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Discussion Starter · #1 ·
I have a SVS 20-39 CS (the passive cylinder subwoofer from our friends at SVS). I'm about to get a proper amp to drive it, and cost wise it looks like a 250W plate amp might be the way I want to go.


The question I have is should I get a plate amp that has been modified with a 20Hz rumble filter (cutting out all frequencies lower than 20Hz I gather) or would the 20-39 CS work better without it?


From the specs, the 20-39 is tuned to 20Hz (hence the model name), so logically it seems like a good idea to throw out anything below that so the driver doesn't get over extended when playing material that dips below 20Hz.


I've played the "Darla tapping on the glass" scene from Finding Nemo using the 100W Mitsubishi amp I currently have connected to my SVS, and at high volume levels I have heard a 'clacking' noise that I believe is probably the driver over extending (I didn't want to repeat the test too many times fearing damage to the driver). Would the rumble filter on the 250W plate amp correct this, or would I just end up missing out on the true low end that the 20-39 CS is capable of?


-cjs
 

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I don't know, should a 100 watt amp be over extending an SVS? Using an Adire Shiva driver in a sonosub I built i'm sending it 1140 watts! obviously gains are nowhere near open.Still seems like that SVS should handle alot more power.


brickie
 

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Discussion Starter · #3 ·
Brickie, I hear what you're saying and I guess what I assumed was happening was that the 100W Mitsubishi (which I picked up for next to nothing and don't have any documentation on) was distorting at high volume levels and causing the clacking noise I heard on my SVS.


The SVS properly needs a 4Ohm load and from the back of the Mitsubishi it looks like it's rated for 6 Ohms, so I'm guessing it's struggling to supply power to the SVS. Would a dirty distorted signal cause an overexcursion? Like I mentioned I didn't want to push my luck, so I basically stopped pushing it until I get a properly rated amp to judge what's happening.


I'm still wondering about the rumble filter though before I place the order. Does anyone know if the amp in the SVS PCi series incorporates a rumble filter to cut out frequencies lower than the sub can handle?


-cjs
 

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It could have been clipping that bottomed the driver but more than likely it was the low bass that is below your sub's tuning frequency. If you have ever graphed a sub in a ported enclosure, excursion skyrockets below the tuning frequency. I'm 99% sure that SVS has some type of filter on their plate amps. Especially since they offer the "black box" that has one.


If you get a standard plate amp from PE or Adire, it will have a filter. The PE amps come with instructions on adjusting the filter and the bass boost. The new Adire digital amps have the filter set at 2hz effectively removing it. You can adjust it also.


-Robert
 

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Collins,


As Robert surmised, you were almost certainly massively[i/] clipping that amp which can cause that sort of problem for any passive sub (and damage ultimately). Just like the old saying "too little power is more likely to burn out a tweeter than too much".


That plus (I'm guessing here) the possibility you hadn't calibrated things with an SPL meter will again lead to over excursion. The fact you can send clipped "square waves" at "only" 100 watts from a questionable amp is indeed something you want to avoid. From a purely physical standpoint the rating of the amp in an instance like this is nearly irrelevant. 1,000 watts of clean power (properly configured and calibrated of course) would be much less stressful on the SVS than what you are doing there.


As for the plate amp, a 20Hz filter (typically called a subsonic filter) isn't a "brick wall" cutting off all frequencies below that. There will be a slope starting around that point usually that will "roll off" frequencies in a more or less gradual manner... which is what you want. If designed right you will have very linear response to well below 20Hz in your room.


I would leave the subsonic filter where it is since this will indeed allow you to push your CS sub a bit harder than you otherwise would do (by simultaneously reducing the load on the amp AND the woofer of the CS at a given rate below 20Hz). Do ensure you have the amp shipped with NO bass boost, or you know how to defeat this entirely. That CS sub requires little or no EQ down low with good room placement, and any EQ added in will tend to have the opposite effect of the subsonic filter.


That is it will put more load on the sub and the amp than you need/want.


Ron

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Discussion Starter · #6 ·
Thanks Ron & Robert


I'll insure no bass boost (the base model PartsExpress amp doesn't have it and the one I plan to get from RythmikAudio doesn't either). And I'll have Brian at Rythmik add the resistor for the 20Hz extension filter on his 250W model.


P.S. You guys do a great job of sniffing out the SVS threads here on avsforum... I think one can get as quick a response here as by emailing SVS directly :)


-cjs
 

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Colins,


You just got lucky ;^) most of us are working issues via e-mail and phone pretty much 12-18 hours a day. We're only able to spend a few minutes during that time to swing by the Forums like we used to (and used to LIKE to do!).


Only so many hours in the day as they say.


Drop us a line direct and I promise we'll do our best to help with any issue (one of the staff is typically screening mail on the weekend too so don't wait till Monday if something pops up). Of course with the sound advice typical at places like AVS we're often not even needed (sniff ;^)


Ron
 

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Quote:
Originally posted by Ron Stimpson
(sniff ;^)
There, there...(no such thing as e-kleenex)


Seth
 

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Very unlikely, as that'll require hacking into the cylinder, and trying to get the PE amp to fit (he might as well just have the active SVS instead)


Probably leave the amp plate on the floor, on the racking.


Is the PE amp sealed though? (or can you see the components- power supply, resistors etc) I guess you'll need to place a DIY casing around the PCB area to make the unit safe.
 
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