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Author Topic: PROOF-Whole vs half space sub loading  (Read 15797 times)

Chuck Simon

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Re: PROOF-Whole vs half space sub loading
« Reply #10 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? 
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Ivan Beaver

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Re: PROOF-Whole vs half space sub loading
« Reply #11 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. 
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Mark Wilkinson

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Re: PROOF-Whole vs half space sub loading
« Reply #12 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....


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Ivan Beaver

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Re: PROOF-Whole vs half space sub loading
« Reply #13 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.
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Ivan Beaver
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Mark Wilkinson

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Re: PROOF-Whole vs half space sub loading
« Reply #14 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.
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John Rutirasiri

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Re: PROOF-Whole vs half space sub loading
« Reply #15 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.
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Ivan Beaver

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Re: PROOF-Whole vs half space sub loading
« Reply #16 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.
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Ivan Beaver
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Tom Danley

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Re: PROOF-Whole vs half space sub loading
« Reply #17 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 donít 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 donít 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 seeís 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 peopleís ears .
Best,
Tom
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John Roberts {JR}

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Re: PROOF-Whole vs half space sub loading
« Reply #18 on: April 06, 2016, 06:07:58 pm »

Good stuff as usual TD.   

Back to work.  ;D

JR 
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Chuck Simon

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Re: PROOF-Whole vs half space sub loading
« Reply #19 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)  ???
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Re: PROOF-Whole vs half space sub loading
¬ę Reply #19 on: April 07, 2016, 11:54:03 am ¬Ľ


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