# Modelling an SDX15....



## favelle (Jan 19, 2009)

Got some 20" sonotube and 6" PVC for the port and I plan on getting an SDX15 coupled with a BASH500. Want to dig as low as possible and this is 100% home theater (Blu-ray). Was thinking around 400L, but there is NO WAF, so can go as big as I want.....

Ideas?


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## Mike P. (Apr 6, 2007)

400 liters would be as big as you'd want to go. You won't gain much in a bigger size. The Bash 500 would need the Hi-Pass filter set to 13.9 hz as shown in the boost table documentation. Maximum air speed is 29 m/s with a 6 inch port 19.5 inches long. You should flare the ends with MDF "doughnut" rings.


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## favelle (Jan 19, 2009)

Port is only 19.5" long? That's not too bad. Should the part be "padded/dampened" as well as the inside walls of the enclosure, or does that matter?


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## favelle (Jan 19, 2009)

Would it be advantageous to decrease the volume then to 350L? 375L? What's the optimum?


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## Mike P. (Apr 6, 2007)

If low end output is what you're after for HT then 400 liters tuned to 15 hz works well. How big is the room?


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## favelle (Jan 19, 2009)

Mike P. said:


> If low end output is what you're after for HT then 400 liters tuned to 15 hz works well. How big is the room?


Room is 12' x 16' x 9' (1700 cubic feet). I am willing to give up plenty in the 30hz-40hz to get more in the 20hz and under.....


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## Mike P. (Apr 6, 2007)

favelle said:


> Room is 12' x 16' x 9' (1700 cubic feet). I am willing to give up plenty in the 30hz-40hz to get more in the 20hz and under.....


400 liters to 15 hz give you the most SPL at 20 hz and under. Is the room sealed off from other areas?


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## favelle (Jan 19, 2009)

Mike P. said:


> 400 liters to 15 hz give you the most SPL at 20 hz and under. Is the room sealed off from other areas?


Yep, one door on the right side, but it is closed during movies.


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## Mike P. (Apr 6, 2007)

You'll do just fine with this setup.


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## looneybomber (Sep 20, 2006)

For maximum low end, why not go with a 14hz tune or even 13.5?

Isn't there a HP filter built into the Bash500's?


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## favelle (Jan 19, 2009)

looneybomber said:


> For maximum low end, why not go with a 14hz tune or even 13.5?
> 
> Isn't there a HP filter built into the Bash500's?


What benefit would I get by going even lower in tune?


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## Mike P. (Apr 6, 2007)

There is no advantage. The lowest the Hi-Pass filter can be modified is 13.9 hz. Tuning to 13.5 hz will result in a less output in the 15 to 20 hz range where most of the low frequency information is.


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## favelle (Jan 19, 2009)

Mike P. said:


> There is no advantage. The lowest the Hi-Pass filter can be modified is 13.9 hz. Tuning to 13.5 hz will result in a less output in the 15 to 20 hz range where most of the low frequency information is.


That's what I was thinking. And this is still only a 15" driver, so there's no benefit to going any lower.

If this was in a sonotube design, what's the best dampening material, or should I even bother?


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## looneybomber (Sep 20, 2006)

A highpass filter is only needed if one is going to push the limits of their sub. The lower it's tuning, the smaller the chance of finding that limit. Depending on the tuning, output levels demanded, and electronics, it may be possible to eliminate the HP filter all together.


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## favelle (Jan 19, 2009)

looneybomber said:


> A highpass filter is only needed if one is going to push the limits of their sub. The lower it's tuning, the smaller the chance of finding that limit. Depending on the tuning, output levels demanded, and electronics, it may be possible to eliminate the HP filter all together.


Yeah, I wish those BASH amps didn't come with an HP at all....it would be way better that way.


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## looneybomber (Sep 20, 2006)

favelle said:


> Yeah, I wish those BASH amps didn't come with an HP at all....it would be way better that way.


...And I thought they were adjustable to below 13.9hz and even defeatable.


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## Mike P. (Apr 6, 2007)

You would have to contact Bash to see if there are resistors values that would allow no HPF. The amp's documentation shows a minimum HPF of 13.9hz with 1 db of boost in the 20 - 24 hz range.


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## favelle (Jan 19, 2009)

Mike P. said:


> You would have to contact Bash to see if there are resistors values that would allow no HPF. The amp's documentation shows a minimum HPF of 13.9hz with 1 db of boost in the 20 - 24 hz range.


What is the purpose of this boost? To flatten the FR?


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## Mike P. (Apr 6, 2007)

It's the way the amp is designed, all HPF's in the Bash amps have an amount of boost associated with it. Minimum is 1 db, and goes all the way up to 5 db. If a sub design rolls off early you can boost the bottom end with the appropriate HPF and boost. The various HPF's allow the amp to be optimized for a variety of box sizes and tuning frequencies.


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## favelle (Jan 19, 2009)

Mike P. said:


> It's the way the amp is designed, all HPF's in the Bash amps have an amount of boost associated with it. Minimum is 1 db, and goes all the way up to 5 db. If a sub design rolls off early you can boost the bottom end with the appropriate HPF and boost. The various HPF's allow the amp to be optimized for a variety of box sizes and tuning frequencies.


That's interesting. Nice way to avoid that dreaded "cliff" at 20hz or so, LOL!


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## Mike P. (Apr 6, 2007)

There isn't much of a cliff in most room when the effects of room gain kick in.


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## favelle (Jan 19, 2009)

Mike P. said:


> There isn't much of a cliff in most room when the effects of room gain kick in.


Such as corner-loading?


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## Mike P. (Apr 6, 2007)

Yes.


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