Ginetto, you can listen to low frequencies in a small room. The pressure will be the same in the whole room at the same time, that's the only difference. It's not something you will notice.
Have you considered multi-subs?
The cochlea is a complex organ and effectively uses surface waves of a membrane (the basilar membrane, principally) around its coils to resonate at low enough frequencies in a small volume - as you will observe from water surface waves they can be much lower velocity than sound in bulk as the surface elasticity can be much lower than the volume elasticity, yet interaact with a similar mass - velocity of an acoustic wave is proportional to the square root of elasticity/mass-density, be it a string, membrane or in the bulk.
Suspend the subwoofer from a frame via wires.
I have built several loudspeakers in which individual drivers are suspended from a wire-mesh cage via thin fishing line. I do this because the loudspeaker concept is a nude open baffle, so there is nothing to screw the drivers to and they are suspended by themselves from an acoustically transparent structure.
In your case, the subwoofer is the primary problem, both its vibration transfer to the small speaker AND to the floor. So you should build a strong frame just slightly larger than the subwoofer, place the subwoofer on a platform, and then suspend the platform from the frame. It only needs to clear the floor and swing free. Because it is freely suspended, the subwoofer will MOVE in reaction to its cone movement. It turns out this causes a loss in SPL, but it is much less than 1dB because the mass of the entire subwoofer is much more than of the moving parts. I did an analysis of this in a paper I published last year because the question of loss had been brought up many times. It's a non-issue. Also, the system is a pendulum. If you were to inject energy at the natural resonance frequency you could potentially cause it to swing. But again this is a non-issue. Even 2 inches of wire forms a resonance frequency that is less than 1 Hz and is independent of the mass of the object being hung. If your wire is say 20 inches long, the resonant frequency will be 10x lower, which is too low to cause any problems. See:
http://hyperphysics.phy-astr.gsu.edu/hbase/pend.html
Hi thank you very much I did not get the wavelength issue right clearly
No I have to keep things as simple as possible I have never ventured in something more than replacing parts in equipment I did some kits an some simple mods on equipment Very basic stuff
Hi thank you very much for your valuable advice
I must confess that i did not imagine that this were a such challenging task
I see many manufacturers placing a sat just on top of the bass box Are all insane ?
i mean is it so difficult to decouple mechanically two structures ? i am not looking for an high end solution
My approach will be the try and see with different materials at the interface sat and bass cabinet
I will put petri capsules filled with water on the tops of both cabinets and look at the water surface
In this way i hope to locate where the vibrations come out
I really that at least one surface will stay calm
I would like to achieve more wide bandwidth than SPLs
What provides a feeling of completeness is a full range bandwidth
For this reason i will select a woofer with a very low fs
Hi good morning please excuse me if i bother you again
i think that really thi exceptional material could be my salvation
i have a question
i wonder how to check that the satellite i.e. the upper cabinet does not vibrate
I have seen a video with an half filled plastic water bottle place on top of the cabinet
The free water surface was rippling a lot
Imho this could be an easy test
Another one i have in mind implies the use of a small mirror taped with biadhesive to the upper speaker front baffle
i can direct a laser point on the mirror from an angle and check if the reflected dot shakes
in the best scenario the upper speaker front baffle will not shake back and forth
having study a little the Xmax issue i think that a crossover point of around 500Hz for a at least 5" midwoofer will make the vibration control on the head speaker a non issue the vibrations will be minimal considering the very small displacement and the low mass of the midrange cone
The severe vibrations will come only from the woofer of course
Moreover i like your creations very much and i am studying your dedicated thread at the moment
After all this is the concept i have always had in mind since i listen many years ago a wilson audio system sat plus bass box
Do you have a video of them sounding maybe ?
thank you very much again
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Inner tube.. I like that.
I'm not sure about your weights. I was thinking a slab. What little energy got through the air, would have a lot on, trying to shake a slab about.
This is a common technique you might of seen used, where aircon is planted on building that was made for it. The plant sits on springs, but they are not sat on the roof. Instead they sit upon large concrete blocks. Something the springs can't transmit enough energy to shake. So the building doesn't resonate.
You can paint the slab. Possibly put it on machine feet. The cup type seems right. I seem to use a lot of underlay though. Rubber crumb and foam. I get though too much to make sense 🙂
Hi ! thank you for the valuable advice The sat will only host a mid and a tweeter I understand that to move any resonance below in Hz (i.e. out of the band covered by the sat) some weight is very useful like 20 punds or more
this concept go back to 1977 when the 1st version of kef 105 appeared followed in the 1980 by the B&W 801
i think that the head and the body were rigidly connected This seems to me very wrong Decoupling them seems to me the right solution
thanks a lot for the advice I am focusing the head at this point
It has to stay still in any moment to avoid any doppler effect ?
I have the distinct feeling that if i take a normal three-way, extract the mid and tweeter and place them in a new smaller heavy cabinet above the original cabinet containing only the woofer, the sound improves
the woofer must be isolated on its own box
imho
Vibrations can be checked with an accelerometer or a vibration meter, but the cheapest cost already 100€.
I don't have made a soundvideo of my speakers, difficult(impossible?) to grab and reproduce the soundscape of a speaker.
I need to update my speaker thread with the information of version 2, I'll see if I find some time this WE.
I don't have made a soundvideo of my speakers, difficult(impossible?) to grab and reproduce the soundscape of a speaker.
I need to update my speaker thread with the information of version 2, I'll see if I find some time this WE.
Hi good morning and thank you very much for your kind and valuable advice
a cheapest qualitative way could a little petri capsule with some colored liquid inside and see for any ripple on the liquid free surface
it could be better to use two small pieces of biadhesive tape to fix it on top of the upper cabinets
a sine generator could be useful to check the contribution to vibes of all frequencies
i will follow the thread with great interest for sure
Thanks a lot again
🙂👍
And then you need an amplifier and a way to display the information gathered,
The mechanics stethescopes i goit were $7 and $21 CAD each. Much quicker, way easier, and more revealing in some ways than the more quantitative accelerometer.
dave
another sylomer testing ... it looks like a great decoupling material indeed
I think it could really be the final solution to decouple the head from the body of the speaker
i do not know the vibration frequency of the table in the test It could be around 100 Hz ?
i am sure the efficiency of the isolation will change with frequency
I think it could really be the final solution to decouple the head from the body of the speaker
i do not know the vibration frequency of the table in the test It could be around 100 Hz ?
i am sure the efficiency of the isolation will change with frequency
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Today it's common to see tweeters and mids, isolated from the cabs to avoid colouration. Usually the same cab though, just with a lossy gasket and I have to imagine captive nuts on springs. The doppler effect from your top box swinging, is why I might use something like carpet underlay, rather than 3 or 4 individual feet. Using sheets of damping material such of this, would make switching through different designs very quick. Rapid prototyping, and proof of concept testing.
I wonder how much use a phone might be. I have the spectroid app, which is somewhat like a spectrum analyser, with waterfall. I have used this already to find resonances in cabs. It's easily as good as putting my ear to a screwdriver 🙂
Phones also have accelerometers. #0# gets me in, on my old samsung. I'm not sure it's useful, but I can graph out movement, as a drum my fingers on the desk beside it. It's an 8yo midrange phone, so results may vary. I thing the mic element is going to be much more sensitive though, and I played tones from youtube, finding it a useful device, I already have.
Hi thank you very much for your valuable advice This confirms my feelings
However some important assumptions they have not been confirmed to me yet
1) only the front panel is the one that produces the sensation of a boxy sound
2) only the mid and tweeter suffer any vibrations generated by the front panel
I believe that both statements are true
if that were the case, everything can be limited to the analysis of the front panel
by mechanically separating the woofer from the panel hosting the tweeter and the mid drivers, many problems are avoided
Instead, in most speakers the drivers share the same front baffle
It is true that the best ones are very heavy and with very thick baffles and this certainly helps
thanks again and absolutely The main difficulty is to put together a bass box For this reason i will be studying the design and construction of subwoofer cabinets
i wonder if there is a kind of state of the art design just to understand what the design goals are
very interesting Thank you very much
the bass box will move back and forth in opposition to the woofer cone displacement In the best case very little
i think that a signal generator could be extremely handy
If a qualitative assessment of the cabinet movement is enough the idea of using colored water is very easy to put in practice
by observing the presence of ripples on the free surface of the liquid any cabinet vibrations will show up very clearly
better to use some bi-adhesive tape to stick the capsule to the top of the cabinet
I'm not sure about the Jelly. You can see that's a couple of hundred hertz, of very physical movement. I would say such a measurement device lacks sensitively.
Your phones mic is designed to pick up the same frequencies, at levels you couldn't use your hand to detect. The spectrum analysis shows just what frequencies are at play. In my testing, I found one of my speakers has a resonance near 1khz, that can be driven harmonically by lower tones. It seems one of my braces isn't glued quite as well as it should be. The phone pressed against it, shows it well. I should also note, commercial branded, not a build of mine.
This is info you won't be able to draw from watching jelly. Plus jelly costs. I bet you have a smart phone already.
Your phones mic is designed to pick up the same frequencies, at levels you couldn't use your hand to detect. The spectrum analysis shows just what frequencies are at play. In my testing, I found one of my speakers has a resonance near 1khz, that can be driven harmonically by lower tones. It seems one of my braces isn't glued quite as well as it should be. The phone pressed against it, shows it well. I should also note, commercial branded, not a build of mine.
This is info you won't be able to draw from watching jelly. Plus jelly costs. I bet you have a smart phone already.
if you are worried about the viscosity water can be used with very similar effect however i am not sure that is jelly it seems colored water to me
the interesting thing is that they also try different frequencies
i would like to carry out this test but i guess i will soak the speakers 😕
seriously i think that the cabinet issue is very overlooked at least in commercial speakers
some use 1/2" fiberboard even for front baffle
next step would be a cardboard speaker
is it a single piece speaker ? with all the drivers fixed on the same panel ?
water can be also used in place of jelly Much less viscous
Sylomer comes in different types of stiffness/loads, when using Sylomer you have to use the correct one and size for the specified weight.
In the data sheet of Sylomer you see the different Sylomer SR types and their values for "Static range of use 1 in N/mm²".
The optimal static weight for a type is between these values: SR/2 and SR,
we calculate the average of this to find the optimal load for a SR type: (SR/2 + SR) / 2
So for SR110 optimal static load = (0.055+0.110)/2= 0.0825 N/mm² +-20%
I use the brown SR110 with a static pressure of 0.7kg/cm²
Bought them in a 5000x50x12,5mm strip like in this webshop.
In the data sheet of Sylomer you see the different Sylomer SR types and their values for "Static range of use 1 in N/mm²".
The optimal static weight for a type is between these values: SR/2 and SR,
we calculate the average of this to find the optimal load for a SR type: (SR/2 + SR) / 2
So for SR110 optimal static load = (0.055+0.110)/2= 0.0825 N/mm² +-20%
I use the brown SR110 with a static pressure of 0.7kg/cm²
Bought them in a 5000x50x12,5mm strip like in this webshop.
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good morning 🙂 thank you very much again i am sold on the solution because i can see the impressive results
i can see a solution for the head speaker and the mechanical decoupling
the bass cabinet instead is still my recurrent nightmare the very acoustically dead ones are hugely heavy and expensive
it is a very challenging design
i can see a solution for the head speaker and the mechanical decoupling
the bass cabinet instead is still my recurrent nightmare the very acoustically dead ones are hugely heavy and expensive
it is a very challenging design
The speaker tested was a 4 way, but I only had one bass driver fitted, as I was testing each enclosure, brace and partition. Resting my phone in various places, in both left and right cabs, comparing the noise. Looking for something raising the pitch of one enclosure, over the other. Although each speaker (L&R) is just one item, I was able to see the difference, and track it down within the cab. It was where a divider meets the baffle. No rattle or movement I could feel, but the phone found it.
I was exciting the area, using harmonics. This midrange noise, was easy to produce by playing bass. If you are unfamiliar with harmonics, them imagine a ruler marked in cm, that stretch out forever. Another ruler beside in, marked in meter, stretching out forever. Beside this, another marking each Km.
The cm rulers has many marks before the meter ruler has one. 100 marks. But that 100th mark aligns with the meters, perfectly. In turn, the meter ruler has 1000 marks before the Km's first. But they align perfectly, and at the same time, some does a mark on the cm ruler. If we view these distances as wavelengths, we see they touch base together, at certain times. Now think of a gong. How you strike it once, but it kind of echo's that, until you hit it again. You might hit it with a frequency of once per second, 1hz, but it resonates all the time, at a higher frequency. Now we need to get in the bath. Lets rock that water gently. Back n forth, at the same speed, or double, it matters not. You are there as it's cresting, and eventually, the water comes out the bath.
That is 3 stories to read between, but hopefully you already know how a 100hz woofer can shake a cab at 400hz. The waves align often enough, to keep it ringing at that frequency. People are isolating tweeters from vibration far below what they can produce, as the harmonics of lower frequencies still interact with the tweeters movement. Movement, I don't think any of us can see at any realistic volume, but a microphone easily detects.
