On balcony doors and bass traps

[fredk]

An interesting thing happened when I went to hang blinds for my balcony door last week.

I needed to put up brackets to hang them so I put on some music, pulled out a chair, climbed up and started marking. For one bracket, I put the chair in front of the balcony door, for the other, I had to position it in the corner off to the side of the door.

For the corner bracket, as soon as I stuck my head up near the corner I got this big boomy bass. For the other, where the chair was in front of the door, there was little or no change in the character of the bass.

It took a few days for this to sink in. So, is the balcony door (6' wide double glass) acting like a bass trap by letting all the low freqency waves through?

I am now wondering whether or not putting a bass trap across the ceiling/wall corner on this wall will be effective or needed, at least across the area where the door is.

I am now thinking that before I put the trap up, I should run a series of bass sweeps and use REW to measure several points along the wall to see what is happening. I could even measure, hang the trap and measure again to see what its effect is at points along the wall and at the seating positions.

Am I on the right track here?

I also wonder to what extend the door effects room modes. I suspect that it would have a substantial effect.

 

[mtrycrafts]

An interesting thing happened when I went to hang blinds for my balcony door last week.

I needed to put up brackets to hang them so I put on some music, pulled out a chair, climbed up and started marking. For one bracket, I put the chair in front of the balcony door, for the other, I had to position it in the corner off to the side of the door.

For the corner bracket, as soon as I stuck my head up near the corner I got this big boomy bass. For the other, where the chair was in front of the door, there was little or no change in the character of the bass.

It took a few days for this to sink in. So, is the balcony door (6' wide double glass) acting like a bass trap by letting all the low freqency waves through?

I am now wondering whether or not putting a bass trap across the ceiling/wall corner on this wall will be effective or needed, at least across the area where the door is.

I am now thinking that before I put the trap up, I should run a series of bass sweeps and use REW to measure several points along the wall to see what is happening. I could even measure, hang the trap and measure again to see what its effect is at points along the wall and at the seating positions.

Am I on the right track here?

I also wonder to what extend the door effects room modes. I suspect that it would have a substantial effect.

No, the door is not acting like a bass trap but what you experienced are the nulls and the peaks in bass and your room interactions. You would have similar effects on the opposite wall if you have one and climbed up to the same height, or, walked around the room.
This would be best demonstrated by low frequency test tones as they are constant while you walk around unlike the music where it changes constantly and you have to figure out if that is in the music or something else, room peaks and valleys.

 

[fredk]

Perhaps I should rephrase that.

Because glass is transparent to frequencies below a certain point and does not reflect those frequencies back into the room, a sufficiently large opening may have a similar effect to a bass trap.

I guess the question should be:
What sort of effect will a large hole in one end of a room have on bass peaks and nulls and corner loading?

 

[mtrycrafts]

Perhaps I should rephrase that.

Because glass is transparent to frequencies below a certain point and does not reflect those frequencies back into the room, a sufficiently large opening may have a similar effect to a bass trap.

I guess the question should be:
What sort of effect will a large hole in one end of a room have on bass peaks and nulls and corner loading?

I seriously doubt glass is transparent at audio frequencies even though it can vibrate and pass on that energy to the other side.

A large hole in one end will pass all that walls energy to the next room/space and it may or may not return. The other 3 walls, floor and ceiling still has a good bit of effect though.
One way to find out is to get that low frequency test disc, play it and walk around the room

 

[bpape]

Glass can indeed pass some bass out of a space - but it's not like an open window by any stretch. You'll still want to address the area as though it were a wall.

When you had your head in the corner, it's just that there's more buildup there since you're at the end of all 3 room dimensions instead of just 2 by the door.

Bryan

 

[fredk]

Thanks gents. It seems my memory was playing tricks on me. For some reason I had it in my head that glass was transparent to frequencies below a certain point.

It mighty still be interesting to take some measurments at the wall. I wish I had an empty wall at the other end to compare to.

 

[bpape]

Oh, it'll definitely pass more bottom end than an insulated drywall wall - but it still reflects some back into the room.

Bryan

 

[fredk]

After some thinking, some wandering about in my room listening to the thump thump of a kickdrum, and some additional reading, I am beginning to appreciate the complexity of sound reflections and room treatments.

I happened to put on Clapton unplugged while doing some cleaning up and noticed a difference in the boost to the kickdrum as I moved around the room. The regular repeated thump of the kickdrum made for a nice way of checking out room accoustics while listening to good tunes.

In the image below I have marked out the areas where I noticed bass boost where:
Red = most -> orange -> yellow -> green = none

I didnt check out the corners in the dining area or by the door, though it would be interesting to see what I found there.

The most surprising one to me was the noticable boost in the kitchen area. I am not sure how this applies to the placement of traps yet, but I did find it interesting. Clearly an irregular shaped room offers additional challenges and large glass doors do pass bass, but not all bass.

 

[PeterWhite]

If at all possible I'd put a trap in the top left corner at that red "X." I'm just now finishing up doing pretty extensive acoustic modifications to my listening room and the improvement in sound is significant. The base nulls are all greatly reduced and everything is clearer.

The room has a drop ceiling so I stuffed Ultra Touch cotton insulation all around the perimeter or the ceiling, extending about three feet in from the corners. I also have some Real Traps Mini and Mondo traps and three of the triangular corner traps. The big base nulls in the center of the room, where the seating is, are still there but nearly so big. You can learn a lot by listening, but I've found the Radio Shack digital meter to be a big help. I also got some software for my laptop that generates tones of any frequency. The music you may be listening to at any one time won't have every frequency, so using the software is much more efficient. It was a free download and there are many options on the web.

 

[fredk]

Thanks for the reply Peter. Given my room shape and furniture arrangements, its was originally suggested I put traps at the wall/ceiling interface at the front and back of the room.

After my walkabout, I wonder if putting something in the corners where the red Xs are (can't go full ceiling to floor) might have a significant effect.

I have the RS meter, REW and associated cabling already, just havn't taken the time to do any measurements yet.

I have lots of work to do on this yet.

 

[PeterWhite]

Thanks for the reply Peter. Given my room shape and furniture arrangements, its was originally suggested I put traps at the wall/ceiling interface at the front and back of the room.

After my walkabout, I wonder if putting something in the corners where the red Xs are (can't go full ceiling to floor) might have a significant effect.

It's made a big improvement in my room. Of course, my listening room has two functions; watching movies and listening to music. What the room looks like is irrelevant.

 

[fredk]

Its not so much looks (though my room is no beauty) as practicality. The aquarium stand has 80 gallons of water in two tanks that I do not want to make the effort to move just now, so I have to work around it.

 

[jostenmeat]

fredk, I was typing away, and now just see the last two posts. Oops, ok. Well, in case looks ever DID matter, I compiled a few amusing WAF-friendlier treatments for someone else recently:

Coffee table trap!!

Planter trap!!!!

Meh

Probably too pricey?

 

[fredk]

Nice! Since I need to put the traps in the top 3' of the two worst corners I need the 'spiderweb-in-the-corner' version.

Actually, the last one is pretty cool. Being of artistic bent, I would love to build some funky looking difusers for 1st reflections.