Confused with room treatment and open baffles.

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Bumpy

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Confused with room treatment and open baffles.
« on: 11 Jun 2020, 09:42 am »
Here is the source of my confusing and I would love help in unravelling this.

1. With OBs, the sound is emitted as a dipole ( figure of eight to front and rear). Therefore the sideways output of the speaker is at a null and all the rules of placing sound panels at the first reflection point on the side walls seem to fall over.

2. I have always understood that the rear output of the dipole is to be preserved as it's this that gives the OBs their unique sound. Now I see people putting absorbers and/or diffusers behind the speakers. So what is that about?

Waiting to do room treatment, but don't know how to proceed.  :dunno: :dunno: :dunno: :dunno:

Cheers Chris

FullRangeMan

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Re: Confused with room treatment and open baffles.
« Reply #1 on: 11 Jun 2020, 09:50 am »
There are said OB loss about 5 dBs relative to a boxed loudspeakers unfortunately, so sound absorbers stuff in the room makes no sense to me, I would prefer a live room. But music is all about personal taste.

Bumpy

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Re: Confused with room treatment and open baffles.
« Reply #2 on: 11 Jun 2020, 09:57 am »
There are said OB loss about 5 dBs relative to a boxed loudspeakers unfortunately, so sound absorbers stuff in the room makes no sense to me, I would prefer a live room. But music is all about personal taste.

There's another spanner in the works thanks :) :)

Not sure where 5dB loss would come from. If the entire rear signal was mopped up that's still only halving the output and therefore a 3dB shortfall.

FullRangeMan

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Re: Confused with room treatment and open baffles.
« Reply #3 on: 11 Jun 2020, 10:16 am »
There's another spanner in the works thanks :) :)

Not sure where 5dB loss would come from. If the entire rear signal was mopped up that's still only halving the output and therefore a 3dB shortfall.
I have read from 4 to 5dB loss, I suppose it vary according the freq being treble sounds less prone to spl loss. When the box is removed the acoustically positive front sound meets the acoustically negative rear sound, in this encounter a partial loss of SPL occurs due the neg/pos discrepancy.

Bumpy

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Re: Confused with room treatment and open baffles.
« Reply #4 on: 11 Jun 2020, 10:41 am »
I have read from 4 to 5dB loss, I suppose it vary according the freq being treble sounds less prone to spl loss. When the box is removed the acoustically positive front sound meets the acoustically negative rear sound, in this encounter a partial loss of SPL occurs due the neg/pos discrepancy.

Good point I had forgotten about cancellations. Maybe that's where acoustic treatments come in.

youngho


Bumpy

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Re: Confused with room treatment and open baffles.
« Reply #6 on: 11 Jun 2020, 11:19 am »
https://www.linkwitzlab.com/rooms.htm

Thanks
The man was a genius. In this one paragraph he seems to answer my questions.

"ORION separation is 8'. They are slightly towed in. The listener is at the apex of an equilateral triangle. Distance to the wall behind the speakers is 4', and to the side walls 2'.
The listener is only 4' from the wall behind, and this might require some heavy curtains and other absorbing material on that wall. As the room gets larger it expands around this triangular setup and especially behind the listener. Sound should just wash by the listener and disappear.

The wall behind the speakers should be diffusive. The rear radiation from a dipole must not be absorbed or it is no longer a dipole. Similarly, the side walls should not absorb sound at the reflection points but diffuse it. A dipole can even be towed in so that the listener sees the radiation null axis in a wall reflection mirror."

ric

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Re: Confused with room treatment and open baffles.
« Reply #7 on: 12 Jun 2020, 01:30 pm »
Interesting, but a bit over my head (no pun intended). As I have said in other posts, I use a pair of DIY shakti hallowgraphs (diffusers?) and thought I would not need them any more when I switched to OB. Wrong. If you have any interest of trying out something similar and have a little carpentry skill, send me a PM, and you can play around with soundfields without going the wall covering route. Have fun!

JWL.GIK

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Re: Confused with room treatment and open baffles.
« Reply #8 on: 18 Jun 2020, 02:16 pm »
For me the room treatment strategies, overall, don't change THAT much from one kind of speaker to another. Every speaker design has its foibles and we certainly want to adapt to them, but acoustics is more about what happens to the sound once it's in the the room than the technology involved in generating the sound.

The dispersion characteristics of the speakers are important, and any speaker sending sound out the rear of the speaker should be dealt with in some way (meaning treating the front wall behind the speaker). Also, remember bass behaves differently in the room than treble, treble tends to be beamy and directional whereas bass tends to move in an omnidirectional way.

But even so, treating the side reflection points will still help. If you're not sure about this, then play some music in your system and stand against the wall at one of the reflection points. All the sound you are hearing is what will be absorbed and therefore not aimed back at your ears.

As always you can send in your room details and we'll take a closer look at your specific situation and come up with a great plan.