SPL, Nearfield Subwoofers, and Brutality - Page 4 - AVS Forum
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post #91 of 145 Old 07-07-2014, 05:34 AM
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Quote:
Originally Posted by Smittyfit View Post
dominguez1 -> interesting post! I too noticed a difference in the "feel" with different designs. Also I have noticed some play better close range, others better far.
I also tested ported vs sealed in my room here:

Ported vs Sealed PVL test

I always thought subjectively that ported subs did a better job a shaking the couch near field. I performed some tests in the link above to support my theory...
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post #92 of 145 Old 07-07-2014, 05:57 AM
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so what do you guys think "feels" better, transducers or a near field ported sub?
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post #93 of 145 Old 07-07-2014, 06:11 AM
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Ported at what ? Ported at single digits ? Or 20hz? Different.

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post #94 of 145 Old 07-07-2014, 06:18 AM
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post #95 of 145 Old 07-07-2014, 06:35 AM
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My vote goes for the real thing; but in order to create enough energy to shake you and your chair at single digits with actual real sound waves is easier said than done. And low bass waves have no respect for sound proofing or containment so achieving this can lead to other problems with other parts of the house or neighbors.

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post #96 of 145 Old 07-07-2014, 10:07 AM
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Quote:
Originally Posted by Bassment View Post
so what do you guys think "feels" better, transducers or a near field ported sub?
both
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post #97 of 145 Old 07-07-2014, 10:20 AM
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Quote:
Originally Posted by dominguez1 View Post
Interested to see your results and your test methodology.
..
Me too.
Meaning - it would be great to find an easy method to verify and then set up a system to get the best experience, at the lowest possible spl.

You also mentioned how the difference in near-field frequency response vs far would affect the tactile feel, and this is an important point.
In a room, where response is adjusted for room acoustics the total radiated intensity will typically fall at lower frequencies.
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post #98 of 145 Old 07-07-2014, 10:38 AM
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Quote:
Originally Posted by dominguez1 View Post
I also tested ported vs sealed in my room here:

Ported vs Sealed PVL test

I always thought subjectively that ported subs did a better job a shaking the couch near field. I performed some tests in the link above to support my theory...
Observations like this is interesting, because they give information that can be used to find theories for a better understanding of what is going on.

If a theory says this is not possible, it is the theory that is insufficient to describe the situation in a good way.
In traditional audio acoustics the velocity potential of the sound field is rarely given any regard.
Theories and mathematical models are always simplified, to enable focus on what matters, and sometimes things that originally was not important may have significance in slightly different situations.

As for ported vs sealed, there is no difference between the sound field, near field or far field.
As long as you move away from the port, say at least a distance equal to port dimensions, they behave the same, they are omnipolar radiating point sources because the radiating area is very small compared to the wavelength.
Measurements comparing sealed and ported confirmes this, there is no difference at all in the velocity field at near field or further away from the source, when the velocity is normalised to pressure.
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post #99 of 145 Old 07-07-2014, 11:12 AM
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Quote:
Originally Posted by Okv View Post
As for ported vs sealed, there is no difference between the sound field, near field or far field.
As long as you move away from the port, say at least a distance equal to port dimensions, they behave the same, they are omnipolar radiating point sources because the radiating area is very small compared to the wavelength.
Measurements comparing sealed and ported confirmes this, there is no difference at all in the velocity field at near field or further away from the source, when the velocity is normalised to pressure.
I agree that there is no difference in sound field itself between ported and sealed. The theory is that ported produces more particle velocity in the nearfield, causing more sound intensity compared to sealed. Perhaps this is because both the driver and port are producing pvl?

I'm very interested to read more info of your reference. You said "measurements comparing sealed and ported confirms this". Do you have data where someone directly measured the particle velocity levels between the two designs and concluded they were the same?
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post #100 of 145 Old 07-07-2014, 01:24 PM
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Maybe a ported sub extends to 15hz in the near field and a sealed sub without EQ extends to around 22hz and above? So the extra extension is noticed and creates more effects.
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post #101 of 145 Old 07-07-2014, 01:41 PM
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Quote:
Originally Posted by dominguez1 View Post
..The theory is that ported produces more particle velocity in the nearfield, causing more sound intensity compared to sealed.
No, once you move away from the close proximity of the port (where velocity can be very large, 10..30m/s), there is no difference:

Near field, one of my Compact Horn Subwoofers, open and closed port, spl and velocity:


Listening position:


And velocity normalized to spl for open port:
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post #102 of 145 Old 07-07-2014, 01:43 PM
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Comparing near field to lp1, however, is something quite different, we see that the velocity is much larger near field, for same spl:
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post #103 of 145 Old 07-07-2014, 01:47 PM
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i dont know that just placement is the important part ...

in one house i had a ported sub next to the couch, in a corner, ... it felt lacking in strength/punch/loudness
i moved to diff house, sub is 10 ft away, 3 ft from a corner, livingroom MUCH more open kinda 3x its own space... but the same ported sub has much more presence and punch i was surprised...
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post #104 of 145 Old 07-07-2014, 01:53 PM
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Just some comments to the plots above:

The velocity normalized shows that velocity for a given spl is exactly the same for both configurations open or closed port, for near field and listening position.
You can see that this is the case because the curves overlap when one is normalized for pressure.

The frequency response for the velocity measurements are not correct, but since the same correction is used for all measurements they are comparable.

Measurements are not reliable at low frequencies below around 10-15Hz.
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post #105 of 145 Old 07-07-2014, 03:29 PM
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Well, I have 4 pcs of 15 inch woofers mounted in my couch directly under each seating.

Why?

I want to feel more vibrations from movies.
Since the woofers are mounted directly under each seat, it shakes the person, not the entire frame/couch.

This solution is "Low cost" as you can do this with cheap drivers and low wattage. Drivers act almost as IB.
The drivers do not produce much sound, just makes you shake. (neighbors friendly)

It's a bit weird at first but when you get used to it, it really takes the movies to another level.

I have a seperate amplifier that I can adjust how much shake effect i want.

So, cheap drivers mounted nearfield, a person sitting on a "flexible" couch, gives a great effect.
My 2 Aurasound NS18 subwoofers does perform great but does not have the same physical effect.
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post #106 of 145 Old 07-07-2014, 03:42 PM
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Quote:
Originally Posted by Okv View Post
Just some comments to the plots above:

The velocity normalized shows that velocity for a given spl is exactly the same for both configurations open or closed port, for near field and listening position.
You can see that this is the case because the curves overlap when one is normalized for pressure.

The frequency response for the velocity measurements are not correct, but since the same correction is used for all measurements they are comparable.

Measurements are not reliable at low frequencies below around 10-15Hz.
apologies if I missed this earlier in the thread but how are you measuring velocity here?
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post #107 of 145 Old 07-07-2014, 06:03 PM
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Quote:
Originally Posted by 3ll3d00d View Post
apologies if I missed this earlier in the thread but how are you measuring velocity here?
(I may have mentioned, if so, it is buried in this or some other thread..)

I made a velocity measurement device out of a retired lf driver, I had some laying around, destroyed 2, and now I have 2 nice velocity probes.

This velocity probe works like a velocity microphone for low frequencies, the theory behind this is well described in any electroacoustics textbook.

Any electroacostic transducer which is not mounted in a box, so that the front and rear is acoustically shorted, will work more or less good. Size should be as large as possible and still very small compared to the wavelengths one wishes to measure.

Such a device will measure velocity in the direction perpendicular to the diaphragm, acoustic velocity has direction as well as magnitude.

So, find an old retired bass driver, 6"-10" will do, I used a 10", it will be good for up to several hundred hz.
Connect it to a microphone input, measure something, see what happens.

This will not measure sound intensity, which is the vector product of velocity and pressure.

There are measurement devices available that may be suitable, just need to make sure they are usable at low frequencies, and they will most likely cost quite a bit more than the usual USB measurement microphone.
Such devices are usually intended for noise measurements.
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post #108 of 145 Old 07-07-2014, 06:04 PM
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Quote:
Originally Posted by Strike Ace View Post
Well, I have 4 pcs of 15 inch woofers mounted in my couch directly under each seating.

Why?

I want to feel more vibrations from movies.
Since the woofers are mounted directly under each seat, it shakes the person, not the entire frame/couch.

This solution is "Low cost" as you can do this with cheap drivers and low wattage. Drivers act almost as IB.
The drivers do not produce much sound, just makes you shake. (neighbors friendly)

It's a bit weird at first but when you get used to it, it really takes the movies to another level.

I have a seperate amplifier that I can adjust how much shake effect i want.

So, cheap drivers mounted nearfield, a person sitting on a "flexible" couch, gives a great effect.
My 2 Aurasound NS18 subwoofers does perform great but does not have the same physical effect.
This looks like a great idea?
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post #109 of 145 Old 07-07-2014, 06:37 PM
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Quote:
Originally Posted by Okv View Post
No, once you move away from the close proximity of the port (where velocity can be very large, 10..30m/s), there is no difference:

Near field, one of my Compact Horn Subwoofers, open and closed port, spl and velocity:


Listening position:


And velocity normalized to spl for open port:
Quote:
Originally Posted by Okv View Post
Just some comments to the plots above:

The velocity normalized shows that velocity for a given spl is exactly the same for both configurations open or closed port, for near field and listening position.
You can see that this is the case because the curves overlap when one is normalized for pressure.

The frequency response for the velocity measurements are not correct, but since the same correction is used for all measurements they are comparable.

Measurements are not reliable at low frequencies below around 10-15Hz.
I don't know how to interpret particle velocity in the graphs you posted? Where is it represented in the graph?

I can't imagine that REW is calculating particle velocity (accurately at least)...are you referring to port velocity?

I don't think we're talking apples to apples here. I suggest reading this paper:

http://www.toyo.co.jp/file/pdf/mft/e..._vibration.pdf
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post #110 of 145 Old 07-07-2014, 06:59 PM
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Quote:
Originally Posted by MKtheater View Post
Maybe a ported sub extends to 15hz in the near field and a sealed sub without EQ extends to around 22hz and above? So the extra extension is noticed and creates more effects.
Yes, in typical setups this would be the case.

However, in my test, I played a 15hz sine wave at the same SPL, so that eliminates the possibility there.
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post #111 of 145 Old 07-07-2014, 07:47 PM
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Quote:
Originally Posted by Okv View Post
(I may have mentioned, if so, it is buried in this or some other thread..)

I made a velocity measurement device out of a retired lf driver, I had some laying around, destroyed 2, and now I have 2 nice velocity probes.

This velocity probe works like a velocity microphone for low frequencies, the theory behind this is well described in any electroacoustics textbook.

Any electroacostic transducer which is not mounted in a box, so that the front and rear is acoustically shorted, will work more or less good. Size should be as large as possible and still very small compared to the wavelengths one wishes to measure.

Such a device will measure velocity in the direction perpendicular to the diaphragm, acoustic velocity has direction as well as magnitude.

So, find an old retired bass driver, 6"-10" will do, I used a 10", it will be good for up to several hundred hz.
Connect it to a microphone input, measure something, see what happens.

This will not measure sound intensity, which is the vector product of velocity and pressure.

There are measurement devices available that may be suitable, just need to make sure they are usable at low frequencies, and they will most likely cost quite a bit more than the usual USB measurement microphone.
Such devices are usually intended for noise measurements.
This is very interesting...it would be great to have a simple solution like this that is precise enough to rely on its measurements. Admittedly I am no physicist, but this does seem a bit rudimentary compared to what I've read of different measuring devices. Here is another snippet of that paper:

Measuring particle velocity
The direct measurement of particle velocity is quite new. Until the
invention of the Microflown in 1994, the particle velocity could only be
measured indirectly. Here three velocity detecting methods will be
described: the ribbon microphone, an ultrasonic detection method and the Microflown.


As stated before, sound pressure gradient shows a great resemblance to
the particle velocity. After all, Eq. (2.10) states that the pressure gradient is
proportional to the particle velocity. However in Fig. 2.25 one can see that
the sensitivity of a pressure gradient microphone increases proportional
with the frequency. For zero Hertz (a DC or constant particle flow) the
sensitivity is zero. The Microflown however originates from a mass flow
Sound & Vibration
2-46
sensor; a sensor that is designed to measure DC-flow. The fast response
time and improved sensitivity is the only difference between a mass-flow
sensor and a Microflown.
A general behaviour of pressure gradient microphones is the lower
sensitivity for lower frequencies and ‘comb filtering effect’ at high
frequencies.
Unlike this crucial difference between pressure gradient microphones and
Microflowns there are also similarities. For instance the polar pattern is the
same for a Microflown and a pressure gradient microphone. The near field
effect (see above “the one-dimensional wave equation”) is also noticed in
the same manner.

Another type of “velocity” microphone is the so-called ribbon
microphone [17]. The operation principle of this type of microphone is
again based on pressure gradient.
In this case an aluminium foil (the
ribbon) is placed under a low tension in a strong magnetic field, see Fig.
2.26. The difference in sound pressure between the two sides drives the
ribbon and the velocity of the ribbon has the same response as the pressure
gradient microphone. The output voltage due to the motion of the ribbon
however is proportional to the product of the flux density, the length and
the velocity of the ribbon. The result is a “flat” frequency response. (The
ribbon moving in a magnetic field has an integrating character, whereas the
pressure gradient microphone integrating the integration of the signal have
to be performed electronically afterwards or acoustically on forehand).
The ribbon velocity microphone is a pressure gradient type of microphone
that has (thus) no DC sensitivity. The selfnoise of such microphones is quite
low since there is (of course) no thermal noise of the airgap. The main noise
source is thermal noise of the electrical resistance of the ribbon.


A complete other way of sensing particle velocity is the principle of
ultrasonic transduction: two parallel ultrasonic beams are launched in
opposite directions.
The travelling time from the transmitter to the receiver
is linear proportional to the speed of sound in the air. When the air is
moving this movement should be added to this speed. The probe consists of
two transmitter-receiver pairs that are positioned opposite directions, see
Fig. 2.27. The difference signal of the ultrasonic sound waves is proportional
to the particle velocity; this type of velocity probe is also capable to
measure DC flow. It is a true particle velocity sensor but it is a distributed
sensor: it doesn’t determine the particle velocity in one spot.
This probe however is not used very often since it is very sensitive for DC
flows as for example wind or movements of the probe. Furthermore it is,
just like the p-p probe, a distributed sensor with the problems associated
with this type of sensing (for example maximal frequency limited by the
spacing). Reflections of the ultrasonic signals caused problems when the
probe was used nearby reflecting objects and at last, due to it physical
dimensions, the probe is difficult to calibrate.
Fig. 2.27: Type 216 p-u intensity probe (Norwegian electronics).
If the signal from only one ultrasonic beam is observed one notices quite
large a pressure sensitivity. This is caused by the temperature variations
that are generated by the pressure variations of the sound field. The
temperature variations cause a variation in the speed of sound which is
measured to detect particle velocity with this method. To get rid of the
unwanted pressure sensitivity a second ultrasonic beam is used in the
opposite direction. The pressure sensitivity of this second beam is the same
as the first one but the particle velocity sensitivity has a phase shift of 180
degrees. The subtraction of both signals got rid of the pressure sensitivity.

A (stereoscopic) Laser Doppler Velocimeter is measurement device
used for estimating particle velocities, by means of specific signal
processing of scattered light.
It is an optical technique allowing direct
measurement of local and instantaneous particle velocity. Its principle is
based on the determination of the Doppler shift of light scattered from
Sound & Vibration
2-48
seeding particles (tracers) suspended in the fluid. Two laser beams of equal
intensity are focused and crossed at the point under investigation, forming
an ellipsoidal volume consisting of equidistant dark and bright fringes. The
scattered light is collected on a photomultiplier.

The Microflown is a particle velocity sensor that is based on a thermal
principle.
It consists of two very closely spaced and thin wires of silicon
nitride with an electrically conducting platinum pattern on top of them. An
example of an older type of Microflown is shown in Fig. 2.28. The sensor is
made from silicon bulk material with platinum electrical connections on top
of it and two platinum temperature sensors. At the top of the die one can
see two sensors sticking out. The electrical connecting wirebonds are also
visible.
The size of the two wires is 1mm in length, 5μm in width and 200nm in
thickness. The metal pattern is used as temperature sensor and heater. The
silicon nitride layer is used as a mechanical carrier for the platinum resistor
patterns. The sensors are powered by an electrical current, causing the
sensors to heat up. The temperature difference of the two cantilevers is
linear dependent on the particle velocity level.
The operation principle will be explained briefly here, a more detailed
mathematical model of the Microflown model is presented in chapter 3. The
two squares S1 and S2 in Fig. 2.29 represent the two temperature sensors
of the Microflown. The temperature sensors are implemented as platinum
resistors and are powered by an electrical current dissipating an electrical
power, causing them to heat up. An increase of the temperature of the
sensors leads to an increase of the resistance as well.
The sensors have a typical operational temperature of about 200ºC to
400ºC if no particle velocity is present and all the heat is transferred in the
surrounding air. When particle velocity is present, it alters the temperature
distribution around the resistors. The temperature difference of the two
sensors quantifies the particle velocity.


Which principle does your driver device most closely resemble? Also, how do you record measurements with that device? What's the unit of measure?
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post #112 of 145 Old 07-08-2014, 09:41 AM
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Quote:
Originally Posted by dominguez1 View Post
I don't know how to interpret particle velocity in the graphs you posted? Where is it represented in the graph?

I can't imagine that REW is calculating particle velocity (accurately at least)...are you referring to port velocity?

I don't think we're talking apples to apples here. I suggest reading this paper:

http://www.toyo.co.jp/file/pdf/mft/e..._vibration.pdf
Look for graphs with "0deg" in the name in the legend, this is a velocity measurement.

Velocity is measured in distance per time unit, as in m/s or ft/sec, but here it is represented in dB, which is always scaled according to some reference level.
Sound pressure is measured in Pa, and on a dB scale it is scaled according to a reference level we call "0dB".
I have chosen the scaling of the velocity plots so that they match the pressure in level if the sound field is developed into a far field plane wave.
This makes it easy to read and compare the measurements because they will be somewhere around the dB values for pressure.

The frequency response for the velocity plots shown here is not correct, but that is not important when the purpose is to compare different scenarios, as long as all measurements are done the same.

The velocity meter will measure velocity in one direction.

REW does not care if it is pressure or velocity or something else, you will have to keep track of what the signals represent when you measure something.
REW does not calculate anything, it just displays the measured signals.
It is the measurment device that determines what is measured, a pressure mic will measure sound pressure, and a velocity meter will measure velocity.
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post #113 of 145 Old 07-08-2014, 10:18 AM
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Quote:
Originally Posted by dominguez1 View Post
...
Which principle does your driver device most closely resemble? Also, how do you record measurements with that device? What's the unit of measure?
Instead of the microphone you connect the velocity meter.
In REW the signal is treated just like an ordinary measurement with ordinary microphone.

Your questions got me thinking it may actually be possible to come up with a method for velocity measurement that is reasonably easy to set up and will give predictable and comparable results.

You would need a retired bass driver, 8" or 10", connect this to a line level input (instead of the mic amplfier output), and then you need a method for making a correction curve to fix the frequency response and get the level right.

The primciple is called velocoty microphone, it is usually described in any book about electroacustics, in a chapter called something like Acoustic Receivers.
The mathematics behind this is not easy to understand unless you have a degree in technical engineering.
Fortunately it is not necessary.
What is required is to know what can be used to measure velocity, that velocity, unlike pressure, also has direction and thus requires several measurements to get the complete picture, and that a sound field has several properties - pressure, velocity, intensity.

I guess you have figured it out by now, but I appreciate questions about anything that is unclear.
Sometimes it is not that easy to describe and explain things, and often important details are left out.
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post #114 of 145 Old 07-09-2014, 10:34 AM
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Thanks for the additional detail...charts make a lot more sense now.

Unfortunately, I don't have the scientific chops (know how) to determine if a driver can be used as a velocity microphone. I know you mentioned that there are many examples of this, can you please provide a link so we can better understand? The general principle of your velocity microphone is that if you short out the driver so that it is no longer sensitive to pressure, than any movement that occurs as sound passes through it would be caused by the particle velocity. That would seem to make sense, but would like some additional academia around it.

Also, just a clarification with my theory: Ported subs produce more particle velocity as compared to sealed as it gets close to the "tuning frequency of the port". This is because both the driver and the port are producing particle velocity. As the frequency moves further away from the tune, the driver will be the primary producer of PVL, and would be equivalent to a sealed sub from a PVL standpoint.

Subjectively, this is what I've noticed in my room compared from my sealed and ported subs nearfield. I didn't get as much 'shake' down low with my sealed as much as my ported, but the mid and upper bass felt very similar.

You mentioned that your subs were "Compact Horn Subwoofers"? Did you mean ported? I'm not too familiar with horns, but how do you close the opening of a horn when the driver is inside the cab and still produce bass? What is your sub(s) tuned to?

In my test, it was with a 15hz sine wave (close to the tune of the port). You mentioned that your device was not accurate in the 10-15hz range? Is that because of the mic or driver?

If you could post pictures of your subs and device connected to your mic, that would also be very helpful.
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post #115 of 145 Old 07-09-2014, 10:46 AM
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Dom, did you eq your nearfield sealed subs to have close to the same response as your ported?
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post #116 of 145 Old 07-09-2014, 10:58 AM
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Dom, did you eq your nearfield sealed subs to have close to the same response as your ported?
Yes. I only played a 15hz sine wave to eliminate any other frequency coloration in the test. I played them both at the same SPL for both the sealed and the ported. Pics, videos, and graphs of the test are in Post 5 of the ULF thread.
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post #117 of 145 Old 07-09-2014, 11:13 AM
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Originally Posted by dominguez1 View Post
..
Also, just a clarification with my theory: Ported subs produce more particle velocity as compared to sealed as it gets close to the "tuning frequency of the port". This is because both the driver and the port are producing particle velocity. As the frequency moves further away from the tune, the driver will be the primary producer of PVL, and would be equivalent to a sealed sub from a PVL standpoint.

Subjectively, this is what I've noticed in my room compared from my sealed and ported subs nearfield. I didn't get as much 'shake' down low with my sealed as much as my ported, but the mid and upper bass felt very similar.
..
I believe your observation is correct, but the theory is wrong.
Once you move away from the port the sound field is similar to sealed, because both are small acoustic radiators at low frequencies.
The measurements confirms this.
I was curious to see if the port actually caused larger velocities because inside the port the velocity is on the order 100 times larger, and if say 1-2m distance still is close enough, the velocity could be higher.
The acoustic coupling is also different, meaning that the sound field around the subwoofer couples back to the driver in a different way compared to sealed.
This is not the case, it is sufficient to move away from the port around the same distance as the dimensions of the port, then the sound field has developed and pressure-velocity relationship is the same as for a sealed system.

Now, if you place something, say a coach, very close to the port, this may be significant as the high velocity of the air in the port could then have a larger impact on shaking the coach.

The Compact Horn Subwoofer used for the measurement experiment is a variation of a rear loaded horn and is similar to a ported box for this purpose, so that it if the port is closed it acts like a sealed box.
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post #118 of 145 Old 07-09-2014, 11:26 AM
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Originally Posted by dominguez1 View Post
..
Unfortunately, I don't have the scientific chops (know how) to determine if a driver can be used as a velocity microphone. I know you mentioned that there are many examples of this, can you please provide a link so we can better understand? The general principle of your velocity microphone is that if you short out the driver so that it is no longer sensitive to pressure, than any movement that occurs as sound passes through it would be caused by the particle velocity. That would seem to make sense, but would like some additional academia around it.
..
There is really no magic mystery around this, the theory behind it is well known and described and the practical implementation I found to work well enough is simple - just use a bass driver with no box, no baffle and connect it to a line level input, and measure.

The output voltage is proportional to the velocity and frequency response is flat for a driver with no suspension.
A practical driver will have a resonance and a low frequency roll-off due to the stiffness in the suspension.
If we could find an easy way to make the correction curve for this resonance and rolloff, and also align level, it would be possible for everyone to measure velocity and have comparable measurements.
Then we would have a way to compare things objectively - the velocity measurement - together with observations from different systems and different persons.
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post #119 of 145 Old 07-09-2014, 11:53 AM
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Originally Posted by Okv View Post
I believe your observation is correct, but the theory is wrong.
Once you move away from the port the sound field is similar to sealed, because both are small acoustic radiators at low frequencies.
The measurements confirms this.
I was curious to see if the port actually caused larger velocities because inside the port the velocity is on the order 100 times larger, and if say 1-2m distance still is close enough, the velocity could be higher.
The acoustic coupling is also different, meaning that the sound field around the subwoofer couples back to the driver in a different way compared to sealed.
This is not the case, it is sufficient to move away from the port around the same distance as the dimensions of the port, then the sound field has developed and pressure-velocity relationship is the same as for a sealed system.

Now, if you place something, say a coach, very close to the port, this may be significant as the high velocity of the air in the port could then have a larger impact on shaking the coach.

The Compact Horn Subwoofer used for the measurement experiment is a variation of a rear loaded horn and is similar to a ported box for this purpose, so that it if the port is closed it acts like a sealed box.
I do not doubt at all that my theory could be wrong and appreciate your test. However, I personally don't believe your test is credible enough to prove the contrary as I'm not convinced your test and measurement device is accurate or precise enough. But it's all good, we can still explore.

Is it possible for you to post pics of your sub and measuring device?

What is your subs tuning frequency?

Is the port and the driver firing in the same direction?

I also have a hard time believing that the air from the port is causing 350lb (with 2 people) couch to shake more than a sealed design...so it must be associated with the sound wave exciting the resonant frequency of the couch more.
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post #120 of 145 Old 07-09-2014, 04:17 PM
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Originally Posted by dominguez1 View Post
I do not doubt at all that my theory could be wrong and appreciate your test. However, I personally don't believe your test is credible enough to prove the contrary as I'm not convinced your test and measurement device is accurate or precise enough. But it's all good, we can still explore.
..
Measurement does not need to be accurate as long as it is consistent so that it is possible to make measurements that can be compared to each other.
The measurement results shows that the sound field is the same, there is no difference, and that was one of the purposes of making those measurements.
The results are also in line with general electroacoustics theories, you will get the same result by modelling the speakers and simulate the sound field.

I don't have a picture and really there is not much interesting to see, it is just an ordinary bass driver with no enclosure and no baffle.
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