MemberDecember 19, 2021 at 5:41 pm
Im having difficulty with near fields for a woofer of my 3 way build. It seems the lowest frequencies fall of a ledge under about 100 htz. Box size was modeled in winsd. included is a screen shot of near fields of woofer, port and Fairfield . Woofer is a 7 inch Dayton RS180P 8ohm. An
y advice appreciated.
MemberDecember 19, 2021 at 10:23 pm
@Rskmd – you are at a resolution that you cannot get accurately outside of a Klippel. At below 100Hz, you need to do ground measurements. Please see the documents related to sub testing here:
https://forums.audioholics.com/forums/threads/erins-cea-2010-subwoofer-testing-master-thread.119322/ (discussing his use of CEA 2010 B instead of A)
https://audioxpress.com/article/cta-2010-a-better-way-to-measure-subwoofers (an argument for CTA, formerly CEA)
And Erin addressed what he used, why, and he also compared results to the near field scanner he owns.
So, part of the problem for under 100Hz is resolution, part is testing methodology. So, I cannot find the CEA text right now or I would send it to you.
https://shop.cta.tech/products/standard-method-of-measurement-for-subwoofers (free paper on testing, revised for 2020, audioexpress explains why the name change; ANSI/CTA-2010-B R-2020)
MemberDecember 19, 2021 at 10:49 pm
@rskmd – you may wish to focus on the free CTA standard paper. It really is a good one (and free, unlike the CEA 2010 A 2012 or the CEA 2010 B 2014, which cost $60 and $90 respectively at ANSI (didn’t check CTA’s website). https://shop.cta.tech/products/standard-method-of-measurement-for-subwoofers
MemberDecember 20, 2021 at 1:05 am
@rskmd – I forgot to mention, do not let the perfect be the enemy of the good.
In this scenario, you will not have an anechoic chamber. You likely do not have a calibrated room. So you will be doing ground measurements in a free field scenario. Focus on that part of the standard.
Erin from Erin’s Audio Corner has compared his ground measurements for free field using his front walk and it compared well to his Klippel measurements, if I recall correctly. He also has used an open parking lot scenario.
So, just do what you can with what you can to get a decent ground reading and you will be fine. Hence, don’t let the perfect be the enemy of the good.
MemberJanuary 6, 2022 at 12:13 am
Although you can’t get accurate bass without a klipper indoors, you can still use time windowing methods to get a decent bass response representative of the driver and enclosure. Another but more difficult method is to get a battery powered amplifier and take your speakers outdoors, ideally into a largish field, have some way to get it off the ground, take your laptop too and take measurements outside, that way you don’t get the room interfering with your bass response, although this method is a pain to do, and may be impossible for some.
For the frequency dependent windowing (FDR) a good typical filter to apply should be one that gives you a 6/1 cycles window since most rooms have a transition frequency of about 600hz. If not looking at that transition frequency 15/15 is a good alternative for 20hz to 20khz, or if these aren’t available the Hamming gating is great too!
Remember to apply Physchoacoustic/ERB filtering to your responses, otherwise imperceptible sharp dips and any tiny dips/peaks will be visible, we don’t want any of those because they are inaudible and will just distract us.
Hope this helps!
MemberJanuary 6, 2022 at 3:04 pm
@rskmd If you want an easier method to measure direct sound than FDW, you can take multiple measurements of the speaker throughout the room. Then in the controls section under “all SPL”, use Time align then Align SPL, and then do a vector average, it should also give a pretty good idea of what the direct response should be (so I’ve heard). I’ll be doing some experiments some time in the future to see how these methods compare to measuring the speaker outside, but it should at least give you an idea of the direct response.