32 replies to this topic

[dwayne]

Hey all i'm attempting to build a sixth order bandpass using the scan speak 30w/4558t00 and the matching passive radiator,
this design came about from influence from Mr Paul Spencer, was worried about its complexeity of tuning, but what the hell.

ok design brief it is for a coffee table subwoofer, and has to please the woman i'll post its transformation once its complete as a final surprise, just build pics for now.

The reason for bandpass is to reduce localisation issues from being so close, this will be used for movies only.

The rear chamber will be tuned using a passive radiator, whilst the front chamber will be tuned using twin 100mm ports.
The panel for which the passive and ports are mounted will be removable for tunning, also my ports are very close to boundaries so may need to shorten them considerably due to them acting like a shelf port.

using winisd this design will plumb down to 24hz half volume and roll off about 68hz, using around 300wrms will push its output midband to around 112db and 102db @ 20hz whilst keeping cone excursion to 16mm peak and port velocity to around 16ms will flare to reduce noise.


The rear volume is 70lts tuned to 16hz and front volume is 40lts tuned to 42hz
once built will tune and test in room for best performance.
some pics:  ss.jpg   32.67K   21 downloads  ss2.jpg   28.69K   28 downloads  home made jasper jig.jpg   38.2K   28 downloads  cutout.jpg   22.72K   33 downloads    testfit.jpg   29.79K   29 downloads

[audible1]

looks great!
send more pics when you are finished.
I am interested in what you think the transient response is like - so please let us know how it sounds (or bring it along to a DIY GTG)

[Paul Spencer]

Watching with interest ...

[gainphile]

Mmmm makita!

please keep us updated!

[Antripodean]

using winisd this design will plumb down to 24hz half volume and roll off about 68hz, using around 300wrms will push its output midband to around 112db and 102db @ 20hz whilst keeping cone excursion to 16mm peak and port velocity to around 16ms will flare to reduce noise.

Good project and a nice driver

I have to say WinISD is hopeless at modelling for a bandpass. Hornresp is useful but ultimately you need to tune it based on response

[Paul Spencer]

Roger is right. It tends to make the peaks look worse, but last one I tried based on the sim was workable.

[svenr]

Hope you have measured the TSP of the driver before finalising the design. WinISD is simply for serious designs, make sure you fine-tune the port lengths, passive radiator mass and volumes to get a reasonable response. I don't fully understand why you use such as narrow bandwidth / highly resonant design at close proximity to the listener. Localisation is no issues for crossover frequencies lower than 150 Hz, and this crossover is way easier realised in the electrical domain.

[Paul Spencer]

Svenr, have you ever tried a sub in a coffee table position? I have and localisation can be a problem even with a low and steep crossover and a low distortion sub.

[davewantsmoore]

Would it be fair to say that .... and acoustic filter will also filter harmonic distortion products (which is what is localisable as they are often above 100hz) ... where as an electrical filter will not.

[dwayne]

Thanks for the encouragement fella's, as for final tuning, thats exactly why i opted for ports so they could be adjusted to suit, as i would have preferred a shelf port, and the passive is easily tuned unfortunetly the internal port end won't be flared. I also have allowed a little over volume which can easily be absorbed if needed. And yes i have tested the driver same as specs or close enough thanks svenr, i used the parts express woofer tester seems to work quite nicely.

Dave that's a very good point, as with what Paul said, i too have built an coffee table sub using two 10"peerless 1727's about ten years ago, and must say it sounded good but was definetly localised and that was crossed over actively at 70hz. So hoping it all comes together, i envisage lots of tunning and testing, as several people have brought up winisd poor modelling of bandpass as Roger mentioned.
And will lug it around to Pauls once complete for some testing..
p.s Paul did you decide on a mic yet?

[dwayne]

Oh yeah Roger thats the other reason i chose the scan speak, hopefully reliable source of drivers where design can be built by many if it turns out good, and great build quality, i too noticed little in tried and tested subs on the net for this model driver.. Hopefully the plunge is worth it.

[Paul Spencer]

Would it be fair to say that .... and acoustic filter will also filter harmonic distortion products (which is what is localisable as they are often above 100hz) ... where as an electrical filter will not.

Yes, that's correct. It's true of both the Synergy horn and bandpass subs. Whise talked about this aspect, as did Whatmough who took up the idea, and Geddes who also does a bandpass sub, in his case I believe he uses a PR also.

[hochopeper]

Yes, that's correct. It's true of both the Synergy horn and bandpass subs. Whise talked about this aspect, as did Whatmough who took up the idea, and Geddes who also does a bandpass sub, in his case I believe he uses a PR also.

Sorry to go a bit off topic but does anyone have any links to technical descriptions of how this works? Does Geddes cover it in his Audio Transducers book perhaps?

Edited by zman, 16 April 2012 - 09:57 AM.

[dwayne]

Hey all just a quick update have been working to the bone lately and not much time for fun..here some progress pics

brace panel
 brace.jpg   6.42K   8 downloads
brace installed
 bracein.jpg   7.41K   8 downloads
port baffle brace
 port brace.jpg   7.31K   6 downloads
additional bracing installed also further supports for the long vents
 bracelast.jpg   5.79K   3 downloads

Also what do you guys think would be the best method of fixing the m.d.f baffle whilst keeping it removable, tee nuts into solid timber or just straight screws? any ideas would be great. cheerz guys

[Paul Spencer]

Good to see some progress!

Tnuts are stronger but ordinary screws are fine unless they are cheapies.

[dwayne]

Thanks Paul, might look at the t nuts due to possibly needing to remove the panel many times for tunning, and wanting it to pull up tight everytime.

[dwayne]

and more pics
 braced.jpg   287.71K   10 downloads
get a grip!
have decided to go with tapered brass or mild steel screws into pine, if becomes problematic will implement t-nuts and bolts.

[dwayne]

and some more progress..getting closer now
 cabling.jpg   10.87K   13 downloads
all innerbond in place as well as glue. box tipped over onto lid piece
 fluff and glue.jpg   10.8K   22 downloads
once happy with positioning weigh the woofer box down!
 weighted.jpg   19.19K   20 downloads

next will be front panel and its cut outs.

[dwayne]

Hi guys have finally finished the box here are the final pics, onto testing phase now.
from what I can tell my example is almost on par with what was expected from winisd. Also localisation is none existent seems to be a success, here are the final build pics. Testing plots will be posted next.
 counter sinking driver.jpg   96.66K   5 downloads
 baffle.jpg   76.62K   6 downloads
 ports.jpg   70.24K   6 downloads
 flared.jpg   85.67K   9 downloads
 baffle complete.jpg   75.17K   12 downloads
 baffle fitted.jpg   66.72K   12 downloads

[Paul Spencer]

Nice job on the ports Dwayne! Looking forward to seeing the result.

[dwayne]

ok test plots
here is the first using
a monophonic pseudo-noise sequence. The Radiator has been weighted 30grams and microphone is 1ft away from either radiator or port see file name.
Testing using Dayton omnimic test software for all tests output from amp unchanged.
 30g port 1ft trk1.jpg   66.34K   11 downloads
 30g rad 1ft trk1.jpg   66.33K   14 downloads
and with 59grams
 59g port 1ft trk1.jpg   66.9K   15 downloads
 59g rad 1ft trk1.jpg   68.53K   12 downloads

next track is with monophonic short sine sweep
30grams
 30g port 1ft trk2.jpg   66.84K   9 downloads
 30g rad 1ft trk2.jpg   67.69K   9 downloads
59grams
 59g port 1ft trk2.jpg   68.83K   9 downloads
 59g rad 1ft trk2.jpg   68.25K   6 downloads

[dwayne]

ok next ones
the following are using a monophonic bass sweep to show bass response and decay
30gram
 30g port 1ft trk4 bass response.jpg   210.72K   10 downloads
 30g rad 1ft trk4 bass response.jpg   214.82K   7 downloads
and 59gram
 59g port 1ft trk4 bass response.jpg   215.76K   4 downloads
 59g rad 1ft trk4 bass response.jpg   220.81K   14 downloads

this was the setup
 testing.jpg   63.23K   24 downloads

and this graph is from the woofer tester to check impedance (59grams), both the 30gram and 59gram show very similar tunings which is the lowest points between the peaks round 17hz and 40hz, pretty close to what i had modeled for in winisd. I seem to think that the 30grams gives a flatter response.
 ss bandpass 130612.jpg   197.46K   25 downloads

Here is what the 59 gram looked like when placed in its intended position and microphone placed in listening position (couch)
track 1 monophonic pseudo noise sequence
 inroom listenin trak 1.jpg   66.35K   18 downloads
track 2 monophoni short sine sweep
 inroom listenin trak 2.jpg   66.41K   19 downloads
and finally bass response and decay
 listening trak4.jpg   217.78K   13 downloads
from what can be seen above i seem to have a big boost in room around the 20-40hz range.

Edited by dwayne, 16 June 2012 - 06:32 PM.

[Paul Spencer]

Are those smoothed? I'm not seeing anything that looks like an inroom measurement!

With your nearfield measurements the mic normally goes as close as you can get without risk of hitting the cone.

If those last ones really are showing inroom then your decay looks unusually good. In that case, lucky you! You might EQ the bottom octave down a little then cross at say 60 Hz or so. How is it going with imaging and localisation?

[dwayne]

Hey Paul yeah they are 1/6 octave, should I have used none? Might try a near field as you recommend, also yes the in room is with sub in final position and mic in listening seat at ear level. I'm pleased to say that I can't localize the sub even though it's only a foot away in front of me, imaging is excellent can't pick anything really happy with it this goes for both movies and music. The next step is final testing and obtaining a minidsp for high pass and any eq required. Looking at the graphs do you think the 30 gram plots are better then the 59 loaded.What is a bad decay?

[dwayne]

ok just quick update have recieved my minidsp in the mail today so will do some final unsmoothed testing this weekend then maybe apply some dsp yay!

[dwayne]

G'day all i have done some more testing, but now i have a weird situation, there seems to be a large dip (massive hole)centered at around 42hz

 track 1 freq port.jpg   69.25K   15 downloads
also to note this is also the tunning frequency, i am at a loss how my measurements are differing from first lot, these ones where done in its final position however i had made the measurements near field, but it also shows through on the listening position.
 track 1 freq list.jpg   68.94K   13 downloads

Is it possible for such a larger dip at the tunning frequency? i was under the impression there would be a peak if any thing. perhaps a higher tuning would help?

[Paul Spencer]

Are we looking at an inroom unsmoothed now?

[dwayne]

Hey Paul yes we are(the last pic), however for a sanity check i ran it smoothed and it still shows a large dip. Is this possible?
quick run down only differences, i did the nearfield as you suggested as close as possible to the driver as oppsed to one foot away. And for nearfield the sub is in its final position, first lot of pics was in different room. This would not matter being near field. Any ideas, could it be the tuning? perhaps the driver has broken in a little bit since testing?

My thoughts are to run tests again, then if i still get same results, cut ports down to raise tuning to hopefully push dip up out band. This may cause localisation problems...

one final thought, i may have used a different amp.....it was a rotel power amp...i'm now using a playmaster sub amp..more testing

[dwayne]

sorry first pic is nearfield on port, the radiator has same response.

[Paul Spencer]

Looks like you are showing just the output of the lower tuned rear chamber. The response of front and rear chambers should be different!

[dwayne]

ok, how do i test each one? originally i had been testing both the port and radiator, and i did do this with same tracks and levels etc, i might have to test it all again, also the second picture is in the listening position, a difference would not be seen correct?

[Paul Spencer]

mic goes right up close to the PR, as close as you can safely go - then the PR output should dominate ... with the ports the mic goes into the mouth in line with the edge of the box. Either way you should isolate relatively well, although when I've done this there was a bit more distance.

[dwayne]

Hey Paul thanks for your toughts, i didn't seem to get much difference between the port and radiator, which could be due to them being relatively close.
i also got round to doing another round of testing, i started with my mic settings, and found the mic level wasn't set to maximum which is required with the omnimic, the results were much better
all near field with 30g mass added to Radiator
this is @ port monophonic signal, pseudo noise setting.
 port trk1 30g (1).jpg   73.73K   4 downloads
and another
 port trk1 30g (2).jpg   74.68K   3 downloads
this is the radiator
 rad trk1 30g.jpg   72.9K   2 downloads
this is a sinewave @ the port
 port trk2 30g.jpg   69.52K   3 downloads
this is with active filter on amp set to 120hz and minidsp set to 50hz to knock out bump at port
 port trk2 30g act120 md50.jpg   63.26K   2 downloads
now at radiator
 rad trk2 30g act70 mdsp50.jpg   62.9K   3 downloads
this is with 6db of boost @ 35hz with a Q of 6 using minidsp to fill in hole
 rad trk2 30g act70 mdsp50 boost 4db@35hz q2.jpg   63.69K   3 downloads

my intial thoughts are that the boost is too much with a q too high, also to note now that i sorted out the mic, will be worthwhile adding weight to radiator to hopefully boost the low end more naturally in the design.

This is now the listening position with active filter @70 on amp and 50 on mini dsp no boost sine wave
 list trk2 30g act70 md50.jpg   63.43K   4 downloads
now with boost 6db @ 35hz, Q=6
 list trk2 30g act70 md50 boost35 6db q6.jpg   63.82K   6 downloads

all settings/graphs have a high pass applied @ 18hz.
so as mentioned before will try different weight to see its effect.

also to note the minidsp is fantastic, quite quick its great to see and hear your results immediately.
Dwayno