Need some help with low frequencies and atmos

[Marc Lombardi]

Sorry, Sonnie, maybe I spoke too broadly or maybe there are two different things going on. But you made me think, and that's always good! :-) If you have measured different response with subs in a given location with the only difference being orientation, that's really interesting. Do you get smoothing of peaks and nulls? Assuming "side-firing" sub design of course .... and I assume a sub designed to fire into the room would not have predictable results if turned downward or pushed up against the wall, and similarly for one designed to fire downward.

I was referring to the principle that lowest frequencies are omnidirectional below the point where the radiating surface diameter is small with respect to the wavelength (i.e. a 12" driver vs 14ft wavelength @80Hz, 28ft wavelength @40Hz, etc). And so I wonder if radiation is omnidirectional, what difference could it make in which direction the radiating surface is pointing? I took a quick look back at writings of Toole and Welti (Harman) and only found one reference to the direction of the sub. The simulations and measurements that Welti wrote about in his paper did not mention orientation, only position. Welti said in an interview that if the driver was "too close" to the wall it could affect acoustic loading, but not much.

 

[Marc Lombardi]

Interesting perspective T. But riddle me this ... the wavelength of 35hz is 32 feet, so how far do you need to move one sub relative to the other to eliminate the additive resonance?

 

[Poulk]

Hi all!
I did homework before asking here

t3t4
I move subs, spin them and change any setting i can. I even try to fire subs in the walls. All the time it's the same peak at 35 hz. And it's not because of a sum of two subs (sunfire play from 15-18 hz but the second one only starts at 35 hz ) i try to measure one sub (sunfire) the same peak. I'm sure where are some positions in the room where sound be much better, but for now, i can't use them So need to work with what i got

Now I thinking about beginning with something simple. And i need advice on this.
First, i try to do proper acoustick treatment, next one be a better second sub (or third ) and after that minidsp (hm or maybe minidsp before new subwoofer?)
As the first step of acoustic treatment, i want to try is two corner bass traps and one membrane absorber.
1) corner traps. i find pretty interesting mineral wool 4 inches deep and with high density (130 kg/m3, idk how properly convert this number to imperial, so leave it as is)
I thinking to make a tall panel about 7 feet high (2 sheets in high) and 2 feet in width. In the front corners of the room.
With this, i have two questions.
a) do i have a sense add two more layers of same (or less dense) wool and fill all the corner?
b) should i cover the front part of a wool panel with some material like aluminum foil, rubber or sth like this? to lower frequency respond?
Should i cover all area or only some parts with this material?
Which material will be better if yes?
2) Membrane absorber. I think do a simple one from wood.
And place it above couch (about 3,5 feet from the ground).
Panel be about 4 feet width and 2 feet high.
Calculation promises it works on from 25-28 hz and to 100 hz with Fo ~50hz
So how do you think it's be a good start point? Or this step is wrong and useless?
After what i will add more absorbers (for mids and high's)
and try to do some diffusers.

 

[Marc Lombardi]

A good start! Hard to say how much it will help, but it will help. And you can measure exactly what each step does. A couple things about velocity-type absorbers (the corner traps) and pressure-type absorbers (membrane traps). Velocity is zero at the wall, so space the corner traps away from the corner as you have them so the velocity is greater than zero. No need to fill the corner. Covering the front surface with heavy paper will improve efficiency, and you can cover the whole thing with speaker cloth. Membrane trap goes against the wall as you have it, the maximum pressure.

 

[Poulk]

Thank you Marc!
I think the thickness of 2 or 3 wool layers will slow down airspeed and add more damping capability of the low bass. But in the same way, the paper must work (lower frequency).
But away, which material be best for covering? thick paper, rubber, aluminum or maybe just plastic film? What will work best?
And should i cover the full front area of panels? Or it's better to leave some gaps for the absorption of mids and highs?

 

[Poulk]

Here's one thought, have you lifted the subs off the floor? Pick 'em up, put 'em on a cardboard box, a thick piece of Styrofoam, anything that could insulate the sub from the floor, then re-test.

No, i make a stands for both subs, with dense foam rubber feet (about 1-1,5 inch high).

 

[Marc Lombardi]

Ethan's recommendation is to use thick paper or thin plastic film. I used thick paper from a home building supply store. Sprayed adhesive and covered the whole front. If you need to absorb mids and highs, you might do that on the side walls in the first reflection point. Although your arch is quite a good absorber!

 

[Poulk]

t3t4
No. Marantz has a separated low fr. boost option. And it gives about +6 db on sub outs. i measure it in both on and off position. graphs i show before is in OFF.
About single sub performances. Here are two curves of two subs measuret one by one.

red is Sunifre 12" green is Whardal 10"
And this graph of sub boost option on and off.

greenline is sub boos off.

 

[Marc Lombardi]

Is it possible that Audyssey is being applied to the Wharfdale and not the Sunfire? The Wharfdale plot where you measure separately sure looks like correction was applied. Are they connected to two separate sub outputs or a single output with a Y cable?

 

[Todd Anderson]

Are your LFE measurements looking basically the same no matter where you place the subs in your room?

 

[Poulk]

Marc Lombardi
I think both subs EQed by audesey (but who knows). And both put in sub 1 and sub 2 outs. WD is ported 10" sub with 150W amp and Sunfire is sealed 12" sub with 1000w amp. Maybe they behave differently in room
Todd Anderson
No measurements is pretty different from place to place. Only spike 35 Hz is on the same place for example, one of the test runs

t3t4
hehe, panels in the room it's not a big problem But I will try set all to default and do measurements again, maybe its change something.

 

[Todd Anderson]

Are you sure that Audyssey didn’t set your mains to “large”?

 

[Poulk]

Are you sure that Audyssey didn’t set your mains to “large”?

Yes, Audyssey set front speakers as Large, but I've changed and tried all variation of crossover from 40-100 Hz and make measurements. The best result IMO was all "small"+80Hz.

 

[Todd Anderson]

You have to watch Audyssey like a hawk. Since you're running subs, you'll want those mains set to large.

Next question, have you played with phase of your rear sub?

 

[Poulk]

With mains sets as large i got much worse curve (and i hear it with my ears )
Yes, I played with phase ALOT WD has only switch 0 or 180" but sunfire has a regulator from 0 to 180, so i try all variation i can on both.

 

[Todd Anderson]

I would try moving that Sunfire to the back of the room... put the WD in the front (likely that will stay on 0). Then do minor tweaks to the Sunfire, just to make sure phase isn't introducing any issues.

 

[Poulk]

t3t4
My HT room is boomy and doesn't have any treatment. so without treatment only EQ can help But IMO is more "last hope" weapon. I mean if you EQed sound too much, it's take off some part from it.
For real I don't remember did I reset all or just run audesey as is of course, I will redo it with all default before any further moves. But I'm pretty sure few tweaks will help a lot to my room.
For this moment I'm pretty happy with the quality of mids and highs in my ht. it has volume and clarity. But the low end is a mess. Literally it hurts to hear.
ps. I read and looks a lot about acoustick panels (and seen this video before), and this towel panel doesn't help me much, because it's working on much higher frequency then I needed it.
Now I make some changes in my pre-plan of stage one )) of acoustic treatment in the room. Hope I see some critics when it's be done