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Differing speaker measurements
Old 13th August 2012
  #1
Differing speaker measurements

Below are three frequency responce graphs for the same speaker:




The first is provided by Alesis, presumably measured in an anechoic chamber. The second is from Philip Newells "Recording Studio Design" book, measured in an anechoic chamber. The third is from a suspended setup: "The speakers were 20 feet from any boundary yielding an anechoic time interval of about 35 milliseconds" more info here

From what I've gathered the typical anechoic chamber is'nt accurate below 100Hz. So what could possibly account for the differences in the mids? Sample variance?
Old 14th August 2012
  #2
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boggy's Avatar
Quote:
Originally Posted by RoadToNever View Post
..............
From what I've gathered the typical anechoic chamber is'nt accurate below 100Hz. So what could possibly account for the differences in the mids? Sample variance?
Probably. Especially if it is not the same year of production.
Different position of microphone (distance and height, relative to loudspeaker) can be second reason.
Even much more expensive studio monitors isn't delivered as matched pairs (e.g. difference is no more than +/-1dB), so differences in boundaries of +/-3dB, are expected.
Old 14th August 2012
  #3
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Hmmm...what about the standard 1Watt/1meter or 2,83Volt/1meter.

If it is so, as you say Boogy, that they can place the microphone and position differently, well, then we can only guess if the speakers is good or not.
Old 14th August 2012
  #4
Thanks.

I discovered the X-axis on the third graph is skewed!
Old 14th August 2012
  #5
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boggy's Avatar
Quote:
Originally Posted by Mctwins View Post
Hmmm...what about the standard 1Watt/1meter or 2,83Volt/1meter.

If it is so, as you say Boogy, that they can place the microphone and position differently, well, then we can only guess if the speakers is good or not.
It is used for drivers efficiency. Complete multi-way loudspeakers change their response significantly if you vary distance of measurements... mostly because delay between drivers which is compensated only at one listening point away from loudspeaker, and because it is not possible with same crossover to compensate it at all listening distances.

Quote:
Originally Posted by RoadToNever View Post
Thanks.

I discovered the X-axis on the third graph is skewed!
Who knows... in second graph I see shallow "saddle" at 200Hz which is not a problem because measurements but with midwoofer driver, same is with slope which results LF roll-off when decreasing frequency (it is a slightly different driver)... so measurements are pretty different... not only because microphone position, and not only because different anechoic rooms... possibly loudspeakers are different too...
Old 14th August 2012
  #6
It's skewed for a fact because I created the graph from an unsmoothed source:
Here you see a bass bump that tops at around 50-70 Hz
Old 14th August 2012
  #7
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Ethan Winer's Avatar
 

Lightbulb

Quote:
Originally Posted by RoadToNever View Post
So what could possibly account for the differences in the mids?
Scaling! heh

The top graph is 5 dB per division with a total graph height of 40 dB. The second graph is 10 dB per division with a 70 dB total span. The bottom graph is only 3 dB per box spread over 54 dB.

--Ethan

The Acoustic Treatment Experts
Old 14th August 2012
  #8
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boggy's Avatar
Quote:
Originally Posted by Ethan Winer View Post
Scaling! heh

The top graph is 5 dB per division with a total graph height of 40 dB. The second graph is 10 dB per division with a 70 dB total span. ........
If I see good, both first and second graphs are 5dB/div...
at least, for first two graphs, scaling is not a reason for differences...
Old 14th August 2012
  #9
Quote:
Originally Posted by boggy View Post
If I see good, both first and second graphs are 5dB/div...
at least, for first two graphs, scaling is not a reason for differences...
Ditto.

EDIT: Doh! Turns out the third graph wasn't skewed after all, the minor divisions are 20, 200 and 2000Hz each.
Old 15th August 2012
  #10
Today I made of subjective comparison of the curves in the first post inverted, 1/3 octave smoothed and applied by Voxengo CurveEQ.


Newell - Alesis - French

Listening to my favorite commercial recordings these where my findings for each curve:
Newell - Mid-scooped and bassy
Alesis - Clear and tight
French - Somewhere in between, colored mids
I guess I'll use the Alesis curve for a while and see how my mixes translate. Who knows it might just be a cooked curve...
Old 15th August 2012
  #11
Gear Guru
Microphone

I don't understand the purpose here, but was the same microphone used for all three graphs?

DD
Old 15th August 2012
  #12
Quote:
Originally Posted by DanDan View Post
I don't understand the purpose here, but was the same microphone used for all three graphs?

DD
I started as curiosity, few speakers have as many as three independent measurements and all of them differed from each other. But I ended up applying one of the measurements reversed and so far I like the results. No info about the mic used but one could assume a measurement mic was used in each case.
Old 15th August 2012
  #13
Gear Guru
Reverse

I understand. Unless you are in an extremely treated, pretty much anechoic space, the room has a vast influence. May I suggest you may find it interesting to explore the whole response and try adjusting that.
I see you are in Sweden. I suggest you try Dirac Live.
DD
Old 15th August 2012
  #14
Quote:
Originally Posted by DanDan View Post
Unless you are in an extremely treated, pretty much anechoic space, the room has a vast influence. May I suggest you may find it interesting to explore the whole response and try adjusting that.
DD
I am well aware it does nothing for the room I'm not sure I understood your suggestion.
Old 15th August 2012
  #15
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DRC

No worries. Dips of up to 20- 30dB are typical in rooms, making the small variations in loudspeakers seem small.
By 'whole response' I meant the combined effect of speaker AND room. Digital Room Correction attempts to 'correct' that, to make it linear for a chosen
small-ish listening area. And it succeeds to a useful extent IMO.
Look up Dirac Live or AudioLense for a full story.


DD
Old 15th August 2012
  #16
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Quote:
Originally Posted by DanDan View Post
..... Digital Room Correction attempts to 'correct' that, to make it linear for a chosen
small-ish listening area. And it succeeds to a useful extent IMO.
Look up Dirac Live or AudioLense for a full story.
..........
Here is another story: Why Can't I Fix All my Acoustic Problems with EQ? written by John Mulcahy (creator of REW software)
Old 16th August 2012
  #17
Gear Guru
Stories

Certainly Eq cannot fix all problems. However in a case where no or little treatment is possible it can work wonders.
A recent IoA survey of active room correction in CRs concurred. i.e. In poorly treated CRs the improvement at the Mix spot was substantial. With well treated rooms, hardly noticeable and obviously unnecessary.
John has a most interesting story IMO on how Eq can shorten Modes. Contrary to popular belief.
But substantiated by others http://accucalhd.com/documents/audio...20Research.pdf
Here's another bunch of interesting conclusions.
https://docs.google.com/file/d/0B97z...GQ4/edit?pli=1

DD
Old 16th August 2012
  #18
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boggy's Avatar
Quote:
Originally Posted by DanDan View Post
Certainly Eq cannot fix all problems. However in a case where no or little treatment is possible it can work wonders.
A recent IoA survey of active room correction in CRs concurred. i.e. In poorly treated CRs the improvement at the Mix spot was substantial. With well treated rooms, hardly noticeable and obviously unnecessary. ........
My experiences are opposite.
Significant treatment of the small room rectify most of non-minimum phase behavior of acoustic response, so filters become more efficient... I mean, especially in small rooms where we always may have something that cannot be solved. But to be clear, if you have resonant null at listening position... there is no filter that can cure this.
Old 16th August 2012
  #19
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How Much

I shared those beliefs boggy. Until I started experimenting.
While I would never use the full words like 'cure', I am very happy with the 'help'. There are some phenomena which are very amenable to Eq, plenty of others not. John has provided brilliant extra graphs in REW to show when Eq is feasible. While peaks are fair game, many claim that reflection nulls cannot be Eq'ed, and Resonant Nulls cannot be filled in.
Well, again John has nuanced stories on that. It seems that some reflections are indeed amenable to Eq.
Many of us have found that BIR and Resonant Nulls get 'filled in' by the more successful Room Correction systems. As happens with treatment.

Many have suggested that DRC is an icing on the cake. A final step towards greatness after treatment.

Fine, but I and the IoA survey have also found that DRC is very useful in a bad situation. Say in a rented space where no significant treatment is possible. Or where there is no Eq on the monitors and a Target Curve is desired.

Much of the past wisdom on these matters appears to me to be vanishing in the wake of new research and activity and more powerful computers.
AudioLense has a time domain element. Convolution is used. Dirac uses Mixed phase filters.

In any case what harm in trying out the new stuff? All I suggested here is that it would be more powerful than reverse eqing published speaker responses.

While DEQX, Trinnov and such require commitment, there are demoes of Dirac Live and the highly regarded AudioLense.


DD
Old 16th August 2012
  #20
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boggy's Avatar
Quote:
Originally Posted by DanDan View Post
........ Say in a rented space where no significant treatment is possible. Or where there is no Eq on the monitors and a Target Curve is desired.
In untreated rented space, personally known headphones and excellent headphones amplifier, may be decision without surprise at end.. I don't like surprises.
Quote:
Originally Posted by DanDan View Post
Much of the past wisdom on these matters appears to me to be vanishing in the wake of new research and activity and more powerful computers.
AudioLense has a time domain element. Convolution is used. Dirac uses Mixed phase filters.
Whatever, we had dedicated processors (DSPs), and even (faster) field programmable gate arrays (FPGAs), absolutely adequate for this audio purposes, for more than ten years ago... so processing power is not an argument (how long we have video DSP?). I believe main reason is that adequate acoustic treatment is anything but not cheap, so there is a big reason to push this type of products.
Quote:
Originally Posted by DanDan View Post
In any case what harm in trying out the new stuff?
Time... people needs years to figure out psychoacoustically if this can help or not, and they waste their time if something cannot help (at end). People can adapt to virtually anything.. but this not means that anything is good...
Quote:
Originally Posted by DanDan View Post
All I suggested here is that it would be more powerful than reverse eqing published speaker responses.
Ok, I go off topic...sorry

Old 16th August 2012
  #21
Gear Guru
Eq

No need boggy, I believe you, like I used to, wish to steer people away from wasting time with things that don't work.
However, I believe things have changed.
bwo (and I) show measured success in FR and Time Domain here in this thread using Dirac and AudioLense.
JohnPM of REW also shows Eq shortening a 50Hz mode.
Flatten Monitors Response - Recommended Software?! Filter Impulse Response?

I fully expect to see active systems performing well soon.
e.g. the Bag End Active Trap with DSP added.

DD
Old 16th August 2012
  #22
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boggy's Avatar
Quote:
Originally Posted by DanDan View Post
..........
I fully expect to see active systems performing well soon.
e.g. the Bag End Active Trap with DSP added.
...
Really!?
Bag End had a way different (and closer to really needed) conception. If we have subwoofer which will "wait" for wave... and respond adequatelly we can change anything in room.. especially if we use DSP and membrane traps on walls with plywood boards + exciters, active boundaries... this will be right active digital room correction... not like other jokes.

We still need diffusers.... well... still some job for woodworkers

I'm still off topic

Old 16th August 2012
  #23
Based on what I've read I'm only compelled to consider Room EQ for the bass range only, for the sole purpose of correcting residual peaks but nothing available seems cater to that specifically. My reasoning is that the omnidirectional nature of low frequencies and makes it valid for a large part of the room rather than small spots like typical DRC. Room treatment with bass traps, absorbers and diffusors are in the plans for my control room, along with a measurement mic for tracking my progress. I'm aware the exercise of reversing published speaker responses is kind of a novelty item in the grand scheme of things but I like it so far and I'll see how I like it after my room is treated. Please let me know if you think I'm looking at this wrong.
Old 16th August 2012
  #24
Gear Guru
Active Boundaries

OT I suppose boggy but I think the stuff we are bouncing back and forth may be of interest to readers.

Here's some Active LF trap experimenting.

active helmholtz resonator

I reckon your 'wait' suggestion, i.e. a delay would probably yield better results than trying to sense using a mic in the corner.

DD
Old 16th August 2012
  #25
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Quote:
Originally Posted by DanDan View Post
OT I suppose boggy but I think the stuff we are bouncing back and forth may be of interest to readers.
I fully agree with you, and I like off topic, or I love to discuss wherever discussion took his place, but I also understand other members who don't like mess here.
Quote:
Originally Posted by DanDan View Post
Here's some Active LF trap experimenting.

active helmholtz resonator
Thanks for the link
Quote:
Originally Posted by DanDan View Post
I reckon your 'wait' suggestion, i.e. a delay would probably yield better results than trying to sense using a mic in the corner.

DD
Yup, I agree, it can be successfully modeled ... microphones may be a problem.
But, be aware that this is all but not cheap room treatment.... I suppose... but it is on right direction (if we like DSP to be involved)
Old 16th August 2012
  #26
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Ethan Winer's Avatar
 

Lightbulb

Quote:
Originally Posted by DanDan View Post
As always, details of the test procedure are minimal. And if they really did measure that in a room, they don't show what happens six inches away.

--Ethan
Old 16th August 2012
  #27
Gear Guru
Fixed

'As always?' That seems like a finely honed view.
So anyone who does research into Digital Room Correction is out to con us?
You could ask them what the test procedures were if you really wanted to know. This is a paper, I think they assume a certain amount of academic responsibility both in output and in how it is intended to be read. I cannot imagine that they have any axe to grind.
Furthermore most of the paper seems to contain theory as to how/why the concept is possible. I am not sure they are out to prove anything here, just interesting research on the road forward.

The multipoint issue has been dealt with repeatedly, as has the poor performance of one particular system which is used to discredit the overall concept.

I strongly suspect robbing energy from a mode, shortening it by Eq, will have useful effect over quite large areas. I mean to test this sometime soon. However, audibly, I have found Dirac to substantially improve a poor response, over pretty much the whole room.
Ethan, afaik you have a parametric equaliser in action in your system.
Are you still using it? Does it work? Is it useful in one particular spot or over a larger area?

DD
Old 17th August 2012
  #28
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Ethan Winer's Avatar
 

Lightbulb

Quote:
Originally Posted by DanDan View Post
You could ask them what the test procedures were if you really wanted to know.
I asked Audyssey to clarify their test method many years ago and I'm still waiting for an answer. heh

Often people who publish technical papers go on to start a company selling the same technology. Not that I'm a cynic or anything!

Quote:
afaik you have a parametric equaliser in action in your system.
Are you still using it? Does it work? Is it useful in one particular spot or over a larger area?
Yes to all of that. But I know the EQ only reduces the volume of the modal peak, and doesn't reduce its decay time. That's all I addressed.

--Ethan
Old 17th August 2012
  #29
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Tested

To the best of my knowledge Audessey, in particular the original version, is and was not highly regarded. The survey I linked showed that some DRC software simply didn't work.
Given the total dissing of Audessey on the RT site I fully understand the lack of response to questions.

I don't think Genelec are selling DRC as an entity separate from their speakers.
Many speaker manufacturers include DRC these days.

Repetition is boring, but I am afraid I cannot let the statement that Eq does not shorten a mode stand. It does sometimes.

This is shown, both in theory as explained by JohnPM and Genelec engineers, at least, and in practice. Flatten Monitors Response - Recommended Software?! Filter Impulse Response?

Ethan, have you examined your own mode using REW facility to show susceptibility to Eq?
Have you measured your mode length with and without Eq?


DD
Old 18th August 2012
  #30
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Ethan Winer's Avatar
 

Lightbulb

Quote:
Originally Posted by DanDan View Post
Given the total dissing of Audessey on the RT site I fully understand the lack of response to questions.
I asked Audyssey for a better explanation long before I wrote the article. From my Audyssey Report:

Quote:
Originally Posted by Audyssey Report
I emailed Audyssey on October 29, 2006, regarding the technical descriptions and graphs ... At the time of this writing, 3-1/2 months later, I have yet to receive a reply from Audyssey.
I still have that email if anyone wants to see exactly what I asked and what tone of voice I used.

Quote:
Repetition is boring, but I am afraid I cannot let the statement that Eq does not shorten a mode stand. It does sometimes.
Yes, sometimes. But what happens four inches away? How about 18 inches away? This is never ever shown. And I know why. heh

Quote:
Ethan, have you examined your own mode using REW facility to show susceptibility to Eq? Have you measured your mode length with and without Eq?
The last time I measured my living room was several years ago, and I wasn't aware of a feature in REW that predicts how well EQ might work. I have measured my room with and without the subwoofer's EQ engaged, but that too was years ago.

Dan, the reason I'm certain of my position is because of the way LF response changes in small rooms over even very small distances. I'm sure you've seen this graph from an article on my personal web site that was measured in the RealTraps lab room:



So how could EQ possible improve one location without totally ruining the response at the other? What would you have the EQ do at 71 Hz where there's a null at one location but a peak at the other? The difference between those two locations four inches apart is 13 dB!

Further, the balance needed to counter the ringing of a mode is critical. It's like nulling two audio files to hear the difference. If the levels are off by even 1/4 dB, or the timing is off by even one or two samples, the null is severely compromised. The same happens when EQing a room mode.

--Ethan
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