Frequency response - AVS Forum
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post #1 of 14 Old 04-19-2013, 03:46 AM - Thread Starter
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In trying to compare different subwoofers and looking at their frequency response specs, what number should be used as a guideline for the lower value? For instance, some subs state that the frequency response is 20-120hz, well the AVR will cutoff the hz above 80-90 so anything above that for me doesn't factor in. Problem is how low is low enough, and even if it gets to say....20-25hz, is it not also important to know/see the frequency response curve to check what frequency the roll off starts at? Do I need to worry about this at all?

If the AVR has EQ like YPAO or Audyssey correct for deficiencies?
Thanks!
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post #2 of 14 Old 04-19-2013, 04:15 AM
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The low number tells you the extension and is helpful for picking out a good HT subwoofer. A lot of subwoofer do not have published frequency response graphs. The upper number also tell you how easy it will be to integrate the sub with the mains. Total output is also important. Others will chime in and add more.

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post #3 of 14 Old 04-19-2013, 04:31 AM
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In theory - if not always in fact - subs are rated to play a test level of output with a variance of no more than +/-3dB within a given range of frequencies. Within that range, peaks will be no louder than 3dB and nulls will be no quieter than 3dB relative to the test level of outptput. This is what is meant by a rating of, say, 20-150Hz +/-3dB.

How low is low enough is up to you and your budget. For music, a sub that extends to ~30Hz @ -3dB is probably fine. For movies - in order to really take advantage of LFE content - extension to 20Hz @ -3dB is, IMO, a minimum.

If your AVR:
- handles bass management (including crossovers), you don't need to worry about the low-pass filter (LPF, or "crossover") on the back of the sub (usually, you either max it out or, if the option is available, you disable it);
- does not handle bass mangement, you use the LPF on the sub to blend the sub with your mains.

Audyssey, YPAO (Yamaha) and MCACC (Pioneer) are various flavours of room correction software. Roughly speaking, they will:
- adjust the distances (relative to the listening position) and levels of your speakers and sub(s); and
- EQ your system to account for your room's characteristics (that may causing playback to deviate from "flat").


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post #4 of 14 Old 04-19-2013, 05:46 AM
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Quote:
Originally Posted by ainsworth View Post

20hz, well the AVR will cutoff the hz above 80-90 so anything above that for me doesn't factor in. Problem is how low is low enough, and even if it gets to say....20-25hz, is it not also important to know/see the frequency response curve to check what frequency the roll off starts at? Do I need to worry about this at all?
You do. I'd avoid any sub that you can't find a measured response chart for somewhere. If they say it has 20Hz response, and that's actually -10dB at 20Hz, it doesn't have 20Hz response.
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If the AVR has EQ like YPAO or Audyssey correct for deficiencies?
Not that much. If it's down -10dB at 20hz then it will require 10dB of boost at 20Hz, which requires ten times the power from the amp and three times the excursion from the driver, which could lead to epic fail. If you want true 20Hz response even accounting for room gain you want response that's no more than -6dB at 20Hz.

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post #5 of 14 Old 04-19-2013, 06:32 AM
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Quote:
Originally Posted by ainsworth View Post

In trying to compare different subwoofers and looking at their frequency response specs, what number should be used as a guideline for the lower value? For instance, some subs state that the frequency response is 20-120hz, well the AVR will cutoff the hz above 80-90 so anything above that for me doesn't factor in. Problem is how low is low enough, and even if it gets to say....20-25hz, is it not also important to know/see the frequency response curve to check what frequency the roll off starts at? Do I need to worry about this at all?

Don't think that frequency response is the sole measure of a speaker or subwoofer. Dynamic range is at least as important.

A sub that works well down to 40 Hz is good for most music as there are only a few instruments that reach lower.
A sub that works well down to 30 Hz is good for almost all music as there are only a very few instruments that reach lower.
A sub that works well down to 20 Hz is good for all music it is the very rare instrument that reaches lower, but further bass extension can matter for sound effects and the like.
A sub that works well down to 10 Hz is a truely amazing thing but its favorable qualities are not always all that obvious.

But response down to XX Hz means nothing unless the response is clean, and this is what separates the boy subwoofers from the men's subwoofers.

IOW, you can have a $200 subwoofer and a $2,000 subwoofer that are both "Flat down to 20 Hz", but they are very different things to listen to. The differences are actually pretty extreme. I can pretty well guarantee that the best $200 woofer that responds down to 20 Hz lacks the ability to generate enough clean at that SPL to be audible during a loud passage in music or a movie.

AFAIK the best data to use to judge subwoofers that is generally available is known as "CEA 2010 Maximum" and a large cache of it can be found here:

http://www.audioholics.com/education/loudspeaker-basics/subwoofer-measurement-data#.UXFDIaKG18E

The usual criteria for "clean response" among subwoofers are SPL for 10% THD and freedom from compression.

Taking as our exemplary low cost subwoofer the $329 BIC ACOUSTECH: PL-200 we find that 20 Hz it has a clean dB rating from 84 to 87 dB.

Problem is that the threshold of hearing @20 Hz is about 74 dB SPL which basically means that the limit of clean output from the (highly rated) BIC ACOUSTECH: PL-200 is barely audible when playing a pure tone. In the midst of a loud sound effects scene in a movie or an orchestral climax, it isn't going to be noticed all that much.

Taking as our exemplary expensive subwoofer the SVS PB-13 Ultra tuned to optimize 20 Hz operation we find more like 110 dB SPL. This is 25 dB or subjectively maybe 6 times louder. In the midst of a loud sound effects scene in a movie or an orchestral climax, it is probably going to be noticed to say the least.

Another way to look at it is that it would take something like 40 or more PL-200s to produce the same clean output @ 20Hz as one PB-13. In terms of what you actually get in terms of SPL @ 20 Hz, the SVS might be cheap at twice the price! Economies of scale!

Just for grins, I have at least 3 friends who live nearby and have large custom subs that are the equivalent of 4 or more PB 13's.

So, you pays your money and your makes your choice. At least you might have some idea about what to expect.
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If the AVR has EQ like YPAO or Audyssey correct for deficiencies?

The main point is that Eq can correct frequency response, but it does zero for dynamic range. Not to diminish the value of eq because it can help with any sub no matter how much dyanamic range it has, by getting the best possible bass extension.

Even within just the realm of frequency response, these peoduct vary quite a bit. Please check on the threads on AVS that are related to the specific product. Audyssey, MCACC and YPAO are families of products and all versions that you may encounter of them are not the same, to say the least!
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post #6 of 14 Old 04-19-2013, 10:14 AM
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Not that the PL-200 measures anything like +-3dB down to 20Hz
http://www.avsforum.com/t/1350479/bic-acoustech-pl-200-data-bass-test-results

And BIC just quotes a "mystery" frequency response down to 22Hz.
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post #7 of 14 Old 04-19-2013, 12:17 PM
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Originally Posted by Joe0Bloggs View Post

Not that the PL-200 measures anything like +-3dB down to 20Hz
http://www.avsforum.com/t/1350479/bic-acoustech-pl-200-data-bass-test-results

And BIC just quotes a "mystery" frequency response down to 22Hz.

I can probably fix that response problem with a parametric eq. Audyssey Mulitieq XT32 can probably do that as well. But, neither of us can fix the lack of dynamic range.
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post #8 of 14 Old 04-20-2013, 01:17 PM - Thread Starter
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Just wanted to say "Thanks!" for the Great explanations! and for the links. I have reviewed these and my appreciation is even greater than before that there is a lot of engineering that goes into subwoofer design. I have pretty much decided to get the SVS PB-1000 (it was not listed but several other SVS subs were), but I guess needed some more data that the extra cost was worth it to me. Besides all the other valuable information in this thread, the link to the subwoofer spreadsheet seemed to indicate one or more subs with 12" woofers were only certified to a small room classification? Which was noted as <1500 cubic feet? Maybe they will test the PB-1000 (since it is new)?
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post #9 of 14 Old 04-20-2013, 04:09 PM
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As to the OP,

The response is just as important as what levels can be reproduced at that response. Ideally, you should really be shooting for the ability to play reference level, which calls for up to ~125dB out of the LFE channel+mains when using bass redirection, across the entire frequency response of the LFE channel spec (3-120hz according to Dolby).

If you just want to recreate the LFE experience you can get at the best theaters, shooting for 20hz is fine. To faithfully playback essentially all the content on a disc, you'll want flat (+/-3dB) response to at least 5hz. It's actually not that hard or expensive or big if you DIY with proven builds.

If you build it, you can approximate the frequency response in your room before you ever buy a thing! smile.gif I strongly recommend a DIY build where you can model the response before you get it in room, measure your room before you build, and measure + EQ the sub(s) in your room after you build.
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Originally Posted by eljaycanuck View Post

Audyssey, YPAO (Yamaha) and MCACC (Pioneer) are various flavours of room correction software. Roughly speaking, they will:
- adjust the distances (relative to the listening position) and levels of your speakers and sub(s); and
- EQ your system to account for your room's characteristics (that may causing playback to deviate from "flat").

Just wanted to correct one piece of info: Pioneer's MCACC does not do ANY subwoofer EQ at all.


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post #10 of 14 Old 04-20-2013, 07:02 PM
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Just wanted to correct one piece of info: Pioneer's MCACC does not do ANY subwoofer EQ at all.
Thanks for catching that error. smile.gif

(For some reason, I was under the impression that MCACC did perform limited sub EQ-ing.)


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post #11 of 14 Old 04-20-2013, 10:26 PM
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Pioneer MCACC corrects for standing waves in the room which is a different approach compared Auddysee. MCACC has filters for the sub that tackle particular frequencies similar to a parametric eq (Frequency, Q and ATT). There are also filters for the center and main speakers.

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post #12 of 14 Old 04-21-2013, 06:07 AM
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Pioneer MCACC corrects for standing waves in the room which is a different approach compared Auddysee. MCACC has filters for the sub that tackle particular frequencies similar to a parametric eq (Frequency, Q and ATT).
Do you have a link to an official-ish page or doc that discusses this? After reading nube's post, I did some Googling to try to find something that details how MCACC works with subs, but I came up empty.

Thanks! smile.gif


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post #13 of 14 Old 04-22-2013, 09:02 PM
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Originally Posted by eljaycanuck View Post

Do you have a link to an official-ish page or doc that discusses this? After reading nube's post, I did some Googling to try to find something that details how MCACC works with subs, but I came up empty.

Thanks! smile.gif

Download an owner manual on a model like the SC 37. page 106-107.

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post #14 of 14 Old 04-23-2013, 04:40 AM
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Download an owner manual on a model like the SC 37. page 106-107.
Will do, thanks! smile.gif


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