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Old 22nd January 2007, 08:31 PM   #1
pjpoes is offline pjpoes  United States
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Default Redoing a subwoofer project

Well I'm still waiting for a price but I decided to see what kind of box Elemental Designs could make for me. My wood working skills are ok at best, and some of what I wanted to do would more easily be achieved with a CNC machine. Elemental has such a machine and will build boxes to your design and specifications for a fee, though previous quotes from them have been very reasonable.

I have the HF version of the 12" RS series Dayton subwoofer and the 500 watt Dayton amp. Currently its mounted in a Dayton 2 cubic foot sealed box lined with dampening material. I was not happy with this subwoofer, and decided I wanted to try a better built box ported and tuned to a very low frequency. I modeled this woofer and came up with two boxes I liked, a 3.5 cubic foot box tuned to around 25hz and a 4.5 cubic foot box tuned to around 21hz. I decided to go with the larger of the two, and I'm having a 1.5" thick MDF box made with heavy bracing and a slot port tuned to 21hz, or so. It will weigh about 130lbs before the woofer and amp are added. I'm also going to upgrade the parts in the amp a little, replace the power supply caps with some better quality caps of larger size, and bypass them. I'm going to upgrade the opamps as well with some AD825's I have around. The box will come in plain MDF, so I'm going to veneer it with a wood veneer. My last veneer project came out great, so I'm excited to see how this comes out. I will post pictures once its finished, but thought I would talk about it now before I commit to anything. Looking for thoughts and feedback from all of you.
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Old 22nd January 2007, 10:44 PM   #2
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Im currently in the middle of a sub woofer project myself, and I encourage you to go for it if u want personally i build my own enclosures because id rather spend my money and other things but if you want it done right then by all means do so but the only thing I see that I would do differently is the tuning of your cabinet, i know the sub is a great sub but for a 12" 21 Hz is calling it close and unless you want a really flat response from it I'd go with the 25 Hz tuning but that's me and 130 lbs, I'm only 15 and i like big and bad too but 130 lbs is a little much for just a 4.5ft^3 enclosure, instead of the 1.5" MDF I'd go with 1" or maybe 1.25" MDF and just dampen it with 3/4 material.
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Old 23rd January 2007, 01:18 PM   #3
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The 1.5" enclosure thickness is because they work with 3/4" sheets and combine them. The only choices are 3/4" or 1.5". If I had my choice I would go with a 1.5" baffle and 1" for the rest. However, for the strongest and least resonant box possible, thicker is better. I've really never found dampening material to offer enough of an improvement to go with it over a thicker box. The bracing is quite imense as well, which contributes to the large weight.

As for the tuning, going with the 25hz tuning requires the smaller box to be flat, and probably would give me a -3db point in the 20-22hz range, which is pretty darn low. I believe it would also give me increased output in the range that matters most. However, I have heard various boxes at various tunings and really like the sound of a box tuned down that low. I think for now I will stick with the lower tuning. I also don't believe that its too much for that woofer, it models quite well with that setup.

I actually have built quite a few boxes now myself, but having worked with both my own cuts and those from a CNC machine, as long as I can afford it, I prefer it. I'm sure a better wood worker with better tools could do a perfectly adequate job, but I have found thus far that I can't easily match the quality I get from machine cut wood. All the edges are cut at 45's so that when they meet up I have a good strong 90. THe bracing is cut with great accuracy and can be made to press up against the woofer magnet for added strength and resonance control. I recently finished a computer speaker project that involved some Tangband drivers, and I made the enclosures myself, and the quality was fine for that. I also made the enclosures for my brothers Scan Speak based monitors, which came out great. I just wanted something better, and I really didn't have time to make the box myself, so I decided to have it fabricated.
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Old 24th January 2007, 02:41 AM   #4
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Should be a great project and a lot of fun. I think the 1.5" walls is a bit over kill. I'm building a new pair of subs with 4.5 cu ft enclosures. The drivers are 15" JBL 2235H. These JBLs are monsters with 20 lb magnets. I am only using 3/4" MDF as it is recommended by JBL for this enclosure. I'm going to use rosewood veneer. Should look very sharp. Don
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Old 24th January 2007, 01:53 PM   #5
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I agree it will look sharp. However, as for the 1.5" being overkill, again, have you compared. I mean, if the idea is to make a box that is as non-resonant as possible, 3/4" really isn't very good at that, especially in the bass region, where the energy is greatest. I'm a big fan of mass loading in general, I prefer mass loaded turntables, isolation devices, speaker stands, etc. In the case of this subwoofer, I want to try a mass loaded enclosure. I currently have a 3/4" box, and it resonates horribly, and its even braced internally.

I would also note that some of the modern 10"-15" woofers with 20mm+ of xmax have been known to destroy 3/4" boxes. Examples are the car subs like Kicker L7 solobarics and JL Audio W7 subs, inwhich the companies had to recall the first boxes they shipped them in because the subs were cracking the boxes. Knowing how these companies operate, and knowing that they would not have moved to a 1" thick box unless they had to, given the extra cost, I would say that in some cases 3/4" is not only not thick enough from a resonances stand point, but also pure strength.

I know my own sub only has something like 12-14mm of xmax, and would not destroy a 3/4" box, but again, I'm doing it for mass loading. I want a box that will not contribute any of its own noises to the project.
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Old 24th January 2007, 10:30 PM   #6
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I'm not familiar with the car woofs you mentioned, but more than likely they are sealed enclosures which can have tremendous internal pressure. Since you are building a ported enclosure you don't have to design for this problem. However, It's not my place to try and talk you out of something you've already given thought to. If properly designed and tuned your port will relieve the excessive stress on the enclosure. If not your port will be blowing air and sounding like gale force winds.

I'm a fan and believer in JBL speakers. My feeling is that a company that designs, builds, and markets speakers that cost in excess of $30K is a good source of technical info. They recommend using 3/4" properly braced MDF for the 4.5 cu ft 2235H driver.

What I'm building is a different looking, yet functionally equivalent JBL B380. And, in doing so following JBL's design specifications. Don
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Old 26th January 2007, 03:12 PM   #7
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I understand your feelings Don about JBL. I happen to disagree simply from the fact that JBL sells 30,000 speakers having little bearing on their enclosure building skills. What you have however is a pro-woofer which is capable of far less excursion and force than the woofers I'm talking about. Such a woofer probably can easily get away with a thinner enclosure without having an impact on sound.

As for the JL and Kicker thing, the original issue was with sealed boxes. However, Kicker then had problems with the ported boxes falling apart as well, and went with thicker MDF. The problem they had is that the woofers basicly vibrated the MDF apart around where the speaker mounted, causing the screws to strip out, and the wood to fall apart. The solution became a thicker box, though I imagine that t-nuts might have worked just as well.

As for our disagreement on box thickness, I think this is because we are attacking the reproduction of bass from two very different directions. You are using a large prowoofer in a setup that will offer greater efficiency in its band. However, it will either require a much larger box, or will not play as deep, or as loud in that deep range, while also having greater distortion, potentially. Though I am not able to measure my setup yet, it should be able to play flat down to 21hz, and have a -3db point around 19hz. It should have a peek output at around 115 decibles free space, and so probably closer to 120-125 decibles in room. Your setup will more than likely play closer to 120-125 decibles free space, and so potentially much louder in room, but will not be playing as low, and one might argue not as loud in the sub bass region. Like I said, I think we are attacking bass from different perspectives and will achieve different results.

Many of the highend home audio companies, JBL included, use boxes in excess of 1" thick in the highend products. Some companies like Wilson or Aerial go so far as ot build boxes in the 2-4" thick range to reduce vibrations, and it has even measurable impacts on the performance of the speaker. My goal with this project was to once and for all develope a subwoofer that will match the performance of the very high end subwoofers from companies like Aerial, that I had used and liked. Just FYI, the cost of a 3/4" box was 200 dollars and 50 dollars to ship, the cost of a 1.5" box is 260 dollars and 60 dollars to ship. I find the 70 dollar difference in cost minor in the scope of the project, and well worth the potential benefit. If nothing else I won't have to worry about anyone trying to steal my subwoofer.
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Old 26th January 2007, 03:34 PM   #8
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Ok I just ran the woofer you mentioned in WinISD Pro, which is what I use for speaker box design, and compared it with the the 12" dayton woofer I am using. Now mind you, I have no way, without measuring, of knowing how distortion will compare, but going by the difference in technologies used, I would just imagine that it would be lower with the dayton. I know someone did do measurements and found it to be one of the lowest distortion woofers on the market, and in a sealed box had distortion on part with servo systems, or so was said.

However, having both in 4.5 cubic foot boxes, both tuned to 20hz, my sub will play flat down to 20hz, your sub will not. Its minus 3db point is 49hz, mine is 19hz. Maximum spl with the power limits and between 0-60hz puts them at about the same, just around 115 decibles. The Jbl being slightly more, but that is at around 60hz. Now in the defense of the JBL, I will say that if you take room gain into account, it should play closer to 20hz, as it is about 10 db's down at 20hz. However I have never found room gain to be the best way to round out the frequency response, I find bass to sound lacking when I rely on it. However, my experience with designing a box to be flat through the range I want it to perform in causes it to sound as I like, with full bass extension.
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Old 26th January 2007, 09:59 PM   #9
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As your research demonstrated the 4.5 cu ft enclosure is not ideal for the 2235H. It functions far better in an 8 cu ft (or so) enclosure. I'm going with the smaller foot print for practical reasons. As I recall the enclosure is tuned to 29 hz, but I may be wrong on this. Because the driver is compromised in the small enclosure it requires a 5 db bump at 25 hz to keep it flat. I have an Ashly EQ to provide this, and a pair of 700 WPC SS monoblocks (one for each sub).

The 2235H/2245H are not the loudest subs JBL makes, but considered by many to be the best in terms of sound quality. JBL makes car subs that can move more air and make more noise, but the trade off is in how well they reproduce the music.

I'm currently using a pair of subs I build with Infinity Kappa 12.1D car audio drivers. It's truly amazing how nice they sound. I was surprised considering the drivers on cost about $100 each. Don
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Old 27th January 2007, 01:07 AM   #10
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The Dayton driver modeled quite well, and you can see how the small enclosure dampens the 2235H below 30hz (this is where the 5db bump at 25hz comes in). Many people run the B380 without the 5db bump as the freqs below 30hz are out of the hearing range for most of us over 40 years old. Since most of what we hear as bass is in the 40hz to 80hz freqs it's important to keep that part of the curve flat. Don

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