A Response to Floyd E. Toole's AES Article "The Measurement and Calibration of Sound Reproducing Systems" - Page 4 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #31 of 41 Old 09-01-15, 10:17 AM
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Re: A Response to Floyd E. Toole's AES Article "The Measurement and Calibration of Sound Reproducing Systems"

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jtalden wrote: View Post
Yes, I understand and agree with this comment and the impact of it. In Harmon's case it makes the understanding of what is done to boost sales and what is real engineering conviction difficult to decide. In Toole's case I am sure it all makes sense within the scope he covers. My only issues why it doesn't follow for me? Usually things we expect to be true bear out in listening sessions whether or not they are real. In this case the clear preference is counter to the expectation.
Regarding Harmans products, I believe on their most sophisticated stereo integrated, there was an option for EQ only<500hz iirc, or the option to EQ full range.
I'm still a bit confused by your case. Aren't you saying no EQ is used/required above 800hz?

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My comparison is between near field axially flat speaker output from 300-20kHz Vs adding the indicated filter that fills a dip around 400Hz that otherwise occurs when measuring at the LP. These are DIY SEAS H1456/H1212 per the 'Equipment List' under my name. DCX2496 provides XO, delay and EQ as needed. The 16L Box is 2nd order/sealed, Qb=~0.5 the poly fiber fill is, if anything, possibly a little over filled from typical. So, there is not much that can go wrong with the MR response from 100-2k range. The speaker is EQ corrected for baffle step, the overall rising response of that driver and for a small resonance peak around 800Hz similar to the response shown in the SEAS driver spec sheet. I have all sorts of measurements and can show some that support this assertion and some that don't. Indoor measurements are somewhat very dependent on window setting and positioning trying to prove it is flat 100-500 is problematic. so we better not go there. I don't have outdoor measurement, but the preponderance of my work suggest the near-field response of the speaker is basically flat with the base EQ until I add this 400Hz filter and one or 2 more below 300Hz to address other modes below the Schroeder.
Yes, I saw your speakers were DIY and figured you would have some form of diffraction loss filtering (how much was added is unclear). Yes, best measured free space, but regardless, it seems you've accounted for that. So obviously more of a speaker/room modal issue.
One of the main reasons I got in the business. A 6.5" midbass is going to be largely omnidirectional to around 800hz, I assume your baffle isn't much wider than 8 or so inch, so you will get a lot of front wall reflection behind the speaker, combined of course, with all other directions as it radiated 3D, so its never quite that simple. Solution there by my way of thinking, is cardioid radiation, something quite doable with DSP. Then EQ if needed. "Fix" the source first.

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jtalden wrote: View Post
Room effects? Yes, mine have serious room effects that appear in the midrange up to 600Hz. The question is, it better to EQ those even though it is above the cited upper end of the Schroeder transition frequency or not. My experience is that it is clearly demonstrable that it is better to EQ out my dip even that happens with 20ms delayed.
It's always source/room effects. Not separable. Put a cardioid or dipole where a monopole was, same room, very different result at the LP. Can't be viewed independent of one another.
Yes, the upper range recommended by the paper may need revisiting and I have always contended with Olive and Geddes et al, that EQ alone is not enough. That the radiation characteristics of the source can go beyond what EQ can address. Then make so called passive/active "treatments" a final step, if needed. Clearly you are hearing audible benefit from EQing higher than recommended.


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No, I haven't changed speakers. I have nice reasonably uniform horizontal dispersion as shown below. I have close phase tracking through the XO so the central lobe is stable. The vertical dispersion is as expected for a 7" MW and 1" dome; fairly narrow and asymmetric (not shown). It's unavoidable with this configuration.
Yes, that is very good response. Perhaps some diffraction effects (not sure of your baffle edge shaping), but very good overall. I imagine a lowish XO. By "different", I meant to see if the 300-600hz dip was consistent.

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jtalden wrote: View Post
If it is recognized that in some cases EQ departing from flat axial speaker output may provide some benefit as high as 300-600Hz then that accommodates my situation. It may be that simple.

Possibly Toole's guideline is intended to provide a very good reliable result that is acceptable for all practical applications and I am just fussing over the last bit of improvement possible beyond that? At least that is one possibility.

It's not like the sound is poor without the filter it is just noticeably better on some material with it. I am very pleased with most all aspects of my current setup. It measures well and has very good SS&I. My interest is as a hobbyist who wants to learn and experiment to develop better understanding and thus drag out the last bit of sound quality that this setup can muster - just for fun. Since I have no source of comparison to other well calibrated systems or to experienced listeners, there is no telling how my setup really sizes-up by comparison. If you or Wayne want to stop by and critique the sound quality, please do. Unfortunately that is probably not going to appear high on your to-do list however.
Nothing to disagree with there and if I'm ever up that way, thanks for the invite. Closest I usually get is Axpona CHI.

cheers,

AJ

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post #32 of 41 Old 09-03-15, 08:42 AM
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Re: A Response to Floyd E. Toole's AES Article "The Measurement and Calibration of Sound Reproducing Systems"

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ajinfla wrote: View Post

I'm still a bit confused by your case. Aren't you saying no EQ is used/required above 800hz?
Sorry for the confusion. It is probably due to my way of thinking of the overall EQ situation. I was trying to differentiate between the 'base EQ' and the 'room EQ' portions of my total EQ settings. I'm calling 'base EQ' the filters that are needed to create a flat near-field speaker response. This would be a part of a speaker design that is intended to be sold commercially. It may include compensation for driver response, baffle step and possibly even diffraction effects. The 'room EQ' portion are the filters needed to achieve the desired house curve at the LP. The point was that above 800Hz the filters needed to create a flat speaker response work reasonably well to also achieve the preferred house curve at the LP. Only possibly a some minor roll-off adjustment would be needed for my LP distance. I am agreeing with the paper that having a smooth direct response of the speaker would work fine above 800Hz in my case.

It was my preference for a filter at 400 Hzthat I was confused about. I, perhaps mistakenly, understood that it would be better not to use that 'room filter' as it is above the modal range.

Some charts may help the understanding. Below is; 'base EQ' for the FL and FR speakers, LP measurement that include the total EQ filters (The 4 shown above and 3 lower ones including the 400Hz filter), 16" measurement with the 'base EQ' (The 4 filters shown). While my total EQ was actually determined at the LP. The measurement at 16" shows that the direct response above 800Hz is relatively flat hence the observation that there is good EQ agreement above 800Hz for these 2 methods in this case.

Other info relative to your comments:
As you noted, I have tried to keep the XO on the low side to help keep a smoother horizontal dispersion handoff between drivers. The XO approximates an acoustical LR-24 at about 2.2kHz. The front wall is 20 feet behind the speakers so no early reflections there. There are the diffraction effects of the box design and possibly that is at least partially why the higher frequency filters are needed in the base EQ to get a flat direct response. I also attached a measurement file of the 3 front speakers as the LP in case other charts of the overall setup are of interest.

A Response to Floyd E. Toole's AES Article &quot;The Measurement and Calibration of Sound Reproducing Systems&quot;-dcx.png

A Response to Floyd E. Toole's AES Article &quot;The Measurement and Calibration of Sound Reproducing Systems&quot;-fl-fr-lp.png

A Response to Floyd E. Toole's AES Article &quot;The Measurement and Calibration of Sound Reproducing Systems&quot;-fl-fr-16in.png

LP DLNA-2-3.mdat
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post #33 of 41 Old 09-08-15, 04:43 PM
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Re: A Response to Floyd E. Toole's AES Article "The Measurement and Calibration of Sound Reproducing Systems"

Thanks and sorry for late reply, got busy with some orders. Looks good.
I think we are in agreement that no or minimal EQ should be needed >800hz and I'm not quite sure if we disagree with Toole, as his own data show issues to 500+ Hz in most rooms, so maybe the "room" to "speaker" transition region is well above 200-300hz, possibly as high as 800hz.
20' from front wall? Lucky you.

cheers,

AJ

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post #34 of 41 Old 01-09-16, 02:54 AM
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Re: A Response to Floyd E. Toole's AES Article "The Measurement and Calibration of Sound Reproducing Systems"

The discussion with Dr. Toole should be interesting for readers of this thread:
http://www.hometheatershack.com/foru...-dr-toole.html

BR,
Raimonds
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post #35 of 41 Old 01-09-16, 08:20 AM
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Re: A Response to Floyd E. Toole's AES Article "The Measurement and Calibration of Sound Reproducing Systems"

Hi Raimonds,
Thanks for posting that.
I have read Dr. Toole's popular book, his recent paper and seen your comments. As you point out, there is little in specific and practical guidelines for studio/home EQ setup. I find it impossible to understand Dr. Toole's research and the citations well enough draw any confident conclusions of my own on how to proceed with EQ. I am looking forward to more detail coming now that both Dr. Toole and David Smith mentioned that something is in the works. Possibly that will be more helpful. My background in product development and application engineering includes some time on an SAE standards committee. There is lots of 'corporate interest' lobbying in that type of process that impedes development of clear standards. No company wants to see their products/practices fall into a disadvantageous market position. It seems to me the music creation industry is all over the place in terms of studio EQ practices. Hopefully the charts I've seen showing gross variability are dated and things have improved. Possibly this new work will push it along. I am not too confident however as the market forces are strong and entrenched.

I am not familiar with your products and practices and I found it difficult to follow your thoughts on how EQ is best done.

> Sound intensity in a window of some size at the LP?
> Localized Power response in a window of some size at the LP via either 'moving mic method' (MMM) or individual mic positions?
> Should there be a defined house curve for a defined setup or are there too many parameters to make that practical?
> I understood that you advise linear phase response at the LP through the full range. Correct? Some hobbyists indicate linear phase in bass range is not as important and others do not hear any improvement. Also I am understanding that linear phase at the LP would be in reference to the direct sound and not in trying to chase the phase rotations due to room influences (reflections and modes).
> Do you agree that a single measurement at the LP position is adequate for bass range EQ?
> Do you agree that in most situations the EQ result above maybe 800Hz will be reasonably similar whether the measurements are done via quasi-anechoic at say 1m Vs the LP if an MMM method is used given that there may be appropriate HF roll-off/absorption due to distance?

If my situation is typical, EQ of the bass and HF range practices seem relatively clear compared to the 300-800Hz midrange. Asymmetric room setup and limited acoustic treatments as I have make the EQ of room effects in that range difficult to address. I would agree that it is impossible for EQ to correct the issues, but find that it can help mitigate the severity of them. A professional studio is better able to address the source of the issues through room design and acoustic treatments. I have self-imposed constraints in that area and instead just want a clearer understanding of a process or guidelines to mitigate the damage.

I am not expecting a detailed response to any of this long post, but If you would care to cite a reference to your thoughts on any of these areas, or provide thoughts on any of this here, I would appreciate that. I am mostly just trying to understand how best to deal with the midrange EQ in a nonideal room situation. I like my current midrange EQ setup far better than avoiding EQ in that range. Many experienced hobbyest have advised that any EQ there to address room effects is not advised. I am more inclined to suggest to other hobbyists that they can improve the sound quality via EQ in this range if reasonable methods are used.
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post #36 of 41 Old 01-09-16, 09:42 AM
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Re: A Response to Floyd E. Toole's AES Article "The Measurement and Calibration of Sound Reproducing Systems"

My uncle has told me that FR is hugely not important... as long as your within a +/- 3 or 5db then your good.

He does praise proper toe of the speakers.... position within the room... and exactly symmetrical layout and having the speakers elevation, plumb and level exact to to an accuracy of .05°. He said this is vital for pinpoint sound-stage.

I've listened and his SSI is amazing even though there are a few faults in the FR (particularly the highs falloff too fast imho).

Master Electrician

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Re: A Response to Floyd E. Toole's AES Article "The Measurement and Calibration of Sound Reproducing Systems"

Thanks Talley,
I take that to mean that the anechoic axial response of the speaker should be flat and room effects should not be addressed. Recently, a smooth off-axis response is also often stated as an important factor. This apparently holds up so long as the room is symmetrical and the setup is ideal for speaker, listening positions and appropriate acoustical treatments. I have seen that often stated before and it is rational to me that very good results could be expected. Most, Including Dr. Toole seem to agree that the bass range still benefits from EQ and I assume your uncle does also. But... Does that mean high end studios do not ever EQ above the Schroeder frequency to achieve improved results? Is 1/3 octave RTA, DRC, Audyssey, YPAO, Dirac, Acourate, et.al., all marketing schemes with no real value? I really don't know what EQ practices are common there, but suspect some EQ is applied. If not, then does this change in the case of non ideal setups as mine? Possibly EQ is more valuable in that case. I would think that it might be even more effective there.

I was mostly fishing for more practical guidance relating to what best practices are. From my experience it seem very beneficial to EQ the midrange and to shape the HF. I am a hobbyist having only experience with my room setup, so I am interested as to how my methods compare to more professional ones.
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post #38 of 41 Old 01-09-16, 06:17 PM
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Re: A Response to Floyd E. Toole's AES Article "The Measurement and Calibration of Sound Reproducing Systems"

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Thanks Talley,
I take that to mean that the anechoic axial response of the speaker should be flat and room effects should not be addressed. Recently, a smooth off-axis response is also often stated as an important factor. This apparently holds up so long as the room is symmetrical and the setup is ideal for speaker, listening positions and appropriate acoustical treatments. I have seen that often stated before and it is rational to me that very good results could be expected. Most, Including Dr. Toole seem to agree that the bass range still benefits from EQ and I assume your uncle does also. But... Does that mean high end studios do not ever EQ above the Schroeder frequency to achieve improved results? Is 1/3 octave RTA, DRC, Audyssey, YPAO, Dirac, Acourate, et.al., all marketing schemes with no real value? I really don't know what EQ practices are common there, but suspect some EQ is applied. If not, then does this change in the case of non ideal setups as mine? Possibly EQ is more valuable in that case. I would think that it might be even more effective there.

I was mostly fishing for more practical guidance relating to what best practices are. From my experience it seem very beneficial to EQ the midrange and to shape the HF. I am a hobbyist having only experience with my room setup, so I am interested as to how my methods compare to more professional ones.
I see value in EQing... but my uncle is a die hard. His system is pure analog. source, pre, amp... speaker done. I think he would value from it but nothing I can do to change his 45yrs of hi-fi.

Master Electrician

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post #39 of 41 Old 01-10-16, 07:00 PM
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Re: A Response to Floyd E. Toole's AES Article "The Measurement and Calibration of Sound Reproducing Systems"

Thanks, guys, for this really interesting discussion (& you especially Wayne, for getting it going)! My knowledge is not sophisticated enough to understand all that has been said, but I do get (and appreciate) some of it. Thanks again.

Jack Brent
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post #40 of 41 Old 01-11-16, 01:35 AM
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Re: A Response to Floyd E. Toole's AES Article "The Measurement and Calibration of Sound Reproducing Systems"

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jtalden wrote: View Post
Hi Raimonds,
Thanks for posting that.
I have read Dr. Toole's popular book, his recent paper and seen your comments. As you point out, there is little in specific and practical guidelines for studio/home EQ setup. I find it impossible to understand Dr. Toole's research and the citations well enough draw any confident conclusions of my own on how to proceed with EQ. I am looking forward to more detail coming now that both Dr. Toole and David Smith mentioned that something is in the works. Possibly that will be more helpful. My background in product development and application engineering includes some time on an SAE standards committee. There is lots of 'corporate interest' lobbying in that type of process that impedes development of clear standards. No company wants to see their products/practices fall into a disadvantageous market position. It seems to me the music creation industry is all over the place in terms of studio EQ practices. Hopefully the charts I've seen showing gross variability are dated and things have improved. Possibly this new work will push it along. I am not too confident however as the market forces are strong and entrenched.

I am not familiar with your products and practices and I found it difficult to follow your thoughts on how EQ is best done.

> Sound intensity in a window of some size at the LP?
> Localized Power response in a window of some size at the LP via either 'moving mic method' (MMM) or individual mic positions?
> Should there be a defined house curve for a defined setup or are there too many parameters to make that practical?
> I understood that you advise linear phase response at the LP through the full range. Correct? Some hobbyists indicate linear phase in bass range is not as important and others do not hear any improvement. Also I am understanding that linear phase at the LP would be in reference to the direct sound and not in trying to chase the phase rotations due to room influences (reflections and modes).
> Do you agree that a single measurement at the LP position is adequate for bass range EQ?
> Do you agree that in most situations the EQ result above maybe 800Hz will be reasonably similar whether the measurements are done via quasi-anechoic at say 1m Vs the LP if an MMM method is used given that there may be appropriate HF roll-off/absorption due to distance?

If my situation is typical, EQ of the bass and HF range practices seem relatively clear compared to the 300-800Hz midrange. Asymmetric room setup and limited acoustic treatments as I have make the EQ of room effects in that range difficult to address. I would agree that it is impossible for EQ to correct the issues, but find that it can help mitigate the severity of them. A professional studio is better able to address the source of the issues through room design and acoustic treatments. I have self-imposed constraints in that area and instead just want a clearer understanding of a process or guidelines to mitigate the damage.

I am not expecting a detailed response to any of this long post, but If you would care to cite a reference to your thoughts on any of these areas, or provide thoughts on any of this here, I would appreciate that. I am mostly just trying to understand how best to deal with the midrange EQ in a nonideal room situation. I like my current midrange EQ setup far better than avoiding EQ in that range. Many experienced hobbyest have advised that any EQ there to address room effects is not advised. I am more inclined to suggest to other hobbyists that they can improve the sound quality via EQ in this range if reasonable methods are used.
Thank you for your valued opinion and questions!
I will try to answer.

*) As I am pointing to focus on loudspeaker performance I do not use such term as Listening Point. Even very early users of my works were referencing lack of any sweet spot and any connection to some listening point when the correction was introduced. Of course, there are some special cases when loudspeakers have very narrow directivity. Special measures are taking place in such cases.
*) The loudspeaker’s Sound Power response (for far field applications) is base.
*) The MMM is a trial to reinvent some part of this work, published in 2005
http://www.google.com/patents/US8121302

*) I did not see any benefit of use of Linear Phase filters in any application. I am using Minimum Phase correction filters from very start in 2002. Because of 1) no latency 2) the minimum phase problems of loudspeaker are corrected ideally- as from amplitude as from phase prospective. The beauty of that you can see in LF correction when large GD caused by main resonance of loudspeaker, is removed.

*) I do not understand any attempts to do some correction from one point measurement (or few points) that are connected to some LP. Because of fact that any trial to fill up some dip on FR (caused by room modes or interference – non minimum phase behavior) is requesting narrow resonant peak on equalizer’s FR. That two „processes” are not with opposite sign – they do not compensate each other as it is with basic assumption of the use of correction that - predistortions, which are introduced by equalizer, will be compensated (neutralized) by distortions of system that we are truing to equalize.

If we are looking for exception quality in LF we should turn to near field setup with appropriate EQ. The TDA EQ is for that.

Our, human, listening perception is build such way that it extracts the „color” of sound source even in case of far field. We will percept any predistortions as distortions of sound source if such predistortions are not closely connected to real distortions of source – loudspeaker. This is true especially up from midrange.


Quote:
... as long as your within a +/- 3 or 5db then your good.
This is true for listening for enjoyment and when „problems” are wide band.

The job of recording/mix engineer is requesting decision making within accuracy of 1...2 dB and the monitor system with respective accuracy is requested.

If you are willing to catch (listen for) nuances of different „handwriting style” of each engineer/producer/label, you should have a loudspeaker system with appropriate accuracy.

Quote:
...the anechoic axial response of the speaker should be flat...
It is impossible to find true axes even for loudspeakers with smooth and wide directivity...


But, if little bit touch the room, the most degradating factor of room are its windows.
Nothing can be more problematic than a real large window next to yours speakers.

BR,
Raimonds
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