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La La Scala

Project OVERKILL - I'm out of control / out of my mind

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When the weather is crap outside but you just cannot wait to start on your dream project 😁

20191026_180214.jpg

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I agree with the title - those drivers a bit too big for those pipes....just to notice...without judgment 😐

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What is your dream project ? Can’t tell if it overkill unless we know the details 

You may be surprised that the members on SNA collectively have hundreds of dream projects 

Me included 😎🤪

 

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Hi guys, they are 2 x 18" Mach5 subs, they have been rebuilt with a PSI kit (hence the logo)... The ports are 10cm, I'm stealing this man's build design, after all my number crunching his doe's still seem most economical... http://grizzlyaudio.blogspot.com/p/mach-1822-ixl-subwoofers.html?m=1

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If the TS parms for the PS1 drivers aren't the same as the Mach5 drivers then the enclosure will not maximise performance. Bracing in the design linked is pretty average.

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10 hours ago, A9X said:

If the TS parms for the PS1 drivers aren't the same as the Mach5 drivers then the enclosure will not maximise performance. Bracing in the design linked is pretty average.

Hi A9X, yeah I totally agree I was concerned about that too, however when I punched in the TS for both drivers in WinISD it recommended the same ports specs for both drivers for the same tuning frequency ( 24Hz ),  and im not sure if you scrolled all the way down in that link to see the final bracing used (ive attached an image), if thats not  enough bracing for a home theater sub then I'd like to know why more is needed?

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IMG_1756.JPG

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Bracing like that is OK but far more effective to have a full width window brace that runs the entire width/height and can be attached into opposing walls.

See attached image (stolen from Google) as an example Screenshot_20191028-133634_Google.jpeg

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I like the way you've attached the pipes to the wood 😉. What glue have you decided to use?

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43 minutes ago, BioBrian said:

I like the way you've attached the pipes to the wood 😉. What glue have you decided to use?

Oh that image is from a guy who's project I'm ripping off 😉... I liked it also, so I'm trying to get as close to it as possible.  I'll put some progress photos soon. 

I'll probably use 'Gorilla Glue or Liquid nails' or combination of both. 

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Nothing like an overkill project!

 

You probably don't want to hear this at this stage of your project, but the ports will limit the output given their size. In fact, it's possible that turbulence could limit the useful output to less than you would get in a smaller sealed design.

 

A large box with ~18mm MDF or ply needs considerable bracing and this can get tricky when using dual bend ports! Large panels need to be braced in the middle with braces that connect opposing walls. You also need your bracing panels to be braced by each other. If you brace it well, then you need to plan your build sequence with the ports.

 

Now is a great time to buy a dolly if you don't have one and figure out your journey from the workshop to the HT in terms of ramps.

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Adding to the above hardwood ply is A LOT stronger than mdf.

Might be something to consider

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Hi guys, thanks for your posts, yeah im using 21mm PLY, and I will be doing cross bracing.  That image with MDF showing the internals with the 2 ports is from the guys who's done a build with these same subs, I will be doing different bracing, but using the same size ports.  Might be a stupid theory but I figured if the 16"  SVS can have 3 x 10cm ports, then this 18" monster will be fine with 2, anything smaller than a 10cm would look silly,  tuned at 24Hz WinISD recommends 55cm, so a lot shorter than what he seems to be using in the above image.  And I plan to make plugs for the ports, so can utilize it as a sealed box too.  The size of the box is about 5 - 5.5 Ft3 after ports and bracing subtracted.

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4 hours ago, La La Scala said:

I figured if the 16"  SVS can have 3 x 10cm ports, then this 18" monster will be fine with 2

That doesn't add up to me.

 

The SVS 16" ported that I looked up had 3 vents, of 3.5" diameter. These are quite long and bent as well. (Agreeing with Paul Spencer) for a significantly larger driver, I'd go more toward 2 x 150mm ports. This would give you much less friction/diffraction, and would fit the same aesthetic.

 

Even though the calculator says it's fine, I've come under considerable flac for considering a single 150mm vent for a 15" subwoofer driver. This is bigger than 2 x 100mm vents. 18" is a much larger Sd.

 

4 hours ago, La La Scala said:

WinISD recommends 55cm, so a lot shorter than what he seems to be using

 

If you make the port diameter larger, you need more length.

 

 

 

 

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Much like Brian above im sure can attest to. The common consensus is that sealed with eq is always easier to get 'right'

A ported sub can be done well and with testing /measuring (and of course eq) can get great results.

But you may end up having to rebuild a enclosure if it doesn't live up to your expectations etc.

Personally I have 4x 15" sealed subs (only allowed to have 2 installed atm) and really don't 'need' any more than that. Even playing 20hz test tones stupidly loud.

At the frequencies we are talking about eq is always going to net better results (IMO)

Integration of a sub is very difficult to get right without

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I like a good vent rather than a port or 2. Results speak.

man1.jpg.508211862ac54b1d18a04eb9cc2c1306.jpg

Note speakers above, large short vent rather than long bent plastic tube, with sharp edges. Which is better ? Well this builder obviously thought vents.

Edited by Dirkgerman

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On 29/10/2019 at 2:31 PM, La La Scala said:

Might be a stupid theory but I figured if the 16"  SVS can have 3 x 10cm ports, then this 18" monster will be fine with 2, anything smaller than a 10cm would look silly,  tuned at 24Hz WinISD recommends 55cm, so a lot shorter than what he seems to be using in the above image.  And I plan to make plugs for the ports, so can utilize it as a sealed box too.  The size of the box is about 5 - 5.5 Ft3 after ports and bracing subtracted.

SVS and Rythmik tend to use multiple ports that are driven by commercial considerations. One is the need for a product they can sell in reasonable volume - hence they can't be too big. The other is that the bigger part of their market like the option of tuning below 20 Hz. So you might plug one of the ports to get sub 20 Hz tuning. What this does is move the peak in port velocity down lower.

 

What works for 15 Hz tuning with a 16" driver is probably pushing your luck with an 18" driver tuned at 24 Hz. Both the higher tuning and larger driver mean you need more port area for similar performance.

 

Keeping in mind, SVS typically represent sensible design compromises. In an overkill style DIY project, it's a good idea to try to go that next step. Of course, you'll quickly find you hit hard limits, where your ports no longer fit or you simply don't want to make the box any bigger. And this is where you start to understand why some people use passive radiators!

8 hours ago, Dirkgerman said:

I like a good vent rather than a port or 2. Results speak.

man1.jpg.508211862ac54b1d18a04eb9cc2c1306.jpg

Note speakers above, large short vent rather than long bent plastic tube, with sharp edges. Which is better ? Well this builder obviously thought vents.

 

A single round port outperforms all other options with the same port area. When you move to two smaller round ports, you have increased the surface area and there is a penalty in performance. With slot ports this is generally a greater compromise, so you need greater area for the same performance. Hence longer ports. Slot ports have thicker walls and therefore also result in a larger enclosure. But they do have practical advantages, like avoiding making the baffle larger to fit large ports and also the way they can integrate with the bracing. Further, you can create some very large flares on each end - much bigger than you can use if you're using a router bit. Each have their place and if you're building it, you will also have preferences around how it goes together.

 

In the example above, it looks like a pro audio music sub, probably tuned an octave higher with higher SPL to mask any port noise. In a home theatre sub, an unflared port like that limits you to around 6 m/s port velocity. When you find your ports starts chuffing at about 90 dB, that's not a happy moment!

 

By far the most difficult is a home theatre port with a high excursion driver and tuning around 20 Hz. Music tends to mask port turbulence and excite audible effects much less than LFE effects on movies, which can happen at quiet points in movies.

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