I need help with "live-end/dead-end" room treatment

[JBryan]

I've read about this a few times but can't quite get a handle on it. My confusion arises from an earlier misunderstanding of the application. I have a masonry wall behind the speakers with a 1/4" panel partition and 4" airspace between them (typically used). I thought that was a damped surface for the bass notes but I now understand that bass waves bounce off the masonry - thus it becomes the "live" wall. Behind my head (approx 15" away from the speakers) is 1/4" panelling with another room behind it. I'm assuming that this is the "dead" wall but I may need to remove the panelling or add damping panels or insulation (like Owens Corning 703) at specific points.

I'm hoping one of the gurus here can enlighten me and help me determine the proper approach to room treatments and where to start. My room is approx. 25x15x8 with another area (15x15) forming an 'L' shape. My speakers are on the long outside wall (25') and the listening position is against the opposing wall (panelling and studs only) backed up against a stairwell.

I've made measurements using the 1/2-octave warble tones from the Stereophile Editors' Choice Test CD and a RadShack SPL meter.

In the past, my treatments were limited to building false corners for the Khorns, filling voids between the FCs and walls with floor pillows and placing wool blankets on the walls behind the speakers and listening position. Any suggestions and advise would be most appreciated.

Thanks, Bryan

[Colin]

what do the tests show? where are the nulls and modes? is there a clap echo?

[sfogg]

Live end dead end is just the opposite actually. The idea of Live end dead end is you want the end of the room with the speakers as dead as possible to avoid early reflections from that end of the room interfering with their direct sound. The end of the room you listen in somewhat live so the room adds its own ambiance to the playback. Without the rooms added 'ambiance' (in 2 channel listening anyway) music can tend to sound dull/lifeless.

Shawn

[JBryan]

"what do the tests show? where are the nulls and modes? is there a clap echo?"

Colin,

I've been able to flatten out the nodes by adjusting the xover point to cut off the Khorn bass bin at 160Hz (which may not be a good solution in the end). Originally, there was an peak @200Hz and again @3kHz. I haven't been able to fix the nulls at 1.25kHz and 5kHz. Also, there is a steady dB drop above 17kHz which seems artificial. The Oris horn/AER driver should measure flat beyond 22kHz according to the specs.

There is a slight ringing coming from the stairway when clapping from the listening position. The ringing is also produced when I clap in front of the right speaker but doesn't occur in front of the left speaker.

Thanks for your time - Bryan

[JBryan]

Shawn,

So you're saying that I need to deaden the masonry wall behind the speakers (I can't move them to the other wall). What would you suggest that I place behind the listening position to make it "live". The wall is directly behind my head (not ideal I know) and it is simply studs and panelling under the stairs.

Also, the initial reflection points on the R speaker is in a bookcase; the Left side is open for 15' past the speaker with a wall of angled guitars at the reflection point. The ceiling is dropped acoustic tile and the cement floor is paded and carpeted - both of which I have little opportunity to improve.

Thanks again -Bryan

[Colin]

first null at 1.25kHz? that seems strange...

[JBryan]

"first null at 1.25kHz? that seems strange..."

Colin,

You may be right but I wouldn't know what strange is in regard to nulls. There is a slight drop at 200Hz and again at 63Hz. Does that make any more sense?

Thanks

[sfogg]

"What would you suggest that I place behind the listening position to make it "live". The wall is directly behind my head (not ideal I know) and it is simply studs and panelling under the stairs. "

It is already live if it is paneling. But if it is that close to you some absorption or defusion might not be a bad idea to try anyway.

BTW.... ignore your measurements, 1/2 octave doesn't show what is occuring very well except for very general info. It isn't fine enough to really see peaks/nulls properly. And 2D doesn't show the difference between direct and reflections.

Higher up the response will likely vary quite a bit. Down low to really measure what the room is doing you need to look at it with 1hz resolution. Room spikes can be very very narrow band.

Shawn

[JBryan]

Shawn,

I know my measurements are simplistic and very generalized but this is all I'm familiar with and a general idea of what's going on is better than nothin' - right?

Actually, I do have a frequency generator, a few mikes and recently a NTI Minilyzer but I haven't read the manual or figured out how to use them yet. Are you familiar with the Minilyzer? If so, I'd appreciate any help offered for my situation.

Thanks

[sfogg]

"and a general idea of what's going on is better than nothin' - right? "

Not always, if you don't understand what you are seeing you can end up making changes based on that misunderstood info which ends up making things worse.

For example... your nulls up high. Are they power response problems in the drivers themselves are is that room induced?

If it is room induced they could be only happening in a very narrow position... if you move the mic a few inches to the side you might see something totally different. If you treated your room based on getting rid of that null at that position you might have made things worse elsewhere. Or if it was in the speaker itself you might go nuts trying different room treatments which have no effect on the null but changes other things elsewhere.

" and recently a NTI Minilyzer but I haven't read the manual or figured out how to use them yet. Are you familiar with the Minilyzer?"

No, haven't used one. But from looking at it... figure out the Minilyzer. Its RTA function with pink noise will give you 1/3 octave resolution (still not great as you will miss a lot but better then 1/2 octave)and it will be *MUCH* faster/quicker/easier (and far more accurate) then the method of charting with a SPL meter. Its sweep function could be used for the same type of measurements too. Charting with a SPL meter is just an exercise in frustration.... you don't really know what you are measuring when you do it this way.

If you are just starting out with measuring your room..... prepare to be disappointed. Few realize how bad things look....esp... the more you look at greater resolution.

Also, be prepared to spend a lot of time learning it and just in general fooling around to get a feel for how it works. Be also prepared for a lot of different thoughts on the topic of the room.

Shawn

[JBryan]

Thanks Shawn - I guess I'll go through the manual and use the Minilzer before I get too carried away. I was hoping for a simple solution like the live-end/dead-end treatment but its never as easy as it should be.

Back to the books!

[Hemihorn]

Re: I need help with "live-end/dead-end" room treatment.

Read this link it will tell you mostly everything you want to know, and is easy to understand. Also, it has a room calculator to tell you the proper dimensions for your room.

http://www.ethanwiner.com/acoustics.html

[JBryan]

Yeah - that's a great read and a primer for anyone who needs a general education of acoustics. I found that and a few other very informative sites while searching the net for "bass traps". Its actually what got me started thinking about making some changes to the room. Before that, the best I could muster was to put up wool panels and use thick pillows and blannkets where I thought the reflections were.

The sites I came across seemed to offer a pretty straight-forward approach to the treatments but I couldn't determine the best way to apply the treatments or where. I came away from the search with the impression that I should deaden one wall and leave another reflective; to set out bass traps as close to the corners as possible and place panels at the initial reflective points on the side walls. Finally, I'd place absorption triangles in the corners at the ceiling on the wall opposite from the speakers.

Of course, I now know that this approach is essentially a shot on the dark not much better than my pillow and blanket treatments. I need to refine the measuring method so I can determine which frequencies need attention and treatments to correct.

I know there isn't a quick fix here and I'll need to read plenty of articles like th one you sent before I can really hope to accomplish anything.

Thanks for your help - Bryan

[johnyholiday]

always important also to keep your Left- Right channel information,

left, right, respectively,red oval = slightly towed in speaker, which

bare room won't do as in diagram points 1,2,3,4,5,8. disclaimer just

food for thought

[johnyholiday]

An some like diamonds for untreated room

[WMcD]

Of course I'm always trying to stir up interest in polycylinders. I trust you saw the collection of articles I posted.

Gil

[DrWho]

Live end dead end is just the opposite actually. The idea of Live end dead end is you want the end of the room with the speakers as dead as possible to avoid early reflections from that end of the room interfering with their direct sound. The end of the room you listen in somewhat live so the room adds its own ambiance to the playback. Without the rooms added 'ambiance' (in 2 channel listening anyway) music can tend to sound dull/lifeless. Shawn

Ah, one of the few things me and Shawn disagree on [] But it's mostly just a personal preference (prob cuz I come from a studio and live sound background where you rarely ever have sound behind you).

I totally agree that early reflection points need to be dealt with, but with khorns in the corner they should be almost non-existant.

The ideal way of going about treating your room is to bust out an ETF and also do some RT60 measurements. In all the rooms I've been in that were measured for correctness, they usually end up with bass traps in the corners, and then absorbtion and diffusion spread throughout the side walls, and then the skyline diffusors along the cieling.

[formica]

The ideal way of going about

treating your room is to bust out an ETF and also do some RT60

measurements.

As a side note... ETF Acoustic just released a new room measurement software called R+D http://www.etfacoustic.com/RPlusDSite/index.html

which is supposed to simplify room optimization. The idea

with this major revision is measuring numerous locations and

establishing the best "averaged" treatment for a sitting area rather

than just one sweet spot.

In other words, it now attempts at interpreting the results from it's measurements rather than just supplying you with raw data.

There seems to be quite a few interesting products coming out but I'm

way behind in keeping up with all these great tools.... I have not even

tried Room EQ Wizard freeware at http://homepage.ntlworld.com/john.mulcahy/roomeq/ yet.

Mike, did you buy the measurement mic and mixer?

ROB

[DrWho]

No, not yet...I've got so many projects I'm working on but I should be purchasing the mic and mixer shortly. Just trying to be patient and land a really good deal. I actually already have an old 8 channel microphone mixer, but it's noisy and has a lot of THD (especially when you crank it). So theoretically all I really need is the mic. But right now I'm finishing an amp selector and just got started building my new squaker and I'm working on a new tweeter too (both of which involve new expansion rates and I'm experimenting with some other cool ideas too). And on top of it all I've got school and four clubs (AES, IEEE, AMD Jerry Sanders Competition, and Kuk Sool Won).

Btw, does anybody have any literature on the RT60? As in the optimal decay rates for each frequency? I understand the concept, but it would be nice to know what the ideal actually is though [] I must confess I haven't searched very hard for it, but it would save a lot of time if someone else had it readily available.

Oh, and I'm also working with a friend (who is a good programmer soon to be CS prof) on a web-based room planner....and then in the background I'm working on an acoustical modelling system geared specifically for home audio. (Though I may just end up porting the data into one of the existing programs - no need to reinvent the wheel).

So ya, Doc is really busy []

[artto]

First of all, dont bother using the RS SPL meter with the test tones CD. Its simply not accurate enough. There is too much variability from unit to unit (and you have no way of knowing what that variation is). You need to use a microphone with a known frequency response curve so you adjust (calibrate) the results accordingly. Also, a spectrum analyzer is most helpful for seeing the results and there are a number of ways of doing this. I havent used the NTI Minianalyzer youre considering but I agree with Shawn that this would be far superior than trying to chart the results of an SPL meter of questionable quality for this kind of application and unknown performance (not calibrated).

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As Shawn mentioned, youre actually doing the opposite of what live end/dead end rooms are. And, in my experience, Khorns dont like a lot of dead surfaces around them. And, if youre sitting too close to the back wall, a live back wall can produce exactly the same kind of time smearing in the sound that reflections from the front or side walls can. Since the Khorn was designed to (for the most part) project most of its sound output from a corner into the room (constant directivity horn), as Mike (Dr Who) mentioned, there typically isnt too much of a problem with reflections off the room surfaces immediately near the speaker.

I didnt realize it until Dragonfry (hasnt been around in a while) explained it, but apparently what I did in my room qualifies as sort of a live end/dead end room because the front and side walls utilizing large polycylindrical surfaces, which also act as bass trapping, provide enough broadband diffusion to produce enough difference between the direct and reflected sound to qualify as a live end/dead end technique without resorting to a lot sound absorption so the room remains relatively live, but well controlled.