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Title: PROOF-Whole vs half space sub loading
Post by: Ivan Beaver on April 05, 2016, 02:01:55 pm
I had a few minutes and wanted to do a little test-for which there has been lots of "discussion" on.

Basically whole space vs half space of subs and what happens to the levels and freq response.

Here is my setup.  I placed a mic 100' away.  To get far enough away so that inverse square law would only affect it a little bit.

I used two different designs of subs (a tapped horn and a "basically" normal bass horn).  I have no reason to believe a normal ported sub would be any different.

No xover was used and just 1 eq filter (quickly applied) to flatten out the response to be easier to look at.  The eq filter is NOT the same on both cabinets.  In both cases it was a CUT only, and no boost was applied.

I measured the cabinet on the ground-then raised it up so the bottom was 15.5' off the ground and measured again.

 That was as high as my forklift would go.  Sorry it was not more.  But you should get the idea.

I did adjust the levels between the different cabinets, but NOT between the measurements of each cabinet.

As you can see, the biggest thing that changed was the HIGHER FREQ-NOT the low freq.  This is because the mic is not on axis with the sub and the higher freq are starting to become a little directional.

So this PROVES (at least to me) that the whole idea of "getting more bass" when the subs are on the ground OR simply that you can "add a magical 6dB" to a whole space measurement is simply false.

Since the mic (or person listening) is already in half space, you get the loading.  But no additional loading when both are in half space.

Yes the curves are not exactly on top of each other, but remember that the distance to the mic is further when the cabinet was in the air.

In both cases the PURPLE trace is the ground and the GREEN is in the air.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Art Welter on April 05, 2016, 02:47:58 pm

I measured the cabinet on the ground-then raised it up so the bottom was 15.5' off the ground and measured again.

So this PROVES (at least to me) that the whole idea of "getting more bass" when the subs are on the ground OR simply that you can "add a magical 6dB" to a whole space measurement is simply false.
Ivan,

What was the distance of the subs and mic to any buildings?

Art
Title: Re: PROOF-Whole vs half space sub loading
Post by: Ivan Beaver on April 05, 2016, 03:11:50 pm
Ivan,

What was the distance of the subs and mic to any buildings?

Art
I just did this in the back parking lot-so not completely free of reflections.

Moving everything to our "reflection free" area would require A LOT more time and effort than I had.  The forklift doesn't move to easy :)

Behind the sub is the building.  It is about 60-70' behind and is basically about 24' high.  It has "lossy" walls.

The building was about at a 45* angle to the rear of the sub

Behind the mic the nearest "large object" is probably 400' or more.  There are some trees and a creek between the mic and the next building

The mic was laying on grass. 
Title: Re: PROOF-Whole vs half space sub loading
Post by: Mark Wilkinson on April 05, 2016, 03:35:32 pm

Interesting...  but is 15ft high enough to consider it a move from half to full space?  Particularly given the long wavelengths involved?

I'm thinking that 15ft over 100ft makes for more of a long flat acoustic mirror, than a change of space.
And that floor bounce summation at all freqs will range from minimally destructive at the longest wavelengths to greater destruction at shortest...like what seems to be going on with the plots..
Title: Re: PROOF-Whole vs half space sub loading
Post by: Art Welter on April 05, 2016, 03:43:31 pm
Behind the sub is the building.  It is about 60-70' behind and is basically about 24' high.  It has "lossy" walls.

The building was about at a 45* angle to the rear of the sub

Behind the mic the nearest "large object" is probably 400' or more.  There are some trees and a creek between the mic and the next building

The mic was laying on grass.
Thanks, the distance to boundary clarifications are important to determine whether there was actually a half space to free space change.

For what it's worth, I have done a similar test on a smaller scale, same results. That said, if the test was done at 15.5 feet with the mic on the ground, then the cabinet and mic lifted 15.5 feet high, the second measurement would show a loss in bass response compared to the first.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Ivan Beaver on April 05, 2016, 03:57:58 pm
Thanks, the distance to boundary clarifications are important to determine whether there was actually a half space to free space change.

For what it's worth, I have done a similar test on a smaller scale, same results. That said, if the test was done at 15.5 feet with the mic on the ground, then the cabinet and mic lifted 15.5 feet high, the second measurement would show a loss in bass response compared to the first.
When I get a chance I can redo the test.  I have a 17' tall mic stand that I could use.

Don't expect anything this week however.

My whole "thinking" was that in almost no case are the people and the cabinet in whole space-so that spec doesn't really tell anything useful.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Ivan Beaver on April 05, 2016, 04:03:57 pm
Interesting...  but is 15ft high enough to consider it a move from half to full space?  Particularly given the long wavelengths involved?

I'm thinking that 15ft over 100ft makes for more of a long flat acoustic mirror, than a change of space.
And that floor bounce summation at all freqs will range from minimally destructive at the longest wavelengths to greater destruction at shortest...like what seems to be going on with the plots..
As I said-my forklift only went that high.  To go higher would require renting in a larger lift.

Since there was not enough of any change to be concerned with, I don't see any reason to spend the money on a larger lift.

And in many cases (except the larger shows) most subs are not much higher than 15' anyway.  And that was to the BOTTOM of the cabinet.

The 100' distance was choosen as a "typical" FOH position (yes it varies), but was far enough away to get an idea of what was happening.

There is NO floor bounce (at least at those freq), since the mic was lying on the ground.

I don't think there is any "destructive interference" going on at the higher freq (meaning 100-200Hz).  I am pretty sure those differences are because the mic is not on axis with the loudspeaker and those freq are starting to narrow a bit.  I could be wrong however.

Either way-there is not enough of a difference to be concerned with.
Title: Re: PROOF-Whole vs half space sub loading
Post by: duane massey on April 06, 2016, 01:35:04 am
Very interesting. Thanks, Ivan.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Mike Pyle on April 06, 2016, 04:09:20 am
As you can see, the biggest thing that changed was the HIGHER FREQ-NOT the low freq.  This is because the mic is not on axis with the sub and the higher freq are starting to become a little directional.

And yet, anyone can hear the difference in bass response between a monitor on a stand versus one on the floor. Why do you think that is?
Title: Re: PROOF-Whole vs half space sub loading
Post by: Ivan Beaver on April 06, 2016, 07:51:27 am
And yet, anyone can hear the difference in bass response between a monitor on a stand versus one on the floor. Why do you think that is?
Part of the reason is the position of the ears-the floor (or other reflective surface) and the speaker.

When measuring subs, the mic is on the ground (to avoid reflections).

Reflections can/will cause all sorts of deviations in the response that are totally position dependent.

So when measuring any loudspeaker, you need to reduce/eliminate the reflections as much as possible in order to get any sort of useful measurement of the device.

The idea of measurement is to measure the device itself-without any outside influences.

At least in the way the device will be used.

For example-I believe that floor wedges should be measured on the floor (since that is their intended position).  Typical full range speakers-no.  You are more concerned with the "non reflective" performance.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Chuck Simon on April 06, 2016, 09:08:10 am
What do you think your results would be if the mic was at "ear" level instead of on the ground? 
Title: Re: PROOF-Whole vs half space sub loading
Post by: Ivan Beaver on April 06, 2016, 10:33:56 am
What do you think your results would be if the mic was at "ear" level instead of on the ground?
I am going to set up the test again soon. Not this week.

One of the measurements will be going ground, 5.5' (ear level) and 16' of the mic on both the ground and flown sub positions.  Of course there will be reflective cancellations, but what about broadband? 

ALSO, there is another test Tom D. wants me to do that might REALLY throw some interesting discussion/fuel on the fire. 
Title: Re: PROOF-Whole vs half space sub loading
Post by: Mark Wilkinson on April 06, 2016, 11:16:27 am
Part of the reason is the position of the ears-the floor (or other reflective surface) and the speaker.

When measuring subs, the mic is on the ground (to avoid reflections).

Reflections can/will cause all sorts of deviations in the response that are totally position dependent.

So when measuring any loudspeaker, you need to reduce/eliminate the reflections as much as possible in order to get any sort of useful measurement of the device.

The idea of measurement is to measure the device itself-without any outside influences.



Thx Ivan, All that makes good easy sense...

But still, I'm thinking with a mic on the floor, when you raise the sub off the pavement, you will still measure reflections...
Not the kind of straight line floor bounce reflections we normally think about ala comb filtering, but a kind of integrated weaving of the primary line of sight waves with their reflections off the pavement.  An outdoor reverberate field...or better yet, interference field ......solely off the pavement.......that decays oh so quickly...

Guessing that your measurements may be showing this with the relative widening magnitude difference as freq rises.

Also think it only makes sense that a 6db gain from going to half space is a theoretical maximum from perfect coupling, and that less perfect couplings at some distances will also gain some portion of the +6db (albeit more freq dependent).  IOW, just like combining subs..

So, I'm really left wondering if anything can be said for the test, in terms of whole vs half space....


Title: Re: PROOF-Whole vs half space sub loading
Post by: Ivan Beaver on April 06, 2016, 12:09:09 pm
Thx Ivan, All that makes good easy sense...

But still, I'm thinking with a mic on the floor, when you raise the sub off the pavement, you will still measure reflections...
Not the kind of straight line floor bounce reflections we normally think about ala comb filtering, but a kind of integrated weaving of the primary line of sight waves with their reflections off the pavement.  An outdoor reverberate field...or better yet, interference field ......solely off the pavement.......that decays oh so quickly...

Guessing that your measurements may be showing this with the relative widening magnitude difference as freq rises.

Also think it only makes sense that a 6db gain from going to half space is a theoretical maximum from perfect coupling, and that less perfect couplings at some distances will also gain some portion of the +6db (albeit more freq dependent).  IOW, just like combining subs..

So, I'm really left wondering if anything can be said for the test, in terms of whole vs half space....
What brought this on was a discussion in which the "other argument" was "When you put the subs on the floor (vs flown) you get more output".

Which this test proves is basically wrong.  There is no more output-at least that is easily noticeable.

Now if you are close to the sub- you will get more output-but that is due to inverse square-NOT whole vs half space.

I really can't wait to do more tests and get some more data.

I just did this real quick.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Mark Wilkinson on April 06, 2016, 12:22:14 pm
What brought this on was a discussion in which the "other argument" was "When you put the subs on the floor (vs flown) you get more output".

Which this test proves is basically wrong.  There is no more output-at least that is easily noticeable.

Now if you are close to the sub- you will get more output-but that is due to inverse square-NOT whole vs half space.

I really can't wait to do more tests and get some more data.

I just did this real quick.

Sure...proves it quite well.  Good luck with future test/ideas.
Title: Re: PROOF-Whole vs half space sub loading
Post by: John Rutirasiri on April 06, 2016, 04:43:59 pm
I am going to set up the test again soon. Not this week.

One of the measurements will be going ground, 5.5' (ear level) and 16' of the mic on both the ground and flown sub positions.  Of course there will be reflective cancellations, but what about broadband? 

ALSO, there is another test Tom D. wants me to do that might REALLY throw some interesting discussion/fuel on the fire.

I was one of those that believed ground stacked subs had more output due to coupling with the ground, so thank you for busting that myth.

When you did the test, was the sub sitting on the forks of the forklift, or did you hang it off the forks?  I ask because most likely the cabinet did not move much sitting on the forks, no matter how loud you cranked (friction.)

In actual use, the subs would be flown (at bottom of a hang or behind the main hang) so there's possibility for the cabinets to move or swing in the air -- they're not stationary.   Given Newton's 3rd law of motion, I would guess there is enough force to move the cabinets, especially at high volume.  (Even on the ground, my TH118's move and dance around.)  I would expect the movement affects the output ever so slightly.

Would it be possible for you to do the next test with the subs "flown?"

Many thanks,
John R.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Ivan Beaver on April 06, 2016, 05:18:39 pm
I was one of those that believed ground stacked subs had more output due to coupling with the ground, so thank you for busting that myth.

When you did the test, was the sub sitting on the forks of the forklift, or did you hang it off the forks?  I ask because most likely the cabinet did not move much sitting on the forks, no matter how loud you cranked (friction.)

In actual use, the subs would be flown (at bottom of a hang or behind the main hang) so there's possibility for the cabinets to move or swing in the air -- they're not stationary.   Given Newton's 3rd law of motion, I would guess there is enough force to move the cabinets, especially at high volume.  (Even on the ground, my TH118's move and dance around.)  I would expect the movement affects the output ever so slightly.

Would it be possible for you to do the next test with the subs "flown?"

Many thanks,
John R.
They were sitting on the forks strapped down-so not moving.

I also was not running high levels-just enough to get above ambient noise.

Yes if they were "hung" several factors could affect it-self movement/vibration and wind.

Both of which will vary quite a bit "depending".

I could hang them, but could not get them as high.

Also the length of the "hang" will greatly affect how much swing they have.  A short hang will not allow for much swing-while a long hang will allow for much greater movement.

So there are A LOT if "it depends" when it comes to the performance when hanging.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Tom Danley on April 06, 2016, 05:59:41 pm
I am going to set up the test again soon. Not this week.

One of the measurements will be going ground, 5.5' (ear level) and 16' of the mic on both the ground and flown sub positions.  Of course there will be reflective cancellations, but what about broadband? 

ALSO, there is another test Tom D. wants me to do that might REALLY throw some interesting discussion/fuel on the fire.

I don’t know about fuel exactly but I would bet that here is a case where there is another layer to the onion yet to be measured, partly obscured using Voltage referenced signals where the effect of loading may be harder to see. 

Remember horns started life being driven with tube amplifiers with a given output impedance.
This made sense then as a matched input and output impedance was the norm for RF and everything else back then because it maximized power delivery but also produced the least change in levels if one end varied in impedance. 
Same for horns in some ways. 

Now days we use a Voltage reference for nearly everything, audio land has no concern for matched impedances, our signals represent a pressure or whatever,  do not normally represent power, we don’t expect (or normally want) amplifiers to deliver constant power to our speakers either, just input Voltage times gain setting. 

Acoustic loading when reflected back through the driver is (I always thought) counterintuitive.   

When the resistive acoustic load on the driver is increased say with a horn, the resistive portion of the impedance goes up, not down and so, the power delivered to the speaker with a fixed Voltage, actually goes down proportionally too.
                 
For example if one had a 50% efficient horn speaker, the amplifier load would be the drivers Rdc + the acoustic load R which for a 50% efficient speaker is approximately equal to the Rdc.    This (resistance dominating the inductances) can only happen (roughly) within the bandwidth limited by the compliance at the bottom (box and suspension spring) and moving mass and or inductance at the high end.   In that case, half the power is dissipated as heat in the voice coil and the other half, radiated as sound power.
 
Thus, if one goes from one to four bass horns (where the added acoustic load is quite noticeable), one see’s the change / increase in Voltage sensitivity and response from loading but to see the complete picture of how loading effects efficiency, one has to examine the change or increase in impedance as well.     
The thing is, it is the current squared divided by the driver Rdc which is the heat produced in the driver so when one increases the resistive impedance with acoustic loading, one is raising the load impedance too, the current is less and the power dissipated in the VC is reduced. 
One should also see some change in the impedance in the experiment Ivan did and it will be interesting to see the magnitude of the effect on impedance. 
Raising the horn should (my money) produce in places, a small lowering of the impedance which produces proportionally more power to be delivered with the same drive Voltage compared to on the ground. 

The difference in loading would be seen factoring in both the change in level and change in power delivered.   

It probably looked pretty funny having a BC that high in the air on a forklift too haha.   
Back to work on a toy for Ivan and the guys to point at people’s ears .
Best,
Tom
Title: Re: PROOF-Whole vs half space sub loading
Post by: John Roberts {JR} on April 06, 2016, 06:07:58 pm
Good stuff as usual TD.   

Back to work.  ;D

JR 
Title: Re: PROOF-Whole vs half space sub loading
Post by: Chuck Simon on April 07, 2016, 11:54:03 am
But doesn't this test just prove that there is no increase in output at floor level?  I think many of us have noticed a substantial difference in low freq output at normal ear level when placing a speaker on the floor, right? From a practical point of view, the audience rarely listens while lying on the floor. Am I missing something?(probably)  ???
Title: Re: PROOF-Whole vs half space sub loading
Post by: Mark Wilkinson on April 07, 2016, 11:59:13 am

Acoustic loading when reflected back through the driver is (I always thought) counterintuitive.   

When the resistive acoustic load on the driver is increased say with a horn, the resistive portion of the impedance goes up, not down and so, the power delivered to the speaker with a fixed Voltage, actually goes down proportionally too.
                 


Hi Tom, trying to understand what you are saying...

So as a start, I thought to maybe just test the effect on impedance in going from full space to quarter space... or should I say hanging out on an open deck space, to sitting against kitchen wall space haha.

I don't have an easy to move small sub so I used Peter Morris's DIY60 MID section as a hopeful fill in.  (It only goes down to 100hz, so i knew whatever effect seen will be reduced.)

Anyway, against my expectations, impedance dropped moving into less space.  I would have thought less space increases load....????

Here's the plots I took.  The one on the left is outside, right is in the kitchen.  I included the real and imaginary components just to see if anything was there...
I don't get it....???
Thx,  Mark

edit: If the answer is less air mass with less space, I get it.   If not, still lost...







Title: Re: PROOF-Whole vs half space sub loading
Post by: Steve Bradbury on April 07, 2016, 12:20:36 pm
Surely rather than use a fork lift to raise the loudspeaker and leave the microphone on the floor, it would be easier to leave the loudspeaker on the floor and raise the microphone?
Title: Re: PROOF-Whole vs half space sub loading
Post by: John Rutirasiri on April 07, 2016, 12:33:54 pm
Surely rather than use a fork lift to raise the loudspeaker and leave the microphone on the floor, it would be easier to leave the loudspeaker on the floor and raise the microphone?

This is about how spatial loading of the sub affects the output.  If the sub is on the ground, then it's half-space (the floor being the dividing plane.)  If the sub on the floor is in a corner, then it's 1/8th space.

The reason for getting the subs off the floor and into the air is to simulate whole/full/free space -- eliminate acoustic coupling with the floor or wall. 

Putting a microphone in the air won't accomplish that.

John R.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Steve Bradbury on April 07, 2016, 12:53:46 pm
Am I missing something where the principle of reciprocity does not apply in this instance? If I am could you provide links/references to any articles that support your claims.

Thanks.
Title: Re: PROOF-Whole vs half space sub loading
Post by: John Roberts {JR} on April 07, 2016, 12:55:19 pm
Not to spam Ivans thread, but here is an interesting white paper from David Gunness
http://fulcrum-acoustic.com/assets/pdf/whitepapers/comments-on-half-space.pdf (http://fulcrum-acoustic.com/assets/pdf/whitepapers/comments-on-half-space.pdf)  exploring constructive and destructive interference from the ground bounce.

We often discuss these different spaces as if the sum from a bounce is flat, but it isn't always and can have audible frequency response effects.

I now return this discussion to the speaker geniuses (not me).

JR 
Title: Re: PROOF-Whole vs half space sub loading
Post by: Steve Bradbury on April 07, 2016, 01:05:57 pm
From the second page of the article linked to above:

Interestingly and importantly, the position of the acoustical source and microphone can be
exchanged and the resulting response will be identical. For example, if either the source or the
microphone is on the boundary (or both), the response will be +6 dB at all frequencies. This is one
example of the principle of duality in acoustics.

Mr Gunness seems to agree with me. His referral to duality is the same as what I termed reciprocity.
Title: Re: PROOF-Whole vs half space sub loading
Post by: John Rutirasiri on April 07, 2016, 01:12:37 pm
Am I missing something where the principle of reciprocity does not apply in this instance? If I am could you provide links/references to any articles that support your claims.

Thanks.

The loudspeaker (subwoofer in this case) provides the room excitation, not the measurement microphone.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Steve Bradbury on April 07, 2016, 01:36:26 pm
John Rutirasiri,

From your response I am assuming that you do not understand the principle of reciprocity. Basically it states that if you swap the positions of the source and receiver (microphone/ear) the result is the same, it doesn’t matter which way round they are.

The following is an extract from the book Reciprocity in Elastodynamics. It was one of the first results that came up with a Google search. I’ve simply copied and pasted it. There are probably better explanations out there if you do a search.

The first reciprocity relation specifically for acoustics was stated by von Helmholtz (1859). This relation caught the attention of and was elaborated by Rayleigh (1873) and Lamb (1888). Rayleigh (1873) briefly discussed the reciprocal theorem for acoustics in his paper “Some general theorems relating to vibrations.” In The Theory of Sound (1878, Dover reprint 1945, Vol. II, pp. 145–8), Rayleigh paraphrased this theorem as follows: “If in a space filled with air which is partly bounded by finitely extended fixed bodies and is partly unbounded, sound waves may be excited at any point A, the resulting velocity potential at a second point B is the same both in magnitude and phase, as it would have been at A, had B been the source of sound.” In this statement it is implicitly assumed that sources of the same strength would be applied at both places. In Rayleigh's book (1878) the statement is accompanied by a simple proof. A similar statement of the Helmholtz reciprocity theorem for acoustics can be found in the paper by Lamb (1888). Both Rayleigh and Lamb generalized the theorem to more complicated configurations, and in time the reciprocity theorem became known as Rayleigh's reciprocity theorem.

Most books on acoustics devote attention to the reciprocity theorem; see for example Pierce (1981), Morse and Ingard (1968), Jones (1986), Dowling and Ffowcs Williams (1983) and Crighton et al. (1992). A book by Fokkema and van den Berg (1993) is exclusively concerned with acoustic reciprocity.

As well as the above referenced texts, reciprocity is also covered in Olson’s Acoustical Engineering and Beranek’s Acoustics (both the original and new version) which most people interested in loudspeaker design should have a copy of.
Title: Re: PROOF-Whole vs half space sub loading
Post by: George Dougherty on April 07, 2016, 10:50:00 pm
Am I missing something where the principle of reciprocity does not apply in this instance? If I am could you provide links/references to any articles that support your claims.

Thanks.

I think I understood Tom's post and, if so, then the answer is that yes there are differences that would make reciprocity not entirely faithful here.

In general, yes it holds true with all other things being equal. It gives rise to the practice of placing a HT sub in your listening position and then walking the room to find the loudest/best response and then placing the sub there to optimize response in the listening position.

In this case, Tom's contention that the proximity to the ground impacts the impedance and output at a fixed voltage would seem to indicate that moving the sub could produce differing results in both positions that wouldn't necessarily be matched by moving the microphone instead.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Chuck Simon on April 08, 2016, 12:26:28 am
In this case, Tom's contention that the proximity to the ground impacts the impedance and output at a fixed voltage would seem to indicate that moving the sub could produce differing results in both positions that wouldn't necessarily be matched by moving the microphone instead.

Now that makes sense to me!  Do those changes in impedance result is something we can actually hear?
Title: Re: PROOF-Whole vs half space sub loading
Post by: Len Zenith Jr on April 08, 2016, 02:36:02 am
Hi Tom, trying to understand what you are saying...

So as a start, I thought to maybe just test the effect on impedance in going from full space to quarter space..

While DATS is a program I use often and useful for finding the frequency of impedance peaks and impedance minima I don't have any faith in its ability to determine absolute impedance. I have ran 3 or 4 consecutive tests in a row and impedance maxima varies conciderably between concecutive tests in a row. Results are only as good as your tools. Give a man a watch and he will be absolutely cetain of the time. Give a man 2 watches and he will never know what time it is.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Mark Wilkinson on April 08, 2016, 12:35:41 pm
While DATS is a program I use often and useful for finding the frequency of impedance peaks and impedance minima I don't have any faith in its ability to determine absolute impedance. I have ran 3 or 4 consecutive tests in a row and impedance maxima varies conciderably between concecutive tests in a row. Results are only as good as your tools. Give a man a watch and he will be absolutely cetain of the time. Give a man 2 watches and he will never know what time it is.

Sure do agree about 2 watches (meters) !

I've had 2 DATS units fail outright, but other than that I've found repeated consecutive tests to have little if any variance.
And when I've checked DATS against an audiotoolbox's impedance sweeps, measurements looked to be the same.....I have to say "looked to be" because the ATB gives data in 1/12 oct vs the DATS continuous curve...

Just now I checked the speaker with the ATB, same conditions as yesterdays posting.  Measurements look near identical.

But that's not saying either one is accurate  ;D
Title: Re: PROOF-Whole vs half space sub loading
Post by: Ivan Beaver on April 08, 2016, 01:19:30 pm
Results are only as good as your tools. Give a man a watch and he will be absolutely cetain of the time. Give a man 2 watches and he will never know what time it is.

I use the term "meters" instead of watches.

Same result :)
Title: Re: PROOF-18Sound and BC18SW115 have different response
Post by: Art Welter on April 08, 2016, 02:24:41 pm
Results are only as good as your tools. Give a man a watch and he will be absolutely cetain of the time. Give a man 2 watches and he will never know what time it is.
I use the term "meters" instead of watches.

Same result :)
And fill the same box with two different brand 18" drivers and you know it's time to change the spec sheet  ;) .

Looks like 4-5 dB difference at 31.5 Hz to me, what's it look like to you?

Art
Title: Re: PROOF-Whole vs half space sub loading
Post by: Jay Barracato on April 08, 2016, 02:44:26 pm
Give an engineer two meters and they will trot out an old comparison with watches and prove they really don't understand the concept of calibration...

Sent from my XT1254 using Tapatalk

Title: Re: PROOF-18Sound and BC18SW115 have different response
Post by: Scott Carneval on April 08, 2016, 02:55:23 pm
Results are only as good as your tools. Give a man a watch and he will be absolutely cetain of the time. Give a man 2 watches and he will never know what time it is.And fill the same box with two different brand 18" drivers and you know it's time to change the spec sheet  ;) .

Looks like 4-5 dB difference at 31.5 Hz to me, what's it look like to you?

Art

Given that the sensitivity is rated at 108db, I would say the -3 point is 40hz and it's more like -7 or -8 at 30/31.5 (depending on which graph you're looking at) 

But the box is rated at 40hz f3 on the website and 35hz f4 on the downloadable spec sheet. Not sure why these two differ, probably just an oversight. They're not necessarily conflicting specs, but different ways of rating it.
Title: Re: PROOF-Whole vs half space sub loading
Post by: David Sturzenbecher on April 08, 2016, 02:57:11 pm
Not to spam Ivans thread, but here is an interesting white paper from David Gunness
http://fulcrum-acoustic.com/assets/pdf/whitepapers/comments-on-half-space.pdf (http://fulcrum-acoustic.com/assets/pdf/whitepapers/comments-on-half-space.pdf)  exploring constructive and destructive interference from the ground bounce.

We often discuss these different spaces as if the sum from a bounce is flat, but it isn't always and can have audible frequency response effects.

I now return this discussion to the speaker geniuses (not me).

JR

Very interesting. Thank you for posting.
Title: Re: PROOF-Whole vs half space sub loading
Post by: John Rutirasiri on April 09, 2016, 09:36:26 am
John Rutirasiri,

From your response I am assuming that you do not understand the principle of reciprocity. Basically it states that if you swap the positions of the source and receiver (microphone/ear) the result is the same, it doesn’t matter which way round they are.

Good to learn something new everyday.  However, wouldn't duality only occur under ideal conditions, such as anechoic chamber and 100% omni responses (so omnidirectional radiation, omni directional polar pattern on the mic, etc.)?

In this case of Ivan's experiment and using your logic, the measurement mic would be put on the ground to simulate half space, and hanging in the air to simulate whole space.  Say you put the foam under the mic to avoid movement, and use guy wires when hanging the mic to prevent it from swinging.  In the case of the mic on the ground, I'm not sure if the omnidirectional pattern of the measurement mic is maintained anymore.  In the case of the mic being in the air, the guy wires to prevent it from swinging would be a PITA to set up. 

IMO it is easier to just lift the sub up with a forklift, which simulates what you'd find in the real world when subs are flown.

Best,
John R.

Title: Re: PROOF-18Sound and BC18SW115 have different response
Post by: Ivan Beaver on April 09, 2016, 10:42:24 am
Results are only as good as your tools. Give a man a watch and he will be absolutely cetain of the time. Give a man 2 watches and he will never know what time it is.And fill the same box with two different brand 18" drivers and you know it's time to change the spec sheet  ;) .



Looks like 4-5 dB difference at 31.5 Hz to me, what's it look like to you?

Art
When we changed drivers in the TH118 (very early on in its history), the measured freq response change was so minimal (around 0.5dB), it was not considered to be worth changing the spec sheet.  Especially when you consider that the driver to driver variance is often more than that.

But I guess if you do like a lot of manufacturers and don't publish ANY response graphs, you don't have to worry about such things. There is nothing to be held accountable to.

Seems to be REAL popular these days :(

A simple number that is not referenced to anything seems to be the "norm".

Yes, you would "expect" the performance to change with different drivers, but this is not always the case.  In the case of some horns, you can end up with very similar results with different drivers.  The horn itself is often the biggest governing factor.  In a ported cabinet, the driver is often the biggest governing factor.

And sometimes a slight change in driver parameters will throw the whole design off a lot.

It depends

The tapped horn I used in this measurement/experiment was part of a "experimental" project for a new product idea. Not a TH118.  I was playing around with it in the "project" and just decided to do the quick measurement outside-the bay door was open, it was a nice day, I got hit with the inspiration/idea  yada yada----------

What we have found during that project is that (in some cases) drivers with very different parameters can "even out" and the response be almost identical.

On a side note-I think some people think I used the eq between the measurements.  NO.  I used it (just a quick throw something in to even out the response a little) on the ground, and then (without changing anything electrically) we lifted the cabinet in the air.  So the SAME eq was used in both the air and ground measurements.

HOWEVER, it was not the same eq point between the different cabinets.

I just mentioned it during the post so as to be "full disclosure" of what I was doing.

Title: Re: PROOF-18Sound and BC18SW115 have different response
Post by: Art Welter on April 09, 2016, 01:13:57 pm
When we changed drivers in the TH118 (very early on in its history), the measured freq response change was so minimal (around 0.5dB), it was not considered to be worth changing the spec sheet. 

The tapped horn I used in this measurement/experiment was part of a "experimental" project for a new product idea. Not a TH118. 
Since the chart was labeled TH118, I thought it was a TH118.
Title: Re: PROOF-18Sound and BC18SW115 have different response
Post by: Ivan Beaver on April 09, 2016, 03:15:10 pm
Since the chart was labeled TH118, I thought it was a TH118.
Yeah-that would be a "logical" assumption. :)

Since there is no model number for the project yet, the "base cabinet" was a TH118-but not a standard one and that is why I labeled it as such (for lack of a better name).

Maybe I should have given it a different name.

But sometimes our "working titles" get a bit weird.

You won't believe what the BC series started out as.  Boarding on "obscene"-but funny.

But I won't post it.

Title: Re: PROOF-18Sound and BC18SW115 have different response
Post by: Merlijn van Veen on April 09, 2016, 03:52:31 pm
I agree with Gunness's paper about the duality or reciprocity BUT, our ears aren't at floor height. More likely something like 5 feet or more above it.

Flown subwoofers and triangulation dictate that some frequencies are gonna cancel, likely resulting in audible changes throughout the audience.

Stacked subwoofers and triangulation virtually negate the chances of this happening, but now we're killing the people in the front.

Pick your poison.
Title: Re: PROOF-18Sound and BC18SW115 have different response
Post by: Ivan Beaver on April 09, 2016, 04:31:14 pm
I agree with Gunness's paper about the duality or reciprocity BUT, our ears aren't at floor height. More likely something like 5 feet or more above it.

Flown subwoofers and triangulation dictate that some frequencies are gonna cancel, likely resulting in audible changes throughout the audience.

Stacked subwoofers and triangulation virtually negate the chances of this happening, but now we're killing the people in the front.

Pick your poison.
That is why I always try to fly the subs-depending on the venue.

The coverage is much more even in both level and freq response across the audience area.

However in some cases-people want it to be louder in front.

SO-It depends.

What IS important is that people realize the differences in the choices they make.

And also with the differences between end fire and "cardioid" directional sub setups.

Most people think they are the same thing.
Title: Re: PROOF-Whole vs half space sub loading
Post by: John L Nobile on April 09, 2016, 07:24:05 pm
Been following this thread closely as I'm moving my system to another room at the end of the month.  I've had my subs centered under the stage and while I like the coupling, they do tend to be loud in the first 2 rows.
I'm now thinking of flying them in the center. It'll be flown from 20" truss so I'm hoping the weight won't be an issue.
I'll discuss it with my install company.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Ivan Beaver on April 09, 2016, 10:33:18 pm
Been following this thread closely as I'm moving my system to another room at the end of the month.  I've had my subs centered under the stage and while I like the coupling, they do tend to be loud in the first 2 rows.
I'm now thinking of flying them in the center. It'll be flown from 20" truss so I'm hoping the weight won't be an issue.
I'll discuss it with my install company.
Just one thing to consider when flying subs.

Either get them close or very far away from the ceiling.

You need to be aware of boundaries and the cancellations they can cause.
Title: Re: PROOF-Whole vs half space sub loading
Post by: John L Nobile on April 10, 2016, 10:10:05 am
Just one thing to consider when flying subs.

Either get them close or very far away from the ceiling.

You need to be aware of boundaries and the cancellations they can cause.

I'm thinking 12 feet from the ceiling. That doesn't sound very far.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Bill Hornibrook on April 10, 2016, 01:15:23 pm
But doesn't this test just prove that there is no increase in output at floor level?  I think many of us have noticed a substantial difference in low freq output at normal ear level when placing a speaker on the floor, right? From a practical point of view, the audience rarely listens while lying on the floor. Am I missing something?(probably)  ???

Yeah I'm with this guy. I can think of a number of rooms throughout the years where taking the subs off a stage and putting them on the floor made a substantial difference in their perceived output. There was one large club in particular (over 500 seats) that after years of an "everything must be on the stage" policy finally allowed subs on the floor. During a soundcheck we took them off the stage and set them directly in front of where they were. There was no repositioning of any kind other than that.

The difference was not subtle. We were so amazed that we moved them back and forth several times... just so we could congratulate ourselves on how much better our subs sounded.

Am I missing something here? Maybe floor cancellation if the subs aren't flown 50 feet in the air?
Title: Re: PROOF-Whole vs half space sub loading
Post by: Ivan Beaver on April 10, 2016, 03:46:08 pm
Yeah I'm with this guy. I can think of a number of rooms throughout the years where taking the subs off a stage and putting them on the floor made a substantial difference in their perceived output. There was one large club in particular (over 500 seats) that after years of an "everything must be on the stage" policy finally allowed subs on the floor. During a soundcheck we took them off the stage and set them directly in front of where they were. There was no repositioning of any kind other than that.

The difference was not subtle. We were so amazed that we moved them back and forth several times... just so we could congratulate ourselves on how much better our subs sounded.

Am I missing something here? Maybe floor cancellation if the subs aren't flown 50 feet in the air?
There are a lot of different factors involved in "tests" like this.

For example.  Room modes.  The room modes can often have a greater effect on sub performance than anything.

And the reflections (which are part of room modes) can greatly affect the output at different locations.

Here is a little "room mode demo" that is often VERY eye/ear opening.

Put a tone into your subs.  Say 70Hz.  It does not need to be loud-just a comfortable level.   

Now walk around the room and listen for the loud and quiet spots. Remember a couple of each.

Now change the tone to something that is not a multiple of the 60Hz.  Say 53Hz. 

Walk around the room again.  Notice how the loud and quiet spots have moved around.

Of course a lot of the particular outcome depends on the physical dimensions of the room-are they multiples of each other and so forth.  But you should get the idea of how much room modes can affect different freq in different locations differently.

So by simply putting the subs in a different location-the room  may have been moved.

Also the construction of the stage can make a difference on how well the subs couple to the building.  Maybe it was very diaphragmatic and "absorbing" a lot of the sub energy at one or more freq.

So each circumstance can be different-and the freq of interest can be different.

The "problem" (and the it depends) is that when you have a couple of factors (say room modes and position) it is hard to say what is actually affecting the outcome you are getting.  More than 1 variable.

I will agree that in some cases, putting them on the floor results in greater output.  But it could be because of something other than in the air vs ground.

With my test, there was only 1 variable-since I was outside and pretty far from reflections.

What I was addressing was the "general statement" about half space vs whole space.

And unless you were in a very LARGE room, when the subs were on the stage-there were nowhere near whole space.

So-as usual-it depends.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Caleb Dueck on April 10, 2016, 04:08:13 pm
I wonder how much higher than 15' and closer than 100' to mic would change things.  We've done many installs with flown subs, the lowest ones were about 24'. 

Boundary interaction seems to be much more important than ground vs flown.  Other than boundaries, flown and ground subs model essentially the same at distance, as Ivan's test confirmed.  The difference is that the front row isn't flattened. 

For us, we model at say 31Hz and 50Hz, and then take into account the boundary interaction(s) through math and experience. 
Title: Re: PROOF-Whole vs half space sub loading
Post by: Ivan Beaver on April 10, 2016, 04:19:39 pm
I wonder how much higher than 15' and closer than 100' to mic would change things.
The whole "point" of the test/post was that MANY people believe that you can "simply add 6dB" to a whole space spec.

And that if the mic is in a half space condition,  you already have the "free 6dB".

If I had seen some sort of level difference (more than shown) and freq specific, then I would agree that further investigation would be needed at higher heights.

But for me to go higher-requires renting a lift-going to a larger area and so forth. THAT would not happen anytime soon.

And Let's say that there is a difference at 100'.  What sort of application would that information be useful in?

I believe specs should provide useful information to help a designer determine if one product is more suitable for an application than another.

Yes we have installs in which the subs are actually close to 200' in the air.  HOWEVER-the audience is still in a half space condition.  Even if in bleachers, the size of the bleachers provide a large enough boundary to put them in half space.

I will do some more measurements by raising the mic to 5.5' (standard ear height) and 15'.  But it may be a little while.  Lots of other things to work on that are more "business" oriented and not so much "curiosity".

Of course-somebody else is welcome to do the tests if they want to and show the results.

Title: Re: PROOF-Whole vs half space sub loading
Post by: George Dougherty on April 14, 2016, 04:10:05 pm
I'm thinking 12 feet from the ceiling. That doesn't sound very far.

The rule of thumb I'd heard was within 2 ft or further than 8ft for your typical sub to not have major cancellation issues caused by boundaries.  That goes for walls and ceilings though the distance also depends on the frequency response of the sub.  I think that covers the typical down to 40 sub, maybe a bit lower.
Title: Re: PROOF-Whole vs half space sub loading
Post by: George Dougherty on April 14, 2016, 04:17:43 pm
Am I missing something here? Maybe floor cancellation if the subs aren't flown 50 feet in the air?
Regarding the no-go-zone 2-8ft from a boundary, your typical stage is going to put the sub right within that region which will cause cancellations at all kinds of frequencies.  Most people don't consider it, but I've had improvements in response just by rotating a sub 90-180 degrees which was sitting near a wall.  The cabinet depth put the driver (when facing the audience) into the +2ft range and caused cancellations.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Merlijn van Veen on April 15, 2016, 01:49:54 am
Regarding the no-go-zone 2-8ft from a boundary, your typical stage is going to put the sub right within that region which will cause cancellations at all kinds of frequencies.  Most people don't consider it, but I've had improvements in response just by rotating a sub 90-180 degrees which was sitting near a wall.  The cabinet depth put the driver (when facing the audience) into the +2ft range and caused cancellations.

+1

If you can't beat them, join them.

By all means, if the boundary is sufficiently large enough to reflect all frequencies ergo wavelengths of interest AND is stiff and rigid (no diaphragmatic action) then couple with it. Just leave reasonable air gap between the front of the speaker and the surface.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Scott Harris on April 15, 2016, 12:59:22 pm
After turning your sub around changing it's distance by 2 feet, do you then adjust the time delay of your tops to bring them into phase alignment?   :-)
Title: Re: PROOF-Whole vs half space sub loading
Post by: Merlijn van Veen on April 15, 2016, 02:32:13 pm
Depending on the XO frequency I might.
Title: Re: PROOF-Whole vs half space sub loading
Post by: George Dougherty on April 16, 2016, 12:10:10 am
After turning your sub around changing it's distance by 2 feet, do you then adjust the time delay of your tops to bring them into phase alignment?   :-)

In this particular case I was trying to polish a turd.  The subs were a pair of MRX528S's 15 feet from each side of a stage in a fan shaped room and about 5 feet from the nearest seating running parallel to the front wall. The Mains were some decent quality EV tops flown in several day lines above the stage front and 2 rows further back with atrocious spacing for coverage.  There was no aligning anything except the flown mains to each other and the best I could do with little slack on the sub lines hanging out of the wall was even out the coverage on either side by rotating the subs.  Next time I went back someone had "corrected" my mistake for me. 

For the best footprint I really wanted to face them, flip the polarity on one and delay it to align with the other but I figured that would be too placement sensitive and I didn't have the DSP handy to do it anyway.  I mentioned the idea of flying them with the mains but that had issues with line-of-sight to stage from lighting instruments.

Oh well...
Title: Re: PROOF-Whole vs half space sub loading
Post by: Luca Rossi on April 16, 2016, 05:25:25 am
So this PROVES (at least to me) that the whole idea of "getting more bass" when the subs are on the ground OR simply that you can "add a magical 6dB" to a whole space measurement is simply false.

Since the mic (or person listening) is already in half space, you get the loading.  But no additional loading when both are in half space.

I think you need to consider that listening ear are at least 1.6 meters above the ground level. Then comb filter interaction will cancel some frequencies.

As you can see there are two deep holes. The first one is at 80 Hz and the second one is about at 240 Hz, (of course the last one is well above frequency xover). This is obvious depends on the height of both subs and listener ear. Another think to consider is that as you move away from the flying source, the comb tends to tilt up. This means that only further away people can be considered fully in half place.

(https://s24.postimg.org/ei3xugs1h/Immagine.jpg) (https://postimage.org/)caricare immagini (https://postimage.org/index.php?lang=italian)

Title: Re: PROOF-Whole vs half space sub loading
Post by: Ivan Beaver on April 16, 2016, 09:38:58 am
I think you need to consider that listening ear are at least 1.6 meters above the ground level. Then comb filter interaction will cancel some frequencies.

As you can see there are two deep holes. The first one is at 80 Hz and the second one is about at 240 Hz, (of course the last one is well above frequency xover). This is obvious depends on the height of both subs and listener ear. Another think to consider is that as you move away from the flying source, the comb tends to tilt up. This means that only further away people can be considered fully in half place.

(https://s24.postimg.org/ei3xugs1h/Immagine.jpg) (https://postimage.org/)caricare immagini (https://postimage.org/index.php?lang=italian)
So have you EVER seen a spec sheet that said the mic was at ear height?  And what is "ear height?  Sitting or standing?

I have never seen that.  Every one I have seen says full or half space. 

THAT is the reason for the measurement.

I do want to redo the test-with more measurements, but that is not going to happen soon.  I have to many things going on.

But others are welcomed to do their own measurements and post the results.

Models are nice-but they DO NOT represent everything that is going on in real life.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Luca Rossi on April 16, 2016, 03:02:51 pm
Models are nice-but they DO NOT represent everything that is going on in real life.

Yes, that simulation represent what's going on in that particular condition. However other situations make no substantial difference with flying subs. The effect is the same, unless the mic is perfectly against the floor as you rightly did for your measurements.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Bill Hornibrook on April 18, 2016, 02:43:12 pm
There are a lot of different factors involved in "tests" like this.

For example.  Room modes.  The room modes can often have a greater effect on sub performance than anything.

And the reflections (which are part of room modes) can greatly affect the output at different locations.


I will agree that in some cases, putting them on the floor results in greater output.  But it could be because of something other than in the air vs ground.

With my test, there was only 1 variable-since I was outside and pretty far from reflections.

What I was addressing was the "general statement" about half space vs whole space.

And unless you were in a very LARGE room, when the subs were on the stage-there were nowhere near whole space.

So-as usual-it depends.

Ok so I'm trying to get my head around this. Is what you're saying is that there's no such thing as an advantage to half space loading versus full space? That the reduction in low end that we all experience when we raise tops on stands or put subs on a stage is caused by room modes? And that the low end would return if we could just get the cabs high enough  - and far away enough -  from boundaries?

In a way, that actually all makes sense. It's just looking at an observed phenomenon from another perspective.

And I know you're going to say "it all depends" ;) In general... :D
Title: Re: PROOF-Whole vs half space sub loading
Post by: Ivan Beaver on April 18, 2016, 07:54:02 pm
Ok so I'm trying to get my head around this. Is what you're saying is that there's no such thing as an advantage to half space loading versus full space? That the reduction in low end that we all experience when we raise tops on stands or put subs on a stage is caused by room modes? And that the low end would return if we could just get the cabs high enough  - and far away enough -  from boundaries?

In a way, that actually all makes sense. It's just looking at an observed phenomenon from another perspective.

And I know you're going to say "it all depends" ;) In general... :D
Room modes and reflections are related and different.

Room modes are based on the distance between reflecting surfaces and the freq that is related to the distance.

Reflections are freq cancellations based on the different arrival times of the direct and reflected signals.

The shorter the difference between them, the higher the freq of cancellation.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Jelmer de Jong on May 13, 2016, 05:49:03 am
I can get my hands on a forklift, some subs and smaart. What should I do to make a valid measurement?
Title: Re: PROOF-Whole vs half space sub loading
Post by: Ivan Beaver on May 13, 2016, 07:25:01 am
I can get my hands on a forklift, some subs and smaart. What should I do to make a valid measurement?
Get away from reflections

Use 3 mic heights and 2 speaker heights

The mic needs to at least 10 meters away or more to help reduce inverse square law effects

The mic heights need to be on the ground. 5,5' and on axis of whatever the subs are at when on the forklift

Make 3 mic position measurements with the sub on the ground And 3 when it is up in the air

Be sure to include phase measurements so the freq of the ground bounce can be seen and identified and ignored

If you wanted to get picky change the mic position each time to reflect the actual path length between the sub and mic

Title: Re: PROOF-Whole vs half space sub loading
Post by: Jelmer de Jong on May 13, 2016, 10:58:55 am
Like this?

(http://i.imgur.com/SCbLFqN.jpg)

Distance from sub to mic will be ~25M and the forklifts will be colormatched.
Title: Re: PROOF-Whole vs half space sub loading
Post by: Ivan Beaver on May 13, 2016, 10:01:53 pm
Like this?

(http://i.imgur.com/SCbLFqN.jpg)

Distance from sub to mic will be ~25M and the forklifts will be colormatched.
Yep.

Just remember that the colors MUST match-or the whole thing doesn't make sense ;)  ;)
Title: Re: PROOF-Whole vs half space sub loading
Post by: David Morison on May 14, 2016, 05:06:26 pm
Yep.

Just remember that the colors MUST match-or the whole thing doesn't make sense ;)  ;)

Yup, and if they're Turbo blue then everything will be 6dB louder  ;)
Title: Re: PROOF-Whole vs half space sub loading
Post by: Jelmer de Jong on May 16, 2016, 04:31:32 pm
The setup:

(http://i.imgur.com/zzSiLjk.jpg)
The windspeed was about 2-3bft so I set avaraging to invinite and let it run for a minute before hitting the spacebar.
I am a bit limited by the forklift, its not a 4x4 so I had to stay on the asphalt, therefore there are some buildings nearby (40ft). I made the measurements diagonal in respect to the buildings.

At first I calibrated all the mics. After this there was no change in mics and cables. I used about 200ft for the sub an 300ft per mic.
(http://i.imgur.com/AvgSvkB.png) (http://i.imgur.com/AvgSvkB.png)

MIC 1 directly in front of the sub. A difference of 4dB is noticeable.
(http://i.imgur.com/TIXsNRg.png) (http://i.imgur.com/TIXsNRg.png)

I made two measurements, one at ~120ms and one at ~30ms distance. I'll start with the one furthest away.
MIC 2 120MS, this is at groundlevel.
(http://i.imgur.com/20RCmLZ.png) (http://i.imgur.com/20RCmLZ.png)

MIC3 120MS, this is at earlevel.
(http://i.imgur.com/o7qcYOZ.png) (http://i.imgur.com/o7qcYOZ.png)

Mic 4 120MS, this is at 14ft in the air.
(http://i.imgur.com/5GxFHrD.png) (http://i.imgur.com/5GxFHrD.png)



Next up a bit closer to the source.
MIC 2 30MS, the is at groundlevel.
(http://i.imgur.com/zpE4Taa.png) (http://i.imgur.com/zpE4Taa.png)

Mic 3 30MS, this is at earlevel.
(http://i.imgur.com/5MEU2aw.png) (http://i.imgur.com/5MEU2aw.png)
Mic 4 30MS, this is at 14ft in the air.
(http://i.imgur.com/CdX8PQZ.png) (http://i.imgur.com/CdX8PQZ.png)

Title: Re: PROOF-Whole vs half space sub loading
Post by: Mark Wilkinson on May 17, 2016, 09:41:14 am

Great work, thank you Jelmer!

At 120ms distance,
it looks like building reflections are coming in, and the effect of subs flown vs ground is getting triangulated out to minimal...

At 30ms distance,
first thing I looked for was acoustic reciprocity as was discussed earlier in thread...
Looks like the sub flown/mic on ground, and the sub on ground/mic at 14 ft,..... are about the same trace....so looks like pretty good reciprocity...
What is a little surprising, is how close the sub on ground/mic at ear level trace , is to those two traces, without some bounce cancellations.

Also look like there is a good case to made for ground stacked subs up close...

Do these observations seem correct to you?
Title: Re: PROOF-Whole vs half space sub loading
Post by: Jelmer de Jong on May 17, 2016, 10:13:57 am
Great work, thank you Jelmer!

At 120ms distance,
it looks like building reflections are coming in, and the effect of subs flown vs ground is getting triangulated out to minimal...

At 30ms distance,
first thing I looked for was acoustic reciprocity as was discussed earlier in thread...
Looks like the sub flown/mic on ground, and the sub on ground/mic at 14 ft,..... are about the same trace....so looks like pretty good reciprocity...
What is a little surprising, is how close the sub on ground/mic at ear level trace , is to those two traces, without some bounce cancellations.

Also look like there is a good case to made for ground stacked subs up close...

Do these observations seem correct to you?

Yes, we made the same observations. I think you are looking for this graph:

(http://i.imgur.com/4DeU38F.png) (http://i.imgur.com/4DeU38F.png)

And here is one where I added the mics at earlevel.
(http://i.imgur.com/czmwtV9.png) (http://i.imgur.com/czmwtV9.png)

I made all the pictures clickable so you can see a higher resolution image. If I happen to be in the middle of nowhere this festival season I'll try to recreate these measurements with the speaker higher in the air(30ft) and with multiple subs v.s just one.


Here is a link to a zipfile containing all the traces (http://content.jelmershome.nl/Sub_Whole_Space.zip)
Title: Re: PROOF-Whole vs half space sub loading
Post by: Merlijn van Veen on May 17, 2016, 10:18:48 am
Great work, thank you Jelmer!

At 120ms distance,
it looks like building reflections are coming in, and the effect of subs flown vs ground is getting triangulated out to minimal...

At 30ms distance,
first thing I looked for was acoustic reciprocity as was discussed earlier in thread...
Looks like the sub flown/mic on ground, and the sub on ground/mic at 14 ft,..... are about the same trace....so looks like pretty good reciprocity...
What is a little surprising, is how close the sub on ground/mic at ear level trace , is to those two traces, without some bounce cancellations.

Also look like there is a good case to made for ground stacked subs up close...

Do these observations seem correct to you?

Kudos Jelmer!

I also concur and am happy that physics isn't abandoning us :)

Both distances confirm the reciprocity.

Title: Re: PROOF-Whole vs half space sub loading
Post by: Merlijn van Veen on May 17, 2016, 10:50:33 am
Few things to be mindful of though that might explain audible differences between flown vs. stacked subs experienced by many of us:

Title: Re: PROOF-Whole vs half space sub loading
Post by: Bill Hornibrook on May 17, 2016, 11:24:14 am
I made all the pictures clickable so you can see a higher resolution image.
I was looking at your graphs embedded in the thread last night, and only discovered this because you mentioned it this morning - so I'm mentioning it again because it really helps.

I also wanted to thank you for taking the time to do this - which must have involved the better part of a day. Very informative!
Title: Re: PROOF-Whole vs half space sub loading
Post by: Luca Rossi on May 17, 2016, 03:31:38 pm
  • Typically our ears aren't at ground level. With flown subs the cancellation caused by the floor bounce is a moving target over frequency response and space. This is apparent from your measurements and is proven in other replies to this thread. In the time domain, time smearing is introduced until we become uncoupled (1/3 WL).
+1 Good point. This is what i tryed to explain in my previous post with the prediction software. They are going to loose efficiency in the upper range because they behave like a low pass filter including notches when the reflected wave is completly out of phase. IMO flown subs are only good to achieve high directivity control (if the array is long enough) and for deep bass slam. Ground stacking is more efficient for mid bass punch and requires less subs.[/list]