# Can room treatment help me here?



## vann_d (Apr 7, 2009)

I'm talking about the dip/peak combo between 200 and 500 Hz. Is this something that can be treated with absorption? What works well in this frequency range? 

I know I have a reflection from the right channel from the fireplace glass because I can see that speaker in it from the listening position. I only have ability to eq in the subwoofer channel.

A little help getting started would be appreciated!


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## bpape (Sep 14, 2006)

It's possible that it's treatable but it's relatively broad. A lot depends on the cause.

A lot depends on how you read that graph. If you assume the sub level is a bit hot, the rest smooths out except for a peak at 200 and a peak at 500. Realistically, the whole thing is pretty close to +/-5 db which isn't bad.

Bryan


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## vann_d (Apr 7, 2009)

Thanks for the reply. 

Yes the sub is deliberately a little hot as I like it that way.

I guess it is pretty close to +/- 5 dB. Perhaps I was thrown a bit because those peaks look larger than the ripple surrounding areas.

I'm not sure what types (magnitude) of peaks are typically treated. 

Sounds like I shouldn't be concerned. True?


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## DanTheMan (Oct 12, 2009)

Check this out: http://dtmblabber.blogspot.com/2010/12/little-more-into-boundary-conditions.html

Looks like your issues may be boundary related. Looks pretty good overall. Would love to see some more graphs from different positions.

Dan


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## vann_d (Apr 7, 2009)

Hmm...yeah I was kinda wondering about that bounce off of the fireplace glass. It is a enclosed system and, like I mentioned before, I can see the RF speaker's reflection in the glass. Here's what I get with the calculator...

side wall cancellation calculation comes out at ~220 Hz
83cm speaker to wall
90cm LP to wall
350 cm speaker to LP

floor bounce 1st cancellation ~ 400 Hz
ceiling bounce 1st cancellation ~ 28 Hz (20 ft ceilings)

distance from baffle to front wall ~2.5 feet puts cancellation ~115 Hz

Perhaps I should experiment with some absorption or diffusion in front of the fireplace. Any ideas?

Anyone do this real time using the RTA features of REW?


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## DanTheMan (Oct 12, 2009)

Can we have some more graphs and a pic of the listening space?

My general advice looks like this: http://dtmblabber.blogspot.com/2010/12/room-treatment-advice-quick-and-dirty.html

I typically only look at the RTA to find the sweet spot and to have a look at the bass in various places. It is interesting to look at the real comb filter (one-toothed comb) problem caused by a stereo pair of speakers and how side wall diffusion can actually reduce it.

Dan


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## vann_d (Apr 7, 2009)

DanTheMan said:


> Can we have some more graphs and a pic of the listening space?


Thanks, I might be able to take more measurements this weekend but the wife is getting sick of it. 

I only have the one good one at the LP. Others were thrown out because receiver settings were not correct or something of that nature. I don't recall the plots at other positions being much different but I was focusing on the subwoofer so I can't say for sure.

I can get some pics of the space up soon though. Thanks!


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## DanTheMan (Oct 12, 2009)

Send the wife out to buy a new purse. Give her a wad of cash or offer a credit card.  If you are only worried about one spot.... one measurement is all you need. Odds are, you will have more than one listener on occasion sitting in more than one place. Taming bass is a pain, but it looks like you are OK there. Midbass is typically a boundary issue b/c modal density is getting high by then. Less smoothing (preferably none) would be better as well.

Dan


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## vann_d (Apr 7, 2009)

Here is a plot w/ no smoothing and a pic of the room. Sorry it's such poor quality. My camera is terrible in low light.

~2ft behind the LP are 3 large windows with plantation shutters (1st story). The front wall is ~20ft tall and is bare (new place and no decoration yet). Side right is also ~20ft tall. Side left is open to other living areas 1st and 2nd floors. The space has no "treatments" except for carpet and cushy sofas.


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## bpape (Sep 14, 2006)

While not perfect, I've seen a lot worse. I suspect treating the front corners and the wall behind the speakers will help a bit. You will likely also have to address the walls directly beside the speakers to minimize boundary issues.

The last thing is that you are likely also getting a resonance from the small space between the TV and the wall behind.

Bryan


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## DanTheMan (Oct 12, 2009)

I think Bryan is 100 percent correct--not much to complain about there. Treating the front wall, corners and maybe some on the side and nothing more to be done. To be honest, what you have is good and there's no urgency to treat. I'd bet it sounds great now. That 300-500 snake if fixed, may expose some other issue......

Dan


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## vann_d (Apr 7, 2009)

Thanks for the advice Gents.

I am happy with how it sounds right now but thought maybe I could be happy(er) by adding some treatments.

I think I'll try treating the front wall a bit and see how it goes from there. I'll post back here when it's done and I've got new measurements.

Thanks again!

-V


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## bpape (Sep 14, 2006)

Well, just remember that we've only addressed frequency response. Nothing has been done to look at decay times and ringing. You will definitely hear an improvement with the places we outlined properly treated.

Bryan


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## vann_d (Apr 7, 2009)

bpape said:


> Well, just remember that we've only addressed frequency response. Nothing has been done to look at decay times and ringing. You will definitely hear an improvement with the places we outlined properly treated.
> 
> Bryan


Oh yeah, thanks for reminding me. You didn't ask for those plots. Here is a decay and a waterfall plot. If nothing else than for record when I come back to this...


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## bpape (Sep 14, 2006)

Can you chop those down so they're just 20-500Hz so I can get a better look? Looks like overall, decay times are still a bit long in the bottom end.

Bryan


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## vann_d (Apr 7, 2009)

Yeah, here you go...

I know I have a gigantic room mode around 35 Hz that I'm already knocking down quite a bit with eq. 

Thanks for taking a look...


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## vann_d (Apr 7, 2009)

I've also discovered that there is a HPF on my sub amp around 30Hz which is messing with things quite a bit (the sub is tuned to 15 Hz). I'll be getting a new amp soon.

The crossover to mains is at 100Hz which is a limitation of my receiver, it's not adjustable.

Here is the sub only with no eq... looks like Pikes Peak :yikes:


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## bpape (Sep 14, 2006)

Are you not cutting off the mains? The response is a lot different with everything vs just the sub.

Bryan


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## vann_d (Apr 7, 2009)

mains are set to small...should be crossed over at 100 Hz.


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## DanTheMan (Oct 12, 2009)

What's the slope?

I hate to ask for more graphs, but could I also see RT60? I like it b/c of the scaling. I like full 20-20k. ha ha. We can be demanding I know.

Oh' some rear wall absorption may also help, but I've never really found a way to radically improve bass under 100Hz other than placement and EQ. Deep--2.5ft--absorption has proven beneficial in my BR. One of these days I'm going to get around to completing it.

The 300-500Hz region could be helped by absorption. Did you have a budget in mind?

Dan


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## vann_d (Apr 7, 2009)

I never really measured the high pass filter. I should do a measurement on it to verify what is going on. I have measured the low pass as -24 dB/oct with corner at 100 Hz (-6dB point). I assumed the hpf was the compliment to that.

I'm only thinking a couple hundred bucks max for some DIY treatments.

Here is RT60 plot. I don't know how to interpret this figure. Maybe you can 'splain me? I only have measurement up to 2kHz because I'm using RS SPL meter.


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## bpape (Sep 14, 2006)

Something is still odd. If the xover point is 100Hz, then your response should be pretty much the same (less any overlap) up to around 90Hz with or without mains - which the response isn't showing. Also, I notice a decent pretty sharp dip right at 100Hz which could indicate a phase misalignment between the mains and the sub.

Bryan


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## vann_d (Apr 7, 2009)

Sounds like I'm going to need to verify with re-measurement. I could very well have messed something up in my bass management settings between the two measurements (sub only and sub+mains). 

Unfortunately, my sub amp is at my sister's house right now so I can't get new sub measurements. (B-day party last night)

I can take measurements of mains by themselves though. I'll try to get something new up today.


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## vann_d (Apr 7, 2009)

Ok, I took new measurements of the main front L/R speakers only with no subwoofer. One set with the mains set to large (full range) and sub set to none in the receiver. One set with the mains set to small and sub on but physically disconnected from the system.

Measurements are at the center listening position. Noise floor (ambient) was a bit high but I had to make due.

I think we can see why something looked funny in the previous charts. It kinda looks like the crossover for the main speakers is a very shallow slope. I would've expected -6 dB at 100Hz.

Anyway here is the frf overlay...


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## DanTheMan (Oct 12, 2009)

RT60 is just the amount of time it takes for a noise to decay by 60dB. Your time is too high for optimum clarity. Somewhere between 0.2 and 0.5 seconds is best for speech clarity. I tend to prefer things on the drier side for surround sound.

Dan


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