Hi all!

I was wondering if bass traps or acoustic treatments in general help with some bad dips i am getting with my subwoofer.

it will help ... just like an EQ will too.

but the best solution to dips and peaks is moving the subwoofer to a better location. (or the listener's location)

I was wondering if bass traps or acoustic treatments in general help with some bad dips i am getting with my subwoofer.

Bass traps do three things:

* They reduce peaks
* They increase nulls
* They reduce ringing at bass frequencies

All rooms need and benefit from bass traps, but ribbit is correct that placement is important too. The usual procedure is to optimize the loudspeaker placements and listening position, then treat with bass traps.

--Ethan

Sorry for the noob question but what is a null? Also... i see you are an acoustics specialist. If I post pictures of my room do you think you can give me some suggestions?

Thanks

Sorry for the noob question but what is a null? Also... i see you are an acoustics specialist. If I post pictures of my room do you think you can give me some suggestions?

Thanks

Null is when you have an absence of sound at particular frequency. For instance, a bassist could be playing a scale, and you notice that one of the notes is very quiet compared to the others.

Or, for that matter, not even there.

Sorry for the noob question but what is a null? Also... i see you are an acoustics specialist. If I post pictures of my room do you think you can give me some suggestions?

Thanks

post your pics ... then shoot Ethan a private message.

he the man.

post your pics ... then shoot Ethan a private message.

he the man.

Thanks for the plug, but let me clarify something. As you can imagine, I get a lot of emails and PMs asking for personal help. I'm glad to help everyone, whether they're customers of my acoustic treatment company or not, but I have to draw the line at free one-on-one consulting.

So for questions not related to my company's products I prefer to answer in the public forum. That way, the effort I put into answering can help others, and they can benefit from the answers of others too. So please post questions here in the forum and I'll be glad to answer. If someone wants to be sure I see their post and comment on it, send me an email with a link to the post from the Contact page of the RealTraps site:

www.realtraps.com/contact.htm

I visit here only once per day, but I check my email constantly.

Thanks.

--Ethan

what is a null?

Here is the frequency response of a typical piece of electronic gear:

________________________________________________


And here is the (low) frequency response of loudspeakers in a room:

http://www.realtraps.com/art_etf1.gif

Any questions? :D

--Ethan

Hi Ethan,

Here is what I have. Thanks

http://i83.photobucket.com/albums/j299/zinje/speakers/P1030769.jpg

http://i83.photobucket.com/albums/j299/zinje/speakers/P1030770.jpg

http://i83.photobucket.com/albums/j299/zinje/speakers/P1030773.jpg

http://i83.photobucket.com/albums/j299/zinje/speakers/P1030776.jpg

http://i83.photobucket.com/albums/j299/zinje/speakers/P1030780.jpg

...So for questions not related to my company's products I prefer to answer in the public forum. That way, the effort I put into answering can help others, and they can benefit from the answers of others too. So please post questions here in the forum and I'll be glad to answer. If someone wants to be sure I see their post and comment on it, send me an email with a link to the post from the Contact page of the RealTraps site:

www.realtraps.com/contact.htm

I visit here only once per day, but I check my email constantly.

Thanks.

--Ethan

yup, that's what I meant.

Hi Ethan,

Here is what I have. Thanks


ooh, look at all those bare walls.

ethan is gonna have a field day with you. :p

Here is what I have.

Hoo boy. :eek:

If you're committed to good sound you'll need to move things around, because the setup you have now needs an extreme makeover. A wall on the left and none on the right harms imaging. Ditto for the lack of first reflection absorption. Then there's the couch right in front of a wall. That's the single worst place because in front of a wall is where the peaks and nulls at all frequencies are worst.

Without a floor plan it's difficult for me to suggest what should move to where. If you're unable to move things, my treatment plan is bass traps in corners including wall-ceiling corners (use stands where there are windows), first reflection treatment on the left in front of the window (or a REALLY thick curtain), and the most effective broadband absorbers possible over much of the wall behind you.

--Ethan

Ok so i was thinking if probably just putting a basstrap in the corner on the rightside of the TV and something on the backwall where the couch is. Do the corner basstraps have to go all the way up the wall? I can't really go all out because of the wife factor. Would it even have any major effect considering I will not be treating the whole room?

Ok so i was thinking if probably just putting a basstrap in the corner on the rightside of the TV and something on the backwall where the couch is. Do the corner basstraps have to go all the way up the wall? I can't really go all out because of the wife factor. Would it even have any major effect considering I will not be treating the whole room?

The more you do, the better it gets. It's that simple.

--Ethan

Zinge,

Wow, that is a tough room! Nice TV, though!

I know Ethan is going to hammer me for this :D but you might look into getting a parametric equalizer for your sub. It can often deal with dips in response, if they aren’t too bad, or aren’t truly nulls.

Any way you can post us a response graph? You already have the sub in what’s probably the best location in the room, so the problem might not be as bad as you think. It may be as simple as a little equalizing and re-doing the furniture to get yourself off that back wall, if you can’t “trap.”

Regards,
Wayne A. Pflughaupt

I don't know how to make a response graph. I just look at my SPL meter when I calibrate the subwoofer see the peaks and dips in a couple places. I am no audiophile by any means, so I feel that if there are peaks, it does not bother me because as far as I can tell everything sounds fine. It's the dips I am more worried about. I feel like I might be missing something. I would rather hear something than nothing at all :P

As far as equalizers go... i heard that it's better used to tame the peaks than raising. Maybe I am not understanding it correctly.

I don't know how to make a response graph. I just look at my SPL meter when I calibrate the subwoofer see the peaks and dips in a couple places. Well, you have an SLP meter and I see a laptop in your pictures. A few more bucks for a USB soundcard and you can measure your room response with REW, which can make a graph for you. Check the Home Theater Shack BFD / REW Forum (http://www.hometheatershack.com/forums/bfd-rew-forum/) for details.

I am no audiophile by any means, so I feel that if there are peaks, it does not bother me because as far as I can tell everything sounds fine. It's the dips I am more worried about. I feel like I might be missing something. I would rather hear something than nothing at all True I guess, but you don’t have to live with the peaks. They can effectively “drown out” all the frequencies not as loud.

As far as equalizers go... i heard that it's better used to tame the peaks than raising. Maybe I am not understanding it correctly. An old wife’s tale that never seems to go away. My EQ is using seven filters, four of which are set for boost in values ranging from 3-9 dB.

Regards,
Wayne A. Pflughaupt

My laptop has a port for a microphone. Is there something in a USB sound card that will make it work better? Do i just use a regular mic? What kind of eq do you have?

Sorry for all the Q's.

It's possible that the "dips" are only there because of the peaks caused by bass bouncing around, getting reinforced, and getting louder. An eq will let you bring the peaks down and flatten the response out. That way you'll be hearing ALL of the bass frequencies, not just the 2~3+ notes or frequencies that are way louder than the rest.

Traps will help a little, but at least in my experience, adding just a few won't fix frequency response so much as it will help get rid of ringing and boominess. It may sound okay now, but if you add some bass traps and hear what it sounds like after, you'll be amazed at the difference.


Also, have you tried the sub in the right corner on the other side of the TV? You can measure with your SPL meter, or with REW once you get that up and running (great software).

Except with an eq it really only works with listening position, whereas bass traps work everywhere. You can get perfectly flat response from your sub with an eq, but whats the point if you have more then one person listening and to everyone else it sounds like crap?

Jared

My laptop has a port for a microphone. Is there something in a USB sound card that will make it work better? Do i just use a regular mic? What kind of eq do you have?

Sorry for all the Q's.Hey, asking questions is how we learn! :D

You can probably use the mic from your SPL meter, if it’s the Radio Shack or certain Galaxy models. They have a RCA line-level output, so the soundcard’s mic input won’t work. From the REW Help Files (emphasis added): “[You will need] a soundcard (internal or external) which supports full duplex operation (simultaneous replay and recording) with line inputs and outputs. Inexpensive soundcards are typically adequate, a reference measurement is used to remove the soundcard's frequency response from the measurement. Examples of USB soundcards which have been found to work well are the Soundblaster MP3+, Soundblaster Live! 24-bit USB External and the M-Audio MobilePre-USB.”

As far as the equalizer, most of us use the Behringer Feedback Destroyer, dedicated to the subwoofer. It’s a budget pro-audio unit with twelve fully parametric filters per channel. The same link I provided before offers plenty of information on how to use it.

Regards,
Wayne A. Pflughaupt

Except with an eq it really only works with listening position, whereas bass traps work everywhere. Well, as Ethan noted above, traps reduce ringing (which more accurately is decay), increase nulls and reduce peaks. However, they will only partially eliminate the median and latter. Here are a couple of charts from the legendary Traps vs. EQ Showdown (http://www.realtraps.com/eq-traps.htm#Top) from Ethan’s web site:


http://www.realtraps.com/eq-traps/fc_empty.gif
Raw Response


http://www.realtraps.com/eq-traps/fc_17mondos.gif
Response w/ 17 RealTraps MondoTraps


As you can see – in this particular instance at least – a relatively large number of traps were best at attenuating decay (above about 30 Hz at least) and reducing nulls. Reduction of peaks was minimal.

So while traps can reduce peaks and relative lows, there is still much room improvement that an equalizer can accomplish. The combination of drastically smoothed response and attenuated decay will make for some smooth and amazingly tight bass. Even if you don’t have room for 17 traps, you’ll still find smooth response to be a big improvement.

You can get perfectly flat response from your sub with an eq, but whats the point if you have more then one person listening and to everyone else it sounds like crap? To begin with, the goal is improved response, not “perfect.” Anyone looking for “perfect” response can only hope to be eternally disappointed.

How well an equalizer works at locations other than the “sweet spot” is largely dependent on the room. In large, irregular rooms, like a family room open to other areas, I’ve found that equalizing at the “sweet spot” also gives excellent results at other room seating that is away from boundaries.

Smaller, perfectly symmetrical rooms are more of a problem. With these rooms, there is typically a “bass hole” of sorts in the dead center of the room. Move from that point towards any boundary and perceived bass levels and extension increases. So in these rooms response does often change considerably from one location to the next. Nevertheless, you will find that equalized response at non-“sweet spot” locations, while not “perfect,” will still sound drastically improved over non-equalized.

The REW program has an averaging function that gives a single chart based on several readings. The BFD has several memories for storing different response curves. So, you could set one memory for an averaged curve for when you have guests in the room, and another for the “sweet spot” for when you’re by yourself.

Regards,
Wayne A. Pflughaupt

Wayne,

You're doing a great job explaining, but I can add a bit more. (And you thought I'd "hammer" you... :D)

> Reduction of peaks was minimal. <

You have to take the improvement as whole - that is, what really matters is the total span from each peak to its adjacent null. Even more important is the bandwidth of the peaks. Wide peaks are far less damaging than narrow ones.

> [avoid boosting nulls is] An old wife’s tale that never seems to go away. My EQ is using seven filters, four of which are set for boost in values ranging from 3-9 dB. <

I'd love to see your subwoofer's distortion levels with and without those boosts in place. :eek:

Nobody says you can't increase the level of a null. The point is more that it increase distortion, reduces headroom, and makes things worse at locations other than where the EQ was adjusted for. If you reduce a peak the damage elsewhere is not nearly as bad as when boosting nulls. Nulls are far more localized than peaks.

Also, ringing is at least as damaging as peaks, and EQ does nothing for that. Even the fancier DSP room "correction" products like the Audyssey that claim to reduce ringing do not. In case anyone missed it, here's my report on what this device can and cannot do:

http://www.realtraps.com/art_audyssey.htm

--Ethan

Wayne,

Knew perfect was to strong a word, plus it is judgmental. My subs response from 90hz-22hz is +/- 2db which I would consider perfect as it is better then the manufacturer's spec.

As for eq causing problems in spots other then the sweet spot, I was referring to the pictures given instead of making a broad statement. The L shaped couch is against a wall, and therefore I would assume that eqing certain frequencies would cause havoc when you move along the couch, especially since you are moving from one wall to another..

Jared

Sorry for misunderstanding you, Jared. I agree, it will very likely be a problem equalizing with the “L” shaped couch in a corner like that. Still, it’s impossible for us to predict for sure – Zinge won’t know until he tries.

Regards,
Wayne A. Pflughaupt

Ethan,

Thanks for the compliment, and happy that I didn’t need the hammering. :D


Also, ringing is at least as damaging as peaks, and EQ does nothing for that. Even the fancier DSP room "correction" products like the Audyssey that claim to reduce ringing do not. Absolutely. There is nothing electronically that can be done for ringing, just like there’s nothing electronic you can do for higher-frequency reverberation. You’d think engineers who are smart enough to design something like the Audyssey would know that. :)

By the way, “ringing” is a pitifully inadequate term for what is essentially excessive low frequency decay times. To me the term evokes a highly shrill and irritating noise, like microphone feedback. Can’t you acoustician-types come up with something better? :)


> Reduction of peaks was minimal. <

You have to take the improvement as whole - that is, the total span from each peak to its adjacent null. Good point – thanks for that...

I know you won’t agree with anything that follows, Ethan, so it’s primarily for everyone else that might be seeing this. :D


I'd love to see your subwoofer's distortion levels with and without those boosts in place. :eek:

Nobody says you can't increase the level of a null. The point is more that it increases distortion, reduces headroom, and makes things worse at locations other than where the EQ was adjusted for. I’ll address the last point first, since it’s the easiest: “Not in my experience.” In every residential room I’ve ever equalized at a primary location, bass response improved at other locations, too. Again, at the ones away from boundaries, and not as well as at the spot the EQ was adjusted for. This was also the conclusion Terry Montick came to during the Traps vs. EQ Showdown (http://www.realtraps.com/eq-traps.htm#Top). Every one of the numerous “with EQ” charts presented show an improvement in response, even though equalizing was done for only one location. And despite the fact that Terry did a really bad job of equalizing in that test.

As far as EQ boost increasing distortion and reducing headroom: I wholeheartedly agree, but at the same time it’s not as cut and dried as that. How much of an issue it is depends on a lot of factors beyond simply boosting a filter.

First, distortion in the bass frequencies is largely inaudible. Most drivers themselves generate distortion figures well over 10%.

Second, if you’re running your sub at say, the 4:00 position then yes, you have no business boosting, because you’re virtually maxed out. But if you’re running your sub at only 10%, then boosting isn’t going to matter a wit. Basically, any electronic increase in gain, be it with an equalizer or simply turning up the sub, is going to reduce amplifier headroom and increase distortion (via increased driver cone movement).

On top of that, consider that movies, especially action flicks, have considerable low-end boost, applied at the production stage. With equalizers. As far as your subwoofer is concerned, EQ is EQ. It doesn’t matter if it comes from your favorite DVD or from your equalizer. Any distortion or headroom issues are the same either way.

Third, at the end of the day, boosting or cutting is largely academic. To explore that, let’s first consider these before and after charts recently posted at the Home Theater Shack:


http://www.hometheatershack.com/forums/attachments/bfd-rew-forum/2192d1171074633-help-15db-dip-24-40hz-leftnright.jpg
Raw Response


http://www.hometheatershack.com/forums/attachments/bfd-rew-forum/2193d1171074633-help-15db-dip-24-40hz-leftside-eqd.jpg
Response w/ several cut-only filters


Notice how much flatter response is below 20 Hz after equalizing with cut-only filters. That’s ultimately going to exact a headroom and distortion penalty - there’s no way around it.

To explain further, let’s consider a couple of common equalizing scenarios. For the first, let’s take a closer look at the charts above. Notice that this fellow had a couple of nasty peaks at roughly 22 and 35 Hz, which he reduced. Now, before equalizing, he was setting his sub level based on those peaks (we all do). You might think that he’s bought himself a lot of headroom by reducing those peaks. Trouble is, now he’s reduced his output by at least 9 dB, from about 86 dB at max (see blue line on the “Raw” chart @ 35 Hz) to 77 dB. So now his sub is going to sound weak, unless he increases its gain by at least that much to compensate. Well guess what? Say goodbye to the “free” headroom!

For our second scenario, let’s say the subject had reasonably flat response, except for a relative low of about 10 dB centered at 40 Hz. Not wanting to boost, he uses numerous filters to reduce everything else down to that 40 Hz depression. What has happened? Well, as before, his sub response is now too low, so he has to turn up his gain at least 10 dB to compensate.

Has he saved any headroom by not boosting? No. The situation this time is that he used the equalizer to electronically reduce the signal below 40 Hz, and above 40 Hz as well. Since he left 40 Hz alone, it is now a hotter electronic signal. That’s right – he succeeded in boosting 40 Hz by cutting everything else around it!

Needless to say, it would have been more efficient to simply apply a single filter to boost 40 Hz as needed, rather than use six or more to reduce everything else around it (and it would have taken at least that many, or more).

I think we can see that there is no free lunch. Any equalizing is going to exact a headroom penalty. It doesn’t matter if you're boosting or cutting. As such, you have to have headroom to spare going it. If you’re running your sub near max, don’t even think about equalizing until you get a more substantial sub.

Regards,
Wayne A. Pflughaupt

Here is my bass trap story.

Here is a graph of my sub(SVS-PB-10-ISD) Before bass traps
http://img401.imageshack.us/img401/9526/suboutphasemr7.jpg
Here is a graph of my sub response after adding two diy bass traps consisting of 2 pieces of 2" OC 703 fiberglass each. They are 2'x4'.
http://img401.imageshack.us/img401/4678/subtreatfinalbx1.jpg
Here is a pic of one of my bass traps
http://img85.imageshack.us/img85/3165/cornertrapms3.th.jpg (http://img85.imageshack.us/my.php?image=cornertrapms3.jpg)
I plan to make two more and have one in all four corners. The change in my room is astounding. I also have two diy 2'x2'x2" panels at my first reflection points and two behind my L and R Front speaker and going to add a 2'x4'x2" on my rear wall.
I have had no experience with EQing in my room but my room sound so much better. Bass is tighter and listening fatigue has been greatly reduced. I can really let my speakers and sub shine.

Here is my bass trap story.

Here is a graph of my sub(SVS-PB-10-ISD) Before bass traps
http://img401.imageshack.us/img401/9526/suboutphasemr7.jpg
Here is a graph of my sub response after adding two diy bass traps consisting of 2 pieces of 2" OC 703 fiberglass each. They are 2'x4'.
http://img401.imageshack.us/img401/4678/subtreatfinalbx1.jpg
Here is a pic of one of my bass traps
http://img85.imageshack.us/img85/3165/cornertrapms3.th.jpg (http://img85.imageshack.us/my.php?image=cornertrapms3.jpg)
I plan to make two more and have one in all four corners. The change in my room is astounding. I also have two diy 2'x2'x2" panels at my first reflection points and two behind my L and R Front speaker and going to add a 2'x4'x2" on my rear wall.
I have had no experience with EQing in my room but my room sound so much better. Bass is tighter and listening fatigue has been greatly reduced. I can really let my speakers and sub shine.
It would be a lot easier to compare the "before" and "after" responses if you used the same scales in each photo. Both your "X" and "Y" axes have very different scales in each photo. :confused:

Pink? Is that to improve the WAF? :D Also, the one trap is positioned in front of a door. Do you move it a lot?

I notice a baby carrier in one of your photos (http://www.flickr.com/photos/maxlongfellow/392797651/) and that the back of one of your panels is not completely enclosed, (http://www.flickr.com/photos/maxlongfellow/401043511/). I would urge caution that you keep the panels away from the kid(s) especially if they're not fully enclosed. Fiberglass is not a good thing for kids (or adults) to be exposed to, either on their skin or by inhalation.

Craig

Wayne,

> You’d think engineers who are smart enough to design something like the Audyssey would know that. :) <

LOL, I plan to quote you on that many times in the future!

> By the way, “ringing” is a pitifully inadequate term for what is essentially excessive low frequency decay times. To me the term evokes a highly shrill and irritating noise, like microphone feedback. Can’t you acoustician-types come up with something better? :) <

Ringing is the technically correct term - a large bell will ring at a low frequency. But I agree that "decay time" may explain better what's really happening, especially to those less technically oriented.

> I know you won’t agree with anything that follows <

Maybe I'll surprise you. :D

> In every residential room I’ve ever equalized at a primary location, bass response improved at other locations, too. <

Sometimes, but only if you equalize to reduce modal peaks (as opposed to non-modal peaks), and definitely not if you EQ a non-modal null. If you have the knowledge and experience to distinguish modal versus non-modal peaks and nulls, I agree you can make things better at more than just one place. I assume this is why the Audyssey setup has you measure at multiple places, so the software can figure out which frequencies have problems everywhere (modal), and which change frequency around the room (non-modal).

> And despite the fact that Terry did a really bad job of equalizing in that test. <

LOL, I ain't gonna touch that one...

> distortion in the bass frequencies is largely inaudible. <

If only.

> Most drivers themselves generate distortion figures well over 10%. <

Better modern subs are a lot lower than that.

> if you’re running your sub at say, the 4:00 position then yes, you have no business boosting, because you’re virtually maxed out. But if you’re running your sub at only 10%, then boosting isn’t going to matter a wit. <

The setting of the physical volume knob on a subwoofer has very little relation to how much power it's putting out!

> Notice how much flatter response is below 20 Hz after equalizing with cut-only filters. <

I care much more what happens between around 60 and 300 Hz.

> Any equalizing is going to exact a headroom penalty. It doesn’t matter if you're boosting or cutting. <

Actually, cutting peaks increases headroom.

Here's one thing you didn't mention, which helps make your point in favor of EQ:

Putting the sub in a front corner will excite the modal peaks and give an unnaturally higher output at those bass frequencies. Then you can cut those peaks with EQ, which increases headroom, lowers distortion, and brings the peaks down closer to match the nulls. My SVS is in a front corner, and I use its one-band cut-only EQ to reduce the worst length mode a few dB. That, along with a lot of bass traps, gets me to within a 10 dB window at the listening position.

My final point :D highlights what may be the biggest limitation of using EQ, even to tame peaks only. The main problem with peaks in an untreated room is their high Q (narrow bandwidth). This makes the notes boosted highly selective, and also creates the extended decay times that make a muddy jumble of a bass line. When you reduce a peak using bass traps you also lower its Q, so it's more of an overall LF boost than picking out one note from many and raising it 10 dB or more. EQ cannot lower the peak Q, so you still have the peaky response and ringing, and it's just at a lower level. This is why the 10 dB window I enjoy in my home theater sounds much better than a 10 dB window created artificially using EQ.

--Ethan

Great info here guys. Thanks! My plan right now is to get that USB sound card hooked up to my SPL so I can create a graph.

It would be a lot easier to compare the "before" and "after" responses if you used the same scales in each photo. Both your "X" and "Y" axes have very different scales in each photo. :confused:

Pink? Is that to improve the WAF? :D Also, the one trap is positioned in front of a door. Do you move it a lot?

I notice a baby carrier in one of your photos (http://www.flickr.com/photos/maxlongfellow/392797651/) and that the back of one of your panels is not completely enclosed, (http://www.flickr.com/photos/maxlongfellow/401043511/). I would urge caution that you keep the panels away from the kid(s) especially if they're not fully enclosed. Fiberglass is not a good thing for kids (or adults) to be exposed to, either on their skin or by inhalation.

Craig
Yes the color was picked out by the wife.
The panels are fully enclosed and I do move the panel by the door when not watching a dvd or listening to music.
Yes I was new using the eq software and was trying different scales. One day I will I re do it on the same scale.