theplummer Posted February 25, 2006 Share Posted February 25, 2006 I just got done making my first subwoofer in many years. It's very deep, but a little boomy. Any thoughts. I made it out of 1" MDF. The exterior dimensions are 37" tall, 22" wide, and 22" deep. I have a pair of old MTX Terminator 15" woofers firing forward, with two 4 1/8" ports between the drivers. There is no divider between the drivers. I figured since they are receiving a mono signal, no big deal. I modeled the cabinet after my Chorus 1's. I have wired the drivers in parallel, to lower the impedence to 4 ohms. I also bridged the Orion 2X50watt amp. It is currently in my garage, and using a car amp. This is how I was able to make the sub without too much domestic protest. Now all I have to do is figure out how to migrate the cabinet into the living room with the HT. Should make ground shaking movies. Do you think the majority of the Boomy problem is because of the concrete floor with no accoustics or do I need to fill the cabinet with Poly fill, perhaps to tighten the cabinet. Any thoughts would be appreciated. Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted February 26, 2006 Share Posted February 26, 2006 port length? Quote Link to comment Share on other sites More sharing options...
theplummer Posted February 26, 2006 Author Share Posted February 26, 2006 The port is only one inch thick, as I modeled the cabinet just like my Chorus I's. They have two 4" holes in the bottom face of the cabinet below the 15" woofer. There is no port other than that. I located the ports in the same general location, except I placed them in the middle of the speaker, between the two drivers. Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted February 26, 2006 Share Posted February 26, 2006 well that's why..... It is going to be boomy. Do not model a subwoofer from a Regular full range..... Esentially you limited the range by adding the two 4 inch ports that are one inch....... Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted February 26, 2006 Share Posted February 26, 2006 I modeled your sub...... to your size dimensions, wattage, etc etc Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted February 26, 2006 Share Posted February 26, 2006 there is quite a jump in that 50-90 hertz range.... No wonder it is soo boomy Quote Link to comment Share on other sites More sharing options...
CAS Posted February 26, 2006 Share Posted February 26, 2006 Holy moly. Did you use winisd? You may want to download and check it out. Quote Link to comment Share on other sites More sharing options...
Zealot125 Posted February 26, 2006 Share Posted February 26, 2006 No offense at all but.....EWWW! You really should model and rebuild. Quote Link to comment Share on other sites More sharing options...
theplummer Posted February 26, 2006 Author Share Posted February 26, 2006 Cas Thanks for your input, but what the H. E. double toothpicks is winisd?, and is there a possible easy remedy for this. perhaps lengthening the ports, or padding the inside of the cabinet similar to a Cornwall. Should I have not ported the cabinet at all. This never made sense to me. Every car sub I've heard in a sealed box seems to only have one note, no matter what frequency has been input. I chose to model the Sub after the Chorus since the specs for the Chorus are pretty good, if memory serves, +or- 3Db down to 45Hz, not quite as good as the Cornwall, 38Hz, but until yesterday I had never seen the inside of a Cornwall to know that the square ports are almost as deep as the cabinet. If I make the ports longer, don't I risk the increase of "chuffing", and also just change where the boomy nature to a different HZ band. I also increased the cabinet size since there are now two 15" drivers pulling at the same time. I almost made two more 4" holes in the bottom front of the speaker to essentially give the speaker the same ability to "breathe" through the ports as the Chorus 1's have two also. (you know, if one 15" driver needs two 4" holes, two 15" drivers must need four 4" holes to be right. I have not bored these holes yet figuring that I could do it later if I heard "chuffing". So far, not going to happen, as I have maxed the amp and actually bottomed the speaker slightly with no chuffing. Once the bugs are worked out, I plan to move this monster into my Living room as I have an extra Adcom Amp thats not being used right now. This would really be good, because my Academy, as good as it is for center duties, really lacks in the heavy hitting center tracks, such as the Eagles, when hell freezes over in DTS, or (as I watched last night) Tomb Raider. I currently have the center on the Sunfire Cinima Grand II set on small, so it sends the bottom of the center channel to the sub. This really taxes my SW10 II. What I'm hoping to do is open up the Center to large, then connect the SW10II to the second center out on the Cinima Grand to give the Academy the help it really needs on the bottom end. Then I could use the homeade job for the Sub duties. Quote Link to comment Share on other sites More sharing options...
theplummer Posted February 26, 2006 Author Share Posted February 26, 2006 Sorry Jay, I ment to thank you also for your input. forgive me I'm kinda new to this computer stuff. Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted February 26, 2006 Share Posted February 26, 2006 ok no quit while your ahead do not double the ports.... There is alot of mumbo jumbo technical terms that come into play with speakers.... And you sorta went in head first with the sink/swin method. Ok the thing is modeling a subwoofer after another speaker is not a very good method. Subs need to go deeper hence the bigger box required. Think violin vs bass! No way can you get the violin to replicate the bass sounds. Second ports can be very good and just as quick as sealed boxes but they need to be modeled well. Here winisd comes to play. If you google winisd you can download for free and legal a program that helps you model. Though there is a deep learning curve which is hinderous and boring to learn. Hence if you been watching the subwoofer section DrWho and I have been modeling and helping various individuals. With the port, Do not add another two. When you add more ports you essentially need to double the port lengths of all of them. if say you had 1 port 4 inches wide and 20 inches deep, for two ports you need to have 4 inches wide and both 40 inches deep. It just works like that ....... Not linear as you would think. Also I am not sure But I think you needed bigger ports. There is two problems with ports, you need them the right length and the right width. Too narrow, you will get chuffling (the whistle port noise) because the air is being forced tooo fast. The wrong length (always too short) and it becomes boomy because it just doesn't have the proper length to allow for the low end. Think Trumpet when the trumpeter would lengthen his trumpet to hit a lower note. I need to do a bit more modeling but not to single you out but here is a good reason to smack those people in the face that say "Well I don't need to model, I like to do real world building as opposed to modeling" Well when you do not model its sorta hard to reverse everything that you just did. Sorry but I will try to help you out as much as possible. The thing is you system is nearly -18 db from the max output at 50 hertz when it reaches 30 hertz. 32 hertz is the usual standard for home theater subs, not computer subs. But usually a good starting point is a f3 (-3 decibals from the normal average) at 32 hertz. I am tuning my sub to be a f3 of 16 hertz but that requires massive size, double you box's volume and 4 passive radiators (speakers without motors that tend to be like a drum that re efforces the bass and makes it go lower). Quote Link to comment Share on other sites More sharing options...
billyjoe72 Posted February 27, 2006 Share Posted February 27, 2006 Yep Jay and Drwho helped me plan my first sub. I'm not finished yet, still waiting on some parts so I don't know whether they are playing me like a puppet just to get me to spend alot of money[] or if they are experts.[]The program they are talking about is a tad intimidating at first. Lots of numbers. Boring if you are not into the tech of the sub I guess. Reading other threads helps ALOT. Numbers don't lie. Math is the language. Too bad I slept during that class. By the way Jay, Kyle got back with me today. Should be 2 weeks on the PR's. He gets his amps from parts express, so I was a day late and a nickel short. I'll have to wait. toodles. Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted February 27, 2006 Share Posted February 27, 2006 Damn, I know he is an authorized dealer from pe Quote Link to comment Share on other sites More sharing options...
CAS Posted February 27, 2006 Share Posted February 27, 2006 Cas Thanks for your input, but what the H. E. double toothpicks is winisd?, and is there a possible easy remedy for this. perhaps lengthening the ports, or padding the inside of the cabinet similar to a Cornwall. Should I have not ported the cabinet at all. This never made sense to me. Every car sub I've heard in a sealed box seems to only have one note, no matter what frequency has been input. I chose to model the Sub after the Chorus since the specs for the Chorus are pretty good, if memory serves, +or- 3Db down to 45Hz, not quite as good as the Cornwall, 38Hz, but until yesterday I had never seen the inside of a Cornwall to know that the square ports are almost as deep as the cabinet. If I make the ports longer, don't I risk the increase of "chuffing", and also just change where the boomy nature to a different HZ band. I also increased the cabinet size since there are now two 15" drivers pulling at the same time. I almost made two more 4" holes in the bottom front of the speaker to essentially give the speaker the same ability to "breathe" through the ports as the Chorus 1's have two also. (you know, if one 15" driver needs two 4" holes, two 15" drivers must need four 4" holes to be right. I have not bored these holes yet figuring that I could do it later if I heard "chuffing". So far, not going to happen, as I have maxed the amp and actually bottomed the speaker slightly with no chuffing. Once the bugs are worked out, I plan to move this monster into my Living room as I have an extra Adcom Amp thats not being used right now. This would really be good, because my Academy, as good as it is for center duties, really lacks in the heavy hitting center tracks, such as the Eagles, when hell freezes over in DTS, or (as I watched last night) Tomb Raider. I currently have the center on the Sunfire Cinima Grand II set on small, so it sends the bottom of the center channel to the sub. This really taxes my SW10 II. What I'm hoping to do is open up the Center to large, then connect the SW10II to the second center out on the Cinima Grand to give the Academy the help it really needs on the bottom end. Then I could use the homeade job for the Sub duties. Hello plummer. A lot of rational ideas that you may be plagued with, such as "if this works here then this would work here" don't work well in enclosure design. Take the T/S parameters from your drivers and model an enclosure with your goals in mind (-3dB at this point, slope this steep, etc.). Download winisd and search the forum for suggestions. If you do just a little more research you'll be up and at it in no time. Winisd is freeware that takes the parameters of a speaker (too complicated to get into right now) and designs optimum enclosures based on your input. For example, the parameters on one speaker may call for a 4 inch by 5 round port while another may call for a 2 by 2, one speaker may need only 2 cubic feet while another may need 8. Tuning is also user variable. It sounds as though you may be taking general concepts and applying them without doing the homework. I apologize if I should have been more bold. Yes, I would start over if I were you. You're not doing those drivers justice with an enclosure like that. Quote Link to comment Share on other sites More sharing options...
theplummer Posted February 28, 2006 Author Share Posted February 28, 2006 Boy do I feel stupid. I guess nevermind is in order, thanks for your input. Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted February 28, 2006 Share Posted February 28, 2006 don't get discouraged... we live and learn... Next time ask someone in the know about a potential for a sub and we will gladly help. Just give the following parameters: size money speakers spl designation how deep amp sealed, ported, pr and a few more that I cannot think of at the moment Quote Link to comment Share on other sites More sharing options...
DrWho Posted March 1, 2006 Share Posted March 1, 2006 Boy do I feel stupid. I guess nevermind is in order, thanks for your input. Bah, you haven't been getting very good advice at all. I'm not even gonna try to address everything. You shouldn't feel discouraged about your setup at all. I can't seem to find any specs on your driver though - would you happen to have them? As far as I can tell MTX never made a "Terminator" woofer? But there's lots of "Thunderbird" drivers...Without the specs you can't accurately predict the behavior of your driver. Do you have any kind of measuring equipment available? Anyways, you are not without hope - how would you describe this boomy sound? For starters you probably have the tuning point of the cabinet way too high. And you can easily remedy this by making the ports longer. What are you using for a port right now? Just a 4" hole in the side of the cabinet? You should try installing something like this: http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=260-329 http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=268-352 (the latter link being my preferred method, but changing the length is harder). Or if you want to go even cheaper you can just go with some standard 4" PVC pipe. Anyways, you will want two 4" ports with a length somewhere between 4 and 10 inches long (giving you tuning points between 35 and 26Hz respectively). With the adjustable ports you can simply tune it by ear until it sounds right (btw, make sure you set both ports to the same length). As far as port noise is concerned, you shouldn't have any problems. I would expect a system F3 somewhere between 30 and 45Hz with a clean maxSPL around 110dB - probably a bit less with the amp you're running right now. (and just in case...F3 and tuning point are two different things. F3 is where the response is 3dB down and the tuning point is the resonant frequency of the port: basically the frequency where the port starts boosting the low end). So ya, get yourself an adjustable length port and play around until you have the system sounding good by ear. You don't want to tune too low (too long of a port) because you'll lose maxSPL, but you also don't want to tune too high (too short of a port) and have it boomy sounding. I would pretty much extend the length of the port until the boominess just barely goes away. And then after that I would add polyfill to the enclosure and apply any necessary bracing (you'll know if you need bracing when you can feel the side walls vibrating). I hope this helps. Despite the impression put forth so far, decent subwoofer design doesn't have to rely on computer modelling. Driver prediction is merely an aid to get a feel for how a driver behaves in a world where it's expensive to build, measure, demolish, and then rebuild (rinse and repeat, etc etc..). Once a design is built, you need to measure the speaker and make the corresponding adjustments - if you can't measure, then there is nothing wrong with using your own ears (afterall, if it sounds good to your ears then what does it matter what the measurements say?) There is nothing inherant with your current starting point that should result in a bad sound. 4 cubic feet per driver is pretty standard amongst car audio subs converted to home use. And going the adjustable port route I mentioned should get you within +-3dB of an ideal curve...depending of course on how good your ears are. If you are interested in DIY subwoofers and want to learn a bit in the process, then I would recommend starting here: http://www.diysubwoofers.org/ and if you want to go more in depth, check out: http://ldsg.snippets.org/ (which gets into a lot more aspects of speaker design) WinISD is a free driver modelling program available here: http://www.linearteam.dk/default.aspx?pageid=winisdpro (I posted a tutorial a while back on how to use the program - step by step, including "optimizing" the calculated best fit for the driver. The learning curve really isn't that steep - especially if you understand how speakers work. And even if you don't, it's not too hard to fiddle with numbers until the graph looks normal) Well I think that's enough to chew on for now...hopefully you'll come back and share your results, or ask more questions. Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted March 1, 2006 Share Posted March 1, 2006 there not new drivers... They are actually modeled in the winisd beta...... Quote Link to comment Share on other sites More sharing options...
DrWho Posted March 1, 2006 Share Posted March 1, 2006 Hmmm....I wonder how accurate the specs are. If they are close, then this driver was definetly optimized for a 4th order bandpass design (very common for car audio applications). Though it would be difficult to convert the current cabinet to such an arrangement. One thing I forgot to mention was to try just plugging the port holes and see if the boominess goes away. If that doesn't fix the problem, then no amount of changing the port length is going to make a better difference. Anothing thing you might try which is a bit crazy would be to remove one of the drivers and then install a baffle inside the cabinet, dividing the internal volume to 5 and 3 cubic feet. Install the first driver to the front just like normal (with the rear of the driver in the 5 cubic foot part) and then install the second driver on the baffle on the inside that is dividing the cabinet. You'll then want to put two 4" ports with a 5" length firing out of the 3 cubic foot part. Not exactly the KISS method, but going this way keeps you from having to completely rip apart what you've got so far. Or if you start over, a suitable 4th order bandpass design for both drivers would involve a 5 cubic foot rear enclosure and 3 cubic feet in front, with two 4" ports of length 3" Quote Link to comment Share on other sites More sharing options...
Timco Posted March 2, 2006 Share Posted March 2, 2006 DrWho, Do you have a link to the above mentioned tutorial on winISD? I would love to read it. Thanks, Tim Quote Link to comment Share on other sites More sharing options...
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