Hipper
Addicted to Fun and Learning
Why don't you answer my reasonable questions instead of, perhaps, trying to trick me into talking about stuff I know little about?
How do you measure a change in the smearing of transients?
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Speaker spikes, pads etc. couple or de-couple your speakers
- Thread starter Snarfie
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Why don't you answer my reasonable questions instead of, perhaps, trying to trick me into talking about stuff I know little about?
How do you measure a change in the smearing of transients?
I did answer your question. The answer is still "Phase response. Pretty standard measurement.".
Don't you have that backwards?
Indeed. A very small part of the energy actually ends up being acoustic energy.
Uf, yes.. I wanted to say that only a small part of the energy ends up rattling the enclosure.
eliash
Senior Member
Interesting approach to calculate cabinet vibration. In case of a fully "floating", i.e. a decoupled enclosure from the floor, only the effective mass of the cabinet at the moving cones will matter.
In case of sine waves causing the vibration, one can use the 2nd derivative of the speakers cone excursion to obtain the acceleration. When speaker enclosure and cone stimulation are sinusoidal, the 2nd derivative will also be sinusoidal. Therefore my conclusion is that the excursion of the cone multiplied by its mass is equal to the excursion of the cabinet times its effective mass where the woofers are mounted.
Regarding the mentioned parameters I applied the ones from my modified Dynaudio Focus 220 speakers which are slim towers of about 1m height and behave completely different than one may assume.
From older Dynaudio Esotec 17W LQ Thiele-Small speaker data the woofers seem to have an effective cone mass of 15g x2, since there are two stacked. Their linear excursion is rated at 6.5mm peak-to-peak as a practical orientation.
Now here comes the surprise: The cabinets weigh about 20Kg, but the effective mass at the woofers is much lower. I used a kitchen scale to "tilt" the enclosure from the top back. The force, when the rear spikes went off the ground, was about 2Kg, app. a 1/10 of the total mass. This means that 6.5mm of cone excursion translate into app. 100um cabinet movement at the top of the tower. This magnitude seems reasonable, as touching the top front or rear of the enclosure with a fingernail feels accordingly.
This amplitude might not be much, but the effect on the tweeter above the woofers is inferior.
From Dynaudio Esotec D-260 Thiele-Small tweeter paramters their linear excursion is about 300um pp (with comparable sensivity as the woofer).
What happens now is that the tweeter output will suffer from Doppler-effect modulation, with comparable excursion of the foreign modulation signal as its own.
Since I have been suffering from annoying distortions, when listening to these speakers, I went a little deeper into music theory and human sound perception.
For instance, when string based instrumentation with vocal company occured, I could hear these distortions.
What is happening here could be abstracted by some (violin) signal around 400Hz modulating the (singers) formants around 2.7KHz. Doing some phase modulation math yield sideband-tones at around -30dB. If they were inside the same hearing band (so called Critical Bands, which have around 400Hz bandwidth at 2.7KHz), they would probably not be audible, but outside the same Critical Band they are probably audible (as distortion). That could be as well the explanation why double bass and drums do not cause that much audible distortion in comparison.
Now what has this to do with the coupling and decoupling of speakers?
In this case, the annoying distortions may be lowered a lot by "nailing" the enclosures as much as possible to solid ground to virtually increase the enclosure´s effective mass. I my case I had these speakers dropped into a wooden floor with their spikes first, when the distortions were worst. Large steel pads (10cm dia. 1cm thick) between the the wooden floor helped a lot, but hollow-drilling the wooden floor down to the cast-plaster, gluing small semi-hard copper shims onto the plaster surface (for protection and ease of alignment) and carefully adjusting the speakers on them appears as the best possible solution. I would have gone also through the plaster layer, down to the concrete floor, but hurting heating pipes close by was too risky.
In parallel I also mounted 3Kg flatsteel bars onto the upper rear inside of the enclosures to balance the enclosure and moved the (anyway rattling) crossover boards away from there, to an iron-free nonmagnetic external cabinet.
The steel-mass also improved the bass attack and precision a lot.
(during mod phase)
(final setup with lowered bass roll-off to separate bass-reflex range extension and room resonance)
So from my perspective there is a trade-off between coupling and decloupling speakers.
- When the enclosure is vibrating too much (lightweight tower enclosures, as described above), coupling is the option.
- When the speakers induce audible resonances into the structure (as into bookshelves), decoupling is optimal.
Some late remarks concerning the above estimation:
At 400hz, the cone movement will be much smaller than the rated 6.5mm and my assumption regarding the effective mass needs correction as well. The mentioned 2Kg "lift-off" (mass)force is as well lower than the effective mass, which the membrane movement drives (the speakers themselves are about 3Kg plus part of the enclosure). Anyway the "lift-off" force is definitely reached when sweeping at decent levels and low frequencies. The enclosure starts to shake on the spikes then...I leave the above for discussion anyway, since the observed distortion effects are still valid (for me).
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The thing is that coupling is not going to affect higher frequencies; you cannot couple so that the stiffness of the structure goes above the loudspeakers highest frequencies. Assume the speaker weighs 10 kg and is placed on stiff cones. If the floor under the cones yields 0.001 mm you will have a compliance of 1e-6/(10*9.81)=10nm/N. The resonance will be 1/(2*pi*sqrt(10e-9*10))=500 Hz. Above this frequency it is only the mass of the speaker that dictates the movement. Usually the resonance of the system is in the upper bass region. If you use soft feet the reonance can be below 20 Hz the mass of the speaker will be charge for the reaction in the entire frequency range of the speaker.
As mentioned the above may be just of academic interest in terms of SQ but this is just to show that spikes and hard coupling does not work as claimed. What may be audible is vibrations in the floor due to coupling but again I have nott seen any DBTs of that.
Also, the doppler effect exists from the driver itself.
As mentioned the above may be just of academic interest in terms of SQ but this is just to show that spikes and hard coupling does not work as claimed. What may be audible is vibrations in the floor due to coupling but again I have nott seen any DBTs of that.
Also, the doppler effect exists from the driver itself.
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Which direction of energy transfer you think may be problematic: from the floor to the speaker (say when truck passes near by shaking the floor) or from the speaker to the floor (because of enclosure resonances)?
eliash
Senior Member
I see no contradiction with the above in principle, there will be resonances in the stand of the enclosure anyway.
I haven´t calculated them in detail, but the question is how the distortion effects react on them. In this case the effective mass is assumed much lower than the total mass of the enclosure, therefore these "enclosure tilting" resonances might be higher than expected. At medium enclosure vibration frequencies around 400Hz the "stiffening" effect of the stand seems still valid (this is the suspected cause from above, but works on higher frequency replay, where the ear seems susceptible to such effects).
When I was trying to track down these higher frequency distortion effects, the measures on the stand (steel pads or direct contact to the floor) worked subjectively more effective than the (finally) installed mass inside the enclosure (but this was surprisingly effective on the bass as described above!). Also the exchange of the original hollow plastic spacers between the sub-stand (black board in the pic) and the actual enclosure against solid aluminum rollers seemed to help a bit on the higher frequency distortions.
The self-induced doppler effect on the woofer cone is of course also present, but the relevant audible effects seem to come mainly from the tweeter in this case, since the crossover is around 1.6KHz...
Anyway, I am glad to discuss the whole issue here, because these perceived distortions caused me even thinking my own ears could be the reason (...they seem to be OK by medical exam...).
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You would need to look on the specific case if you want to quantify the problems; speaker type/mass, room, and floor will affect the results. Regardless, you will find that isolating the speaker will show the least measurable problem.
How about answering the question instead of offering meaningless vague answer?
It is not meaningless.
Here is a link to an article written 1989, in Swedish though
https://www.faktiskt.io/phpBB3/viewtopic.php?p=766908#766908
https://www.faktiskt.io/phpBB3/viewtopic.php?p=766908#766908
Not even a mention of what publication it was? I assume not peer reviewed?
No not peer review. It is from the Music and Audio-Technical Society in Sweden. They have a quite scientific approach to music reproduction.
Since people ask for anything published or proof on this subject, I just want to link to what has been done. I hope that is ok, otherwise I can stop now.
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I actually use some of the Townshend products myself, though not for my speakers.
I was testing various ways of isolating my turntable from vibrations, especially floor-borne, and had all sorts of materials that I measured via a siilar seismometer app to the one in that video. Upon seeing the Townshend videos, and consulting some people who seemed to know what they were talking about, I ordered some of his spring-based pods. They were far and away the most effective isolation devices both measurably on the app and simply feeling the difference of vibrations getting through with/without the pods. Nothing else - sorbothane, various footers etc, came close.
I've been intrigued by the idea of using the podium product under my speakers, just to see what happens. The springs are so obviously good at stopping the transmission of low vibrations it seems to me there would likely be some actual, real-world effect in isolating vibrations from the speaker cabinet to the floor. Though I have no idea if it would render a useful sonic benefit.
One of the isolation products I tried for my turntable set up were the Isoacoustics pucks - same principle as the Gaia and other footers. At one point I tried them under one of my speakers and the sound did seem to change a bit, but to my ears not necessarily for the better, and I ended up preferring my speakers as they normally are, sitting directly on the carpeted floor, no spikes. Due to the fact the pucks raised the speaker, I could not be sure the slight sonic change I heard was directly due to the purported properties of the puck, or due simply to raising the speaker a bit higher, altering the driver/tweeter orientation slightly to my listening position, changing a bit of the floor-bounce characteristics or whatever.
One thing I like about the Townshend podium is that it is deliberately very low profile so as to not raise the speaker off the ground, change tweeter height etc.
eliash
Senior Member
It seems all true what they are claiming, but they don´t mention any self induced distortion effects as discussed above (though they admit some bass? thumpiness, if I understood it right?).
If the speakers would be constructed ideally, i.e. with enough own mass and mechanically decoupled midranges and tweeters (from the woofers; as could be true for some Wilson WATTs or similar heavy exemplars) then decoupling seems to become fully applicable.
My take: In a non-ideal world one has to cope with the "sold" limitations at their price...did you notice btw., the higher the price, mostly the higher the weight of the buddies, though unfortunately not a linear relation?!...
Some more inspiration for own experimentation:
(Blued S235JR steel, laser-cut, 12mm thick, front dia. 100mm, rear 120mm, 3.2.mm milled half-sphere recess - <50bucks for 8p, w/o blueing and milling...)
(Advanced solution w 2x10mm semi-hard copper shims, 12mm hollow drilled, not necessarily w higher WAF, but thought to be better than above, 12bucks for 8p, w/o hollow drill (China) and polyester glue (Stabilit Express). The shims need to be glued to the plaster layer...and you need to be sure about the final speaker position!)
More "hardcore" stuff:
(3Kg flat steel bar provisionally mounted rear upper side into Dynaudio Focus220 cab, where the crossover was located)
(Final setup with self-sticky acoustic felt on top of the steel bar, which adds about the same amount of weight to the rear as the speaker systems on the front - for tilt mass optimisation)
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Snake oil.
You keep claiming that but what is your scientfic view on spikes vs soft feet in terms of making the speaker fixed. Soft feet can be made of mouse pads if you include price as a factor of snake oil.
