Room and speaker interaction type thread.

I've a small, soft walled room with a 2m ceiling, and the Audiophysic setup method works smashingly. 1.5m from back and sidewalls, speakers about 2m apart and 1.5m from the listeing seat, chair seat right up against the wall with a foam mattress behind it.

A pretty close setup, but sound just seems to slosh aimlessly around the room otherwise. It gives a very dark and beefy sound though, which might irk if you like a bit of sweet and nice.

Regarding toe in, a good rule of thumb is to adjust the speakers so that the inner side of the speaker can't be seen from the listening position.

 

If your spreadsheet doesn't know the reflected gain (which is actually loss!) then how do you know the amplitude response across the room?

We can also safely assume that your spreadsheet is (quite) inaccurate if: the room isn't rectangular, contains any large absorbing objects (like furniture) and has any openings like doors, or recesses like window cavities, fireplaces etc.

In-room measurements are definitive - your spreadsheet might be a good starting point, but that is all it is.

 

Thanks Dat19... :beer:

 

I tried out Merlins calcs earlier this evening and have just stopped while my son goes off to bed..

Remarkable and welcome improvements are evident..

I have ended up with the speakers further into the room by a fair margin and was able to get the speakers about right side to side.

Much more bass weight but all the same tunefulness and speed this is the reverse of my expectations as by moving the ports much further from the back wall I would have expected less bass.

Sounds so much better and was free! Have tested using the Cinematic Orchestra and one bass break that left me disappointed before, puts a big big smile on my face now!

Can't do a double blind test but it's pretty easy to hear a marked improvement in bass weight!!

If it is only a guide it seems to work pretty well.

Thanks Merlin. I'm a very happy tweaker this evening...

 

Tried my speakers firing down the long axis of a 21x12x8 room and had no bass at all. Tried them across the short axis and hey presto - bottom end!

The great forgotton side of hi - fi.

Shakti stones my a*se!

 

For once Dat we might agree. the spreadsheet is a good starting point , I never claimed any more than that

What it will allow you to see, very quickly, is the axial modes prevelant in a rectangular room. With this information, you can get an idea as to how to use the room modes to your advantage. It's a guide to working with the room rather than against it. Furniture and coverings start to really impact above 300hz, with the exception of say a large sofa which we assume will be placed to the rear of the listening area.

Let's say you have a second order node at 73hz across the room. this will result in a cancellation every 46". Now if you place the speaker half way between these cancellations you will experience a peak. Half way between the two is a good starting point. This is just in one dimension. Results should be referenced against similar nodes in the two other planes and adjustments made to suit.

Got any better suggestions for something to give you some guidelines in about 2 minutes Apart from a Tact of course

 

We must put a stop to that, and I have a feeling that my suggestion will do so

Bought one of these this week for $300 to use as a parametric EQ.. It also has a real time analyser, so I bought the mic for a lark..

http://www.behringer.com//DEQ2496/deq2496_big.jpg

Won't get to fiddle with it until Christmas.. I''l take the top off and post some equipment porn pics for Wm and Isaac..

I'll have a look at the manual for the TACT and see if they are in any way comparable..

 

We must put a stop to that, and I have a feeling that my suggestion will do so

Bought a Behringer DEC2496 Ultracurve this week for $300 to use as a parametric EQ.. It also has a real time analyser, so I bought the mic for a lark..

Won't get to fiddle with it until Christmas.. But I'll take the top off and post some equipment porn pics for Wm and Isaac..

I'll have a look at the manual for the TACT and see if they are in any way comparable..

 

Hi Steve,

"I have experimented with various kinds of bass traps (DIY) and found them all to be quite useless. To be any use at room resonance frequencies, I have come to the conclusion that bass traps need to be very large and that their construction is a bit of a black art."

I had my room tuned by an audio engineer. I was sceptical before meeting this guy but he tuned a room at work for an audio visual presentation system so we tried him out on that first! he has tuned numerous studios, some Hi-Fi shops and many listening rooms in houses.

He turned up with a portable and measured the in room response by feeding the signal from his portable into my preamp. We then checked some theoretical calcs to see if they agreed with the main room modes, which they did. He then installed some bass traps tuned for that mode. We listened and re-measured. This showed a reduction in the mode. We then installed many more bass traps (12 in total). This had a significant effect on the mode which was what I was after.

Basically what I am trying to say is that your DIY efforts, as you have found, are not likely to work. You need to target the right frequency range and then manufacture a bass trap that works in that region. If you don't then the large energy levels in the bass mean that you won't change the sound.

Ian

 

Hi Ian! Well I did go into the theory thoroughly and I did design the bass traps to have a strong action at the required frequency. I even tried a Helmholtz type trap which acts at a specific frequency but it seemed to have no effect on the response curve that I could measure. I concluded that for those designs, I had to make them bigger in order to have an effect but that would have been a touch impractical (and an expensive experiment at that).

What is the design of the bass traps you are using and would that design be amenable to a spot of DIY?

I can't imagine my living room with 12 bass traps in it. There wouldn't be any room left for me

 

That would make them bear traps then

 

:duck:

 

Hi Chris,

Sorry to have sounded as if you hadn't tried the right approach! From what you have written you tried the right approach but not in the right magnitude!

"What is the design of the bass traps you are using and would that design be amenable to a spot of DIY?"

They certainly are. What I have is tubes that my wife calls giants bog rolls! They are roughly 1.3m tall and 0.3 m diameter, made out of thick cardboard. They have a bung (rubber or very dense foam) that can be moved up and down the tube to get the right length to reduce the bass energy in the room. Obviously you will need to determine the length of tube you require and then set the bung in the right place.

I needed 8 tubes in my room before we could measure / hear any response changes. Mine are hidden behind floor to ceiling curtains by the patio windows and behind the sofa.

I hope that lot helps.

Ian

 

How do you hide a 30cm thick tube behind a curtain

And what was the measured drop in response with 8 traps

The main bass peak in the room is typically 20 dB. By how much was it reduced?

All the corners of my room are in use at the moment. I would have to get rid of some furniture if I wanted to accomodate these traps.

 

Get a notch filter...

 

Hi Chris,

"How do you hide a 30cm thick tube behind a curtain"

Floor to ceiling height curtains, off the wall to some extent and perhaps they are slightly smaller diameter tubes. Nobody has evr spotted them behind the curtains.

"And what was the measured drop in response with 8 traps"

Can't remember any figures as it was a while ago.

"The main bass peak in the room is typically 20 dB. By how much was it reduced?"

Again we used the measurements as a reference but used our hearing to determine whether it was worth doing. And it certainly was.

My room has a laminate floor sitting on insulation, on floorboards, on joists over a big void. This made the main room mode quite severe so it was a dramatic effect for me reducing the main mode.

I wouldn't go with LowRider's suggestion of a notch filter. The Audio Engineer that helped me out uses them at times in studios but says they often add other bad effects (generally phase problems) whereas the acoustic treatment described has no acoustic nasties it just works.



Ian

 

Well, if he doesn't want 30 cm thick things in his room, neither do I, is there another choice...

Anyway, I also have a ressonance at 48 hz, it doesn't bother me much with most music, unless I play really loud, but the other day I found out that it was amplified by vibrations transmitted from the floor to the player, so I placed Isobearings underneath and now it is much less bothering, so much less that I stopped using the notch filter... :MILD:

Technobear, maybe you should give it a try... :latte:

 

If you can hide a man behind a curtain you certainly can a bog roll.

 

Hi Chris and Lowrider,

"Well, if he doesn't want 30 cm thick things in his room, neither do I, is there another choice"

Sorry, operator error on my part. The tubes are in fact 10cm in diameter, I measured them last night!

Ian

 

I'll have to see if I can find that brochure from the cardbord tube company tomorrow. The narrow tall tube sounds a bit like the Room lens treatments, have you tried placing the tubes close together?

Also I use True RTA for my measurements. It's pretty flexible though having to drag the desktop system into my room to make the measuremets is a pain.