Sub position almost always at the front??

[Dr Force]

Hi guys

I have noticed in alot of members set ups and on the DD website that the Sub is positioned at the front with the front and centre speaker.

Is this a coincedence or is there some sort of science to the eventual sound.

Thoughts welcome

[Nimby]

The greater the separation of the subwoofer from the front speakers the greater the interference between the sound output from all of them due to phase effects. Low frequencies (deep sounds) have very long soundwaves. When one soundwave meets another out of phase they cancel each other at that particular frequency making that sound much quieter. When two soundwaves meet each other in phase they reinforce each other at that frequency making that tone sound louder.

The pulses of sound pressure waves coming from the subwoofer are better off being reinforced by the front speakers for maximum impact and the flattest frequency response. Imagine the sound pressure waves as big bubbles. When they join in phase they become a bigger bubble. When they meet out of phase they burst each other.

When the subwoofer and speakers are close together they can mutually reinforce each other's sound output. When separated they cancel each other's output.

There is also the problem of being able to isolate the source of the low frequencies from the subwoofer as being different from those coming from the speakers. The greater the distance which separates them the greater the chance of identifying the source of the deeper rumbles.

[Andywilliams]

Originally Posted by Dr Force

Hi guys

I have noticed in alot of members set ups and on the DD website that the Sub is positioned at the front with the front and centre speaker.

Is this a coincedence or is there some sort of science to the eventual sound.

Thoughts welcome

All i know is that when i had my ultra -2 at the back of my room it performed very well with music but with movies on certain material i could locate the sub (80hz x over) which really spoils the experience. When placed at the front i never experienced any localisation ever so at the front does seem to intergrate easier without problems, some avforums members have managed (bass oldie) to intergrate there subs at the back of the room but i guess it isnt easy.
Andy.
PS i did try at the middle sides of my room and it was even worse than at the back.

[russ.will]

As Nimby says, you stand the greatest chance of smooth integration with all speakers firing from the same plane, or as near as possible. Theoretically, if you arranged all of your speakers/subs around you in a perfect circle, there would be no phase related issues at all where ever they were placed - all sound wave fronts would arrive at the same time and therefore in phase. However once in a room with the associated reflections from the walls/floor/ceiling then these start to give the brain directional clues and it makes sense to have speakers that relate to each other subjected to the same environmental effects*.

That doesn't mean inbetween the front three is definitely the best place though, as all rooms are different and all can suffer in weird in weird ways from those same reflections within. In the course of trying a few subwoofers in my room, I've only occasionally been able to try a couple of subs inbetween the front speakers. In my room, it results in a broad 80-100Hz suckout that no amount of twiddling can dial out, but as I say that's my room and it's combination of shapes, positions and physical makeup.

The best position is still near the front though as whilst smooth integration with music is less problematic, the huge impacts in movies can be felt coming from other directions. Even if you don't feel it's audibly locatable, your body/brain still knows where it's coming from and that can spoil the effect.

Russell

*Anyone successfully running Audyssey MultEQ will notice a larger, more homogeneous soundfield, precisely because of it's ability to suppress the rooms contribution particularly with respect to time based delays from reflections. Don't ask me how they do it though.

[Dr Force]

This all makes perfect sense, so when i finalise my speaker placements I will definately put the sub at the front.

Does it matter where at the front? My set up will have my front three speakers on a wooden AV cabinet so the sub will sit slightly infront but to the very left against the wall slightly away from the corner of my room.

I know putting subs in corners can cause some boomy sounds so I may actually benefit a little by bringing it forward a tad........yes/no??

Thanks

Dave

EDIt: just read through Russ's post so its kind of answered my post.

[russ.will]

That's exactly where mine is:



Albeit, it's normally a bit smaller than the PB13U shown.

Russell

[Dr Force]

Thanks for the effort Russ

here is where I propose to put mine.the room shape and size is about what its like in real life (2.4m x 4.4m).

The sub is marked in red.Its downward firing, sitting on decent carpet on a solid concrete floor.