Do you think you need a subwoofer?

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.

I think this is one of the most important threads on Audiogon for all to read and understand.

I have purchased a Velodyne DD15 (should arrive in about 4 weeks), and when funds allow I will try adding another for true stereo low freq. I'll experiment with crossing over my Dynaudio S1.4s ~80hz and see how that goes.

Questions: What is the difference between high-pass and low-pass? Also - on the DD series, there seems to be a graphic EQ as well as a parametric EQ. The parametric EQ has a Q value that can be modified. Is that parametric EQ something that I would want to fiddle with, or should I be able to accomplish everything with the more simple visual EQ? The velodyne documentation is a little light on describing what the purpose of the parametric EQ is relative to the visual EQ.

Thanks,

Todd

Dear Todd: Congratulations for your choose !!. The high-pass filter is the one that do the crossover for the frecuency range that will handle for the main speakers, example: frecuencies from 80Hz and up; and the low-pass is the filter that send the frecuency range to the sub, example: 80Hz and down.

The parametric EQ allow to perform adjustements with a specific frecuencies, that's it that the filters in a parametric EQ are variable and with a variable Q ( broad band ). In a graphic EQ the frecuencies and the Q are fixed.

Maybe you will have to use both of these EQ. You can know it when you try to do the integration to your system/room.

Regards and enjoy the music.
Raul.

What does it sound like when running strictly a subwoofer or two below 80Hz?

And what should I listen for when adjusting phase?

I finally got a decent amp for my pair of passive subs, a Samson Servo 550 (275wpc). It's a pro/live amp used in clubs/bars/etc.

Anyway, I feed my subs via a Paradigm X-30 active subwoofer crossover with line-level inputs.

I am currently feeding the X-30 directly from my cd player's "fixed" outputs and my monoblock tube amps from it's "variable" outs while rebuilding my passive transformer volume control.

Anyway, last night while playing assorted jazz, classical, and rock I would intermittently turn the volume down on my main speakers to listen strictly to the subs output.

I expected to hear distinct, clear-cut, drum strikes or the clean resonance of standup bass strings, but that isn't what I got. Everything was rather muted in a undefined way. It certainly fleshed things out when mixed in with the mains speakers, but I expected more attack, I guess.

The best description would be a line that an audio reviewer once used - the subs recreate the trailing edge of a note rather than the leading edge. More resonsce and decay than strike.

I've tried varying the x-o frequency from ~60Hz-120Hz.

Does this seem right?