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My thoughts on DIY are these: As the project grows in complexity and ability, you begin to reap the rewards. If you plan on building a single box sub, sealed or ported try to find a price point you are trying to beat.Most times you can buy that sub cheaper on the web.


Now if you decide to do a multi-driver subwoofer powered by multiple amplifiers and some custom electronics to reach way down in the single digit frequency response you will begin to see where your cash output is getting you some big rewards.


WTS, do your research and be sure your sub you plan on building isn't sitting on a shelf in a warehouse somewhere in this big ol' USA for half the money.


I even wonder if my project sometimes couldn't be had for the same amount somewhere in cyberspace.
 

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Discussion Starter #43
15". Sorry, did I slip up and say 12" somewhere?


Just at the moment it's modelled using the specs SteveCallas recommended. 190 liter enclosure, etc. To get to the port length he specified, I ended up with a tuning frequency of 21.17Hz. This gives what looks to be a reasonably flat response into the mid-20s, starts to roll off around 25, and still crosses 20Hz at 110 dB. If that's where the amp's rumble filter cuts in anyway, that's not too bad.


The problem is there's a hump in the middle of the xmax graph (which seems to always happen on ported designs), and the hump is exceeding xmax at around... 36 Hz or so. Then it goes up for a bit, and then drops back down below xmax again at around 26 or 27. Then it goes back up and crosses again at 17 or 18, but I don't care about those if the rumble filter cuts in at 20 (which is where someone says it is on this plate amp, but the PE site doesn't say anything one way or the other.)


EDIT: Also, when I applied the PE-PlateAmp filter from unibox, the frequency response graph got somewhat less appealing looking. Much more of a hump in the mid-20s, with everything above that coming in softer.


EDIT2: As near as I can tell, the box is just too big. Even going down to 152 L, I'm still exceeding xmax, but by less. Worse though, the smaller the box I end up with, the shorter I have to make the port, so that it's not longer than the enclosure. Gah. How far should the internal end of the port be from the enclosure wall, at a minimum?
 

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Discussion Starter #45
I appreciate your efforts. Maybe I just need to throw a less powerful amp at it? If I drop to a 150 Watt amp, I lose a bit of overall SPL, but things seem a bit more workable.
 

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Ok, I found the problem. I had opened a previous Quatro design and started tweaking the enclosure and port but didn't realize the power was at 200 watts for the previous design vs 240 watts for yours.


Try 5 cubic feet and 21hz tuning which is basically a 30" long port and see what you think of that.


Again, I really apologize for that.
 

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Discussion Starter #47
That's better, but it's still exceeding xmax by about 1mm in the 25-35 Hz range. And of course it rolls off earlier too. :p Maybe it really would be better to drop to a somewhat less powerful amp. PE's amp options are somewhat limited though. There's a 120W, and then there's the 240W, some 250's and then it's up to 500. :rolleyes:


Then again, I guess this is only if you crank it all the way? I mean, 1mm isn't that much, so if I just know I shouldn't crank it up to full blast (and you shouldn't anyway, of course) it ought to be alright, right?
 

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Discussion Starter #49
Uh-oh. Another problem. I just figured it out and at 21 Hz, the port would have to be like 30 inches long. For a 5 ft^3 enclosure, that doesn't seem to be very tenable, especially with a 15" driver. A 5ft. cube is about 20" on a side, so there's not a whole lot of room to try to make it longer in one dimension.


Also I guess this is rolling off a bit sooner than I was hoping to see. Maybe I just can't expect so much out of this driver.
 

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Have you tried quantity 3 of 4" double flared ports? Both Unibox and WinISD Pro will accept modeling multiple cylindrical ports. The smaller dia should get the length down to being reasonable for a box and upping the quantity to three should keep the airspeed down.
 

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Discussion Starter #51
Let's see, when I enter 3 ports of 10.16 cm (4 in.) in Unibox, at 21 Hz tune, I get 109.46cm. port length. Do I divide that length among the three ports? If so, that comes out to 14.36 in. per port, which should be workable.


I wish I had somewhere handy to stick a shot of the FR graph. I probably ought to sign up for a photobucket or something. It's essentially flat at 112 dB down to about 30Hz, where it starts a gentle rolloff that gets steeper as it goes. It crosses the 20 Hz line at about 108 dB, which I guess isn't really too bad.


I'm told this amp has a built-in rumble filter at 20Hz (though that's not confirmed). It looks like the driver would start to seriously exceed xmax around 18Hz or so anyway.



Here's another question: when figuring out the box volume, I know I'm supposed to subtract some for the driver, and also for the bracing. Do I also subtract for the volume of the ports? (Figuring out how big the box actually needs to be is getting complicated :rolleyes: ).
 

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the way port length is calculated is based on total area of the port, not the number of ports. this means that you can have one port to three ports and as long as the total area of the ports are equal, the length of all the ports will have to be the same to get the same tune... one 6 inch diameter port 30 inches long will have the same tune as 2 4.24 inch ports 30 inches long.


you cannot split this length or change it or the tune will not remain the same.


if you want a shorter port, you must reduce the total cross sectional area of the port or ports. this will shorten the port length neccesary for a given frequency tuning, but smaller ports mean higher air velocity in the port for a given spl.... at a certan point this air speed will become audible and your port will "chuff"


you can cheat a little by having very large and smooth port flares on the inside and outside ends of smooth walled port tubes... this allows a higher air speed without being audible (think air noise around a boxy truck as opposed to the air noise around a streamlined car...smooth curves are quieter).


It is also better to have one port as opposed to 2 or 3. One port has less total port wall area for the air volume it can move... so the walls of the port tube therefore imparts less turbulence to the air volume if there is one instead of more...


so.. the best you can do is one port with large smooth port flares. this will allow you to have air speeds inside the port of about 20 m/sec for a 4 inch port up to 34 m/sec for an 8 inch port. the smallest diameter port that keeps air velocity below the above maximums will be the shortest port you can use in your design. once again, if you reduce the watts to the driver, you will reduce airspeed and can use a smaller port.... at the expense of maximum volume!!!
 

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Discussion Starter #54
Quote:
Originally Posted by SteveCallas
Is that what you are looking at?
Pretty much. :)


I guess I'm still not clear on the port stuff. The more ports I add, the more port length unibox is telling me I need. So I assumed that length was intended to be divided among the ports. I take it that is incorrect? Because I keep ending up with ports that are far longer than my box. :confused:
 

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Well what do you plan on the dimensions of the box being? It sounds like you may have to settle on 1 4" driver, which would not be very long, but port noise can become a problem down low. That's another reason why a sonosub is a good idea, but as was mentioned earlier, the Quatro isn't suitable for down firing.


You could go with 3, 3" ports like 12andy did. Each one will be about 23.5" long and port velocity looks pretty good, esepcially if you flare all 3.
 

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maybe i wrote too much... i tried to explain why you want only one port if you want the shortest port length.


These are the rules:


1. to have the shortest port for a given tune, you should have ONE port with VERY GOOD port flares (great ones for cheap at 3 inch and 4 inch from parts express!!! I have some extra 4 inchers if you live close....)


2. the smaller diameter you make the port, the shorter the port will be for a given tuning frequency.


3. the limit for small diameter is air speed inside the port. too small will force the air to move .

too fast and you will hear whooshing or chuffing. Somewhere in unibox, there is a spot that says something like "port air velocity" or there is a graph called the same thing. you want your maximum port velocity to never exceed about 20 m/sec for a single 4 inch port up to 34 m/sec for an 8 inch port. If your velocity is higher, you need a larger diameter port and a longer port.....
 

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Discussion Starter #57
Well, the volume I have been working with (and I can't remember exactly how I got it) is 141.6 L, which for a cube is approximately 20.5 in. to a side (this is without accounting for bracing, the driver, etc.). I could make it a bit longer and shorter/skinnier, so that would net me a little bit more space, but I'm still having a lot of trouble fitting ports in this thing. 23 and a half inches would be pretty tight I think.


This is all trying to tune at 21 Hz, so maybe I need to tune it higher, or just make the box bigger. I have some MDF lying around that's like 22 inches wide, so I was kind of trying to work with that. :p
 

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Yeah I guess your best bet is to make one of the dimensions as long as you can so you can fit the 3 3" ports that are each 23.5" long and still give them some breathing room at the opening of the port. Or you can have the ports extend outside the box, but that would just look silly :D
 

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Discussion Starter #59
Quote:
Originally Posted by patrickrio
maybe i wrote too much... i tried to explain why you want only one port if you want the shortest port length.


These are the rules:


1. to have the shortest port for a given tune, you should have ONE port with VERY GOOD port flares (great ones for cheap at 3 inch and 4 inch from parts express!!! I have some extra 4 inchers if you live close....)


2. the smaller diameter you make the port, the shorter the port will be for a given tuning frequency.


3. the limit for small diameter is air speed inside the port. too small will force the air to move .

too fast and you will hear whooshing or chuffing. Somewhere in unibox, there is a spot that says something like "port air velocity" or there is a graph called the same thing. you want your maximum port velocity to never exceed about 20 m/sec for a single 4 inch port up to 34 m/sec for an 8 inch port. If your velocity is higher, you need a larger diameter port and a longer port.....
Okay, that helps clear it up some. I'm thinking I'm just going to have to resign myself to a bigger box. Which is fine, I was just trying to work with some scraps I had lying around.

Quote:
Originally Posted by SteveCallas
Yeah I guess your best bet is to make one of the dimensions as long as you can so you can fit the 3 3" ports that are each 23.5" long and still give them some breathing room at the opening of the port. Or you can have the ports extend outside the box, but that would just look silly
Hmmm... I hadn't thought of that... That would look pretty silly, wouldn't it? :p Still...


Stupid laws of physics.
 

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hey steve..... i am at work and dont have winisd here..... have you tried to enter the parameters for this driver to check his volume and port calcs?????
 
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