bass trapping above k horn corners

[DAX616]

I am ready to buy mega lenrds by aurelex to place above my k horns behind accoustically transparent fabric. My room dimensions are approx 29' x 25' x 8' with the horns on the smaller wall.Is there any reason I should not do this? One of the reasons I feel I need bass trapping is because I get killer bass in my kitchen above my listening room. It rattles the cabinets and thumps the floor, with only modest results down stairs.

T.C.

[DrWho]

Before investing all the time and money, have you ever listened above the khorn? Put on some bass heavy music and see if you hear any bass build up above the speaker...if you don't hear any, then putting bass traps there won't be of much use.

Other than that I see no reason not to. I would do a few tests first though to make sure you get the results you want before making it permanent.

[colterphoto1]

Wait for a response from Artto, our resident expert, before doing anything. In my elementary opinion, your Auralex foam is a product meant to control room reflections and standing waves WITHIN a room, where your problem is primarily one of sound BETWEEN rooms.

A different approach may be in line, although some room treatments in a K-horn listening room is probably not a bad thing either.

Michael

[DAX616]

I understand the transimission problem. Really I only mention this to demonstrate the speakers are capable of monster bass. The true problem is the "lack of bass" inside the room.This is probably caused by cancellation. Corners are great places to stop this as far as I understand. The khorn uses corners.I dont want to interfere with knorns performance by taking away that corner above them. Of course I havent done this yet. I can tell you that the perimeter and the corners are boomy from working around the room. I'm interested to see if any one has tried this or if this is a bozo no no.I'm familiar with "master hand book of accoustics" so any reference is useful. I believe Arrto was going to try something like this in his room behind his masonite panels. To be sure of his intentions though, he would have to post.I'm more likely to trap "big" rather than small to see a marked result. Thanks for the responses.

[DrWho]

Since you'll be using a screen in front of the treatment anyway, you might consider putting a curved masonite panel in front of the bass trap as well...(artto is a huge fan of them too, lol)

Just last summer I was in a room where I was experiencing absolutely no bass at the listening position. I installed 2 curved masonite panels above the speakers and then another panel in the cieling-wall corner in the middle...All that bass came back and more. I had originally tried the panels in the back of the room, but I had better results from the front of the room. In addition to the bass, the midrange smoothed out a ton and the room sounded less congested.

I don't think putting bass traps on top of the khorns is an inheritantly bad idea...doesn't klipsch have a khorn room in Indy with the auralex lenrd bass traps sitting on top of the speakers? I wasn't there, but I think I remember reading something like that...though I'm not sure if I'm confusing it with the thought of putting some SVS cylindrical subs on top

[DAX616]

What you described dr who is what I'm looking to achieve. I would either build a cylinder and pack it with mineral wool, or I would use the aurelex. I think the combo makes for a resonant absorber. Given the limited space the aurelex seems to be more efficient in the low bass region. According to the data I have seen on polycylinders they are not as effective in that area. They are supposed to be great diffusers with in their capabilities. I do plan to have an array between the speakers.The screen by the way I am hoping will be "transparent". I remember your post and I'm glad you found some success.

[D-MAN]

The bass traps should go in the opposite corners IME, not the ones with Khorns in them. This is to absorb as much as you can before it reflects back (axial modes).

I have flat panels above my horns in the upper corner, not bass traps.

DM

[DAX616]

What did the flat panels do for you? Did you notice a change with(out) them?

[DAX616]

Hey D man, just a thought. Reflections happen at all boundaries, the rear wall as you mentioned, the ceiling, the two walls,that form a corner.By trapping @ that corner you are "absorbing" reflections from three virtual speakers.Now the question is do the reflections from " behind" the speaker reinforce the bass or diminish it?

[artto]

Klipsch uses an Auralex MegaLENRD on top of each Khorn in their Indy Heritage demo room. In fact, thats where I first saw MegLENRD as they were not in Auralex catalog yet. Klipsch also had other various sized tube traps (ASC bass traps?) placed around the room, particularly along the rear wall.

I see nothing wrong with putting a MegaLENRD on top of the Khorns. Just be careful to not let the area around the Khorns get too dead. Also beware that just because bass traps are installed right over the Khorns, that does not negate the need for additional bass trapping in other parts of the room.

When I first installed the MegaLENRDs in the rear corners, you hear the modes shift, or rotate, to new locations. For instance, the loudest bass response had now rotated from the corners to mid-wall locations. Eventually Ill be making the whole upper half (above grade portion of the walls) of the front and side walls bass traps by installing full-depth Roxul behind the Masonite polycylinders. This should substantially kill any remaining mode problems left in the room.

In one rear corner I have 3 MegaLENRD stacked 6 high. In the other rear corner, the ceiling/rear wall is penetrated by part of a staircase (sealed off) and a couple rows of record cases. These large features help break up the low frequencies in that corner so not as much additional bass trapping is required there. I took a small side table, the kind that come three together and interlock into sort of a cube (like Scandinavian Design had), turned it upside down so the table top can slide on the floor, and put the MegaLENRD on top of the upside down legs/frame. This kept the MegaLENRD exposed on all surfaces for maximum absorption efficiency at low frequencies. But now I can also slide the LENRD around, in and out of the corner and tune it as needed.

[D-MAN]

The flat panels above the corner horns face the listening position and are flat to the upper edge of the corner/ceiling. They tend to clarify the soundstage to a degree and allow an increased sense of depth. My horns are also on the "short" wall.

The bass absorbers are meant for corner use (mine are 16" dia. cylindrical x 4 ft" bass traps called "Tube Traps"). The axial modes (longitudinal) reflecting off the back wall will have a tendancy to allow bass to "build up" in the corners. Reducing the amount of reflected bass waveforms at the back wall (corners) will reduce them in your forward corners too (after the reflection from the back wall).

Your best bet is (in order):

1) side absorbing panels at the first reflection point.

2) back wall absorbtion for axial modes

3) ceiling absorbtion panels at the first reflection point

4) bass traps in back wall corners

5) front wall absorbtion panels

I am assuming carpet, if not then add floor/throw carpet at #3.

DM

[formica]

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On 3/8/2005 3:21:49 PM D-MAN wrote:

The axial modes (longitudinal) reflecting off the back wall will have a tendancy to allow bass to "build up" in the corners. Reducing the amount of reflected bass waveforms at the back wall (corners) will reduce them in your forward corners too (after the reflection from the back wall).

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Actually all the walls, ceilings and floors are ALL responsible for defining the room modes... not just the rear wall. The placement and effectiveness of bass traps will depend on the geometry (shape) of the room, and the front can be equally effective depending on the room. Reducing the bass accumulation in any corner will reduce the room mode's effects. There are mathematical models to predict these, but they become very complex in non-rectangular rooms, as well as the fact that they don't take many construction factors into account.

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On 3/8/2005 8:04:58 AM DAX616 wrote:

One of the reasons I feel I need bass trapping is because I get killer bass in my kitchen above my listening room. It rattles the cabinets and thumps the floor, with only modest results down stairs.

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Since the room is existent, you should try to measure your room response in different locations to establish where bass traps would be most useful. DrWho was on the right track with listening in the corners. If you have one, bring a SPL meter with you.

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On 3/8/2005 3:21:49 PM D-MAN wrote:

Your best bet is (in order):

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Ummm... depends what you are trying to treat. Those aren't "in order" if you are trying to treat a strong resonant frequency in the bass region, which is what DAX616 asked about in his first post. My list would be along the following lines:

1) making sure everything is in phase (through testing... not just "+" to the "+" and "" to the "") at your seating position.

2) measure the room to try to establish problem areas and frequencies

3) apply an appropriate acoustical treatment that matches the tests.

But that's just me...

Rob

PS: Dman, here are a couple more for good meausre...

[D-MAN]

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PS: Dman, here are a couple more

for good meausre...

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Rob, yes, I meant in general for BEGINNING attempts at controlling a room, not specifics for controlling bass problems. (But lateral and up-and-down are not called axial modes).

So now what - don't tell me that YOU think I can't take a correction or two? From YOU?! not a prob, dude! Am I out of hand (again)?

DM

[dragonfyr]

While there are a plethora of treatments for just about every situation, I am surprised that few on this site consider actually measuring the room with the appropriate tools, identifying problems, and then treating the actual problems!

There are indeed many options to many problems! But just as in taking medicine for sickness, it makes no sense to go out and simply start taking all sorts of medicine simply because you think something is wrong! Why not find out exactly what is occurring and deal specifically with the issues at hand? You may find yourself rather surprised at the diagnosis and remedy!

Among so many who feel justified in spending absurd amounts for interconnects, equalizers, and so many other items based upon sacred convictions rather then acoustics, may I suggest that you (or others) consider having someone qualified in the use of TEF or SMAART to actually analyze the room and suggest specific treatments for speaker placement, absorption, diffusion, abfusion, etc.? Specific treatments can be identified for EXACT spots via 3D POGO resolution minimizing the shotgun treat everything approach even if it results in an aggravation/degradation of the room response! The average cost should be no more then $300-500 and I bet you could even negotiate a return trip to verify the effectiveness (proof of performance) of the treatments. Once you have the results there are many options available ranging from those that you may want to do yourself to employing specifically designed products such as Peter DiAntonios RPG systems.

And if you are willing to spend lots of money anyway and explore the treatment yourself in a more informed manner, you can always obtain a copy of EASE and model the room yourself and auralize it (model the acoustic response based upon the changed reflective parameters) by adjusting the reflective/absorptive coefficients of the reflecting surfaces (etc.). But I seriously suggest that you refrain from the latter unless you are willing to invest in training and the associated tools! After all, merely purchasing an MRI unit doesnt automatically render you a surgeon!

All in all, having the room analyzed will result in an optimal listening space based upon real analysis rather then lots of money spent on guessing based upon the well meant recommendations from folks who have not even seen the room nor are familiar with the characteristics of the reflective surfaces and assorted complex characteristics of the room, let alone to the complex nature of the actual speaker-room interaction.

Just a thought

And no!!! A frequency domain RTA will NOT accomplish this!

[DrWho]

Not to disagree with your point but...

I can't remember which it was, but there was a performance hall that was built to be acoustically perfect according to all the "rules" (the same rules the TEF, SMAART, and EASE all use). In the end, the place ended up sounding rather awful. They tore the place down and rebuilt it the "old school way" and it turned out to be one of the better sounding halls. I really wish I could remember the name of the place...I want to say the Foellinger Great Hall down at UIUC, but I'm not sure. Anyways, my point is that when it comes down to it, good acoustics is still an artform, despite the technical side that we so readily analyze and model. I suppose it could be argued that a good surgeon is an artist as well...it's basically the same point I'm trying to make.

For the vast majority of us that do not have the money to invest in such methods and equipment, the naked ear is a perfectly good tool for measuring an acoustic space and even choosing the correct treatments. After all, it is the ear that is going to determine how good the end-results are.

Another great example to show the art over the math is the act of EQ'ing a system...even with the coolest measuring equipment and DSP technology, I find myself tweaking the EQ by ear (as do many other sound guys). All the cool toys we have for measuring and modeling and what not were created by some other person who decided what numbers and formulas to use based on what he felt represented good sound. There's nothing in the programs or equipment that wasn't thought up by another person. Not to discredit the testign equipment, but to show that we aren't yet capable of providing a perfect model that corresponds to out hearing. I would argue that we're very close, but it's not perfect...that's why we still end up tweaking by ear.

Nevertheless, those spending crap loads of money on interconnects really should consider getting the measuring equipment in there and even getting professional advice. There are very few people that get to play with all the toys and treatments available on a regular basis and it's those people that will be most equipped to providing a best solution. They're like artists with more colors of paint to choose from.

[dragonfyr]

To quote...

I can't remember which it was, but there was a performance hall that was built to be acoustically perfect according to all the "rules" (the same rules the TEF, SMAART, and EASE all use). In the end, the place ended up sounding rather awful. They tore the place down and rebuilt it the "old school way" and it turned out to be one of the better sounding halls.

Another great example to show the art over the math is the act of EQ'ing a system...even with the coolest measuring equipment and DSP technology, I find myself tweaking the EQ by ear (as do many other sound guys). All the cool toys we have for measuring and modeling and what not were created by some other person who decided what numbers and formulas to use based on what he felt represented good sound. There's nothing in the programs or equipment that wasn't thought up by another person.

___________________________________________________________________

I must admit to being a bit confused by some of the above. The fact that someone claimed to have insight and designed a poor performing hall does NOT invalidate proper methods. If such is a valid method for evaluating 'things' is there Anything that is not fundamentally and fatally flawed? Or is it now where I should be a smart aleck and interject some obligatory complaint about Bose or Monster as so many do without any real understanding of the real issues with their product lines... For every bad product or hall you want to name, I am familiar with too many that have been done correctly. Come visit Bass Performance Hall in Fort Worth for a truly amazing experience. These techniques were correctly applied and the result is one of the premier acoustical halls in the world! Period! A rare case of design done well and properly, & where the acoustics were not the first thing sacrificed (as they usually are) when budgets seem to inevitably run over!

And to say that all the acoustical analysis methods are the same and arbitrary? Huh? OK, so Richard Heyser's ideas are just snake oil. And while I am not claiming that he was infallible, I defy anyone on this site to demonstrate any of his ideas to be flawed. I only wish that I was as 'limited' in my understanding as he was during his all too short life! And I would be ecstatic to encounter another on this site who has even explored his ideas in depth.

(And for those who wish to start, may I point you to "Time Delay Spectrometry: An Anthology of the Works of Richard C. Heyser on Measurement, Analysis and Perception". The only such work of collected writings of an individual published by the AES. Two other works of interest are "Sound System Engineering" by Don & Carolyn Davis, and "Theory & Design of Looudspeaker Enclosures" by J.E. Benson, 1993. And for those unaware of Benson, you might enjoy the photo in the preface of Benson, Thiele, Small, Ashley and Paul Klipsch! And Don Keele, of whom ALL of you should be well aware!, wrote of Benson's work:"It is a classic and even more comprehensive then Thiele and Small's loudspeaker papers as published in the AES Journal; (if you can believe that!)."

Acoustics is one of the rare sciences that is unlike so many others that have already reached a point where most of the systems are well understood and simply a matter of plugging values into well behaved models. Acoustics is at a point where significant advances are occuring as we speak. The ramifications of Heyser's work are still only beginning to be felt in acoustical design. And for so many to keep looking backwards in their attempt to stunble forward is to miss a great opportunity. And that opportunity is enabled by adopting a fundamentally new paradigm. And it is not sufficient for us to adopt an attitude of "Well we did it like that at Woodstock, so why should we consider any other options!?"

And to paraphrase from an ever so appropriate Calvin & Hobbes:

"It's true Hobbes, ignorance IS bliss! Once you see things you start seeing problems everywhere...And once you see problems, you feel like you ought to fix them...And fixing problems always seems to require personal change...and change means doing things that aren't fun! I say phooey to that!

But if you are willfuly stupid, you don't know any better, so you can keep on doing whatever you like!

The secret to happiness is short-term stupid self-interest!

(At which point Hobbes points out that they are hurtling toward disaster in their wagon and observes); We're heading for that cliff!!!

Calvin: I don't want to know about it!

(And of course there is the conflagration at the bottom of the aforementioned cliff,and Hobbes observes: I'm not sure I can stand so much bliss!

To which Calvin replies: Careful! We don't want to learn anything from this!

Indeed! And while you are entitled to think however you choose, there are fundamental limitations to the use of EQ in a non-minimum phase environment. You can move your frequency domain nulls and polar lobing about (to some degree), EQ does not resolve the anomalies created in the time domain! This can be demonstrated empirically, subjectively, and mathematically and verified through proper testing. In fact I can propose a Very simple demonstration that I would challenge anyone to resolve via the use of EQ. And anyone can replicate it! And I haven't even mentioned the use of a Bessel array (oops!;-) But don't argue with me, I am not the originator of such 'arbitrary and subjective' thoughts. Take the time and become aware of their ideas and take issue with THEM!

My regret with this site is that so many already 'know' everything and refuse to uncover their ears and research some of the new ideas for themselves. And for many that would involve more then reading a review in some armchair stereo review magazine or simply bashing a competitive company. And while experimentation is indeed wonderful, simply following the old methodologies does not invalidate nor validate the newer ideas. It is not always easy, and the understanding does not come cheaply without some sweat.

After all, just look at the weekly cable debate. Shouldn't there be a basis for understanding the limitations of this issue sufficient that new people can be referred to more then a simple emotional diatribe? And yet it still rages! And it is so ironic that the basis for so much of the criticicm about Bose technology is known only anecdotally and is still not understood by so many! Few understand that it is based precisely on Dr. Bose's refusal to acknowledge the value of Q and overlapping sound fields (superposition) while going to great lengths to propogate precisely the small time differential reflected signals (the Haas effect) that are so destructive to intelligibility! It is ironic that the very things that Bose refused to acknowledge in the realm of acoustical engineering, instead preferring to forge ahead with their substantial investment in marketing at the expense of better sound, have earned them such a bad reputation here, but the variables that were demonstrated to be fundamentally flawed in their systems are held ONTO so tightly in other lines of discussion! It was precisely their rejection of the concept of the primacy of the time domain that has lead them to be held in such low regard by many! (And of course there is the infamous embarassing encounter in the early 90's at the Indiana fieldhouse with Altec and JBL with Don Davis & TEF!) It is truly ironic, and to my thinking unfortunate that so many yet understand this, but are not shy to trash others.

There are some really remarkable advances in acoustics that have redefined the landscape in the past 20 years, and are only now producing significant results, and it would be nice if they were explored in more depth here without the cries by so many to drown these ideas out. And the advent of recognizing the pre-eminence of the time domain upon the acoustical realm is one such concept that is no longer in dispute excpet from those ignorant of its profound impact. It is simply an idea that requires an change in thinking and an adoption of a new paradigm. It is not radically difficult to understand, but it will cause you to challenge some old ideas! And as a result it has been slow to be understood and excepted by some. And it is the rejection of these ideas that is primarily behind so many companies becoming known for their prowress of marketing over engineering!

And may I suggest to all, that rather then simply dismissing the ideas or discrediting them simply because a messenger may inadequately present them to your satisfaction, that you seek out the sources and other avenues where the concepts are being actively presented. And if anyone is interested in researching any of these ideas I, and I am sure others, would be glad to list many credible sources and resources. But by all means, question, think and explore! But PLEASE don't let a Luddite mentality result in rejecting that which you do not yet have a complete understanding!

[dragonfyr]

By the way, thanks Doc for your reply! My response is NOT intended as an afront, but rather as a stimulus to encourage all to ask a few more questions rather then to simply dismiss ideas which may be new of a little foreign before rejecting them!

[DrWho]

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On 3/28/2005 5:08:56 PM dragonfyr wrote:

By the way, thanks Doc for your reply! My response is NOT intended as an afront, but rather as a stimulus to encourage all to ask a few more questions rather then to simply dismiss ideas which may be new of a little foreign before rejecting them!

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No, thanks for the reply...Might I inquire as to some of these sources of information? I would love to find a pool of information (aka, a school) where one might indulge in learning specifically topics related to audio, but even after 2 years of searching I am yet to find such an institution...nor do I have unlimited funds for purchasing all the cool books out there either. I'm hopefully going to attend UIUC in the fall to major in EE, with an emphasis on audio as this is the closest thing I have found (that also provides a secure future). I would love to be on the forefront of audio research...perhaps even invent something really cool. (I hope that's a modest enough goal...already got a few ideas). Anyways, I hope I wasn't coming across as belittling the research and models already out there (and I didn't mean to lump all the models into one group either). I've been asking questions since I was 8 and I'm hoping I don't lose that desire to have to know all the guiding principles (At 21 I still find it fascinating so I'm off to a good start)

Btw, I was under the impression that some of the DSP technology (especially being used in line arrays) was working in the time domain...I had a demo a while back and the effects were amazing, but now I'm not positive if it was actually working in the time domain (I know there was some individual speaker control going on). From an electronics standpoint it wouldn't be that hard to do...it's just writing the bloody program

[sfogg]

"Btw, I was under the impression that some of the DSP technology (especially being used in line arrays) was working in the time domain.."

The Tact system and the Sigtec do work in the time domain to a degree.

What is also being done for room correction in the bass (minimum phase corrections) using traditional parametric EQs is to do the analysis in the time domain instead of the more traditional amplitude measurements.

If you think about it the standing wave peaks/nulls in a room is a symptom of the problem, not the problem itself. The actual problem is a resonance in the room.

If you take the traditional approach of just looking for peaks with an RTA and knocking them down it is first off very easy to miss the peak if you aren't measuring at the position of the peak itself. Second aiming for a flat amplitude isn't really subjectively the best idea as that correction is only valid for the place the measurement was taken. IOW one of the common complaints of EQ only being effective for one point in the room are somewhat correct for this measurement approach.

But what causes the standing wave peaks/nulls? A wave at a specific frequency that keeps bouncing back and forth within the room longer then other frequencies. The room literally holds on to the note longer and 'rings' at certain frequencies. The ringing causes the bass to sound bloated and it hides details in the music (even much higher in frequency) that occur while the room is ringing.

The ringing effects most places in the room (sound bouncing back and forth within the room) so if you make a time domain measurement you can get good information from almost any place in the room unlike the traditional amplitude methods that need to be in a peak to give any good info.

If you then address the ringing with the parametric EQ to put less energy into the room at those frequencies you reduce the ringing at that frequency throughout the room.

So by looking at the rooms resonance problems in the time domain you get both better measurement constancy as well as better consistency throughout the room for the audible benefits of EQing it.

Shawn

[formica]

This post has become alot more interesting than i would have initially expected.

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On 3/28/2005 10:45:02 PM sfogg wrote:

The ringing effects most places in the room (sound bouncing back and forth within the room) so if you make a time domain measurement you can get good information from almost any place in the room unlike the traditional amplitude methods that need to be in a peak to give any good info.

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I just wanted to post a simple example of what shawn was referring to the analysis in the time domain. This is just a basic waterfall graph produced in ETF... which clearly shows a dominant resonant frequency at about 46.9Hz.

http://forums.klipsch.com/idealbb/files/ETF-room-water-fall.jpg

A good place to start.

Rob