Sub Output Safety Margin

[Muzykant]

Thank you so much for your time, Ed. Your insight is appreciated. Like Kurt, I would like to know if continuous loudly mixed low drones, sweeps and rumbles, often found in today's movies, pose any danger to the subs. It would also be helpful to know what would be the audible or visible signs of a sub in distress. Thanks again!

Just to clarify, although I do own six SVS subwoofers, they are in four different rooms (and two different houses). Two Ultras are in my 3100 cubic feet theater room, two SB-2000s in another similar sized room complimenting my Prime towers (now used for music, but soon to be expanded into a theater), one SB-2000 with five Prime satellites in a 1500 cubic feet bedroom (just got the setup and am loving it), and one more SB-2000 in a much larger open space used as part of a 2.1 music setup.

 

[herbu]

I bought my second Ultra over a year ago and still to this day have not driven them hard enough to get any tactile feel during movies or music.

I think "no tactile feel" is an indication you are FAR from over-driving your subs. 2 Ultras in a 3100 ft3 room can rupture your spleen w/o damaging themselves.

 

[Ed Mullen]

I don't feel any music/movie source material poses any inherent danger to a subwoofer.

With that said, there are certain movie passages which can exacerbate overdrive artifacts (e.g., port chuffing, woofer snapping/popping/farting, garbled/distorted bass, obvious deep bass compression, etc.).

Again it gets back to the clean/linear limits of the subwoofer being consistent with the room size, source material, subwoofer calibration level (i.e., amount running hot) and the overall playback level.

All subwoofer have limits, and when they are exceeded the user should either reduce the sub calibration level, reduce the master volume setting, or step-up to dual subs or a more powerful model.

The goal is to keep the subwoofer system operating linearly so it doesn't complain and doesn't compress deep bass passages, and then the system will sound/perform great. Users run into problems when they routinely ask more from the subwoofer system than it can cleanly deliver, but are unwilling or unable to add more subwoofer capability.

 

[KEW]

I don't feel any music/movie source material poses any inherent danger to a subwoofer.

With that said, there are certain movie passages which can exacerbate overdrive artifacts (e.g., port chuffing, woofer snapping/popping/farting, garbled/distorted bass, obvious deep bass compression, etc.).

Again it gets back to the clean/linear limits of the subwoofer being consistent with the room size, source material, subwoofer calibration level (i.e., amount running hot) and the overall playback level.

All subwoofer have limits, and when they are exceeded the user should either reduce the sub calibration level, reduce the master volume setting, or step-up to dual subs or a more powerful model.

The goal is to keep the subwoofer system operating linearly so it doesn't complain and doesn't compress deep bass passages, and then the system will sound/perform great. Users run into problems when they routinely ask more from the subwoofer system than it can cleanly deliver, but are unwilling or unable to add more subwoofer capability.

Thanks Ed!

As I read it, we have nothing to worry about until we start hearing sounds of the sub being over-driven.
Those sounds will be audible as "wrong" and, if we ignore them, we run the risk of damaging our subs.

Of course it should be pointed out that there may be some subs in existence which do not have the protections the products of major manufacturers like SVS do.

 

[Muzykant]

Ed, thanks again for your response. I think I will turn the system up on my next movie night and see what happens.

 

[PENG]

I myself have balanced my sub with my towers and it is at 1/4th of power it has available. Yes it gets loud on movies but I'm more worried about something falling down than the sub breaking down. I myself wouldn't run my sub at max, 3/4th if it was needed, but its not.

You cannot go by the volume dial. Depending on the input signal to the sub, you an reach its rated output even when the volume knob is at mid point.

 

[tyhjaarpa]

You cannot go by the volume dial. Depending on the input signal to the sub, you an reach its rated output even when the volume knob is at mid point.

You are correct. I wasn't thinking about running the signal hot. So after all best way is to listen your sub for sounds that don't belong there.

 

[PENG]

You are correct. I wasn't thinking about running the signal hot. So after all best way is to listen your sub for sounds that don't belong there.

I knew what you meant in the first place. I just got a little concerned that the OP may take it literally, especially when he's asking about safety margin. Theoretically he could have no safety margin at all even if the volume is set very low. AVRs and prepro's subout levels tend to vary quite a bit and I don't think you can define or tell if the signal is "hot" easily. In my case, I have to set my subs volume at or well below the 10 O'Clock position; and that's with the level trims in the negative territory so the signal is hardly "hot".

Regarding the "best way", your last sentence is totally valid at least based on Ed Mullen's SVS products. As Kurt mentioned you do have to be selective of the test material. He mentioned the introduction to "Edge of Tomorrow" so that could be suitable for such test.

Being more conservative, I don't want to push my subs to the point where I could hear sound that don't belong, not even just for a quick test. I always prefer the more complicated methods.

 

[herbu]

I think I will turn the system up on my next movie night and see what happens.

May I suggest this method...
> Do your initial speaker setup w/ Audyssey.
> Set the sub volumes using the gain on back of the subs such that your AVR shows 0dB adjustment.
> For your movie, increase the sub volumes in your AVR +3dB.
> Listen at whatever overall volume you want.
> If you don't hear any of the obviously bad things described above, you're OK.
> For your next movie, try increasing the sub volumes in your AVR to +6dB.
> Listen, and if no bad sounds, you're still OK.

I found that the Audyssey sub volume setting most favorable for music. It sounds like the bass is accurate and not overly emphasized. So for music, I leave the sub volumes in the AVR at 0dB, or simply listen in Direct.

For TV/Movies, I like enhanced bass. I usually boost the sub volumes to +6dB. We have watched many movies with hot bass and LFE... and listened very loud. The windows flex like a trampoline, the tables shake, the glass of tea skitters across the table, the chairs shake and I have to pee. So far, no damage to my subs.

My room is bigger than yours by a lot, (cathedral ceiling and "T" shaped). I have an SVS PB13Ultra and a Rythmik FV15HP. Honestly, I think if you have yet to "feel" any bass in your movies, you have a lot of available bass you're not using.

 

[Muzykant]

Thanks to everyone that answered.

herbu, thanks for your suggestions. I do not have a receiver with Audyssey capability. I have Emotiva UMC-200 (now discontinued) connected to XPA-5. It has its own room correction software, but I never used it. I calibrated the levels for speakers and subs using a digital SPL meter and UMC-200 pink noise. I set up distances using measuring tape. Subs are calibrated to sound 5db louder than speakers (as far as I remember; it has been a while). Subs' gain is set to minus 12 for each sub, sub level is at 0 on the processor.

I have not applied any equalization yet because of my old believes that it spoils the sound. However, after reading extensively on the subject, I am ready to admit that I am probably wrong about it. I am willing to give equalization a try. I just ordered UMIK-1 microphone and will download REW software. I think UMC-200 has pretty good equalization capabilities, and I will try to put them to use once I take some measurements.

 

[annunaki]

As a DIY sub enthusiast I do build in a small buffer. I usually test however with sine sweeps in advance and can identify when the limits are close.

That being said, only once in a n my 12W7 and behringer EP2500 & DCX2496 have I ever experienced a "non-linear event".

In Captain America winter soldier, there is a scene with a vending machine, just prior to it breaking the bass drops extremely low, guessing near 10hz or below, the amp clips, my lights dimmed and the sub went non-linear just as the amp goes to clipping. Scared the crap out of me. Knock on wood I have yet to damage a speaker or electronics to date.

 

[herbu]

Subs are calibrated to sound 5db louder than speakers...

I have not applied any equalization yet because of my old believes that it spoils the sound.

Calibrating your subs 5dB louder than your speakers IS equalization.
If you have 2 Ultras, a 3k ft3 room, watch movies like Edge of Tomorrow and have never gotten any tactile feel from the subs, you must listen at a very low volume.
Crank it up!!!

 

[Muzykant]

Calibrating your subs 5dB louder than your speakers IS equalization.
If you have 2 Ultras, a 3k ft3 room, watch movies like Edge of Tomorrow and have never gotten any tactile feel from the subs, you must listen at a very low volume.
Crank it up!!!

I actually don't remember if the subs are 5db louder. I remember deciding between 75 or 80dB, so I assume I calibrated to 80. I will check again when UMIK-1 gets here (any day now).

So you are saying that adjusting the gain on the subs is also considered equalization, even though the signal they are receiving is linear, with no cuts or boosts for specific frequencies? Do you mean this is equalization for the system's resulting overall sound?

You are right, I turn the volume up until the dialogue is comprehensible and stop there. Usually it sounds quieter than if the person was actually talking where the center speaker is.

 

[herbu]

So you are saying that adjusting the gain on the subs is also considered equalization

I consider boosting or attenuating any frequency, or band of frequency, equalization. Whether the response within that band is flat or not doesn't matter. You are still changing the original signal.

I turn the volume up until the dialogue is comprehensible and stop there. Usually it sounds quieter than if the person was actually talking where the center speaker is

You can probably get a good price for your Ultras on ebay or craigslist.

 

[Muzykant]

I consider boosting or attenuating any frequency, or band of frequency, equalization. Whether the response within that band is flat or not doesn't matter. You are still changing the original signal.

Interesting. I am not sure I entirely understand the relationship between the original signal and subwoofer gain dial. Which setting would preserve the original signal?

You can probably get a good price for your Ultras on ebay or craigslist.

What!! Sell my babies?!

 

[herbu]

Which setting would preserve the original signal?

The setting which, combined w/ your AVR setting, yields a sound balanced w/ your other speakers. (It is what Audyssey, YPAO, or a known input signal and SPL meter are for.)

If for a given input level, you set your other speakers to yield 70dB at your chair, your subs should be set to also provide 70dB, for that input level, at your chair. You can control your sub(s) level two places... the gain on the sub, and the sub volume control in your AVR. The two should combine to give you the desired volume at your chair, so there is not a specific "setting" for your sub gain control.

 

[Muzykant]

One thing always confused me about level matching using pink noise... Suppose, you have two speakers and a sub, and pink noise registers 75dB for each at your seat. What happens when two speakers together are playing above the crossover point? Wouldn't their combined output be 3dB or so louder than the sub above the crossover point? What happens when you use more speakers for music?

 

[herbu]

Suppose, you have two speakers and a sub, and pink noise registers 75dB for each at your seat. What happens when two speakers together are playing above the crossover point?

What happens? You hear what the sound recording engineers want you to hear. If they want something to sound like it's coming from the Left, it sounds like it's coming from the Left.

As for overall volume, that's entirely up to you and your volume control. You can balance your speakers at 75dB. Or you can balance them at 80dB, or 70dB. Either way, you are "balancing" your speakers with respect to each other, not to the level of input. YOU control the overall level w/ your volume control.

 

[Muzykant]

Okay, I now understand my question was pretty dumb. The processor probably sends combined signal from the two speakers to the sub, so stereo music playback is perfectly balanced. I did, however, notice a change in balance between subs and speakers when switching to all (5) channel stereo mode. The bass became noticeably quieter.

One thing I want to say from personal experience. Sound engineers are all different, with their own preferences and skill sets. At least, when it comes to equalization, some of them don't get it right. As a musician, I've recorded in many studios over the past 25 years. I know how my acoustic instrument sounds in real life, and only select few had the skills to preserve that sound on tape. Usually the sound was either prettified or just plain unbalanced, too sharp or too bassy, etc. Microphone placement, sensitivity, compression, reverb, and even speakers and headphones used in the studio, all have effect on the sound you hear on recording. And they can all create problems. It all depends on the sound engineer and his skills, personal preferences, and his ear.

 

[KEW]

Very true. The recording itself can be the weakest link in the chain. Compression seems to be the most ubiquitous violation these days.
We generally take the attitude that we are stuck with the quality (or lack thereof) as recorded. It would be a never ending quest if we were trying to "undo" bad recordings. You may have some success given your intimate familiarity with the correct sounds, but the controls at your disposal don't compare to what was used to muck it up and you are talking a different set of settings for every recording.