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First DIY Project :Subwoofer help

post #1 of 18
Thread Starter 
So I'm still in the conceptual stage of my subwoofer build. I'm looking to build something that will play up to 100-120Hz and have decent sub 20Hz output. I'm not ready to do a ported sub so I'd like to stay sealed just for the sake of simplicity. I have a sub in mind that I'd really like to use and I modeled it using an old excel spreadsheet. Since I have a mac and am still trying to justify going the parallels route that's all I've got for the moment. I'd really appreciate it if someone could take a look at the model I've got to see if the FR graph seems right based on the specs. My only issue is that I had to fudge the Sd spec since it wasn't provided, so I used the Sd spec off of another sub I'm considering. Thanks for looking and for any help in advance.

PAPmodel.jpg
post #2 of 18
Sd should be around 800 cm2 for a 15" driver, you have the SD of an 18". You also need to cut the xmax in half.
post #3 of 18
Thread Starter 
Ignore that I entered in all my own specs, the excel was downloaded from the internet and came with a bunch of drivers pre-installed (albeit old) and I couldn't find a way to make everything blank so I just entered in all my own specs and left the name as whatever was there

I am doing an 18inch driver so I guess that means everything looks about right?
post #4 of 18
That Qtc of 1.785 seems quite high and the curve gets quite a peak on it at 50Hz or so. I'm thinking your enclosure needs to be much, much larger for that sub. The freq response curve should gradually slope off when going lower frequencies.

It would help if we knew what drivers you were looking at and what your goals (size, output, room config) are.
post #5 of 18
Quote:
Originally Posted by SilentJ20 View Post

That Qtc of 1.785 seems quite high.
That would be the result of the listed Qes of 2.33, which isn't impossible, but close to it.
post #6 of 18
yeah, the qes figure appears to be wrong.

that is way outside typical subwoofer parameters. i suspect that it is not audira, but adire. the adire audio brahma 15" had a qes of 0.52, which is about what one would expect given its design.
post #7 of 18
Thread Starter 
Here are specs and like I said earlier don't bother looking at the name of the sub on the spec sheet. Thanks.

F(S)38, Q(MS)6.94, V(AS)3.248 cubic feet/91.96 liters, M(MS)415.40 grams, Revc dual 2 Ohms, Q(ES)2.333, SPL 85.37DB 1W/1M, Q(TS)1.746, L(E)1.24 MH, BL 12.76.
post #8 of 18
ah, what you have there is an extremely weak motor and heavy moving mass combined with an extremely tight suspension.

almost a bass drum of some sorts.

anyways, the frequency that you plotted appears correct. without some e.q. work, that sub might sound a little "one note".
post #9 of 18
Quote:
Originally Posted by fuzz092888 View Post

Here are specs and like I said earlier don't bother looking at the name of the sub on the spec sheet. Thanks.
F(S)38, Q(MS)6.94, V(AS)3.248 cubic feet/91.96 liters, M(MS)415.40 grams, Revc dual 2 Ohms, Q(ES)2.333, SPL 85.37DB 1W/1M, Q(TS)1.746, L(E)1.24 MH, BL 12.76.
If accurate it's not suited to subwoofer use, or any other use IMO.
post #10 of 18
Trio 12 with 1 (15") or 2 (12") passive radiators (technically ported with ability to tune the PRs externally) might be a good first project. It was for me.
post #11 of 18
Thread Starter 
Sorry for the long response time, but I've been talking to the guy who builds these things and it still seems like it's worth a shot, even if it does turn out to be a dud. $350 for an 18" driver and the specs on the one I ordered won't be exactly the same. He's changing a few things to suit my build, like exchanging aluminum voice coil for copper and a few other tweaks.

I had seriously thought about the trio12 with 2 passives, but decided to give this a shot first. If this doesn't end up the way I want it to, I'll probably end up building something from CSS. Hopefully by the time this is done the SDX 15 will be out.

Thanks again, I'll report back when I finally receive shipment of the sub.
post #12 of 18
Quote:
Originally Posted by fuzz092888 View Post

Sorry for the long response time, but I've been talking to the guy who builds these things and it still seems like it's worth a shot, even if it does turn out to be a dud. $350 for an 18" driver and the specs on the one I ordered won't be exactly the same. He's changing a few things to suit my build, like exchanging aluminum voice coil for copper and a few other tweaks.
I had seriously thought about the trio12 with 2 passives, but decided to give this a shot first. If this doesn't end up the way I want it to, I'll probably end up building something from CSS. Hopefully by the time this is done the SDX 15 will be out.
Thanks again, I'll report back when I finally receive shipment of the sub.
Quote:
Originally Posted by Bill Fitzmaurice View Post

If accurate it's not suited to subwoofer use, or any other use IMO.

So you're going to ignore Bill's and LTD's comment and just spent the $350? confused.gif
post #13 of 18
Thread Starter 
Quote:
Originally Posted by pbc View Post

So you're going to ignore Bill's and LTD's comment and just spent the $350? confused.gif

I'm going to ignore their advice because I believe something is being lost somewhere in translation here. Simply Sound Audio is a very small subwoofer company (translation: one guy making subwoofers) that use drivers from the company I'm buying mine from. I have yet to read a bad review about the Rumba 12 from Simply Sound and most would say that within it's price range it's a top performer.

I'm not saying they don't know what they're talking about, far from it, but I'm saying that if I can get a hand built in the USA sub that looks like a monster and performs like the rumba does, but in a bigger badder version (18" to be exact) then I think it's worth a shot. If it works out, great. If not, then I'll move on to something else. All I know is that Paul (the owner and builder of the subs) has answered every e-mail I've sent to him quickly, put up with all of my questions, is helping me design a box to ensure I'm going to get the performance I'm looking for, and is tweaking the sub design slightly so that it better meshes with what I'm aiming to get. So my subwoofer will have slightly different specs than what I've posted.

I do appreciate their advice and opinions and instead of saying I'm ignoring it, which I don't feel I am, I'd rather say that I've taken it into consideration and feel that the risk is worth $350 because if it works out then I found a tremendous bargain. If not, then I've got pie on my face. Either way I feel confident I'll be able to deal with it biggrin.gif
post #14 of 18
What these guys are trying to say is that the specs given for this woofer if accurate are WAY WAY beyond the boundaries of what is normal in a BAD way. The motor is extremely weak to be motivating the cone area of an 18" driver with over 415 grams of moving mass. BL^2/RE assuming 4 ohms is 40.7. I consider 80 to 100 to already be on the weak side. This results in the driver wanting a huge enclosure to get a good response shape. On top of that the suspension is VERY tight which puts the FS very high which would be odd if this was an IB driver. The sensitivity will be very low as a result too. I would never buy a driver with these specifications especially not at $350 where there are tons of good options. Those specs point to some serious deficiencies in some areas and there don't appear to be any significant extra strengths to outweigh them.

For $350-400 you could buy a Fi Q18D2 (American made in NV)
an SoundSolutionsAudio Xcon 18D2 (Made by Fi in NV)
2 Dayton Audio RS15's or DVC15's from PE
3 Alpine SWR-1243D's
2 Alpine SWR-1522D's
An 18Sound 21LW1400
2 Peerless XLS12's
6 Infinity REF 12's from Amazon
2 TC Epic 12's
And the list goes on and on...All of these drivers have better attributes and have been vetted by tons of people as good buys.

BTW I know which company you are reffering to and I'm not dissing their products but looking at the parameters they have listed for the 1K series which is the only one that they have them available for is not very encouraging. QES numbers over 1 are way outside of the normal range. Actually anything over 0.7 is even strange to see. To be honest looking at the design of the subs which appear to have plenty of steel in the motor and a generous amount of ferrite while using an overhung 4 layer 3" voice coil it is very odd that the motor force is so weak. Almost seems like a typo or something. There may be some serious errors in their specs listed.
post #15 of 18
Thread Starter 
Thanks Ricci, I know about a few of the subs you listed, my thing was wanting to try something new and based on thing I've heard about the rumba and from what looks like pretty good build quality I figured it was worth a shot. I did notice the way out there specs when I was comparing to some other 18" drivers.

Based on the pictures and what seems like solid build quality I was guessing that there must me something odd with the specs. I wasn't ignoring or disagreeing with what Bill and LTD were saying because I know that they know what they're talking about. Curiosity has just gotten the better of me and I feel the need to find out for myself if these things are as bad as Bill and LTD say they might be or as good as I hope it could be.

Thanks for the input though, I appreciate it.
post #16 of 18
Maybe contact them and just ask if they are sure that those parameters are correct. Because the BL, QES and other Q values are really odd.

Actually I believe I know what they have done. They list the parameters as measured with the coils in series. However I would bet that the parameters were actually measured with the coils in parallel. At which point if you enter the RE as the value from the coils in series will dramatically alter and diminish the apparent motor force and performance. If you input their parameters LE, FS, MMS, SD (1178 cm should be close) RE (enter as 1ohm for parallel coils not 4 for series) and BL you will get a qes of about 0.610 and a QTS of about 0.560. These values are much closer to what you would expect to see and make much more sense. Sensitivity goes up a lot and box size down. Also the LE listed at 1.24 would be VERY low for this type of woofer with a 4ohm imp especially with no mention of shorting rings or a pole cap but it makes a lot more sense at 1.24mH with a 1ohm imp.
post #17 of 18
Thread Starter 
Thanks again Ricci, I'll shoot Paul an e-mail now and see what he has to say about that.
post #18 of 18
Thread Starter 
Here's what I got from Paul

The specs listed are one possible iteration of parts that can be used that yields a high q suitable for IB use but will also work sealed or ported contrary to what the small signal specs seen to indicate. Coils are flat aluminum and were wired in series.

BL^2re with copper coil is 144tm. like I said the posted specs are 1 possible iteration with that motor. BL is 22- 24 tm with copper coils and no other change. You can post up there if you like. Its up to you. Suspension is actually pretty loose and the high FS on that one is due to the VERY light aluminum voice coil. MMS can have a drastic effect of FS.

He also attached the picture of the new 18" cones

IMG_0482_n_EO_IMG.jpg
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