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Discussion Starter · #1 ·
Some times the front door is open as well as the entryway door, some times the front door is closed but the entryway door is almost always open. I shut it again tonight. When both are opened up SPL seems down but ULF movement up. Shut the front door and movement gets a bit lower but SPL a bit higher. Seal it up and its even louder, but much less movement.


I prefer opened up as ULF is all movementand no sound, and even with the doors opened up it's still plenty loud for my tastes.


Anyone else have an enclosable/reversable listening room to verify similar experience? I assume this can't be measured, REW shows increased SPL the more it is sealed up.
 

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Discussion Starter · #2 ·

Quote:
Originally Posted by LTD02 /forum/post/20983324


"I think there is pressure, then there is flow."


kw, your comment is dead on accurate. very good observation! sound waves create pressure zones and velocity zones depending where in the wave you are. shifting this around by opening the room moves you into and out of various zones. if you want "pants flapping", sit in a velocity zone.


there is a whole lot more to bass than a flat frequency response. of course, this upsets the whole applecart, so don't expect a kind response from folks. :)


let me see if i can dig up something to demonstrate the point visually.


[crap, i can't find the presentation that shows this effect. i think it was a toole or welti presentation that used a george washington figure-head in a room. maybe someone else knows what i'm talking about and can link it up. argh, wish i could find it.]


the idea is that as you get closer to boundaries (walls, ceiling, floors) the pressure goes up, but the velocity goes down. whether we are in a pressure zone or a velocity zone, that will create a different experience.


the pressure vs. velocity way of sensing sub bass hasn't really been explored other than anecdotally (sp?). who is studying this in the academic world?


i think kw should get credit for opening this whole new can of worms, well, at least in part. props man...very big props.

I prefer less SPL and more movement
 

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pressure vs. velocity is a really interesting area of investigation for how we sense sub-bass. kw is on to something here. while not a completely novel idea, his experimental data definitely suggests that for sub-bass, we need a model that includes something more than frequency reponse.
 

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Discussion Starter · #4 ·

Quote:
Originally Posted by LTD02 /forum/post/20983423


pressure vs. velocity is a really interesting area of investigation for how we sense sub-bass. kw is on to something here. while not a completely novel idea, his experimental data definitely suggests that for sub-bass, we need a model that includes something more than frequency reponse.

when I first began to notice, I started pondering what type of instrument could measure this. My floor, bleechers/bed, ceiling, walls.... everything moves much more...you feel it much more...but it sounds quieter and SPL readings are lower.


So what type of instrument could we develope or already exhists that we could use as is or modify?
 

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I've tried to open this discussion in the distant pass, but always faced jeers from the experts.


Here's a graph, mic in the same position for both traces at the LP, no post EQ, measured with a window closed vs open. Of course, the ULF increases vs the conventional wisdom that says it should be more in a sealed room:




Bosso
 

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Quote:
Originally Posted by bossobass /forum/post/20983514


I've tried to open this discussion in the distant pass, but always faced jeers from the experts.


Here's a graph, mic in the same position for both traces at the LP, no post EQ, measured with a window closed vs open. Of course, the ULF increases vs the conventional wisdom that says it should be more in a sealed room:




Bosso

I have seen this exact same thing in my room, I get more measured output with the door leading down to the basement open, around 2db, from 10-5hz if I remember correctly. I'll try to post a graph tonight.


Wem
 

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Quote:
Originally Posted by Viperoni /forum/post/20983744


I have a feeling that this is related to cancellation due to standing waves bouncing back within the room (vs expanding/flowing out of it)

but with it just being a window, like bosso tried, shouldn't cause a big enough effect for the "bouncing waves" theory.
 

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I may be completely missing the point of what you guys are getting at, but I would think one of those contraptions that they put on your door to measure your home's efficiency of insulation would be a place to start? I'd think it would have something to do with the movement of air, and those things are pretty sensitive. Sorry kids are coming onto class, I'll try to edit and explain a little better if someone else doesn't beat me to it.
 

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Quote:
Originally Posted by bossobass /forum/post/20983514


Here's a graph, mic in the same position for both traces at the LP, no post EQ, measured with a window closed vs open. Of course, the ULF increases vs the conventional wisdom that says it should be more in a sealed room

I wonder if a correction needs to be applied; I remember Tom Danley saying something about it being necessary under some conditions because microphones may erroneously convert velocity into pressure.


Not sure I've got that right but something like that.
 

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"I prefer less SPL and more movement"


this is actually a pretty cool idea, because based on where you sit in your room and the dimensions of the room, you might be able to calculate which frequency/ies is your velocity zone wheelhouse, then just put a big boost on that frequency. since it is all subbass, you probably won't hear anything, but there will be more pant flapping power. this is probably what you were trying to accomplish with those low tuned subs with giant peaks right on the tuning frequency. everybody, including me, thought that was just a mistake, but now, there is an explanation for what is going on.


this one isn't what i was thinking of, but shows the idea on slide 10:

http://www.linkwitzlab.com/LF-SL/Bas...stics_P773.pdf
 

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Quote:
Originally Posted by noah katz /forum/post/20985866


I wonder if a correction needs to be applied; I remember Tom Danley saying something about it being necessary under some conditions because microphones may erroneously convert velocity into pressure.


Not sure I've got that right but something like that.

I don't see where that would apply here since a) at the dBSPL level the measurement was made at, velocity is irrelevant, b) the measurement was taken indoors (no wind) and, most importantly, c) the mic position and levels and all other conditions were identical except for a window being open vs shut.


My answer is that in a sealed room, although at frequencies below the modal frequencies the room cannot support a standing wave, there still must be areas of reinforcement and no reinforcement depending on the shape of the room and where in the room the mic is placed.


This variation will not be a very large one, but some of that effect will be lessened when an opening is made for the extremely long waves to escape, or more so pass by the mic than combine with reflections.


The other thought is that the measurement was made with the original point source emanating from 2 locations, non-equidistant to the mic. This is a possibility that's related, but, IMO, less likely.


Still, for me, the bottom line is that I just don't know.


I think of not's system. He clearly sees boost to single digits and his room is very large and not sealed. If room gain's a given, I would like to know what the formula is for where opening size begins to create losses to room gain.


MKT could help with door open vs closed in his very sealed room, if he ever gets his new mic up and calibrated.


Bosso
 

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Quote:
Originally Posted by Erich H /forum/post/20986927


I thought most cars with subs sounded louder when you opened one window? Well, I mean if you're sitting in the driver seat and the passenger rolls down the window.


Maybe you just ported the entire room when you opened the door or window.

Usually it'd sound louder but not neccesarily meter better... but this depends too.


FWIW, I di 146.3db with all the windows up and 146.1db with the drivers window down... explained all the looks while cruising by



That being said, I also like the theory of an open window/door turning the room into a giant ported box... it shouldn't be too hard to estimate either.
 
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