Film-Tech Forum ARCHIVE: Adding subwoofers to surround speakers

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Posted by Thomas Jonsson (Member # 1902) on 11-03-2016, 03:33 PM:

Dolby Atmos uses subwoofers for the surround sound. Is it a good or bad idea to do this with Dolby 5.1 or 7.1? Has anyone tried this? If so, did it improve the sound or was it a waste of money?

Thomas

Posted by Pete Naples (Member # 761) on 11-03-2016, 03:52 PM:

It's not a new, nor a bad idea. Predates Atmos by many decades. Most common surround loudspeakers don't have great bass response, so adding subwoofers on the surround channels makes a lot of sense.

Most processors don't facilitate this, so you'd need crossovers on the surround outputs for bass management. The more configurable DSP based processors can do this out of the box.

Posted by Marco Giustini (Member # 4544) on 11-03-2016, 05:05 PM:

Never a bad idea to add subs [Smile]

but a 5.1/7.1 track is mixed using cinema surrounds, which are usually dying around 50Hz if you are lucky. There is a chance that they applied a high pass filter on the soundtrack anyway or that whatever happens below, say, 50Hz is not supposed to be heard.
Personally, I'd invest into surround subs only if the rest of the auditorium is top notch. If you want to go that direction, you'll have to install a crossover to drive the subs.

Posted by Monte L Fullmer (Member # 2797) on 11-03-2016, 05:33 PM:

We run ATMOS in two of our large houses.

5 speakers behind screen.

2 sub bins under the screen.

LCR surround channels with a sub channel for the surrounds where two small subs are located in the upper corners of the house. We had dedicated amps for these subs.

Then, the VOG (Voice of God) speaker array up in the ceiling.

Posted by Harold Hallikainen (Member # 5405) on 11-03-2016, 08:45 PM:

The USL JSD-60 allows you to mix surrounds into the LFE to extend the low end on the surrounds. The latest firmware version with the "crossover board" makes the LFE2 output a separate mix so you can use the LFE at the screen for the LFE channel and mix surrounds into LFE2.

Harold

Posted by Mike Babb (Member # 1379) on 11-04-2016, 07:49 AM:

We've done this in 5.1 and 7.1 with a Trinnov Ovation. We program the surrounds as 2 way and send the lower frequencies to the subs in the back of the room. We also did 2 way surrounds with low frequencies going to dual 15" and mid and high going to horns, the same speakers as the stage. We have also used subs in the rear of the room, with a seperate channel, delay and eq setting. All of these resulted in more low end and a better experience. I understand they've experimented a bit with this in France as well at one of the multiplex chain. Ovation also has bass management settings but I haven't experimented with it yet.

Posted by Pete Naples (Member # 761) on 11-04-2016, 09:58 AM:

Those bi-amped, full-range surrounds worked rather well, didn't they Mike? [Wink]

Posted by Marco Giustini (Member # 4544) on 11-05-2016, 05:31 AM:

I'd willing to invest my money in bi-amped surrounds rather than surround subs to be honest.

Posted by Randy Stankey (Member # 64) on 11-05-2016, 11:09 AM:

I don't think that subs in the surround channels makes a lot of sense.

Low frequency sound is virtually non-directional. You could practically place your subwoofers in the bathroom and most people wouldn't be able tell the difference.

The expense and complexity involved with low frequency surround would be a waste, in my opinion.

Posted by Harold Hallikainen (Member # 5405) on 11-05-2016, 12:26 PM:

I tend to agree with Randy that we cannot detect the direction of low frequency sound very well. However, due to the limited low end response of surround speakers, it seems like it'd be worthwhile to inject the low frequency surround into the auditorium from somewhere. With the JSD-60, you could form a crossover for the surrounds by putting a "channel filter" on the surround channels that gives a low cutoff. You could then mix the surrounds into LFE1 or LFE2 output which contains a 125 Hz LPF. If you put the surround low end into LFE2, there might be a separate set of surrounds in the rear of auditorium. With object based sound, we'd like to be able to pan a sound off the screen to the side of the room and have the timbre not change.

Harold

Posted by Randy Stankey (Member # 64) on 11-05-2016, 03:00 PM:

quote: Harold Hallikainen
it seems like it'd be worthwhile to inject the low frequency surround into the auditorium from somewhere

I agree with that.

A second channel for the subs could be a good thing if you do it well.

Posted by Mike Babb (Member # 1379) on 11-07-2016, 10:58 AM:

Lower capability in the surrounds sounds good to me, I did an install awhile ago where they used surrounds with 15" drivers and I remembered being very impressed by that too.

Pete's install used exactly the same speakers for surrounds as the stage channels, sounded really good.

Posted by Randy Stankey (Member # 64) on 11-07-2016, 02:32 PM:

On one hand, I usually just accept that surround speakers are smaller than the main channels but, on the other, it puzzles me why they are different.

While I understand that size and weight are likely to be the main reason for the difference, I get confused when technicians and designers say that the auditorium needs to have a uniform soundfield. Wouldn't it be easier to achieve a uniform soundfield if all speakers are exactly alike?

Of course, surround speakers probably don't need big horns like the front channels. They don't usually have to send the sound waves as far but that's no reason why all speakers shouldn't be more alike than different.

I'm not rich enough to build my own theater they way I think it should be so, until that day comes (if ever) I just have to say, "It is what it is..."

That's probably the figure of speech I hate the most.
[Roll Eyes]

Posted by Daniel Schulz (Member # 1881) on 11-07-2016, 05:34 PM:

quote:
Never a bad idea to add subs [Smile] but a 5.1/7.1 track is mixed using cinema surrounds, which are usually dying around 50Hz if you are lucky. There is a chance that they applied a high pass filter on the soundtrack anyway or that whatever happens below, say, 50Hz is not supposed to be heard.
Personally, I'd invest into surround subs only if the rest of the auditorium is top notch. If you want to go that direction, you'll have to install a crossover to drive the subs.

Agreed with this. This is somewhat less relevant in the D-Cinema era, as you can in theory mix with full range surrounds, but in the digital-sound-on-film era surround channels didn't go below 80Hz. In fact the 80Hz cutoff was baked into the DTS format, but roughly followed for SRD and SDDS tracks as well. I think even in the D-Cinema era, if your surround arrays are capable of playing back cleanly down to 80Hz you're playing back everything the mixers are placing in the surround channels in the 5.1 and 7.1 mixes. It's only with the Atmos/DTS:X mixes that there is any expectation on the part of the mixers that full-range sound can or should be panned around the auditorium.