Hi,

I've heard recently that woofers of the speakers must not be placed at the vertical center of my room.

My room is about 243 cm height, the centers of my woofesr are at 113cm (bottom 104-top at 118) and the twitters are at 119cm witch is quite the half height of my room.

Should it make any trouble in the sound ?

The placement of the LF drivers relative to room surfaces (walls too) is important, but you should investigate WHY that's important, and not simply invest your faith in something you "heard recently".

I know that i’ve Done some changes to my studio configuration and it sounds actually very bad in my 10x14..
I think I ll make news changes asap to find the best place to set the speaker and my listening position too.
Concerning the height of the LF, I think maybe decrease the height of my room by placing few panels attached to the ceiling . Any suggestions to that plan ?

your speakers are pretty much at a 'normal'/convenient height (ear level) which is okay as long as you're getting a reasonable response...

You want the acoustical axis of the speaker firing at an imaginary point a few cm behind your head. A thick cloud or rigid backed cloud (assuming large/massive enough) can help negate the negative effect of having the LF driver at mid height. You can also flip your speaker upside down and raise it up so that the LF driver is above the middle line. You still want the acoustical axis aimed directly behind your head at ear level. No matter which approach you try from all the advice youve received, verify results with REW.

You also might find the info linked in this thread helpful.

Speaker placement

while there is no doubt there is some useful information to be shared in the threads jason has been mentioning (amongst many others), imo they mostly neglect the fact that many folks cannot move/lift their speakers much in their small rooms for practical reasons and cannot apply much absorption to their rooms either.

from an acoustician's point of view, this is unsatisfying: s/he wants to tune the room...

from an engineer's point of you, you may either adopt the acoustician's advice (and mess up your room by making it a lot smaller, up to about 50% and beyond is quite common) or (almost) totally neglect it: you don't tune the room, you only need to tune the speaker's response.

as long as you get reasonable response at your listening position and you're the only one in your room who needs to hear reasonably well, you may forget about how your speakers sound in all other places but at your listening position. you then better spend your money on minimal trapping/absorbers but use some eq to correct your speaker response for this single position. mostly, a 4 band parametric eq is enough. for more sophisticated tweaking, modern speaker controllers offer a lot more filters/options.

you can carry your dsp everywhere and get good results almost regardless of environment while you mostly cannot carry your traps, absorbers, diffusors anywhere...

any analyzer app is a helpful tool to measure speaker response. for more detailed analysis, you need some serious fft such as rew, smaart etc. - it takes time and experience to learn how to interpret data though (as most any thread in this forum clearly shows...)

I agree 100% with that statement. The LP is all that matters in a control room. However you get there is irrelevant. Accurate is accurate.

thanks for your advises.
indeed I got a lot of stuff / gear in a small and this is not a room built like a studio. The is two doors, a large bay window and an other window in a corner. Furthermore I am a pianist so a 88 keys is in front of me. Anyway, I think I first have to find where is the best LP in that room without doing any changes to the acoustic treatment. I will try to share more of my config /room spec etc. I ll take time to read a maximum of threads about this subject. It seems there are few unavoidable rules concerning basic speaker placement befor going deeper in the accuracy.

hi,

I decided to approch the question of the acoustic of my room in an overall way. so if you have suggestions, they will be welcome
thanks

best LP and speaker placement in my room

On the other hand, a decent studio designer would do both! First he would design the room to have good "raw" response, then treat it to the point where the major issues are under control and digital tuning becomes possible (it cannot be done in an untreated room), then he would use digital tuning to "put the cherry on the cake", so to speak, by tweaking the last few outstanding issues.

I would disagree that "following an acousticians advise would mess up the room".

I would also disagree that it is possible to tune the speaker's response in a lousy room. Floyd Toole has clearly explained why that does not work. If the speaker has significantly non-flat free-field response, then there's nothing that you can do to fix that with EQ. The real point here is to start out with good speakers that DO have pretty flat response, naturally, then treat the room, then use digital EQ to reduce the remaining issues where possible, and apply the room curve (if any is needed/wanted).


- Stuart -

i'm okay with that besides that
a) most any speaker these days at short distance has a reasonably flat frequency response different story with bigger distance though (where the room comes into play) so unless you're in a concrete cavern with some kinda weird dimension and use absolutely no treatment, dsp always can improve results (even under above mentioned conditions, although not enough to make it acceptable)
b) if you're aiming at having a good 'raw' response, things may change entirely when bringing in a different pair of speakers with different specs and positioning them differently than a previous pair.
whish this would work; imo it doesn't...

That isn't really true. The room loads the speaker acoustically, so any effect that the room loading has on the speaker cone movement will be evident even at short distances. In any event, it isn't valid to measure speaker response in the acoustic near field: you have to be in the acoustic far field to be able to do that accurately. And as you mentioned, at larger distances the room has even more effect on the measured response. It is still possible to get usable data by windowing the measurements, but that has its own drawbacks, such as placing a limit on the lowest frequency you can validly look at, and reducing the resolution. Which is why the only valid measurement of a speaker is one taken in an acoustic free-field, or anechoic chamber.

In simple terms. if you take an acoustic measurement of a speaker in a typical room, you cannot avoid also measuring the room as well. They are inextricably tied together, because the speaker itself is affected by the room loading, as well as by artifacts such as SBIR from the rear wall, and modal response.

The room is in play at all realistic, valid distances. If you measure too close (in the acoustic near field), then you aren't getting valid measurements anyway. If you measure too far away, you are getting more room than direct sound. There's no place you can measure in a typical room that reveals the true response of the speaker.

Sorry, but that isn't true. Certainly, a "concrete cavern with weird dimensions and no treatment" would be the worst possible situation, and digital tuning would be absolutely unable to do anything about that. Digital tuning can only function successfully in a room where most of the acoustic artifacts are already under control, with suitable acoustic treatment. Trying to use EQ to "correct" a room that exhibits artifacts is not going to work. You might end up making the frequency response look better on a REW graph, but that doesn't mean that the room actually is better.... FR isn't even the most important aspect that you should be looking at. A room can have flat FR, and still sound lousy... The only time you can successfully use EQ on a room is when the acoustic conditions are met.

You seem to have missed the point I was trying to make! I don't want a good raw response! I want to SEE what the raw response is so that I can treat it suitably, to get it to the point where digital EQ can be used. You can't do that in an untreated room. Or rather, you CAN do it, and the FR graphs can look flatter, but that does not mean that the acoustic response of the room has improved. Many, many high-end rooms do not have truly flat frequency response, and yet are considered to have excellent acoustics...

The room response will not change much from having different speakers (assuming that both sets are reasonably good), but it could change if you put the speakers in a different location, as you could be triggering a different set of modes like that, and producing a different set of reflections at the mix position. That's why it would be a bad idea to change the location of the speakers if you do decide to swap them (assuming that the old ones were already in an optimal location). When I design "soffits" for interchangeable speakers, I design them so that pretty much any typical studio monitor could be put in, and the acoustic axis would end up in the same place. There's no need to move the speakers, just because you swapped them for a different make/model. As long as the on-axis free-field response is reasonably flat in both cases, they should be positioned in the same location.

What MIGHT change with different speakers, is dispersion: the Q or directivity of teh speakers could be different, which implies that the new ones would illuminate the off-axis side walls, floor, and ceiling differently, and that would likely need some tweaking in the acoustic treatment.

The other thing that might change is that your new speakers could have better low frequency extension, and thus could trigger modes that the old ones weren't really exciting very much. That could also require tweaks to the bass trapping.

But apart from that, there shouldn't be too much change in overall acoustic response just from swapping speakers. In my experience, it works just fine if you do it right.


- Stuart -

Right! There are a few key rules. Basically, for a small room you can't get your speakers far enough from the front wall to avoid SBIR in the low end, so you don't have much choice: you have to put them right up tight against the front wall, with only a small gap of about 4" where you will insert a 4" panel of suitable porous absorption.

Why? Because with the speakers far from the front wall, the first SBIR dip will be at a frequency where the wavelength is too long to treat successfully with porous absorption. The closer you place it to the front wall, the higher the first SBIR dip moves up the spectrum. With a 4" gap, it is in range where porous absorption can have a useful effect.

Another rule: Set up the speakers such that the acoustic axis is at your ear height, or maybe a bit above. "Standard" height is 120 cm, which is about 47 1/4", because that's the typical ear height for most people when seated. But you can move the speaker a little higher, as long as you make sure your ears are not more than a one or two degrees off axis vertically. Having it higher can be beneficial in reducing comb filtering and reflections coming off your desk surface. But don't put it so high that yu have to tilt it down to stay on-axis: big mistake.

Another rule: I'm sure I'll take some flak for this, but: Forget the famous equilateral triangle! It's a myth....

Well, OK, it's a myth that this is the only possible way to set up your speakers: it isn't. It's merely a good starting point, and works for most rooms, but is NOT necessarily the best for any room at all! It is nothing more than a simplified misrepresentation of how it should actually be. That "equilateral triangle" thing is all over the internet, in all types of books, all over YouTube, and every place else you look. But that does not make it correct. It would only be correct under two very specific conditions:

1) If the speakers and your head were set up some place where there is no room around them: out in the open, where the speakers are not "acoustically loaded" by the room, and there are no reflections or reverberant field. And:

2) For all listeners who have had their ears surgically transplanted onto their eyeballs! :shock:

Think about it. Every speaker manufacturer will tell you that the absolute flattest, cleanest sound from their speakers is "on axis": when your ear is lined up perfectly with the acoustic axis of the speaker. Yet all of those "equilateral triangle" diagrams show the acoustic axes from the two speakers interesting in the middle of the engineer's head, which means that the ears are NOT on axis! The EYES are on axis... :roll: So if your ears are in your eyeballs, the equilateral triangle is the correct way to set up your speakers. For the rest of us, the speakers need to be set up so that the acoustic axes are aimed at the ears, not the eyes.

In fact, there are some indications that show the axes should actually be aimed a bit outboard of the ears, not directly at them, since the head itself affects the sound as it approaches the ears, and also to create a wider sweet spot around the mix position. Thus, the acoustic axes from your speakers should intersect at some point several inches behind your head, not in the middle of your head. Usually it turns out that the speakers are aimed at a point about 12 to 18 inches behind your head.

There are good locations for the speakers in the room, and there are bad locations. There are also good locations for the mix position (engineer's ears) in the room, and bad locations. In most rooms, creating the "equilateral triangle" puts the speakers in a bad location, or the head in a bad location, or both. And if you put them both in good locations, then you no longer have an "equilateral triangle". My answer to that is: "So what?" There's no logical or acoustic reason why the distance between the speaker cones must be identical to the distance between the cone and your ears. Yes, the distance from the left speaker to your left ear must be the same as the distance form the right speaker to your right ear, in order to ensure that the two sounds arrive in phase and at the same intensity: Absolutely. But that has nothing at all to do with the distance between the speakers! In what way does that distance cause the sound to be better or worse? Answer: In no way!

In fact, if you look at the polar response of the human ear, maximum sensitivity is at about 50° off to the side, not 30°. So spreading the speakers further aprt and angling them in a bit more would actually be a good idea.

The ONLY reason why everyone shows the "equilateral triangle", is supposedly because of standardization. The theory is that if all control rooms have the speakers 30° off then they should all sound the same: all the sound stages should be identical, and all the stereo images should be perfect copies of each other, and all the sweet spots should be the same size and shape.... and of course, that is pure garbage! Even for rooms where the speakers are set up spot on for the "equilateral triangle", it is very evident that they don't sound alike, the sweet spot is not the same, the stereo imaging can be different, and the sound-stage too. So this is not a valid reason.

In other words: the triangle is a myth.

The truth is that the speakers should be set up at the best point in the room for YOUR speakers in YOUR room, and your head should be set up at the best location for YOUR head in YOUR room, then angled correctly such that the acoustic axes of the speakers intersect several inches behind your head, usually around 12" to 18" back.

But that means they won't be angled at 30° any more! :shock: Yup. So what? There is nothing magical about 30°. It just happens to be the angle you need to create an equilateral triangle, but once you abandon that myth, then you are automatically abandoning the need for a 30° angle: Yes, both speakers must be angled exactly the same, so the angles on each side are identical, but it does not have to be 30°. Anywhere from 25° to 35° is just fine, and under certain circumstance you could even go as far as 20° and 45°. Not more than that, though, for other reasons that I don't have time to go into here.

But you don't have to take my word for it: try it out for yourself! In your house, set up your speakers in the classic text-book "equilateral triangle", 2 feet away from the front wall, 1/3 and 2/3 of the room width, angled exactly 30°, with your chair set up so that the axes pierce your eyeballs and intersect in the middle of your head, then carefully listen to your favorite music like that (flat EQ: don't adjust!). Listen to a few songs that you know really well, and pay attention to the bass tightness, accurate definition in the mids, clarity in the highs, as well as the width of the sound-stage, and clarity in the stereo imaging. Move your head side to side, and forwards / backwards, to see how that changes, and how big your "sweet spot" is. Thne quickly and silently (all sounds turned off, so as not to lose the mental reference of what you just heard) move everything around to set it up the way I outlined above: Speakers against front wall, set further apart, angled the same ubt to pit behind your head, not at your eyes... and now and listen to the same songs again, at the same volume, once again paying careful attention to all of the above.

Then tell me which setup works best... Which one gives you the best stereo imaging, clearest sound-stage, and broadest sweet-spot, as well as the tightest bass, best definition in the mid range, and clearest, detailed high end?

Don't believe all of the "one size fits all" hype about how so set up your room. All rooms are different. All need different setups. Very seldom does the best setup work out to be a 30° equilateral triangle.

Unless your ears are in your eyes!

(Let the flak attack begin...)


- Stuart -

on some topics, i'm getting to vastly different conclusions based on my (extensive) experience of working in a multitude of studios and measuring/adjusting their speakers...

thank you stuart for exposing yourself to flak attack to help my crappy room

it's very rewarding to have an informed feedback like yours.

If I resume :
1°/ putting the speakers with a small gap of about 4" (within porous) from the front wall
2°/Setting up the speakers such that the acoustic axis is at your ear height, or maybe a bit above.
3°/Forgetting the famous equilateral triangle

I read that the front wall should always be the shortest of the room and also that the LP had to be exactly 38% of the length of the room. Do you agree with that ?

attached to this post a (crappy handmade..) plan of my room with the current set up and some picture (and a REW capture but i'm not sure tohave done it at the right loudeness)
should I place my speakers on the right wall (376cm) ?
even if it is mainly un large 300cm bay window ? (plus I should rethink the positioning of my material..)

would you have some advice on that? thanks a lot

I have made an other thread about the specifications of my room :
best LP and speaker placement in my room

4/ remove the foam.
Even if this foam are sold in acoustic shop they haven't acoustic properties usable. Only the high is absorbed nothing under 500 Hz where all the issues are concentrated.

+1 unfortunately, it cost me $2k to learn this lesson

witch ones are you talking about ?

The auralex blackfoam or even the hofa or GIK products ?
I think even if the hofa or gik doesn't suit as well as DIY custom stuff, I should like to think that they trap some freq behind 500hz.

Anyway, before mooving entirely my studio, I'll begin by getting near front wall.

This topic always confuses me a bit. 4" of fiber directly on the wall will have little effect under 200-300hz according to the online PAC. Typical studio monitors are around 12-15" deep, add another 4" for the fiber, and this would put the front wall SBIR null around 170-200hz, wouldnt it? Is an absorbtion coeficient of .4 really sufficient? Ive typically heard other designers say that unless you can put absorbtion that can absorb the SBIR null behind the monitors, put none and put the speaker up against the wall. They typically recommend 8"+ of fiber, but that never makes sense either. The thicker the absorbtion you put, the bigger the distance from speaker to the wall gets, and the deeper the null goes. It seems like theres never a distance where depth of fiber cancels out the SBIR null 1 for 1. Im obviously missing something here, so if you could help clarify this i would be greatly appreciative.

The auralex is what got me. The Lenrds will be somewhat usefull, but the 2" panels are of little bennifit.

The foam has a precise definition. Auralex

I don't know the hofa product.

Gik has 4 inches of tickness and work fine above 1000hz.

There are no miracle in audio.

Don't believe everything the prediction calculators tell you!

Take a look below, at the actual specs for OC-703, as published by the manufacturer. For the 125 Hz octave, 4" of OC-703 with ASTM A mounting (up against the surface, no air gap) has a coefficient of 0.84, and for the 250 Hz octave, the coefficient is 1.24! I think that's good enough to have a decent effect on 170-200 Hz. And lower.



In fact, if you take a close look at Frank's thread over at John Sayer's forum, you'll see a pair of "before" and "after" graphs when we put insulation on his ceiling. There's a very substantial improvement in the low end, well below 200 Hz. Even down at 80 Hz there's a measurable effect.

But don't get me wrong: I'm not saying that 4" of 703 will totally cure SBIR from the front wall: Probably not... but it certainly does a very decent job of reducing it. And it sure is way better than having the speakers a foot or two away from the wall.


- Stuart -

Gotta take one for the team, sometimes!

Be careful when you see things like "always" and "exactly" when it comes to "rules" for setting up rooms... Like the equilateral triangle, it isn't "always" necessarily so.

So first the "always on the shorter wall" rule. Yes and no. Yes if your room is small, no not necessary if it is large. By "large" I mean that it is wide enough that, if you set up the room "sideways", with the speakers on the long wall firing down the shorter axis, then the reflections from the rear of the room will arrive at your ears more than about 30ms after the direct sound. If the room isn't wide enough for that, then set it up long-ways, with the speakers against the short wall, firing down the long axis of the room.

Why? Because if there are reflections arriving at your ears within that 30ms window, and especially within about 20ms that messes up your ability to determine directions accurately, and therefore also your perception of frequency response. This is sometimes referred to as the "Haas time", and is a big part of the specs behind the RFZ room design concept. Avoid reflections with the Haas time, then have a diffuse hopefully reverberant field coming back at a level of about 20ms down below the level of the direct sound, and decaying away at the correct rate for the room after that. That "gap" of 30ms with no reflections is sometimes called the ITDG: Initial Time Delay Gap.

However, there may be other over-riding reasons why you would want to have the room set up in one orientation or another, such as issues with symmetry, doors in inconvenient places, structural columns that can't be moved, etc.. So here too the "rule" is flexible, and might need to be ignored or modified.

OK, now for the 38% "rule". As far as I know, Wes Lachot laments ever having put that out in public, because it never was meant to be a "rule". It was merely an observation that, theoretically, for a perfectly rectangular room, the 38% spot has the least objectionable modal issues. That's all. Yes, it's a good place to start when deciding on your mix position: a useful guideline. But it is not the "written in stone" best position for all rooms, always. I seldom end up with the mix position exactly at 38%: often it is a little in front of that. The only real "rule" here is to stay away from 25% and 50%, if you can, as well as a small margin around that since those are theoretically the worst modal spots.

For that shape room, you probably have the best layout. It's the only layout orientation that gives you decent symmetry, which is arguably more important. However, I would suggest moving the mix position a bit further forward: it seems your head is pretty much at the 50%spot right now. Also, push your speakers up against the front wall, as I mentioned, with the 703, etc... Give it a try, then adjust the mix position, speaker spread distance, and angles, doing multiple REW tests to find the spot that has the smoothest overall response, and the fewest nasty first-order reflections.

A while back, I wrote some instructions for calibrating your system with REW and doing initial tests. It's over at the John Sayers forum: John Sayers' Recording Studio Design Forum •

View topic - How to use REW to analyze the acoustics of your room... . Follow that, and you should get valid, usable REW measurements.

Absolutely agree! That foam is not doing you any favors. You will need major bass trapping in your room, so get rid of the foam and build bass traps. Big ones. Then put absorption on your first reflection points (but decent absorption, such as 4" OC-703).

And also clean out the "clutter", to get your room symmetrical and with as few "obstacles" around as possible. Make the left half of the room a mirror image of the right half. Take out anything that you don't absolutely need all the time, 24/7, and leave just the minimal possible in there.


- Stuart -

so done.

I got closer to the front wall as much as I could.

I didn't placed 4" porous but my both GIK monster bass trap (about 6,7" plus 1" air gap due to the way I fixed it) "stick"to the wall, and the speacker neighboring as well as I can (because of the XLR connector).

I also angled the drivers so it converges around 25cm behind my head at the vertical height of my ears.

no equilateral triangle anymore.

and so...

I think it is better.

I am quite tired and my mind play triks on me so the REW may be a better indication.

I'll be back in my room with clear ideas and fresh ears. thank you all for your very appreciated participation. cheers

I am very familiar with that data. I use to refer to the data compiled on bob golds site often until i was told by many on GS that this data was for reverberation chambers and therefore irrelevant for small room acoustics. I would think it would still be relevant though. In a small room you should get so many reflections off of the close proximity of boundaries that it almost is random incidence as well. I wish everyone was just on the same page about everything. It would make learning so much easier

The data is MEASURED in reverberation chambers, yes, in order to get valid results for random incident sound. But that does not make it invalid or inapplicable to real rooms. Of course, the over-unity values are confusing, because of the way the numbers are calculated, without taking into account diffraction, edge surface area, etc., but that does not make the data wrong: it just means it has to be taken in context. The point is that even relatively thin porous insulation (4") does have surprisingly good absorption at low frequencies (the 125 Hz octave band). If you prefer to believe the "it only works at quarter wavelength" guys, then you'll be greatly mislead, because that simply and demonstrably is totally false. As Andre has pointed out, there is significant absorption for a porous absorber that is only 7% the thickness of the wave for normally incident sound, and 3.5% for randomly incident sound. That isn't just theory, either: it works in practice, in real-world rooms, not just reverb chambers. I have documented it many times on the JS forum. Andre is absolutely correct.

Perhaps it has something to do with the folks who work only in theory, using just mathematical constructs and calculations, without actually checking if their assumptions are valid in the real world. If they would get our from behind their computer screens and try out their theories in real studios, they might find that theory and practice don't always match perfectly. They problem is that with some of those people, when reality doesn't match theory, they want to blame reality...

OK, if you still don't believe me that 4" of 703 between the speaker and the wall can have a measurable and useful effect, try it for yourself! I'm sure you have a room where you could test this, and a decent set of speakers, so do the test for yourself. Do several REW tests with the mic in a fixed location, and the speakers at different distances from the wall, moving them in small increments starting from a couple of feet away, down to 0", making sure that you have one test at 4". Then repeat that with 4" of 703 against the wall. I think you'll be pleasantly surprised at the results.


- Stuart -

You are only showing the full-spectrum frequency response curves: I would need to see the actual MDAT files to analyze it completely. Maybe you could post that here, or perhaps put the files on DropBox and post a link.

Great! I love it when reality matches theory...

By the way, your panels are not very wide: You need much wider panels than that: they need to extend for about twice to three times the width of the speaker itself (empirical rule of thumb: no math to back that one up). They also need to extend up higher than you have them now, by about the same amount.


- Stuart -

The measures in reverberant room are irrelevant. Edge effect, initial conditions dependent, extrapolation and Not directly measurment so each measure are valid only in one reverberant room.
This fact are well known, explain by D'Antonio or Lafond in france and others but business as usual, some pro continu to use this kind of measures.
You cannot have an absorption greater than one.