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Discussion Starter #1 (Edited)
Now that all the hardware is ready to go, I'll be building a ported enclosure for my sub, and already have a bunch of questions in designing it. I still have more research to do, but I thought I'd post my findings here. First of all...

My requirements:
  • Home theater use exclusively
  • 20 to 80 hz
  • Smallest enclosure as possible, in the 6 to 8 cu ft. range
  • Ported (slot or round, I haven't decided)

My hardware:
  • Acoustic Elegance AV15-H 15" driver
  • Behringer EP4000 amplifier
  • Reckhorn B2 Bass management from CSS

If all goes well, I will be building two of these, each powered off of one channel of the amplifier.
 

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Discussion Starter #2 (Edited)
I was playing around with box size verse spl output. I came up with some options in the 6 to 8 cubic foot range. Only a 1 to 1.5db drop between them. The first picture shows SPL vs. box size. The second shows cone excursion at 1000 watts, and with high and low pass filters. The third shows air speed vs tube port size.
 

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Discussion Starter #3 (Edited)
I was using an online tool and came up with this slot port sketch - although I think the slot height is too small. I would double-up the MDF on the face of it. As pictured, it is on it's side. I would position it with the slot against the floor. The box volume as shown is almost 7 cu. ft., but with bracing and the driver, it would be right around 6.5 cu. ft. At 6.5 usable cu. ft., I'd be about minus 1.5 db at 20hz compared to an 8 cu. ft. enclosure. With room gain, I don't think this is noticable, but it does shave nearly 25% off of the required volume.
 

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My suggestions when it comes to modeling with round ports, model only what is attainable. For example, you have a 7" port listed, but good luck ever finding one of those.

Then I have to wonder at what frequency you want to cross your sub over to your mains? Reason is, typically, folks will tune their subs in the teens and you're tuning close to 20hz. If you wanted to tune lower, but keep internal volume relatively small, your first port resonance will become an issue if you're crossing it over an octave or less below the 1st port res.

Also, what are you going to use for a HP filter?
 

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Looney,

Unless I am missing something, he is using the port area of Winsid for the size of slotted port (based off of the diameter and length and his information above about slots). I am not sure how Winisd would work like that since the “shape” shows a circle but I think that is what his is testing (Hawk correct me if I am wrong). It also looks like he will cross over at 80 according to the lowpass filter he put in.

James
 

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Hawk,

I was just reading up on Winisd and if you click the circle in the "vents" tab it will change it to a square to be used for a slot port design.

James
 

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Discussion Starter #7 (Edited)
Since it will be used for movies only, I'll be using the LFE port of my receiver, and i will set it to 80hz. I will be adding a low pass filter around 16 or higher depending on the final tuning of the port. I'll probably use the Reckhorn B2 Bass management from CSS. I like that it would handle both subwoofers, and has the equalizer functions that could help flatten the response a bit. I doubt I'll find anythign less than 100 bucks that would do the same.

Exo is correct, I was trying to get a sense of the windspeed by setting it between 6 and 8 inches (I'm still playing with the port size, but it should be in this range). The 2.25 X 21 inch slot port I'm currently showing is basically the same as a square point with a diamter of 7.75, so I'll switch over to the sqaure shape and put in the correct value. Thanks for the tip Exo, I didn't realize that was an option.

I'm not sure about the 90 degree turn in the port. I'll probably put a 45 deg wedge in there to smooth it out a bit. But only a small one as i want to preserve as much interior volume as possible.

Also, is there any problem with having the slot only .75 inches from the floor? Should I flip it and put the port at the top?

So from the looks of this so far, would you guys say I was on the right track? Any other tips you can provide?
 

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For a folded slot port you want to have it as close to square as possible. 90 degree turns are fine if you have the appropriate cross sectional area. I do suggest routing the port edges or using quarter round.

Also generally tuning below Fs is considered a bad idea. Your Fs is 21 hz.
 

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Exo: I gotcha. I didn't know he was using round ports as a supplement for slots.

For a folded slot port you want to have it as close to square as possible. 90 degree turns are fine if you have the appropriate cross sectional area. I do suggest routing the port edges or using quarter round.

Also generally tuning below Fs is considered a bad idea. Your Fs is 21 hz.
Tuning below fs is not a problem. It's done quite often in pro audio world. In home audio, it's ok too. With that driver, he could tune into the teens if he wanted, so long as box size increased too in order to fit the port.
 

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Discussion Starter #13
Can anyone provide me their opinion on whether or not the slot port should be at the bottom of the enclosure, or at the top. The bottom seems to be too low, since it will essentially be .75 inches fromt he floor. Are there any considerations to make with the orientation?
 

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Can anyone provide me their opinion on whether or not the slot port should be at the bottom of the enclosure, or at the top. The bottom seems to be too low, since it will essentially be .75 inches fromt he floor. Are there any considerations to make with the orientation?
the port being near the floor will effectively increase length, lowering tuning, which could be beneficial
 

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I know that in the DIY circles that 6+cu ft is considered small but you listed small as a requirement and I don't see that as a small box. What about going the PR'd route? I think you could go a good bit smaller by using a pair of PRs.
 

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Discussion Starter #17
you know, I didn't really consider it all that much. I'll do some modeling and see how much can actually be cut off the box size. As it is right now, I can get somethign that could probably pass for an end table size, which is satisfactory to me. If I can make it sleeker with PR's without too much compromise, I'll seriously consider taking on the added cost. Do you know a place to get decent 15 or 18 inch pr's on the cheap?
 

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Discussion Starter #19 (Edited)
I just ordered the Reckhorn B2 Bass management from CSS. This will provide the high-pass rumble filter I need, and will also let me (hopefully) smooth out the response a bit.

I looked into PR's a bit, but was not too impressed with the size reduction vs price increase equation. I'll play around with winisd some more, but I'm already pretty close to my ideal size as it is...

I would really prefer a 19 X 19 X 28 (exterior dimensions) enclosure. It would perfectly fit my "end-table" size requirement. As it stands, it looks like I will be closer to 22.5 X 22.5 X 32 (exterior). With the port, and bracing, this gives me an internal usable volume in the 6 to 7 cubic foot range and can still pass as an end-table. So I'm not too far off.

I'm having a problem determining just how small I can make the port. Can I really get by with a 2 X 15" slot port (similar to a 6.5" diameter round port), or is it too small? I tried to model the air speeds, but I don't have a good sense of the real-world meaning of it. I heard a big difference in a test setup with too small of a port. I basically stuck a 3" diameter pipe in the back of the 4 cubic foot enclosure with the same driver as an experiment. The results were: sine waves (way too noisy); regular music (some chuffing); movies (somewhat noticable on LF effects - although it was kind of neat feeling "wind" on some of the explosions). So I don't really know.

I also thought of making the slot out of 1/2" mdf to save some extra interior space.
 
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