Bass ports and monitors

[Mornats]

I've been reading up a bit on acoustic treatment for rooms to help me mix properly on speakers. I know that I need bass traps galore at the very least plus other bits of treatment. At the moment I'm renting a flat so can't install anything and don't really have the space to put massive bass traps all over anyway as my music room is my living room. So I'll have to save all that for if/when I get a dedicated or better room that I can customise

Anyway, the purpose of this post is to mention something I've found quite interesting. When I'm playing music on my Yamaha HS7 monitors (the white ones in the pic below) there's very little bass when you're listening in the sweet spot in front of them. The bass disappears almost completely when you move back into the room and get around halfway in. Then if you sit at the back of the room you get the bass at a level I'd expect. So, it's a rubbish room that obviously needs treatment as the bass is being cancelled out quite a lot.

However, check out the black Tannoy speakers on my computer desk. When playing music through these the bass is fine. It's fine everywhere in the room. No change, good volume, everything you'd want. So what's the difference? Well, those Tannoys used to be owned by the Tannoy sales rep I got them from 25+ years ago. He'd bi-wired them and "custom sealed" them. I wasn't entirely sure what he'd meant by that but I've realised that he'd turned ported speakers into non-ported speakers. Nothing comes out of the bass ports at the back. The Yamaha's however, have bass pumping out of their bass ports. I remember reading in Mike Senior's Mixing Secrets for the Small Studio that he says never get ported small monitors, always go for un-ported. So I reckon my problem with bass is due to having ported monitors. So I wonder if using un-ported monitors would give me the better bass performance that I'm getting from my Tannoys? It's an interesting observation at least and my recent discovery of what "custom sealed" means has answered the question of why my hi-fi never seems to have the same acoustic issues as my monitoring system!

Pic of my messy living room:

[roman_sub]

I think speaker positioning may be a more significant factor here. I'm guessing the room is rectangular, rather than square, so you are likely to have different reflections and different standing waves when 'firing' sounds from these different positions.

 Have you tried swapping over the speakers, to see how they perform in each others places?

I also wonder whether the HS7s are too close to the wall, given they are rear-ported. They look to be almost touching the wall, which would likely contribute to the uneven bass response. Something like a foot away from the wall should help...

Edited February 7, 2018 by roman_sub

[Mornats]

The room's almost square rather than rectangular. Good idea about swapping the speakers over. If that doesn't make a difference then know it's not their position that's causing it.

I've tried the HS7s in their current position and have moved them incrementally out from the wall until they were around 2 feet from the wall and there was no noticeable difference in the bass response. They probably are too close, but as I can't move them out further it's more convenient to have them up against the wall. I'd knock over the speaker on the right every time I came into or left the room otherwise.

It seems odd that my hi-fi speakers are positioned in what I'd thought would be the worst position whilst the monitors are in the best yet the sound doesn't reflect that! When I get the chance I'll swap their positions and will report back.

[Skol303]

Firstly, every domestic room is 99.9% guaranteed to be a “rubbish room”! Unless you’re lucky enough to have an especially large space, or even luckier a large space with non-parallel walls, then you’re going to suffer a plague of room mode and reflection problems, that will have greatest impact on the low frequencies (sub-300Hz or so). These cause certain frequencies to be in phase - causing ‘boominess’ - or to be out of phase and cancel each other out (called nulls or nodes). Cancellations of -30db or more are not uncommon and can sometimes cause certain frequencies to disappear altogether. These are the peaks and troughs in bass level that you're hearing as you walk around the room.

So don’t fret! What you’re describing is totally normal

Also, what you’re describing is almost certainly a modal issue - i.e. caused by low frequency standing waves resulting from your room dimensions and acoustic treatment (or lack thereof). Switch the speakers around and I’d bet the same issue persists to a large extent.

[Side note: sealed cabinet monitors are often a better option that ported cabinets (although ported designs have come a long way since my youth, when they tended to have a huge yet flabby low end). Notably, sealed designs are a better option because they have a more gradual low frequency roll off, so they tend to produce low frequencies with more clarity than ported designs. And contrary to popular belief, you can push rear-ported monitors much closer to the wall than is often advised].

But anyway. Here’s a really useful tool that I’ve used when working on my own acoustic treatment at home:

https://amcoustics.com/tools/amroc

And here is the equally useful notes page that companies it:

https://amcoustics.com/articles/roommodes

Type in your room dimensions and it will calculate your problem frequencies and where in the room they are likely to cause most havoc ('high pressure zones'). Read the results and weep! If your room is square - as you mention - then unfortunately you’re going to suffer the worst of these modal/reflection issues. Acoustic physics is a cruel mistress.

Ultimately, if you have an untreated room, your mixing is always going to be based on guesswork to a large extent. And that might be perfectly fine - we are, after all, a community of hobbyists. Just bear in mind that what you hear through monitors - and especially the detail of what's happening in the low end -  is a lie to some extent (or in some cases, a large extent). Take comfort from the fact you are in good company - every home studio suffers these problems and a lot of professional studios do too; that's why so few pro studios are happy to make their room frequency/decay measurements public  

If acoustic treatment isn't an option, just reference on headphones as much as you can. That's by far the best 'Plan B'.

PS: acoustic treatment is a big topic, so I might combine this tread and other into a sticky on the subject in due course.

Edited February 8, 2018 by Skol303

[paulbuzz]

1 hour ago, Skol303 said:

Here’s a really useful tool that I’ve used when working on my own acoustic treatment at home:

https://amcoustics.com/tools/amroc

And here is the equally useful notes page that companies it:

https://amcoustics.com/articles/roommodes

Extremely interesting! Thanks for pointing that out!

[Skol303]

1 hour ago, paulbuzz said:

Extremely interesting! Thanks for pointing that out!

Very welcome

It's one of the best room mode simulators I've found. Similar thing here too, but not quite as useful:

https://www.hunecke.de/en/calculators/room-eigenmodes.html

There's also a 'Room Sim' tool in the Room EQ Wizard (REW) free software that's useful and requires only the room dimensions - gives an approximation of the frequency response below 300Hz based on speaker position/ speaker frequency response/ listening position etc.

All of these are very approximate and no substitute for taking acoustic measurements in the room itself, but they're a useful starting point.

Edited February 8, 2018 by Skol303

[Skol303]

13 hours ago, Mornats said:

I've tried the HS7s in their current position and have moved them incrementally out from the wall until they were around 2 feet from the wall and there was no noticeable difference in the bass response. They probably are too close, but as I can't move them out further it's more convenient to have them up against the wall. I'd knock over the speaker on the right every time I came into or left the room otherwise.

Contrary to popular belief, you want your monitors as close to the front wall (i.e. the wall you're facing) as possible. Think mm rather than cm!  [EDIT: this applies even if they are rear ported]

Better still, you want your monitors inside the front wall (soffit mounting), but that's beyond most home studios.

Why? Because it helps to reduce what's called SBIR (speaker boundary interference response), caused by out of phase reflections - mostly from the back wall - causing a BIG dip in the low end somewhere between 60-100Hz. Having your monitors either very close or >2m or so away from the wall pushes this dip to higher frequencies (monitors close to wall) where it can be more easily treated with broadband traps, or to lower frequencies (monitors far from wall) below the audible spectrum. Most home rooms don't have sufficient space for monitors being 2m from the front wall, so pushing them up close is by far your best bet.

Link here with great explanation:

http://arqen.com/acoustics-101/speaker-placement-boundary-interference/

EDIT to say that having your monitors close to the wall will cause a big boost in low frequency response. But that can be fixed with EQ... the big null caused by SBIR can't be fixed with EQ (the more you try to boost the null frequency, the more it will cancel out resulting in the exact same null: 10-10 is no better than 1-1).

Edited February 8, 2018 by Skol303

[Mornats]

I bashed my room measurements into a couple of those tools you mentioned. First up is https://amcoustics.com/tools/amroc which gave me this:

 

Then I popped them into Room EQ Wizard and changed some options to what seemed right (wasn't sure what I was doing really):

Finally, here's how close my monitors are to my wall. Not sure if I can get them any further back as the stands are pretty much against the skirting board.

 

I guess this means I should rely more on my ATH M50x headphones for mixing. Maybe I should cut my losses, sell the Yamahas, go back to my little M-audio BX5As and use the money to grab a pair of Sennheiser HD 600 headphones... I bought the Yamahas last year as I wasn't getting any bass out of the little M-audios. Seems my room was the issue and I could have saved a bit of cash.

[lowdown]

If you are getting a decent sound out of the Tannoys, why not use them?

[Mornats]

Good question but there's a reason. My hi-fi soundcard (Asus Xonar Essence) is what I use to go into my amp then my Tannoys. Whilst I can play tracks in real time on that at times, it often can't cope with most of my orchestral ones, especially when I'm running synths and effects too. It quite often crashes if I push it hard. One time it crashed and the dogs down the road started barking and I had a little ringing in my ears. So I try to avoid it as it was obviously pushing out some seriously loud high frequencies that I couldn't hear but were in the damage-dealing range. The latency is far too high to use it for recording from my midi keyboard too.

So for recording and mixing I use my Focusrite Forte. I don't have a way of getting that to use my amp or speakers unfortunately. Otherwise that would be a good solution.

Just to add, for general music listening, the Asus soundcard is superb. Can't praise it high enough. For music creation though, it doesn't cut it but to be fair, that's not its intended use.

[lurksalot]

My room is an L shape with a 'vaulted' ceiling but it goes flat where the L goes off 

I can't really use the software to predict anything here 

[Skol303]

3 hours ago, Mornats said:

I guess this means I should rely more on my ATH M50x headphones for mixing. Maybe I should cut my losses, sell the Yamahas, go back to my little M-audio BX5As and use the money to grab a pair of Sennheiser HD 600 headphones... I bought the Yamahas last year as I wasn't getting any bass out of the little M-audios. Seems my room was the issue and I could have saved a bit of cash.

Your room shape isn’t actually too bad! Notice how it’s close to the ‘Bolt Area’, which indicates that the room modes are quite evenly spaced.

It does however suffer from the classic home studio issues (as does mine and I’ll bet everyone else’s here): potential for ‘boominess’ or nulls around 40-45Hz (not too problematic unless your monitors are truly full range) and 65Hz (exactly where I also have a room null - and difficult to treat with bass traps).

It looks like your monitors are as close to the wall as possible. Every centimetre does count (!), so if there are any to spare then use them.

It’s not a terrible room… and you can certainly use your monitors for mixing; you need to be aware that the low end is always going to involve some guesswork/ referencing. Again, this applies to everyone including some pro mix rooms. If acoustic treatment is out of the question, then my suggestions would be to:

• Keep your monitors. Despite low end guesswork, they’re far better than headphones alone for working out stereo placement and other mix decisions.
• But yes, get some good headphones too! I’m in the market for a pair of Sennheiser HD 600 or 650s myself.
• Consider investing in Sonarworks room EQ software. “It’s no substitute for acoustic treatment” wail the hordes of acousticians… but it does help. In my room, it helped a lot. And while it can’t fix room nulls (no EQ can), it can do a great job of flattening the peaks in your room, making your monitors more worthwhile. I have friends who run commercial studios who use it, so it’s not just for kids. I also have a friend who recommended me a professional equivalent (a hardware DSP) that cost £4000, which I politely declined. Sonarworks costs around £250 for the full version with measurement mic (which you’ll need) and is worth every penny in my opinion. The mic also sounds nice on acoustic guitars

 

1 hour ago, lurksalot said:

My room is an L shape with a 'vaulted' ceiling but it goes flat where the L goes off 

I can't really use the software to predict anything here 

That room might actually be good in terms of acoustics mate! Irregular-shaped rooms and vaulted ceilings can sometimes work in your favour. Only snag is you won’t be able to use any of the tools linked above to work out your room modes ‘cos they all assume a regular box-shaped room.

A very rudimentary test you can try is play some low frequency tones (say, somewhere around 60-100hz) or play a track you know well that has a lot of low end - and walk slowly around the room. Listen for where the bass sounds boomy, where is sounds weakest and where is sounds most even - the latter is your new listening/mixing spot! I just hope it's not in front of the TV  

[lurksalot]

That's a great idea , I think that is on the cards when I get this months effort recorded 

[Mornats]

Cheers! Lots of good advice and info. I'll see if I can record some audio or a video of me walking around my room so you can hear the bass. From my seating position heading backwards it starts off as 3/10 (with 10/10 being normal bass volume) then drops to 1/10 then hits pretty much zero in the dead centre of the room then goes to 4/10 in the back third then 9/10 when sat right at the back of the room. It's a lesson in room acoustics and just how much it buggers up yer bass!

One thing I may do is use TeamViewer to remotely access my PC from my MacBook Pro so I can mix whilst sat at the back of the room!

I've got Sonarworks headphone calibration which I find is helping mixes on headphones translate better so I'll keep an eye out on the room version being on sale.

[Skol303]

6 minutes ago, lurksalot said:

That's a great idea , I think that is on the cards when I get this months effort recorded 

You're welcomer! PS: this is the suggested set up for L-shaped rooms, with the speakers firing down the length of the longest section.

Better still if you can position yourself facing into in the top-right hand corner, so your desk would be at an angle rather than flush with the wall. That way you’d get a more even response from the left and right speakers.

[Skol303]

13 minutes ago, Mornats said:

Cheers! Lots of good advice and info. I'll see if I can record some audio or a video of me walking around my room so you can hear the bass. From my seating position heading backwards it starts off as 3/10 (with 10/10 being normal bass volume) then drops to 1/10 then hits pretty much zero in the dead centre of the room then goes to 4/10 in the back third then 9/10 when sat right at the back of the room. It's a lesson in room acoustics and just how much it buggers up yer bass!

You'll struggle to get a meaningful recording of the frequencies that are causing problems! (typically 60hz or so). But give it a shot, why not.

The middle of the room should always be avoided for mix/listening position. Bass frequencies tend to build up at the back wall (as you're noticing), which is why it's always a good idea to add a lot of acoustic treatment there - it helps to prevent back wall reflections that cause phase cancellation elsewhere in the room. I'm trying to fix this very issue myself at the moment - planning on DIY-building a new batch of bass traps this weekend in fact!  

The often quoted 'golden rule' is to put you mix/listening position 38% of the way down the length of the room, but take that with a large pinch of salt. I started there in my own room but have since crept forwards towards the front wall - and my frequency response improved. But my room is a different shape.

That's one of the problems with acoustic stuff... one size most definitely does not fit all! And hence experimentation is the key to happiness. Or a whole new world of GAS (you have been warned!).

Edited February 8, 2018 by Skol303

[lurksalot]

9 minutes ago, Skol303 said:

You're welcomer! PS: this is the suggested set up for L-shaped rooms, with the speakers firing down the length of the longest section.

Better still if you can position yourself facing into in the top-right hand corner, so your desk would be at an angle rather than flush with the wall. That way you’d get a more even response from the left and right speakers.

My monitors are on the opposite wall where the white door is. My cream leather sofa bit the dust many moons ago and the room now has no TV   . 3 walls have brick faced finishes so no smooth surfaces , I guess that might help to mix it up a bit 

[Mornats]

You know, I did an experiment where I moved my couch to be sat along my back wall. I was hoping the mass of it would act as some sort of a bass trap but it made no difference.

[Skol303]

PS: I understand that acoustic treatment isn't possible in your room (Mornats), but I bet if you put a hefty 'gobo' style bass trap immediately behind your mix position (i.e. a portable bass trap on stands) then you'd spot a noticeable difference in the low end, as it would help to cancel some of the back wall reflections where currently they are free to cause havoc. Just an idea. You could very easily DIY a bass trap for this purpose:

1. Build a wooden frame of the size you want (20mm strip wood is ideal)
2. Fill it with this stuff or equivalent.
3. Wrap the wooden frame with any fabric that allows air to pass through it - this stuff is great.
4. Add some feet to it stands up.
5. Bob is your uncle!

Edited February 8, 2018 by Skol303

[Mornats]

Sounds like a good idea. Maybe a couple of bags of that stuff stacked up on top of each other behind me may do! (My DIY skills are zero.)

[Skol303]

3 minutes ago, lurksalot said:

My monitors are on the opposite wall where the white door is. My cream leather sofa bit the dust many moons ago and the room now has no TV   . 3 walls have brick faced finishes so no smooth surfaces , I guess that might help to mix it up a bit 

That's not a bad place to have your set up at all (i.e. on wall with the white door in the graphic).

Your problem is lack of a cream leather sofa! Did I not mention how crucial that is?! Has to be cream or salmon pink mate, take your pick. Any other colour messes up the bass frequencies something rotten 

Brick is no different to plasterboard to be honest. Bass frequencies just pile on through plasterboard and bounce off the brick anyway... and travel through the brick too (as anyone who's ever lived next to me in a semi-detached house will testify).

[Skol303]

6 minutes ago, Mornats said:

Sounds like a good idea. Maybe a couple of bags of that stuff stacked up on top of each other behind me may do! (My DIY skills are zero.)

I've seen photos of a room where a guy filled loads of cardboard boxes with Rockwool and stacked them up. Worked for him!

Important point to note: the mineral wool needs to be in a vessel that allows air to pass through it - keeping it in the plastic wrapper will be no good, and leaving it in a loose container will cause the fibres to get into the air and may irritate your lungs (the Knauf stuff I linked to is one of the safest available - used by commercial acoustic companies - but it's always best to play it safe). If you can make a wooden frame, you can make a bass trap! Just get some stripwood and metal angle brackets to join them together. You could rustle up a portable bass trap for around £50.

Edited February 8, 2018 by Skol303

[Mornats]

Looks like I've got a project then  

If I moved my sofa to just behind my mix position and moved my monitors down so they're at the same level would this give me some indication of how much a bass trap would help? Or is a sofa (fabric one not leather) useless in this regard? I'm just thinking that hearing *some* difference would spur me on to build a bass trap.

[lurksalot]

It's gotta be pink 😂

[Skol303]

2 minutes ago, Mornats said:

If I moved my sofa to just behind my mix position and moved my monitors down so they're at the same level would this give me some indication of how much a bass trap would help? Or is a sofa (fabric one not leather) useless in this regard? I'm just thinking that hearing *some* difference would spur me on to build a bass trap.

Hmmm... I doubt the sofa would do much as it's probably stuffed with the wrong sort of material (Rockwool works because the fibres are light enough to become 'excited' by the bass frequencies and so the sound energy converts to heat). But hell, if it's just a case of moving your sofa then give it a shot! Best if you can stand it on its edge upright somehow. Keep a camera running in case of accidents to score your £250 from You've Been Framed  

But yeah, don't expect an earth-shattering difference. One bass trap on its own - and especially one sofa - won't have a huge impact, but it will have some impact. And in my limited experience, acoustic treatment is about seeking every advantage you can get. Small victories winning the war, etc.

If you do decide to build a trap, try to make it as thick/deep as possible and tall enough to cover your head when at your mix position. 60cm of Rockwool is often quoted as the ideal - but that's super thick and I don't have any traps that deep myself (although I have some that are close to that at the front of my room). Aim for a minimum of 20cm thickness, which would be two slabs of the Knauf mineral wool I linked to above.

And of course the good thing about gobo-style traps is a) you can move them out of the way when not in use and b) they don't need fixing to a wall, which makes them ideal for rented and/or multi-purpose spaces.