[Vosper]

I have built a tactile couch using a couple of Aura Interactors stripped and bolted into the bottom. I have it running from the subwoofer out of my Denon HT receiver. Problem is, the sub out is set to crossover at 80hz, and I only want the tactiles to go from around 30hz and down. Currently they make some rather bad noises above that frequency, and I'd prefer the sub to deal with that. Is there something that I can put in-line in order to cutoff the frequencies above 30hz? I am looking for something cheapish.

 

[rickcr42]

sure man, just add a passive low pass filter inline with the transducers set at 30hz (though that seems too low to me,i would go at 50-60hz).

Also you might consider a high pass filter at 20hz.the "bad sound' you are experiencing might just be the transducer bveing overdriven at a frequrncy too low for it to reproduce,a common problem with woofers.

 

[ooheadsoo]

Cheapest thing I can think of: http://www.partsexpress.com/pe/showd...number=266-250

But I don't know how well it will work at first order slopes.

 

[Vosper]

Quote:

Originally Posted by rickcr42 sure man, just add a passive low pass filter inline with the transducers set at 30hz (though that seems too low to me,i would go at 50-60hz). Also you might consider a high pass filter at 20hz.the "bad sound' you are experiencing might just be the transducer bveing overdriven at a frequrncy too low for it to reproduce,a common problem with woofers.

OK, that sounds good. If I were to use a high-pass, would this do? Could I just attach it inline with this?

 

[sluggo]

Do the sofa shakers have their own amp or are they sharing an amp with something else? Reason I ask, it's going to be very expensive to make a passive half-octave bandpass filter in the 20-30Hz range if it has to pass speaker current.

The Harrison FMOD is only for line level signals. It will not work on the output of an amp. And it is low-pass only, it will not filter frequencies below it's stated cutoff (50 Hz), so if you want to limit the shakers to the 20-50 Hz range you will need something else.

Something like this http://cgi.ebay.com/ws/eBayISAPI.dll...729363430&rd=1
would do the job, and for only 99 cents =)

 

[Vosper]

Quote:

Originally Posted by sluggo Do the sofa shakers have their own amp or are they sharing an amp with something else? Reason I ask, it's going to be very expensive to make a passive half-octave bandpass filter in the 20-30Hz range if it has to pass speaker current.

Well the transducers have their own amplifiers, the ones that came with them. At the moment I am splitting the sub-out from the receiver to the sub and to the couch. Off the top of my head I'd say it was line-level but I'm not sure, is this not likely?

Quote:

The Harrison FMOD is only for line level signals. It will not work on the output of an amp. And it is low-pass only, it will not filter frequencies below it's stated cutoff (50 Hz), so if you want to limit the shakers to the 20-50 Hz range you will need something else.

So I can't put two Harrison FMOD's inline (a highpass and lowpass) to get the required frequencies?

Quote:

Something like this http://cgi.ebay.com/ws/eBayISAPI.dll...729363430&rd=1 would do the job, and for only 99 cents =)

I didn't think equalisers like that would be adjustable to filter everything but 20-50hz?

 

[sluggo]

Quote:

Originally Posted by Vosper Well the transducers have their own amplifiers, the ones that came with them. At the moment I am splitting the sub-out from the receiver to the sub and to the couch. Off the top of my head I'd say it was line-level but I'm not sure, is this not likely?

Aye, the sub-out will be a standard line-level output. I must have missed that the first time, sorry. Take a look in your receiver's manual for the frequency range of this output, as it may already be filtered below 20 Hz.

Quote:

Originally Posted by Vosper So I can't put two Harrison FMOD's inline (a highpass and lowpass) to get the required frequencies?

Well, you can, but there's a couple of problems with doing it that way. The big problem is with the interaction between the filters. These filters are 12dB per octave only when looking into the high impedance input of an amp. If you have the highpass filter and the lowpass filter back to back, then the output of the first filter "sees" the input of the second filter rather than a nice stiff 20k input. This will change the operation of the filter, and you will not get the expected roll-off. You could put them back to back if you isolate them from one another with a resistive element, but that's more work. (Edit: I see Harrison sells 3dB attenuators in the same format for this sort of thing).

Another (smaller) problem is that even if the first problem didn't exist, there is a fair amount of overlap in the frequency range. A 12db/octave 50Hz low pass filter is going to be down about 1dB at 25Hz. The 20Hz high pass is going to be down about 1dB at 40 Hz. Sum the two filter responses and you will be down perhaps 3dB across the board between 20 and 50Hz. Not a big deal for this situation since the first problem will be much worse, but I felt it needed mentioning.

And, there's the cost of the two filters. (Edit: plus attenuators)

Quote:

Originally Posted by Vosper I didn't think equalisers like that would be adjustable to filter everything but 20-50hz?

If you feed the linked equalizer from your sub-out, you can make changes (gain/cut) at 31.5 Hz and 63 Hz. Turn 63 Hz all the way down, leave 31.5 flat, and play with the subsonic filter (not sure what it's high pass is set to). There are other types of equalizers (usually called parametric equalizers) that allow you to set the center frequency, the slope, and the gain/cut for up to 5 or more bands. These tend to be more expensive, but I'm sure there are some cheap used ones out there.

If you're handy with a soldering iron, a dual op amp and some R's and C's will do exactly what you want for under $5.

 

[rickcr42]

couple of things :

1- the Fmods should be fine even though you could do it cheaper with a tiny box and some parts.But DIY is not for everyone.

2-even if you tap the output from an amp a simple two resitor matrix (four for stereo) will convert the speaker level signal to a line level signal (or you can purchase them)

3-always a pretty good idea to have a bottom end cutoff at some point,especially with ported bass cabinets and /or if you have a vinyl playback system in house.The amount of power wasted and the potential for woofer damage is something i like to try and avoid so mine is always "in system" .
You would see this more often if not for the "spec monsters" who would rather have a ruler flat frequency graph and perfect square waves over common sense and system protection.The people get what they want and just like paying for a $500 front panel and $200 knobs wrapped around a $50 circuit filters and tone controls have gone the way of the dinosaur in high end gear.

Of course if you want filters and tone controls they will be more than happy to sell them to you at a premium cost ! Pretty face plate and knobs included

****edit****

may be useful-

http://www.valvediy.com/pllcpg1.html