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Tactile FAQ

 

Tactile FAQ
 

Q: Even though the Q10B states it has an impedance of 8 Ohm , why does mine show a different value?

A: Impedance does not mean resistance. Impedance is the term used for resistance that varies with frequency. In other words impedance is not a fixed value. The stated 8 Ohm impedance is a targeted average that it will stay around during the majority of its operating range, both with regards to frequency and amplitude.

When you measure it with a meter you are measuring the coils DC resistance. As soon as you apply an actual signal to the device the coil starts moving, thus generating EMF and using energy. This movement brings the impedance up from the static DC resistance of the coil itself.

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Q: My tactile transducer does not perform as expected ?

A: There are two types of exiters/bass shakers. There is the piston based tactile transducer like we make. And there are the coil based vibrators. The Piston based types are ideal at high power low frequency output and can really move things physically, however they are not able to work at higher frequencies due to the weight of the moving mass. The coil based vibrators can make a lot of buzzing at higher frequencies, but cant really shake anything at lower frequencies due to limited power and moving mass.

The MQB1 should not be crossed over higher than 80hz. Its linear operating field is up to 50, it will operate fine up to 80 but from 50 and up it starts going out of phase with the signal. The signal is faster than the device. If you are setting it at 120 then a lot of energy is being dissipated in the device since it can not be turned into movement effectively.

If you do not feel vibration unless it is set to such high frequencies, the following could be an issue :

1. the signal source does not contain the proper low frequency content to make the transducer work.  You must look at the signal with a spectrum analyzer and verify that it has ample content of sub 50hz content.

2. The object being vibrated is a combination of the following :

a. too heavy
b. too well terminated to ground.
b. is composed of high/low density materials between the shakers attachment point and the surface desired to be vibrated. (kinetic isolation)  

It is important that the tactile transducers only be used in true vertical position. If they are mounted on the standard or PB1 Bracket it can easily result in some sideways motion, especially if the mounting place for the bracket is not absolutely rigid.

Using the bracket puts enormous torsional forces on the mounting spot, and even modest movement can result in the piston hitting the inside of the cylinder of the Q10B resulting in a clunking sound. If this can not be remedied  by  further fastening down the bracket, it is best to remove the bracket and mount the tactile transducer directly to the surface of the object being shaken. This will eliminate the horizontally directed torsional forces and remove any clunking sound.   

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Q: What are the best settings and amplifier for my tactile unit?

A: We recommend that you have roll off or high pass at 20 Hz or a brick wall filter at 15 Hz on tactile transducers. A tactile will indeed respond to frequencies below 5 Hz, but the amplitude it can play back at those frequencies is very low. It simply runs out of stroke. Every time you go down one octave in frequency, it requires 4 times more stroke to keep the same amplitude, as frequencies below 15 Hz will only be reproduced in very low levels - typically not enough to be seen as powerful.
We would recommend our XJ-700R amplifier for tactile operations - it is made specifically for this purpose and is great for it. It has the adjustment possibilities required to ensure optimum operation of the tactile.

http://earthquakesound.eu/home-audio/amplifiers/xj-700r.aspx


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Q: Can I mount two or more shakers?

A: It is possible to mount two or more shakers. Hardly any signal sources have any stereo content below 80 HZ, so setting them up in stereo for regular music and movie playback would be inefficient. Also the LFE channel in movies is a monaural channel, so there is no stereo signal to begin with.

If you are using it in a special effects capacity (e.g. a theme park or museum) a stereo effect might be usable depending on the setup, but it is too specific to give any general advice about.

Any amp can in principle be used to power them, however it is important that the amp has very high damping so it can accurately control the tactiles, as they are moving a heavy mass and have massive EMF.

 Earthquake amps are uniquely suited to drive the tactiles because of phase and crossover being build in, along with variable gain. With an XJ amp from Earthquake you have everything you need for the optimal implementation in one box. If using a standard stereo amp you would need separate electronic crossover and phase adjustment.

 

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Q: Do you have a frequency response graph for the tactile transducers?

A: Frequency response is not as easily measured in tactile transducers as it is in dynamic speakers, as the response from a transducer such as the MQB-1 is kinetic force and not sound pressure.

Tactile transducers do not roll off in the traditional sense - in frequencies below 15 Hz, it will just use up its available piston travel at a much lower amplitude than it would at higher frequencies. So if you want to drive it to max excursion into low frequencies you should use a frequency adjustable voltage limiter to avoid bottoming out the transducer.   

If you are interested in reproducing ultra low frequencies  the Q10B transducer has a much  longer stroke and will be able to output more into the lowest of frequencies.

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Q: Can three MQB-1 MiniQuake match one Q10B?

A: In terms of kinetic energy three MiniQuakes will be close to one Q10B .  If the individual seats are isolated so vibration does not travel well between them, then a mini at each desired focal point is optimal.  If the design allows for vibration to freely travel without a strong ground termination,  we would recommend a single Q10b.

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Q: What frequency range does the Q10b support? 

A: The actual frequency response is 1 to 80HZ above 80 HZ the piston moves slightly out of phase with the signal proportionally increasing up to about 150HZ. Beyond 150 the majority of the signal energy is converted to heat.  We recommend that the unit should not be used at high power at frequencies above 120 HZ.

We have altered the specifications over time to best reflect the usage that will give optimum results in the typical home cinema environment. For special industrial and military applications it can be used to its full bandwidth and power capability.

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Q: What type of amplifier should I use to run tactiles at ultra low frequencies (15Hz and lower)?

A: To run the tactile at ultra low frequencies an old school "Heavy Iron" Class AB amplifier should be used, as switching output amplifiers (Class D and derivatives) are not designed to operate at those frequencies as they come too close to DC for comfort and they usually have a high pass filter or modulator limiter build in to prevent passing of super low signals.

For all actual audio uses such as music, home theater and gaming - an Earthquake XJ-300ST or XJ-700R is the optimal amplifier to use. They have superior control of the piston movement due to high emf absorption and high current capability unique to the class J output stage. 


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