I know there have been a lot of suggestions and you have tried many of them...have you run sine sweeps?
I played some speakers at the DIY get-together in Grand Rapids a few years ago and ONE person in the whole crowd told me he heard a buzzing in the left speaker. I intended to look into it but ended up listening to the speakers for nearly a year in my home office and never noticed anything. I was a little skeptical, but I eventually got around to it and ran sine sweeps. In a very narrow range, say 240hz to 270hz they buzzed like a saw - it was loud, no doubt whatsoever that it was buzzing. Outside of that range, quiet as can be. These were some of the earliest speakers I built and I'm quite sure it is due to poor bracing. I intend to wedge an extra brace in at some point but I don't currently use them so its on my to-do list.
I played some speakers at the DIY get-together in Grand Rapids a few years ago and ONE person in the whole crowd told me he heard a buzzing in the left speaker. I intended to look into it but ended up listening to the speakers for nearly a year in my home office and never noticed anything. I was a little skeptical, but I eventually got around to it and ran sine sweeps. In a very narrow range, say 240hz to 270hz they buzzed like a saw - it was loud, no doubt whatsoever that it was buzzing. Outside of that range, quiet as can be. These were some of the earliest speakers I built and I'm quite sure it is due to poor bracing. I intend to wedge an extra brace in at some point but I don't currently use them so its on my to-do list.
With a completed cabinet, there are limits on what kind of bracing you can install. The best approach is to target the areas of the panel or panels which are vibrating the most. Sine sweeps or pink noise probes with the stethoscope will be most effective in helping you locate the areas. Once you know the areas you need to target, you can come up with ideas on how to stiffen them up.
Bracing does not have to be particularly strong or robust. plywood is fine. This post might give you some ideas.
https://www.diyaudio.com/community/threads/new-project-tower-3-way-with-twin-8s.378223/post-7037908
OK if polyfill did nothing it might be a panel resonance and looking at your picture of the empty box I do see some issues there.
I see nothing that couldn't be fixed with some glue and some sticks and bricks tho; some blocks in the box corners to couple the side panels together and some vertical struts on the sides.etc.
I hate to waste materials and I usually glue the speaker cut-outs to the box panels at random, cutting large woofer discs into halves or quarter sections sometimes but I use a lot of 42*19mm or similar when I make boxes and odd scraps of MDF glued in funny places at odd angles
Picture for giggles as this was a much larger box, 600 litres + after making an allowance for bracing and the shelf port
I see nothing that couldn't be fixed with some glue and some sticks and bricks tho; some blocks in the box corners to couple the side panels together and some vertical struts on the sides.etc.
I hate to waste materials and I usually glue the speaker cut-outs to the box panels at random, cutting large woofer discs into halves or quarter sections sometimes but I use a lot of 42*19mm or similar when I make boxes and odd scraps of MDF glued in funny places at odd angles
Picture for giggles as this was a much larger box, 600 litres + after making an allowance for bracing and the shelf port
Attachments
To add further evidence towards “it’s a longitudal box resonance” theory, here are @tmuikku hornresp simulations of the Yamaha NS-5000:
https://www.diyaudio.com/community/...tubes-reverse-engineering.399659/post-7362755
Yamaha cabinets are near identical to Coral’s and sims show 250 Hz first mode, just as I measured on real system.
It’s not a panel resonance, nor cone or surround resonance. Maybe let’s stop with ideas not based in theory or measurement, those are not constructive and only add doubt and uncertainty.
@wafflesomd could you please do port and woofer NF scan and show both graphs like in my previous post?
https://www.diyaudio.com/community/...tubes-reverse-engineering.399659/post-7362755
Yamaha cabinets are near identical to Coral’s and sims show 250 Hz first mode, just as I measured on real system.
It’s not a panel resonance, nor cone or surround resonance. Maybe let’s stop with ideas not based in theory or measurement, those are not constructive and only add doubt and uncertainty.
@wafflesomd could you please do port and woofer NF scan and show both graphs like in my previous post?
Isn't it nice how wavelength corresponds to physical objects size 🙂 anomaly in frequency response can be quite reliably mapped to physical size / features as long as measurement data is reliable. Certainly simulators are reliable and a good way to zone in to problems. And to learn about it, intuition thinking loudspeaker systems and their features with wavelength.
What is special in this case, or it is actually quite common, that its the lowest mode, the most longest wavelength that is the hardest to tackle with absorption. Polyfill must be packed quite tight to have any effect. If there is problem with standing waves its always the lowest one, all the above are progressively easier to handle and less problematic. Well, lowest mode is easy to tackle as well: position the woofer on the center of the dimension. Or multiple woofers with their acoustic center at the center.
I got rid of ports, its nothing but problems in home hifi and not really necessary in my opinion. Just use big enough cone, enough amplifier power and DSP to have any knee you want with a closed box and problem solved. Enough ways to the system so that the modes or other issues of any structure don't ruin the pass band. Of course, sometimes a port would benefit overall sound if the system has to be some form factor or something, but it just comes with trade-offs, extra hustle that then needs to be dealt with or tolerated.
What is special in this case, or it is actually quite common, that its the lowest mode, the most longest wavelength that is the hardest to tackle with absorption. Polyfill must be packed quite tight to have any effect. If there is problem with standing waves its always the lowest one, all the above are progressively easier to handle and less problematic. Well, lowest mode is easy to tackle as well: position the woofer on the center of the dimension. Or multiple woofers with their acoustic center at the center.
I got rid of ports, its nothing but problems in home hifi and not really necessary in my opinion. Just use big enough cone, enough amplifier power and DSP to have any knee you want with a closed box and problem solved. Enough ways to the system so that the modes or other issues of any structure don't ruin the pass band. Of course, sometimes a port would benefit overall sound if the system has to be some form factor or something, but it just comes with trade-offs, extra hustle that then needs to be dealt with or tolerated.
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Yes, it always amazes me how much of a speaker behavior one can infer simply from photos and dimensions.
Thanks. Seeing both on the same graph at the same level puts things into right perspective. Port output is much cleaner than I expected, 1st longitudinal mode is down 11 dB rel. to port main resonance.
4” port rel. to 12” woofer has 15 dB of area correction (20xlog10((10/4)^2), where 10 is actual radiating diameter of a typical 12” woofer). So 74 dB peak at ~170 Hz will be equal to 59 dB as radiated by the woofer. Coherently summing 83 dB (woofer level at 170 Hz) and 59 dB gives 83.5 dB in the far field.
0.5 dB - even 1 or 2 dB - narrow bump in the frequency response won’t be objectionable or even audible, so we can write off cabinet resonance as the source of any unpleasant coloration of the lower midrange. My next guess is the woofer to mid crossover.
4” port rel. to 12” woofer has 15 dB of area correction (20xlog10((10/4)^2), where 10 is actual radiating diameter of a typical 12” woofer). So 74 dB peak at ~170 Hz will be equal to 59 dB as radiated by the woofer. Coherently summing 83 dB (woofer level at 170 Hz) and 59 dB gives 83.5 dB in the far field.
0.5 dB - even 1 or 2 dB - narrow bump in the frequency response won’t be objectionable or even audible, so we can write off cabinet resonance as the source of any unpleasant coloration of the lower midrange. My next guess is the woofer to mid crossover.
Right now I just have two 250hz low pass and hi pass filters in EQ APO for the woofer to mid transition. I haven't measured the speaker with all drivers connected outdoors because man, that is a bit of pain hauling my three amps and desktop out. I would like to eventually get some good on and off axis data outside to see how my xover is really working. I did get one set but the woofer response didn't quite look right and I didn't trust it, I assume I will need to do a close mic measurement and splice that in. I am also no longer using the tweeter from that data set so I will need to do a new one.
fwiw which is probably not much, these are my filters to help tame the problem area
fwiw which is probably not much, these are my filters to help tame the problem area
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Hi @wafflesomd I saw this post and thought of your speakers!
https://www.diyaudio.com/community/threads/accelerometer-testing-of-loudspeaker-drivers.267734/
https://audioxpress.com/assets/upload/files/George NtanavarasAccelerometer.pdf
https://www.diyaudio.com/community/threads/accelerometer-testing-of-loudspeaker-drivers.267734/
https://audioxpress.com/assets/upload/files/George NtanavarasAccelerometer.pdf
I added some braces to my c note speaker cabinets today and boy did that make a difference, so much so that it's fairly apparent my big speakers need more bracing. I'll try to knock some of that out this week and see if it helps at all.
FWIW, a quick ear test but putting my ear next to the each panel, the potential resonance is most clear on the rear panel right behind the woofer. That's the most scientific method I have of hearing the panels at the moment. I'm surprised by this as the rear is 1-1/2" thick vs. the rest of the cabinet being just 3/4".
So I ended up getting the house to myself for a few days and I stayed up all night cutting some wood and adding braces to one cabinet. I put one across the baffle between the midrange and woofer, one joining the side panels in the middle that connects to the back, and a few on the bottom. To my ears everything from the woofer has improved. Plugging the port lets me turn off my ~180 cut filters. It seems my cabinets are definitely woefully underbraced. Placing ones ear next to the panels, the unbraced cabinet is really singing in comparison.
I'm not the biggest fan of the sealed sound, seems you lose quite a bit of low oomph. I'll try to fill it back in with EQ. I have two subs I need to integrate as well. Perhaps my inner cabinet materials could be reduced. I have about half the coverage of OC703 in the newly braced cabinet and it is the better sounding speaker.
I'm not the biggest fan of the sealed sound, seems you lose quite a bit of low oomph. I'll try to fill it back in with EQ. I have two subs I need to integrate as well. Perhaps my inner cabinet materials could be reduced. I have about half the coverage of OC703 in the newly braced cabinet and it is the better sounding speaker.
Boy, today was a kick in the guy. I took the big speakers down today to measure and add braces to other one. I hooked up my Amiga speaker (Paul C.) and wow, they are just miles better than my big speakers. I brought up some mixes I had done on the big speakers and they were full of issues. The amigas image quite a bit better, don't have the big resonance problem, they just sound right.
I'm sitting here and I just can't bring myself to put the effort into bracing the other cabinet, I just don't have the drive to work on these anymore. They are so big and heavy that any work takes a ton of effort.
To be honest I should've known better. All of my research told me this sort of design is just a bit dated, hard edges on the baffle, large baffle potentially reducing imaging (I was unsure of this but it seems to track with what I hear. The large 12" being in the same spot as the mains reducing optimal placement for bass radiation.
At this time, my plan is to rebuild a nice bookshelf and sub/bass module.
I'm sitting here and I just can't bring myself to put the effort into bracing the other cabinet, I just don't have the drive to work on these anymore. They are so big and heavy that any work takes a ton of effort.
To be honest I should've known better. All of my research told me this sort of design is just a bit dated, hard edges on the baffle, large baffle potentially reducing imaging (I was unsure of this but it seems to track with what I hear. The large 12" being in the same spot as the mains reducing optimal placement for bass radiation.
At this time, my plan is to rebuild a nice bookshelf and sub/bass module.
A large baffle potentially improves imaging due to the increased directivity index and improved waveguiding.
People have been gravitating toward small baffles now for many decades (it's not that new), and IMO drawing the wrong conclusions. It's one thing to build simple squared off boxes but I've heard better imaging from larger boxes when well designed.
in this case the larger baffle didn't improve imaging, it's noticeably worse than my thinner speakers.
I figure I can easily repurpose the cabinet to use as a sub, and just put a good bookshelf above them. running them lower will help avoid the nasty resonance. it's been nice hearing music without that honk down there.
I figure I can easily repurpose the cabinet to use as a sub, and just put a good bookshelf above them. running them lower will help avoid the nasty resonance. it's been nice hearing music without that honk down there.
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This is the kind of wide baffle that can produce excellent imaging. I don't know if AllenB had the Sonus Faber in mind when he spoke of a wide baffle, but this is one good example of a large, wide baffle creating directivity. Notice how much baffle there is above and around the tweeter.
With reduced directivity index you can improve imaging by reducing room interaction. Care needs to be taken not to introduce undue cabinet interaction.
@hifijim I wasn't think as specific as that, but good example.
Consider the term waveguide speaker design as a fancy way of saying I'll keep the sound under the control of a baffle in a consistent way, as much as possible. It then follows that the baffle has to be the right size to do that. It happens that room interaction reduction is the goal. Usually waveguide speaker designers come to wondering how low in frequency they can or should do this.
@hifijim I wasn't think as specific as that, but good example.
Consider the term waveguide speaker design as a fancy way of saying I'll keep the sound under the control of a baffle in a consistent way, as much as possible. It then follows that the baffle has to be the right size to do that. It happens that room interaction reduction is the goal. Usually waveguide speaker designers come to wondering how low in frequency they can or should do this.
All I know is I have both in front of me and the thinner baffle one images considerably better, it has a depth the larger one simply doesn't. The amiga extend beyond themselves and 'disappear' much better. The larger speaker makes it far more obvious you're listening to a speaker and the sound does not extend beyond it's width.