How much loudness is enough for HT?

[Phil Olson]

Just curious about how loud speakers should play in a home theater environment. I thnk the 5.1 encoding allows for 105dB for the main channels and 115dB for the LFE.

After calibrating my receiver I normally listen to movies at least -10dB and usually -20

Is that 105dB supposed to be at the listening position? If that's the case, can I get away by sizing my amps/speakers for 95dB at the listenin position?

Assuming a 10' distance would that mean the speaker itself needs to be ~100dB/1m? Would then the LFE need to be 110dB1/m?

Thanks!

P.S. My room is dedicated and will be acoustically treated to an RT60 of about .35, (pretty dead and absorptive), if that makes a difference.

[Cal Weldon]

Hi Phil,

How loud you want it is strictly up to you. I like it loud and am running a H/K 55 watts for L-C-R and 25 watts for the rears in a 5.1. I also run a powered woofer.

The speakers I use are about 90-92 dB sensitive (total driver count: 24) and the room is about 250 ft^2. I am about 12 feet from the mains. That is more than loud enough and there is no shortage of headroom. By the time we get to 100dB, it's scary loud. Here's the right front:

[Brett]

Interesting question, one I've been podering for a bit as I have some large mains under construction and have been trying to figure out what sort of poweramps to use. For music, I'll use my tube jobs as they'll be loud enough (speakers are >100dB/W/m), but will use some SS for background and HT.

In my audio travels I've discovered I am conscious of dynamic effects and distortion, so I designed for a >120dB capability (with sufficient power) for the mains. I don't think it'll ever hit that even on peaks, but it's nice to know it'll be idling most of the time.

I'm also trying to work out specs for the design of the rears (FR, SPL etc) and power for them too.

[GM]

Greets!

DD/DTS reference is 85 dB/channel, 95 dB/LFE (assuming the other channels are nominally flat from 20-20 kHz) at the listening position with 20 dB dynamic headroom, hence the 105, 115 dB limits/listening position. If all mains/surround channels are set to 'small', then the LFE channel in theory must be able to handle ~122 dB/listening position peaks for 5.1, ~122.8 dB/6.1, ~123.5 dB/7.1.

This is too loud for most folks in a typical HT due mostly IMO to the fact that the typical speakers used (even many $$$ units) can't handle the SPLs at the vanishingly low distortion required for low listening fatigue, so tend to dial it back to suit the most sensitive viewers and/or to protect the speakers/whatever during high SPL effects scenes.

WRT loss over distance, SPL requirements will vary by frequency due to the speaker's directivity, placement and room gain, so no simple solution short of designing to the 6 dB/doubling of distance 'worst case' scenario.

GM

[Brett]

Something tangible, thanks. Do you know of a link to detailed specs with distortion figures etc? Might as well aim for the standard.

[Phil Olson]

Cal,

If I calculate right your 55W will give about 107dB but being 4m away will knock that down to about 95. You'll be aided by reflections if your picture is any indication, (nice speakers by the way!). 95dB is indeed loud.

Brett,

Sounds like you're going the pro driver route. Awesome! I thought about it but really didn't want to deal with the large cabinets required.

In my limited knowledge, I think sound quality depends on the type of distortion. If I recall, clipping is very bad and quite noticable, while IM and THD are much less important. Somewhere I read that even 10% may not be that noticable but have no knowledge if that is correct or not. I'm sure it's personal preference like every thing else so like most things, 10% of the population will be super sensitive, 80% will be somewhat sensitive, and 10% will be tone deaf.

GM,

Thanks, that's kind of what I remember. I did forget that the fall off is 6dB, not 3dB. The good news is that most of time, movies are rather quiet.

The speakers I am designing should have wide directionality so I've got that going for me! I'll have low end room gain somewhat but since I'll have a lot of base trapping going on I won't know how much until I'm farther along and can measure it.

It would be great to have a spreadsheet that everyone could use to determing speaker requirements and therefore amp requirements. One would have to guestimate live room/dead room corrections, etc. but it could be a good ball park tool.

If I recalculate, I'll need about 116dB/126dB at the listening position. Knocking that down 10dB, will give me a reasonable 106dB/116dB Main/LFE to shoot for as a minimum considering my listening preferences.

One consequence for me is that it has eliminated the simpler gainclone amp designs since my speakers will not be terribly efficient.

Any thoughts on standards regarding distortion specs, rules of thumb, etc.?

[Brett]

Originally posted by Phil Olson
Brett,

Sounds like you're going the pro driver route. Awesome! I thought about it but really didn't want to deal with the large cabinets required.

Indeed. I don't use anything else these days, though I am contemplating a waveguided Fountek neo5, but that's as close as I can see me ever going to typical 'phile drivers again.

Originally posted by Phil Olson
In my limited knowledge, I think sound quality depends on the type of distortion. If I recall, clipping is very bad and quite noticable, while IM and THD are much less important. Somewhere I read that even 10% may not be that noticable but have no knowledge if that is correct or not. I'm sure it's personal preference like every thing else so like most things, 10% of the population will be super sensitive, 80% will be somewhat sensitive, and 10% will be tone deaf.

Yep, clipping of amps, or drivers over excursing is plainly audible to me. However dynamic compression and THD also annoy me, so I'm looking to build something with the efficiency alnd low distortion of horns, with fewer drawbacks.

Originally posted by Phil Olson
If I recalculate, I'll need about 116dB/126dB at the listening position. Knocking that down 10dB, will give me a reasonable 106dB/116dB Main/LFE to shoot for as a minimum considering my listening preferences.

Seems like a good target, but even with efficient speakers that needs a lot of power.

Originally posted by Phil Olson
One consequence for me is that it has eliminated the simpler gainclone amp designs since my speakers will not be terribly efficient.

Ditto. I'm looking at some of the class D and (I'm shocked to hear myself saying this) AB SS designs.

Originally posted by Phil Olson
Any thoughts on standards regarding distortion specs, rules of thumb, etc.?

I've been looking on the DD and DTS sites for specs, and also googling but can't seem to find anything definitive.

[Cal Weldon]

Originally posted by Phil Olson
Cal,

If I calculate right your 55W will give about 107dB but being 4m away will knock that down to about 95.

Hi Phil, yes, I should have said 100dB at 1 meter.

Either way, it's too loud and this comes from a guy that likes it loud. Multiple drivers help control distortion.

[Phil Olson]

Cal,

I'm going to do a WMTMW or MTMWW for the same reason. My current Snell LCR's actually have two tweeters most likely to get the volume up at reasonable distortion.

Brett,

It's definitely more than a couple hundred watts but should be doable with the 49830 and multiple FET pairs. I probably could do a BPA-400/500 as well but the FETs seem easier.

If you find any specs on distortion please let me know. It seems most of the companies, including THX, are rather tight lipped about their specs.

[GM]

Originally posted by Brett

Something tangible, thanks. Do you know of a link to detailed specs with distortion figures etc? Might as well aim for the standard.

Not AFAIK, folks pay a 'pretty penny' to become THX certified and try to earn a living off the knowledge, but if we look at a cinema's requirements we can 'backdoor' it close enough IMO and not surprisingly it boils down to having controlled directivity/~flat power response to suit the seating distance/layout in our acute hearing BW and sufficient dynamic headroom to keep distortion low just like for a multi-channel cinema, so for a typical HT some form of waveguide or CD horn is required/channel combined with 6 - 8 dB of dynamic headroom.

The room obviously is a big part of a sound system, expecially for a multi-channel one, so dialing in the desirable RT60 seems a 'no-brainer'. JBL's cinema design manual has a nomograph and if your room is < 1 k ft^3, then it ideally needs to be able to do double duty as a ~aneochoic chamber.

GM