# Can Someone Look at my SPL Graph and Give me Advice on What's Going On with My Room?



## marsx (Feb 16, 2010)

Hi,
  

Above is an "All SPL" graph showing the general frequency response of my room with 1/6 smoothing from 45hz to 20,000hz (I also included a waterfall from 45hz to 500hz).

Notice how the bass seems to go from 45 hz up to 90hz just above 85db, then from 90hz to about 140 the dbs steadily rise, reaching a peak of close to 100db staying loud at about 95db through 450hz or more, then hoves around roughly around a baseline of 90db from 500hz to 3300hz, and then from 4kz to 20 kz it goes down from 85 db to land at 80 db in a fairly linear fashion.

I have a 14' x 11' room with floor-to-ceiling traps of 4" OC 703FRK in three of the four corners. (The 4th corner has doors, so no traps). 

Can you tell anything from this rather strange SPL graph. Particularly the low SPLs below 125hz, the broad peak from 125hz to 400hz, the stable sound pressure from 400hz to 3300khz, and the then the continuous dropoff from 4khz to 20khz?

I also offered a waterfall graph from 35hz to 500hz to offer some time info.

Any advice on what kinds of treatment I should consider next, to get the low end louder, to tame 125hz to 400hz, and what to do about the continuous dropoff above 4khz, if anything.

All advice would be greatly appreciated.

Thanks,

Wade


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## Tonto (Jun 30, 2007)

It looks pretty good to me, but I assure no I'm no expert on REW. I'm assuming this is without a sub. It looks like some ringing @ 43 Hz. This is a pretty long wave, I expect those 4" panals are just not thick enough, corner traps may do a bit more. A sub may also help boost that lower end. These are older speakers as well, how do you have them positioned in the room? And have you measured each speaker by itself? This might identify a tweeter problem. I'm sure someone with more knowledge will chime in shortly.


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## bpape (Sep 14, 2006)

At most, look at 1/12 octave to get a better feel for what your ear will actually hear. General level below about 125 seems low in general but hard to really say what's going on with any smoothing on. Where is your seat in relation to the length of the room?


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## marsx (Feb 16, 2010)

Hi,

Thanks for response. I have setup against the close to window wall, so I am in last third of long orientation of room. I am sitting just above 5 feet from window wall in long orientation(13.75'), so behind me there is an additional 8-9 feet. I placed the speakers all over room and found that this position gave me best stereo imaging. However, no matter where in the room and no matter what orientation, the spl below 125hz was low, no matter whether using my JBL 4410M my Yamaha NS10M (the originals), or even tried a pair of Yamaha HS50m (no subwoofer). I checked with 1/12 octave smoothing, and there are dips and peaks, but the overall level is still 5-10 db below everything up to 4khz. 

As I said, I have tried t rule out any specific equipment problems by trying two different amps, three different sets of speakers, two different calibration mics and two different preamps (and even an AKG414) as well as my ears. 

I also found that if I point the mic directly at the bass port of one of the 4410s from about a foot away, the spls stay fairly equal, but once the frequencies get above 125hz, the sound in the room definitely gets louder. There seems to be little doubt, that somehow, the room is acting like a broad range helmholtz resonator, sucking out the low end frequencies. Has anyone ever heard of this; is there anything I can do to counteract? Should I get a subwoofer - if so, should I add it to the NS10s or to the 4410s or is there a subwoofer that can be switched between the two for double duty?

I'm at a loss. As I said, one wall is almost all window; could that be sucking bass out? The other thing is that the floor is on top of a crawl space, could the crawl space act like a helmholtz resonator? I would have thought the crawl space would act more like a resonator and amplify the low end. But whether I'm looking at a meter from a mic or using my ears, there is no question that the room sucks the low end out. But then as I said from 125hz to 400hz, the room definitely is boosting a lot of the mid lows. For this my 4" bass traps should be of help and I could probably use more. Am I correct in this assumption?

Any help, still appreciated. If you think it would provide you with more insight, I'll post a snapshot of the SPLs with 1/12 octave smoothing.


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## bpape (Sep 14, 2006)

it would really help to have some pictures and.or a sketch of the room.


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## Wayne A. Pflughaupt (Apr 13, 2006)

Might want to check this post on how to properly scale your graphs. Your scaling for the FR graph is making things look better than they really are. And a waterfall with a 70 dB lower limit isn’t good for much. 

Other than the way the response graph looks, do you have an issue with the way things actually sound? Because it’s not unusual for a good-sounding in-room response to have a downward slope from lows to highs. The high-end droop could also be cause by poor measurement technique, like pointing the mic straight up while using a 0-degree calibration file.

Regarding the low end, if you have a room with symmetrical shoebox dimensions, they are notorious for displaying weak bass levels anywhere near the center of the room.

Regards, 
Wayne


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## marsx (Feb 16, 2010)

Hi Wayne,

Thanks for the response and I'll read the link you recommended regarding scaling my graphs properly. 

However, in response to your questions: First, yes, the SPL graph does represent roughly the way the room sounds, at least when listening to sine waves at different frequencies. For instance, when I use the sound generator in REW and play a sine wave starting at say 40hz and then hold the mouse on top of the up arrow so I can listen as the sine wave frequency moves up at a much slower pace than when taking a measurement, I definitely hear what I'm seeing; the bass sounds relatively quiet until the frequency gets above about 125-150hz and then between 125hz and 400 hz, it's definitely louder overall, with some very loud peaks every so often and then when the sine wave frequency gets above 500hz the loudness to my hears seems to taper. However, I don't notice the bass sounding particularly weak when I listen to music.

In response to the other quesions: I aim the mic at the ceiling and use 90 degree cal file from Cross-Spectrum. And, as I said, the same sound respose occurs with different speakers, different amp, different preamp. I have tried pointing the mic directly at the bass port of the JBLs from about 1 foot away, when I so that, the SPL of a changing sine wave frequency seems to stay fairly steady; however, as soon as I move the mic away far enough for the room to have influence; I can't stress enough, it's as if the room is sucking out the very low end from 30hz to 125-150hz, before it then gets wito about 400hz and without smoothing from 150hz to 400hz there definitely are some big peaks and nulls that you can see and hear. But though there are slight peaks and nulls below 150/125 (somewhere in there), the overall spl shows lower and sounds lower. I am at my wits end on this; and, as I said, since it happens with speakers that are rated with a Freq. Range of +/-2db from 45hz and a different set which are rated at Freq. range of 60hz to 20khz with +/-2 or 3db (not sure), I know it's not the speakers.
. 
In regards to your questions regarding the room and where I sit, the room is not square and not even an true rectangle, as one of the long walls begins to taper inwards starting at halfway point by about 20 degrees. And, also, I am situated close to, and facing, the wall on the long end of the room where half of the area of the wall is basically window (covered by sound blankets). Could the windows be sucking bass (the speakers being close to and in front of the windows, with windows behind). Further, I am not near the center of the room at all (at least relative to the size of the room). The room is 13.75 feet long in the direction I am oriented, and I am sitting just over five feet from one wall. 

I have a question about something you wrote: when you say " Because it’s not unusual for a good-sounding in-room response to have a downward slope from lows to highs," do you mean the lows are like mine in many graphs starting low and sloping up as it gets louder or do you mean the reverse?

Thanks for your feedback, any other thoughts would be most welcome.

Sincerely,

Wade


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## Wayne A. Pflughaupt (Apr 13, 2006)

marsx said:


> However, I don't notice the bass sounding particularly weak when I listen to music.


That’s curious, I’d think that bass response measuring dead below 125 Hz would definitely sound weak. That makes me wonder about your measurement technique: Are you using the standard REW sine wave sweep that takes maybe two or three seconds to complete? Have you tried using the pink noise option to see what that gets?




> I aim the mic at the ceiling and use 90 degree cal file from Cross-Spectrum.
> I can't stress enough, it's as if the room is sucking out the very low end from 30hz to 125-150hz, before it then gets wito about 400hz and without smoothing from 150hz to 400hz


Mic orientation issues would only come into play at the upper frequencies, not the bass (you mentioned the high end droop in your first post, that’s why I asked). Hence, 90-degree measurements are generally not recommended for full-range measurements because they can get questionable results above ~2 kHz.




> In regards to your questions regarding the room and where I sit, the room is not square and not even an true rectangle, as one of the long walls begins to taper inwards starting at halfway point by about 20 degrees.
> Further, I am not near the center of the room at all (at least relative to the size of the room). The room is 13.75 feet long in the direction I am oriented, and I am sitting just over five feet from one wall.


Basically the bass “dead zone” applies to any room, no matter what the shape; it’s just worse in symmetrical rooms. Still, your listening position relatively close to the wall should overcome that. I think I’ll echo Brian’s request for some pictures and a floor diagram, and I’m interested to see your replies in the first paragraph about your test signals for measurement.




> I have a question about something you wrote: when you say " Because it’s not unusual for a good-sounding in-room response to have a downward slope from lows to highs," do you mean the lows are like mine in many graphs starting low and sloping up as it gets louder or do you mean the reverse?


As I said, “downward slope *from* lows *to* highs – IOW, just what your graph shows. You might want to take a look at my house curve articles – see my signature. :T

Regards, 
Wayne


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## marsx (Feb 16, 2010)

Dear Wayne,

You posted a few responses to my thread which was entitled - " My Room is Eating Low End - From 45hz -150hz - Any ideas to help"

I believe I have figured out the problem after much reading and would like to hear your opinion on the matter. As I posted, my room (13.75' x 11.25' x 8') demonstrates a significant overall lower SPL from 20hz to about 125hz of about 10dbs. There is one mode at 80hz, which comes up to "unity" (i.e., SPL at 1,000hz), but otherwise the low ends is substantially lower. After doing much research, I believe I have found the culprit and would love your opinion of my analysis and, if you agree, if you have any ideas of how to deal with it. I believe the bass is escaping the room in two ways. First, the wall behind the speakers is about 75% window (covered with thick moving blanket). Bass definitely can escape there, as you can hear it outside. Also, and, I believe, more importantly, the carpeted floor has an 18" crawl space beneath it. I believe the floor, which is made of 1" thick wood slats, is acting like a broad range massive panel absorber, sucking the bass out of the room (along with the back window). I cannot find any other logical explanation, having ruled out the all other components (of which I have tested at least two sets) and two sets of speakers, one set which has a 10" woofer and is rated at 45hz - 20khz +/-2db. Further, if I point the calibration mic right at the bass port of the speaker and keep the mic no less than a foot from the speaker, then the bass SPL is roughly equal to the rest of the frequency range; however, as soon as I pull the mic back into the room, the SPL drops 10 dbs rather quickly. 

I would be interested in hearing your opinion of this theory; if you think it holds water. If you do agree, do you think there is anything I can do (a subwoofer, or just a boost of the whole low end with EQ). 

Either way, I would love to hear your opinion.

Thanks for your help. This has me very preoccupied and before I move further with measurements or room treatments, I have to solve this broad low end frequency range low SPL problem.

I hope you have a chance to respond.

Thanks,
Wade
Read more: http://www.hometheatershack.com/for...o=1&photoplog_searchquery=marsx#ixzz3EDhG90Sa


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## bpape (Sep 14, 2006)

While the window will certainly pass some bass out of the room, not that much. And the floor, generally if anything with a 'springy' floor, you'll end up with a peak, not a wide dip like that.


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## marsx (Feb 16, 2010)

Thanks Bryan!

Any thoughts on what could cause weak sound pressure below 125hz? BTW, when I can I will post the SPL graph without smoothing, but I can't get to that computer right now. I can say that there are a few nulls and a couple of peaks below 125hz, with the highest peak at 80hz, buy that peak just reaches the average level of SP for frequencies above 125hz, while the nulls are quite low. I don't have a lot of resonant or cancelled frequencies below 125hz, just overall lower sound pressure, as clearly reflected in the smoothed graph above. (Some have advised a subwoofer, but from everything I've read, that will just make things sound worse in my fairly small, rectangular room.)

I should mention, however, that when I listen to music I am familiar with, the low bass frequencies don't seem weak, but then I listen to classic rock, not electronica or rap. Do you think the low SPLs in the low end is a problem I should worry about, or am I over thinking this? 

On another "note", any advice on the continuous SPL drop starting above 3500hz and continuing through 20khz?

Any advice would be greatly appreciated.

thanks
wade


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## bpape (Sep 14, 2006)

My gut tells me that the speakers are just not capable of filling the room all that well #1. #1 - if you don't look at it as a wide null but more a peak (narrow and broader) from about 125-400, then it's a different story. If you get rid of that one single peak about 125, then you're essentially at +/-5db which is what you strive for in a non-purpose built space. If it were me, I'd be concentrating on looking for what is giving you that peak and the generally hot level up to 400.

You can do a sub most certainly and it pretty much never will hurt you more than it can help in a situation like this AS LONG AS you're willing and able to put it where it needs to be. If not, then it can make things worse certainly.


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## Wayne A. Pflughaupt (Apr 13, 2006)

marsx said:


> Dear Wayne,
> 
> You posted a few responses to my thread which was entitled - "My Room is Eating Low End - From 45hz -150hz - Any ideas to help"
> 
> I believe I have figured out the problem after much reading and would like to hear your opinion on the matter. As I posted, my room (13.75' x 11.25' x 8') demonstrates a significant overall lower SPL from 20hz to about 125hz of about 10dbs.


 My office is almost exactly the same volume as your room and I have no problems getting good low end down to 30 Hz, even with the door open.

I think Bryan nailed it when he said “My gut tells me that the speakers are just not capable of filling the room all that well.” I mean, your Yamaha HS50 speakers only have 5” woofers, and the NS10’s only have 7-inchers. You simply can’t expect much bass much below 125 Hz with speakers like that. Sure, your JBL 4410s should do better than that, but as mentioned in your other thread, if you’re sitting anywhere near the center of the room you aren’t going to get much low end from them either.

So how am I getting good low end in my office that’s the same size is yours? Simple: I have a good 10” subwoofer. If I turn it off and just run my desktop speakers with 5-1/4” woofers? Not much happening below 100-125 Hz - no surprise.

I hope this doesn’t sound rude, but IMO you’re chasing your tail trying to figure out what’s wrong with your room (if indeed that is the issue). In the unlikely event that there is a fundamentally problem with it, it will probably require a massive reconstruction to fix it, and I doubt you’re willing or able to do that.

You can easily solve this problem with a subwoofer, it’s as simple as that. It’s a tried-and-true approach that’s been working great for audio applications for more than 25 years now: The mains can be located for optimal imaging, and the sub separately for optimal bass performance. Cross it over at the usual 80-90 Hz and all your bass problems will be relegated to the sub, which will make them easy to deal with. You’ll be able to locate it for best response, and then clean up with a parametric EQ and/or bass traps. Then turn it up loud as needed to compensate for that middle-of-the-room bass “hole.” Bingo, you’re in business. :T 

Regards, 
Wayne


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## Tonto (Jun 30, 2007)

Agreed, which is exactly what I was hinting at back in my first post. 

Do you have a friend (with a pair of more capable speakers) that would let you borrow them to try in your room? Might be the fastest/easiest way to test our theory. And my curiosity is peaking now.


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