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Old 18th January 2017, 05:54 PM   #1
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Default Can you prove port summing works?

Hi everyone,

Very very smart and well respected people have written about how to measure ported speakers in a quasi- anechoic manner. The results are always very pretty. Like this graph from Stereophile's Wilson Sabrina measurements:

Click the image to open in full size.

This is textbook. I get the theory. I really do. My question is, do any of you fine readers have proof this works in a room?

I ask because all the other data measuring and adjustments I use DO work. I mean, I have evidence in far-field that the theory matches practice. For instance, baffle step compensation. Adding this to near-field clearly fixes a problem correctly.

I do not have any proof this is accurate for ported speakers. Again, I know many smart people have relied on this methodology. What I'm asking of you measurement wizards is if you have confirmed and would be able to post data about summation and far-field measurement agreement, or help me get a better far-field measurement that aligns more accurately.

Best,


E
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Old 18th January 2017, 05:57 PM   #2
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The way to prove it would be via direct measurement compared to summing the near fields of port and woofer. Unfortunately direct measurement of these low frequencies can really only be done outside because inside there will be room response that you cannot deconvolute from the measured response. So I think you will be hard pressed to find evidence because outdoor measurements are not commonly done.

I do have faith that if you performed such a measurement you would indeed find that the two would agree.
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Old 18th January 2017, 06:06 PM   #3
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Charlie,

Then my question is, without trying to insult, what good is a method you cannot reconcile with in-room far-field? I mean we normally evaluate these methods on their agreement with far-field, right? If we can't do that.... ????

Maybe this required multi-point averaging?

Best,


E
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Old 18th January 2017, 06:12 PM   #4
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Quote:
Originally Posted by eriksquires View Post
Charlie,

Then my question is, without trying to insult, what good is a method you cannot reconcile with in-room far-field? I mean we normally evaluate these methods on their agreement with far-field, right? If we can't do that.... ????

Maybe this required multi-point averaging?

Best,


E
Ask yourself "what is the in-room farfield actually measuring' and you will find your answer. If the model does not include some contributions then of course it will differ from the 'in room far field'... If you want/need them to agree, then you have to add the contribution of the room to the model.
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Old 18th January 2017, 06:28 PM   #5
Lojzek is offline Lojzek  Croatia
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Erik, for the fun of it, measure the spl with port open/stuffed.
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Old 18th January 2017, 07:58 PM   #6
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Lojzek,

Been thinking just that!!! When I feel better I will.

E
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Old 18th January 2017, 09:49 PM   #7
Lojzek is offline Lojzek  Croatia
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You're not going over the threshold, are you? I know what would make you healthy in a sec! Sofia in a Murcielago as your future wife.
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Old 18th January 2017, 10:13 PM   #8
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For some reason it's a lot easier to imagine Sofia Loren LEAVING me in a Murcielago....

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Old 18th January 2017, 10:58 PM   #9
Sonce is offline Sonce  Macedonia
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Quote:
Originally Posted by eriksquires View Post
I do not have any proof this is accurate for ported speakers.
Yes, you have. It is called the superposition principle.
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Old 19th January 2017, 12:15 AM   #10
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OP displays the theory, at least for the classic tuning. But put it in a room, and what do you get? And there isn't the same adherence any more to classic tuning - so things might be very different.

I've been posting about an analogous puzzle: open baffles. Everybody knows the textbook picture of total annihilation of the front wave when the dimension are just so. But a moment's thought about a dipole baffle a few feet from a back wall, and you have a quite different picture of waves and phases and timing all bouncing around and interacting pretty randomly and changing instant by instant as the trumpet note changes a tiny bit.

Likewise for the horrible picture of comb filtering. Horrible in the textbook with pure sine waves. But only self-styled gurus hear it in a room (and have the super-perception to distinguish it from a dozen other psycho-acoustic influences?

I have no opinion about ported box summation (since I do my best to avoid them).

Ben
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