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post #1 of 6 Old 06-28-2020, 06:24 AM - Thread Starter
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Ported box HPF questions

Hi all

Decided to turn my sealed sub in to a ported sub tuned to 16 or 17hz

But I have a NX6000d amp (inuke dsp)

The lowest I can set the high pass filter is 20hz. I know there is a work around but don’t know what it is. So questions.

1. what is the work around for the inuke

2. What the correct HPF type to use for ported.

3. Why does the group delay go up so much on Winisd when applying a HPF.

4. Think of of using 2 x 3” ports which shows a air velocity at 16hz of around 40ms and is around 27ms at 20hz. Is this ok?

I assume that winisd doesn’t take in to account flared ports so this should be less in reality and also bearing in mind this is with the full 1000w applied.

And also some people say that group delay and air velocity isn’t really important below 20hz when watching a movie at reference levels. Don’t know how true that is.

Any help appreciated. Thanks


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post #2 of 6 Old 06-28-2020, 01:49 PM
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https://www.avsforum.com/forum/155-d...l#post54675028

Butterworth 12dB/oct or steeper is typically used for HPF

Group delay is a normal side effect of filters. I'd suggest you ignore group delay at this stage of your learning. You will not be able to hear it at the levels and frequencies that are relevant to this design.

A lower port velocity would be better, so if you can make the ports bigger you probably should, but without the full details of the box I can't really give you specific advice.

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post #3 of 6 Old 06-28-2020, 02:23 PM - Thread Starter
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Thanks for the reply. I now understand how to achieve things on the inuke side.

The driver is an alpine type R 15 with a usable 25mm of Xmax before running in to trouble.

The TS parameters lend themselves to being able to use sealed or ported. In relatively small enclosures.

Winisd actually says I could use a 6 order butterworth filter. This must be due to the large Xmax of the driver.

According to winisd it will gain me around 7db at 5”15hz and 20hz compared to sealed.

the box is 140litre (actually a bit more I think) internal volume once driver is in and bracing is taken in to consideration. Sealed qts of around 0.59

I can go larger ports if needed and also due to the design of the box. I’m planning on running the ports externally to save space in the box.

Hope this sounds feasible.

The box isn’t big enough to get -3db point at 16hz so it’s hot optimally built . But still seems to be very beneficial anyway. 7db is 7 db and with 2 of them and room gain, I bet it will be pretty loudish. (Winisd says around 110 db at 15 and near 115db at 20) for one sub.


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post #4 of 6 Old 06-28-2020, 02:42 PM
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Quote:
Originally Posted by trojantrow View Post
Winisd actually says I could use a 6 order butterworth filter. This must be due to the large Xmax of the driver.
I'm not sure what you mean by you "could" use a 6th order BW HPF. You can always use any order filter, it just depends on what frequency. The "ideal" HPF for your box will likely be between 2nd and 4th-order rather than as steep as 6th-order.

Quote:
Originally Posted by trojantrow View Post
According to winisd it will gain me around 7db at 5”15hz and 20hz compared to sealed.
Yes, and that is the strength of the ported box over sealed. However, it's very important to make sure you are making the port big enough to actually create that additional output that shows up in the model.

Quote:
Originally Posted by trojantrow View Post
the box is 140litre (actually a bit more I think) internal volume once driver is in and bracing is taken in to consideration. Sealed qts of around 0.59

I can go larger ports if needed and also due to the design of the box. I’m planning on running the ports externally to save space in the box.
You can make this size work at your desired tune of 16/17Hz with external port(s). So you are converting an existing box? What are its existing dimensions?

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Audio: Denon AVR-X4400H 7.2.4 Atmos
Mains: Fusion-15 LR, Fusion-8 Center, Ported Volt-10 Surrounds, Custom 45°/45° Double-Angled Ported Volt-6 Atmos
Subs: The Two Towers (HT18 32cf 11.5Hz x 2), UM18 4cf x 2, Crowson MAs x 4
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post #5 of 6 Old 06-29-2020, 03:45 AM - Thread Starter
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Sorry about my relative lack of knowledge on the area. But what I meant is when modelling in Winisd it seems that a 3rd order would be ideal for the driver and box I’m using as the excursion of the driver is kept in check.

But I think it’s out of the question anyway as the inuke only supports 6th order at the least. I think I would have just got a bit more low end and less group delay with 3rd order set a few hz lower than tune but you told me not to worry about that anyway.

Yes I’m converting a sealed enclosure. It’s actually built in to a solid rose wood furniture cabinet reinforced with mdf to make it very heavy and 36mm thick all round. rear firing to front wall so you can’t see it and don’t even know it’s a sub. So wife friendly.

Identical sub to rear firing to wall.

The plan is to run the ports from back of box internal to front of box where driver is. (Around 400mm) length where driver is and then go external and bend 90 degrees and run along the wall to the side about her 450mm or so.

This will achieve port length and not be visible due to being between the cabinet and front wall. And won’t obstruct ports as will fire out the side.

Hope this makes sense.

One thing that confuses me is port compression. and I don’t know if it’s relative to port air velocity. But how do I make sure that it can create the DB that winisd says. Without compression?


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post #6 of 6 Old 06-29-2020, 05:53 AM
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Ported box HPF questions

Quote:
Originally Posted by trojantrow View Post
Sorry about my relative lack of knowledge on the area. But what I meant is when modelling in Winisd it seems that a 3rd order would be ideal for the driver and box I’m using as the excursion of the driver is kept in check.

But I think it’s out of the question anyway as the inuke only supports 6th order at the least. I think I would have just got a bit more low end and less group delay with 3rd order set a few hz lower than tune but you told me not to worry about that anyway.

Yes I’m converting a sealed enclosure. It’s actually built in to a solid rose wood furniture cabinet reinforced with mdf to make it very heavy and 36mm thick all round. rear firing to front wall so you can’t see it and don’t even know it’s a sub. So wife friendly.

Identical sub to rear firing to wall.

The plan is to run the ports from back of box internal to front of box where driver is. (Around 400mm) length where driver is and then go external and bend 90 degrees and run along the wall to the side about her 450mm or so.

This will achieve port length and not be visible due to being between the cabinet and front wall. And won’t obstruct ports as will fire out the side.

Hope this makes sense.

One thing that confuses me is port compression. and I don’t know if it’s relative to port air velocity. But how do I make sure that it can create the DB that winisd says. Without compression?


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6db/oct is first order, not 6th order. 12db/oct is second order, 18db/oct is third order, etc.

You will not get the output that winisd claims due to compression. Under 20 m/s is ideal, but even then compression is present.

Chris
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