Bass Traps: Do they fix this common problem?

[dtximages]

More pics

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Another one of the front. This is the wide wall in my pdf file

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Rear wall, surround speakers (Klipsch Quartets on stands)

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More.

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And more. The couch in the middle with the blanket is the dead spot.

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A screen shot in HD

[dtximages]

Sorry I didnt dress up for the pics. This seating position is about 13 feet from the front screen.

[mas]

anyway, my sub is placed in between my center and right speaker in front. under the screen. i looked into many different placements.. same dead spot. move my listening position front or back 1.5 to 2 feet and you have tons of bass. i was hoping to hear more positive things about bass traps.

ok flipping my room, youre right i dindt want to hear that haha. now you have me wasting more work time drawing out new plans! i think ill move the main speakers over there and see if music sounds good.

ok SO, BASS TRAPS WONT FIX MY LIFE??????? EVEN BIG ONES? I thought they were meant to smooth out bass and stop the the reflected bass wave thats cancelling my good wave out. is that just good theory and doenst really work?

Lots of confusion here.

Standing waves ae not a simple issue of reflections. And if room dimensions reinforce resonance at certain frequencies which persist in time creating both a LF latency (boominess) as well as exaggerated gain at those frequencies, damping the resonance (a latency in time) is not going to magically fill the null of the pressure wave created due to the sound wave being large compared to the room dimensions!

This is not a case of simple superposition with a "stop the the (bad)reflected bass wave thats cancelling my good wave out". "Is that just good theory and doesn't really work?" Nope! This is a case of misunderstanding the theory!

Bass traps are not used to tame nulls. They are used to mitigate peak resonances. And while aspirin may be effective in mitigating a fever, that does not imply that it is necessarily effective in treating hypothermia! Not even a BIG aspirin!

And your room orientation is working against you BIG time. I know that you have put allot of effort into your room. But you are encountering what is unfortunately a very common occurrence. In far too many installations, acoustics fall far down the initial list of priorities in the planning and asset allocation stages, only to suddenly become a primary concern in the final performance analysis!

In a closed pipe, peaks ocur at the terminating ends of the pipe (whereas in an open pipe, nulls occur at the open end). Thus the seating position can be resonably envisioned to be close to where one might expect a null to be given the wavelength for the frequencies involved. Again practical stimulation may make some of these apparent that measurements would further identify with precision.

Traps damp resonances that is a result of a room dimensions. They do not change the effective size of the room that determines the spacing of the peaks and nulls of the room. And your choice of orientation of the room with the alcove being a fundamental part of the forward space (as you essentially have at least 3 room spaces interacting - with many more permutations), not only will the imaging suffer due to the asymmetrical reflection of the early order reflections, but you are providing fundamental stimulation of the modes of the 'wide' room (using the convention of the diagram) within a room which will combine non-linearly with the stimulation of the 'vertical' room in a room.

While I cannot guarantee that all problems will cease to exist in the reverse room orientation, I can guarantee that imaging will improve and that the alcove can potentially be used to good acoustical advantage if certain additional steps are considered acceptable.

Unfortunately, sometimes the physics of sound take precedence over what we wish would occur. And then we have a choice. we can work with nature from inception anticipating potential problems, or we can blame nature and the tools at our disposal with which we have to work for our failure to anticipate sonic anomalies after the fact. But the available tools will not necessarily solve all problems to which our choices have either created or contributed.

You did ask. (BTW, please don't misinterpret my comments. You have put allot of effort into the room and you deserve compliments for this ! I do not mean to denigrate that! I am simply reacting to the acoustical elements... ;-)) )

Addendum: The D'Appolito MTM configuration wasdesigned to mitigate a consequence of the odd order non-signal aligned Linkwitz-Riley crossover which results in an upward 15 degree on axis polar lobe tilt. By inverting the configuration, superposition is used you counteract the vertical polar tilt by using interference patterns to create 'another' anomalous downward polar tilt that sums to a more on axis normal (perpendicular) lobe. And off axis anomalies are further aggravated. But this is not the optimal solution which is accomplished by simple signal alignment. Ah the 'wonders' of passive crossover design.

[Strabo]

Front speakers: Chorus II & Forte II stacked for diappolito (ms?) design

Thanks guys

I'm curious, looking at your pictures, are the top set of speakers (Forte's?) mounted upside down with the grills turned around to be upright?

Edit, Does it work with two tweeters, MTTM?

I don't know anything about the DAppolito configuration but is it designed to work with horns? From my limited reading, isn't it used to offset some crossover issues not room issues?

Funny, I have a similarly shaped room that is set up completely different with a focus on the sound over the video. We all have our priorities I guess.

[dtximages]

Ok thanks for the suggestion. I think I could probably flip the room around one saturday. But lemme ask you this. Is there anything I can do/put in the alcove to make it disappear. I know im asking alot here and maybe only cris angel could do something like that but its worth asking.

I sent my pdf to auralex and theyre going to run a test on it. im sure they will come back with thousands of $ worth of suggestions that ill laugh at.

I also found out that the MEGALENRDs are about $350 each. I need at least 8 of them if i went that route.. but im not after hearing all of your feedback. I posted some pics on the HT forum.

[dtximages]

Strabo:

yeah those are forte IIs upside down. The D'App. design seems to work well and was suggested by a local long time klipsch dealer. He quit selling klipsch when they started making low line stuff. He's a Herative/tube guy and knows alot about sound. In fact he has met PWK and sold my dad a pair of Cornwalls in the 70s. Anyway, it seems to work wonderful. If found it to be more dynamic and more punchy. you just have to be careful about boomyness. It can creep in if theyre placed poorly. Both the chorus and forte are awesome sounding speakers with incredible dynamics that klipsch simply doenst make anymore (barring Heratige and maybe RF7).

Last night i was experimenting. I was more pleased with the bass response when i moved my couch all the way back to about 2ft from my back wall. that sets me about 22 feet away i think. during the elton john concert dvd from the Royal Albert Hall, my shirt sleeve felt it was visibly moving. I just hate being so far away and so close to my surround speakers. plus it messes up the room configuration. i suppose i could move my couch fwd/back depending (blah).

[mas]

Yes, there is something that you can do with the alcove! But you would want to 'flip' the room for the option to be effective.

And I will be fascinated to hear the results of Auralex's "test" on a 2D drawing.

Why do I say this? Because even RPGs Sizer and Optimizer assume a room that is a PERFECT rectangle (as in ideal, no doors, variations, deviations, etc. An ideal mathematical rectangle...) for calculating room modes! And they are useless for none ideal rooms. And most real world rooms are not ideal. And still, measurements are much more accurate!

And not even EASE or CATT-A can resolve a small acoustical space with precision simply because the sources are assumed to be in the far field (as they are in a large acoustical space) and the speakers are assumed to be 'point sources' - which a speaker in the near field is not! (as each driver is still functioning in the near field as an indivuidual entity and are experienced this way - in the far field the wavefront does not vary with distance from the unit).

And they are the MOST advanced modeling tools in the industry. Ah, but they are not in the business of selling other stuff either!

Sorry for my scepticism, but I wish this were the first time I have heard this.

If you like, PM me with contact info and we can talk.

[dtximages]

Ok how can I tell by using measurments whether or not my problem is from room geometry or not? Is that possible? Also, from rereading this thread, bass traps only make the base flatter and should kill boominess. they dont rejuvinate a dead spot. Is that the overall consensus on the issue?

What can I do to the alcove to mitigate its effect?

Thanks

[Don Richard]

Look here:

www.moultonlabs.com/more/design_considerations_for_an_idealized

There is a lot of info here, some of it will apply to your problem.

Don

[dtximages]

Here is another layout of my room. I have included possible places to put room treatments on the walls / corners. I have tenatively included arrows to get a general idea of the reflection points. I will probably add bass trapping to the back wall's top corner/ceiling. Is this enough information for someone who knows more than I do to give me some more pointers/tell me im an idiot? Please say that nicely haha. Besides turning the room around, what else am I missing?

Flipping the room around is not a good option right now because of support columns that would be in annoying line of eye when watching the screen.

OH the front wall is a thin curtain.

Let me know what you think or feel free to mess around with this and send it back to me! Thanks so much.

Home Theater Diminsions Absorbtion.pdf

[dtximages]

Sorry thats not in color. It wouldnt let me upload an excel document. If you would like it with color Ill email it to you. You can email me at chris.spruiell@protective.com.

thanks

[dtximages]

Well I just picked up some rockwool made by Delta. Its called Delta 4 Board. Its 2'x4'x2". I got it for $.35 per square foot. Ill start on my SuperChunk project sometime this week maybe. Depending on work of course. Heres a link to my avsforum thread. Surprisingly, no one has said over there that this will NOT help the dead spots/modes whatever. Theyve all said it will because its all caused by unwanted reflections and enough absorbtion will kill most/enough of those reflections. who knows. Im going to begin with the rear two corners.

Check out the avsforum thread here: http://www.avsforum.com/avs-vb/showthread.php?p=13600059#post13600059

[Me Loves Khorns]

Post some pics as you go.

Paul

[DrWho]

I know next to nothing about this but bass traps absorb / remove bass. Why are you considering them? If you want to reflect bass into your seating position you probably need something reflective.

I don't have the time to go into this, but that line of reasoning is totally skewed...the cancellations are the results of reflections being outta phase - increasing the amount of reflection just increases the amount of cancellation.

The real goal here is to get rid of the reflections that cause the cancellations. The only way to do that is to reduce the amplitude of the problematic reflections. Asorption (although not very efficient) would be a perfectly valid approach (albeit not all too often practical in a typical home setting when dealing with the long wavelengths of bass).

[dtximages]

Yeah and these traps are going to be huge too. I hope I can get enough to tame the really low frequencies the way i want them. it seems like the lower my speakers go, the more the problem is noticable. however, thats not confirmed without measurements.

can I get the radio shack spl meter to hook into my computer and out put a graph or frequencies? i dont understand what the number dial means on those units. oh well guess ill figure it all out. and im charging the camera now. the rockwool plant was really interesting how they make all this stuff. ill take pics of that later if theyll let me.