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Acoustics of corners
Acoustics of corners
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Old 28th January 2018, 06:08 PM   #111
gedlee is offline gedlee  United States
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Quote:
Originally Posted by scottjoplin View Post
prefer it.
"it", what is "it"? My point is that there can't be any "pressurization" so what exactly is "it" that you don't like?
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Old 28th January 2018, 06:13 PM   #112
scottjoplin is offline scottjoplin  Wales
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And my point is that there is a degree of pressurisation as the cone moves out from a sealed box in my not quite sealed room. It's a small room, I've used both sealed and open baffle and it definitely feels different on my ears and feels like pressure, what else could it be?
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Old 28th January 2018, 06:29 PM   #113
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It's not static pressure, I hope we can agree to that. What I find most people dislike in bass in rooms is a strong mode which creates a booming effect and maybe a feeling of "pressurization". This will not occur for a dipole if the mode is low enough in frequency, only a monopole will excite it. The solution is to EQ the room better so that this doesn't happen. The dipole can never be EQ'd to achieve the same response as a monopole in a small room, so a dipole not not really a solution, its a band-aid.
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Old 28th January 2018, 06:40 PM   #114
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by gedlee View Post
It's not static pressure, I hope we can agree to that.
Yes of course.
Quote:
What I find most people dislike in bass in rooms is a strong mode which creates a booming effect and maybe a feeling of "pressurization". This will not occur for a dipole if the mode is low enough in frequency, only a monopole will excite it.
This sounds like what I've experienced
Quote:
The solution is to EQ the room better so that this doesn't happen. The dipole can never be EQ'd to achieve the same response as a monopole in a small room, so a dipole not not really a solution, its a band-aid.
Do you mean the same low frequency response of a monopole, say, below approx 40Hz. I appreciate a dipole isn't a solution to room modes, is that what you mean?
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Old 28th January 2018, 06:54 PM   #115
gedlee is offline gedlee  United States
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I mean that dipole just cannot extend the bass to lower frequencies in a small room the way a monopole can. The bad rep that monopoles get is because they are not used properly and not because dipole are superior. My room only has monopoles and it has a nice smooth LF response down to 20 Hz - no dipole can do that. Of course It's not trivial to setup, but I get annoyed by implications that dipoles are somehow inherently superior because people have only heard inferior monopole setups.
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Old 28th January 2018, 07:07 PM   #116
scottjoplin is offline scottjoplin  Wales
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Gotcha, I can get down to 32Hz quite comfortably, I'm experimenting with IB for the last octave. Dipoles are a compromise, but quite a good simple one if you can accommodate them. Room modes are still a slight pain in the backside though, they annoy me (a bit)
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Old 1st February 2018, 08:56 AM   #117
DorinD is offline DorinD  Romania
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Got L=4.7mH, R=2 ohm, C=470uF and did another set of measurements:

1. RLC_shunt vs. Short-circuit vs. No absorber

2. RLC_shunt vs. Short-circuit (for better visibility)

I would say that both short-circuit or RLC shunt look better than no absorber. And RLC shunt has a little margin over short-circuit as two dips look better. This is only measurement, I will go on listening the RLC thing too see if I can hear a difference.
Attached Images
File Type: png RLCshunt_ShortCircuit_NoAbsorber.PNG (89.5 KB, 218 views)
File Type: png RLCshunt_vs_ShortCircuit.PNG (83.8 KB, 209 views)
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Old 2nd February 2018, 03:08 PM   #118
jlo is offline jlo  France
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Back to my first question :
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Originally Posted by jlo View Post
we know that corners are places where all low frequency modes are present with max pressure and no velocity. For this reason, many people (and many books) say that basstraps are preferably placed in corners. This is also often said for fibrous materials (despite no velocity in corners). For sure, at opposite corner, the effect will be heard. But at listening place ?
I think that found one explanation after a nice discussion with somebody who was active in the development of the AVAA from PSI : this active absorber is a nice tool to understand some acoustics because you can easily compare and measure when switching it on/off.
My explanation : when you place this absorber or a passive resonator or absorbant in a corner (ie anything that has some acoustic inluence in low frequencies), this "absorber" can be considered as a re-radiating item. Generally its dimensions are smaller than the low frequencies wavelengths concerned. Due to the small dimensions, the directivity of the re-radiation is wide and so will influence and distord the original soundfield everywhere in the room.
Does this make sense ?
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Old 2nd February 2018, 03:21 PM   #119
gedlee is offline gedlee  United States
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At low frequencies in a small room one cannot talk about "directivity, because waves can only follow the modal pattern being excited, so no, that explanation does not make sense.
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Old 2nd February 2018, 08:40 PM   #120
jlo is offline jlo  France
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Quote:
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At low frequencies in a small room one cannot talk about "directivity, because waves can only follow the modal pattern
Yes but the modal pattern is changed due to the change of impedance at the corner.
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