Sub Output Safety Margin

[Muzykant]

Just curious, do you guys leave any safety margin when you use your subs and do you ever crank them up all the way. In subwoofer discussions I often see decibel numbers for peak output at given range thrown around. Those indicate the performance limits, like car's top speed, but do you guys ever reach those in real life?

I heard that prolonged constant signal, such as sine wave, can overheat the voice coil and cause permanent damage. Do you ever worry about such things? How do you, for example, deal with the scene in Interstellar where the main character is being sucked into the black hole? Or the beginning tones of Edge of Tomorrow? Do you turn the volume down during such scenes or leave it to your subs to sort it out?

I myself lately have been a bit paranoid about these things. I constantly get up and check on my subs' excursion to make sure it's never past 1 inch both ways, even during the loudest (and lowest) peaks. I know my subs' peak excursion is about 50 mm, so keeping it at below one inch both ways seems safe to me. Such phobia is driving me crazy and prevents me from enjoying the content, be it music or movies.

Anyway, what do you guys do? How close do you get to the limit?

 

[slipperybidness]

When a sub driver hits its excursion limits, you know it! It is a hideous sound. Trust me, if you hear it, you will be making a mad dash to the sub to turn it down.

The good news is that doing that 1 time likely won't kill the sub. So you are probably being over protective of your sub.

Many subs have built in limiters too. That is a safe way to handle these concerns.

 

[Muzykant]

Yes, my subs have generally been touted as indestructible because of the DSP-controlled amplifiers. But while DSP prevents overexcursion, does it prevent overheating?

 

[KEW]

The best answer is to contact the manufacturer . Chances are they do have thermal overload protection on the unit , but they are the only ones that would know for sure. If you told us the model of your sub we might have a better idea.
Read some of Josh Riccis reviews and often he will talk about how the sub behaves as he drives it past its limits.
I believe the better design subs of today are pretty much idiot proof as in you cannot hurt them if you try . They would just shut off first.

 

[Muzykant]

Thanks for your replies. My subs are SVS SB13-Ultra (x2) and SB-2000 (multiples).

But I was also curious to know how the forum members drive their subs in relation to performance limits.

 

[KEW]

Well, my subs (Rythmik E15HP) were set to 12 oclock when I ran audyssey, then I had to turn them down more for audyssey to run, so I am being fat, dumb, and happy on the assumption that I am not really pushing their limits.
For HT, I usually bump the subs up 6dB which probably loses the safety margin, and I must admit, every time I run something extreme like the intro to Edge of Tomorrrow I find my a$$hole draws up tight in apprehension that something might break (be it a sub or something vibrating off of a shelf).

I don't think you need to be too concerned, but I wouldn't trust me on that, nor should you!
It is a very good question and seems like more sub companies would address it!

Get a hold of Ed Mullen at SVS, tell him you are not enjoying your subs for fear of overloading them, I am betting he will tell you about safety measures in the design and what to listen for if you actually do overload them and how much of a risk there really is.

Please post here what info he provides!

 

[ImcLoud]

I think my subs are around 1/2 way, once in a while for demo purposes I will max them out, but I dont think its anything that will hurt them..

 

[tyhjaarpa]

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.

 

[Muzykant]

Thank you for your replies.

I did, in fact, contact Ed Mullen a few months ago. My question was about my Ultras' perceived output in the lower frequencies. I thought a good way for me to describe what I was hearing in relation to the subs' cone movement at different frequencies was to reference different pitch sine waves. And that's when Ed warned me about the dangers of playing prolonged sine waves. He also said not to worry about output when playing normal content.

But sine waves, or material like prolonged high volume rumble, can be found in both music and movies. So I am still not 100% sure what the safe level is.

 

[markw]

What he's saying is that under normal use with the material it was designed to reproduce at normal listening levels you'll be fine. Just don't connect a sine wave generator, which generates pure sine waves, with a powerful amp to it and try to push it to it's limits.

 

[Muzykant]

Thank you, Mark. I wish for someone to define "normal listening levels" for the "material it was designed to reproduce". Is it anything before the amp's compression starts to kick in? For how long can you safely play the material with heavy low bass content at the higher end of the "normal listening levels"?

To make an analogy with cars, mine makes most power at 8500 rpm and redlines at 9000 rpm, but fuel cut-off is 500 rpm higher. When I want to accelerate hard I shift between 8500 and 9000, knowing that I have a few more revs before absolute limit is reached. While the car is designed to accommodate such high shifts, what about keeping that redline for extended period of time?

 

[markw]

Well, if you keep the revs in the redline for a period of time, you'll blow the engine. That's why they have the redline.: To keep idiots from blowing engines. Of course, some will ignore that to their detriment.

It looks like ypu'll have to sacrifice a sub in order to determine where it's failure point is. ...or was.

 

[Muzykant]

Nah, I am too careful to do that. It was just a theoretical analogy.

 

[KEW]

Maybe call Ed again and ask him specifically about something like the intro to Edge of Tomorrow.

Honestly, I look at it like this: There are many, many guys out there who are all about cranking it to show off, running at stupid extremes, yet we hear very little about blown subs (and many of these guys would brag about blowing their subs!).
So, I think they truly are pretty idiot -proof!

 

[Muzykant]

Thanks, Kurt. I don't want to bother Ed too much. He probably has too much on his hands already. Maybe I will shoot him another e-mail at some point.

I feel I have not been pushing my subs enough for the fear of breaking something. 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.

 

[KEW]

I feel I have not been pushing my subs enough for the fear of breaking something. 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'm sure you are right!

From Josh Ricci's Databass entry for the sb13 ultra:

As expected from SVS this is another bulletproof and solidly performing unit. It offers quite a bit of output from a unit this size and is very well protected.

You can look at the long term output compression sweeps for your subs. If you can find a good explanation of this test and get a good SPL meter, you may have a good reference. Ricci is pushing the sub beyond it's ability and measuring where that limit is. Again, Ed should be able to help interpret the testing. You have bought 4 subs from SVS. You should not feel the least bit hesitant to take advantage of his expertise! You've paid for some premium gear, you should be able to fully enjoy it.

The long term output compression sweeps for the SB13U indicate good tracking of the output with negligible compression through the 105dB nominal sweep. The next two increases in level to the 110dB and 115dB nominal levels trigger heavy compression in the deep bass centered near 23Hz. During the 115dB sweep the SB13U is compressing full bandwidth and is out of headroom. It reaches levels over 110dB above 40Hz and about 97dB at 20Hz which is pretty solid for a subwoofer of this size. The SB13U also has good distortion performance with THD not getting out of hand in the deep bass until the subwoofer is driven close to its limits. When driven very hard the distortion remains controlled and well behaved in the top of the bass range where the distortion is dominated by the 2nd harmonic. In the deep bass the 3rd harmonic dominates as usual.

 

[Muzykant]

Awesome, thanks Kurt! I know, I also spoke to Ed on the phone one time. I actually own 6 subs and 7 speakers from SVS, all bought directly from them. I really like the company!

 

[KEW]

I called SVS and let them know about this thread. They plan to post here!

You have to love their CS!!!

 

[Ed Mullen]

Hi guys -

There are different schools of thought and design philosophies on limiter/compressor settings as it relates to the ability to push the subwoofer into audible overdrive artifacts.

It would be easy to completely eliminate any overdrive artifacts, but that would typically leave too much dynamic headroom on the table. Conversely, the limiter/compressor shouldn’t be set so loosely that it allows the subwoofer to damage itself via mechanical driver failure or amp failure.

Generally the best compromise allows some mild overdrive artifacts when the subwoofer is pushed beyond its linear/uncompressed limits, to let the user know the subwoofer is being over-driven.

If the user isn’t given any audible overdrive cues, he may simply keep increasing the overall system level and experience severe output compression, which robs the presentation of deep bass dynamics and realism – which is not an ideal situation either.

In the end, if the customer’s overall playback level, preference for running the sub channel hot, source material and room size are inconsistent with the clean/linear limits of the subwoofer model in question, the customer should be aware of this (via a combination of subjective output compression and/or mild overdrive artifacts) so he can make a decision to either reduce the sub channel level and/or master volume, or simply upgrade to a more powerful model or duals, etc.

Regarding sine waves in specific, no home audio subwoofer is designed to handle continuous sine wave playback at high levels - and this practice is considered abusive. There is no rest period for the voice coil, and eventually it can cause thermally related failure of the voice coil insulation and/or former adhesives.

Our voice coil assemblies are quite durable - for example Josh has never smoked one even with the very challenging reverse FR sweeps. But they do have thermal limits which can eventually be exceeded if the sine wave is played for a sufficiently long period at drive level - which is why we don't advise this practice by our customers.

The exception would be low SPL (75-80 dB in-room) test tones for a few seconds each for the purposes of manually plotting FR - that is fine. But with programs like REW and gear like the UMIK-1 - manually plotting the FR is basically a thing of the past.

 

[KEW]

Ed, does the introduction to "Edge of Tomorrow" present any concern to you as being a danger to subs?
The OP here has a pair of SB13-Ultras and multiple SB2000's.