Yes, literally there are five feet. The 5th foot is in the center -- allowing one to pull the unit halfway out without the chassis falling down to tear up the shelf.

The first time I went to an Aventage demo, they said it was designed to minimize vibrations. My first thought was “They can’t just make the chassis stiffer?”.

If they really cared about the shelf, they’d have used a track, like the ones on a tank or crane. :D

I heard that explanation. Maybe they could not just make it stiffer.

Imagine a rope pulled tight across a twenty foot length. Imagine wind blowing past it. The rope will vibrate in the middle. Each end of the rope will be a node (a place that is stationary along a vibrating... rope). One would have to pull it maybe four or five times as tight to minimize the vibration.

However, a string in the middle, anchored below the rope and pulling down slightly, will create a node in the middle; there will still be nodes at each end. Sure, each half will then have its own vibration problem, but the relationship of length to tension will be double, the length of each vibrating section will be halved, and the frequency of any oscillations will double, meaning the amount of movement of each half will be smaller. Putting a foot in the middle does WAY more to stop vibration than you'd think it would.

Of course, the Yamaha guy then made the whole thing puzzling by stating that they added a fifth foot to their DVD players and it made things worse. I don't remember just what was worse, but that surprised them more than the fifth foot helping an amplifier.

Ffrom [Link: amazon.com]:



On the other hand, this unit is discontinued and the thumbnail illustrations for newer units don't show this. Maybe they've quit doing it.

Having originally studied architecture at an engineering school, I absolutely refuse to believe they couldn't stiffen the chassis if needed.

The vibrating rope (or cable) can be stabilized with a weight or something as simple as a piece of sheet metal that's essentially square and bent across the diagonal and attached in the middle. This is done for power and cable lines between poles in places where high wind speeds are common- it really changes the resonant frequency more than anything but it also modulates the amplitude of the cable's movement. The problem with using tension is that if a cable breaks, the whole thing collapses away from the break, violently.

As far as stiffening a chassis like this, it could be done in many ways- stamping ribs into the bottom, screwing flanges to hold sub-assemblies to the bottom or suspending the top of a vertically-oriented assembly/heat sink from a higher point on the sides and also at the bottom would do a lot to prevent bending (also called 'deflection'. It would act in a similar way to a truss- much less material than a solid beam or joist, but it can support the same amount of vertical load.

BTW- that pedestrian bridge that collapsed at the college in Florida last month- the link shows that the ends don't appear to have been anchored to the ground or some kind of foundation and the reports stated that it was erected very quickly. Quickly, I understand but under-designing it seems to be the cause. It seems that the bottom failed and pulled the ends onto the face that had supported the bridge. This could have been caused by people walking in unison, creating oscillation that coincided with the resonant frequency of the supported span and if that had happened, I would expect people to panic and run. This wasn't the case in this one, since it wasn't open for pedestrian traffic. The rendering I saw showed that the span was flat, with no arch- unless the upper section is supporting the lower and it truly can support that load, it would have been much stronger if it had been arched upward and the ends had been anchored, as long as the trusses had been designed properly. It appears that the walkway has cables in the concrete- if some of these failed or weren't properly tensioned, it explains why it fell.

[Link: ocregister.com]


This link doesn't show much arch to the walkway- the deflection just from gravity would cause the concrete to sag below the ends and that causes the cables to be the sole support mechanism. If it was tensioned AND arched before casting the concrete, it would be much stronger.



[Link: study.com]


WRT the DVD player's fifth foot- you wrote that it does more to stop vibrations than we would think- it also changes the resonant frequency of the chassis and that's probably where they ran into problems- if the foot is hard-mounted, it can transmit vibrations that cause the disc to flutter and if that happens, the laser can't focus. If they had used a foot with some kind of viscous material, I bet it wouldn't have been so bad. I'm surprised they would have this problem- it's so easy to test.

I had a manufacture tell me not to blow air in to the Processor but suck it out. this would stop the blown air from changing the Bias. thus not affecting the sound.

not sure if this is true but it sure sounds good.

I’m not so sure about the Yamaha reps technical prowess. I can recall an amplifier claim on some older receivers. I forget what they called their circuit feature. When I went to the rep demo introducing the product, they cornered me and asked me to explain what all of this meant. (There were supporting graphs and such) I said that it was a nice story and that another manufacturer had made an almost identical presentation ten years prior. (and this was very similar to presentations shown in textbooks)

I’m not saying that there can’t be any benefit to vibration suppression, however, I am not sure how tightly this is coupled to the listener jury’s opinion. If one is observant, all sorts of correlations can be made. I have a solid plastic rod that I can simply pass through an amplifier, near the tone control (without touching anything), and one can clearly observe the distortion trace jump around.

If you have ever run an amplifier into a dummy load, you have noticed that the amplifier directly emits some sound under heavy load. (Much of this is from the power transformer.) This sort of phenomenon is usually symmetric — meaning that external sound can influence the amplifier. Again, I’m not sure how this will effect the listening jury. It would be an interesting test to perform. Place an amplifier near a speaker, listen for a while, then move the amplifier to another room, acoustically decoupling the amplifier from the speaker.

Blown air can cause static electricity and if it's blown directly at a fan, the fan can be damaged because it's spinning much faster than it can handle.

I had a rep tell me that ADS car power amps were designed to use NASA spec wire after I told him the standard 10ga primary wire didn't fit their terminals.

Sony and some other companies had higher-end products and when Sony was making their Esprit line, just about everything had a heavy plastic compound in the base to dampen vibrations. Some companies had a granite or marble slab that was used to add weight to the stand, to do the same. Seems that some are trying the opposite- "if it's light enough, maybe the sound will blow right by".

lol

This thread went right off the rails about here...


I bet an added foot was cheaper.

You're right, that IS exactly what I said:

I don't think it's a proper use of the word "modulate" to describe a reduction in amplitude. If it were, every volume and tone control is a modulator.

I was saying the use of the foot has an effect similar to the tension setup I described. "The problem" you just mentioned has no place in this discussion because it doesn't exist with a foot. A foot is not going to break or fall off.


Your list of ways all sound like they would cost more than adding a fifth foot. Every solution you offer would work but would add height and weight to the component, causing added expenses in fabrication, increasing packing and shipping costs, even making it more difficult for us to get all the components into the cabinet. Hearing this list, I'd feel pretty good about myself if I had been the one to suggest a fifth foot!


That's true, but even worse: there's a video somewhere that shows people working on the left end (same orientation as all the other videos) at the moment that it collapsed. They were messing with the tension and the idiots didn't stop traffic below the bridge.


Why do you say this (presumably "this" is what we're talking about) could have been caused by people walking in unison when the bridge wasn't open yet? It is true that a nuclear explosion would also have damaged it quite a bit, right? See how that has no relevant place here?


That's so true! I'm guessing that they found an improvement with the amps, so they slapped one on the DVD Players, then were amazed that it didn't help, and just removed it with no further research.


These guys couldn't warn about the plasma falling out, so they reached for bias changing. Bias is a DC voltage applied to force a device (transistor, tube, even a RELAY!) to operate in a particular part of its response curve, usually the most linear part. A freakin' light breeze isn't going to change that!

Yeah, it's seriously hilarious! How the hell do beginners learn anything with all of us jokesters around?