Over excursion protection for subwoofer

[Buzzy]

Hi ! I am looking for a circuit that can prevent a subwoofer from over excursion so that it doesn't bottom out. I don't know what is the right name for this kind of circuit.

I shall also elaborate what i am trying to do here. I upgraded the driver for my SVS subwoofer i bought some time ago. So i have the old driver which is in perfect working condition. I have built an enclosure for it. The original SVS subwoofer has variable subsonic filter switch with 25Hz, 20Hz, 16Hz and bypass settings. http://www.svsound.com/products-sub-box-plus2.cfm I would like a circuit that will do the same. But i think i will not need so many. Maybe just the 20 Hz filter.
Thank you.

 

[Bakmeel]

Why are you afraid that in the new design your woofer will bottom out? Do you expect the new application to be of such different loading or more power capabilities?

Anyway, I would say that you are looking for current limitation. For my knowledge, speakers are current-driven transducers, and their excursion is a function of current provided to them.

Bakmeel

 

[AndrewT]

I am looking for a circuit that can prevent a subwoofer from over excursion so that it doesn't bottom out.

it's called ears, brain and fingers. They form a feedback system to tell the sensible, it's gone too loud.

 

[Buzzy]

Its not the loudness factor. It plays fine but when play movie with bass that extends down to 5Hz can hear funny noises in the woofer. Quite a few movies have this kind of crazy bass. Thats y i want to protect the woofer from breaking apart.

 

[dudaindc]

it's called ears, brain and fingers. They form a feedback system to tell the sensible, it's gone too loud.

T.F.F. AndrewT

 

[dangus]

Maybe use a limiter circuit (as in compressor/limiter), and stick a circuit in the sidechain that models the excursion limitations of the driver? That would be something like what Bag End does for their subs to prevent the 12dB/octave boost from clipping amps or sending cones into outer space. (Although they may use a VCA to tune a high-pass filter to limit low bass without affecting mid or high bass.)

There used to be a single-chip compressor/limiter from Analog Devices, but I expect you could buy a complete used compressor/limiter or a new one from China pretty cheap.

Or maybe you just need a sharp high-pass filter. 24 dB/octave? Marchand Electronics should have a kit like that.

 

[Buzzy]

I have found a circuit which is a rumble filter from rod elliot website Project 99 Rev-B. http://sound.westhost.com/project99.htm

Is this the one i should be using ?

I want to achieve the frequancy graph shown at the end of the page in this website http://www.svsound.com/products-sub-box-plus2.cfm . For now i have subwoofer frequency response down to 5Hz. This causes some funny noises in the driver even when i don't turn up the volume too much. Pls help. I am now stuck and unable to complete my subwoofer project.

 

[AndrewT]

yes, that ESP circuit is a rumble filter.
6pole (-36dB/Octave) instead of the more usual 2pole or 4pole.

 

[unclejed613]

-36db/octave? that's about as close to a "brick wall" filter as you can get

 

[EWorkshop1708]

Maybe a better woofer?

 

[unclejed613]

depends on the cabinet. at 5hz there might not be any back pressure, and any woofer in that enclosure will flop around like a grounded fish.

 

[head_spaz]

Most of the newer drivers use shorting rings in the voice coil to prevent over-excursion.

ESP's rumble filter should work.

I had a sub making funny noises recently. A close inspection revealed that the foam surround was deteriorated, allowing the diaphragm to flap around. Replaced it with an Audax driver with a rubber surround. Fixed.

 

[unclejed613]

at one time, rumble filters were necessary to roll off low frequencies that came from the surface of what my children call "big black CDs". now we need them with digital media because the movies we watch have sounds that can literally "bring down the house". i'm surprised there isn't a big market for "sensurround" drivers that bolt to the floor for everything 20hz and down (between 5hz and 20hz is a whole 2 octave range).

you're talking about the aluminum rings on the voice coil. not really a "shorting" ring but a magnetic "brake". aluminum is "antimagnetic" and opposes any magnetic force applied to it, which is why it's used as brakes for maglev trains, and magnetic dampers for tonearms. some of the dual coil voice coils on newer drivers would be better used as servo driven voice coils, and the amp could actively prevent overexcursion, and do it in such a way that it would lessen the amount of distortion heard from the driver.

 

[Milsdrewbulch]

I have two installations of the ESP Project 99 rumble filter and it works very well, however is is only going to protect your driver from over-excursion at inaudibly low frequencies (below 17 Hz in the standard configuration). To protect your drivers from over-excursion at any frequency, Rod Elliott also publishes Project 53. He does not sell a PCB for it due to low demand (I guess), so you have to make it yourself on a piece of board. I have done this and it works well (introducing only slight tapping sounds as it compresses). It is a frequency-independent method of limiting the power output of a power amp by reading its high voltage output and shunting excess line level input to ground. I used a readily available Vactrol optocoupler (now called "Vactec" I think) as well as the additional opamp buffer circuit and it works well. However it is somewhat superfluous with some modern power amps that have active current limiting to achieve the same end.

 

[mikeford]

A piece of tape and a marker can work pretty well, use a test signal, find the volume setting where the driver is getting busy, mark that point on the tape with the marker.