[jlafrenz]

Have you ever tried a near-field setup? If this were my room I'd have the speakers 3-4 feet apart, very close to the front wall at the top of the drawing, and I'd sit 3-4 feet away. That will likely give you the largest sound field available in that room, short of lining all the walls with diffusers. It's at least something to try when you have a spare half hour.

--Ethan

How far off the front wall would you suggest? The problem I see is that I would be very close to my rack. My other concern is the sub placement since it is an OB and siting directly to the side of it is not ideal.

[rbbert]

Book shelves may be better then a flat wall but it is not really going to diffuse the sound.

I'm not sure I understand this statement.  Assuming that the books are many different sizes, I understand that there will be some absorption, but the shelves and rear wall will only reflect.  So you have reflective surfaces (some with a little absorption) of many sizes and depths; isn't that a diffusor?

[jlafrenz]

I'm not sure I understand this statement.  Assuming that the books are many different sizes, I understand that there will be some absorption, but the shelves and rear wall will only reflect.  So you have reflective surfaces (some with a little absorption) of many sizes and depths; isn't that a diffusor?

This may help.

http://www.gikacoustics.com/education_diffusion.html

[jlafrenz]

Ethan, here is the PM you requested I post publicly so that you could elaborate.

"Thanks for your comments in the thread I created about my room lacking dynamics. I have turned to your website to gain some more knowledge about my situation. In placing my first reflection point panels, I have found that there are some differences for placement depending on method. I first placed my panels using the mirror method. I wanted to double check them so I used the calculation from your website. According to this, my panels are not placed correctly and are too far forward. I also read about the RFZ and noticed it stated the first reflection points should be halfway between the speaker and the listening position. This placement also did not match with where my panels were located. I double checked the math and revisited your formula. I happen to noticed (using the example numbers you give) that the placement calculated is not at the half way point. I am hoping that you can clear up the confusion for me. I feel that I may have easily overlooked something or there is a good explanation as to why each method is yielding different results."

[DTB300]

I'm not sure I understand this statement.  Assuming that the books are many different sizes, I understand that there will be some absorption, but the shelves and rear wall will only reflect.  So you have reflective surfaces (some with a little absorption) of many sizes and depths; isn't that a diffusor?

I would call them reflection-cases, not diffusion.  Diffusion is a set mathematical pattern - bookcases with books in them are not.

[Ethan Winer]

In placing my first reflection point panels, I have found that there are some differences for placement depending on method. I first placed my panels using the mirror method. I wanted to double check them so I used the calculation from your website.

The mirror method is very good, and leaves no room for miscalculation. So that trumps all else. But the placement is different for the side walls and ceiling, so maybe that's the source of confusion. Assuming your tweeters are at ear level, the reflection point (center of an area really) for the ceiling is exactly halfway between your ears and the loudspeaker. But for the side walls, the center point is a little forward of the halfway point. How far forward depends on how close the speaker is to the wall. For a center speaker in a surround setup, the reflection center point is also halfway. But (considering the left or right speaker), when it's closer to the wall the angle changes.

--Ethan

[Ethan Winer]

How far off the front wall would you suggest? The problem I see is that I would be very close to my rack. My other concern is the sub placement since it is an OB and siting directly to the side of it is not ideal.

Well, I was just suggesting an experiment. If it works out you could consider moving the rack and sub. Your rack is in the center left-right, so you could move the speakers all the way up against the front wall without bumping into it.

The closer a speaker is to the wall behind it, the higher in frequency the series of inevitable SBIR peaks and nulls begin. Absorption can then more easily handle those higher frequencies. This is why the best place for speakers is directly in the wall, though that's not possible for most people.

--Ethan

[Tyson]

Or it could be that the speaker manufacturer designed the speakers power response to sound good in a typical (bare) room, and it's the acoustic treatments themselves that are causing the problem.  A speaker tuned to not sound "bright" in a bare room will usually sound dull in a well treated room.

[cheap-Jack]

(1) Any time you are very close to a boundary you will hear reflections, even with acoustic foam.I'm surprised the sound is "clear".  I'd predict it would be a bit muddy.

A listening position too close to rear wall can cause the bass to get boomy.

(2) Speakers too far away from listening position and you might get a bass echo.

Sorry, what you mentioned above never happen in my basement audio den.

I only installed standard drop-ceiling with 2'x4' glasswool ceiling panels & thin wooden panels backed with standard wood studds & glasswool infill as wall covering for the surrounding concrete wall. Wall-to-wall carpet with thick rubber underlay to cover the bare concrete floor.

NO no special acoustical treatment ever added despite there only 7feet ceiling-floor clearance.

I am sitting right against the backwall with my ears only 15" from it & pretty far way from the loudspeakers - 133" from my ears on axis to the speaker front panel centre. The loudspeakers are mounted on lead-filled steel tripod 6 ft apart & 56.5" from the front wall meaured at the loudspeaker front panel centre.

With such oddie 'back-to-back" setup, my music sounds superb - no booming bass nor RF ringing even cranked up very loud. Precise imaging & lifelike soundstaging. 30Hz pipe organ sub-sonic notes (via my 10" 100W sub) sound
awsomely real & subtantial.

I repeat - NO special acoustical treatment ever added. My amp is only a 15Wx2 tube amp.

c-J

[Roc]

C-J,

I'm glad to hear that someone else is using the "back against the wall" system set-up with good results.
My ears are about 24" from the back wall without boomy bass, but at 20" I start hearing it. 
When you get it just right the bass is full and extended.
I'm amazed that you can have good focus and clarity without acoustic treatments.  Is your room extremely wide perhaps ?

Dave

[cheap-Jack]

C-J,
I'm amazed that you can have good focus and clarity without acoustic treatments.  Is your room extremely wide perhaps ?

Dave

Yes, the basement is 900 sq feet of long rectangular shape which houses a small guest room, a sundry store room & my DIY workbench, all located far end of the basement. So I've chosen to have my audio den at the other empty end of the basement along its shorter side.

That explains why I have to be seated against the backwall (longer side of basement) to allow more free space for the music to travel to my ears.

Of course, I could have moved my 2-way bookshelvers & my sweet spot around facing the longer side of the basement. . But then I might have to go for a larger pair of loudspeakers & higher power amp, etc etc etc.

As the music sounds so open & balanced, I don't think to need to go thru all
such undue hassle.

c-J

[Ethan Winer]

My ears are about 24" from the back wall without boomy bass, but at 20" I start hearing it. When you get it just right the bass is full and extended.

I got your PM, so I'll gladly comment. The problem with having a reflecting wall very close behind you is the severe bass nulls. Now, if your head were at the wall you'd get an overall bass boost without peaks and nulls, but then the high frequency comb filtering would make the music sound strange. Some peak / null combinations sound more pleasing than others, so it's possible to get acceptable results. For example, at a foot and a half away, the first (lowest) null is around 190 Hz, which could be considered a boomy sounding range. But the response really is pretty bad in front of a wall, even if the particular combination of peaks and nulls sounds pleasing.

--Ethan

[cheap-Jack]

Hi.

I got your PM, so I'll gladly comment. The problem with having a reflecting wall very close behind you is the severe bass nulls.

But the response really is pretty bad in front of a wall, even if the particular combination of peaks and nulls sounds pleasing.

--Ethan

You may throw the books at me, again.

My very picky ears don't detect any such problems. My music sound awesome & well balanced even I wave my head around at my sweet spot 15" from the untreated backwall.

Is there someting missing in yr books?


c-J

[Hank]

Bass traps in the corners are 4' thick and 8ft tall

   4 foot thick x 8 foot tall traps may be TOO much absorption.  If your speaker angles are accurately represented in your drawing, their triangle apex is WAY out in front of your chair, instead of just behind your head where it should be.

[Ethan Winer]

My very picky ears don't detect any such problems.

Have you ever measured the response using a microphone placed where your ears usually are? It's a real eye opener! Unless you have highly effective treatment on the wall directly behind you, at two feet away you'll have a severe (30 dB) null at 140 Hz, a 6 dB peak at 280 Hz, another deep null at 420 Hz, and so forth at 140 Hz multiples. If this forum allowed attachments I'd upload a graph for you.

Again, as explained above, depending on the specific peak and null frequencies, this skewed response might be perceived as sounding good.

--Ethan

[cheap-Jack]

Hi.

Have you ever measured the response using a microphone placed where your ears usually are?

--Ethan

Yes, I did carry out a realtime measurement using a Yamaha audio frequency spectrum analyser with its callibated microphone placed right at my sweet spot at my same ear level.

I did not read any dales & hills across the entire spectrium from 20Hz to 20KHz.
With my reference music CD music on, I can see the realtime acoustical effect inside my basement audio den. Surprisingly pretty smooth with music signal swing up & down, showing bass signal peaks around 30Hz inline with the music.

No dales & hills ever detected on the screen with the analyser mic. around 15" from the untreated backwall.

c-J

[jlafrenz]

I was doing some listening tonight and have some positive results. Most of it has to do with speaker placement. I left the sub off for all my listening.

I left off using the Cardas method an equal lateral triangle which really opened up the sound, but left me close to the back wall and lots of bass build up. I couldn't really listen to it for very many songs. The best way I can describe it is think as if you were humming the song to yourself as you listened to it. This is what it sounded like. This needed to be changed.

Next I tried the 38% rule from Ethan's website. Again forming an equal lateral triangle. This helped a lot with my bass issue, but it seemed to make the sound lack some depth and a bit flat. The vocals were also congested. I really thought about leaving it this way as I could probably listen longer with this setup that the first, but I still wasn't happy.

Determined to make the Cardas setup method work (it worked great is my last room) I tried it again. This time a light bulb came on in my head. A couple of weeks ago I read "Get Better Sound" by Jim Smith. Good read with lots of tips. I remember him saying that he put his listening position at 83-90% of the distance between the speaker. Forgive me if my numbers are a little off, I loaned the book to a friend so I couldn't look it up to double check. So I put my seating position at 83% which put me the furthest from the rear wall with this speaker placement. This was sounding really good. The speakers seemed to really disappear even though I seemed physically close and the sound was coming from the room. Still a bit of bass build up, but the overall sound was much improved from where it once was.

My final attempt was to put my listening position at 38% in from the rear wall and then use the 83% to place the speakers. This also sounded really good. Had a real nice balance of sound. Not quite as open as the previous method and I did hear some details directly from the speakers as opposed to the room. It does get the toes tapping though. I'm not sure that these are exactly technically right, but they seem to sound better (to my ears anyway).

Its a tough call between the last 2 configurations. I am going to have to do some more listening. I should add that I made the first reflection points 4" think as well for all these different placements. I am wondering if I should also add more panels to the rear left side of the room where the door area is or make the front wall ones thicker. This should help me fine tune some things, but wanted to seek everyone's advice. Everyone in this thread has been very helpful with suggestions.

[Ethan Winer]

No dales & hills ever detected on the screen with the analyser mic. around 15" from the untreated backwall.

Not sure how that could happen, unless substantial averaging was applied. But even then, the comb filter response in front of a reflecting boundary is well known and repeatable. I'll be glad to run a sweep using Room EQ Wizard showing the response that occurs at that distance and post it here if you'd like.

--Ethan

[Ethan Winer]

Next I tried the 38% rule from Ethan's website. Again forming an equal lateral triangle. This helped a lot with my bass issue, but it seemed to make the sound lack some depth and a bit flat. The vocals were also congested.

Yes, that placement is meant to optimize the low end. Do you have absorption at the side-wall reflection points? That's also needed for best results. It makes sense that being very close to the speakers improved clarity, because even without absorption for reflections you get more direct sound.

--Ethan

[cheap-Jack]

Hi.

Not sure how that could happen, unless substantial averaging was applied. But even then, the comb filter response in front of a reflecting boundary is well known and repeatable. I'll be glad to run a sweep using Room EQ Wizard showing the response that occurs at that distance and post it here if you'd like.--Ethan

Yes, please do so. But I want to see the floor plan showing detailed positioning of yr testing equipment & what signals used for the test.

My hearing goes inline with the measurements I took with the Yamaha spectrum analyzer. If there were standing wave resonance dips & peaks, I bet you I can detect it let alone the spectrum analyzer findings.

I just can't complain at all with the superb sound from my humber 2x15W home-brew system:- see-thru transparency, precise imaging, lifelike soundstaging, clean & natural bass with balanced HF. Musical & engaging -
without any acoustical treatment added.

c-J