Do i really need a low pass crossover for my Tactile Transducer build?

[jjabba]

I'm building a tactile transducer setup for my sofa using:

1x Sure Electronics AA-AB32178 2x50W 4Ohm Class D Audio amp
2x AuraSound AST-2B-4 Pro Bass Shaker Tactile Transducer

The amplifier board is feed full frequency pre-amp audio from my existing 2.0 channel amp (it's actually mono pre-amp split into stereo input on the Sure Electronics board).

I've been looking at using an active crossover before amplifying
or
a passive lowpass circuit for each of the AuraSound Shakers.

I still don't know however, if the drivers in the AuraSound AST-2B-4 Shakers would suffer any damage if I just skip filtering out higher frequencies all together...

Any thoughts on this?

[Millstonemike]

I don't know about the Proshaker's ability to handle the HF content. But it would be fairly simple to use a PLLXO (Passive Line Level XO) between the signal feed and the amp. A simple series resistor then a small cap to ground in front of each of the Sure amp's + inputs (e.g., 4.7K resistor and 0.47 uf cap yields 1st order LP at 72 Hz).

[jjabba]

Thanks for that suggestion Millstonemike!
I ran a quick simulation of the circuit (see attached picture).

How did you come to chose those particular components (Resistor and capacitor) for the 72Hz low-pass?
Are there some standard values for PLL input/output loads that I should consider when designing a PLLXO?

[Millstonemike]

Thanks for that suggestion Millstonemike!
I ran a quick simulation of the circuit (see attached picture).

How did you come to chose those particular components (Resistor and capacitor) for the 72Hz low-pass?
Are there some standard values for PLL input/output loads that I should consider when designing a PLLXO?

Rough values are usually selected based on source output impedance (usually <200 ohms) and / or sink input impedance (likely 30K ohms for the TDA3116 chip in the sure amp).

The equation C = 1 / (2 * Pi * R * F) or F = 1 / (2 * Pi * R * C). Remember the cap values are in uF so .47 uf is 0.00000047 in the equation.

[jjabba]

Thanks Millstonemike,
I went ahead and got these two components to build a first order lowpass.

1. Capacitor 0.47uf: https://www.parts-express.com/dayton...citor--027-206
2. Resistor 4.7k ohm: https://www.parts-express.com/47k-oh...-pcs--003-4.7k

After trying it out it seems to do pretty well as far as the low pass filtering goes, but with a rather significant insertion loss. I re-read this excellent summary of Passive Line-Level Crossover and noticed it does say:

A passive line-level crossover (PLLXO) is a very good solution if you don't need circuits that are too complex circuits and can live with the insertion loss.

In my case the input signal comes from my (mono) pre-amp out (volume controlled) and not a line-out. Thus I'm depending on my main amp volume to control the "volume" of the tactile transducers. With the insertion loss introduced I currently have to have the mid and high range speakers at an uncomfortably high volume in order for the tactile inducers to shake as desired.

Is there is a good way to calculate the insertion loss introduced by this PLLXO RC-lowpass circuit?

[Wolf]

If you like voices coming from your butt, then skipping the filter is perfectly acceptable, just be aware that whatever goes to the shakers will come from down under and in an Australian accent.


Truthfully, you don't want sound from shakers- you only want shaking. This means xover about 50Hz or lower, and actively is your best bet.
Later,
Wolf

[1100xxben]

Thanks Millstonemike,
I went ahead and got these two components to build a first order lowpass.

1. Capacitor 0.47uf: https://www.parts-express.com/dayton...citor--027-206
2. Resistor 4.7k ohm: https://www.parts-express.com/47k-oh...-pcs--003-4.7k

After trying it out it seems to do pretty well as far as the low pass filtering goes, but with a rather significant insertion loss. I re-read this excellent summary of Passive Line-Level Crossover and noticed it does say:



In my case the input signal comes from my (mono) pre-amp out (volume controlled) and not a line-out. Thus I'm depending on my main amp volume to control the "volume" of the tactile transducers. With the insertion loss introduced I currently have to have the mid and high range speakers at an uncomfortably high volume in order for the tactile inducers to shake as desired.

Is there is a good way to calculate the insertion loss introduced by this PLLXO RC-lowpass circuit?

The insertion loss will be based on the input impedance of your amplifier. Assuming the output impedance of your source is negligible, your pass-band insertion loss will be:

20 x log(Ri/(Ri+Rf))

Ri = Input impedance of amplifier
Rf = Filter series resistance

If your amplifier input resistance = 30k and your filter resistance = 4.7k, then your insertion loss would be 20 x log(30k/(30k = 4.7k)) = -1.264 dB.

One thing you can try is shifting your values by a decade (i.e. change your series resistor to 470 ohms and your cap to 4.7 uF).

It appears that you are using something like a 1 watt resistor, which is not necessary. You can easily use a 1/4 or 1/8 watt resistor. Also, you're getting into some larger capacitor values. You may want to go with an NPE cap and you only need a cap rated in the 10-20V range. Anything higher is OK, just not necessary.