Grown-ups only please to offer support

[7_V]

Originally posted by Steven Toy
Speakers are the only system components that are active in a physical sense - i.e: the driver units move back and forth.

So, in order for transients to be reproduced accurately without smearing or overhang, the drivers should move and the cabinets stay completely still with absolutely no wobble whatsoever.

Moreover, if the cabinets are allowed to wriggle atop something squidgy like Sorbathane, the tweeters will also move slightly, so bye bye focused image.

It may be ok to stick something compliant and squidgy under amps, less so under CD players, but surely never under speakers.

Spikes are the only way under speakers - they provide rigidity for the speakers, and a single point - or four single points provide the lowest surface area possible of contact with the ground through which energy transfered back up into the speakers is minimised.

Hi Steven. I understand exactly where you're coming from on this spikes v squidgy thing and I agree that the speakers have to be held still, with only the drivers allowed to move.

However, I'm not entirely sure that speakers do move with the right squidgies and I'm not entirely sure that they don't move with spikes. This is an issue which many speaker designers are unresolved on (well alright, some are unresolved, some think they know and most don't give a sh*t - they'll do what everyone else does anyway).

Squidgies first ...
Yes these move but they have a very low resonance. In other words, they go backward and forward very slowly - at 1Hz or 2Hz, far below the audio spectrum. The speakers won't move any quicker on these things so, in practice, they stay still.

Think of stiring a big bowl of highly viscous liquid (thick and sticky that doesn't flow easily) with a heavy wooden spoon. Now stir it fast. Not so easy eh?

Spikes next ...
I'm 52 and when I was a kid I had loads of fun with my brothers and sister playing my mother's old 78s on a wind-up gramophone. We'd lower the arm onto the shellac and the contact wasn't made by a stylus but by a needle. This needle was like a modern day spike and of course like a spike, it coupled to the surface and transferred all the acoustic vibration from the record to the arm where it was amplified acoustically and made music to our ears. I'll never forget "Binga, banga, bunga I'm so happy in the junga". A classic.

Did the needle stop vibrations in the tone-arm? No, otherwise no music.
Do spikes hold a speaker still? I don't know.

If the spikes are properly set up we'd be talking micro-movements and if the speaker doesn't move, the floor certainly will. Do we want that? Then again, if the floor vibrates the movement certainly could be transferred back to the speaker.

So, that's my thinking on the subject. I don't know the answer and I hope that I've convinced you that it's not a clearcut question.

Personally, I'm coming up with both alternatives for my Nonsuch speakers so I can listen to what sounds best. I guess I'll just sit on the fence and see which way I wobble.

 

[julian2002]

most built in isolation (spikes or squidgy feet) strike me as both a blessing and a curse as most of implementations use 4 feet when 3 would provide a more stable base. as it's virtually impossible to level 4 feet on anything but a mirror smooth surface you are going to get rocking (especially in a speaker) from this more than from anything else.
one solution i saw that struck me as quite ingeneous was having 2 spikes about 1/3 of the way from the back of the speaker so that it would naturally topple forwards. then have an adjustable tie connected to the wall behind the speaker and to the rear of the speaker. adjust the tie so that the speaker is balanced on the 2 spikes. rubber stops could be placed under the front to save the speaker if the tie broke. this way you get almost perfect isolation from floor bourne vibration. as for how it sounds i've no idea but the drawings and idea seemed pretty cool.
cheers


julian

 

[titian]

Originally posted by 7_V
So ...

It seems to me (theoretically) that - in a hi-fi system - the major part of the vibration is imparted through the floor by the speakers - mechanically. Only a minor part comes through airborne sound.

A few days ago when I read this I agreed with it. In fact when I am hearing my system the most vibrations I feel are coming from the floor (I have quite a bad 'moving' one).

An hour ago I was listening to Beethoven's 6th symphony quite loudly while I was surfing in some online newspapers. I was also drinking some water from a one and a half leter plastic bottle. There was still about 300-400 ml in the bottle and I just lifted it to drink while a loud passage was playing. I got surprised how the bottle was vibrating! Incredible much more than my floor! I tried to do the experiment several times and I had the same result. The airbourne sound was making more vibrations to the bottle than I was feeling when I was touching the floor. I tried to use different type of materials and I noticed that the heaviest one vibrated the less but only when they where filled up. As soon as you use an empty box with any kind of material (like all the hifi units) the vibrations appeared again! I didn't have much time to continue my experiments (also because I would like to do other things now) but I just thought of finding your posting, mentioning the minor part of vibrations coming from airborne sound, and telling you about this experience.
have a nice day

 

[I-S]

Re: Re: Grown-ups only please to offer support

Originally posted by titian
...and I noticed that the heaviest one vibrated the less but only when they where filled up. As soon as you use an empty box with any kind of material (like all the hifi units) the vibrations appeared again!

Much as I suggested before. You're seeing the interaction between mass and damping (energy absorbtion/dissipation).

 

[titian]

Isaac
what you and others suggested before in this thread is only trying to get rid of vibations coming from the floor not airborne.
A granite shelf for example or a very heavy stand will not reduce (much) the vibrations caused by airborne sound to the hifi components. The units themselves must be built to be able to absorb these direct vibrations.

The usage of granite is very discussed in the HiFi world. Some prefer a 2.5 - 3 cm plied wood: it is heavy it absorbs much more and it is much cheaper...

 

[I-S]

Indeed. Hence the inside of the lid of my cd player being covered in dynamat, and I've got a sheet of similar heavy damping material that was surplus. No idea what it is (trade name), but it's similar to dynamat and was free...

 

[7_V]

Re: Re: Grown-ups only please to offer support

Originally posted by titian
An hour ago I was listening to Beethoven's 6th symphony quite loudly while I was surfing in some online newspapers. I was also drinking some water from a one and a half leter plastic bottle. There was still about 300-400 ml in the bottle and I just lifted it to drink while a loud passage was playing. I got surprised how the bottle was vibrating! Incredible much more than my floor! I tried to do the experiment several times and I had the same result. The airbourne sound was making more vibrations to the bottle than I was feeling when I was touching the floor.

That's an interesting observation, titian but I'm not sure that it can be interpreted to mean that there's a lot of energy in the airborne vibrations.

I think that the bottle was acting as a helmholtz resonator. If you ever drink water from a one and a half litre plastic bottle while playing loud music again, notice the frequency of the vibrations and see if they get lower as the water gets drunk (or you do if you use wine instead of water).

A bottle is a specific shape which will resonate at certain frequencies. It actually takes very little energy to get it going.

Certainly there are airborne effects but I believe that they have far less energy than the mechanical effects.

Mind you, it certainly makes me wonder how important the 'helmholtz resonator' effect is for equipment cabinets ...

 

[I-S]

Fairly important I should think...

Not least because that is the principle on which ported speakers work.

However, before my CD player had the dynamat put in, when sitting on its granite/inner tube combo, late at night with the volume right down I started to notice an odd noise. Pausing the CD made it clear. The CD player was resonating at a specific frequency induced by vibration from uneven discs (it didn't happen consistently between discs, but was consistent with individual discs). The sound produced was exactly as if blowing across the top of a bottle.

 

[7_V]

Originally posted by Isaac Sibson
... The sound produced was exactly as if blowing across the top of a bottle.

So, the plot thickens.

 

[dunkyboy]

Well, not only are plastic water bottles Helmholtz resonators, but their mass is also very small, at least compared to, say, a high-end CD player... though it's definitely something to think about.

Dunc