[Ethan Winer]

You could always use your ears as a last resort.

Yes, but that's not as reliable as you might think. The main problem is the key of the music interacts with resonances and comb filtering in the room. So a speaker placement that sounds perfect for a tune in the key of A might be totally boomy - or totally thin - for music in another key. Using software like REW lets you nail the placement exactly because you can see what happens at all frequencies at once.

--Ethan

[satfrat]

You could always use your ears as a last resort.

Yes, but that's not as reliable as you might think. The main problem is the key of the music interacts with resonances and comb filtering in the room. So a speaker placement that sounds perfect for a tune in the key of A might be totally boomy - or totally thin - for music in another key. Using software like REW lets you nail the placement exactly because you can see what happens at all frequencies at once.

--Ethan

Guess my only point is that of personal preference in that maybe one should trust what they like and not what they read on a gage. Tools are great n'all but there's no accounting for personal tastes in sound,,, or so I've been told.

Cheers,
Robin

[stevenkelby]

Nulls and peaks have nothing to do with personal preference! They exist or they don't, and you won't know where unless you measure accurately.

Whether you like peaks and nulls or not is irrelevant to the discussion, I think.

[zybar]

Nulls and peaks have nothing to do with personal preference! They exist or they don't, and you won't know where unless you measure accurately.

Whether you like peaks and nulls or not is irrelevant to the discussion, I think.

Well said and spot on!

You might like the way your system sounds before you measure, but I can pretty much guarantee that if you are able to accurately measure AND make the necessary changes to improve the measurements, you will like your system even more!   aa

George

[Ethan Winer]

Guess my only point is that of personal preference in that maybe one should trust what they like and not what they read on a gage.

I knew that was your point, which was why I spent the time to explain why measuring is better anyway.

Once you measure and move things to make the room as flat as it'll get, then you can use an EQ to screw it up again.

And Yes, if you call me a "meter reader" I'll take that as a compliment.

--Ethan

[stevenkelby]

Ethan, assuming a properly treated and set up room, do you think EQ is ever useful for home stereo listening, or that it will almost always do more harm than good. I'm on the fence and genuinely curious. Used to think EQ was required anyway, but now understand it doesn't fix a lot of what's wrong with a room and I have not tried one that did not alter the sound for the worse.

Thanks,

Steve

[bpape]

I'll not answer for Ethan but I'll throw in my 2 cents. 

I think that there are 2 options.

- If you're using a subwoofer in the setup (or multiples), then EQ can be useful on the sub channel. 

- If you have a VERY high quality EQ and you're making small adjustments, then they can be useful full range.  I'd never put a cheap/moderate EQ in my mains loop.

That all said, most times, if the equipment is voiced to your preference, mates well with other equipment you have, and the time is taken to properly set up speakers, seating, and treatment, EQ should not be needed.  If the room is an absolute disaster acoustically, then try to get it to a point where you minimize nulls at the expense of peaks which can more easily be dealt with via moderate EQing.

Bryan

[satfrat]

Guess my only point is that of personal preference in that maybe one should trust what they like and not what they read on a gage.

I knew that was your point, which was why I spent the time to explain why measuring is better anyway.

Once you measure and move things to make the room as flat as it'll get, then you can use an EQ to screw it up again.

And Yes, if you call me a "meter reader" I'll take that as a compliment.

--Ethan

It wasn't meant as an insult Ethan, sorry I butted in.

[Ethan Winer]

Ethan, assuming a properly treated and set up room, do you think EQ is ever useful for home stereo listening

I never recommend EQ for use above 300 Hz or so. If someone is not happy with the mid and high frequency range, that is easily solved with acoustic treatment. And if after treatment you're still not happy, then getting new speakers is the right solution. Before someone chimes in to say new speakers are too expensive, there are plenty of good speakers these days that don't cost an arm and a leg.

The only time I personally would use EQ is below maybe 60 to 80 Hz where conventional bass traps are less effective. Even with all the bass traps in my living room, I still had a small (3 dB) peak around 40 Hz due to the length mode. So I use the one-band cut-only parametric EQ built into my SVS subwoofer. The EQ did not remove the ringing, but in the big picture it reduced the peak enough and I'm happy.

--Ethan

[Ethan Winer]

It wasn't meant as an insult Ethan, sorry I butted in.

Not at all! It's just that from spending too much time at the Stereophile forum I've become overly sensitive to people who tend to dismiss measurements saying "by ear" is always best. I'm not opposed to listening! But in this case measuring is much better.

--Ethan

[dguarnaccia]

Howdy folks,

Well, I'm back. It's taken me quite some time to finish the treatments in my room. Since my last post, I've complete tube traps all the way to the ceiling in every tri-corner, and stuffed the tubes with tightly rolled R38 for additional absorbtion.

I've also added some nice GIK 244's and some ATS traps in the room as well. I'm still baffled though by this one large null right at 80-90 hz. Here is an REW graph of just the sub



Originally, I thought I might be having some phase issue between my subs and fronts, but I don't think that's the case. Here is the front right all by itself



This image is both sub and front right



My question is this. With all the traps I have, I still can't kill this Null. I've even tried moving the listening position forward, and I've moved my sub everyone and can't seem to improve things. Anyone have anything else I can try?

Thanks,

Darren

[youngho]

Hi Darren, I was wondering if you could specify where your speakers and sub are located now, as well as which listening position your measurements were taken from. Interesting problem.

[dguarnaccia]

certainly,


They are in pretty much the same location as my room layout diagram here




The speakers are about a 2 feet off the front wall, and approximately 3.5 feet from the sidewalls. (hard to tell from the diagram)

The sub is just left of the center of the room. I've tried moving the speakers and sub more forward into the room, but it didn't seem to make much of a difference. I went as far as 4 feet off the wall (about as far as I could get away with in terms of WAF) and the effects were negligible.

I've tried the sub in different locations every two feet around the front half perimiter of the room, and oddly enough, the front wall seemed to yield the best result.

What I'm confused about is what is causing that large dip with just the subwoofer playing?  The two large dips around 85 hz and 90-110. What would cause this?  Is this just a room mode?  Is there anything I can do about it beyond speaker placement and more bass traps? 

[*Scotty*]

dguarnaccia, You appear to have nulls at the frequencies you listed that are due to the room dimensions. If you divide 1100 by 85Hz you get about 13ft. for a wave length,dividing by 90 yields 12.22ft. and 100Hz gives 11ft. If your measurement position is about in the middle of the room you should find the nulls you are seeing at this location. Have you tried finding a measuring position in the room with the flattest response curve. You may have to relocate your listening chairs and loudspeakers to find a position in the room which yields the best response below 150Hz. It is very unlikely that you will achieve a flat response curve at all positions in the listening area occupied by your chairs which appears to be over six feet in depth.
You may have to go to Home Depot and purchase several rolls of pink insulation and cover the entire back wall behind your chairs with homemade tube traps by stacking the rolls floor to ceiling. If they are stacked four high to make a "tube trap" you may need 12 to 16 rolls to cover the area in front of the back wall with "tube traps". Home Depot should allow you to return the fiberglass rolls for your money back if you decide not to keep them. You won't be opening up the plastic they are packed in as it is transparent to the wavelengths you wish to absorb. Any thing less than this much absorbing material behind you probably won't fix your problem. This is basically a big problem and will probably require a correspondingly large solution to fix it.
Good luck,
Scotty

[oneinthepipe]

moved to new thread

[youngho]

Scotty, the formula for first-order modes is actually 565 divided by the room dimension (corresponding to the half wavelength for the resonant frequency, so that the reflected waves superimposes almost perfectly with the incident waves). You multiply by two for the second-order modes, which would actually have an antinode (or pressure maxima, aka peak) at the center of the room. This probably explains the two broad peaks around 40 and 60 Hz seen when the right speaker alone is playing. Don't forget that the fenestrations (windows, doorways) will shift the corresponding resonant frequencies downward from the calculated values, as well as the nodes and antinodes towards the fenestrations. My guess is that the relative null in the low 50s Hz with the right speaker alone may be due to lack of modal reinforcement between the second-order length and width modes.

Dguarnaccia, you didn't specify measuring location, but I'll assume front row, center. The rather sharp (high Q) null in the low 80s is a little interesting, especially if you find it at all listening positions and also with the sub in various places. If so, is it possible that you have a Helmholtz resonator/absorber that you didn't identify? Are you measuring with windows or doors slightly ajar? Do you have a whole bunch of vases (an empty glass Coke bottle has a resonant frequency of 185 Hz with a fairly high Q for absorption, for example) or some other empty containers like that? Perhaps something with slats (like a QRD diffusor) or perforations? Maybe even your HVAC? Perhaps Ethan and Bryan might be able to comment on this.

If you can't kill this null, how much would you be willing to spend? You could replace your raised platform with the TH-SPUD from Danley, discussed here: http://www.avsforum.com/avs-vb/showthread.php?t=1076691. I practically guarantee that this would fix your problem.

[dguarnaccia]

Hmm...I feared that might be the case.  I don't think I have any open containers, and I don't have any Helmholtz resonator/absorbers. Just good old fashion fiberglass panels and tube traps.  I'm verified all windows and doors are sealed. I suppose it could be the HVAC.  One question, if I added a second Sub in the back wall, would that improve things?  Would having 2 subs on opposite walls have any impact on that null?

In terms of budget, I have to keep things fairly modest. I can usually do incremental stuff in the 200-300 range, but I fear the Danley stuff is out of my reach for now. Someday though...someday

[Vinyl-Addict]

I would recommend pulling your speakers well out into the room. Listen & measure as you move them. I would also suggest playing with toe-in after you pull them out into the room. Don't forget to mark prior speaker position with tape.

[youngho]

Dguarnaccia, I was only speculating. I didn't know if you had some gigantic collection of empty beer cans or bottles, for example. Ignore what I said.

Sorry, stupid me, I didn't look at your initial information about crossover. Clearly the right is having some major cancellation, and the subwoofer is crossed over at 60 Hz, so it's not helping the situation. My guess is that the subwoofer really needs to be off the front wall, looking at the REQ graph, since the two cancellations are combining. Moving the subwoofer didn't help significantly because you crossed it over so low, obviously.

There are two simple things to try:
1. Cross over the sub and speakers at 80 Hz or even higher, and play with phase. For example, if you crossed over from speakers to subwoofer at 120 Hz, that would be better than you have now. If both subwoofer and speakers are playing in the region from 80-120 (maybe crossed over at 100 Hz?), then the combined output may boost fix the mid-bass suckout as long as the phase is set correctly However, my suspicion is that the subwoofer needs to be somewhere else entirely, like the back wall.
2. Run the speakers full-range, and optimize their setup as Vinyl-Addict suggests. Add the subwoofer, perhaps on the back wall, running up to 120 Hz, and slide it around and play with level and phase you're able to achieve a smoother response. Adding other subwoofers would help even more. The sweet spot seems to be three, according to Earl Geddes. Because of the fenestrations of your room, Todd Welti's paper on multiple subwoofers does not apply. Nonetheless, the evidence suggests that multiple bass sources can sometimes help ameliorate the negative effects of standing waves in the bass frequencies.

Easiest place to start would be #1. Do you mind giving it a try and seeing how things work out?

[dguarnaccia]

Thanks Young and VA,

I did some more testing. Moving the XO up to 120 does help smooth things out, but the downside is the powered woofers and fast cones in the fronts loose their midbass slam.  I'm hosting an Audio party this weekend, and so AV123 sent me a second sub to try out (and show off of course) and the second sup did help smooth things out. I put the second sub on the back wall just to the right of center to position inversely to the other sub. I'll now I have one fairly deep, narrow spike at 90, but the rest has smooths out a bit. I'll do some more testing, but I figured I report back my initial findings.

Thanks for the feedback so far.

DG