Triticum Agricolam

+1 to this. Nails provide almost no clamping pressure, they just keep stuff from sliding around. Screw provide good clamping pressure, but they take a LOT more time. I only use them when I can't clamp a piece properly, and then I usually use pocket screws. A person can NEVER own too many clamps.

That's a pretty neat looking little amp. Digital only audio output seems to be the way of things now. Looks like you have found a good solution. I'll be curious to hear what you think of it.

Yes, and shrinking the box will reduce the peak in output around tuning and flatten your frequency response. This does come at the price of reduced peak output though (before you add more power). Sizing a box is is all about balancing the trade off between getting max peak output (a large box) and getting a smooth frequency response and good sound quality (with a smaller box). There isn't a single "best" size. It's always going to depend on what kind of performance is most important to each person.

Glad I could help! Making the box bigger will get you more output, but only around the tuning frequency. You mentioned previously that you noticed output rolled off on the higher notes. Making the box bigger will make that effect more pronounced. If you want to get louder overall, you need to add power and/or add cone area (along with box size).

Its just a link to a web page. The calculator was created in Google Docs so I think it should work fine from your phone. It does take a lot of port area for these higher power systems. Its just like the exhaust on a car though, if you make a lot of horsepower you need to flow a lot of exhaust. I think the "9-12 sq in per cube" guideline for aero ports is robbing a lot of folks of a LOT of output. The nasty part about an undersized port isn't so much the port noise (which is annoying) its the port compression. Its the silent killer, it robs you of output but you don't hear the output you aren't getting. Its hard to notice the absence of something. It can easily rob you of 3 dB or more of output around tuning, that like throwing half your amplifier power (or more) out the window. As far as a port being too big and resulting in a sub bottoming out easier, that's at least 90% false. If the port ISN'T big enough it will actually result in MORE cone excursion around the tuning frequency, not less. Much below tuning I can see where a larger port MIGHT result in higher cone excursion, but at those frequencies you are at the point where the box is no longer providing mechanical control regardless of port size and you should be using something else to prevent mechanical damage (like a high pass filter AKA subsonic filter).

How much port area you need depends on the size of the box, the tuning frequency, and the amount of input power. What is your tuning frequency and how much power are you running? There really isn't such a thing as "too much port area", what can happen is a port can get so long that you begin to have pipe resonance issues, but that usually doesn't become a consideration until the port gets up past 40" long. Be wary of anyone who gives port area recommendations based purely on box size, that's like saying "if you are 6' tall you wear a size 10 shoe". It may not always be wrong, but it isn't always going to be right. The BEST way to determine how much port area you need is using simulation software (WinISD, etc) and seeing what port velocities you get. If you can't do that, here is a port area calculator that takes into account box size, tuning, and input power:

Yup, its been a while.

Here is how I developed the formulas that go into this. Most people tune their ported boxes to between 30-35 Hz, as long as you stay in that range you can ignore tuning frequency for the most part. So that leaves us with box volume and input power. I've noticed that if you view input power in terms of how many watts you have divided by box volume (which I'm calling "power density") there is a lot of similarities between different systems. For example, if you have a 4 cubic foot net volume box and you are going to be putting 2,000 watts of power into it, your power density is 500 watts per cube. Different size systems with the same power density are going to require very similar amounts of port area per cube to have similar port velocities. So a 4 cu ft, 2,000 watt system needs just about the same port area per cube as a 2 cu ft 1,000 watt system does. When looking at systems with different power densities, a system with double the power density of a different system does not need twice the port are per cube to keep port velocities similar, it only needs about 50% more. Using that info if you calculate the power density of an enclosure (say 500 watts per cube) and then take the square root of that number (22.36) this gives us a value that can be used to calculate port area that will scale properly with different power densities. The absolute max port velocity I like to see through a slot port is 30 meters per second. To keep port velocities right around 30 m/sec you can multiply the square root of the power density by .605 and that will give you how many sq in per cubic foot of box volume you need. So in my example of a 500 watts per cube enclosure that means you need 13.5 sq in per cube. Round or aero ports are tolerant of slightly higher port velocities and slot ports are, so with those ports your multiply the square root of the power density by .5445. This will give you a slightly lower required amount of port area. 12.2 sq inches in my example. Like I said, 30 m/sec is the max I like to see. At that point you will still be loosing some output to port compression and port noise is fairly likely. If possible using more port are than that is a good idea. I like to keep port velocities under 22 m/sec if I can. This applies to both slot and round/aero ports. To do this the number you multiply by is .82, so for my example we end up with 18.3 sq in per cube. Previously I said as long as you are tuning between 30-35 Hz, you can ignore what the tuning frequency is, but what if this is a bandpass box with its much higher tuning? Or what if you want to tune to the low 20s? Fortunately differences in tuning frequency affect how much port area you need similar to changes in input power. To compensate for different tuning frequencies I take the square root of the tuning and multiply it by .17677 and then multiply that by the results of my formulas above. This results in very similar peak port velocities regardless of tuning frequency.

I came up with this the other day and posted it on SMD, I figured I should post it here too. Hopefully someone will find it useful. I'm sure most people here have come across the "12-16 sq in of port area per cube" guideline for slot ports and the "9-12 sq in per cube" for aeros. The problem with both of these is they only consider box volume. Both input power and tuning frequency, along with box volume, have a great effect on how much port area you need. This is why I've been recommending to people to NOT use those rules of thumb. Online you can find several websites (such as carstereo.com) that have port area calculators using the formulas developed by Dickason or Small. These have a similar problem of ignoring input power and these formulas aren't really relevant for our modern, high Xmax subs. The best solution is to use box simulation software (WinISD, BassBoxPro, etc) to determine how much port area you need based on the specifics of your system. However this is time consuming and not everyone has access to that software or has the desire to learn how to use it well. I wanted to come up with something is quick and easy to use, and should hopefully give a lot better results than the rules of thumb or the obsolete formulas. Here it is, to make this easy I'm using Google Docs: https://docs.google.com/spreadsheets/d/1VREceNxz9YOcFlI8O_TG62-4O-l3Q2IjD5qsEkVVh28/edit?usp=sharing This is what it looks like: This will probably always be a work in progress, but so far I think it should work pretty well. I encourage everyone to use it and give me your feedback! Please note that due to the fact its a Google docs document multiple people can edit it at the same time. So if the numbers are changing on you while you use it, its someone else, just have patience.

What do you hope to accomplish with a bandpass box?

That's a bit of a complicated question, but the short answer is no, the tuning of your sub enclosure shouldn't effect where you cross over to the sub at, generally speaking. As with everything, there will always be exceptions.

True ****. I never build an enclosure without modeling it.

Thanks! It was fun to do. Hopefully someone else will find the info useful too.

I posted this over on SMD, I figured I'd put it up here as well. So I've been wanting to experiment with a series tuned 6th order bandpass design for quite a while. A conversation I've been having with another SMD member has finally motivated me to proceed with this experiment. First a little background. You don't see a lot of series tuned BP6 boxes out there and there is even less information on how to design them. What I have been able to find has mostly been conflicting information as to if and how the tunings for the different chambers interact with each other. Some info said they don't interact all all, some said the rear chamber will be tuned lower than if it was vented to the outside, and other info said both chambers will affect each other's tuning. I really want to know what happens so I built a test box to see what's going on. Here are some pictures of the box construction. Its mostly made out of 3/4" OSB. I used OSB because I don't care how the box looks, it actually stiffer and holds screws a little better than MDF, and its $14 a sheet. The box has a 3 cube rear chamber that I was shooting for a 24 hz tuning, the front chamber is 2.4 cubes with a target 54 Hz tuning. The sub is a Dayton Titanic 15" I picked up a while back for a song. Here is the basic layout of the box. The shorter port panel in the rear chamber is removable so that I can adjust the tuning. This is the box, ready to go. The front chamber ports are completely external so I can change them without affecting chamber volume. The three 4" ports are just press fit into the panel so I can pull them out and cut them down easily. There is a small window looking into the front chamber so I can see what the cone excursion looks like. With a little bit of sawdust on the cone it's very easy to see what frequency it stops moving and thus is the tuning frequency. Here I put a bunch of foam board insulation in the rear chamber to decrease its volume and further raise the tuning. You can see my Behringer NU3000DSP amp off the left that I was powering the thing with. The question: The question I'm trying to answer with this project is "how does the tuning of one chamber affect the other?" The experiment: To answer the question I individually changed the tuning of each chamber and measured if/how it affected the other chamber. The results: The results were pretty conclusive, the tunings of the two chambers are both linked together. This was not the result I was hoping for or expected. I expected that changes in the front chamber tuning would affect the rear chamber, but not vice-versa. However what I found was when I lowered the rear chamber tuning it lowered the front as well. Conversely, when I raised the rear chamber the front chamber's tuning was raised as well. When I sealed off the rear chamber, making it a 4th order bandpass, I then measured the front chamber and its tuning frequency was significantly lower than when the rear chamber was allowed to vent into it like normal. As I expected, changes to the front chamber's tuning frequency also affected the rear chamber in a similar fashion. This means anyone who tries to design one of these boxes using the regular methods for tuning a ported box or 4th order bandpass is in for a big and unfortunate surprise. Conclusion: This was definitely a worthwhile project for me. While I did not get the answer I was hoping for, at least I did get an answer. Unfortunately this means that designing a series tuned 6th order bandpass is a total pain in the ass. Everything is fine until you want move the two chambers tuning frequencies closer together or farther apart. Then it becomes like a dog chasing its own tail, you may be moving, but you aren't getting anywhere. Based on what I've learned I would venture a guess that the vast majority of series tuned 6th order boxes other people have built are not functioning like the builder's think they are. I know boxes don't always have to work as intended for people to be happy with them. I just wonder what kind of performance they are leaving on the table. When I was done playing around with the thing I threw it in my Jeep to see how it sounds. It actually sounded really good, quite punchy. I still need to drag the box outside to measure the frequency response and efficiency. When I do I'll be sure to post the results to this thread. For anyone that is interested, the Hornresp software can model series tuned 6th orders and it turns out it models them correctly. That's where I got the data indicating that the front and rear chamber will both affect each other, so I guess whoever wrote that piece of software knew what they were doing.

Welcome!