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Old 14th July 2011, 06:50 PM   #1
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Default Driver excursion control

Im considering build a sub using the Dayton 12 HF-4 (thisll be my first build), Im modeling it in WinISD. The sub would be a net 4.1 ft3 box with two 4x 37 ports tuned to roughly 20 Hz.

When I set the power to 250W excursion is well controlled above 17 Hz and it generates a flat curve at about 108.5 109 Db above 28 Hz. When I up the power to 400W I get a flat 110.5 - 111 Db in the same frequency range and excursion goes above Xmax + 10% in an area around 28.5 Hz.

Does WinISD model this accurately? Adding 150W only boosts SPL by 2Db but excursion goes up by 4mm? Im wondering if I really need a 500W amp for this setup or if 300W is going to be both safer and sufficient. Probably some of this has to do with the room and room setup: (20 x 15x 8.5 rectangular carpeted, open beam ceiling, 5 open entryways of about 30 each).

Id rather not try to control excursion at 28.5 Hz by filtering any ideas about this?
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Old 14th July 2011, 07:45 PM   #2
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The box is a bit too small, hence why it's bottoming out at 28Hz.
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Old 14th July 2011, 07:54 PM   #3
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I'll assume that you are talking about the Dayton RSS315HF 12"

Generally you are not going to run your sub(s) wide open since you want them to integrate with the other speakers in your system but you do want them and the sub amp to be capable of clean undistorted peak levels when necessary. The Xmech of that Dayton drivers is about 20% higher than their linear Xmax limits.

Most music and HT use is not a steady sine wave at one particular frequency but rather is dynamic - you should probably OK with your design but f you could make your enclosure closer to 6 ft^3 you would see a smoother response and less of a Xmax hump @ around 28Hz.

If the price differential between the 300W sub amp and the 500W sub amp isn't too bad I would go with the 500W amp

Last edited by Cokewithlime; 14th July 2011 at 07:58 PM.
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Old 14th July 2011, 09:32 PM   #4
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Hmm, maybe I'm doing something wrong but, WinISD indicates that, keeping all other params constant, adding more volume to the box increases excursion and port velocity. The param that seems to decrease the 28 Hz excursion is moving the port tuning closer to the problem area i.e. to a higher frequency.

That kind of makes sense, a larger volume of air doesn't provide as much damping as a smaller one.

Anyway I added in a 2nd order High Pass filter at 20 Hz and bumped the tuning to 21.5 Hz and things look much better!
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Old 14th July 2011, 09:58 PM   #5
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Quote:
Originally Posted by boris81 View Post
I am observing a similar behavior in WinISD Pro with a sealed box.
With all parameters the same decreasing the box size lowers the excursion requirements dramatically.

Can somebody explain this?
A smaller box has a stiffer air spring, which reduces excursion.

It also reduces output level, requiring a few decisions:

Will the additional power required offset the lower efficiency of the smaller box?

Will the driver sound as good when pushed harder to make up for lower efficiency ?

Design is fun.
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Old 14th July 2011, 10:00 PM   #6
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yeah, I realized it as soon as typed it up.
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Old 14th July 2011, 10:27 PM   #7
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some hints:
add a second order hi-pass at 18hz. (all the dayton amps have it.)
use 4.3ft^3
limit yourself to 250w with that driver in a BR box. excursion is the limiter in a BR box not power. 108db will be enough.

Your ports look good at 36"x4" port velocity at 20hz is under 10m/sec.

edit: i should mention, I've used that driver often. in a 4.3ft sealed box with a 240w amp it kicks like a mule and sounds great, better than BR .

Last edited by revboden; 14th July 2011 at 10:42 PM.
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Old 14th July 2011, 10:31 PM   #8
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Quote:
Originally Posted by weltersys View Post
A smaller box has a stiffer air spring, which reduces excursion.

It also reduces output level, requiring a few decisions:

Will the additional power required offset the lower efficiency of the smaller box?

Will the driver sound as good when pushed harder to make up for lower efficiency ?

Design is fun.
Yah that's what I was alluding to in saying a smaller volume provides more damping, but you said it clearer.

So to look at the issue of reduced efficiency due to having to overcome the greater resistance of a smaller air volume, I increased my box volume from 4.1 ft3 to 6 ft3 while looking at the SPL graph. My nice flat curve got a + .5 Db bump at 27 Hz and a slight decrease in Db at higher frequencies. The frequencies below 25Hz got a more of a boost by about 1 - 2 Db. But excursion becomes problematic at 28Hz again so I'd likely have to raise the port tuning which would reduce some of these low freq. gains.

All in all I can't say the increase in box size by about 50% is worth the boost below 25Hz, at least IMO. I think I'll stay around 4.1 -4.3 ft3.

Last edited by Sonoran; 14th July 2011 at 10:38 PM.
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Old 14th July 2011, 11:01 PM   #9
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Quote:
Originally Posted by revboden View Post
some hints:
add a second order hi-pass at 18hz. (all the dayton amps have it.)
use 4.3ft^3
limit yourself to 250w with that driver in a BR box. excursion is the limiter in a BR box not power. 108db will be enough.

Your ports look good at 36"x4" port velocity at 20hz is under 10m/sec.

edit: i should mention, I've used that driver often. in a 4.3ft sealed box with a 240w amp it kicks like a mule and sounds great, better than BR .
The 18Hz second order high pass is what keeps you at 250W, a 20Hz second order high pass lets you run 400W. It looks like the SPL below 25 isn't that different between the two: 250W + 18Hz hp filter & and the 400W + 20Hz hp filter. But the frequencies above 25 get about 2 more Db.

Is a 2 Db boost really that noticable?

Is a "BR" a vented box?

I figure I'll make the vented box and if I want sealed output, say for music or something, I'll just plug the ports. Best of both worlds IMO
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Old 14th July 2011, 11:07 PM   #10
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sorry,

one more thing, if you are crossing over higher than 80hz the 36-37" port will ring. for a crossover at 100hz limit yourself to 32" length unless you use an elbow. Then each section should be less than 32".
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