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MercedesBerater

DIY build - need help/advice

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1 hour ago, capo72 said:

You will get a lot more bang for your buck with tapped horn, and the builds are not that much more difficult.

Building a maze is as easy as building an empty box?

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I wrote "not that much more difficult". IMO it's worth the extra effort, but I defer to you, you're the tapped horn expert. I've only built 1. I don't know why I bother offering my opinion anywhere on the internet anymore. This forum, like so many others are so frustrating to me lately. I hate the internet, I think I need a break!

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2 hours ago, capo72 said:

I wrote "not that much more difficult". IMO it's worth the extra effort, but I defer to you, you're the tapped horn expert. I've only built 1. I don't know why I bother offering my opinion anywhere on the internet anymore. This forum, like so many others are so frustrating to me lately. I hate the internet, I think I need a break!

No insult meant.  My apologies if it came off that way.

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2 hours ago, capo72 said:

. I hate the internet, I think I need a break!

relax  , we're all just talking to each other and  exchanging ideas , and  discussions must be engaging .

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i've found kind of what i was dreaming up...well, one of many dreams. 

 

dual 18's in a large ported box.  i am not so great with WinISD - i think i've kind of reverse engineered it pretty accurately - i just can't figure out how long to make the port. 

 

BOX=   22.5" wide,  28" deep,   54 tall

dual 18  UM18-22's

Speakerpower SP1-2400

 

slot port =  3.5" tall  x  18" wide..... which the bottom of box would make it 28" +   ?????? how far up the back of the box?  to tune it to 11hz.   

(SeatonSound did a very limited run, 6,  of these and they were tuned to 10.5hz.  just can't figure how long to make the port to achieve that.)

 

Thoughts???   because THIS....THIS makes me happy.   I could look at these for days....

Image result for terraform d18

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On 2/10/2021 at 8:52 AM, MercedesBerater said:

I want to build a stack of four UM18-22 in each corner.

What size is your room?  I have two Ultimax 18's each in a 4.25CF sealed cabinet powered by a Crown K2 (800 watts RMS to each sub)  I have one in the front and one in the side/back area to smooth out the nodes.  In a 22 by 18 foot space, there is more bass than anyone would ever need.

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Ok, here is what i have got modeled up....  this is laying on it's side.... the port would be on the bottom.

 

 

dual UM18-22's  

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this is the SPL graph

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transfer function magnitude

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cone excursion   (with a highpass filter, butterworth 15hz  n=2)

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air velocity

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does anyone know the effect of polyfill?  i read somewhere that in large(r) enclosures it isn't as effective as small(er) enclosures and is kind of like a 25% increase in box volume. 

 

is this true?  i tried re-modeling the box as 16cu/ft and also  20cu/ft leaving every other dimension and spec the same.  it looks like it gives almost a 3db bump starting at 20hz, down to 12hz and then rolls off pretty hard.  

 

does this seem like a fair guess on what some polyfill will do?

 

then the question is... how much? 

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1 hour ago, MercedesBerater said:

does anyone know the effect of polyfill?  i read somewhere that in large(r) enclosures it isn't as effective as small(er) enclosures and is kind of like a 25% increase in box volume. 

 

is this true?  i tried re-modeling the box as 16cu/ft and also  20cu/ft leaving every other dimension and spec the same.  it looks like it gives almost a 3db bump starting at 20hz, down to 12hz and then rolls off pretty hard.  

 

does this seem like a fair guess on what some polyfill will do?

 

then the question is... how much? 

From the  guys over on the JBL: a rule of thumb of 10% increase in apparent volume. However the details are important. 1) all sides, top and bottom (not the back of the baffle) 2) 1 to 1.5 inch thick 3) not poly fill rather something like HVAC duct liner (about 3 lb/cu ft) or sometimes pressed fiberglass or Rouxal . Of course there is the usual rambling discussion about "dust and particles".

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@PrestonTom  ohh that's a good idea to use a more rigid type thing,  maybe even carpet underpad like Jute?   that would be more tidy to spray glue  in place. 

 

in a ported enclosure, would you line the inner side of the port that faces the subwoofer, but not inside the actual port cavity - right? 

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13 hours ago, MercedesBerater said:

@PrestonTom  ohh that's a good idea to use a more rigid type thing,  maybe even carpet underpad like Jute?   that would be more tidy to spray glue  in place. 

 

in a ported enclosure, would you line the inner side of the port that faces the subwoofer, but not inside the actual port cavity - right? 

 

No, you have missed my point. Do not use carpet pad or jute (too dense).

 

If you are having problems finding the correct material (insulation blanket), then go to home depot or lowes and buy the Rouxal "Safe n Sound". The material is too thick (3.5 inches), but you can carefully peel off the paper backing (moisture barrier) and then peel it in two again to get approximately 1-1.5 inch thick sheet. This is the simple, cheap and available. 

 

There will be enough material so that you do not need to worry about the port. In fact, keep material away from the port entrance. 

 

Is this is a new build or a retrofit? If it is retro fit, then use material similar to the existing stuff and do not try and re-design the enclosure.

 

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@PrestonTom    got it,  i have some spare safe-n-sound laying around to split up into slices. it does 'delaminate' pretty well into thinner sheets. 

 

it will be a fresh build.  see earlier in post for dimensions and modeling in WinISD.  

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3 minutes ago, MercedesBerater said:

@PrestonTom    got it,  i have some spare safe-n-sound laying around to split up into slices. it does 'delaminate' pretty well into thinner sheets. 

 

it will be a fresh build.  see earlier in post for dimensions and modeling in WinISD.  

 

One trick that I have used is to make the cabinet about 10% larger and the port about 10% longer than "necessary". Stuff the cabinet and then run impedance sweeps (google on how to do this). Then start decreasing the length of the port tube until the impedance plot shows that you have "reached" the desired port tuning. It is best to run these sweeps with the cabinet in the approximate position that you will use it (i.e., near a wall or near a corner, etc). The beauty of this is that it takes some of the guess work about internal volume and compensation for drivers, bracing etc.

 

good luck,

-Tom

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And so it begins... 

 

here I’m test fitting the panels & brace.  There will be more bracing in the subwoofer areas, but will need to draw a window design with subwoofer cutout.  So I’ll make all of those at the same time. 

B97B052C-762D-4E86-8172-519EAE35C769.jpeg

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Bracing done. 
 

next up— cut out woofer holes & amplifier hole.  Then run and secure subwoofer power and ground  wires and leave excess coil so subs can he hooked up easy. And wire isn’t flapping around inside.

then add poly-fil  sheeting to the outside wall surfaces before closing up the side wall. 
 

then wait until the wife isn’t looking and order the subs & amp.  🤣

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On 2/10/2021 at 8:52 AM, MercedesBerater said:

(ported box square vent =  18" wide x 4"tall x 35.54" length (last value won't let me change it)  

 

 

On 2/10/2021 at 8:52 AM, MercedesBerater said:

 Box dimensions roughly 22'' wide, 22'' deep, 7 feet tall.  (~22 cu/ft)

 

Without studying too much, my opinion is that it's because your box is tiny for four of those subs in a ported box.  Your internal dimensions are basically 18 cubic feet at best after driver displacement, not counting bracing, assuming 3/4" wood.  Doesn't count a thicker baffle either.  That's small even for a sealed box, you really need 4 cubic feet each after displacement.  And you're trying to port it?  Those drivers need at least 8 cubic feet each, preferably 12, each.  You're trying to cram four into an 18' cubic foot box.  That doesn't count the port either though which is another foot and a half with these dimensions.  Your box is basically the size that it needs to be for one ported one, it's undersized for two even at like 20 hz tuning.  Parts Express did an 8 cubic foot build and they recommended stuffing it with poly-fill to reduce the port velocity to keep it from chuffing, really needs to be bigger.  

 

If somebody really wants a F18 build for cheaper, just come pick mine up, I even have the Seaton F18 amp, it's the 4,000 watt speakerpower that was programmed by Mark.  Same size, same stuffing, same amp.  It's as close as you're going to get.  

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On 2/16/2021 at 4:07 PM, MercedesBerater said:

does anyone know the effect of polyfill?  i read somewhere that in large(r) enclosures it isn't as effective as small(er) enclosures and is kind of like a 25% increase in box volume. 

 

 

In a sealed box, polyfill dissipates the shockwave behind the cone which is why it acts like it's in a larger box in a smaller box, the cone is allowed to move more at lower frequencies.  R-19 insulation has about the same effect but with the added benefit of absorbing the back wave more, which polyfill is poor at doing.  The Seaton F18's use insulation and they're stuffed pretty good.  

 

In a ported box, polyfill does about the same thing but the effect is that it cuts down on the port velocity.  That can keep you from chuffing but it also kills the backpressure from the port which could have negative effects.  At the tuning frequency the cone will move more, raising the impedance, and possibly putting it at a higher risk of damage due to overexertion.  Depending on how hard you stuff it, you're going to end up somewhere between a proper ported box and a sealed box.  

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@Paducah Home Theater 

I only have two 18's per box now.  my original plan was a stack of 3-4 in each corner, but i was nervous about separate cubes vibrating and the stack toppling over.

 

acutal exterior dimensions are 

 56" tall,  30deep, 23 wide. 

18.5" long slot port,  3.5" tall x 18.5" wide.  (according to a few websites, this should be an 18-19hz tune.)

+poly fill. 

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Is the driver baffle going to be double thickness?

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