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38% rule vs. distance to monitors.

pistol-pete, muokattu 13 Vuodet sitten.

38% rule vs. distance to monitors.

Youngling Viestejä: 1 Liittymispäivä: 30.5.2009 Viimeisimmät viestit

I have a pair of 8240 with autocal.
The room has some treatment with traps in all 4 corners, and about 15 absorbers on walls.
Monitors are shooting along length of room which is almost 7 meters long.
Placing monitors close to the wall yields a good respone.
The problem is that the best listening position is somwhere around 265 cm from same wall (about 38%).
After dsp correction i get a very flat response with this setup. No negative value (cancelation) in the low frequency, and no larger boost then 2 db. ,and no larger dip or boost in hi an mid than 2,5 db.Problem is that i end up some 2 and half meters from monitors.
The info on the 8240 states that distances over 2 meters is in danger of screwing up the image.
But if I move listning position closer, like 1,5-2,2 meters i suffer from cancelations in the bass at 10 db.
Any advice? Should I try even more basstraps and go for no moore than 2 meters from monitors?
Or should remain in the rooms sweetspot and secure the imaging with some treatment?
If so what would that treatment be?

Best regards
christophe-anet, muokattu 13 Vuodet sitten.

Re: 38% rule vs. distance to monitors.

Jedi Knight Viestejä: 188 Liittymispäivä: 23.3.2009 Viimeisimmät viestit
Hello Petter,

Thanks for your post and detailed setup arrangement. Glad to hear that you are ending up with a very good response thanks to AutoCal. Now, a listening distance of 2.65 m is a bit unusual for 2-way systems indeed. The further away you are from the loudspeaker the more the reverberation field dominates. The imaging is less accurate and the frequency response balance depends increasingly on the room acoustical properties.
Now, the 10 dB dip at LF you indicate when you move closer to the loudspeaker is clearly a room mode or standing wave cancelation phenomena.

So, few suggestions and options to try:
1. If you keep the listening position in the best location;
a) and you also keep the 2.65 m listening distance; in that case you should really make sure that the direct path between loudspeakers and listening position is clear from any objects, reflection surfaces, etc... That path should be absolutely clear from any reflections to make sure there will not be any compromise in sound imaging. To control the imaging, acoustic treatment materials can be applied on the side walls between loudspeakers and listening position.
b) you could possibly make the listening distance shorter in moving the 8240A closer to you, say 1.6 m? Then, run AutoCal again and see what happens in the low frequency below 100 Hz? It might be acceptable.

2. You move the listening position:
A short listening position is good, once again some 1.6 m, but then you have the room problems you have mentioned. You could move the measurement mic up and down and see how that dip behaves by running AutoCal few times at few different heights. If the dip varies in amplitude while moving the mic, you know it is a vertical standing wave minima problem. Then the cure is to add damping materials on the ceiling above the listening area to minimize this cancellation. If you apply the same procedure to the length and width of the room you will gain additional knowledge about the source of the cancelation. Then you could apply some further damping materials along the dimension that displays cancelation problems.

Hope this will be of some help. Please let us know your findings!
Best regards,