflown_ebook/ebook_2_sound_and_vibration.pdf
Measuring Sound Intensity:
1st - Microflown Acoustic Camera
2nd - Sound Intensity Mapping of a Speaker
3rd - Low Frequency Mapping of Sound Intensity of Speaker/Subwoofer
In the ULF thread and @coolrda 's Vibsensor thread, we've been discussing how different sub designs (sealed, ported, horn, etc.) can produce different tactile responses. When placed nearfield, these differences become more pronounced. Our focus has been largely from a ULF tactile response (TR) standpoint.
One of the theories is that ported produces more TR than sealed around the tune. I first demonstrated this in the ULF thread in this post:
Ported vs Sealed in my room
Recently, others have also done similar tests, but used a far more accurate measuring system with VibSensor:
@derrickdj1 example
His martysub is tuned to 20hz, and you can see in the above (scales were adjusted on images so that you can directly compare) that 20hz is much higher compare to his sealed Marty (plugged vents).
@MKtheater example
MK ported his IB setup, putting him at around a 7hz tune. You can see from the above how much the 10hz TR changed, even when he was running his sealed setup much hotter.
Within the spoiler below, I put together a much more detailed analysis of MK's example above:
Below is your IB Response superimposed over your ported response. They were superimposed so that the 85db and 95db lines were matched as that is the calibration point of each as you mention above.
You'll notice here that they are within 2db or so at 10hz. Remember, we are looking at 10hz because that is the frequency in consideration to test the hypothesis that around tune, ported produces more TR. Mk's IB ported setup is tuned to 7hz.
However, when MK took readings with the VibSensor, he took the reading for his sealed IB running 10db hot. When he did the ported reading with VS, he ran flat.
In the below graph, I increased the IB by 10db to compensate for running his IB hot.
As you can see, MK was running 8db hot (once you calibrate the two responses) when comparing FRs. Yet the Vibsensor shows drastic differences in the TR at 10hz...18db difference!
More evidence that TR can be increased without an associated increase in SPL, and that around port tune, ported subs produce more TR as compared to sealed.
You'll notice here that they are within 2db or so at 10hz. Remember, we are looking at 10hz because that is the frequency in consideration to test the hypothesis that around tune, ported produces more TR. Mk's IB ported setup is tuned to 7hz.
However, when MK took readings with the VibSensor, he took the reading for his sealed IB running 10db hot. When he did the ported reading with VS, he ran flat.
In the below graph, I increased the IB by 10db to compensate for running his IB hot.
As you can see, MK was running 8db hot (once you calibrate the two responses) when comparing FRs. Yet the Vibsensor shows drastic differences in the TR at 10hz...18db difference!
More evidence that TR can be increased without an associated increase in SPL, and that around port tune, ported subs produce more TR as compared to sealed.
----------------------------------------------------------------------------------------------------
If we assume that around the port tune there is more Tactile Response, then you could apply the same approach for LF frequencies, and more specifically mid-bass frequencies.
The reason I created this thread was to try out an MBM nearfield in support of this theory.
Based on the above, it appears that this mid-bass "chest slam" or "shortness of breath" effect is in the 50-100hz range.
I know HSU has an MBM offering and it's tuned to 50hz. But the problem with that design IMO is that the driver is downfiring. In order to get max Tactile Response, the driver and port should be facing the main LP. I've heard great things about the HSU though, I just think there might be a better solution.
I searched google, and really couldn't find anyone else that makes MBMs....BUT, if you think about it, an MBM is just a high tuned sub. Most PA subs have high tunes as they are geared toward music. With that being said, this opens up a lot more possibilities!
For my HT, I don't have a lot of space behind my seats as I already have two FV15HPs behind me as well as a second row.
So I do have size restrictions as well when thinking about this sub...it pretty much has to be no bigger (and preferably smaller) than the FV15HP...
So I found this $299 gem:
Behringer B1200D-PRO
Specs
It doesn't specify tune, but the FR is 60hz to 130hz. The frequency range is 45hz to 180hz (-10), although I'm not sure what that means...
It's only a 12in driver, but it claims to push 122db at 1m. This will be placed nearfield, so I'm not really concerned about it keeping up.
Also, I'm really doing it to see if it can be an improvement...I'm not currently lacking in mid-bass today by any means (2 FTW21s, 2 FV15HPs nearfield, Fusion 12 LCR, and Volt 10 for surrounds).
Thoughts? Any other subs or MBMs come to mind? Is this a solve for max mid-bass slam?
Testing Update 6-1-16: FV15HP vs 1200D
Subs:
Rythmik FV15HP - 15in Driver w/12hz tune
Behringer 1200D - 12in Driver, w/65hz tune
Distance:
10.5in behind the Main Listening Position
Content:
47hz Sine Wave
Level:
88db
Measuring tool:
LG G5 running VibSensor 2.0.0
Each sub was placed in the exact same location, and each was calibrated to 88db. I placed the LG G5 at the MLP and ran the tests.
The results are in....
As you can see, the 1200D has almost 2X the PSD and acceleration as the FV15HP at the same frequency and the same SPL.
Additionally, I don't believe this is at the tune of the 1200D. If VS was able to measure around 55hz, I believe the difference would be even larger...
Conclusion:
VibSensor does not lie...no subjectivity, just the data. Another example that "at or around port tune", there is more TR in the nearfield because of the increased Sound Intensity.
- Sound Intensity is how we 'feel' sound and causes the Tactile Response (vibration) of objects
- Sound Intensity (SIL) = Pressure (SPL) * Particle Velocity (PVL)
- If SPL is held constant, and there is more Tactile Response than there MUST be more PVL
- @3ll3d00d ran a model in hornresp comparing a 14hz tuned 12in sub vs a sealed 18in UXL that shows that ported designs do produce more PVL around tune (see image below)...many many multiples more in fact, extending about an octave
- This means that a sealed design at 90db SPL will be less tactile that a ported design at 90db around tune.
The below graph (data points extracted from hornresp) show that the ported box produced much more PVL (10 TIMES more) compared to sealed around tune . And it looks as though the elevated PVL continues to about an octave over the sealed.
Given this, it's no wonder why all the examples above demonstrate that ported subs are more tactile around tune.
Research on Near Field and Sound Intensity
There's a lot of good discussion with regards to the near field and its benefits. I wanted to take a moment and define it based on what I've researched. Caveat: I'm an enthusiast not a scientist.
I originally talked about the nearfield almost 4 years ago in this post.
I will try and summarize it below and use the ISO 12001 definition of near field:
First defining Sound Intensity:
Sound Intensity (SIL) = pressure (SPL) * particle velocity (PVL)
Sound intensity has a direction as particle velocity is a vector quantity. This means it has a magnitude and direction. Pressure is a scalar quantity and has a magnitude, but no direction.
Sound Energy is a form of energy associated with the vibration of matter.
Sound Intensity is sound energy per unit time per unit area.
Sound Intensity is how we 'feel' sound on our bodies.
While bass waves are said to be omnidirectional (meaning we cannot locate the sound with our ears), the intensity of those waves are directional. This means we can feel where the waves are coming from in the right conditions. (e.g. Feel a NF sub with the driver pointed directly at your LP and then turn it 180 degrees away and see if you can feel the difference; the answer is yes.).
Now, on to Sound Fields...
Sound travels through various Sound Fields.
- Far Field - Pressure and Particle Velocity are in phase. In this sound field, because they are in phase, when SPL peaks, so does PVL. Therefore, to understand Intensity, you just need to measure one of the quantities (SPL). When we measure SPL in the far field, we can expect that the Intensity will be the same regardless of the distance (e.g. 115db 25ft away will feel the same as 115db 40ft away).
- Near Field - Pressure and Particle Velocity are NOT in phase (as defined by ISO 12001). This means that when PVL is at its peak, SPL is not. In fact, in the Near Field, PVL is greater than SPL in the Near Field (see page 2-15 in this paper). This is commonly referred to as "the near field effect". This means to get an understanding of Intensity (or how we feel sound) in the near field, we need to know SPL and PVL.
- Near Field Region - ISO 12001 (see 1.1.2.2 in prior link) defines that a frequency is in the near field if it is within a wavelength. An 80hz wave is 13.7Ft. A 20hz wave is 54.8Ft. Given those lengths and the placement of our subs from the LP, most bass waves in the typical home theater room will be considered in the near field; meaning to understand Intensity or how we feel sound, SPL measurements are just not enough. We also need to understand PVL.
- The Very Near Field It is the sound field that is very close to the source (see page 2-16 in prior link) where it behaves more like an incompressible fluid. This means there is very little SPL, and mostly PVL. The paper describes that this region occurs when the distance r from the moving object (speaker cone) is much smaller than both the wavelength *and* the object dimension L (eq. 2.36), which in our case would correspond to the driver diameter. Being that these ULF frequencies are much greater in length than the typical subwoofer diameter, the very near field would be the driver diameter (15in, 18in, 21in, depending on sub).
What does this all mean in practice...
The majority of sub frequencies in our HT's exist in the near field. This means that just understanding SPL is not enough to understand Intensity, or how we 'feel' sound.
Sound intensity is dependent on distance. The closer to the source, the more intensity you will have. It is also directional.
In the Very Near Field, the physics starts to enter fluid dynamics and starts to behave differently than the near field. It is said that this has high levels of PVL in this field relative to SPL.
To optimize (have the highest levels) Intensity:
- Put the sub as close as possible. You'll get additional Intensity if the proximity of the LP is less than the driver diameter of the sub.
- Use ported, horn, bandpass, etc.; anything with a vent. Hornresp has modeled particle velocity, and the models show increased levels of PVL compared to sealed in the near field. However, what it does not model is the behavior of the Very Near Field.
Sources:
https://www.bksv.com/media/doc/br0476.pdf
http://www.who.int/occupational_health/publications/noise1.pdf
http://www.microflown.com/files/media/library/books/microflown_ebook/ebook_2_sound_and_vibration.pdf
Measuring Sound Intensity:
1st - Microflown Acoustic Camera
2nd - Sound Intensity Mapping of a Speaker
3rd - Low Frequency Mapping of Sound Intensity of Speaker/Subwoofer