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Old 11th June 2009, 06:28 AM   #1
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Default Amplifier + Rumble Filters

I have manged to get my hands on a NHT SW2Si Passive subwoofer. I was thinking of using the "sub out" of my Harman Kardon AVR7000 receiver into a Behringer A500 power amp to drive the sub. I don't believe that the A500 has a rumble filter and have no idea if the receiver has one built in [I doubt it]. In reality do I actually need a rumble filter? Specs for the sub are 1 x 10" driver in vented alignament, response is listed at 27Hz to 500Hz. I have no idea what the port is tuned to.

The manual for the sub says "The SW2Si Subwoofer is designed for use with an external crossover and a monaural amplifier. The SW2Si does not have an internal crossover, so it should not be connected to any other amplifier or integrated amplifier unless it has a low-pass filter. Using the SW2Si without a low-pass filter will not damage it, however the resulting sound will be undesirable."

Obviously the receiver has an adjustble crossover [low pass?] to set the frequency at which it starts giving sound to the sub.

Alternatively I could use an o-Audio Bash amp and make it into a powered sub or is there a simple way to add a rumble filter.
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Old 11th June 2009, 01:51 PM   #2
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Is this for home theater? if so i would have thought that "Rumble" was an important part of the LFE.

You could use a large value capacitor bank to exclude infrasonic information, but large values cost large dollars ( I know -I've done it )

Was this the unit on e*** Australia last week?

What I think they mean in the instruction are that the driver has bad break-up noise when it reproduces hiher frequencies; but I could be wrong
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Old 11th June 2009, 01:58 PM   #3
jbell is offline jbell  United States
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I've got the same 10" sw2 sub in my living room, great jazz sub. However I have the matching nht amp that has a high pass 'rumble filter' as well as the adjustable cross over 'low pass' filter.

For your set up, be careful if you don't have a 25hz high pass rumble filter watching movies with below 25hz LFE content. If you want a cheap amp that will match well, (although there is shipping....) and has high and low pass filters, jack hidley has a great plate amp that's dirt cheap, and has schematics on how to change the rumble filter to your liking. (have to use a soldering iron) http://home.comcast.net/~jhidley/ However, you may find that the native 29hz filter to be to your liking.

The best output I've found from this sub is firing into a corner, oriented like this.
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File Type: jpg sub-corner.jpg (4.9 KB, 180 views)
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Old 11th June 2009, 11:50 PM   #4
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I will use the sub primarily for home theatre duties but that's not to say it will never be used for music either. I have plans to build a sub [was thinking Shiva with 500w o-audio bash - sealed] but am always on the lookoout for bargains. I saw this sub and a work collegue highly recomended it [he used to have one] so I thought it would be a good interim for the time being... yes it was the one on e*** Aus last week. For the money I don't think I could have got or built anything better.

"Is this for home theater? if so i would have thought that "Rumble" was an important part of the LFE" - Do you mean that yes I sould include the filter or it would already be part of the LFE channel of my receiver?

As I will be looking to DIY my own sub in the future, I would prefer to purchase an amp that I can use for that project too. Hence the Bash amp or Behringer. Is there a simple diy rumble filter that I can purchase [or ready made]? I could try the huge capacitor bank option as I have quite a number of capacitors [+25 10,000uf 35V] left over from a chip amp that I could utilize. I have already looked at the filters from http://sound.westhost.com/project99.htm which could be an option. I am fine with soldering and building circuits etc. Or if I am carefull can I do without it?
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Old 12th June 2009, 12:55 AM   #5
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XO caps are usually non-polarized
Rebuild of old box and driver

Have a look at the picture of the capacitor bank
100V NP rat-tails cost $145-

What i meant about rumble was that LF sound effects often included VLF ( infrasonic ) information and if being used for HT the speaker needs to be able to reproduce as much of that LF as possible.
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Old 12th June 2009, 01:11 AM   #6
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Are these the type of caps that you are talking about http://jaycar.com.au/productView.asp...T&SUBCATID=877

Whats the formula for working out the amount of capacitance vs cutoff frequency?

Could you not use an electrolytic cap with a high quality snubber / bypass. I have read about this being done on crossovers before. I would have thought that the quality of components wouldnt matter as much with a sub given the low frequency.
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Old 12th June 2009, 07:59 AM   #7
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They are what I used.
The formulas are in the "Cookbook"
But the cookbook assumes you use a box that gives a Qtc of 1.1

page 46 of 6th edition For sealed boxes

C= 0.234/Re * Fc

where Re is the nominal impedance of the driver.
It says in the cookbook that this works best with drivers having a high Qms Which Kicker subwoofers do.

The values are big; for my sealed box the filter bank was 1750uF for an aproximate cut at about 16Hz.
But I then put the woofer in a bigger box, what that did to the cutoff frequency and boost I don't know.

but the general formula to determine values is

C = 150000 / F R where R is actual impedance
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Old 17th June 2009, 07:20 AM   #8
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Just out of interest, does anybody know the Ts specs of the 10" driver used in the SW2Si sub?
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Old 22nd June 2009, 04:07 AM   #9
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I hooked up the SW2Si sub over the weekend. I am currently only using my receiver in stereo mode so could easily use the centre channel amp as the sub amp... works a treat. Initial impressions were mixed. There is no doubt that this is a quality sub, tight and musical, not boomy at all. It integrated pretty seamlessly with my mains right from the beginning. The system didnít really sound much different with the sub on or off. My mains do reach pretty low -3dB 43 Hz I think. The lowest crossover frequency setting my receiver is 80Hz which is higher than I would have liked. There was more obvious low end extension with some music and little with others. The main difference was in the soundstage and depth. This changed quite a bit when comparing with and without sub. I think the soundstage was much wider and the mains seemed to disappear more with the sub on, and less of a sweet spot for listening. Because I have been listening for so long without a sub I am unsure if I actually like it better or not. Without the sub the mains were more forward and direct... itís kind of hard to describe.

Only noticed on one track where there must have been some subsonic info as the sub was wobbling a little. Didn't feel like I need the rumble filter for audio tho at moderate listening levels anyway... will have to see for movies.
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