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The Allison Effect or how putting your cab in the wrong place can really suck tone...


alexclaber

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Thanks to Bill Fitzmaurice (horn speaker guru) for mentioning this and getting me googling...

 

The Allison Effect was named after Roy Allison who realised that room boundaries seriously affect bass reproduction, not only in terms of boundary reinforcement (generally good for us) but also boundary cancellation.

 

"The best bass response is achieved by having the bass source either very close to or very far away from reflective surfaces. This generally means close to the rear and side walls and floor and far from the far wall and ceiling."

 

Why is this?

 

If you place your speaker 1/2 a wavelength away from a boundary then, at the frequency that corresponds to that wavelength, the sound will be reinforced significantly. We're talking the kind of boost you get from cranking a parametric EQ with Q narrow. If this particular frequency is a boomy/muddy one, it will not be fun. And if you're playing an acoustic instrument, feedback city...

 

The flipside: If you place your speaker 1/4 wavelength away from a boundary, then at the frequency that corresponds to that wavelength (twice the previous frequency if the speaker hasn't moved) the sound will be cancelled significantly. A typical amount would be -15dB at the null frequency. Nasty. Truly tone sucking.

 

The solution? Place your cab so it's less than 1/4 wavelength (of the upper bass range i.e. 100Hz) away from any boundaries OR more than 1/2 wavelength (of your lowest frequency) from any boundary.

 

How does this relate to the real bass playing world? A 41Hz (low E) sound has a wavelength of 27.5 feet (I'm sorry, I'm still hanging onto the Imperial system). A 31Hz (low B) sound has a wavelength of 36.5 feet. So, fellow four stringers, you need to place your cab at least 13'9" away from any walls (fivers, 18'3"). So that's how to avoid peaky boundary reinforcement.

 

To avoid notching boundary cancellation you need to be within 1/4 wavelength of a boundary in the range of 31 to 100 Hz. So really you need to get your cab within 2'10" of a boundary. Which part of the cab, you may ask? The bit that's making the sound, i.e. the bass speakers themselves and the ports. So given that most bass cabs are 14"-20" deep, you need to get the cab really close to the back wall, but not so close that the ports' operation (if rear-ported) is affected. Think 6"-12" away.

 

So what's the best solution on the gig? Place your cab on the floor or on a short stand. Place it close to the rear wall. Place it close to one side wall. The far wall and the other side wall should be far enough away unless you're playing a boxroom. The ceiling will often be a pain, but one boundary causing nulls and peaks is a lot worse than all six getting in on the action.

 

Alex

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The thing I like about all of this is that these "rules of thumb" push my cab away from me. Since I stand more "up front" in my band, it will help my sound blossom to my ears.

 

I'll tell you that under low volumes I've violated these rules (about the back wall) without negative results. This was coffee house type stuff - as I say - low volume.

 

I have had times when I could not meet these requirements. My band played a small room about a year ago. It was a struggle to figure out where to put all the equipment and still fit ourselves. I ended up with my speaker nicely elevated above a PA main speaker, but it was 6 feet from the back wall. This should have been bad according to the rules. It was mitigated because the room didn't have a flat ceiling (large pitched roof). All the sound was all over - I don't know how we sounded as good as we did....

 

Thanks to Roy Allison for discovering this. I can't help but combine the discoverer with the Elvis Costello song when I cry out "Allison - I know this room is killing me. Oh Allison - my sound ain't true"

 

Tom

www.stoneflyrocks.com

Acoustic Color

 

Be practical as well as generous in your ideals. Keep your eyes on the stars and keep your feet on the ground. - Theodore Roosevelt

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Can't say that I fully comprehended what you wrote, but then again science/physics and all that was never my cup 'o' tea. Will re-read it tomorrow, when I am of more sound mind (had an Ethics exam today ...)

 

Anyway, my 2 cents: when I practice in my room, using my Peavy TKO 65W amp, the B string on my Ibanez is 'hardly' audible. But when I play in bigger rooms it sounds better.

 

Probably has nothing to do with what you posted :freak:

 

BTW, "The Allison Effect" would be a cool name for a band :D

"I'm a work in progress." Micky Barnes

 

The Ross Brown Shirt World Tour

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  • 1 year later...

Could it be the celebrated day for Mr. Groove?

 

If so, happiest of days to you Alex and let me take a moment to voice my personal appreciation of all you bring to this forum.

"He is to music what Stevie Wonder is to photography." getz76

 

I have nothing nice to say so . . .

 

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Originally posted by Tom Capasso:

The thing I like about all of this is that these "rules of thumb" push my cab away from me. Since I stand more "up front" in my band, it will help my sound blossom to my ears.

Me, too. I have found - no surprise I guess - that I sound better when I stand farther from my cab. Why am I just noticing this? Well, I mostly use my rig as a stage monitor and as we usually play small stages, I am usually standing right by it. One night, I was able to get out in front during a break and actually hear what others are hearing...and it was good.

 

I am going to try and make it so I am farther away from now on. I barely touch a knob once the gig starts so theres no need to be really close.

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Originally posted by C. Alexander Claber:

Birthday bump!

 

Alex

Is it your birthday Alex? If so, I need to go upstairs and record a little ditty that I been meaning to commit to disk...

Old bass players never die, they just buy lighter rigs.

- Tom Capasso, 11/9/2006

 

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Originally posted by robb.:

you know, i really appreciate the sound of the HT-112 close-up on stage -- it's really tight and cuts well. out in the audience, it's considerably bigger and thicker, and sounds fuller and warmer, but not boomy or muddy. to me it's a win-win.

 

robb.

Agreed, it does cut well up close, and that's probably what you want a monitor to do. I guess I was trying to say that it sounds soo much more full out in the room.
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Happy B-Day C. Alex.

 

One thing that should not be overlooked is phase cancellation. If your stage amp is out of phase with the FOH system then you will have a very hard time hearing yourself on stage no matter how loud you set your master volume. I have run into this problem while gigging and running sound for other bands.

 

Some speaker manufacturers wire their speakers in reverse to "the norm". If your band has it's own sound system try reversing the phase of either your amp or the PA system and see which way your amp sounds louder - you may be surprised. It's really easy if you're using "banana plugs" on the output side of your power amp - just unplug and put the + pin in the - jack and the - pin in the + jack.

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Happy Birthday, Alex!

 

In a perfect world I would try out your suggestions.

 

In the world I live in, the band is stuffed into a corner, on the back wall, or somewhere else where there is not enough room to move once we all have our gear in place. So I just have to hope that it will sound ok and none of my notes will be cancelled out or reinforced by those pesky standing waves.

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Happy birthday Alex, and let me add my thanks for your always interesting and useful posts. Apropos of nothing, on the day you were born I was fixing helicopters in Fairbanks, Alaska.

 

 

www.ethertonswitch.com

 

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Not to be mistaken for the Orbison Effect, discovered by Roy Orbison -- if you where dark glasses and stand perfectly still while singing and playing, it drives the chicks wild.

 

Sorry, couldn't resist.

 

Great info, Alex. Thanks.

"Tours widely in the southwestern tip of Kentucky"
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Originally posted by C. Alexander Claber:

I'm sorry, I'm still hanging onto the Imperial system

You and the United States. :D

 

Happy belated birthday, Alex!

 

Excellent post. There are certain forum members whose posts I make sure to pay particular attention to, as the knowledge they have to pass on is priceless. I won't name them all here for fear of forgetting someone.

 

Rest assured that you sir, are one of them.

Push the button Frank.
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Jeremy,

 

all you have to do is make sure that the front of your speaker is 24 inches from the back wall, and not more than about 3ft from the side wall. The ceiling hopefully will be about 3-6 foot from your speaker so no problems there.

 

The main issue is if the speaker is too far forward or too far from the side wall.

 

Jammed right in the corner is actually quite a good place to be.

Feel the groove internally within your own creativity. - fingertalkin

 

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Originally posted by TimR:

Jeremy, The ceiling hopefully will be about 3-6 foot from your speaker so no problems there.

Do you remember the name of the venue with the 3' ceilings? I need to avoid that place.

:D

Rocky

"Democracy is two wolves and a lamb, voting on what to eat for lunch. Liberty is a well-armed lamb, contesting the vote."

Benjamin Franklin

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The Royal Chace Hotel. I'll never forget that night! Stage 2ft high, cabinet 2ft, that left just over 3ft to ceiling. Side to side stage was about 15ft. Front to back about 10ft. It was like playing inside a five sided box which then opened up onto the main area.

 

Result. Uncontrollable feed back from Sax, and Singers mics. Drums and bass horrendously loud just to get enough volume out onto the main area.

 

Couldn't roll back enough frequencies on the fold-back to stabilise the feedback, Singer complained all night that she wasn't loud enough. every time I turned her up it just fed back.

 

Next time we are offered a gig there I will think twice. :mad:

 

You need to come to sone of our Ye-olde-drinking establishments. Seriously some you cannot actually stand up in without bending your neck, and I am 5'8".

Feel the groove internally within your own creativity. - fingertalkin

 

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