Some comments from Floyd Toole about room curve targets, room EQ and more

[QMuse]

Here's the before & after, I've finished EQ'ing for this "session" today, I chose the 2dB Low Shelf Curve from one of my previous posts as I ran out of available filters to EQ the 3dB and 5dB Low Shelf Curves, and it allowed more headroom for volume, less overall boost....EQ'ing only the 20-550Hz region:

Before EQ:
View attachment 59470

After EQ (actual measurement) - 3dB of overall Input Gain Lost:
View attachment 59471

And I also have this following graph as a option too, which is the same as the above except with allowing REW to boost the little trough at 60Hz, but that cost an extra 2dB of Input Gain Loss:
After EQ (actual measurement) - 5dB of overall Input Gain Lost:
View attachment 59472


Subjective Listening Experience:
In terms of listening to scenes from the film Prometheus back to back comparing those 2 curves, it's a bit of a toss up between them. There is a feeling of slightly fuller bass from the last graph, but there is slightly more detail to be heard in the 2nd graph...these were played back at same volume level (I chose the same Input Gain Loss in both for this listening experiment).

Conclusions & Questions:

• I'm leaning towards using the 2nd graph above more than the 3rd, because it's 2dB less Input Gain loss and there is slightly more detail to be heard in general using that one (for some reason), with the trade-off being it's slightly less full in the bass.
• Using Var Smoothing is very very unforgiving on the bass area (thereby showing every tiny sharp dip & peak), is there any merit in using more smoothing in that area to potentially save on number of filters used?
• I think I've chosen the right peaks and area to EQ right? The 20-550Hz area?
• It looks to me like the dip at 75Hz / 110Hz / 135Hz are all impossible and right not to EQ?
• I also couldn't get rid of the peak at 120Hz, I think it's because it's slap bang inbetween two sharp dips.
• With miniDSP I had 12 filters at my disposal, and I used them all so I have nothing left over to EQ above 550Hz, do you think it's wise not to EQ above that area from what you see in my graphs anyway?
• When I use Equaliser APO for music listening (the previous is all talk re TV/Movie watching), I'll have more filters available, so it's possible I could EQ the curve above 550Hz, do you think this would be wise though? The broad peak at 1800Hz looks like it could be brought down, but that's right at the crossover point. Also, in light of the lack of anechoic data for this JBL 308p Mkii, is it wise to leave this area unEQ'd too?

Yeah, so I've got a few questions there, I would be grateful for people's thoughts & analysis on it.

This looks very good!

What I would ssuggest is to take your speaker in the middle of the room, put it on some stand and measure it from app 1 meter with sweep. If you apply gating of 6-7ms you should be able to get pretty accurate pseudo-anechoic response from 1kHz onwards and based on it you should be able to apply correction in that region.

Alternatively to time gating you can also try to apply a FDW of 4-6 cycles. Choose appropriate value depending on the ammount of reflections in your room untill the phase response doesn't need wrapping. This way you should also be able to get a picture how phase response looks.

This is how such measurement looks with my speaker, blue is with 7ms gating and violet with FDW of 6 cycles. As you can see they are practically identical and that is why I actually prefere FDW instead of gating as FDW also gives you phase response over the entire frequency range.

500-1000 Hz region is kind of a mixed bag as that is where room interference mixes with speaker dominated response. IMHO opinion it can be corrected based on MMM spatial measurement taken from your LP. I suggest you use psychoacoustic smoothing and apply some low Q corrections to smooth it where necessary, but be carefull not to overdo it.

 

[Robbo99999]

To both questions the answer is yes.

But only for the specific directivity of that loudspeaker as the generated response at the listeners position also depends on it.

Unfortunately http://seanolive.blogspot.com/2009/10/audios-circle-of-confusion.html and the reason why many older recordings rather tend to sound bass shy (being mixed with not room-corrected large monitors) but if that circle is overcome and all recording engineers just use neutral monitors corrected in the bass region to their room than we won't have that variable any longer.

Yes, so matching the room curve of the recording engineer would be the most accurate solution, and I can see what you mean by the Circle of Confusion. In that link they did indeed measure a number of recording studios, and there is for sure a lot of variation there! The median curve is showing a "Flat Response" that isn't sloping down apart from a small bass hump, but given the variation the applicability of choosing a room curve close to the median is not overly useful. I suppose by choosing a slightly downward sloping room curve then you're saying that on average you're gonna have more bass being heard than the recording engineer envisaged, and given that "more bass" is not really an annoying feature to a lot of people, then that kind of makes sense as a safe bet to choose as a target curve......so praps choosing such a downward sloping curve is the better of two evils in terms of covering all the possible recording studio curves with the least amount of annoying/negative qualities coming to the surface.

This looks very good!

What I would ssuggest is to take your speaker in the middle of the room, put it on some stand and measure it from app 1 meter with sweep. If you apply gating of 6-7ms you should be able to get pretty accurate pseudo-anechoic response from 1kHz onwards and based on it you should be able to apply correction in that region.

Alternatively to time gating you can also try to apply a FDW of 4-6 cycles. Choose appropriate value depending on the ammount of reflections in your room untill the phase response doesn't need wrapping. This way you should also be able to get a picture how phase response looks.

This is how such measurement looks with my speaker, blue is with 7ms gating and violet with FDW of 6 cycles. As you can see they are practically identical and that is why I actually prefere FDW instead of gating as FDW also gives you phase response over the entire frequency range.

View attachment 85023

500-1000 Hz region is kind of a mixed bag as that is where room interference mixes with speaker dominated response. IMHO opinion it can be corrected based on MMM spatial measurement taken from your LP. I suggest you use psychoacoustic smoothing and apply some low Q corrections to smooth it where necessary, but be carefull not to overdo it.

Thanks, that was a very old post of mine you quoted, so I can't even remember exactly how I had my room & speaker layout at that point, but it's definitely different to now. At the moment I have my 2 speakers at least a meter from all walls and listening/watching at just over a 2m equidistant triangle. My actual measurements don't look much different in terms of the resulting EQ'd curves in terms of accuracy to the curve, but I've chosen now to use a "Full" Harman Curve for all Movies/TV/Music. I'm hoping that Amir will measure the JBL 308p Mkii (which is the same speaker I have), it's in his pipeline to do he's said......at which point I'll have a go at using his spinorama measurements to EQ the mids & treble (above the room modes). At the moment I'm happy with the my EQ'd results so far, so I'm not gonna do anymore tweaking until I get to see a spinorama. I have a feeling the JBL 308p Mkii might not measure that well, so that might be a little niggle in the back of Amir's mind that he could do without the slightly tricky waters of reviewing a not so well performing Harman product......I mean I'm pretty sure it's fixable with EQ in my experience, but yeah.

 

[thewas]

Room response measurements should always be considered with upmost care as we don't know how the windowing and smoothing was chosen. Also most monitoring is done in nearfield where direct sound dominates and thus the slope is less falling than under usual hifi listening conditions. This means that it is not a good choice to try to replicate the room curve of the recording room also due to the possibly different directivity and room reverberation characteristics plus the room response is usually unknown. Instead, like Toole recommends the most sensible choice is to use neutral on axis and with smooth directivity loudspeakers as a basis and just use tone controls or EQ if needed to adapt for personal taste, loudspeaker and room characteristics and recording flaws.

 

[QMuse]

Room response measurements should always be considered with upmost care as we don't know how the windowing and smoothing was chosen. Also most monitoring is done in nearfield where direct sound dominates and thus the slope is less falling than under usual hifi listening conditions. This means that it is not a good choice to try to replicate the room curve of the recording room also due to the possibly different directivity and room reverberation characteristics plus the room response is usually unknown. Instead, like Toole recommends the most sensible choice is to use neutral on axis and with smooth directivity loudspeakers as a basis and just use tone controls or EQ if needed to adapt for personal taste, loudspeaker and room characteristics and recording flaws.

I fully agree.

I'm hoping that Amir will measure the JBL 308p Mkii (which is the same speaker I have), it's in his pipeline to do he's said......at which point I'll have a go at using his spinorama measurements to EQ the mids & treble (above the room modes).

You really don't have to wait for that to happen - as you can see from numerous measurements made by @napilopez the technique I described works well enough for you to EQ for neutral on-axis response and to check what will happen with horizontal axis response once you do it.

 

[Robbo99999]

You really don't have to wait for that to happen - as you can see from numerous measurements made by @napilopez the technique I described works well enough for you to EQ for neutral on-axis response and to check what will happen with horizontal axis response once you do it.

Noted

 

[Hipper]

One factor not mentioned is age related or other hearing loss, which is a very individual thing. We tend to lose hearing at the higher frequencies. This is briefly touched on in Toole Third Edition, page 196, and chapter 17. However this is mostly about prevention of damage. What would be more interesting is if there is any research as to if it is a good idea to try and adjust with EQ for hearing damage, whether it might do more harm to hearing and if it can actually improve the listening experience. I can't hear above 10kHz so wondered if rolling off the sound above 10kHz would have some sonic benefits and perhaps reduce the 'strain' on the tweeter. I couldn't hear any difference when I did this and have no idea if the life cycle of the tweeter would be lengthened or if there would be a sonic negative. In addition, if say there was a loss of 5dB in my hearing at 8kHz, would it do any harm to my ears if I added 5dB at 8kHz with the EQ?

A further factor is that not only are some recordings deficient in bass as noted, but some are also poor in the percussion areas. Therefore not only a bass control but a treble control is required. I try to do the latter with my equaliser. I consider that music engineers can also be deficient in hearing and that may affect their productions.

Finally something not yet mentioned is the interaural crosstalk of a typical stereo speaker set up, discussed by Toole on page 159. To summarize, in a stereo set up, your left ear not only hears the sound from your left speaker but also some from the right speaker. This bends round your head to your ear and the extra distance travelled - 7"-8" - leads to interference of the two sounds causing comb filtering which causes a dip at around 2kHz of perhaps 6dB. Apparently this is partially made up by side wall reflections. Of course the 2kHz region is a key area for the stereo phantom image. I've tried to control side wall reflections with room treatment and still get a strong centre image. You can also control the interaural crosstalk, either with room treatment on the inside of the speaker or using DSP - known as Ambiophonics. I keep meaning to experiment with this.

 

[JoachimStrobel]

One factor not mentioned is age related or other hearing loss, which is a very individual thing. We tend to lose hearing at the higher frequencies. This is briefly touched on in Toole Third Edition, page 196, and chapter 17. However this is mostly about prevention of damage. What would be more interesting is if there is any research as to if it is a good idea to try and adjust with EQ for hearing damage, whether it might do more harm to hearing and if it can actually improve the listening experience. I can't hear above 10kHz so wondered if rolling off the sound above 10kHz would have some sonic benefits and perhaps reduce the 'strain' on the tweeter. I couldn't hear any difference when I did this and have no idea if the life cycle of the tweeter would be lengthened or if there would be a sonic negative. In addition, if say there was a loss of 5dB in my hearing at 8kHz, would it do any harm to my ears if I added 5dB at 8kHz with the EQ?

A further factor is that not only are some recordings deficient in bass as noted, but some are also poor in the percussion areas. Therefore not only a bass control but a treble control is required. I try to do the latter with my equaliser. I consider that music engineers can also be deficient in hearing and that may affect their productions.

Finally something not yet mentioned is the interaural crosstalk of a typical stereo speaker set up, discussed by Toole on page 159. To summarize, in a stereo set up, your left ear not only hears the sound from your left speaker but also some from the right speaker. This bends round your head to your ear and the extra distance travelled - 7"-8" - leads to interference of the two sounds causing comb filtering which causes a dip at around 2kHz of perhaps 6dB. Apparently this is partially made up by side wall reflections. Of course the 2kHz region is a key area for the stereo phantom image. I've tried to control side wall reflections with room treatment and still get a strong centre image. You can also control the interaural crosstalk, either with room treatment on the inside of the speaker or using DSP - known as Ambiophonics. I keep meaning to experiment with this.

EQing for high frequency loss is difficult, as the required gain soon reaches 10-30db. That is out reach for most tweeters and a valid thought might be the introduction of special EQable speakers and amps for the elderly.
More promising is the EQ process for the 3-8 kHz range where real hearing loss as in true loss happens. It is known, that the typical ISO loudness correction curves are based on young’s people hearing and are hence only valid for them. Likewise, it is a truly interesting thought, if the room correction frequency dip is valid across all ages. I would, and have, convolved hearing EQ with a room curve, but used the one from Toole’s book as base without change.
Head related transfer functions tackle the question around ear to ear crosstalk. It is not discussed a lot so far.

 

[QMuse]

One factor not mentioned is age related or other hearing loss, which is a very individual thing. We tend to lose hearing at the higher frequencies. This is briefly touched on in Toole Third Edition, page 196, and chapter 17. However this is mostly about prevention of damage. What would be more interesting is if there is any research as to if it is a good idea to try and adjust with EQ for hearing damage, whether it might do more harm to hearing and if it can actually improve the listening experience. I can't hear above 10kHz so wondered if rolling off the sound above 10kHz would have some sonic benefits and perhaps reduce the 'strain' on the tweeter. I couldn't hear any difference when I did this and have no idea if the life cycle of the tweeter would be lengthened or if there would be a sonic negative. In addition, if say there was a loss of 5dB in my hearing at 8kHz, would it do any harm to my ears if I added 5dB at 8kHz with the EQ?

A further factor is that not only are some recordings deficient in bass as noted, but some are also poor in the percussion areas. Therefore not only a bass control but a treble control is required. I try to do the latter with my equaliser. I consider that music engineers can also be deficient in hearing and that may affect their productions.

Finally something not yet mentioned is the interaural crosstalk of a typical stereo speaker set up, discussed by Toole on page 159. To summarize, in a stereo set up, your left ear not only hears the sound from your left speaker but also some from the right speaker. This bends round your head to your ear and the extra distance travelled - 7"-8" - leads to interference of the two sounds causing comb filtering which causes a dip at around 2kHz of perhaps 6dB. Apparently this is partially made up by side wall reflections. Of course the 2kHz region is a key area for the stereo phantom image. I've tried to control side wall reflections with room treatment and still get a strong centre image. You can also control the interaural crosstalk, either with room treatment on the inside of the speaker or using DSP - known as Ambiophonics. I keep meaning to experiment with this.

I choosed not to correct for hearing loss. I'm 56 and when I tested my hearing recently it turned out that it is ok up to app 8kHz after which it falls and I'm not able to hear pretty much anything above 13kHz. But I expect my music, especially voices to sound as similar as possible to what I hear when listening live voices in my everyday life, hence I saw no need to apply any correction for m hearing loss.

 

[Robbo99999]

Amir released an anechoic measurement of the JBL 308p Mkii speaker yesterday (https://www.audiosciencereview.com/...ds/jbl-308p-mkii-studio-monitor-review.17338/), and I own that same model of speaker, so I took the opportunity to create an Anechoic EQ for them. I've tested the Anechoic EQ without any Room EQ and it sounds great, previously I was using Room EQ. Today I did some different Room EQ's on top of the Anechoic EQ, and I'm not quite sure where I stand with Room EQ right now.....I think it's actually more important to have a flat speaker in your room rather than relying on Room EQ based on the excellent experience I've had yesterday with the Anechoic EQ on my speakers without using any Room EQ.

Based on my different RoomEQ's I've done on top of the Anechoic EQ and my listening tests on them I do think Room EQ cleans up the bass a little and makes it more defined so you can follow bass lines in busy electronic music a little better, but at the same time it did reduce the general impact of the bass level slightly - I used the track Supermassive Black Hole from the band Muse as my test track because it's a high quality recording whilst being very very busy as well as including a dense & impactful bass line, which I know like the back of my hand and from listening on Harman EQ'd headphones I know how well defined that bass line can really be. (In fact, I'm kinda crazy, each time I listen on my headphones I play the beginning portion of that track to verify a good headphone positioning, and by listening to this track a lot it becomes an excellent benchmark.). Anyway, based on my testing of my RoomEQ's on top of the Anechoic EQ I really don't think it makes a great improvement to my JBL 308 speakers....it's a toss up with losing a little impact of the bass on one side whilst gaining a tad more definition in the bass....it's a very hard call to know which one I really prefer....which leads me to conclude that a flat speaker in a room is the most important element. Following is an outline of some my different Room EQ's I tried along with my Anechoic EQ pictured to start with, this is more for curiosity or discussion, but I'll include a few notes as I lay down pics of the EQ's:

JBL 308p Mkii EQ's:
All EQ filters created manually by me in REW, no automatic filter generation. Y-axis dB spread is 45dB on all graphs, so 5dB more zoomed in than the graphs Amir uses (he uses 50dB), so just a little stricter on that front. In listening tests I volume matched in as much as I accounted for the variations in negative preamp per EQ by adjusting dB level on my E30 DAC.

Anechoic EQ of Listening Window:
So the following was my baseline anechoic EQ from Amir's speaker review (upon which I applied Room EQ which I'll show in other pics)
(for TV/Movie watching I'll be using just the Anechoic EQ as it happens to fit perfectly within the 12 available filters of my miniDSP 2x4, but for music listening via my laptop with Equaliser APO then I have the flexibility to decide on RoomEQ combined with Anechoic EQ vs just using Anechoic EQ alone because unlimited number of filters available in Equaliser APO)

One Sixth smoothing Room EQ which is on top of the previous Anechoic EQ:
The following is only doing Room EQ below 300Hz, I did listening tests with doing Room EQ below 500Hz, but in listening test only focussing below 300Hz sounded slightly better - I was prompted to focus mainly below 300Hz after reading up that generally transition frequency is up to 300Hz, so tested vs my previous practice of doing RoomEQ below 500Hz. This pictured EQ is the best sounding Room EQ I did, and is the one I'm in a bit of a toss up with in comparison with just using the Anechoic EQ on it's own, pictured above.

I also did listening tests with EQ's created at different smoothing levels (I rejected the following Room EQ's in favour of the previous ones):

Var Smoothing Room EQ on top of Anechoic EQ:

One Third Smoothing Room EQ on top of Anechoic EQ:

Another strong point of relying just on the Anechoic EQ without applying any Room EQ is that the speaker sounds better throughout the whole room at various positions, Room EQ seems to make it sound worse as a complete whole in the room - if you were to walk about in it for instance.

Yeah, it's a bit of toss up between the One Sixth Smoothing Room EQ vs using the Anechoic Listening Window EQ on it's own. I thought I'd present my findings because it is on topic re Room EQ here, and I thought it might help some folks narrow down some good sound, plus it might be an interesting continued discussion......one thing's for sure is that the Anechoic EQ being used alone or in conjunction with Room EQ is an improvement over just using Room EQ on it's own as I was having to do previously!

 

[thewas]

An anechoic linear FR is always a better basis for room correction as you can see then what the room superposes additionally (in the opposite case you don't know what comes from the room and what from the loudspeaker) and thus chose your target curve more approximately, often for example the average of mode peaks and dips.

 

[Robbo99999]

An anechoic linear FR is always a better basis for room correction as you can see then what the room superposes additionally (in the opposite case you don't know what comes from the room and what from the loudspeaker) and thus chose your target curve more approximately, often for example the average of mode peaks and dips.

Yes, I decided to line up the target line on the treble section due to it not really being influenced by the room and knowing that I had anechoically flattened out that response before measuring, so I used that as the basis of truth. I then flattened out the peaks above that line as well as boosting a low Q dip area slightly, but I only did this below 300Hz as I figured that between 300Hz and 1kHz might be 'anomolies of measurement' as there was quite some variation from measurement to measurement in that area (perhaps a combination of listening to the room & listening to the speaker between 300Hz and 1kHz so kept faith with the anechoic measurement in this area), whereas the major peaks & troughs sub 300Hz lined up quite well from measurement to measurement regardless of where I measured on my couch listening area. EDIT: I'll attach a screenshot of all my measurements overlaid to illustrate that point:

 

[thewas]

Just as a general advice, doing MMM measurements rminimises the for correction unwanted local variations.

 

[Robbo99999]

Yeah, I've heard about that, although I measured at six different positions 20cm each side of centre, and about 15cm between front & rear measurement - that's all for RoomEQ at one listening position.

 

[bo_knows]

"if one has selected well-designed loudspeakers"

Key phrase that Dr. Toole inserts religiously whenever discussing this topic.

But how to know if yours are 'well designed' without being supplied a proper set of measurements?

Another circle of confusion....

I was about to say the same, after reading his material, the main point is always "BUY A BETTER SPEAKER".
I can't argue that KEF Reference 3/5 measure and sound better than my KEF R500. I guess I better start saving money. LOL

 

[ernestcarl]

Room EQ seems to make it sound worse as a complete whole in the room - if you were to walk about in it for instance.

More so "excessive room EQ" esp. the boosting kind to fill nulls in one listening position.

In my open plan living room, the only EQ I use is a general broad tone control in the bass and treble. That's it. There's too much bass variation differences as there is not one listening couch/chair or area to focus on -- people stand, sit, walk about or even sit on the floor... cook in the kitchen or dine on the table etc.

 

[tuga]

More so "excessive room EQ" esp. the boosting kind to fill nulls in one listening position.

In my open plan living room, the only EQ I use is a general broad tone control in the bass and treble. That's it. There's too much bass variation differences as there is not one listening couch/chair or area to focus on -- people stand, sit, walk about or even sit on the floor... cook in the kitchen or dine on the table etc.

High performance stereo is innevitably a single-seater experience.

For a more uniform response over the whole of the room there may be other more adequate options. And in my view "people stand, sit, walk about or even sit on the floor... cook in the kitchen or dine on the table etc." are probably not as demanding or expected to pay attention at things like imaging and soundstage.
Perhaps you'd be better off pursuing something else, f.e. a multi-room system driving multiple omnis (Bang & Olufsens?).

 

[ernestcarl]

High performance stereo is innevitably a single-seater experience.

For a more uniform response over the whole of the room there may be other more adequate options. And in my view "people stand, sit, walk about or even sit on the floor... cook in the kitchen or dine on the table etc." are probably not as demanding or expected to pay attention at things like imaging and soundstage.
Perhaps you'd be better off pursuing something else, f.e. a multi-room system driving multiple omnis (Bang & Olufsens?).

That was only for that particular open-plan room space. I use a dedicated space for more serious listening.

 

[amirm]

Anyway, based on my testing of my RoomEQ's on top of the Anechoic EQ I really don't think it makes a great improvement to my JBL 308 speakers....it's a toss up with losing a little impact of the bass on one side whilst gaining a tad more definition in the bass....it's a very hard call to know which one I really prefer....

That is the general trade off and I run into this all the time with speaker reviews. Many times you want that extra bass as opposed to less of it but clean.

The situation changes drastically though the lower the speaker goes as far as response. It will then activate the room modes more and gets you really boomy bass. The 308 is in that transition area so your experience makes sense.

As I say all the time, you must uses your ears as a final arbiter in EQ changes. This is because we can't get perfection so trade offs need listening tests.

 

[Pio2001]

Thanks for sharing your experiments, Robbo99999 !

I was prompted to focus mainly below 300Hz after reading up that generally transition frequency is up to 300Hz, so tested vs my previous practice of doing RoomEQ below 500Hz.

I depends. I do my room eq up to 600 Hz.

It would be interesting to know if the strong variations between 100 and 200 Hz in your frequency response are physically caused on the speaker side or on the listener side.
The room simulator of REW can help you find this.

I also did listening tests with EQ's created at different smoothing levels

For me, the main variable is the target curve, rather than the smoothing. The success of my room eq strongly depends on slight differences between targets.

 

[Pio2001]

Another strong point of relying just on the Anechoic EQ without applying any Room EQ is that the speaker sounds better throughout the whole room at various positions, Room EQ seems to make it sound worse as a complete whole in the room - if you were to walk about in it for instance.

I know that this is uncommon, but I am in the opposite situation : the room eq makes the sound much better all around the room (and even in the next rooms).
My situation is simple, without any eq, my system makes the noise of an elephant's herd. With eq, the elephants are gone.

I measured a set of frequency responses in various positions in the room. All measurements are single point sweeps, and therefore look quite jagged, compared to a proper MMM or multipoint measurement.

The red dot is the sweet spot. The blue dots are extra measurement positions.
Text, from top to bottom: armrest, center, sofa, table left, table center, table right.

In each of the following pictures, there is one measurement with room eq OFF, and one with room eq ON. The one with room eq OFF is always the one with strong peaks in low frequencies.
The room EQ is exactly the same in all graphs.

Sweet spot :

25 cm to the right of the sweet spot :

80 cm to the left of the sweet spot, sitting in the next place:

150 cm behind, sitting at the table, seat 1:

150 cm behind, sitting at the table, seat 2:

260 cm behind, sitting at the table, seat 3: