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Author Topic: Liar Liar-pants on fire  (Read 11625 times)

chuck clark

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Re: Liar Liar-pants on fire
« Reply #20 on: August 30, 2011, 04:07:34 pm »

You are basically correct and your competitor is showing a bit of ignorance when it comes to wave propagation in an elastic medium. However, here are a few points to ponder. Your chart shows the wavefield only for 63 hz. The peaks and valleys will shift position as the frequency changes, meaning a VERY complex wavefield in reality.
Also the 6 db rule means the 100' distance will minimize the initial wave interference to a significant degree. Is the Ease software factoring that into the equation?
Inconvenient truth: all bass reflex designs are "out of phase" with themselves at ALL frequencies in their operating range EXCEPT the "tuned" frequency. Yet bass reflex designs sound amazingly decent!
One final point: even your theoretically perfect simulated point source design will have out of phase waves  bouncing  off the major reflective boundaries of the venue. (i.e. walls, floor, ceiling, partitions, etc.) Sooo, unless you enjoy doing more math than einstien it might be time to experiment by actually placing some spkrs. in the space, putting on some favorite bass content, and having a "walk-about" the facility to check the visceral experience the customer is looking for. Happy sailing on those waves out there!
Chuck
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Ivan Beaver

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Re: Liar Liar-pants on fire
« Reply #21 on: August 30, 2011, 05:23:19 pm »

You are basically correct and your competitor is showing a bit of ignorance when it comes to wave propagation in an elastic medium. However, here are a few points to ponder. Your chart shows the wavefield only for 63 hz. The peaks and valleys will shift position as the frequency changes, meaning a VERY complex wavefield in reality.
Also the 6 db rule means the 100' distance will minimize the initial wave interference to a significant degree. Is the Ease software factoring that into the equation?
Inconvenient truth: all bass reflex designs are "out of phase" with themselves at ALL frequencies in their operating range EXCEPT the "tuned" frequency. Yet bass reflex designs sound amazingly decent!
One final point: even your theoretically perfect simulated point source design will have out of phase waves  bouncing  off the major reflective boundaries of the venue. (i.e. walls, floor, ceiling, partitions, etc.) Sooo, unless you enjoy doing more math than einstien it might be time to experiment by actually placing some spkrs. in the space, putting on some favorite bass content, and having a "walk-about" the facility to check the visceral experience the customer is looking for. Happy sailing on those waves out there!
Chuck
I just chose 63 Hz as a "middle of the road" freq.  Yes any other freq will have a different pattern.  There was no reason to post different freq.

All the model shows is the actual freq response.  It does not show the "impact" (or lack thereof) of the same signal arriving at different times.

Yes with higher freq this can add to the "experience", but with bass, it is more about the impact/punch-the MAIN thing the purchaser is looking at.  Multiple arrivals will smear the sound and it will be less "punchy".

AGAIN- EASE cannot model below 100Hz.  THe model shown is NOT EASE, and the speakers in the model have the correct sub data-so they are fairly accurate-not counting what the walls absorbing the sound would do at different freq.  Pretty impossible to predict-so the walls are considered to be solid in construction

Yes the model (both the one presented and EASE) take into account the loss over distance. And as you notice the area right in front of the cabinets does not have as much interference as the rest of the room.

It does not matter how far you are from the source-if the distance from the other sources is large as well.

ALSO, there is no roof or floor in the model presented.  It is a 2D representation.  When you add those, it gets even more interesting-especially trying to predict what a roof will do as far as reflections/absorbtion goes.

Would you care to explain the phase "Inconvenient truth: all bass reflex designs are "out of phase" with themselves at ALL frequencies in their operating range EXCEPT the "tuned" frequency."
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Gary Creely

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Re: Liar Liar-pants on fire
« Reply #22 on: August 30, 2011, 10:19:00 pm »

The thing with ease (like with any tool) it is only as good as the guys using it. It is also easy to manipulate the results, really easy. The usefulness of an EASE plot as anything more than a sales tool comes down to the competency and integrity of the person using it.
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Brad Weber

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Re: Liar Liar-pants on fire
« Reply #23 on: August 31, 2011, 07:37:56 am »

Not to be a twerp, but if you're clever, you CAN model below 100Hz in EASE using omni-directional sources.

You have to scale all the dimensions and then make sure you scale your graphs by the same amount and you can see the same interference effects you would expect.

Only with omni sources and it gets confusing quickly. It's not something I would want to show a customer, but for experimentation there is some valid information as long as you think it all through.

Jeremy
But the guy said he modeled the particular speakers he was trying to sell in EASE.
But did they actually say that they actually modeled the subs proposed at under 100Hz?  They pretty obviously had an agenda so could it be that they modeled something proposed and said it showed no interference and that was interpreted by the Client, either through their lack of understanding or through that being the intended perception, as being that they modeled the subs proposed at an appropriate frequency?
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chuck clark

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Re: Liar Liar-pants on fire
« Reply #24 on: August 31, 2011, 04:53:54 pm »

Would you care to explain the phase "Inconvenient truth: all bass reflex designs are "out of phase" with themselves at ALL frequencies in their operating range EXCEPT the "tuned" frequency."

Sure, the port in bass reflex designs let's the 180 degree out of phase backwave off the cone out of the box to the front so that it is 180 degrees late or back in phase with the wave coming off the front of the cone at the frequency the box volume/port is tuned to, thus re-inforcing the energy of the front wave at the tuned frequency. As you move away from the tuned frequency that backwave gradually arrives  progressively further away from that ideal arrival time and eventually one octave away it is out of phase again and can cause over-excursion of the cone by UN loading the cone. This is really just a statement of fact when you begin to get a handle on the physics of wave propagation and how bass reflex designs work.
Does that help?
Chuck
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Tim Weaver

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Re: Liar Liar-pants on fire
« Reply #25 on: August 31, 2011, 11:54:34 pm »

In the spirit of the post title, for Ivan!

http://t.co/jyd2Jhl

Quote
The Q418 is 117kg and believed to be the world’s first quad 18” pro-audio loudspeaker.

Smoke crack much?
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Craig Leerman

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Re: Liar Liar-pants on fire
« Reply #26 on: September 01, 2011, 12:09:02 am »



Quote
The Q418 is 117kg and believed to be the world’s first quad 18” pro-audio loudspeaker.


Too Funny!  For those not getting the joke, I give you a picture of the very popular and well toured EV Manifold MT-4 subwoofer. Quad 18s in a manifold cabinet.

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paul bell

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Re: Liar Liar-pants on fire
« Reply #27 on: September 01, 2011, 10:22:41 am »

Thanks for the picture Craig!

I was just discussing that cabinet with a few friends yesterday.

When used in installs, you'd need to rotate the box 90 degrees once a week to reduce the top & bottom drivers from sagging.

As I understand it, early Prince tours used these cabinets.
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Greg Longtin

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Re: Liar Liar-pants on fire
« Reply #28 on: September 01, 2011, 03:33:04 pm »

Chuck,

Sure, the port in bass reflex designs let's the 180 degree out of phase backwave off the cone out of the box to the front so that it is 180 degrees late or back in phase with the wave coming off the front of the cone at the frequency the box volume/port is tuned to, thus re-inforcing the energy of the front wave at the tuned frequency. As you move away from the tuned frequency that backwave gradually arrives  progressively further away from that ideal arrival time and eventually one octave away it is out of phase again and can cause over-excursion of the cone by UN loading the cone. This is really just a statement of fact when you begin to get a handle on the physics of wave propagation and how bass reflex designs work.

Actually, let's not confuse the summed response of the speaker and port with the impedance of the box/port on the speaker.  'Unloading' is caused by the impedance dropping with frequency.  Nothing to do with the summed response (or the respective phase between speaker and port output)...

Greg
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Re: Liar Liar-pants on fire
« Reply #28 on: September 01, 2011, 03:33:04 pm »


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