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Discussion Starter · #1 · (Edited)
Hello All,

I'm planning a new 15" slot ported design, probably based around a Tempest-X2 driven by a 500W plate amp or 1000W standalone amp (haven't decided). The subwoofer will double as an end-table and will be replacing an Epik Valor. External dimensions will be 24H x 20W x 28D, 3/4" MDF, slot port 1.5" x 18.5" x 30", tuned @ 20Hz, internal volume approx. 5.3 ft3. These specs seem to be modeling well in WinISD Pro with this driver using an HPF @ 18 Hz.

So I gave Sketchup a whirl last night for the first time. I've attached the file for review. Is the single brace sufficient? Is there enough clearance between the port opening and the underside of the plate amp? I modeled a 3/8" roundover for the port flares, how important is this radius? Any feedback would be welcome.

Thanks,

Steve

Edit 3/14/10: Updated plate amp enclosure drawing and added 2" port height version of enclosure for 1000W standalone amp.

PlateAmp (500W)
5.3 ft3 internal volume
20 Hz tune
1.5"H x 18.5"W x 30"D Slot Port
HPF = 18 Hz
Maximum Port Velocity = 15.25 m/s

ExtAmp (1000W)
5.15 ft3 internal volume
20 Hz tune
2.0"H x 18.5"W x 42"D Slot Port
HPF = 18 Hz
Maximum Port Velocity = 15.85 m/s
 

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Re: New Tempest-X2 15" Slot Ported Design - Feedback Appreciated

1.5" is way to thin for a slot port. 2.5" at least is suggested. Flaring is only useful for looks.
 

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Discussion Starter · #3 ·
Re: New Tempest-X2 15" Slot Ported Design - Feedback Appreciated

1.5" is way to thin for a slot port. 2.5" at least is suggested. Flaring is only useful for looks.
I've targeted keeping the port velocity below 25 m/s based on a recommendation from Kevin (Exodus) in a previous thread. Additionally, Kevin posted a sample down-firing design for this same driver with a 1.5" slot port height. This port with 500W doesn't exceed 16 m/s. Is there some reason I shouldn't follow the advice of the driver manufacturer?

I'd rather not have to increase the port height any due to port length/box volume trade-offs.
 

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Re: New Tempest-X2 15" Slot Ported Design - Feedback Appreciated

Hi there,

Ive just simulated your sub with 750 watts and with the hpf engaged you will only see max 18.5 m/s velocity so you won't have any issues at all that I can see and at 1000 watts you are at 21 m/s.

With a 2.5" port you would need it to be 52" long and with a 2" port you would need to make it 41" long.

You may want to consider doing a 2" port which will go up 14" up the back of the sub which will be fine but there won't really be room for a 52" length port.

A 2" port will bring it down to 16 m/s and thats with a 1000 watts of input power.

I would go the 2" route mate. :T

cheers

Graham
 

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Discussion Starter · #5 ·
Re: New Tempest-X2 15" Slot Ported Design - Feedback Appreciated

Hi there,

I would go the 2" route mate. :T

cheers

Graham
I think my plan will be if I use the 500W plate amp, I will leave the port as is. If I decide on the 1000W rack mountable amp I will expand it to 2" as I'll have the back wall free for the extra port length.

Thanks for the advice.

Steve
 

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Mike,

Thats a google sketchup file. Downlaod Google sketchup for free. Its the best free program you can get. That's what I used to design my subs. Its absolutely brilliant. Download it, you will see what I mean.

cheers

Graham
 

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Plenty of people have built the slot ported design. I've not received one complaint about port noise so I think the 1.5" is sufficient. No harm in going bigger if you want the extra margin of safety but I wouldn't obsess over it if you need to keep it 1.5".

Kevin Haskins
Exodus Audio
 

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Personally I would still go for a 2" port and chuck 1000 watts at and get another 3db across the board out of it. With a 2" port and double the power the port velocity will be the same as a 1.5" port and 500 watts. Here's some pics to help you mull over it. You really want to get the best out of it in my personal opinion. :T

Cone excursion is still in check too.

I agree with Kevin that the 1.5" will be fine but I don't think you will be doing the driver justice with only 500 watts.

cheers

Graham
 

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Discussion Starter · #11 ·
I agree with Kevin that the 1.5" will be fine but I don't think you will be doing the driver justice with only 500 watts.
Graham/Kevin,

Thanks for the feedback. I'm starting to agree that if I'm going to do this project, I might as well maximize my investment and go with the 1000W amp. I would feel better with the 2" port height @ 1000W. I'll create an external amp Sketchup drawing with the 2" longer port for any that are interested in it and attach it to the first post of this thread.

Steve
 

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Discussion Starter · #14 ·
That will be great. I am interested in building one with the Dayton SA1000 amp. Thanks.
Ok ... updated first post of this thread to include larger slot port enclosure better suited to 1000W standalone amp (like the SA1000).

Enjoy.
 

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Re: New Tempest-X2 15" Slot Ported Design - Feedback Appreciated

1.5" is way to thin for a slot port. 2.5" at least is suggested. Flaring is only useful for looks.
Flaring is about more than just looks. A number of years ago I was experimenting with different flares, from no flare up to 72mm radius on a 100mm vent. I was using a 12" driver in a 70L box with 46mm excursion at 20 Hz. No flare lead to massive turbulence and air was coming out the vent like a fan. You could feel it blowing from some distance. 18mm radius made a big improvement, 36mm a similar improvement, and 72mm also noticeable. With the latter, the air didn't seem to "blow" at a distance but made a more gradual transition. In all cases, chuffing was still audible, but went from a noisy obnoxious sound to a quiet noise that could be masked by other content.

I had a discussion with Collo on another forum, but didn't anticipate what he'd do with the ideas we talked about. He did a whole lot of experiments, then created a great little application for predicting if a port will chuff or not. The info is here:

http://www.subwoofer-builder.com/flare-testing.htm

Anyone building a vented sub should read this and download his application flareit.exe

Of course, slot ports are different as the aspect ratio is very different. Perhaps a small radius has more effect, but it's certainly not true to say that flares don't do anything. What you want to do with the flare is size it so that the aerodynamics are not a bottleneck at the ends. Each vent has a certain "core limit" where velocity is too high and the frictional resistance causes excessive turbulance and chuffing. Ideally you make the port flare big enough so that it can handle velocities up to that point.

What most do is accept a compromise, as this approach leads to big flares and a design that often isn't practical or is difficult to realise. The result is a sub that won't chuff even if you try with sine waves. Of course, real material is more less demanding as there is masking content and a wider distribution of frequencies, so a sine wave chuff test is more rigorous than most situations will require.

I read an AES paper on vents that actually shows that the best profile has two radii - one which has a very large radius where the cross sectional area increases from the centre to the ends, and another at the ends where there is a transition. This is virtually impossible for a diyer to realise in a circular vent, but could easily be done with slot ports made with 3mm MDF bent into shape. This is one feature of a slot port that I haven't seen tried, but if I was going to make a slot port it's what I'd do. The paper is called

Maximising performance from Loudspeaker ports
No 4855
Alex Salvatti and Doug Button
JBL Professional
Northridge, CA, USA
Allan Devantier
Infinity Systems
Northfidge, CA, USA

Very interesting paper, just wish I could figure out the formula that actually determines tuning!!!

Of course, you have to choose a point to draw the line between practical and ideal and decide how far you want to go.
 

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Discussion Starter · #18 ·
How is the build going dboff01?
It's not.

With other home project and financial obligations, I'll be lucky if I can build before the end of the year. If you've seen the Money Pit with Tom Hanks, that's pretty close to my life. :)

In the meantime, I continue to model (WinISD) and draw (Sketchup) various enclosures/drivers/configurations to determine ultimately what I will build when I get the chance.

Steve
 

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It's not.

With other home project and financial obligations, I'll be lucky if I can build before the end of the year. If you've seen the Money Pit with Tom Hanks, that's pretty close to my life. :)

In the meantime, I continue to model (WinISD) and draw (Sketchup) various enclosures/drivers/configurations to determine ultimately what I will build when I get the chance.

Steve
Bummer.

What design changes were you thinking of making?
 

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Re: New Tempest-X2 15" Slot Ported Design - Feedback Appreciated

I read an AES paper on vents that actually shows that the best profile has two radii - one which has a very large radius where the cross sectional area increases from the centre to the ends, and another at the ends where there is a transition. This is virtually impossible for a diyer to realise in a circular vent, but could easily be done with slot ports made with 3mm MDF bent into shape. This is one feature of a slot port that I haven't seen tried, but if I was going to make a slot port it's what I'd do. The paper is called

Maximising performance from Loudspeaker ports
No 4855
Alex Salvatti and Doug Button
JBL Professional
Northridge, CA, USA
Allan Devantier
Infinity Systems
Northfidge, CA, USA
Just for reference, this paper is available here.

Very interesting paper, just wish I could figure out the formula that actually determines tuning!!!
Do you mean this one?

Of course, you have to choose a point to draw the line between practical and ideal and decide how far you want to go.
That's very true.
 
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