Hi thank you very much again Yes also the room will contribute But i would like to avoid that the speaker is the cause Once i will have a very unboxy speaker i will be quite sure that any boxiness will be due to the acoustics of the listening environment
I have already focused the challenge The woofer cabinet
There is a material Corian used for kitchen tables It is very hard but i am not sure about its stiffness Maybe it could be ok for baffle ?
but it is important to have a test procedure to check for resonances
Possibly there is another way To increase mass instead of stiffness An increase of cabinet mass will move resonances down in Hz
Someone mentioned that low frequency resonances are less udible
For me to increase mass would be so much easier than to increase stiffness
I will have only to understand how to use lead sheets wisely and safely They are wonderful damping material Imho the very best
i could cover all the internal sides and make the cabinet very very heavy
but it is toxic unfortunately
Once i hit with an hammer a lead slab Only a deaf thud Impressive The best
Thanks again and very interesting I really need a signal generator possibly one with a nice knob to make some sweeps
i am sure any resonance will pop up immediately
I am still not sure about the range to cover with the woofer I read values from as low as 80Hz to even 600Hz
This would mean a cone midrange ranging from 8" to 4"
Dome mids are nice but the very good ones cost a lot
this is a very fundamental design choice Still open to debate
i am still undecided
The first thing I notice when I open the speaker is that there is little to no damping inside. It has to sound "boxy" and is most easily corrected by adding damping (polyester wadding usually). Damping the sides of the box with bitumen or rubber sheets, or adding stiffeners is a bit more difficult, that's more extensive work. Another problem is when they install the bass in a box that is too small. Then the Q factor is too high and it sounds "boomy" and not "boxy". This is difficult to correct, a larger box is needed. I think room acoustics can create a "boomy" effect, and a "boxy" one is unlikely.
Hi its me again I have thought a little more about this and i think that decoupling could be not necessary
dealing with resonances in the sense of eliminating them from both cabinet will result just in placing a not resonant head above a not resonant bass cabinet There will be no resonances that can pass from one cabinet to the other Even simpler than i thought
The goal is to get not resonant cabinets in first place Good
i think that the key parameters are stiffness and mass Damping can only act by increasing mass of course
so i would prefer high mass damping to polyester Like the damping use in car audio installations
Lead sheets glued and secured to panels would be by far the best and cheapest way to add mass to the cabinet But it is very toxic
Exactly ! bracing is more challenging A very old application was in the b$W Matrix line I had the Matrix 1 that i destroyed to see inside
Very interesting Reflex design is another challenge It is not easy to get it right Experiments are needed
Thank you
The problem with speaker box panel resonances is serious and audible. The bigger the speakers, the worse. If you just compare the surface of the box and the surface of the membrane, it is clear that even small vibrations of the box can be heard because the surface is much larger than the drivers themselves.
There are many speakers on the market that have Qts higher than 0.7-0.8, especially smaller speakers. The boxes are too small. Part of that is also a result of using a coil in front of the bass with a higher DC resistance. Let's say I measure driver TS parameters, Qt is greater than 0.5, and they put it in a small box with a bass reflex. It's an old trick that adds warmth and the impression that the bass is deeper than it really is, but also adds boominess and a tendency to sound like one note bass.
Agreed 100%, and the absolute worst possible shape to start with is a cuboid, which 99% of both manufacturers and DIYers do!
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Some manufacturers put the drivers in resonant boxes to get a specific sound. They know everything well about damping and stiffening, but they do it on purpose. And it's cheaper too. This is how you get a "live" sound, which is not far from the truth, because the box plays its own song. 🤣 And live sound is always very different from commercial recordings.
Well-damped and stiff speakers sound too clean and boring anyway, that's just FiFi, and we've gotten over that a long time ago. Today we are looking for a lot of excitement and goosebumps. 😁
Well-damped and stiff speakers sound too clean and boring anyway, that's just FiFi, and we've gotten over that a long time ago. Today we are looking for a lot of excitement and goosebumps. 😁
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For woofer cabinets, damping it with bitumen or lead based cladding does not solve it as it brings the resonances down in frequencies so they are still there but only lower (muddy bass). Bracing and stiffness of the cabinet are the main things that removes them. Stiffness is important to be more inert to vibrations, and bracing brings the frequency up, if you do it right, out of the passband of the woofer, and also reduces the amplitude of the resonance. Damping with lining can help also, but only for the higher frequencies (where bitumen and lead can work if the cabinet is seperate from the bass).
Best material that i know is still high quality void free birch wood. Some (Genelec) manage also to do it with a metal enclosure, but i think that is hard to do diy. I guess that some forms of (geo)polymers are also suited as they are heavy and often almost inert to vibrations, but again hard to do diy.
And MDF that is thick enough (very thick) can do it also, but it's not nice to work with and not that healthy for you and the envirroment, plywood is better overal.
Best material that i know is still high quality void free birch wood. Some (Genelec) manage also to do it with a metal enclosure, but i think that is hard to do diy. I guess that some forms of (geo)polymers are also suited as they are heavy and often almost inert to vibrations, but again hard to do diy.
And MDF that is thick enough (very thick) can do it also, but it's not nice to work with and not that healthy for you and the envirroment, plywood is better overal.
Stiffness increases resonant frequency. Mass lowers resonant frequency.
Mass does not act as dampening. Absolutely not,
Dampening is only possible by transforming motion energy into heat. Highly viscous materials as shear layer between hard panels or other materials with "dampening" behaviour can do this.
Stiffening panels reduces vibration and can increase the resonant frequencies above useful driver range.
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Lots of thinking but less doing.
So let me reveal a little anecdote of mine with a pair of dumpster find speakers from several years ago, the type of super cheap ones often following with a mini component stereo, like these Philips fwcb399 speakers
These have quite a thin fiber wood walls, maybe a mere 7-8 mm, except for the front which is made from molded plastic and is maybe 2-3 mm thick and not much bracing at all like the ones seen in your attached image.
These speakers have a very boxy poor sound, so decided to play with these speakers just for fun by doing few small iteration changes to them, such as removing the grill to the tweeter which removed some hash (the super tweeter were fake), stuffing the box with damping materials (these had actually none inside), listened to them and the boxy sound had decreased quite a bit although still far from acceptable sounding, adding even more damping material and it improved a bit further, until the last step, separating the front from the box with speaker drivers in place, like this:
ie. they would become an open baffle type of speakers, and placing the naked panel without the box on top of the woofer, and voila.. the boxy sound was virtually gone, that despite the crappy thin plastic front panel, so where does the boxy sound come from then, Gino? :)
Well, maybe the journey of anticipation, and thinking, is what brings more of satisfaction..
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At a talk by Bruce Edgar years ago he mentioned putting sand on a speaker surface and watching for where it jumped. Maybe less messy than water.
Yes i guess so The physics of resonances is beyond my ability to understand There are a lot of variables
- cabinet geometry
- panels size and material
- presence of bracings
- damping layers etc.
you mean the area of the baffle around the woofer ? because a cabinet can be made narrow short and very deep
i guess this could be a good decision It will need more space in the depth direction
like a long horizontal pipe closed on one side and with the woofer on the other side There will be no baffle to speak of
this only for the cone drivers of course
Thank you for the interesting link Work on lead can be very unhealthy
One thing is to glue some sheets to the internal panel another to work on lead with tools
With my biggest regret i will have to abandon the idea of using lead
I could bolt some iron profiles to the cabinet It will increase both mass and stiffness
No, I mean the total area of the box in relation to the area of the membrane. Large surface area means high efficiency, the speaker easily excites the panels without damping and stiffening. A large front baffle causes different problems. Reflections from baffle surface for example. The large width of the speakers again means that the baffle step is much lower than in narrow boxes.
Thanks a lot I see some speakers with very thin walls I read of some designers considering a speaker like a musical instrument a musical box
i tend to disagree Any coloration/resonance will cause a distorsion that will add at the musical signal I will hear the music and the box
i do not like at all
i think that well damped speakers can sound very dynamic and with low THD/IMD also at high SPLs For me its more than enough
Yes i understand that But someone stated that low Hz resonances are much less impacting on the overall sound
But you are right The best situation is no resonances at all That is clear And only high stiffness can provid that
👍
Very good to know Thank you So braced birch wood
metal is much stiffer than any wood Everytime i see a metal cabinet i salivate I have to chance to get one
I am sure that a sub with a metal enclosure should sound sublime
I have some Teac and Kef little speakers with aluminum boxes But they are good from 200Hz up maybe
Metal subs are gorgeous
all aluminum cabinets Definitive
Hi thanks ! then i think i am mistaking what dampening means For me dampening is to absorb vibrations And mass does
Lead a high mass material is sublime for dampenig It kills any vibration completely
i see There is mass and mass A steel mass does not damp anything Lead is a metal without the metal structure
But a very rigid cabinet will not need any damping in the best case Unfortunately to apply some sticky pads is much easier than to brace
Perfect ! message received loud and clear