[gkinberg]

Hi Jim and circle members. I have SongTowers with dome tweeter in a rather large room. My listening room is open to two hallways, kitchen and dining room. In all, at least 6800 cubic feet. My songtowers can't really fill it with bass frequency. Therefore I am considering getting a sub (or possibly two). I'd like the sub to handle around 80 Hz and below. So how do I shrink my Songtowers to roll off around 80 Hz? Unfortunately this may involve some sort of external crossover but I'd like input from the experts. Current chain is audio PC to Benchmark DAC USB version to Sonic Frontiers L2 to McIntosh MC7106.

Thanks, Garth

[Austin08]

You will need something like dsp2.0, minidsp.....or purchase a sub which has HP & LP filters. I am sure other  circle member will have a better suggestion.

[dmatt]

You have a preamp to amp connection between your 2L and your McIntosh amp so you could install an inline high-pass filter between the output of the preamp and the input of the main amp.  That would reduce the frequency response going to your Salks.  To get the signal to the subwoofer(s), you would use the second output from the 2L (it conveniently has two) straight to the subwoofer input.

The inline filter could be a simple first order filter consisting of just a capacitor in series with the hot lead from the preamp output.  That would roll off the frequency response of the main speakers by 6 dB per octave.  The value of the capacitor is a function of the input impedance of your main amp and the desired crossover frequency.  There is a discussion about this type of inline filter in the following thread:
http://www.audiocircle.com/index.php?topic=114608.20

You can use the following calculator if you know the amp input impedance and the crossover frequency:
http://www.the12volt.com/caraudio/crosscalc.asp#ccc
For instance, if your amp's input impedance were 20K ohms and you wanted an 80Hz crossover, you would use a capacitor with a value of  .09947 ufd.

Putting a filter between the preamp and amp is basically the approach taken with the Vandersteen 5A speakers and also with their 2wq subwoofers.

Nice speakers you have, by the way.

[TJHUB]

I use FMOD filters from Parts Express for my HT2-TLs with good success.  They are transparent, inexpensive, and don't require additional interconnects.  You just put them on the inputs of your amp, and you're all set.  They are the same type of thing dmatt posted about.

You do need to size them correctly based upon your amp input impedance.  For example, I use 50Hz FMODs on my Odyssey amps that actually work more like 70Hz.  Here is a simple guide:

A 50Hz high-pass FMOD is:

50Hz when the amp impedance is 97k ohms or higher
70Hz when the amp impedance is = 22k ohms
100Hz when the amp impedance is 10k ohms or less

[martyo]

I use FMOD filters from Parts Express for my HT2-TLs with good success.  They are transparent, inexpensive, and don't require additional interconnects.  You just put them on the inputs of your amp, and you're all set.  They are the same type of thing dmatt posted about.

You do need to size them correctly based upon your amp input impedance.  For example, I use 50Hz FMODs on my Odyssey amps that actually work more like 70Hz.  Here is a simple guide:

A 50Hz high-pass FMOD is:

50Hz when the amp impedance is 97k ohms or higher
70Hz when the amp impedance is = 22k ohms
100Hz when the amp impedance is 10k ohms or less

Do you notice an improvement with the midrange being that the drivers are doing "double duty" with the bass and mids?

[Nuance]

I use FMOD filters from Parts Express for my HT2-TLs with good success.  They are transparent, inexpensive, and don't require additional interconnects.  You just put them on the inputs of your amp, and you're all set.  They are the same type of thing dmatt posted about.

You do need to size them correctly based upon your amp input impedance.  For example, I use 50Hz FMODs on my Odyssey amps that actually work more like 70Hz.  Here is a simple guide:

A 50Hz high-pass FMOD is:

50Hz when the amp impedance is 97k ohms or higher
70Hz when the amp impedance is = 22k ohms
100Hz when the amp impedance is 10k ohms or less

^ This is what I'd do, for what it's worth.  I've heard the FMODs at work in Terry's system, and they do what they are supposed to and don't seem to effect the signal chain negatively.

[Carl V]

what would you guys do if you wanted to roll them off a bit higher up say 125Hz?
assuming good subs(2) placed well....and the ability to EQ?

[Atlplasma]

I have the SongTowers with the ribbon tweeter and an M&K sub. I listen to music using a Dodd buffer and a couple of Hypex mono blocks. To get base to the sub, I use an M&K low pass filter. I found that I preferred to run my speaker full range. To do that, I splitt the signal out of the preamp so the sub gets 80 hz and below and the Salks run full range.

[TJHUB]

Do you notice an improvement with the midrange being that the drivers are doing "double duty" with the bass and mids?

Absolutely yes!  I can easily hear it, and so have others in their own systems.  It makes sense that removing the lowest frequencies from the driver also lowers the distortion.  The bass I get from my subs is MUCH cleaner than running the HT2-TLs full range as well.  Win-win.

[TJHUB]

what would you guys do if you wanted to roll them off a bit higher up say 125Hz?
assuming good subs(2) placed well....and the ability to EQ?

There are many high-pass frequencies to choose from.  Just know that not many subs sound good over 100hz.  You have to have a good one for that.

[Saturn94]

Absolutely yes!  I can easily hear it, and so have others in their own systems.  It makes sense that removing the lowest frequencies from the driver also lowers the distortion.  The bass I get from my subs is MUCH cleaner than running the HT2-TLs full range as well.  Win-win.

+1

Same experience here. 

[gkinberg]

Thank you all so much for your great and detailed responses. My amp input impedance is 20K and I assume that I will want to roll off around 80 hz so the specific ones you guys mentioned should work well. I may have more questions before I actually purchase the resistors or filters.

So far as the sub goes I will mostly choose one of the Rythmik offerings. Due to my room size I am considering the F25; the duel 15 in model. Hypothetically, If I purchase this in kit format, does anyone have a feeling how much a handyman or wood worker "should" charge me to assemble the sub for me?

Would there be any advantage or disadvantage to running the sub off of my benchmark DAC second analog outputs as oposed to my Pre's?

Thanks again, Garth

[gkinberg]

TJHUB,

The FMOD High pass filters that you suggested are a 12 dB/octave slope which is a 2nd order crossover correct? I was thinking about a 6 dB or 1st order XO because I thought that 1st order had less phase issues (points of inflection in the phase curve). Am I right in this or is it a non issue and I'm just being a nervous nelly?

Thanks, Garth

[TJHUB]

TJHUB,

The FMOD High pass filters that you suggested are a 12 dB/octave slope which is a 2nd order crossover correct? I was thinking about a 6 dB or 1st order XO because I thought that 1st order had less phase issues (points of inflection in the phase curve). Am I right in this or is it a non issue and I'm just being a nervous nelly?

Thanks, Garth

Just try them. They are cheap and have a 45 day return policy.