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Bass punch threshold


TTS56A

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There was a thread on the tactile bass subject, but a new one for measurements could be interesting.

 

I am using those measurements for setting up systems, in combination with other measurements it gives more information about what is going on.

It is especially valuable when setting up multi-sub systems.

 

If instrumentation and correction curves are different, the measurements may not be comparable.

It will still be possible to see how the sound field behaves, as it will reveal directivity.

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http://www.avsforum.com/forum/113-subwoofers-bass-transducers/2118090-vibsensor-accelerometer-test-thread.html

 

There has been little attention paid to midbass punch tactile response in that thread. We have main be concentrating on subwoofer/ULF type bass signals and how we can compare each others 'tactile response' from one system to another.

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From AVS forum, this is what has been explained!

 

One hypothesis relates to the way sound wave propagate. In the near field, or even out doors, the sound wave moves in one direction first compressing the air molecules on one side of the listener, then moving across the listener's position, and finally increasing pressure on the opposite side of the body. The pressure change is in ONE DIRECTION ONLY. As the pressure wave moves across the body, following compression of the air is rarefaction of the air--a negative pressure zone. As this rarefaction of air creates a negative pressure zone, the listener is then "pulled" back toward the sound source.

So, positive pressure gives a linear "push" and it is then followed by a negative pressure which gives a linear "pull". Thus the listener is rocked back and forth as the sound wave passes by. This creates the physicality.

Now, take a subwoofer placed in a car or in a home room. When a tone is played, the wave will begin to propagate in one direction. However, it will then be met with reflections off the boundaries. So what actually ends up hitting the listener are bass waves from ALL DIRECTIONS. The air molecules are compressed and rarefied, which creates the SPL, but there is no directional change. That is the key. Integrated across the entire body of the listener, there is no net directional change in pressure. It pushes in all at the same time, then it sucks out (rarefied) all at the same time. As a result, the pressure goes up and down. SPL is measured, but there is no movement back and forth of the listener. No physicality, at least in some sense.

 

 

I agree 100% each word. This can explain why my different tactile feeling when i was to listening to my friend's car. 

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And further:

 

A further ramification of this is that various subwoofer designs could have more or less physicality depending on the extent to which they produce linear bass waves. Horns, for example, are frequently described as having more punch than direct radiators all other things equal. Within this model of physicality, this could be explained by the fact that a sound wave must travel some distance before exiting the horn, thus putting the listener effectively into the "far field" where bass waves are nearly planar even while standing directly in front of the horn itself.

The same might also be true of large radiators and/or large numbers of them relative to small diameter radiators, as the former creates something much closer to the planar wave of the far-field.

 

:) 

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From AVS forum, this is what has been explained!

 

One hypothesis relates to the way sound wave propagate. In the near field, or even out doors, the sound wave moves in one direction first compressing the air molecules on one side of the listener, then moving across the listener's position, and finally increasing pressure on the opposite side of the body. The pressure change is in ONE DIRECTION ONLY. As the pressure wave moves across the body, following compression of the air is rarefaction of the air--a negative pressure zone. As this rarefaction of air creates a negative pressure zone, the listener is then "pulled" back toward the sound source.

 

So, positive pressure gives a linear "push" and it is then followed by a negative pressure which gives a linear "pull". Thus the listener is rocked back and forth as the sound wave passes by. This creates the physicality.

 

Now, take a subwoofer placed in a car or in a home room. When a tone is played, the wave will begin to propagate in one direction. However, it will then be met with reflections off the boundaries. So what actually ends up hitting the listener are bass waves from ALL DIRECTIONS. The air molecules are compressed and rarefied, which creates the SPL, but there is no directional change. That is the key. Integrated across the entire body of the listener, there is no net directional change in pressure. It pushes in all at the same time, then it sucks out (rarefied) all at the same time. As a result, the pressure goes up and down. SPL is measured, but there is no movement back and forth of the listener. No physicality, at least in some sense.

 

 

I agree 100% each word. This can explain why my different tactile feeling when i was to listening to my friend's car. 

 

The resulting effect on the perceived sound is correct, but the description of the cause is partly wrong and seems like an attempt to describe the physics in more simple and popular terms.

 

In the near field of an acoustically small source the direction of the sound field is not a plane wave, rather it is an expanding spherical wave and the particle velocity and pressure is out of phase - the velocity is higher relative to pressure than in the far field, but the net intensity is not higher because of this phase shift.

 

In the far field the sound propagates like a plane wave and the relationship between the particle velocity and pressure is fixed, and they are in phase.

 

To get something physical from a sound wave, something you can physically feel on your body, there has to be some transfer of energy from the sound wave to the body. 

The first requirement for that to happen is that the sound has intensity - there has to be transfer of energy.

 

The size of the room relative to frequency is important - at very low frequencies there is no transfer of energy, at slightly higher frequencies boundary effects creates narrow bands in frequency where some places there is a gain, other places cancellation.

At higher frequencies the room contributes with reverberant sound which has no direction and no intensity.

 

At very low frequencies the size of the radiator is always very small compared to the wavelength, but it is still possible to change fundamental properties of the sound even at the lowest frequencies, because it is possible to create a radiator that is large compared to the dimensions of the room.

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One hypothesis relates to the way sound wave propagate. In the near field, or even out doors, the sound wave moves in one direction first compressing the air molecules on one side of the listener, then moving across the listener's position, and finally increasing pressure on the opposite side of the body. The pressure change is in ONE DIRECTION ONLY. As the pressure wave moves across the body, following compression of the air is rarefaction of the air--a negative pressure zone. As this rarefaction of air creates a negative pressure zone, the listener is then "pulled" back toward the sound source.

 

To the extent which this is possible, it would only work for very high frequencies.  The wavelength for low frequencies is very long, so the pressure difference between opposing sides of a person's body would be vanishingly small.  The pressure difference across the body would drop rapidly below 1 kHz or so.  That is, unless you were lying down while listening to the concert or speakers, orienting the long part of your body with the wave.  :)

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Exactly, @SME.

 

Also, the pressure has no direction, it is a scalar value.

It is the particle velocity of the sound wave that gives it a direction.

 

It is the force from the sound waves acting on the body that gives the tactile sensations.

How large this force is depends on pressure, particle velocity and the phase between those.

 

And it depends on the acoustic impedance of the medium - a body is kind of blupsy and not very solid, compared to the floor.

So the body may respond well to a sound field with high velocity and not very high pressure, while the floor needs pressure to move.

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Anyone tried to do velocity measurements?

 

Ceiling absorbers for the room is finished, testing them as side wall absorbers now, and only one 120x120cm absorber has significant impact on bass.

The bass sounds more balanced, deeper, less coloration, and there is punch on bigger drums, well, sort of.. too much roll-off, it needs to be louder below 80hz. 

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The wavelength for low frequencies is very long, so the pressure difference between opposing sides of a person's body would be vanishingly small.

 

Let me understand... There is no pressure difference, because the overpressure cycle is longer than the body thickness, so the pressure is forcing equal in front and back of the body. This is ok... But if the pressure difference is lower, shouldn't be particle velocity lower too?

 

Isn't then the particle velocity proportional to the pressure difference?

 

If for frequencies <1 khz, there is no pressure difference through our chest, the intensity should be less. am i wrong?

 

 

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Working on the room, starting to see an end to it now, almost all acoustic treatment in place.

 

I can not help it, but I continue to imagine the tactile feel has increased each time something is changed.

Measurements will reveal if that is possible, and if so, it should possible to analyze and find out what exactly what cause improved tactile feel.

 

Was going to say that A/B-testing acoustic improvements are not practical, but in this case it may actually be an option, because some of the absorbers are mounted on mounts that allow for very easy removal.

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So far there seems to be a correlation between improved decay and tactile feel.

 

The velocity does not change much - so far, but it was already quite good after the front wall fix.

 

Also, so far the guidelines given in the "How to.." article are still spot on, if you follow these you will get good sound.

 

But it is not finished yet, it will take several more days of building.

When the room is more or less completed, and the end result is more determined, I can start a thread on the room and the acoustics.

 

I have quite a lot of data now on this, because I was able to do measurements for each step, testing the effect of different acoustic treatment.

The measurements can then be compared and analyzed, to see if it is possible to learn something.

 

The lacking part of the data set are the listening impressions - they are affected by what I think I heard, and as time goes by, I will not even remember how it was.

This is very relevant for the tactile punch issue - the perception will be highly subjective and different form person to person, from day to day.

What is a "hard hitting midbass" - some may experience something that hits in the upper chest with a very noticeable thump, as being "hard", while someone else will require a physical hit that slams your chest violently and cause you to almost loose your breath.

A measureable, physical quantity is what is needed here.

SPL alone does not work.

 

Just mentioning it - making a recording of the acoustic space with microphones will not be sufficient to give a good representation.

The tactile feel differences are lost, the direction of reflections are lost, the direction of the direct sound is lost.

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Let me understand... There is no pressure difference, because the overpressure cycle is longer than the body thickness, so the pressure is forcing equal in front and back of the body. This is ok... But if the pressure difference is lower, shouldn't be particle velocity lower too?

 

Isn't then the particle velocity proportional to the pressure difference?

 

If for frequencies <1 khz, there is no pressure difference through our chest, the intensity should be less. am i wrong?

 

Thinking about this further, I think it is possible that what you're describing could be perceived.  First of all, the pressure difference will be a maximum when the body dimension is about half a wavelength.  A person may be 10-18" (or more) thick, assuming a front-to-rear travelling wavefront?  Just guessing here.  That means there's a peak at around roughly 400-700 Hz below which the pressure difference will tend to roll-off because the wave keeps getting longer as you go lower.  However, the roll-off is slow (yes, I'm correcting what I said in my previous post) for at least a couple octaves.

 

The body definitely has strong vibro-tactile sensitivity at around 250 Hz.  Depending on how the information is processed, I can see it being theoretically possible for those perceptions to assist with localization to somewhat lower frequencies than are possible with the wars, but this is definitely stretching into purely hypothetical territory.  What about forces?  Well, I think most would agree that 110 dB is enough to get some feeling of kick.  Yeah?  That involves rms pressure difference of a whopping 12 Pa max.  (Note that atmospheric pressure at seal level is 101300 or so Pa.)  The human body surface area is about 2 square meters.  As such, any net force from the pressure difference can't be higher than 2 * 12 = 24 N.  That's newtons, units of force.  To put it into better perspective, compare it to the force of gravity on a 70 kg person at 686 N.  So, the G-forces involved here are definitely less than like 0.035.  That figure doesn't seem especially impressive to me.

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Good posting SME   :)

 

In these days i did a lot of measurements with continuous sines and pulses... and yes, for frequencies < 70-80 hz the same outdoor pressure was perceived a little more exciting than the indoor. I've also established that for frequencies below 40 Hz, the bass is more likely slamming, between 50-120 Hz i noticed what i would call punch, and from 150 Hz to almost 300 Hz more likely "punchy" or mid-bass punch.

 

By the way i think we need to consider the peak net pressure rather then rms. However in my experiences 110 db peak is a bit over the threshold in the 50-120 Hz range, nothing impressive at all. A good dual 18" with 1kw in a vented enclosure is capable of at least 135 db peak at 1 meter in half place (outdoor, well away from boundaries). In a medium-size concert for a strong bass reinforcement, i've always seen at least 15-20 of these double bass cabinets. Then i would think that 40-50 meters away, the pressure is still around 120-125 db peak.

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The lacking part of the data set are the listening impressions - they are affected by what I think I heard, and as time goes by, I will not even remember how it was.

This is very relevant for the tactile punch issue - the perception will be highly subjective and different form person to person, from day to day.

What is a "hard hitting midbass" - some may experience something that hits in the upper chest with a very noticeable thump, as being "hard", while someone else will require a physical hit that slams your chest violently and cause you to almost loose your breath.

A measureable, physical quantity is what is needed here.

SPL alone does not work.

 

Just mentioning it - making a recording of the acoustic space with microphones will not be sufficient to give a good representation.

The tactile feel differences are lost, the direction of reflections are lost, the direction of the direct sound is lost.

 

Agree. SPL alone is not enough to describe what is happening. Nor is the impulse/decay time related data. Neither is the particle velocity, reflected energy or mechanical vibration of the ground/walls/boundaries. All are needed and most are linked. Attack and decay are important. Outdoors without reflection would do very well in this regard.  Most of the study has been interested in what happens at the ear which is a simpler, smaller affected area problem. The rest of the body is a huge and far more complicated sensor when it comes to powerful and lower frequency content. Quantifying what is happening at the ears versus the entire body surface combined with the ears is like moving from working in 2 dimensions to 3.

 

I look forward to seeing what you guys discover with the particle velocity sensors. (I keep seeing mention of woofers used for capturing this data. What is keeping this from simply being a large low quality microphone like a Yamaha subkick? How are the characteristics of the woofer being taken into account and what are the characteristics desired in the woofer chosen for this? Forgive me, I still have not had time to do research on measuring PV.

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Good posting SME   :)

 

In these days i did a lot of measurements with continuous sines and pulses... and yes, for frequencies < 70-80 hz the same outdoor pressure was perceived a little more exciting than the indoor. I've also established that for frequencies below 40 Hz, the bass is more likely slamming, between 50-120 Hz i noticed what i would call punch, and from 150 Hz to almost 300 Hz more likely "punchy" or mid-bass punch.

 

By the way i think we need to consider the peak net pressure rather then rms. However in my experiences 110 db peak is a bit over the threshold in the 50-120 Hz range, nothing impressive at all. A good dual 18" with 1kw in a vented enclosure is capable of at least 135 db peak at 1 meter in half place (outdoor, well away from boundaries). In a medium-size concert for a strong bass reinforcement, i've always seen at least 15-20 of these double bass cabinets. Then i would think that 40-50 meters away, the pressure is still around 120-125 db peak.

 

It's interesting that we have different opinions about how different frequency ranges feel.  Of course, this thinking is tricky because so much bass is wind-band, covering more than one of these ranges at once.  And I think people here often discount stuff above 40 Hz because it tends to be weaker in the PVLs or SpecLab graphs, or whatever.  But assuming tactile sensitivity increases with increasing frequency (at 40 Hz at least), which is consistent with evidence, a lot of the stuff that looks pretty mild in a PvA or Spec may contribute the lion's share of the punch in the soundtrack.

 

I disagree that 110 dB is only "a bit over threshold" for tactile sensation, but this may be a matter of personal opinion to some extent.  I also do not routinely listen to car systems with > 130 dB or what not.  As you say, "110 dB == nothing impressive at all", but I think 110 dB can be very impresive.  IMO, the threshold is closer to 90 dB or even lower.  I believe a lot depends on what else is going on musically and acoustically.  If the room is dead quiet and the bass is all you can hear, you might even be able to feel below 80 dB.  But if you are in a very noisy large venue with a lot of reverb, it might take peaks > 110 dB at the seats to punch above the noise floor, especially with a full band playing at full tilt including a bass player that the kick may have to compete with. 

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So far there seems to be a correlation between improved decay and tactile feel.

 

The velocity does not change much - so far, but it was already quite good after the front wall fix.

 

Do you think that the big change in velocity may have had to do with a more general shift of the response from being dominated by reflected sound to being dominated by direct sound?  Adding that initial treatment may have cut the decay time enough to give you the more directional sound-field you are seeing.  The question is, how much does that actually improve tactile perception?  How much does cleaning up the excess bass energy improve tactile perception because of its influence on the pressure response?  Can you make an experiment that can differentiate between the two effects?

 

I realize I haven't done a good job explaining why I disagree that particle velocity matters so much.  Let me try again (even though I may fail).

 

In the near field of an acoustically small source the direction of the sound field is not a plane wave, rather it is an expanding spherical wave and the particle velocity and pressure is out of phase - the velocity is higher relative to pressure than in the far field, but the net intensity is not higher because of this phase shift.

 

For an acoustically small source, you don't have to get very far away at all before the response is essentially far field.  It's only when the source is *not* acoustically small that the near-field vs. far-field distinction comes into play.

 

More generally, near-field vs. far field do not determine wavefront shape.  Instead, in the far-field, the wave front shape becomes unimportant to the problem.  A spherical wave in the "far-field" is so big relative to the *thing* that you are studying (the thing which establishes the context for near-field vs. far-field) that it can be considered a plane wave.  Think of the earth.  You know it's round, but lacking an enlightened education, you might mistake it for being flat.  That's not at all the same thing as saying that a spherical wave from an acoustically small source transforms into a plane wave as it propagates.

 

To get something physical from a sound wave, something you can physically feel on your body, there has to be some transfer of energy from the sound wave to the body.

 

Actually, thinking about this carefully, there's no particular reason feeling sound should require significant energy transfer into the body, even though in practice it might be.  Certainly at least some energy transfer is required, but it's just as possible that sensation is maximized when either pressure or velocity are maximized, without the two necessarily being maximized at the same time.  (i.e., multiplied)  The real problem is understanding what the pressure and velocity are.  That's actually a lot harder for reasons I will explain below.

 

The first requirement for that to happen is that the sound has intensity - there has to be transfer of energy.

 

Let's suppose sensation *does* correlate with energy transfer (which is probably essential for sense organs that lie underneath the skin because

energy must travel to them).  Sound intensity is indeed a measure of density of energy transfer in a particular direction through a point in space.  Furthermore, sound intensity is also equal to the produce of pressure and velocity at that point in space.  This much is true!

 

However the sound intensity that you measure at various points along the interface between the air and your skin will be substantially different than the sound intensity that you will measure in the absence of a body, whether in the near-field, far-field, reverberant field, or the complete mess that is the acoustic responses of most listening rooms.  The sound intensity you measure at a point in a room (via microphone and velocity meter) is a measure of how much energy is moving through the air at that point.  *But what you want to know is the sound intensity along the interface between the air and your skin.*

 

This leads to a much more complicated situation than the textbook near-field and far-field models I see routinely discussed here.  You are considering transfer of energy not *within* a single medium (i.e., air) but *between* two media (i.e., air and skin).  The problem is that those two media have very

different physical properties.  Air is very compressible and it's molecules tend to move a lot in response to pressure.  On the other hand, liquids and solids are much more dense and are almost incompressible.  They do still compress enough to transmit vibration, but their molecules move much less for a given pressure.  This is crucial.  At the point where the air and skin make contact, both the pressure and the velocity in the direction perpendicular to the area of contact will be the same.  The imperfect mating between media (the air and skin) causes energy to reflect or diffract around the body.  This is a problem of matching acoustic impedances.  It's impedance (defined as pressure divided by particle velocity, or a related quantity depending on the type of impedance) that's important, but that deserves a more detailed discussion that I don't have time for right now.

 

However, the implication here is that it is low particle velocities and not high particle velocities that would be most desired.  Indeed, you might get the best bass punch by holding your chest into a hole in a very large baffle (probably with a gasket or something).  That's where you'll have a pressure maximum and velocity of almost zero within the air due to the influence of the large boundary.  The same idea applies when trying to maximize energy transfer between a speaker driver and the air or maximizing the absorption achieved using resonant bass absorbers.  In both cases, they work best in areas of the room where the impedance of the air, in their absence, tends to be higher.  Subs are more efficient in corners.  High frequency drivers are more efficient when horn loaded.  Impedance matching is the key here as I would expect it to be with energy transfer into the body, and so low particle velocity in the air in the vicinity of the driver or resonant absorber or human body is best.

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Agree. SPL alone is not enough to describe what is happening. Nor is the impulse/decay time related data. Neither is the particle velocity, reflected energy or mechanical vibration of the ground/walls/boundaries. All are needed and most are linked. Attack and decay are important. Outdoors without reflection would do very well in this regard.  Most of the study has been interested in what happens at the ear which is a simpler, smaller affected area problem. The rest of the body is a huge and far more complicated sensor when it comes to powerful and lower frequency content. Quantifying what is happening at the ears versus the entire body surface combined with the ears is like moving from working in 2 dimensions to 3.

 

I look forward to seeing what you guys discover with the particle velocity sensors. (I keep seeing mention of woofers used for capturing this data. What is keeping this from simply being a large low quality microphone like a Yamaha subkick? How are the characteristics of the woofer being taken into account and what are the characteristics desired in the woofer chosen for this? Forgive me, I still have not had time to do research on measuring PV.

 

Theory and methods for audio has always been spl and any regards for tactile has mostly been based on experience.

Acousticians know the wave equation and the relationship between p, pv, sound intensity, and how this relates to the acoustic surroundings - acoustic impedance.

When you talk to audio engineers about this, they think you have lost it or joined the snake-oil. 

 

A consequence of this assumption that p - spl - alone is what describes sound, is that there is little knowledge about how the complete sound field properties relates to the perception of sound.

 

Send me a pm and I will send you the description for the velocity measurement.

Many microphones are actually velocity measurement devices - they react to the particle velocity, rather than pressure.

A condenser measurement microphone will not work, it measures pressure.

 

A velocity ribbon mic would work, but a bass driver works better for very low frequencies, and that was what I intended to measure.

A bass driver has a large area, which is good for low freq, the high mass and coil inductance limits the usable high frequency response to around 1K, but that is fine for this application.

At first the idea was to measure mostly well below 100hz, to be able to develop methods for multi sub calibration - flat frequency response, and also preserve the velocity and intensity.

Then I found that those measurements provide valuable information also at higher frequencies, because it shows the direction of the sound and gives an indication about sound intensity.

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Do you think that the big change in velocity may have had to do with a more general shift of the response from being dominated by reflected sound to being dominated by direct sound?  Adding that initial treatment may have cut the decay time enough to give you the more directional sound-field you are seeing.  The question is, how much does that actually improve tactile perception?  How much does cleaning up the excess bass energy improve tactile perception because of its influence on the pressure response?  Can you make an experiment that can differentiate between the two effects?

...

 

Hard to say for sure what the front wall fix did, because I do not have measurements data from the room before building the front wall, only some old measurements with other speakers.

 

But the sound field now definitely has more direct sound and less boundary reflections, which can be seen from the velocity measurements because the sound is more directional.

 

Let me see if I understand your question.

Improved directionality - which indicates increased sound intensity, compared to improvements on frequency response.

I can have a look at the data, maybe it is possible to see something.

 

A note on decay:

What is important here is early decay - late reverb can not have any significant contribution to any tactile feel, because the level is down by at least 10-20dB or more, and that is too low in level to contribute any significant changes in the sound field intensity or velocity.

 

 

...

For an acoustically small source, you don't have to get very far away at all before the response is essentially far field.  It's only when the source is *not* acoustically small that the near-field vs. far-field distinction comes into play.

 

...

 

Depends on the frequency, distance to the source must be large compared to the wavelength to be far field.

 

I will read through the rest of your post again later, and see if I have something meaningful to add, thinking about the perception part.

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..

Let me see if I understand your question.

Improved directionality - which indicates increased sound intensity, compared to improvements on frequency response.

I can have a look at the data, maybe it is possible to see something.

 

The frequency response overall was better before fix, adding the front wall and ceiling absorbers and especially the side wall absorbers has made the response look worse.

 

But the phase is improved, and it is smoother, as in less small peaks and dips, but larger deviations overall.

 

The room is not finished, as it is now it is not what i would say acceptable.

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