[Dan_ed]

Hi all,

I'm hoping one of the experts can give me some ideas on how to treat my listening room. My bass horn rolls off pretty quickly below 35 Hz so I'm not concerned with the extreme low end. However, I would like to improve on the dips around 43 and 63.

http://www.flickr.com/photos/9665311@N07/1250486440/

This is the measured response using the bass horn and mains. There are some interactions between 70 and 80 Hz that will probably require xover changes. Interesting that it shifts the big dip up 10 Hz.

http://www.flickr.com/photos/9665311@N07/1250486444/

The room is L-shaped. The listening area is down the length of the foot which is ~15x21 with a drop ceiling just a few inches shy of 8'. The top of the L is to the left of the listening position and is ~15x14. There is about 2' of space above the drop ceiling. Nothing up there but pipes and AC ducts. The ceiling tiles are the generic Home Depot type.

Here is a picture from the listening end. It doesn't show the bass horn, but this horn is located behind the left speaker. It's on wheels so I can move it if that is suggested. As you can see I do have DIY bass traps and I've added a couple more along the front wall. What you can't see is that I've also added 8th Nerve seems and tri-corner traps, and there is DIY absorption on the first reflection point on the right. The left speaker, in effect, doesn't see a reflection point.

http://www.flickr.com/photos/9665311@N07/715112673/

TIA,

Dan

[woodsyi]

The easiest thing to do first would be to stuff your ceiling space above the ceiling tiles with fiberglass insulation.  I used 10" or R30 stuff but I think any batting over 6" (R18?) will do.  I would stuff the tricorners and all the edges along the wall.   

[Dan_ed]

Thanks woodsyi,

would it be better to use backed insulation and if so, should the backing be up or down against the ceiling tiles?

[bpape]

Above the tiles it doesn't matter faced or not.  The idea is to get it full up to the floor above.  Concentrate primarily on the perimeter 2' and over the listening position.

I'd also like to see you take measurements again but this time with the mic about 1' farther forward than you had it before.  Trying to determine if one or more of your nulls are coming off the back wall behind the listening position.

Bryan

[Dan_ed]

Hi Bryan,

I did think of moving the mic, but don't remember exactly what the plot looked like. Just that it didn't strike me as being different. I was expecting to see the nulls move a bit.  I think I'm 4-5' off the back wall.

I'll measure the listening position and do the plot again this evening.

[bpape]

Try about 8' off the back wall and about 6" off center left to right with the mic at ear height too and see what happens.

Bryan

[Dan_ed]

OK.

BTW, regarding the perimeter insulation. Should I go completely around the room or just worry about the part I'm using for listening?

[bpape]

Acoustically, it's all one space.  All the corners will help.

Bryan

[Dan_ed]

Well, I have some explaining to do. Turns out the measurements I took earlier were very close to what I got this evening at 8' from the back wall. 

The listening position is 4' from the back wall. Here is the plot of that measurement with the mic at ear level and just to the left of the seating position.

http://www.flickr.com/photos/9665311@N07/1253092856/

[bpape]

Well, that looks more doable.  At least it's peaks instead of sharp nulls.  We can play with positioning a bit and hit the back wall and potentially help with a few of those. 

Any possibility of replicating that new measurement but centered in the room just to veriy?  I'm 99% sure that most of the big issues are length related and most likely, where you were was combining with some non-axial modes were causing the issues.  Hey, there's worse things than a little extra oomph at 30Hz 

Bryan

[Dan_ed]

No problemo!

Here's just the bass horn from the sweet spot.

http://www.flickr.com/photos/9665311@N07/1252698449/

And for giggles, here's are bass and mid-bass horns from the sweet spot.

http://www.flickr.com/photos/9665311@N07/1253557910/

[bpape]

OK.  What is the 'sweet spot'?  4'?  8'?  Centered left to right?

Bryan

[Dan_ed]

That's where my ears are.  aa

It is 4' off the back wall and centered in that rectangle that makes up the foot. So roughly 7-71/2' from the right side wall. The room opens to the left of this spot. Imaging is very good thanks to the absorption on the right wall.

This position puts me about 12' from the mouth of each main speaker. The mains are about 1/3 into the room from the front wall. So about 7' into the room.

I have to say I'm much happier after seeing these last results. If I can just boost 60-100Hz region and maybe reduce the 30Hz bump a little I'd be ecstatic! This is what I'm hearing, that bit of a hole in the mid-bass.

[bpape]

Well, good luck with that.  I hope it's something that you CAN boost.  Normally, we try to cut peaks - not boost nulls.  Boosting nulls (these aren't really nulls though - just a suckout so it may work) will just push your amp harder. 

Before doing that, you might try pushing your speakers back toward the wall behind them 6" or so.

Bryan

[Dan_ed]

Thanks,

I'll try moving the speakers back and may be able to get the ceiling filled before too long. It's really only about a foot between the tiles and the floor above. I'll just have to con someone into helping me stuff the insulation up there. Now that I have a means to measure results I have a real fighting chance with softening the peak.

I'm still running a simple 1st order xover with little tweaking to this point. It was setting up to tackle that task that led me to the acoustic issue. I don't know if a Zobel on the mid-bass will help things or not at this point. But that's another story.

[Dan_ed]

I just took a look a plot of the system out to about 15kHz. Turns out what I was thinking of as a low point in the 60-100Hz region is inline with the rest of the response from about 600Hz on out.

So, I really have 2 peaks. One at 35 and one from 150 to 200Hz. No boost required! 

[bpape]

<smithers voice>  Excellent! </smithers voice>

Much easier to deal with.  I suspect you'll get some help with the upper one from the insulation in the ceiling.  The lower one is probably going to require some position tweaking and some specifically targeted treatments in terms of placement.

Bryan

[Dan_ed]

Kewl! 

I've got a second bass horn coming, at some point. I can do the ceiling now and then wait on the lower peak until the second horn arrives.

Maybe I can run the two bass horns out of phase.