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Reciprocity Theorem in practice
Reciprocity Theorem in practice
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Old 14th September 2017, 01:09 PM   #31
bentoronto is offline bentoronto  Canada
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Reciprocity Theorem in practice
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Originally Posted by CharlieLaub View Post
But it is possible to substitute a smaller sub that still has enough bass extension since that will be easier to place 4 feet off of the ground.
OK... that's the next question that needs investigation. Hard for me to picture learning about one speaker by testing another.

But is there value in reciprocal testing when you test with a speaker that is easier to put on your chair?

B.
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Old 14th September 2017, 01:30 PM   #32
chris661 is offline chris661  United Kingdom
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Originally Posted by bentoronto View Post
OK... that's the next question that needs investigation. Hard for me to picture learning about one speaker by testing another.

But is there value in reciprocal testing when you test with a speaker that is easier to put on your chair?

B.
So long as the assumptions I mentioned earlier hold, I see no reason why not.

ie, you can't use a 5" PC subwoofer to simulate a giant tapped horn, since the TH will be changing the shape of the room as it moves.

That said, if the smaller sub still has the bandwidth of the bigger sub, it should work just fine.

Chris
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Old 14th September 2017, 04:23 PM   #33
bentoronto is offline bentoronto  Canada
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Reciprocity Theorem in practice
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Originally Posted by chris661 View Post
since the TH will be changing the shape of the room as it moves.

That said, if the smaller sub still has the bandwidth of the bigger sub, it should work just fine.
Respectfully, your first point negates the theory of reciprocity (although prolly somewhat true!).

On your second point, all subs differ from one another in FR in dramatic ways in a room. The object of moving subs around it to mix-and-match the sub FR to the room modes (and when lucky, they will complement one another very nicely, as Matt's first panel shows).

So, can you take any sub and think it can be stand-in for another sub? It is possible that the reciprocal method nicely addresses major room mode influences and, therefore, you can. I am not sure if Matt's data address this question... perhaps a closer look at his box resonance(s) will clarify it. Dunno.

B.
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Old 14th September 2017, 04:41 PM   #34
scottjoplin is offline scottjoplin  Wales
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Thank you reloader, that is conclusive
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Old 14th September 2017, 05:05 PM   #35
chris661 is offline chris661  United Kingdom
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Originally Posted by bentoronto View Post
Respectfully, your first point negates the theory of reciprocity (although prolly somewhat true!).

B.
No, it doesn't.
One of the assumptions made by the theory of reciprocity is that both the source and receiver are very much smaller than the room and the wavelengths under consideration. When that's no longer true, the theory needs to be modified for those second-order effects.

Chris
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Old 17th September 2017, 04:16 PM   #36
bentoronto is offline bentoronto  Canada
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Reciprocity Theorem in practice
I was reading about 6th order and ROAR boxes with oodles of sims and almost no actual performance measurements. So I was wondering if the reciprocal method might be helpful in getting systems out of the drydock and into the water?

The problem is that sims provide posits for how a system will perform in ideal locations. In practice (and for those lacking anechoic chambers with low frequency capacity), that means figuring out how to test you sub in a large empty space out of doors and even hanging in the air. (There are some inspiring pictures on the web of just such testing using large cranes to hoist the speaker in the air.) Sure, it can be done but quite a feat even just at ground level and away from civilization.

Could you make measurements with a bunch of different small speakers placed in the location to later filled by the device to be tested. That would provide an image of the room influence. Then, when the device is put in place you could assess the difference.*

Just wondering.

B.
*of course, you aren't doing anything reciprocal here but the thought was inspired by Matt's evidence showing that the "ghost" of the room - for THAT speaker location and your specific chair location - is superimposed on the whatever speaker is placed in the test location; by averaging a few different subs, you are getting a better image of the room impact... and if you have doubts about this proposal, then you have doubts about the Reciprocity Method
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Last edited by bentoronto; 17th September 2017 at 04:25 PM.
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Old 17th September 2017, 05:24 PM   #37
just a guy is offline just a guy  Canada
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Quote:
Originally Posted by bentoronto View Post
I was reading about 6th order and ROAR boxes with oodles of sims and almost no actual performance measurements. So I was wondering if the reciprocal method might be helpful in getting systems out of the drydock and into the water?

The problem is that sims provide posits for how a system will perform in ideal locations. In practice (and for those lacking anechoic chambers with low frequency capacity), that means figuring out how to test you sub in a large empty space out of doors and even hanging in the air. (There are some inspiring pictures on the web of just such testing using large cranes to hoist the speaker in the air.) Sure, it can be done but quite a feat even just at ground level and away from civilization.

Could you make measurements with a bunch of different small speakers placed in the location to later filled by the device to be tested. That would provide an image of the room influence. Then, when the device is put in place you could assess the difference.*

Just wondering.

B.
*of course, you aren't doing anything reciprocal here but the thought was inspired by Matt's evidence showing that the "ghost" of the room - for THAT speaker location and your specific chair location - is superimposed on the whatever speaker is placed in the test location; by averaging a few different subs, you are getting a better image of the room impact... and if you have doubts about this proposal, then you have doubts about the Reciprocity Method
There's no need to hang speakers in the air, you can test them on the ground. The ground is a large uniform boundary, close enough to infinite in size that it will provide a near perfect reflection.

What you seem to be asking is if you can measure the room gain curve. Of course you can. Here's an article on it.

Data-Bass
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