Acoustic Room Treatment

What's the rest of the equipment?

Where are the speakers placed?

What modelling software have you used to look at speaker positioning?

How have you determined the In Room response?

What is the extent of the 45Hz peak?

Can you distinguish the 42Hz and 45Hz components?  If not why not?

What level of frequency smoothing did you use?

What's the precise layout of the room?

What acoustic damping and diffusion do you already have?

What about your Mode 0 vertical resonance?

You haven't provided any where near enough info for anyone to help other than make general suggestion that are little more than guesswork in any specific situation.

Changing the speakers (40 to 19) will give about a 2dB reduction at best.

It took me just over a year to get this right (I now have +-2.5dB 15Hz - 200Hz 1/12 octave in room).

Two questions I forgot..

What is the construction of the room (walls floor ceiling) and what are their resonance properties (i.e. measure their post-impulse emission spectrum)?

Does the resonance a 45Hz meet minimum phase criteria?

Go buy the ClioFW by Audiomatica, and their microphone. Measure your room properly. Educate yourself. Then make informed decisions. 

Anything else is just stabbing in the dark.

Huge posted:

Two questions I forgot..

That did make me laugh! Now where's me coat?

Hi Huge. The rest of the equipment is simply a Hugo TT dac and laptop computer. The speakers are placed about 80cm (measuring from front face) from rear and side walls. Speakers are sealed design. The room size is 4.02m x 3.76m.

not used any modelling software but did measure room response using room eq wizard - backed up by human ears listening looking at sound pressure meter at certain frequencies. When playing 45hz through speakers move to the middle of the room and the problem disappears. does this backup standing waves idea?

seems to be 10-12db hump.

42Hz and 45Hz components are very similar.

layout of room is typical bay window chimney breast design. see https://1drv.ms/u/s!At2gHdIhMLswgYE-EWaQeyoxXWVFqw

the sides and chimney breast wall are solid brick, the listening wall behind is lath and plaster.

no acoustic treatment as yet,

What about your Mode 0 vertical resonance? - no sure?

Does the resonance a 45Hz meet minimum phase criteria? - not sure?

Many thanks.

Hi Halloween Man,

OK, using REW is good - I used it for most of my own work.

First use the Room Simulation to model your system and work out a good starting position for the speakers and your listening position.  It won't always give you the right position, but it's a good place to start, and it can also (later) be used to judge how much acoustic absorption you need.

The lack of resonance in the middle of the room does support the principle that the primary problem is the standing wave.

Solid walls are bad for resonances, lath & plaster is usually quite good.

Look at the REW 'Minimum Phase' plot - any area of sharp deviation (or outside of 45° as I recall) is likely to be a point that you won't be able to correct with your current speaker positioning.

Did you get a lesser peak in response at somewhere 65-80Hz?

When you've optimised the speakers and listening position, use the room simulation again to work out the average absorption you need on each wall to control the resonances.  Then we'll know roughly what's necessary and can talk sensibly about how to do it.

Thanks Huge. I've had a play with room sim in rew and although helps its just not practical to bring speakers out into room too much due to family. The most I can bring them out side or front is around 1m each (measuring from centre of front face). The sofa is also fixed around 30cm from back wall.

There is a lesser peak 65-80hz. 

How do you go about working out average absorption needed on each wall? 

Use the room sim and adjust the wall absorption parameters until the resonance peaks match you current room and not the values.  Then increase the wall absorption 'til you get the reduction that you need.  The necessary aborbtion ratio in the model gives the approximate ratio of the area of absorber that you need to the area of the wall surface (you may be shocked how much area you need!).

It does need some adjustment for the efficiency of the absorber (but despite some claims that can't really exceed about 1.25).

jon honeyball posted:

Go buy the ClioFW by Audiomatica, and their microphone. Measure your room properly. Educate yourself. Then make informed decisions. 

Anything else is just stabbing in the dark.

€1800 and many more facilities than are necessary for HiFi room measurement - it's just not necessary to spend that amount unless you're doing professional setup and need to demonstrate compliance with defied standards (particularly ISO).

thanks. so setting the front and back wall to 0.4 and left and right to 0.1 gives me an acceptable response. what does this mean in real terms? what product am I therefore looking for?

If your ceiling height is 2.5m (you haven't yet given all your room dimensions), your bass traps on the front and back walls need to cover an area of approximately 1.67m²; assuming a (pressure mode) absorption coefficient of 1.2 @ 45Hz.

If you're going down the commercial route (rather than DIY), then you'll need to look into the specification of commercial products to find something that has good absorption that low (rare, most only start absorbing significantly above about 65Hz).  The DIY route is cheaper but you'll need more area (typically about 2 to 3m²).

Thanks Huge. Ceiling is 2.74m. Do you think GIK Acoustics Scopus Tuned Membrane Bass Trap (T40) would be suitable? If so, how many do you think I would I need? They have a return policy so if they do not work then I can simply return them.

Calculation indicates you'd need 5 or 6 of them (but this is just a guide, you may get away with 4, or if you're really unlucky could need 8!)

I tend to think better of GIK than many manufacturers as
1)  they use sound principles
2)  they do publish their performance tests
3)  the result don't look to be inflated

However I have no experience of them.

thanks huge your advice has been really useful and very much appreciated. i might order some and give them a try. i really want to avoid downgrading speakers as i love them, the mid range is unreal (in that it sounds so real).

start off with four and if that has an effect and more needed i can always order more.

Halloween Man posted:

... the mid range is unreal (in that it sounds so real).

   That's the same reason I picked the Spendor SP2s 30 years ago, but things have moved on since (and got more expensive!).

Halloween Man posted:

start off with four and if that has an effect and more needed i can always order more.

Yes a good idea.

Consider also Vicoustic Wavewood. It will work most of the time.

Chag -

Chag... posted:

Consider also Vicoustic Wavewood. It will work most of the time.

Chag -

No completely wrong for this application: the lower limit of it's main absorption band is 320Hz.

huge, does it matter where on the walls the bass traps are installed? should i aim for the corners and reflection points (where speaker sound bounces off a wall before hitting listening position)? does height matter - is it best to keep to speaker bass driver height? thanks.

Huge posted:

jon honeyball posted:

Go buy the ClioFW by Audiomatica, and their microphone. Measure your room properly. Educate yourself. Then make informed decisions. 

Anything else is just stabbing in the dark.

€1800 and many more facilities than are necessary for HiFi room measurement - it's just not necessary to spend that amount unless you're doing professional setup and need to demonstrate compliance with defied standards (particularly ISO).

in the context of a power supply or a loudspeaker cable from Naim, it seems like good value to me. Having designed and built a number of ISO compliant listening rooms over the years (and just been measuring my current one) I'm pretty sick and tired of great hifi being put into rubbish rooms, and then people attempting to tweak their way out of the mess. Get the tools, get the knowledge, and get it done right. The room is as much a part of the system as the equipment you put in it -- arguably even more so.

Sure, get your dealer to do it for you. If you can find one who has a grasp of the subject. Which is, unfortunately, very unlikely.

Bitter? Maybe. But way too many dealers are happy to sell systems costing 10s of thousands into dreadful room acoustics, and then to womble on about cable dressing when the issue is the elephant in the room.

And randomly moving acoustic wedges and absorbers around a room seems like an exercise in futility to me. But hey, its their time not mine...

Jon,

Strangely I totally agree.

However for most people even understanding REW or DIRAC is a challenge!  Most people would be overwhelmed by Clio FW, for them it's not money well spent.  For you, yes it a brilliant tool to get it right.  And I also agree few dealers seem to understand even the basics of room acoustics.

I'm part way through sorting out my room:  The fundamental box resonances are fixed:  Now I'm going to start looking at reflections and nulls (particularly an isolated very sharp null at 208Hz that I don't as yet understand - I will though!)

another product that looks effective and may work for my issue is rpg modex corner or module, less bulk than the gik tuned bass trap (10 inches thick!)

if i decided to step down to scm19a then atc said i should experience a reduction of 3-4db at 45Hz. doesnt solve the problem but may make it less severe if acoustic treatment fails to be effective.

req is a useful tool and free. it verified what my own ears (and what i was feeling in the chair!) was telling me.  i'm not seeking perfection just need to tame a hugely irritating low frequency bump.

Huge posted:

Jon,

Strangely I totally agree.

However for most people even understanding REW or DIRAC is a challenge!  Most people would be overwhelmed by Clio FW, for them it's not money well spent.  For you, yes it a brilliant tool to get it right.  And I also agree few dealers seem to understand even the basics of room acoustics.

I'm part way through sorting out my room:  The fundamental box resonances are fixed:  Now I'm going to start looking at reflections and nulls (particularly an isolated very sharp null at 208Hz that I don't as yet understand - I will though!)

i just have a huge hatred of voodoo when physics explains things just fine

if you are near cambridge, give me a shout -- i have all the kit for room measuring, including a "HOW MUCH????" sound level meter that has a noise floor of 17dBA

Halloween Man posted:

another product that looks effective and may work for my issue is rpg modex corner or module, less bulk than the gik tuned bass trap (10 inches thick!)

if i decided to step down to scm19a then atc said i should experience a reduction of 3-4db at 45Hz. doesnt solve the problem but may make it less severe if acoustic treatment fails to be effective.

req is a useful tool and free. it verified what my own ears (and what i was feeling in the chair!) was telling me.  i'm not seeking perfection just need to tame a hugely irritating low frequency bump.

When I was looking into this I was impressed with GK's willingness to engage, and as Huge says, their products seem to make sense. I also came across the RPG modex units, and they seem impressive on paper, but the manufacturers were less helpful.

overall adequate treatment of a problem room can be quite expensive with commercial panels (though in the context of high end hifi the cost is maybe not that bad if thought of as a fundamental part of getting the system right). my own decision after looking into it was that I would have a go with DIY panels on the basis that the cost is far less and allows me to spend more on the things I can't make myself, and also they would be easier to adapt to available space, which is a major consideration. But it will have to wait until I have some spare time.

Of course,, the other solution to the problem is to change listening room, but not often a viable option!

How difficult is it to make a 40Hz tuned bass trap? I would not know where to start! I guess in the grand scheme of things an extra £1k in getting your room right is good value. You could buy a cable costing many times that and not get so profound results. i now consider the room to be just as important, if not more so, as any equipment you have.

atc actually put me onto rpg so perhaps they have some experience with them.

i did suggest a house move to my wife to accommodate an ideal listening room but you can imagine the response (a bit like my current room response)