Do bass traps produce noticeable audible difference?

Bass traps absolutely improve the sound of music, whether regular stereo or the music in a movie sound track. In most rooms the improvement comes across as more bass, with less change in bass amount and quality at different locations around the room. Bass traps also make bass instruments clearer, so you can better hear the individual notes. I'm not sure what you mean by blending a subwoofer with the other speakers, because that depends in part on placement and the crossover frequency.

You can hear the improved sound quality with acoustic treatment (not just bass traps) in this video:

Hearing is Believing

--Ethan

+1. Ideally you'd measure your room to figure out where the issues are and how big they are before adding bass traps. If the issues are in the low bass (<100Hz) other solutions such as multiple subs and/or EQ are more cost effective in my opinion and less visually intrusive. But regardless of that nearly all rooms need bass trapping to deal with the 100-300Hz range where a lot of instruments and voices have the most energy.

When you send a test signal through your speakers that sweeps the frequency scale, the signal itself is equal volume at all frequencies (looks like a straight line), but the in-room measurement has peaks & dips (looks like a roller coaster). The up & down response you see is a result of the room reflecting sound back, which interferes constructively (peaks) and destructively (dips) with the direct sound from your speakers.

Those peaks tend to dominate what you hear, making sounds at those frequencies really loud, which masks sounds at other frequencies that are quieter. If you listen to a recording of a bass guitar, you'll wonder why you only hear some of the notes. It's a sobering exercise to listen to a recording through a pair of headphones and then listen through your speakers to hear what details have been covered up.

If you can smoothen out the response, you'll hear all sounds more or less equally. Which means that sounds that used to be covered up will now be audible, letting you hear much more detail in the bass range. Listening to that bass guitar recording again, you'll hear all those notes that had been masked by the loud peaks and buried in the dips. Meanwhile, your friends will be wondering how you found such an articulate and detailed sounding subwoofer, not suspecting that you tuned the room and not your sub.

I absolutely fully agree with what sdurani has said above. Getting a smooth response is the key! This means measuring the frequency response of your room to start with.

Otherwise everything else is just a guess.

When I think of a residential listening room with problematical bass response I think of a number of different audible problems:

(1) The sound is out of balance, and the bass, mid bass, midrange and treble or some of them have incorrect balance. The music generally sounds thin, boomy, tinny, thick, forward, recessed, etc. Differences in the natural balance of recordings is overemphaized which may leave you with the sense that some recordings are strikingly good and others are very poor.

(2) Bass sounds seem to drone on, instead of having reasonable articulation. There is a loss of the sense of hearing different instruments and voices and instead there's just this boomy muddled hum. Vocals and instrumental solos get lost in the backup instruments. Dialog gets lost in environmental sounds.

(3) Sounds in certain parts of the bass region may be withdrawn or overemphasized. This is most noticeable when a musical scale or part of one is played on a bass instrument. Usually the musician plays the notes so that they are equally loud or follow some general progression of increasing or decreasing. Under damped resonances in the room are heard as the intensity of these notes rising and falling illogically, and some notes may even seem to disappear while others stand out excessively.

The music and dialog is easy to listen to without straining to hear some sounds that are getting lost or having to ignore other sounds that are unnaturally loud.

Yes, of course. They may also improve the consistency of the sound throughout more areas of the room instead of just a few tiny sweet spots.

If you listen to the Earl Geddes lecture I posted in the speakers and also the subwoofer forum earlier this week, he will somewhat bombastically say that bass traps don't work, and then sort of clarify himself by saying that they don't absorb bass but rather have their strongest effect in the upper bass and lower midrange regions. There is some truth in this because by cleaning up response above say 60 Hz, we can start really hearing what's going on at say, 30 Hz. The ear's sensitivity goes away as the frequencies go down and we need to clear away and better control what is happening at upper frequencies to really enjoy the deep bass sounds. Thing is that really good deep bass improves our perception of the entire frequency spectrum. Cleaning up the bass can make the treble sound better.

If you have well trained ears the need for measurements is reduced. However most people with well-trained ears who can effectively diagnose problems by ear still like to take measurements because it makes it easier to get good results.

For people who are just getting their feet wet in audio, measurements are a real boon because they don't depend on having trained ears. Learning how measurements and perceived sound quality work together can shorten your learning curve.

with all due respect to him, it sounds like simply another case of operator error regarding proper design of LF absorbers - be it of velocity-based porous absorbers or pressure-based resonant.

any small residential space can benefit from LF absorption.

for typical DIY application of broadband porous absorbers (eg, pink fluffy fiberglass, mineral wool, owens corning rigid fiberglass, etc), measurements are not initially needed. size and sufficient thickness are key variables in a porous LF absorber which affect the LF roll-off of their effectiveness.

measurements can be used to experiment with listening position and sub(s) placement, to find the best practical 'starting point' response within the room. they can also be used to identify the effectiveness of the treatments (LF absorbers), and to also experiment with their placement for maximum effectiveness.

if you have a particular modal issue (eg, axial mode) - these are best tackled with pressure-based resonant absorbers, of which measurements are required to identify the troublesome mode(s) such that the treatment can be designed appropriately.

porous LF absorbers (which is what you will commonly see here), do not require any 'tuning' - they are broadband absorbers and do not require measurements to construct and place.

Localhost. Can you explain a little bit about what a "pressure-based resonant absorber" is and how it is constructed? Are these different that Low Frequency Porous absorber? If so, how are they different?

Also, what is a good material to use when building a set of bass traps? I know that OC703 is optimal with wall mounted absorbers, but I have no idea of how to construct a set of bass traps. An advise?

Also, can anyone post a link to some good sources for OC703 mail order?

"pressure based resonant absorber" combines two concepts that might be separated for clarity.

"pressure based" means an absorber that works well in areas where air pressure is high and velocity is low such as at a wall.

"Resonant absorber" means that the absorber works best over a relatively narrow band and absorbs energy by means of a damped acoustical or mechanical resonance.

Here is an example:



The holes in the perforated metal sheet form resonant chambers of sorts.

Porous absorbers tend to be broadband and work best were the air velocity is high such as spaced from a wall.

The best material depends on the specifics of the rest of the trap. Deep traps work best with less dense absorptive material. Dense material such as 705 are best for absorbers that are only a few inches thick.

First try to get it locally. Most regions have a distributor that caters to contractors. Thermal insulation is an example of Low density absorptive material. Google is your friend!

While you are Googling you might want to take a look at Chris Whealy's Excel spreadsheet.

http://www.whealy.com/acoustics/Porous.html

Yes, an expert consultant (or vendor) can tell you what to get and where to put it just by seeing photos of the room. Measuring isn't truly needed, though it never hurts to 1) see how bad things are before treatment, and 2) see hard evidence of how much better it got after treatment. Not that your ears won't know!

--Ethan

If you want to learn how this all works, here's a link to the Master Handbook of Acoustics. Not sure why this isn't more popular...
http://andrealbino.wikispaces.com/file/view/Master+Handbook+of+Acoustics+-+5th+Edition+-+F.+Alton+Everest,+Ken+C.+Pohlmann.pdf

The critical paragraph for new folks like you who hear people talk, but can't seem to hear the problem in their room:
Reading this paragraph confirmed suspicions I had regarding my above-grade, well paneled room, with open basement below and attic above, and three free-standing walls. Room construction and dimensions matters tremendously in the bass range, and room furnishings and content affect higher frequencies. They may not be terribly effective, but size matter. The Sabine equation, (Absorbance = absoprtion coefficient X Area), tells us that large structures don't need to be very effective to have large absorbance.

The final bit is that absorption coefficient is a function of frequency. If you do have acoustic issues, the treatment should be tailored to the need. Adding absorption at frequencies where it's not needed just creates a different problem. Page 219-220 of the link above has a nice case study for bass mode reduction.

This is the biggest reason to measure your room, so you treat actual problems using acoustic devices designed to address the frequency range of interest, with minimal collateral damage. If you have a room whose RT(frequency) is a straight line with a slight downward slope in the 0.3 sec. range, there's nothing to fix, but lots to break.

HAve fun,
Frank
Edited by fbov - 1/31/13 at 11:06am

RT and Sabine's equations are not relevant in an acoustical space that lacks a statistically random-incidence reveberant sound-field such as our residential rooms. RTxx is also invalid in any space where the measurement is not taken well past Dc and with a true omni-source.

the waterfall/CSD will clearly detail the LF decay times within the modal region (modal ringing).

You can either PM me, or start a dialog with my associate Jim via our Contact page:

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

We do not over or under suggest.

--Ethan

You can start out without measurements but since the price of admission and ease of use is so good now with packages like Room EQ Wizard, XTZ, Omnimic it really doesn't make any sense to me not to measure. For less than the price of one 'bass trap' you can get yourself set up with REQ or if you are a beginner and value 'plug and play' and ease of use (but accept the software limitations this implies to keep everything simple) with XTZ or Omnimic.

I see measurements are absolutely necessary, otherwise how do you know what the problems are and how do you know when you have resolved them? Without measurements you are shooting blind, especially with bass trapping as the bass issues vary hugely from room to room and are dependent on many factors including listener, sub, speaker placement, room size, room dimensions, standard room or open plan, etc. If you have a big null at 50Hz and a big peak at 30Hz then bass trapping isn't going to do much for you unless you are using either custom built products or the higher priced items like the MSR Springtrap or RPG Modex Plate.

I think its a given that if you are doing your own system tech, want the best possible sound quality in your context, and are spending more than a $grand or two for the system, that there is no question about whether you will have a measurement setup, just when.

One of the questions I am considering is whether or not one can add the measurement setup to the system before or after you obtain the $500-600 AVR with Audyssey XT32 and get as good results for appreciably less money.

Yes, of course measuring is useful. I do this for a living. But it's not strictly needed. Believe it or not, there are many people who either don't have a computer connected to their system, or are intimidated by the perceived complexity of REW and similar programs. Any room can be made vastly better with bass traps and other treatment placed entirely by eye by someone with knowledge and experience. That's all I'm sayin'.

--Ethan

You've been reading too many books... The predictive accuracy may be compromised in small spaces, but the understanding conveyed is unchanged and the desired end result is identical.

Regardless room size...
- It is true that more sound is absorbed when larger areas are treated.
- it is normally accepted that flat frequency response is desirable, regardless if it's a source or a sink.

If you choose to argue with the nomenclature, at least recognize the value to a little understanding for the OP and add some of that kind of value to your responses.

Have fun,
Frank

if you were able to refute my statements, then you would have without merely resorting to the personal attack (read: a distraction)


it's not "nomenclature". in physics and acoustics, words have meaning.

forgive me for steering the OP away from your erroneous claims regarding ANYTHING to do with "reverberation times" with respect to residential rooms. RTxx calculations are not valid.
Edited by localhost127 - 2/4/13 at 4:54pm

Which is why I don't like seeing threads where people are going on about REW and calibrated mics and such. It *IS* making it way more complicated than it needs to be.

There are other programs out there (TrueRTA being my favourite) that are a lot simpler to use and work straight off the bat. You can use the calibration mic that came with your AVR connected to the mic input of you computer. You don't even necessarily need the computer connected to your sound system, as just downloading and ripping a track of pink noise to a CD then playing that through your sound system while your computer records the room's response will work and tells you heaps.

No reason not to do the same with REW.

Note that other software still requires a PC.

I don't think that hooking up a HDMI cable to your AVR or running a line from the PC's headphone jack to your AVR's line in would be such a problem. Do it all the time for other reasons.

I agree that going on and on about REW like it is the one and only way does the cause of audio no favors.

You could add Dayton's Omnimic to this thought.
Edited by jim19611961 - 2/5/13 at 6:17pm

I'm of the REW, OmniMic, measure everything, verify everything camp.

However, I understand there's an enormous amount of people that want something much easier, and the first thing that comes to mind is the Rives test disc, with Radio Shack corrected tones (and un-corrected), and a simple RatShack meter.

This would enable someone to achieve an overall balance, and knock down the big modal resonances. Subjectively, this would help quite well, and it doesn't get much easier or much more simple.

^^^^

I agree, although tedious.

I found RAW a lot fussier to set up. It wanted mic calibration files and was always reporting problems with the mic volume levels and such. It's like it was written by computer nerds for computer nerds. TrueRTA just worked without fuss first time.


True, either way it wouldn't take much to get your sound system to play pink noise. Heck, my AVR can play its own full range pink noise signal to each individual speaker channel one at a time in the manual EQ setup menu.

Yes I actually want to get one of those next, as I have removed the sound card from my PC and have also disabled its on board audio. (in order to streamline USB as much as possible) So no 3.5mm mic inputs for me at the moment. I want to get myself a USB calibration mic.