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Room EQ, do's and dont's

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The miniDSP runs a set of big (6.5 cubic foot sealed) speakers with 15" drivers, 6" mids and ribbon tweets that are suspended from the ceiling. All drivers are high efficient 94+ db sensitivity. The room is a 16x20 with 11' ceilings with the mains on the 16' wall, no room treatments to speak of (yet) but plenty of books on the walls. There is a sealed 15" home built sub under the left speaker and a small 10" Sony sub in the corner under a built in desk 20' away on the long access of the room. As it is a workspace full of equipment I don't have many (any) options on speaker or sub placement so I have to work with what I can. The speakers are hung equal distances 16" from sidewalls and 25" from the back wall, 7' from the floor, 10" to ceiling and are 6' 10" apart from one another. They are angled down and toed in to the listening space. There is precious little on the net about flying speakers for home audio, plenty for event sound reinforcement and stage work though but little of it translates to high fidelity listening environments.

As I said though, it's a work in progress and incomplete build. Things move slow in the winter here so I'm not inclined to be in the woodshop and build new boxes and baffles when it's 30 degrees out so these new mids and tweets I'm auditioning are in crude little "satellites" flying off the main boxes. Ugly as sin and hardly ideal so when I measured them for tweaking I was pleasantly surprised despite the 10dB peak to peak variations. A lot of it will get ironed out with proper boxes so I haven't dug in deep with too much analysis beyond these frequency response measurements and a glance at the waterfalls until I finish the complete build. The room problems have been consistent from many measurements over the years. They sound amazingly good though as is. A picture or two is worth a 1000 words so:

Edit: The measurement from the post above is the average taken from 17 mic positions around the room from which I created separate EQ for the left and right channels in REW. The "sweet spot" measurement has 5dB peak to peak variations and quite a bit better even at 1/12th smoothing but the room modes are still apparent (and exceed that +/- 5dB).
 

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OK, here's an example of what I mean. Should be enough to get you started.
Consider the 70 Hz dip, which has a wavelength of about 16'.
SBIR: if the speakers are 4' from the front wall, this dip might be caused by SBIR. The 70 Hz bass wave propagates spherically, hits the back wall and bounces forward. It's covered 8', which is half a wavelength at 70 Hz, so it's 180* out of phase with the original wave propagating forward, so it creates a null.
LBIR: if the listener is 4' from the rear wall, this dip might be caused by LBIR. The 70 Hz bass wave passes the listener, hits the back wall and reflects forward, passing the listener again. As it does so, it's covered 8' which is 1/2 wavelength so it's 180* out of phase with the incoming wave, creating a null.
Room mode: your 16' distance is the wavelength of 71 Hz, so it sets up standing waves at 71 and 36 Hz. Those standing waves have stable peaks and nulls at certain fixed positions along the 16' distance. So at 71 hz, you will measure big peaks or big dips in the response depending where along that path you measure. Usually, the difference is so big you can easily hear the change in frequency response as you slowly walk from one wall to the other.
So, mess around with speaker & listener positions, see how the peaks & dips change frequency.
Then you'll see how much you can fix by moving things around, then what's left you can tackle with room treatments, then finally use EQ to fix whatever remains. To clean up the spectral decay, you'll need absorption. Something like large diameter tube traps for the bass (which you can easily build yourself), thick acoustic foam for the mids and highs. These are broad spectrum and clean up the decay overall. Then you can use narrow bandwidth resonators or absorbers for specific ringing frequencies, which are often at the room modal frequencies.
 
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Yes, I follow your logic but, as I said, work in progress so until I finish the new speaker boxes I won't address any specific issues but room issues can always be dealt with. The front of the speakers are indeed 16' from the reflecting wall but that wall is covered in books so adding something to diffuse the back wall reflection is probably the best place to start for that 70hz problem. You bet I'll be building these things myself, another project for the warm summer months...

Like I said, no options to move speakers around the room. Gotta work with what I can. Also, this is a work space - I could tune things directly for a "sweet spot" but I move around in here so prefer to try to optimize things for an overall "room sound" - a lot of you can't wait to get home and listen to your rigs, I can't wait to get to the studio and be emersed in mine all day and frequently into the night. :p

Thanks for the analysis though! Beyond more books, room treatment is at the top of the list.
 
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If room treatment is the top of your list, and you're into DIY, here's how I built my tube traps. They are broadband absorbers that tamed bass modes in my room by 10 dB, as well as improving spectral decay, and making the bass much tighter and cleaner. At 2' diameter 7' tall each, it would have cost thousands from ASC, where I built them myself for about 10% of that cost. If you're starting out, in my experience you can't go wrong with that as a first step.
 
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Nice write up but I would like to see some pics along the way. I'm limited in floor space where I can give full on tube traps, I could probably do one full height in the corner by the sub and another half height one in another corner. Given the speakers proximity to the ceiling I've always been concerned about the reflections coming from there, similar to floor reflections given by traditionally placed speakers but other than some light fixtures and a fan there's nothing to interfere with that like a couch or rug might!

Maybe suspend an area rug from the ceiling? :eek: Seriously, I've thought about it - it's a work space. I don't care about veneered cabinets or visible cable runs. (But will never put in an ugly acoustic drop ceiling despite that.)

Here are a couple more pics of the waterfall and impulse measurements but, once again, these are from the aforementioned room measurements and are an average response based on those 17 mic locations. The waterfall is at 1/12th smoothing.

My method of EQ for the room is a variation on this previously shared link earlier in this thread but, like Krunok, I limit the amount of gain and Q allowed for drivers above the 3-400hz range:
https://www.reddit.com/r/audiophile/wiki/room-correction

Impule from average.jpg
waterfall from average.jpg
 
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Your room has some serious ringing around 70 Hz. Broad spectrum absorbers will help overall, but you'll probably need a tuned resonator for something that strong and narrow. With tube traps, the diameter determines the effective freq range, and the height (total volume) determines how much effect you get. So whatever you can add, will help, and if you can't add much, start in the corners to get the most out of it.
Here's what mine look like; they are 3'6" tall each, with a pair stacked in each corner. In-construction pics I don't have, but my page above links to another site that has someone else's in-construction pics. Mine are built similarly.
1552600289167.png
 
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Either that, or a tuned membrane bass absorber that I mentioned in post #116, which you can also DIY. With these, the resonant frequency is based on the density of the flexible membrane and the depth of the sealed enclosure behind it.
GIK makes some pre-built tuned to specific frequencies (40 Hz, 70 Hz).

But I would suggest applying broad bandwidth treatment first (like tube traps). That's going to give overall improvement to articulation and cleaner faster spectral decay overall, which these resonators don't do.

Put differently: if you fix the strong narrow modes without doing anything else, the room will still sound bad, or only slightly better. The improvements are narrow bandwidth and will be masked by broad spectrum slow decay overall. But if you tackle the broadband first, the room will sound much better overall, cleaner and tighter, then the benefits of tuned resonators will be more apparent.
That's just my amateur experience based opinion.
 

Krunok

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Your room has some serious ringing around 70 Hz.
Not really - as it dies before 300 ms I wouldn't agree with the term serious. It actually looks quite good to me assuming it is a living environment and not a studio.
 
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Very much a live environment, a large 4.5x7' table full of lead sits in the middle of the room screwing up the subs dispersion and lots of other solid heavy metal surfaces for things to bounce around on.

bindery header.jpg


I did some research last night on room treatments. It seems conventional folk wisdom that books are good diffusers is mostly false. Oh well, I'm not getting rid of my books so I'll treat the areas I can when I can. First priority is to actually finish that speaker project, anyone who looked at those photos I posted above can see that there are all kinds of problems with those prototype satellites as is...
 

Krunok

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Very much a live environment, a large 4.5x7' table full of lead sits in the middle of the room screwing up the subs dispersion and lots of other solid heavy metal surfaces for things to bounce around on.

View attachment 23668

I did some research last night on room treatments. It seems conventional folk wisdom that books are good diffusers is mostly false. Oh well, I'm not getting rid of my books so I'll treat the areas I can when I can. First priority is to actually finish that speaker project, anyone who looked at those photos I posted above can see that there are all kinds of problems with those prototype satellites as is...
Wow - you really like books, do you? I would never touch anything in that room to make sound better, it looks perfect as it is now. :)
 
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LOL, books are my livelihood, that's bindery equipment, just ran some in wall speakers into the pressroom as well with enough SPL to compete with running equipment. Books, the stereo and trout are the big 3 here....

Glad you like the space Krunok, come visit and we'll listen together. :)
 

Krunok

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After receiving comment from @pos that my filters kind of have too many taps ( :D ) I decided to rebuild them in a more simple manner, so here they are:

Left:


Right:


Both speaker response:

P.S. Although the graph suggests otherwise from what i can hear bass goes down to 33Hz and not deeper


Left and right:


Phase left and right:


Step left:


Step right:


Group delay:
 
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andreasmaaan

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Although the graph suggests otherwise from what i can hear bass goes down to 33Hz and not deeper
Many recordings are high-pass filtered at 30-ish Hz. And many instruments naturally contain little content below that anyway. Bass extension to 33Hz should be quite adequate for much music, with little missing if your system doesn’t extend lower.
 
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Ok, I wasted a day last week doing measurements and trying to flatten out the system in different ways too. Question: Any subjective improvement in the sound? Just asking because even though my measurements showed an improvement I didn't like the sound as much. With the miniDSP I have 4 preset configurations so can compare between different XO settings or EQ in real time. Sometimes I don't like with what I come up with and then it's back to measuring again....
 

Krunok

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Ok, I wasted a day last week doing measurements and trying to flatten out the system in different ways too. Question: Any subjective improvement in the sound? Just asking because even though my measurements showed an improvement I didn't like the sound as much. With the miniDSP I have 4 preset configurations so can compare between different XO settings or EQ in real time. Sometimes I don't like with what I come up with and then it's back to measuring again....
Well, I can only try 2 variants, with filters active or disabled, and I definitely like more when they are active. It is also very easy to distinguish between them as you are able to easilly follow bass guitar lines when filter is active, much less so when they are disabled.
 
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Ultimately that's what matters!

While there is a definite science and process to measuring - difficult rooms and attempting to average responses sometimes give wild results is my experience. Always learn something new along the way though and some of us geeks even consider it fun. ;)
 
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