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daverich4
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Filling in the missing bass

For the first time ever I'm setting up a dedicated listening room. Previously, speaker location/listening location was pretty much dictated by the room. Now I have a lot more freedom in placement but have a question about how to do so. RealTraps has a set of tones available on their web site in 10Hz steps from 10-300Hz. When playing them back the first time with the way I initially placed the speakers/listening position I found that in general, the tones between 50Hz and 110Hz were way down in volume compared to those above and below that range. Not equally down but down just the same. Moving the speakers a little closer to the wall helped and moving the listening position further away from the speakers also helped. But what surprised me the most was that standing up or crouching down to the floor was like turning my Ref 3 volume from 30 up to 40 for most of the range. That's not true for the 60-69Hz range, forward or back, up or down, nothing will bring them up in volume but for the rest of the tones, listening at anything BUT tweeter height gives a big boost to the bass. Does anyone have any idea what might be my next step other than standing to listen to my system? I haven't given a room or system description because I assume there's some basic audio theory at play but I'd be happy to provide that information if it's of any use. I do have a set of the RealTraps Mondo Traps in the corners behind the speakers but that's the only specific room treatment that I'm using. Thanks.

Kal Rubinson
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Re: Filling in the missing bass

You do not describe the room nor the speakers. The simplest route might be to make a diagram that you can post or send to Ethan Winer at www.realtraps.com. He is pretty nice about helping.

Kal

j_j
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Re: Filling in the missing bass

Well, with the dimensions of the rooms, wall surfaces, and layout, one might be more able to make a guess.

It sounds offhand like you've got some room mode reinforcing in at least 2 dimensions, but it's hard to be sure.

Have you tried putting a humongous beanbag chair in the listening spot and seeing if that has any effect? (really!)

Not suggesting that you use it for room treatment, but it might offer some help in regard to what modes are bugging you the most.

rabpaul
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Re: Filling in the missing bass

Looks to me you are doing this by ear. Perhaps a better approach would be to plot the room with a SPL meter placed at your listening position at ear level. You can then move things around to get the best you possibly can and then send this to plot to Ethan for more advice on what to do and where.

daverich4
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Re: Filling in the missing bass

Thanks for all the responses. The room is about 19'x23'with the speakers along the short wall. (Wilson Sophia II's). They're about 2 feet out & 9' apart. Right now, the listening position is about 8 feet from the back wall although I've found some improvement in moving it a little closer to the back wall. What confuses me however, is the lack of bass when seated yet no lack when standing or crouching down to the floor. It's like there's a cone of bass silence about 40" off the floor. I thought bass was non-directional? I was expecting peaks and dips on the horizontal plane but while I know the treble can change with the vertical location I've never heard of the bass doing so. Thanks.

Kal Rubinson
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Re: Filling in the missing bass


Quote:
Thanks for all the responses. The room is about 19'x23'with the speakers along the short wall. (Wilson Sophia II's). They're about 2 feet out & 9' apart. Right now, the listening position is about 8 feet from the back wall although I've found some improvement in moving it a little closer to the back wall. What confuses me however, is the lack of bass when seated yet no lack when standing or crouching down to the floor. It's like there's a cone of bass silence about 40" off the floor. I thought bass was non-directional? I was expecting peaks and dips on the horizontal plane but while I know the treble can change with the vertical location I've never heard of the bass doing so. Thanks.

This is not too surprising as the bass does change with position more than treble does (aside from the differences between on and off axis). You do not state the vertical dimension of the room but it seems that you have a mode with a null at 40" from the floor. The solutions include not sitting with your ears at that height (elevate the sofa?), bass trapping to minimize that mode and electronic EQ for it. I doubt that speaker repositioning will help much.

Kal

j_j
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Re: Filling in the missing bass


Quote:
The solutions include not sitting with your ears at that height (elevate the sofa?), bass trapping to minimize that mode and electronic EQ for it.

I wouldn't go for the electronic EQ myself. When you have a big bass node like this, it means, ironically, that the room is storing too much energy at that frequency, and that you're sitting in a volume velocity peak (where the air is going back and forth at that frequency) rather than a pressure peak (where the air isn't moving, but the pressure is changing.

Room treatment would seem to be indicated to me. The key is to realize that standard absorbers work on volume velocity. In order to damp a pressure node, you need a membrane (or more complex methods) to convert pressure to velocity, and then absorbtion material.

The speed of sound is about 1153 feet/second. If you figure out the wavelength of the bass frequency you're missing (that would be 1153 / frequency_in_Hz), you'd want some damping material that would be at least half that length in at least one dimension in order to have any substantial effect. For maximum effect, then you'd place it where you don't hear as much bass (i.e. in a volume velocity peak), which may seem odd, but that's how it works.

If I can be pedantic for a minute, allow me to explain a bit more.

At any point in the atmosphere, there are 4 variables in the soundfield. One is more or less (at bass frequencies at least) what you hear, that's the pressure component. The other three are vertical, horizontal front-back, and horizontal left-right velocity vectors that describe how the air is moving at that point. If you're at a bass peak (according to your ears) then you're at a point where the velocity vectors are minimized. If you're at a null, the pressure is minimized, and velocity maximized. This is why a null represents energy storage, which otherwise must seem just a bit, well, confusing.

The one joker in all this is if your speakers don't radiate at that frequency. I suppose it could be the case, but that's rather (understatement alert!) unlikely.

ethanwiner
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Re: Filling in the missing bass


Quote:
But what surprised me the most was that standing up or crouching down to the floor was like turning my Ref 3 volume from 30 up to 40 for most of the range.


This is pretty typical. Bass response especially varies all over a room, and small changes in position can make a big change in SPL. With only two MondoTraps in a room that size, the obvious solution is to get more.

If that's not possible for whatever reason, this short article describes a way to find the best places for a small number of traps:

Pink noise aids placing bass traps

But again, in all honesty, more traps is the better choice if possible.

--Ethan

_________________
www.realtraps.com

Kal Rubinson
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Re: Filling in the missing bass


Quote:

Quote:
The solutions include not sitting with your ears at that height (elevate the sofa?), bass trapping to minimize that mode and electronic EQ for it.

I wouldn't go for the electronic EQ myself.

It was my last option.

daverich4
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Re: Filling in the missing bass

Kals suggestion about changing my seating did help some. Using a higher chair with a more upright position brings up the bass level a little. I already have a Behringer equalizer that uses a built in pink noise generator and a calibrated microphone to adjust the response but if possible, I would like to avoid using it as a solution to my problem. Ethan's post suggests that more bass traps would help so I think I'll follow up on Kals original suggestion and ask him for some help. Thanks again for all the replies.

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