I was under the impression larger woofers are able to maintain dispersion at lower frequencies.
Also that diffraction page on here you linked, the data is cut off above where my problem is. I'm not seeing the info on bass, maybe I missed it.
I know it seems hard to believe from your perspective, but issues like this are very common when designing a new speaker. I have never designed/built a speaker which did not have some sort of mysterious issue that needed solving, and often a speaker has several issues.
The problem is likely solvable. In my opinion, you have an acoustic resonance (standing wave), just as @VoxCelestial has suggested, but this is just a theory. You need to do some troubleshooting to find the source of the 200 Hz resonance you are perceiving.
First step is a near field scan of the port (as @VoxCelestial suggested). A perfect port will show a big peak at the tuning frequency, and nothing else... But real ports have other resonances. Sometimes the resonance is due to the size/shape of the port, and other times the resonance is due to the size/shape of the cabinet with the resonant sound leaking out of the port.
Next step is to do a near field scan of the woofer, and see what that reveals.
Another diagnostic tool which is very useful, but inexpensive, is a mechanics stethoscope. You play pink noise, and probe each panel with the stethoscope. A non-resonant panel will sound more or less like pink noise... If you have a bad resonance, it will be very easy to detect with this method.
A structural resonance will normally be localized to a particular panel, and even a particular spot on a panel. An acoustical resonance will be present on all of the panels.
Once you have this data, you will be in the position to devise a solution... we can help... but you (and we) need the data.
If you truly find this process to be exhausting and frustrating, then perhaps DIY speaker building is not for you... Doing this kind of investigation is a big part of this activity. But I hope you stay with it. Once you get this solved, your speakers will be something to be very proud of. They look great.
j.
I'll get more data posted, in the meantime would a contact mic be appropriate to slap on panels and see how they're vibrating.
While rounding edges certainly helps improving the response of a speaker, the impact on room modes below the Schroeder frequency is very limited to non-existent.
Hey there,
I would say that many of us are now quite perplexed by your '200Hz' problem.
I think that because you cleverly made a removable front baffle - you stand to have a 'bonus' re. a solution.
Although mentioned much earlier, I would get that port out of the corner.
After all things from bracing to damping, there is one other thing that I can suggest as a solution for what you are hearing >
You could insert in series with your woofer a 'fairly subtle' passive notch-filter centered @ 200Hz. My attachment shows the arrangement.
I am leaving the LCR values for someone else to advise you. (Rx could even be omitted)
GOOD LUCK Again🙂
I would say that many of us are now quite perplexed by your '200Hz' problem.
I think that because you cleverly made a removable front baffle - you stand to have a 'bonus' re. a solution.
Although mentioned much earlier, I would get that port out of the corner.
After all things from bracing to damping, there is one other thing that I can suggest as a solution for what you are hearing >
You could insert in series with your woofer a 'fairly subtle' passive notch-filter centered @ 200Hz. My attachment shows the arrangement.
I am leaving the LCR values for someone else to advise you. (Rx could even be omitted)
GOOD LUCK Again🙂
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OH - I didn't know. Your very first post never mentioned that ?
You posted an impedance curve, so I assumed a passive design.
(maybe something 'active' is causing your problem)
You posted an impedance curve, so I assumed a passive design.
(maybe something 'active' is causing your problem)
I removed that first chart because the measurement rig had issues on that, there are more accurate sweeps on other pages in the thread.
Here is woofer close mic without DSP filters. Green is sealed. Not really sure what the cancellation at 612 is, one would assume port resonance but it doesn't go away with the port plugged? I'm using three big wads of foam wrapped in socks to block the port, so I can block some of it, or the entire tube.
It is internal resonance of the driver, likely surround or centering spider. Quite common for woofers and subs. Impedance response should have small peak at that frequency too.
When you make a near field scan of a woofer, there is an upper frequency limit to the data. At higher frequencies, the wavelength gets smaller, and at some point the wavelength is about the same size as the driver, and then you get cancellations. I believe this is what the 612 Hz cancellation is. When doing a near field scan of my 12" woofers, 500 Hz is as high as I can go before the data becomes unusable.
Your near field data looks good, and it shows that the source of the 200 Hz resonance is NOT coming through the cone of the woofer. So that rules out a driver problem.
j.
Your near field data looks good, and it shows that the source of the 200 Hz resonance is NOT coming through the cone of the woofer. So that rules out a driver problem.
j.
Hifijim: I agree with the upper limit of NF measurement. But the rest....? I looked at hificompass NF measurements of several ~12" drivers, and some 6-7" drivers. If the cancellation was strictly caused by the method of the measurement, all drivers of the same size would have same dip in the measurement. But it is not true. See 32w/4878t01, no dip, very similar driver 32W8878t11 has the dip. Same goes for MW16P and MW16TX, MW19P and TX etc. So the dip comes from the driver. Of course it is usually emphasized by the method of the measurement and farfield the issue dissappears.
https://hificompass.com/en/speakers/measurements/eton/eton-12-680/62hex-out-kharma-exquisite-grand
https://hificompass.com/en/speakers/measurements/eton/eton-11-612/c8/50rp
https://hificompass.com/en/speakers/measurements/sbacoustics/sb-acoustics-sb34nrxl75-8
https://hificompass.com/en/speakers/measurements/sbacoustics/sb-acoustics-sb42fhc75-6
https://hificompass.com/en/speakers/measurements/scan-speak/scanspeak-32w/4878t01
https://hificompass.com/en/speakers/measurements/scan-speak/scanspeak-32w/8878t11
https://hificompass.com/en/speakers/measurements/eton/eton-12-680/62hex-out-kharma-exquisite-grand
https://hificompass.com/en/speakers/measurements/eton/eton-11-612/c8/50rp
https://hificompass.com/en/speakers/measurements/sbacoustics/sb-acoustics-sb34nrxl75-8
https://hificompass.com/en/speakers/measurements/sbacoustics/sb-acoustics-sb42fhc75-6
https://hificompass.com/en/speakers/measurements/scan-speak/scanspeak-32w/4878t01
https://hificompass.com/en/speakers/measurements/scan-speak/scanspeak-32w/8878t11
