Serious Problem

Serious Problem

Posted by layman (A) on July 14, 2012 at 05:21:28

In Reply to: The forgotten factor. posted by Belgarchi on July 11, 2012 at 22:04:18:

Above:
Power Response curve of a modern speaker design (Grand Utopia BE).

This is one of the rare instances where I disagree with Duke.

"Floor Bounce" otherwise known as the Allison Effect does not just occur on (one) axis but actually everywhere in the room. The direct sound from the speaker and the reflection of that sound from the nearest boundary will always be out of phase (and cancel each other) at a certain frequency determined by the distance between the drive unit and the nearest boundary (or boundaries as is usually the case).

The Allison Effect is a power response problem by definition and is all too evident aurally when listening to speakers who's designers have ignored this important aspect of wave mechanics. The Allison Effect can usually be heard as a suckout in the "power" passband or around 150 Hz to 300 Hz (given common speaker design woofer placement). The suckout is particularly destructive with orchestral music resulting in greatly diminished scale and a thin, unbalanced sound that emphasises high frequencies at the expense of lower frequencies. This also affects vocals especially the tenor range of male vocals and the mezzo range of female vocals (making them sound unnatural and muffled). Since the power response suckout is usually accompanied by a boost (wave addition) at frequencies below the cancellation, you also get "Barry White voice" where most male voices sound like Barry White.

Rock and pop music usually emphasize mid-bass frequencies (50 Hz to 75 Hz) and therefore power response cancellations are not as noticeable with these genres of music (unless the woofers are way up off the floor in which case the frequency of the power response notch moves down).

I would say that 95% of current speaker designs are afflicted with Allison Effect type power response problems, which is very obvious if you look at power response graphs (measurements of reverberant field energy) rather than on axis frequency response graphs. Like the above and below examples.

Power response curves courtesy Stereophile (Open in New Window)

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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

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)

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