Addressing a Null

I have no bass traps in my living room, and it looks flatter than Ethan's.

It is, however, a room with no parallel surfaces to speak of. It's got walls on two adjacent sides, an interrupted wall with a stairwell in both directions in the third, and a kneewall and a-frame roof on the 4th side. The a-frame roof goes up to a shed roof at about 30 degrees that is the main part of the roof.

No, didn't design it. Just bought it. Some architect had way too much fun here.

Wayne A. Pflughaupt said:

I see at the link that you have 44 of them.

Click to expand...

I now have 55.

So your 400 sq. ft living room has just 125 sq. ft. left, I’ll bet – LOL!

Click to expand...

At 25 by 16 with an (average) 9.5 high ceiling, it's more like 1580 square feet of surface area. The room is absolutely not overly dead at mid and high frequencies. Below is a recent photo.

--Ethan

j_j said:

I have no bass traps in my living room, and it looks flatter than Ethan's.

Click to expand...

I love you to death JJ, but I have to call BS on that. Unless your living room is six times larger than usual. Can you post a high resolution waterfall of the LF response taken at the listening position? And no fair doing what one wise guy HT "designer" did at AVS a few years ago, when he put the measuring microphone a foot in front of the subwoofer!

--Ethan

Awesome Ethan! :b

* The picture on your screen; it's not a real projected one?

Ethan Winer said:

I love you to death JJ, but I have to call BS on that. Unless your living room is six times larger than usual. Can you post a high resolution waterfall of the LF response taken at the listening position? And no fair doing what one wise guy HT "designer" did at AVS a few years ago, when he put the measuring microphone a foot in front of the subwoofer!

--Ethan

Click to expand...

I see you didn't read the description, then? And I am very sure of my measurements. It helps that I have no parallel walls, and the volume is rather much, with the 20' peak in the ceiling.

gshelley said:

Amir,
Are you suggesting phase adjustment, or, something more like Nyal has outlined (e.g. Trinnov etc.)?

Click to expand...

Yes, delay and phase are the same thing on a subwoofer control.

Wayne said, "Wow. I can’t imagine how many bass traps it takes to get a waterfall like that! Scratch that, I see at the link that you have 44 of them."

Then JJ said, "I have no bass traps in my living room, and it looks flatter than Ethan's." Along with this he said, "It is, however, a room with no parallel surfaces to speak of. It's got walls on two adjacent sides, an interrupted wall with a stairwell in both directions in the third, and a kneewall and a-frame roof on the 4th side. The a-frame roof goes up to a shed roof at about 30 degrees that is the main part of the roof.
No, didn't design it. Just bought it. Some architect had way too much fun here."

I am with JJ on this, I have no bass traps in my room and I am fortunate that my room was built to the Golden ratio (Golden Proportions). My response is flat to below 20hz with no bass overhang and the bass starts and stops on a dime! No boom boom in this room. Also I listen at a live sound levels at times and the room sounds great even when playing loud.

I have listened to the anechoic rooms and they sound terrible and look even worse. There are numerous threads here and elsewhere that show that these treatments don't work. Even with mucho treatment several posters here do not show a good in room response even with a fully padded room.

Ethan then went on to say, "I love you to death JJ, but I have to call BS on that. Unless your living room is six times larger than usual. Can you post a high resolution waterfall of the LF response taken at the listening position?"
Where JJ replied, "I see you didn't read the description, then? And I am very sure of my measurements. It helps that I have no parallel walls, and the volume is rather much, with the 20' peak in the ceiling."
Well thats enough evidence for me, don't bother posting the graph as I can't read them anyway!

I don't put much credence in these computer programs, I listen with my ears and they tell me everything I need to know.

So why are some audiophiles over treating rooms? And why do some, though fortunately very few, audiophiles destroy the purity and essence of their systems with equalization?

My answer to those two questions are that most have bad rooms (that is a lost cause and you can never to achieve good sound no matter how much padding), and don't choose great speakers in the first place . Get those two things correct, then you don't need the audiophile padded cell!

Wendell

An audiophile friend of mine asked me why I don't believe in these measurements and besides my hearing what I hear I can quote what Dr Floyd tool said as quoted by Amirin one of his excellent articles.

"By the way, much of this was probably intuitively obvious as you noticed how quiet your room was despite the high SPL numbers shown on the meter. As Dr. Toole, one of the top experts in acoustics and speaker design is fond of saying, “two ears and a brain are much more analytical than a microphone and a meter!” Indeed, your ears told the truth better than the measurement device."

Wendell

amirm said:

Yes, delay and phase are the same thing on a subwoofer control.

Click to expand...

Well they do the same thing but pedantically speaking they are not the same. A 1ms delay represents a different phase shift at say 20Hz vs 80Hz because the wavelengths are different.

gshelley said:

Amir,
Are you suggesting phase adjustment, or, something more like Nyal has outlined (e.g. Trinnov etc.)?

Are we saying room modes and SBIR are the same?

Click to expand...

There are ways of seeing reflections easier than looking at the FR. Looking at the phase or excess group delay trace is one tactic.

I don't think Room Modes (resonances) and SBIR (phase cancellation) are the same.

Nyal Mellor said:

(...) I don't think Room Modes (resonances) and SBIR (phase cancellation) are the same.

Click to expand...

And you think well ... http://store.acousticfrontiers.com/Speaker-Boundary-Interference.html

and http://redspade-audio.blogspot.pt/2011/02/sbir-speaker-boundary-interference.html

NorthStar said:

Awesome Ethan! :b

* The picture on your screen; it's not a real projected one?

Click to expand...

Right, I put the camera in place, then shot the screen with the lights completely off, then again with the lights on. Since the camera didn't move between shots, it was easy to paste the screen portion onto the lighted portion. BTW, after all the years I've been showing this photo, you are only the second person to notice this. The other person is my video / camera expert friend Mark Weiss, also a member here.

--Ethan

theguesswho said:

I have no bass traps in my room and I am fortunate that my room was built to the Golden ratio (Golden Proportions). My response is flat to below 20hz with no bass overhang and the bass starts and stops on a dime! ... I listen with my ears and they tell me everything I need to know.

Click to expand...

I imagine you'd be very surprised if you saw a graph of the LF response and ringing of your room.

There's nothing wrong with listening to assess room acoustics! But it's very limited for a number of reasons. One big reason is that music contains only certain frequencies, which may or may not align with room resonances or nulls. If your room has a severe ringing peak at 110 Hz, it may not show up unless the bass plays an A note. All rooms have peaks and nulls, even yours. So to assess it fully you'd need to spend literally hours playing different pieces of music in different keys. Versus a sine wave sweep that tells you everything you need to know - peaks and nulls, ringing, RT60, early reflections - in ten seconds. Further, measuring will tell you exactly how large a peak is, and exactly how long a mode decays for. This is why professional acousticians and audio systems engineers use measuring software!

BTW, a good room ratio doesn't avoid peaks and nulls and ringing. All home-sized rooms have those issues, even when the walls or ceiling / floor are not parallel. One reason for a "good" ratio is to avoid multiple modes at nearby frequencies which combine to be even stronger than a single mode. Another is to avoid a large span between modes, which gives a sort-of "hole" in the response.

--Ethan

j_j said:

I see you didn't read the description, then? And I am very sure of my measurements. It helps that I have no parallel walls, and the volume is rather much, with the 20' peak in the ceiling.

Click to expand...

I read the description. I won't press this further JJ, but if I'm ever in your area I will visit you and demand to see waterfalls!

--Ethan

Nyal Mellor said:

Well they do the same thing but pedantically speaking they are not the same. A 1ms delay represents a different phase shift at say 20Hz vs 80Hz because the wavelengths are different.

Click to expand...

Same is true of the so called "phase" control on a subwoofer. The circuit used is actually quite simple and is called an "all-pass filter." This is a filter which has constant amplitude but has a phase which changes with frequency -- exactly what the delay does. Here is its response:



They are simply implemented in analog domain by cascading a low-pass and high-pass filter. That backs out their magnitude response change (top graph), leaving one with just the cascaded phase shift per graph below.

This is what I know of their implementation having looked their circuit design. Do you have a source that says differently?

amirm said:

Same is true of the so called "phase" control on a subwoofer. The circuit used is actually quite simple and is called an "all-pass filter." This is a filter which has constant amplitude but has a phase which changes with frequency -- exactly what the delay does. Here is its response:

They are simply implemented in analog domain by cascading a low-pass and high-pass filter. That backs out their magnitude response change (top graph), leaving one with just the cascaded phase shift per graph below.

This is what I know of their implementation having looked their circuit design. Do you have a source that says differently?

Click to expand...

Amir,

Never have seen a circuit with such a wide margin - almost 720º! The typical simple circuit only allows 0-180º phase and inversion:

http://sound.westhost.com/project103.htm

There is a detail I never thought about - most subwoofers have a graduated phase scale. What should be the frequency chosen for this scale?

Fortunately the Behringer DCX 2496 digital crossover allows changing both delay and phase and I never had to face this problem!

I should have been more clear that the response I showed was from a random all-pass filter online and not ones used in subwoofers.

Ethan Winer said:

Right, I put the camera in place, then shot the screen with the lights completely off, then again with the lights on. Since the camera didn't move between shots, it was easy to paste the screen portion onto the lighted portion. BTW, after all the years I've been showing this photo, you are only the second person to notice this. The other person is my video / camera expert friend Mark Weiss, also a member here.

--Ethan

Click to expand...

Thank you Ethan for that description; I wouldn't have guessed it that way.
...Mark is an avid photographer/videographer/subwoofer explorer, so I'm not surprised here. :b

* I'm sure other people noticed it too; they simply did not comment, or ask about it.