Oversized ported box - consequences to driver. - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #1 of 8 Old 01-28-16, 06:03 AM Thread Starter
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Oversized ported box - consequences to driver.

Hello all,
There is a question I would like to ask.
Having completed a 12 inch ported sub build, I was told by someone who knows more than I do that the box volume is way too big for the t/s parameters of the driver so if I play the sub at any substantial loudness the driver will self-destruct. The thing is I programmed the t/s parameters into WinISD while planning the box and everything looked alright to me. The cone excursion simulation was well within limits at the maximum planned wattage for the sub with the Highpass factored in. Now the question is, does it mean that after WinISD modelling I still have to go back and do generic calculations on the Vas and Qts relationships as well as the appropriate Fb in order to confirm the final box volume and tuning for a given driver? I thought WinISD takes all these into account when all the relevant graph plots appear satisfactory or is there a relevant WinISD relationship that is not obvious which I need to learn about for example between the impedance and excursion plots relating to underdamping?
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post #2 of 8 Old 01-28-16, 07:06 AM
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Re: Oversized ported box - consequences to driver.

WinISD will show you which design looks best for a given set of T/S parameters. If you think your cabinet is a bit off you can do a test to check your outcome. BUT your driver wont self destruct unless your feeding it to much power below the port tune without a Hpass. Also if your cabinet is WAY to big for the driver you can push the driver past its limits with smaller amounts of power. BUT if you post your simulation we can all have a look and go from there.

Also tell us what your cabinet and port dimensions are also.

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post #3 of 8 Old 01-28-16, 08:50 AM Thread Starter
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Re: Oversized ported box - consequences to driver.

Thanks for your response, dual 3cuft boxes each with dual 3.375"ports of length 37 " each (19.7hz tuning) . The driver is the 12" Epik sentinel used in the Epik sentinel Subwoofers. Attached are the WinISD driver and simulation files as well as an image of the driver.
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post #4 of 8 Old 01-29-16, 01:32 PM Thread Starter
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Re: Oversized ported box - consequences to driver.

Hello?
Papi? Are you there?
Anyone else care to comment on this please?
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post #5 of 8 Old 01-29-16, 06:19 PM
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Re: Oversized ported box - consequences to driver.

Looking at your WinISD file I doubt you will have any problems running them at 400 watts as long as the HPF is setup correctly.
Also, I wouldn't consider 3 cu ft to be a big box either.

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post #6 of 8 Old 01-30-16, 01:20 AM Thread Starter
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Re: Oversized ported box - consequences to driver.

Ok Bill thanks.
Now this system was designed with a ceiling of 600 watts. In your WinISD perusal what do you find to be the 400 watt limitation here, is it the value of the highpass, the 'oversizing' of the box, the port airspeed or any other issue? I want to know what I could have done better given my aspiration which was a fair amount of infrasonic extension without so much spl in a reasonably small box.

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post #7 of 8 Old 01-30-16, 01:33 AM
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Re: Oversized ported box - consequences to driver.

The main thing is not to exceed the cone excursion!

With 400 watts and a HPF you will be very safe from exceeding the cone excursion limit.
You should be still OK up to about 500 watts although you will not notice a lot of difference between 400 and 500 watts since perceived loudness is a logarithmic scale.

There is a rule with designing subwoofers.

1. Size
2. Bass extension
3. Spl

Choose any two....

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post #8 of 8 Old 01-30-16, 08:35 AM Thread Starter
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Re: Oversized ported box - consequences to driver.

[The main thing is not to exceed the cone excursion!]
If you remodel that simulation with 8 times the present box volume with the same wattage, tuning, and Hp filter you would still not exceed the excursion limits. Does it therefore mean that WinISD should not be trusted at least in this regard and oversight should be exercised over some of the box predictions to avoid damage?
[1. Size
2. Bass extension
3. Spl

Choose any two....]
True! It is with respect for this law that a low Vas, low Qts driver was desirable. This speaker box simulation was a desperate balance of compromises.
What started the entire controversy was when I noticed some distortion while playing the subs at a moderate volume. This I later discovered was due to my over enthusiastically setting the eq with a 5db gain at 20hz. When I modelled it on WinISD, I discovered my foolishness. But someone had already made the conclusion that the cause was an oversized box.
Tell me is it within the rules to post the link to my build which is on another forum?

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Last edited by Toffkanda; 01-30-16 at 08:42 AM.
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