What is considered "acceptable" subwoofer frequency response?

[Saurav]

Actually, what is realistically do-able? I know this depends on an enormous number of factors, so let's simplify a few things right away - no EQ, no BFD, no room treatments or bass traps. "Normal" sized room, 15'x20'x12', normal furniture. In my case, the sub is a DIY - NHT 1259 in a roughly 3'x2'x2' sealed enclosure, completely stuffed (or looks like it, I took the driver off today to check, I didn't buyld this).

I'm sure the ultimate goal is +/- 3dB or better, but is that achievable just with position/crossover/phase? I built my crossover, so I can play with cutoff frequency, slope, and so on.

Anyway, I've been playing around with the sub's position and orientation (thinking maybe it might excite a room mode more if it fired down that room direction), and I've got it to a point where I can go from 200 Hz down to 30 Hz (I don't register anything at 20 Hz, but that's not really an issue, as this is for music only) without having to switch ranges on my RS meter, so that's a +/- 5dB, I guess. There are still some sharp swings within 10 Hz increments, so I'll experiment some more, but I would just like to get some feel for this from people who've done this much more than I have.

A couple more questions:

* The bass is totally different at different points in my room. Can I do anything about this without room treatments?

* Upper floor apartment, springy wooden floor, all wooden construction. Would more bass get transmitted to the neighbors through the structure, or the air? Should I spike the sub to the carpet, or would that just increase the amount of bass being sent to the guy downstairs? I would think that it would. Spikes on a granite slab, or anything like that? Any other suggestions? I haven't had any complaints yet, but any general advice on how to keep as much bass inside my room as possible would be most appreciated.

Thanks,

Saurav

 

[Chris Tsutsui]

I don't do it often but +/-5db on a few occasions doesn't seem that bad.
Wouldn't spikes on a slab that is on carpet defeat the purpose of spikes? How about an oil filled shock suspension for the cabinet like I have. (JK)
Keeping bass to a wooden apartment is like keeping a lie. It's going to slip out and cause damage.

I would move the sub around the room until you find the area with the largest sweet spot. Hmmm, no fine tune electronic adjustments and you are attempting to get equal SPL throughout the sound frequencies? Perhaps you'll need the "perfect" driver.
I would get speaker spikes though.. I'm no scientist but here's a little experiment I made up:
Take your palm and hit the ground hard and notice what it sounds like.
Then take a spike (like a pen or phillips screw driver) and hit the ground with the same force. Then see which one was louder... More than likely the palm or fist hitting the ground was significantly louder than the single spike. Thus -- you may conclude a sub with small spike feet will be quieter on the floor/walls than a sub with a large base that rests on the carpet.
Sound is traveled through the vibrations cause there probably isn't a tuned port between apartments.
I don't think acoustically treating the room would the wisest of options before getting an adjustable amp or equalizer.

 

[Saurav]

I don't think acoustically treating the room would the wisest of options before getting an adjustable amp or equalizer.

That's a good point. I'm using a normal plate amp which has the usual controls, plus there's another DIY crossover in the middle which works with the sub's crossover to give (what I think) should be a better match with my bookshelves.

That brings up another question - should I leave my ported bookshelves as they are, run them full-range, and use a 4th order slope on the crossover's XO to fill in the bottom? Or should I stuff the bookshelves' ports and use a 2nd order XO on the sub? The speakers go down to about 50 Hz or so. I'd rather not put an electronic XO in the main signal path, if I can avoid it. I'll probably try both eventually, but again, any general advice would be appreciated. What is the effect of stuffing a speakers' ports, other than changing the rolloff slope? Does it interfere with the design/sound above the -3dB point significantly?

 

[Richard Greene]

My experience is that +/-6dB or better is usually

(but not always) good enough so you can listen happily

without a parametric equalizer.

With a parametric equalizer you should be able to cut frequency response deviations heard at your listening position in half (at least).

However 90% of rooms I've measured exceeeded +/-6dB unless equalization was used.

Measurements made using 1/6 octave sine wave tones to fully excite bass resonances -- not pink noise or warble tones that fail to excite room bass resonances and make a pretty frequency response curve on a chart.

 

[Saurav]

I have sine wave tones that I burnt onto a CD-ROM. Not exactly 1/6 octave, but 20Hz, then 5Hz increments from 30Hz to 80Hz, then bigger increments to 200Hz.

However 90% of rooms I've measured exceeeded +/-6dB unless equalization was used.

And did that go up and down with fairly small frequency increments? In my case, It swings back and forth about 3 or 4 times in that frequency range. I know a nice smooth single hump or dip in the middle would be much nicer (and much easier to take care of), but that's not what's happening.

 

[Rich Kraus]

since you have the software to do it, maby you might consider what i did:

make a test disc with tones 10hz-90hz one hz spacing. "waste" tracks 1-9 with pink noise or whatever, and use tracks 10-up for tones. that way test tone= track number for easy refrence. map the response to each tone on graph paper and youll really know whats going on.

its tedious as all get out (and the tones made my wife nausious, untill she said enough of that and went shopping...) but it gets the best map of your problem areas.

my worst spike was at 37 hz if i remember correclly, and i would have never hit this using anything else but one hz spacing.

then give up and buy a parametric, its worth the trouble once you get it set up. i use the ashly pqx-571 and i like it, but i think im the only one here that dosnt use the BFD.

oh and spikes? id use spikes on any surface the speaker could slide on, like carpet. this plants the enclosure to the floor so all the cones energy goes to moving the air, not the cabinet.

oh and whats dooable? i dont know but mine is +/- 2 dB 21-78hz in the sweet spot. (now move four or five feet away from the spot, well thats another story...)

 

[Saurav]

oh and whats dooable? i dont know but mine is +/- 2 dB 21-78hz in the sweet spot.

Was that with or without the EQ? I'm just curious to know what can be achieved without throwing an EQ or bass traps into the picture.

 

[Robert_Gaither]

The only way to get the best overall performance is to spike, eq, and treat. Odds are if you don't you will listen to your setup louder (to get the same effect) and will be more irritating to the neighbor anyway (trust me, the peaks technically is more noticible to both you and your neighbor and taming them in effect is like lowering the volume at that freq).

Depending on how loud you listen depends on whether you should filter the bass from your mains, since you state you live in an apartment, I would only run the mains full and bring the sub up to fill if your system has that capability. Sealing the ports on your main is a subjective thing and if you hear the sub intrude on vocals then I would seal them if it helps if it were me but otherwise I'd leave it as is. Definite eq only the sub as it is the main one that will be affected the most by room modes. If you don't want to treat the room for bass, I would at the least get rid of first order reflection for the mains as this will improve almost all facets of your mains performance the most.

 

[Rich Kraus]

thats with the eq. withought i had one ~16db spike and one ~8db spike. the big one centered at ~37hz the smaller one in the mid 40's. (i cant remember the actual centerpoints or values, but my guesses are close enough for this discussion)

parmetric EQing on a sub has to be the best bang for the buck subwoofer upgrade available. id recomened it to anyone, regardless of what sub they run, but the more capible your sub is, the more it makes sence to make the most of it.

i tend to agree that you should make it sound as good as possible, and avoid complaints by modualting volume when they are home. my big peak came through loud and clear even when everything else was pretty calm, find and fix the peaks and youll go a long way twards pleasing all involved.

 

[Saurav]

Thanks. I had a situation similar to yours, where I had to change the SPL meter's range up and down in order to register some of the frequencies. Now, it stays within the same range setting, so that's a start. I guess I'll look into EQs once I'm done with some of my other pending projects.

 

[Saurav]

If you don't want to treat the room for bass, I would at the least get rid of first order reflection for the mains as this will improve almost all facets of your mains performance the most.

That's kinda sorta taken care of, with the furniture arrangement and things like that.