Using REW and EQ APO - tackling a big hump!

[Ally-007]

Hi folks, I've been experimenting with REW and Equalizer APO software, to compensate for (a) the room acoustics in my small home studio and (b) the imperefections of the speakers. In this case, I was using a pair of 3-way monitors (Moukey M20-3). The EQ compensation settings were generated by REW, and then loaded into Equalizer APO. When I ran a second REW test, with the compensation settings loaded and activated in EQ APO, I saw how the curve is flattened considerably. However, there is still one bug hump centered around 141Hz. It's there, in approximately the same place, with all of the three sets of speakers I've tested, so I guess it could be room resonance. How can I deal with that? Any advice, please? See my screencap: Purple line is before compensation. Red is after compensation. Many thanks!

 

[bouldersoundguy]

The first thing to do is determine whether it's a room issue or a speaker issue. A large peak at 141 sure sounds like a room resonance or standing wave to me, and the best way to deal with that is acoustic treatment.

 

[rob aylestone]

Can you not just reduce that hump with EQ? It will only be valid of course for a mic at the place your measurement mic was placed, but it';s a guide. Second question is that while there is the hump, can you hear it as a 'bad' sound? One of my students has a hump like this, and it makes one of my basses sound better?

 

[Ally-007]

The first thing to do is determine whether it's a room issue or a speaker issue. A large peak at 141 sure sounds like a room resonance or standing wave to me, and the best way to deal with that is acoustic treatment.

A standing wave is my suspicion. A waterfall graph does shows that that resonance around 141 Hz is lingering more than any other frequency. The thing is, I don't really have any vacant wall space to add acoustic treatment. All my wals are already covered with shelves full of random boxes or piles of this or that, which must, in itself provide a lot of acoustic dampening. The only flat area not thus covered, is the ceiling (not much floor space is vacant), so maybe the ceiling is the problem. I will have to delve into the formula for calculating wave lengths when I feel more awake.

 

[Ally-007]

Can you not just reduce that hump with EQ? It will only be valid of course for a mic at the place your measurement mic was placed, but it';s a guide. Second question is that while there is the hump, can you hear it as a 'bad' sound? One of my students has a hump like this, and it makes one of my basses sound better?

The odd thing is that I'm not hearing anything that I'd describe as an obvious 'problem resonance', whatsoever. But maybe I'd notice the difference if it was eliminated. Regarding what you suggested about using EQ, I was hoping that I could find a way to manually tweak the settings generated by REW and loaded into Equalizer APO, but I haven't found a way to do that. I'm not sure why REW doesn't compensate for that peak sufficiently, when it generates the EQ settings file. Edit: I meant to say, I don't notice a problem resonance when listening to music. I only really notice it when running a frequency sweep. (The frequencies aound 141 Hz sound louder).

 

[rob aylestone]

I think the concept of using specific software to do room tuning is just a bit odd. For years in live events we used 32 band graphics to remove room resonances and phantom honks. The trouble was that even that was tuning by science ignoring your ears. While we were using them to flatten the response to as close to a flat line, the home hifi folks were using them to create smiley faces? Knowing your room has problems that a ⅓ octave graphic or other tool can cure is a good starting point. Just don't get carried away, because your mics are not flat, neither are your monitors, so what exactly are you adjusting?

 

[bouldersoundguy]

Try measuring at a variety of locations. Also, play some commercially produced music and listen from different positions.

 

[Ally-007]

I think the concept of using specific software to do room tuning is just a bit odd. For years in live events we used 32 band graphics to remove room resonances and phantom honks. The trouble was that even that was tuning by science ignoring your ears. While we were using them to flatten the response to as close to a flat line, the home hifi folks were using them to create smiley faces? Knowing your room has problems that a ⅓ octave graphic or other tool can cure is a good starting point. Just don't get carried away, because your mics are not flat, neither are your monitors, so what exactly are you adjusting?

Thanks.. When listening to music, at my normal listening position, at my mixing desk, I don't really notice a problem resonance. However, if I run a frequency sweep, I definitely notice it; the frequencies around 140Hz sound noticeably louder. It happens regardless of what speakers I use. I'll have to look further into ways to compensate that frequency range with EQ.

 

[Ally-007]

Try measuring at a variety of locations. Also, play some commercially produced music and listen from different positions.

Thanks for the suggestion. It sounds like a good idea. Unfortunately, changing my usual seat location for mixing & mastering is not really an option in this room, but I'll do what you suggested, as it's certainly possible to sit or stand at a different location, temporarily, when playing back mixes.

 

[bouldersoundguy]

That's not what I'm saying. I'm suggesting that you see how it measures and sounds at different positions in order to narrow down likely causes. If it sounds and measures different in different places, it's most likely a room issue. Eq isn't a great solution to that problem.

 

[Ally-007]

That's not what I'm saying. I'm suggesting that you see how it measures and sounds at different positions in order to narrow down likely causes. If it sounds and measures different in different places, it's most likely a room issue. Eq isn't a great solution to that problem.

Okay, will do. Here is a test I just ran, using my flattest monitors (Edifier MR4) with no EQ compensation, testing at three different stitting and standing microphone positions. I used a measurement microphone with mic calibration. All curves have 1/3 smoothing.
Red line: my usual seated listening location.
Yellow: usual location, but 2ft further back
Green: usual location, but standing height.
Blue: center of room, standing height.

 

[rob aylestone]

Well, its hardly level, but the thing to decide is how it impacts. Play your favourite music in the room and see how your humps impact a proven great recording. You could then work out that you have a bit too much low end at one point, and a bit too much higher up. Two alternatives then exist. Use an eq setting that reduces it. Not ideal, but essentially that curve you produced, but upside down. If that restores flatness, slap that on everything before you start mixing. Put it permanently in your output channel. Or, you just learn how your room impacts on the sound and cope with that in your head. Dont forget that your plots dont show all the parallel wall reflections that impact the sound of the room, in any other way than a few spikes. Flat is not perfect in any sound source or rooms or repro gear. Everything messes up the sound. The only thing that matters is your mixes played on different systems. What annoys me are those rogue notes. The two or three on your piano sound that seem to leap out of your left hand or the bass guitar that sounds odd in a certain area through the monitors. If you know its your room and not in the recording, you can cope. If in the space it sounds horrible, forget eq based treatment and fix it with proper traps. If you can see it but not hear it, forget it.

As long as your mixes transfer to other people’s systems, and headphones of all types, that is it. Very often measurement mics show big issues and people over react, but there are loads of famous studios that have anything but flat responses, but sound great. Often, their humps and valleys are called ‘character’.

 

[Ally-007]

Well, its hardly level, but the thing to decide is how it impacts. Play your favourite music in the room and see how your humps impact a proven great recording. You could then work out that you have a bit too much low end at one point, and a bit too much higher up. Two alternatives then exist. Use an eq setting that reduces it. Not ideal, but essentially that curve you produced, but upside down. If that restores flatness, slap that on everything before you start mixing. Put it permanently in your output channel. Or, you just learn how your room impacts on the sound and cope with that in your head. Dont forget that your plots dont show all the parallel wall reflections that impact the sound of the room, in any other way than a few spikes. Flat is not perfect in any sound source or rooms or repro gear. Everything messes up the sound. The only thing that matters is your mixes played on different systems. What annoys me are those rogue notes. The two or three on your piano sound that seem to leap out of your left hand or the bass guitar that sounds odd in a certain area through the monitors. If you know its your room and not in the recording, you can cope. If in the space it sounds horrible, forget eq based treatment and fix it with proper traps. If you can see it but not hear it, forget it.

As long as your mixes transfer to other people’s systems, and headphones of all types, that is it. Very often measurement mics show big issues and people over react, but there are loads of famous studios that have anything but flat responses, but sound great. Often, their humps and valleys are called ‘character’.

Okay - thank you for the insights, Rob. I don't honestly notice any obvious problems when listening to most music, especially when I have Equalizer APO compensating for my room resonances to some extent. However, I'd like to make the curve as smooth as possible (maybe close to a Fletcher Munson curve) for mixing & mastering. I'm thinking of looking for a hardware graphic equalizer to connect between my audo interface and my active studio monitors. Then I will no longer be wondering if Equalizer APO is actually having any effect, due to, say the audio driver that is currenty in use. However, space on my desk is very limited. How many EQ bands per side do you think would suffice, based on the response curves I posted here?

 

[rob aylestone]

32 - 1/3 octave. anything else is not so precise and adjustable.

 

[Ally-007]

32 - 1/3 octave. anything else is not so precise and adjustable.

TY... No chance of fitting something like that on my desk, so it looks like software will have to be the solution, after all.

 

[bouldersoundguy]

I'd put as big and thick of an absorption panel above the mix position as I could fit.

 

[Ally-007]

I'd put as big and thick of an absorption panel above the mix position as I could fit.

Thank you for the suggestion, B. I think it's worth a shot. I have a foam mattress in the garage which might do it, if I can devise a way to attach it to the ceiling.

 

[Ally-007]

Update: I've now got a significantly smoother and flatter curve, after stuffing rags into the rear bass ports. I think at least part of the problem was that by necessity, the left monitor is very close to the corner of the room. The right one is just close to a wall. There's more of a bass roll-off now, but I have a subwoofer which can mitigate that, when needed. Stuffing the port on an active monitor does worry me a bit though, as I fear it could lead to overheating of the internal amplifier. (When I did this, once before, on a different pair of active monitors, I noticed the speaker containing the amp got pretty warm.) What do you think, folks?

 

[GONZO-X]

should not cover the port.
was not designed for that.
better to upgrade the monitors with front ports.