[vinyl_guy]

Thank you all ...
 
At trhis point - I am considering either ideally trading them for neutral / wheat colored traps or covering them with fabric with or without art ...
 
Best Regards ...
Sunil.

Good luck and good listening

Laura

[Nyal Mellor]

That might be true in theory, but I've never seen proof in practice. I've had a few email exchanges with Dr. Toole about this, and once I asked him if the measurements he did improved the ringing a few inches away. He never replied. This to me is the key. Even if you can flatten a null and reduce the ringing for the one cubic centimeter where the measuring microphone is placed, if all the ringing is back three inches away that's not a practical solution. The two times I've done this experiment, EQ was unable to reduce ringing:

Audyssey Report
EQ Versus Bass Traps

I'd love for an EQ proponent to do a proper documented test, as I've done, and show what they measure. I've asked for this more than a few times!

--Ethan

Ethan/All

This paper is also worth reading The Loudspeaker-Room Interface-Controlling Excitation of Room Modes http://www.aes.org/e-lib/browse.cfm?elib=12329 on the subject of use of EQ to control room mode resonances.

Nyal

[Ethan Winer]

This paper is also worth reading The Loudspeaker-Room Interface-Controlling Excitation of Room Modes http://www.aes.org/e-lib/browse.cfm?elib=12329 on the subject of use of EQ to control room mode resonances.

Been there, done that a few years ago when this came up at the AVS forum.

That article is an academic exercise with no practical application:

* Applying a notch filter appears to add artifacts as shown in Figure 9.

* The notch depths were chosen by how much they reduce ringing, which is not necessarily related to the level change needed to achieve a flat response.

* As far as I can tell all of the "proof of concept" graphs through Figure 11 are simulations and not real room measurements. What room has RT60 times of exactly 1.4 seconds at each of the first four modes?

* As far as I can tell, this text from page 12 does not describe a real-world test, but was another simulation with filters applied to recorded signals after the fact. Versus having the filters inserted in the playback path and each location measurement shown as it was captured:

"To check that the method used is spatially robust the measurements used for Figure 6 were also filtered. The pre-filter was calculated from the preferred seating position, position 1 in Figure 4, but applied to measurements taken at all four positions. Decay curves with and without pre-filtering at 32Hz, 60Hz and 92Hz are shown in Figure 21, 22 and 23 respectively. One can see a general improvement in the control of the decay time at all four positions."

In an open space the wavelengths will indeed dictate the "size" of EQ correction. But in an enclosed room the size you'll find in most homes, there are so many reflection paths that the response can change dramatically at very low frequencies over a span of only a few inches. That's clearly shown in the Figure 1 graph below. The same multiple paths also make it nearly impossible to create an inverse function electronically using a parametric EQ.

A few years ago I emailed Audyssey asking (very nicely!) for any graph and data etc they had to support that claim. I also asked for clarification on THIS page of their web site - room size, microphone position, and so forth. I didn't even get the courtesy of a confirmation they received my email. And their site still has nothing to back up their claims. Indeed, when I TESTED the Audyssey system it clearly did not reduce ringing. In fact, at some frequencies the ringing got worse!

It makes no sense that EQ can reduce ringing for a usefully large area. When I discussed this with my math and DSP expert friend Bill Eppler he confirmed that with all such DSP code, the more correction that is applied, the smaller the improved area becomes. So at this point I don't feel the burden of proof has been met, especially since the test and methods in that AES article are so ambiguously described.

I would be thrilled if a small unobtrusive device could really improve room acoustics at bass frequencies! This is the holy grail for acoustic treatment makers, and if EQ really could reduce ringing I'd be all over it immediately and have my own version for sale.

A single pole electronic filter (the EQ) can "counter" a single pole acoustic filter (the room) if it matches exactly what the room is doing. In this case the EQ is set to be the reverse of the room. This is the theory by which an EQ can reduce ringing, and it's valid. But a room is not a single-pole filter! A room is much more complex for two reasons. Assuming a plain rectangle room:

1) There are three dimensions.

2) Each dimension has multiple resonances at harmonically related intervals.

So to counter the effects of the room's filter you'd need three electronic filters, one for each dimension, plus each filter needs multiple poles to account for the harmonic series of resonances. Two poles are needed for each harmonic. So if we consider only frequencies below 100 Hz in a room, say, 25 by 19 by 8 feet, there are 8 resonant frequencies, which means 16 poles are needed. And that's just for mode frequencies, not counting the multiple reflection paths that create additional peaks and nulls (though not more ringing frequencies).

It gets more complicated when you consider the effect of the speaker and listener positions in the room. Most poles contribute something less than 1.0 to the response at any given location. As soon as you move the listening position even a little, the complex relationship changes, and with it changes the response.

--Ethan



Figure 1: This graph shows the low frequency response in a room about 16 by 11-1/2 by 8 feet at two locations four inches apart. Even over such a small physical span, the response changes substantially at many frequencies. SOURCE

[youngho]

That might be true in theory, but I've never seen proof in practice. I've had a few email exchanges with Dr. Toole about this, and once I asked him if the measurements he did improved the ringing a few inches away. He never replied. This to me is the key. Even if you can flatten a null and reduce the ringing for the one cubic centimeter where the measuring microphone is placed, if all the ringing is back three inches away that's not a practical solution. The two times I've done this experiment, EQ was unable to reduce ringing:

Audyssey Report
EQ Versus Bass Traps

I'd love for an EQ proponent to do a proper documented test, as I've done, and show what they measure. I've asked for this more than a few times!

--Ethan

Ethan, you always go on about this modal ringing. Perhaps Floyd Toole had other things to do. I'm just going to post once in this thread, so I'm not going to reply, either.

Looking at your first link, Audyssey Room EQ, KR's room is 15x16x8, so the lowest axial peak would be about 35 hz. Presumably any "ringing" below 35 Hz would be non-modal.

Figure 1 of Audyssey Room EQ shows that the easily perceived "modal ringing" due to the monster peak without Audyssey at just above 40 Hz becomes difficult to perceive because all frequencies between 20 and 56 Hz are now much closer to average when Audyssey is engaged, with corresponding increases in their decay time. That peak in the time domain "modal ringing" at just above 40 Hz is now flanked on either side by several similar "ringing" (presumably non-modal) peaks. Presumably perception of "one note bass" below 56 Hz without Audyssey would be different with it, and I'd actually prefer the very low bass performance with the Audyssey in these figures.

Figure 2 from Audyssey Room EQ is a little confusing. It seems to use different settings for frequency and time resolution, and it seems to have been done at a different position than figure 1 was (the FR curve at time=0 is clearly different from figure 1). I'm going to guess that the data was cherry picked.

Looking at EQ versus Bass Traps, I particularly enjoyed Terry's comment "However use of 17 MondoTraps demonstrated no waterfall chart improvement below about 70 Hz, which are most of the subwoofer frequencies for the typical crossover frequency of 80 Hz." Ironically, looking at Curve No. 1 "No traps No EQ" (http://www.realtraps.com/eq-traps/r+d_fc_empty.gif) and Curve No. 2 "17 traps No EQ" (http://www.realtraps.com/eq-traps/r+d_fc_17_traps.gif) actually makes it looks like the ringing at ~20 Hz is worse in terms of decay time with 17 traps than without (the other low bass peak looks very slightly higher with the 17 traps, but it's hard to tell).

What I am going to do for my own home is to use four subwoofers crossed over at 80 Hz and processed with the JBL BassQ device, which costs about as much as four MondoTraps and which I expect to have much more effect below 80 Hz than four MondoTraps.

Toole's book contains references for the minimum phase argument. He acknowledges that the behavior is only approximate.

[Ethan Winer]

I'm just going to post once in this thread, so I'm not going to reply, either.

I'm editing my post because what I wrote wasn't useful or professional. I do have to ask why you posted if you're not willing to have a discussion. Regardless, no data was cherry picked. What I measured is what is shown. As for 17 MondoTraps not reducing ringing below 70 Hz, that's a limitation of the way the traps were placed, which was my fault:

Since we couldn't easily install MondoTraps in the wall-ceiling corners where they should be, we placed more traps than usual along the walls.

If you watch the more recent Hearing is Believing video you'll see bass traps making a large improvement in both response and ringing all the way down to the lowest mode around 40 Hz.

--Ethan

[Nyal Mellor]

That article is an academic exercise with no practical application:

Not true, the people who wrote it work for Meridian, and the thinking behind it is implemented in their 861 and G68.

* The notch depths were chosen by how much they reduce ringing, which is not necessarily related to the level change needed to achieve a flat response.

The point they are trying to make is that it is more about making decay time as constant as possible in the bass frequencies rather than worrying about a ruler flat frequency response.

[Nyal Mellor]

Ethan,

Surely you can't deny that EQ is a useful tool for dealing with room mode resonances? It can be very effective at reducing the audible impact of resonances below 100Hz where room treatment becomes increasingly uneffective. How would you treat a 10dB room mode resonance peak at 48Hz otherwise? My experiments have shown that applying a high Q filter, say 20-50, matched precisely to the frequency of the room mode, can have a massive audible impact. One which is super easy to hear. We aren't talking small perceived changes here.

Sure, I'm not saying if you use EQ then you don't need acoustic treatment, but I am saying EQ has a place as a tool for audibly improving a room's acoustics.

Especially if we are not worried about improving the acoustics at many places in the room but only care about one location which is quite typical for a two channel system.

Maybe your terminology is different; when I talk about ringing I mean the audible boominess that results from an undamped modal resonance. EQ is definitely effective in reducing the resonance, so in my mind it is also effective at reducing the ringing.

[Ethan Winer]

Surely you can't deny that EQ is a useful tool for dealing with room mode resonances?

Of course not, and I was clear in my Audyssey Report that I use EQ to cut a mode around 40 Hz that remained after putting many bass traps in my living room HT:

To be clear, I am not opposed to the use of EQ to reduce the one or two lowest modal peaks in a room. Conventional broadband bass traps are less effective once you get below about 50 or 60 Hz. So even if an equalizer or DSP device cannot reduce ringing, just lowering a peak's level and the amount of its ringing (if not reducing the decay time) improves the sound in a very real way. Indeed, I have 40 RealTraps in my own living room home theater, but I also use the one-band cut-only EQ built into my SVS PB12-Plus/2 subwoofer to tame the worst modal peak around 40 Hz by a few dB.

So obviously I'm not opposed to all use of EQ.

I'm not saying if you use EQ then you don't need acoustic treatment

Yes, but many people do in fact believe that. If you read the ad copy for loudspeakers with built-in EQ you'd think the EQ can totally fix all room-related problems. Elsewhere in this forum someone recently said, "I would also consider digital room correction to help reduce the echo." So there's a lot of myth-taken understanding about what EQ and DSP can and cannot do.

Especially if we are not worried about improving the acoustics at many places in the room but only care about one location which is quite typical for a two channel system.

That's the whole point of my "Four inches apart" graph above. It proves conclusively that in a home-sized listening room the response varies wildly over very small distances. So it's impossible to correct the response for both ears at the same time, let alone an area wide enough to encompass several seats in a home theater as is often claimed.

Maybe your terminology is different; when I talk about ringing I mean the audible boominess that results from an undamped modal resonance. EQ is definitely effective in reducing the resonance, so in my mind it is also effective at reducing the ringing.

Ringing is the continued sounding of a tone after the source has ceased. Room EQ does not reduce the ringing as claimed. That's kinda the whole point of my posts and graphs and Audyssey article. Yes, companies that sell room EQ claim it reduces ringing. But I have never seen proof that EQ can reduce ringing for an area larger than 1 cubic centimeter. I've been asking for this for years, and not one EQ proponent has ever shown proof. One 15-minute session with REW could prove their point! But all I see is that one AES article which showed simulations instead of real-world tests. Or Toole's article that omits a key detail - what happens two inches away.

Nyal, I'm not opposed to EQ, and I agree it can help at the one or two very low frequencies bass traps can't totally fix. The only time I object is when claims are made that cannot possibly be backed up. Those claims are that EQ reduces ringing by a meaningful amount, and that it does so for a usefully large area. Also, boomy peaks are not the only problem. In many rooms deep nulls usually are the more damaging problem, and even EQ proponents acknowledge that EQ cannot fix that.

--Ethan

[ctviggen]

Ringing is the continued sounding of a tone after the source has ceased. Room EQ does not reduce the ringing as claimed. That's kinda the whole point of my posts and graphs and Audyssey article. Yes, companies that sell room EQ claim it reduces ringing. But I have never seen proof that EQ can reduce ringing for an area larger than 1 cubic centimeter. I've been asking for this for years, and not one EQ proponent has ever shown proof. One 15-minute session with REW could prove their point! But all I see is that one AES article which showed simulations instead of real-world tests. Or Toole's article that omits a key detail - what happens two inches away.

Nyal, I'm not opposed to EQ, and I agree it can help at the one or two very low frequencies bass traps can't totally fix. The only time I object is when claims are made that cannot possibly be backed up. Those claims are that EQ reduces ringing by a meaningful amount, and that it does so for a usefully large area. Also, boomy peaks are not the only problem. In many rooms deep nulls usually are the more damaging problem, and even EQ proponents acknowledge that EQ cannot fix that.

--Ethan

If EQ reduces a peak by, say 10dB, wouldn't that reduce ringing in the sense that the ringing time period is defined in part by the height of the peak?  That is, a peak of 100 dB should ring for less time than a peak of 90 dB would. 

I hope this is true, because I'd like to tame the boom from my Salk HT3s, and was hoping a bass amp with the ability to reduce a single peak would help do so. 

[Nyal Mellor]

If you read the ad copy for loudspeakers with built-in EQ you'd think the EQ can totally fix all room-related problems. Elsewhere in this forum someone recently said, "I would also consider digital room correction to help reduce the echo." So there's a lot of myth-taken understanding about what EQ and DSP can and cannot do.

On this point we are in complete agreement. And we need to educate everyone so they understand this. In my mind three things that a room correction product can't fix - speaker boundary interference, strong early reflections and long reverberation times. These can only be fixed by acoustic treatment or through careful choice of system configuration e.g. use of limited dispersion loudspeakers to reduce need to treat reflection points or crossing over to subs to limit need for treatment to solve speaker boundary interference.

[Ethan Winer]

If EQ reduces a peak by, say 10dB, wouldn't that reduce ringing in the sense that the ringing time period is defined in part by the height of the peak?  That is, a peak of 100 dB should ring for less time than a peak of 90 dB would.

The overall level of the frequency and its ringing will be reduced by the amount of cut applied by the EQ. But the relative sustain time is not changed. However, the audible effect is improvement because the SPL level of peak and its ringing are reduced. If EQ vendors would say it that way I'd have no problem!

--Ethan

[Ethan Winer]

On this point we are in complete agreement. And we need to educate everyone so they understand this. In my mind three things that a room correction product can't fix - speaker boundary interference, strong early reflections and long reverberation times. These can only be fixed by acoustic treatment or through careful choice of system configuration e.g. use of limited dispersion loudspeakers to reduce need to treat reflection points or crossing over to subs to limit need for treatment to solve speaker boundary interference.

Then we're totally on the same page.

--Ethan

[Nyal Mellor]

The overall level of the frequency and its ringing will be reduced by the amount of cut applied by the EQ. But the relative sustain time is not changed. However, the audible effect is improvement because the SPL level of peak and its ringing are reduced. If EQ vendors would say it that way I'd have no problem!

--Ethan

I think this is the point of confusion with the terminology. I would argue that we have reduced audible ringing if we apply an EQ filter to cut a room mode resonance at 60Hz such that the time it takes for that frequency to decay into the noise floor is similar to the frequencies around it. It may not be necessary to make the decay time exactly the same, just enough so that psychoacoustically we can not distinguish it.

Maybe the mathematical definition of ringing is different, not that I have ever seen it written down. In your mind maybe you are referring to ringing as the rate of decay in dB / sec i.e. the decay slope?

[Ethan Winer]

In your mind maybe you are referring to ringing as the rate of decay in dB / sec i.e. the decay slope?

Yes, exactly. Ringing amount is the rate of decay, independent of the room's ambient noise floor.

--Ethan