RE: The forgotten factor ??

Posted by layman (A) on July 18, 2012 at 20:01:54

In Reply to: RE: The forgotten factor ?? posted by jedrider on July 18, 2012 at 16:36:50:

Above:
Power response curve of Grand Utopia BE.

You are seeing (and experiencing) the Allison Effect in action.

The speaker's direct sound and the reflection of that sound from nearby boundaries will alternately cancel each other or reinforce each other at specific frequencies determined by the distance between the drivers and those boundaries.

The frequency of power response nulls (cancellations) due to the Allison Effect can be determined using the following formula:

Frequency of Null = 1130 (velocity of sound)/Distance in feet x .3 (quarter wave coefficient).

Power response nulls become much more severe when the woofers are the same distance from multiple boundaries.

Below the frequency at which direct and reflected sound cancel each other (creating nulls), they reinforce each other, creating shelving bass boost (easilly heard as you move speakers closer and closer to boundaries - bass response shelves up as the bass drivers get closer to the boundaries and the speakers can sound boomy and distorted).

That is what you are seeing in the example that I attached above (power response curve of the Grand Utopia BE)... a severe cancellation around 100 Hz (you can work out the distance between the Grand Utopia BE's woofers to nearby boundaries in this example using the formula I provided) followed by shelving bass boost at frequencies below the cancellation (where the direct and reflected sound reinforce).

The null and the bass boost issues could be reduced by placing the speakers so that the woofers are a different distance from each room boundary and none of the boundary distances are multiples of the others. With such placement the power response curve of the speakers would flatten out.

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Follow Ups Full Thread

Topic - The forgotten factor. - Belgarchi 22:04:18 07/11/12 (25)

RE: The forgotten factor ?? - jedrider 16:36:50 07/18/12 (1)

RE: The forgotten factor ?? - layman 20:01:54 07/18/12 (0)

Serious Problem - layman 05:21:28 07/14/12 (5)

RE: Serious Problem - Thorsten 08:39:11 07/14/12 (4)

Again confused - Belgarchi 17:59:08 07/15/12 (1)

RE: Again confused - Thorsten 23:41:37 07/15/12 (0)

Here we go again... - villastrangiato 11:03:17 07/14/12 (1)

RE: Here we go again... - Thorsten 11:17:41 07/14/12 (0)

BDS is not that big a problem if spkrs are positioned to get maximum and smooth room gain. - Timbo in Oz 20:54:22 07/13/12 (0)

Nodes are worse yet... - Scholl 17:59:39 07/13/12 (1)

RE: Nodes are worse yet... - Kloss 08:06:26 07/14/12 (0)

How about... - Presto 11:20:59 07/12/12 (1)

Should work well. (nt) - Belgarchi 16:42:25 07/12/12 (0)

RE: The forgotten factor. - Thorsten 09:09:29 07/12/12 (8)

Don't agree at all - Belgarchi 16:40:24 07/12/12 (7)

I agree lets get rid of floors who needs them - Kloss 08:04:16 07/14/12 (0)

I agree with Duke and Thorsten - djk 23:42:46 07/13/12 (0)

RE: Don't agree at all - Thorsten 22:12:37 07/12/12 (0)

I agree with Thorsten - Duke 21:30:27 07/12/12 (3)

I don't agree or disagree - just have a more insightful, maybe even more useful comment... - villastrangiato 10:20:47 07/14/12 (2)

insights - Duke 11:21:17 07/14/12 (1)

RE: insights - villastrangiato 12:05:54 07/14/12 (0)

Paging Roy Allison.......nt - viridian 08:08:02 07/12/12 (2)

Great Roy Allison Interview - layman 20:08:03 07/18/12 (0)

Yep, I forgot him, good point. (nt) - Belgarchi 16:41:24 07/12/12 (0)

Follow Ups

RE: The forgotten factor ?? - layman 20:01:54 07/18/12 (0)

RE: The forgotten factor ??

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