bullet Posted December 29, 2014 Share Posted December 29, 2014 (edited) How we going guys? Ok so ive decided to build a set of bookshelfs and wow... The info out there is rather confusing at first. The drivers in question are the SB15NRXC30-4 with maybe the sb26adc tweeter.. so the box ive decided on is a 14.49lt box (bassbox pro) and wherei get stuck is the fb and f3 numbers. The fb from memory is 43hz and the f3 is around 45-47hz (I'm on the train atm) with port velocity maxing out at 19ms now I know that f3 is when it starts to roll off on the low end but what's the box tune for? Max output at that freq? The response curveit simulates looks good and should, in theory, sound pleasing but how can I really tell? Thanks for all your forth coming info and advice :-D Edited December 29, 2014 by bullet Link to comment Share on other sites More sharing options...
VanArn Posted December 30, 2014 Share Posted December 30, 2014 For a classic Butterworth fourth order alignment Fb and F3 are at the same frequency.The manufacturers specification for the SB15NRXC30-4, gives Fs at 41 Hz and Vas as 16.7 L. I prefer to confirm the T&S measurements of the speakers as it is normal to encounter variations in the parameters from different production batches.Simulated programs are useful for showing response variations when changes are made to the enclosure details.Using a calculation for a B4 enclosure with expected losses includes,suggests a slight increase in the effective internal volume to 15.76 L with a vent tuned to 40 Hz (Fb),as being another choice. Link to comment Share on other sites More sharing options...
bullet Posted December 31, 2014 Author Share Posted December 31, 2014 Ok so ill try simulate a slightly bigger box and should I buy one of those tester thingues to measure the drivers actual t/s parameters? I've seen lsk sell em for around the $100 mark. Link to comment Share on other sites More sharing options...
Sub Sonic Posted December 31, 2014 Share Posted December 31, 2014 (edited) The DATS tester you mentioned is invaluable to me, I use it almost as much as the Omnimic. As well as measuring the T/S parameters of drivers, it can check impedance curves, cap, resistor and inductor values among other things. Whether or not your level of experience will allow you to use it's full capabilities I don't know, but it is certainly a very capable tool. If you have a little experience with DIY or some electrical/electronics experience, you should find it pretty easy to use. Regards, SS Edited December 31, 2014 by Sub Sonic Link to comment Share on other sites More sharing options...
bullet Posted December 31, 2014 Author Share Posted December 31, 2014 Ive got the omnimic haha umm06 or something like that. It's a brilliant little thing haha as for my questions though, still dont know the answers :'( Link to comment Share on other sites More sharing options...
Sub Sonic Posted January 1, 2015 Share Posted January 1, 2015 (edited) Ok :-) As VanArn suggested, you could measure the actual parameters (with something like DATS), and then plug the values into a speaker enclosure calculator. The bonus of having the DATS is that after you make an actual enclosure you can see exactly what frequency it is tuned to - for a closed box it will be the peak of the single impedance "hump". A bass reflex enclosure will (if tuned correctly) have two impedance humps, the box tuning frequency is the lowest point on the graph between these two humps. This frequency is the Fb, or box tuning frequency. With the DATS it is about a 5 second job to run an impedance sweep to find out these details. You can then use your measurement mic to check the actual frequency response. I hope this helps? Cheers! SS Edited January 1, 2015 by Sub Sonic Link to comment Share on other sites More sharing options...
henry218 Posted January 1, 2015 Share Posted January 1, 2015 here's what i have simulated before Link to comment Share on other sites More sharing options...
bullet Posted January 1, 2015 Author Share Posted January 1, 2015 awesome reply SS Ill order a DATS tomorrow and measure the drivers. as for freq response, ive run a free air sweep on them and they actually have a nice curve compared to the one they showed on their website, which i found wasnt all that nice.. maybe they need to be broken in first haha Henry218, thats a smallish box haha 10lts is probably a lil smaller than i was after but i can see that the graphs are sorta similar for most of the way except for having more lower freq response with a 15ltish box Link to comment Share on other sites More sharing options...
henry218 Posted January 1, 2015 Share Posted January 1, 2015 For typical small midwoofer, its better to have smaller box with gentle hump as this is useful to make it more enjoyable. If you are planning to use subs, then bigger box wouldnt matter. Link to comment Share on other sites More sharing options...
bullet Posted January 1, 2015 Author Share Posted January 1, 2015 They wont be used with a sub but thats good info to know for future projects as ill trying out some 5" satellite speakers to go with the towers ill build after these.. those will need accurate midrange etc rather than low end freq response. These guys will be used in stereo in a bedroom only so i want them to have a good extended bottom end Link to comment Share on other sites More sharing options...
bullet Posted January 2, 2015 Author Share Posted January 2, 2015 Another question i had, just so i know how it all works is that when i click on the "Suggest Fb" it tunes the box downt to 35.11hz but the F3 is at 88.36hz so wouldnt that kinda make the response die off quickly towards the bottom end?? or am i missing something and still not fully understanding how it all works haha :-P Link to comment Share on other sites More sharing options...
VanArn Posted January 2, 2015 Share Posted January 2, 2015 At this stage on the learning curve a study of the T & S parameters and how the many possible alignments interact would help you to get the most from your project.Basically given a beautiful set of numbers for the parameters,only one simple calculation is required to find the correct box volume.A simulation program is redundant under these circumstances as otherwise you can end up with a multitude of answers that are not necessarily the best choice.Picking too low a tuned frequency and possibly a much larger enclosure will require an auxillary filter(equalisation) to maintain a flat response.The boost to the low frequencies can overdrive small bass speakers and also lead to bass doubling. 1 Link to comment Share on other sites More sharing options...
bullet Posted January 5, 2015 Author Share Posted January 5, 2015 Ok so i did the DATS check on the drivers and came up with a new box for it.. lucky as the new box came to what you had previously suggested.. almost. 15.72lt vb but tuned to 50hz with f3 being 46.16hz and the curve looks flatter than before while having a smaller slope on the down low.. Ive got most of the box completed and i just gotta fit the front of it. Ill tune a "sealed" sine sweep test and note its response then ill port it to what its meant to be and do it again then comes the fun time of fitting the tweeter and finding the sweet spot haha fun times ahead! Ill post some pics of the box in the morning 1 Link to comment Share on other sites More sharing options...
bullet Posted January 11, 2015 Author Share Posted January 11, 2015 Ok so here are a few pics of the build, insides, rear and "finished" product. Still gotta flush the drivers via a panel on the front and then I'll round the edges etc but its mostly finished. The curves were measured in my terrible for acoustics room but still was rather surprised how it came out. The 2nd response is the port response. Peaks where I wanted it to. The last pic is where it was measured haha Overall I'm really impressed with how it sounds. Incredibly detailed, fast and punchy going surprisingly deep when in a proper room (movie room) Although I noticed that on mums pioneer amp the speaker is quite bright while on my yamaha it's fairly smooth and I guess, perfect. They sound better than my towers which I was having a hard time finding worthy replacementa hence the diy.. next comes towers with SS gear ;-) Link to comment Share on other sites More sharing options...
bullet Posted January 29, 2015 Author Share Posted January 29, 2015 So I tweak the crossover tons (read made new one haha) and I got a much better, flatter, clearer sound with a smoother bottom End too. Also extended the port, braced the box more and lined it differently. I got this from measurements note that bump in the middle is inaudible so I'm guessing it's the horrible room. Link to comment Share on other sites More sharing options...
MKSOUND_HT Posted January 29, 2015 Share Posted January 29, 2015 Wow well done those look really nice. Will you end up painting or covering the enclosures long term? Link to comment Share on other sites More sharing options...
bullet Posted January 29, 2015 Author Share Posted January 29, 2015 (edited) I havent quite decided.. I think that if anyone ever wanted a pair (family, friends or whoever) id finish them in timber veneer so they look as good as they sound, but i think for myself in my bedroom, i may paint them in a matte, metallic graphite colour..make it look a lil high tech haha Any ideas or suggestions?? Ps. the speaker in the photos wont be the ones im using. ive made another one that has about 10 screws altogether so its about 400% cleaner looking than that one.. it also doesnt have out of size wood haha that box was my very first and a prototype which came out a lil crooked etc. i made another one myself via a different process and that one is perfect haha everything was cut properly this time (had the sisters bf cut the first box coz chippy) Edited January 29, 2015 by bullet Link to comment Share on other sites More sharing options...
bullet Posted February 12, 2021 Author Share Posted February 12, 2021 Its been over 6 years and they are still going so damn strong. Im very very happy with em! I think it might be time to build a floorstander now.. 1 Link to comment Share on other sites More sharing options...
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