# I Think I have Figured Out My Low End Low SPL Problem - Would Like Feedback as To my Theory



## marsx (Feb 16, 2010)

Hi

I posted another thread 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 opinions 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 10db (aside from one mode at 80hz, which comes up to the SPL at 1,000hz). Other

After doing much research, I believe I have found the culprit and would love opinions 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. 

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 in my system(of which I have tested at least two sets) including two different sets of speakers, one set (JBL 4410A Studio Monitors) 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 at the same level as the rest of the frequency range; however, as soon as I pull the mic back into the room, the SPL drops 10 db rather quickly compared to frequencies above 125hz or 150hz. 

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

Either way, I would love to hear your opinion.

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.

Thanks for your help.

Thanks,
Wade


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## AudioNut1962 (Oct 11, 2014)

Wish i had more time to reply. Having breakfast at my favorite weekend coffee spot and laptop has 3 % left.

In short, your room is physically not allowing low bass to be reproduced by it's size limitations. It takes 56 feet to produce a 20 hertz note which would mean a Room that is 27-28 feet long can produce that freq. I can do the math for you on your home when I get home. There is hope by the way!:sn:


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## TomFord (Jul 15, 2014)

Is that the only place you can put the sub & do you have it in the corner?

I'd get it away from the window if you can. Never heard of what the other poster suggested. Find it hard to believe without hearing more. 1 thing I did with mine that I believe would help you more is placing it on top of acoustic foam. Saw a design on Amazon that is was very simple to make opposed to spending 40$ since I already had what was needed. It was just a thin layer of plastic on top of the foam. Yet foam alone would help with what you have below. Granted it won't be a significant improvement most likely but it & the other acoustic treatment you need will double your output giving you the additional 3 db


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## AudioNut1962 (Oct 11, 2014)

According to the math your room can efficiently only produce an 82 hertz note. Without getting into 1/2 and 1/4 wavelength discussions, from experience small rooms always have played havoc on getting smooth low bass. I decided to post a link from a guy that I met 15 or so years ago. He has some serious room acoustics knowledge. I think after reading this article you will understand more of why your room size is the primary issue. Placement of your sub and listener position is about the best method to finding the sweet spot in your room without going homemade. There is another way to reproduce low bass in a small room but I must ask if the room is a dedicated room first! That should be a hint! A homemade....... 

Well,I tried to post the link. Need five posts first. Google positive feedback issue 13. Rives Audio. Let me know if you find it.


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## AudioNut1962 (Oct 11, 2014)

http://www.positive-feedback.com/Issue13/rives.htm

Here you go. Enjoy.


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## orion (Sep 18, 2009)

I would do the sub crawl first and find out where the best placement is and then try and use an isolation pad and see if it helps at all. With the size,of,your room you are going to have issues but try a few things,first and see , if it can get,you closer,to where you want to be


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

marsx said:


> 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 don’t see it. As I mentioned in your other thread, I have a nice computer system with a subwoofer set up in my home office, which is nearly the same dimensions as your room. What I didn’t mention there is that my office is on the second floor and there is a bedroom directly below it. My flooring is carpet over 1-1/2” thick wood plank. If your theory is correct I should have a significantly worse “broad range panel absorber” issue than you do, as the bedroom below is significantly larger than your crawl space. Yet, as I mentioned in the same thread, I have no bass deprivation issues that a subwoofer didn’t solve.

Not seeing the window as an problem either. My window is only perhaps 30% of the wall, but wouldn’t you think a 30% window open would be worse than a 75% window closed? Below are a couple of subwoofer graphs I measured. The second one was taking with not only the window wide open, but the door as well. As you can see, there is little appreciable difference between them.









*Sub with Window and Door Closed








Sub with Window and Door Open*​

Regards, 
Wayne


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

AudioNut1962 said:


> According to the math your room can efficiently only produce an 82 hertz note.


That’s curious; my room is the same size as the OP's and I can easily hear 28 Hz and lower sine waves generated from my subwoofer.




orion said:


> I would do the sub crawl first and find out where the best placement is and then try and use an isolation pad and see if it helps at all. With the size,of,your room you are going to have issues but try a few things,first and see , if it can get,you closer,to where you want to be


All the sub crawl will tell you is the location where the bass is loudest, not necessarily the most accurate. And really, the sub crawl became obsolete once REW came on the scene allowing people to make sophisticated and accurate measurements dirt cheap. As the OP mentioned in his other threads, he has REW. :T

Regards, 
Wayne


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## marsx (Feb 16, 2010)

Wayne,

 

Thank you for your response. I'm glad you posted graphs of your room. They gave me a point of reference to view the low end in my graphs. 

Here is an SPL graph I had on my laptop that I could upload to compare with yours. I can't take any measurements right now because my studio is in disarray. 

If you ignore what's happening below 70hz and just focus on where the SPLs are from 70hz and above on yours and mine, you have a rise of more than 10dbs from 70 hz to roughly 120hz, which is similar to what happens on my graph above (I may have different smoothing setting and this was a measurement of large freq. range). The big peak from approx. 130hz to 150hz, I can probably tame with more bass trapping; nevertheless, I just don't understand the low, low SPL below 70hz; especially compared to your room.

Nevertheless, thanks for providing your graph as it makes me feel better about the critical bass range around and above 65/70hz onwards. If you have any thoughts about what might be causing this, I'd love to hear them. (I've ruled out phasing, as my speakers are definitely in phase and, as I've said, I get similar graphs with two sets of speakers and two different amps (tried on each set of speakers); I've tried different preamps and a different mic as well. The only possibility I could think of is that perhaps my NS10s don't start generating strong bass until above 65hz, so maybe my JBL 4410a speakers have a problems with low end? However, each speaker has the same response and I've done a lot of research on them and they're supposed to generate strong bass starting at 45hz with the Freq. Range starting at 33hz. FYI, here is a quote from a major audiophile mag. review of the 4410a speakers when they came out: " The woofers provide a solid bass response that goes fairly deep."

I'm seriously confused. Any thoughts?

A Postscript: If you happen to have an SPL graph of your room from 20hz to 20,000, I would love to see the overall response of your room. If you don't, I understand.

Thanks again,
Wade


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

marsx said:


> The big peak from approx. 130hz to 150hz, I can probably tame with more bass trapping...


That’s actually very good response. That 130 Hz peak no big deal. A parametric filter EQing it switched in and out would make no audible difference with program material.



> I just don't understand the low, low SPL below 70hz; especially compared to your room.


Perhaps a full-range graph with no sub would be instructive. All graphs posted below are smoothed for 1/6-octave, which appears to be what yours was. As you can see, my speakers “dead end” just north of 100 Hz and have something of an exaggeration in the same 100-200 Hz range that yours do. 









*Swans M200 no EQ*​



> Nevertheless, thanks for providing your graph as it makes me feel better about the critical bass range around and above 65/70hz onwards. If you have any thoughts about what might be causing this [lack of extension in my room], I'd love to hear them.


Really impossible to say, every room is different and the rooms that were used for the reviews weren’t the same as yours. 




> However, each speaker has the same response and I've done a lot of research on them and they're supposed to generate strong bass starting at 45hz with the Freq. Range starting at 33hz.


 Well, my speakers are rated to 62 Hz and I recall seeing reviews that reported that their bass output, while certainly not room-rattling, was good enough that you could get by without a subwoofer. Well, you see what I got!




> A Postscript: If you happen to have an SPL graph of your room from 20hz to 20,000, I would love to see the overall response of your room. If you don't, I understand.


No problem. Probably could have saved you considerable anxiety if I had posted these graphs sooner, but I only generated them a week or so ago! Like I’ve been saying all along, a subwoofer is the solution to your problem. Hopefully these graphs will confirm that.









*Swans M200 / Velodyne SPL 10 RGB no EQ








Swans M200 / Velodyne SPL 10 RGB with EQ*​

Regards, 
Wayne


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## marsx (Feb 16, 2010)

Thanks so much for your response. It has been really helpful and appreciated and makes me feel much better about my room and system. 

I wasn't clear about one thing you said regarding EQing my peak between 130hz and 150hz. When you say: 

" A parametric filter EQing it switched in and out would make no audible difference with program material."

are you saying I SHOULD EQ it down or I shouldn't?

Regarding a Sub: I currently am driving the JBL 4410as with a 200 watt per channel into 8 ohms, Rotel 993. It currently has one empty channel that could drive a 200 watt passive sub, or I could get an active. What kind of subwoofer would you recommend? How many watts? Active/passive? Any particular brand or specific Subwoofer for my speakers? And, where would you set the crossover point at?

Again, your advice has been and will be enormously appreciated.

I look forward to hearing back from you.

Sincerely,
Wade


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

marsx said:


> I wasn't clear about one thing you said regarding EQing my peak between 130hz and 150hz. When you say:
> 
> " A parametric filter EQing it switched in and out would make no audible difference with program material."
> 
> are you saying I SHOULD EQ it down or I shouldn't?


Just saying that EQing it won’t make an audible difference. I mean, it’s only ~4 dB to begin with: 










Once you add a sub you’ll want a house curve (see my graph below), and at that point it’ll be wiped out, a peak of only a dB or two.

In my experience a lot of response anomalies that look bad on a graph are barely audible, if that. For instance, check my full-range graph below (that I posted on the previous page):










That dip at 2 kHz looks pretty nasty, doesn’t it? Six dB deep and one octave wide. However, when I play pure sine wave tones (generated courtesy of REW) at 1500 Hz, 2000 Hz, and 3000 Hz (i.e. at the center of the trough and on either end of it) they measured 85, 84, and 85 dB respectively! With music I don’t even notice a deficiency there. In fact, I used 6 parametric filters to improve response between the “No EQ” and “With EQ” graphs on the previous page, and most of them aren’t audible with music when I switch them out. Switching them in and out _is_ audible with pink noise (so I guess they’re contributing _something_), but not so much with program material. 




> Regarding a Sub: I currently am driving the JBL 4410as with a 200 watt per channel into 8 ohms, Rotel 993. It currently has one empty channel that could drive a 200 watt passive sub, or I could get an active. What kind of subwoofer would you recommend?


Depends. How low do you want (or need) to go? I wouldn’t do less than a 10-incher. A good-quality 10 should have no problem getting down to 30 Hz. If you need 25 or 20 Hz you’ll probably need a 12-incher. This is generally speaking, of course – there certainly are subs in these sizes that do better or worse than these figures. 




> How many watts?


Again, depends on now loud you want or need. In a room your size any decent active sub should get you all you need. With active subs, watts don’t really matter much because the sub and its associated electronics are designed and built as a system. All that ultimately matters is _output_. For instance, a sub in an undersized box that gets really low extension most likely has a very high powered amplifier to compensate for the inefficiencies necessary to get low output from a box that’s smaller than normally used for a driver that size, while a more conventionally-designed sub can get the same extension and volume with less amplifier power. You’d really have to read up on the physics of subs, you can get qualified info on them in our Subwoofers forums.




> Active/passive?


The great majority of off-the-shelf, pre-manufactured subs are active. The advantage they have is convenience for the end user: an all-in-one package that includes an amp and electronic crossover. Most passive subs are DIY. In addition to needing an outboard amp, they also require an outboard electronic crossover as well.




> Any particular brand or specific Subwoofer for my speakers?


It’s hard to go wrong with a good name-brand model _from a company known for its subs_, like SVS, HSU, Velodyne, Paradigm, etc. Some name-brand _speaker_ company’s subs aren’t all that great.




> And, where would you set the crossover point at?


Well, your room seems to brick-wall response at ~150 Hz, so that might be a good place to start.

Regards, 
Wayne


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## vann_d (Apr 7, 2009)

AudioNut1962 said:


> Wish i had more time to reply. Having breakfast at my favorite weekend coffee spot and laptop has 3 % left.
> 
> In short, your room is physically not allowing low bass to be reproduced by it's size limitations. It takes 56 feet to produce a 20 hertz note which would mean a Room that is 27-28 feet long can produce that freq. I can do the math for you on your home when I get home. There is hope by the way!:sn:


I feel this is a strange misunderstanding that has somehow propagated within the car audio community or, perhaps, used to propagate within the car audio community.

The reality is that room size has nothing to do with low frequency reproduction except to increase it! It is the phenomenon known as "room gain".

Out of curiosity, I read the article linked and I agree with all that was stated. The article does not seem to pertain to the arguments about small rooms not being able to reproduce low frequencies. It does, however, seem to give valid advice about room treatments for bass frequencies.


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