Do you think you need a subwoofer?

Skushino - Dave Whiner's ModeCalc shows that I have 2 room modes at 70Hz, 3 at 141Hz, 2 at 211Hz, 3 at 282Hz, and 2 at 353Hz.

Running the IM-Bens w/o the subs is no real problem except when a sustained note(s) hit that 70Hz fundamental mode and it's harmonics(?) 211/282/353. Especially the 282Hz notes, seems like there is a 6+dB jump in output with distortion. Noticable, annoying because everything else is so pure and clean, but not ehough to destroy the music.

So far, I've found that lower Marimba/Xylophone/Vibraphone keys really overload the room because of their sustained resonance and decay. Cello can, but i haven't found any works that have hit that long note yet.

I've been looking at pro sound crossovers(Rane) or even some of the digital crossovers(Behringer, etc.) this last week.

But, the IM-Ben's are designed to run fullrange without any crossover at all on the 6.5" Fostex FE-168 Sigma drivers. The only components used (I think) is an adjustable 12dB/octave high-pass filter for the Fostex T-900A supertweeter >16kHz.

I'm a little leery of introducing any X-O into the mix even though all the room modes fall in teh IM-Bens range.

As for the subs, my inital experiments with both subs added into the mix have been pretty bad. I don't have a dedcated sub amp(s) yet, so I've been trying to use some solid state integrated amps/receiver that I have lying around. One's a Audio Refinement Complete(50wpc) and the other is a Harmon Kardon AVR 20 II (60 wpc).

Needless to say, it sucks - flabby, mushy, unrecognizable bass. The other problem is that the Paradigm X-30 sub x-over that I have is outputting noticable distortion/breakup.

Currently, I have the Bailey's in between the IM-Bens(10 ft. apart) facing directly forward. Terry Cain suggested starting with this position because it provides the most bass energy.But, the subs do seriously the room even at low volume - wall panels start to buzz/rattle and there is some extremely low frequency energy being generated.

I need to try positioning the subs at various angles inwards, then outwards to see whether that reduces some interactions. After that, I'll move them outside the main speakers at various angles to see how that works.

Unfortuantely, I cannot locate the subs in the corners because the living room side that the speakers are on is open and overlooks my dining room below. The rear wall is 5 feet behind the railing.

As Raul has pointed out, dialing the sub/mains intergration in perfectly could take months.

Raul -

***Btw, I choose ( too ) 1st order filter for the high-pass on my system. This high-pass filter is inside of my 20.6s. It work for me.***

I will first try placing caps before my amp inputs, for easy changes. I like the idea of permanently locating the filter inside the amp.

***I think there are no rules here other than: test, test and more tests***

My satellites go to ~80Hz. My concern is that a 1st order crossover accomplishes too little for my goals:

1) minimize overlap between sub and sats (only 6dB down at 40Hz and 12dB down at 20Hz!!!)
2) eliminate LF signal from amp, for less distortion

I will test, test, and test. How did you deal with the overlap?

scott

Darkmoebius - Like you, I am on the steep part of the learning curve. Here is an article about sub integration I found interesting:

Getting the bass right

Unlike Terry, the author advocates many reasons for corner placement of subs, to cancel nodes. In any case, you might enjoy the article. Let me know your results if you try placing the subs outside your mains.

scott

Skushino - Fantastic article!!!!!

I didn't get the concepts the first time I read it, but the next morning I went through it again using the Excel Room Mode Calculator spreadsheet with my room measurements and everything made sense.

First of all, I had to re-measure my room because I realized that I was using a false length distance AND I got my room width wrong. I had been using 16'x20'x8', when in reality my room is 15'x23'10"x8'. Length-wise, I hadn't accounted for the distance that the rear wall that extends back over the dining room.

Then, using the Room Mode Spreadsheet, I was able to find the proper 12' mid-length seating position at the 1st & 3rd(71Hz/24Hz) order nulls. Then, position the speakers at the 2nd order 5.75'(47Hz) null. That leaves me with the lone 4th order 94Hz length mode.

Width-wise, sitting dead center of the room puts me at the nulls of the 1st & 3rd (38/113Hz) modes. I can then put the mains and subs exactly on the the 2nd & 4th nulls (75/151Hz) at 2ft & 3.75ft from the side walls. That looks to provide almost complete cancellation of the the width problems.

So, by experimenting with speaker & seating placement< i should be able to do away with most of problem bands except the single 94Hz legth mode. Although, I an sure I can find a way to dampen that one, too.

Unfortunately, I won't get a chance to try any of this out until next Monday because my brother and his wife are visiting with their 2 year old. Everything gets packed away from Natasha's curious fingers.

Screenshoot of my RoomModeCalc ouput.

Unfortunately, in the length mode, the closest my speakers can be to the rear wall is the 2nd order 47Hz null(5.75ft). Which makes sitting at te preferred mid-room 1st & 3rd null (12 ft) serious near field listening six feet from the speakers. That just doesn't work for me.

But, it is possible to sit right in between the 3rd & 4th nulls at 19.75 ft and 20.75 ft. Both the 71Hz and 95Hz modes should be as close to their nulls as possible.

On the other hand, the 24Hz mode will be at it's absolute worst. Since I don't have an amp for my subwoofers yet, and the main IM-Ben's only go to 40Hz, this shouldn't be a problem. When I do have an amp, EQ'ing that mode down should be no problem.

I kind of like that solution because I didn't want to add any crossover into my main fullrange signal outside of it's stock 12dB/octave high pass filter for the super tweeter.