davewantsmoore Posted March 19, 2014 Share Posted March 19, 2014 That's not lots of stuffing IMO they also show exactly the same impedance wrinkles Yep. Except the little one at 200hz which is caused by your internal cabinet dimension(s). More stuffing on the floor and/or roof will make it go away Link to comment Share on other sites More sharing options...
henry218 Posted March 19, 2014 Share Posted March 19, 2014 (edited) Zog, you will need to cross braced all sides, you can start at just behind the magnet for the vertical, then put the horisontal behind the vert brace, add more if you still see the wrinkles. as its a big box, inherently you need to have more bracings. i saw a very different wrinkles between free air and in box. Edited March 19, 2014 by henry218 Link to comment Share on other sites More sharing options...
davewantsmoore Posted March 19, 2014 Share Posted March 19, 2014 (edited) i saw a very different wrinkles between free air and in box. Perhaps you missed the different scales... They are (EDIT: the Z features) identical. Rough picture is hard to see, but will hopefully help. Edited March 19, 2014 by davewantsmoore Link to comment Share on other sites More sharing options...
henry218 Posted March 19, 2014 Share Posted March 19, 2014 wow, Dave you got a very good eyes . yeah the 200hz prob standing waves within the box, the rest could help if there's cross bracing behind the magnets, but i could be wrong. Link to comment Share on other sites More sharing options...
davewantsmoore Posted March 19, 2014 Share Posted March 19, 2014 (edited) the rest could help if there's cross bracing behind the magnets, but i could be wrong. Yes, you are wrong, because the features also appear in the fee air curve (as Zog suggested). They are part of the driver ... and you would expect them for a 15", as it is well outside it's piston range. EDIT: but might be fixable my modifying the driver, perhaps by putting something absorbent on the basket frame, etc. ... but I wouldn't stress.... a LR4 slope as low as the CD/horn can take, would be a recommendation to avoid it (and help in other ways too) Edited March 19, 2014 by davewantsmoore Link to comment Share on other sites More sharing options...
henry218 Posted March 19, 2014 Share Posted March 19, 2014 (edited) Yes, you are wrong, because the features also appear in the fee air curve (as Zog suggested). They are part of the driver ... and you would expect them for a 15", as it is well outside it's piston range. EDIT: but might be fixable my modifying the driver, perhaps by putting something absorbent on the basket frame, etc. ... but I wouldn't stress.... a LR4 slope as low as the CD/horn can take, would be a recommendation to avoid it (and help in other ways too) what i meant by putting a bracing behind the magnet is a cross horisontal bracing from the back panel to the woofer's magnet Edited March 19, 2014 by henry218 Link to comment Share on other sites More sharing options...
davewantsmoore Posted March 19, 2014 Share Posted March 19, 2014 what i meant by putting a bracing behind the magnet is a cross horisontal bracing from the back panel to the woofer's magnet Oh, if you mean that more obstructive bracing could help with the 200hz blip... then yes. It will break up the top/bottom, and side/side dimension some, which will affect the bump. It won't change the higher frequency blips. They are part of the driver. Actually physically bracing the driver itself might affect them (and is good practice), but I strongly doubt that. Link to comment Share on other sites More sharing options...
zog Posted March 19, 2014 Author Share Posted March 19, 2014 Thanks guys, quite interesting! So as I understand: The approx 900hz wiggle in all graphs is part of the driver, and I shouldn’t worry about, as I'm crossing over at 600hz - even in future iterations of the crossover I don't see myself going any higher than 800 anyway. The 200hz blip that appears (slightly moved around) in both the 90L trap enclosure and 131L "good" enclosure measurements - is probably not related to the enclosure size or bracing directly as it appears in the graph for 2 completely different enclosures, but may be some resonance or vibration in the driver when it is bolted into a baffle. It might be fixed by extra cabinet bracing or supporting the driver.. but might not. I do have an approx 211 hz notch in the F.R. for the 50cm graph that might correspond, but a few other F.R. graphs I've done further away at different angles and locations it's "lost in the noise" of other effects or just not there, so right now I won't lose sleep over it, though I might play with chocking something under the driver next time I have the box open and re-run the impedance sweep to see. Other possible thing: I haven’t used any tape/gasket stuff under the lip of the driver, as it seems snug enough screwing the M6 allen bolts down against the quite flat rebate cutout. Link to comment Share on other sites More sharing options...
henry218 Posted March 19, 2014 Share Posted March 19, 2014 cross bracing is very very important. i hope you will do this the next time you open the box up. i would recommend using 50mm insulation for the stuffing, you dont have to line it, can place on the same spot that you put the egg foam. will you measure further? if you can post the frd on both drivers and determined the acoustic offset, i can run my sim to give you my version Link to comment Share on other sites More sharing options...
zog Posted March 19, 2014 Author Share Posted March 19, 2014 cross bracing is very very important. i hope you will do this the next time you open the box up. i would recommend using 50mm insulation for the stuffing, you dont have to line it, can place on the same spot that you put the egg foam. will you measure further? if you can post the frd on both drivers and determined the acoustic offset, i can run my sim to give you my version Hi, I had advice that the 3 horizontal braces I've used would be fine so I I'll stick with them for now. Plus the box is glued shut - the only entry point is through the 352mm driver hole. I might paint that bituminous black stuff inside further down the track, seems to be what all the cool kids are doing I will be measuring further - but for now I'm only looking at miniDSP crossover/EQ setup if thats what you are going to sim - not a passive crossover. Though notching down the woofer response will surely give me enough HF headroom for the CD waveguide HF rolloff compensation for a passive crossover. I do need to redo the time alignment stuff though, what I've got in place now is from the old enclosure. Link to comment Share on other sites More sharing options...
henry218 Posted March 19, 2014 Share Posted March 19, 2014 i have sim for active xover pls make sure you measured the phase for the frd. my recommendation is : 1. measure at tw axis at 120cm distance, gate between 4-8msec for both mid and tw (keep the mic position), so u will have 3 kinds, mid, tw and combined. this is to determined acoustic offset. 2. measure nearfield (max 2cm from dustcap of the woofer) if you dont have gating function, thats fine also, i will sim baffle step and estimate the woofer farfield response and you can judge if its correct. cheers Henry 1 Link to comment Share on other sites More sharing options...
hochopeper Posted March 19, 2014 Share Posted March 19, 2014 (edited) i have sim for active xover pls make sure you measured the phase for the frd. my recommendation is : 1. measure at tw axis at 120cm distance, gate between 4-8msec for both mid and tw (keep the mic position), so u will have 3 kinds, mid, tw and combined. this is to determined acoustic offset. 2. measure nearfield (max 2cm from dustcap of the woofer) if you dont have gating function, thats fine also, i will sim baffle step and estimate the woofer farfield response and you can judge if its correct. cheers Henry Google Hilbert Transform ... The hard part of extracting minimum phase response is already implemented in a ACD tools ... Thank Charlie Laub. I believe and python / MATLAB scripts for getting minimum phase magnitude response are done too. PORC has a Hilbert transform step in it too ... I remember seeing that when I submitted a (unrelated) patch or two for that project last year.Remember to properly gate the impulse response and compensate for baffle step is perhaps equally important Edited March 19, 2014 by hochopeper Link to comment Share on other sites More sharing options...
henry218 Posted March 19, 2014 Share Posted March 19, 2014 (edited) yeah, i have all the necessary from jeff b and charlie laub, its one of the best gift for diyers from diyers the phase is crucial for detecting anomaly in measurements. Edited March 19, 2014 by henry218 1 Link to comment Share on other sites More sharing options...
zog Posted March 19, 2014 Author Share Posted March 19, 2014 The penny just dropped and I've realised you are discussing this package, which I was previously unaware of: http://audio.claub.net/software/ACD/ACD.html .. looks interesting, somehow I missed this. Link to comment Share on other sites More sharing options...
davewantsmoore Posted March 19, 2014 Share Posted March 19, 2014 The approx 900hz wiggle in all graphs is part of the driver, and I shouldn’t worry about, as I'm crossing over at 600hz - even in future iterations of the crossover I don't see myself going any higher than 800 anyway. Yep. You could tinker around and see if you can work out where it's coming from if you're interested. Prodding and poking drivers while looking at the Z can be interesting. It will give you an insight into how dynamic impedance is. We always tend to think about impedance as a fixed 'curve', since it's presented that way... but in reality it changes a lot (cone position, surround/spider effects, etc, etc.) The 200hz blip that appears (slightly moved around) in both the 90L trap enclosure and 131L "good" enclosure measurements - is probably not related to the enclosure size or bracing directly as it appears in the graph for 2 completely different enclosures Only some experimentation will tell you for sure... but my guesstimate is that it is related to your internal enclosure dimension(s). 200hz corresponds quite closely to (half) your height dimension (which is made slightly longer with stuffing) .... chuck a bunch of stuffing in there (a small blanket or something) as an experiment, and see if it changes the measurement. Wiggles in the electrical impedance on their own are a concern for passive XOs (but not for active speakers) ... but when something is reflected in the electrical system like this, it's hard to know if it's a "concern" until we work out the cause. I do have an approx 211 hz notch in the F.R. for the 50cm graph that might correspond, but a few other F.R. graphs I've done further away at different angles and locations it's "lost in the noise" of other effects or just not there, so right now I won't lose sleep over it, though I might play with chocking something under the driver next time I have the box open and re-run the impedance sweep to see. Yeah I would instinctively say that this is a boundary cancellation (floor?) ... but it's weak due to the closeness of the measurement. You are definitely on the right track that lots of experiments is the way to figure this out. Do a bunch of crazy things to rule in or out different hypothesis. Measure at different angles/distances to see if it's an acoustic cancellation outside the box ..... stuff the box, or put something in there to break up the dimensions to see if you can tell if it's an internal acoustic cancellation. Brace the driver to see what effect that has.... Brace (or damp crudely) the outside of the cabinet temporarily (large clamps are handy) ... etc. etc. The beauty of this is they don't have to be anything fancy or permanent ...... and not only will you (hopefully) track down this issue.... but it can potentially give you insight into what else matters or (just as importantly) what might not matter. I might paint that bituminous black stuff inside further down the track, seems to be what all the cool kids are doing If you are keen, do some of the above experiments before you do. Clamp big bits of big ugly wood to the outside of your enclosure (bracing!) .... or, stand mattresses or blankets up against the box (damping) .... just do some stuff, so that when you blacktak the inside, you have some data to look at. It might be obvious, it might show nothing .... but you'll have a better chance of knowing if the black stuff "makes any difference" ..... and hey! if the blackstuff makes the speaker "sound obviously better", and you measured "no difference".... well at least you have a real life data point which tells you that your measurement procedures need to improve. if you dont have gating function, thats fine also Incorrectly gated measurements will give poor results.... as although they normally produce small variations in smoothed frequency response curves, these changes are over a wide bandwidth. A 0.5dB peak with a very low Q (over a wide bandwidth) may totally transform the tonal character of a speaker. Link to comment Share on other sites More sharing options...
davewantsmoore Posted March 19, 2014 Share Posted March 19, 2014 somehow I missed this. It's a good quick tool for iterating XOs Link to comment Share on other sites More sharing options...
zog Posted March 20, 2014 Author Share Posted March 20, 2014 OK, here are some .FRD done with Room EQ Wizard (umik-1 calibrated microphone). I renamed from .frd to .txt so I could attach them here. CD = compression driver (i.e. tweeter). all miniDSP config EQ/Xover/gain/delay flattened out before measurements, done on left speaker only, all done with identical mic position, gain etc, except for unmuting/muting the appropriate drivers. The woofer 2CM from dustcap measured quite loud, I think it was starting to get close to the limits of the mic (distortion a tad high).. but the amplitude and phase info identical on a lower volume measurement so I left it as is. Didn't do gating as I haven’t figured out Room EQ Wizard gating dialogue yet, this seems something that can be added on afterwards anyway as mentioned.. All done in room. acd1_woofer_and_CD_at_120cm_onaxis_with_CD.txt acd1_woofer_only_at_120cm_onaxis_with_CD.txt acd1_CD_only_at_120cm_onaxis_with_CD.txt acd1_woofer_only_nearfield_2cm_from_dustcap.txt Link to comment Share on other sites More sharing options...
henry218 Posted March 20, 2014 Share Posted March 20, 2014 cool, ill do it tonight. 1 Link to comment Share on other sites More sharing options...
davewantsmoore Posted March 20, 2014 Share Posted March 20, 2014 Didn't do gating as I haven’t figured out Room EQ Wizard gating dialogue yet, this seems something that can be added on afterwards anyway as mentioned.. Yep. Gating can be performed later where required. The woofer 2CM from dustcap measured quite loud, I think it was starting to get close to the limits of the mic (distortion a tad high).. but the amplitude and phase info identical on a lower volume measurement so I left it as is. Cool. No harm in turning it down some, and noting the level reduction you used. cool, ill do it tonight. What will you do for the off-axis response of the woofer? The tweeter? (I guess you can see it a previous post) Link to comment Share on other sites More sharing options...
davewantsmoore Posted March 20, 2014 Share Posted March 20, 2014 Hmm... Which horn did you end up using Zog? Link to comment Share on other sites More sharing options...
henry218 Posted March 20, 2014 Share Posted March 20, 2014 Yep. Gating can be performed later where required. Cool. No harm in turning it down some, and noting the level reduction you used. What will you do for the off-axis response of the woofer? The tweeter? (I guess you can see it a previous post) it will have approximate power response. if after the xover implemented and somehow doesnt sound right then he can do average response. in most cases on axis is good enough, he will need to tweak it anyway Link to comment Share on other sites More sharing options...
henry218 Posted March 20, 2014 Share Posted March 20, 2014 (edited) hi Zog, here is my first attempt for the xo, your measurements are hard to work with as no gating applied so im seeing too many reflections . please use this on your miniDSP W : LR2 @ 400hz Tw : 1st order BW 6db @ 3500hz, EQ on Tw -6db @250hz Q:1 INVERTED the rest of freq shaping should be based on your taste, i hope this helps cheers Henry Edited March 20, 2014 by henry218 1 Link to comment Share on other sites More sharing options...
henry218 Posted March 20, 2014 Share Posted March 20, 2014 here is my sim Addtional EQ 3db @2500hz Q:2 -3db @10,000hz Q:2 6db @16,000hz Q:3 1 Link to comment Share on other sites More sharing options...
zog Posted March 20, 2014 Author Share Posted March 20, 2014 hi Zog, here is my first attempt for the xo, your measurements are hard to work with as no gating applied so im seeing too many reflections . please use this on your miniDSP W : LR2 @ 400hz Tw : 1st order BW 6db @ 3500hz, EQ on Tw -6db @250hz Q:1 INVERTED the rest of freq shaping should be based on your taste, i hope this helps cheers Henry Wow thanks! I'll run these up shortly! Time to get to grips with the gating in REW.. or use arta/holmimpulse... they all have strengths and weaknesses. Link to comment Share on other sites More sharing options...
henry218 Posted March 20, 2014 Share Posted March 20, 2014 (edited) the sim was based on LR4 acoustic TF, there are rooms for improvement, but unfortunately with current data, i dont know which one to correct. if you can, pls do a fresh settings, ignore all EQ in the mean time so you can hear whats going on. Edited March 20, 2014 by henry218 Link to comment Share on other sites More sharing options...
Recommended Posts