New THX trailer - A BIG workout for your sub (1 Viewer)

[John S]

I have a somewhat bargain 15" Velodyne Sub from Circiut City, that was supposed to be a special OEM build for only Circiut City, it was touted as THX certified even, and while it definetly made me stand up and take note of the new THX trailer, the sub hanlded it with seeming ease, at or at least very near reference levels.

I think 9 on my Denon is true reference or there so abouts, and I was at 11 as far as the somewhat meaningless volume indicators went. Rumbled the glass doors and dishes in a china cabnet real good though... lol

 

[steve nn]

Hi John. If you are refereing to the CHT-15 Velodyne sub, then it will handle any thing you put to it. It has a limiter that will effectively keep it from going beyond a certain point. Thus you can never bottom the CHT-15 out/bring it to it's knees sort of speak. Great subs for the (right) price imo. I used to run a ct-150 and a ct-150 with a CHT amp in a dual setup.

 

[MingL]

Certain in the likes of the vels and servo15 have limiters that make the sub virtually impossible to bottom-out. The drawback is that these limiters limit the output volumes unproportionally to input signal. (This is similar to P1dB compression point for microwave engineers)

Other subs use some highpass filter and/or mechanical box designs to prevent the driver from bottoming out in the very deep bass stuff (

 

[Bart]

Maybe this is a newbie question, but what is "Dolby Reference Level"?

Bart

 

[John S]

Bart, For myself I mean true theater levels, which are loud if ya ever really pay attention, many systems won't even push that loud.

 

[Zack_R]

Maybe this is a newbie question, but what is "Dolby Reference Level"?

Bart, there is a HT primer guide, somewhere in one of these forums that explains it better than I can but I'll give you a brief on it.

Basically Dolby reference levels are the levels that movie theaters purportedly play back the audio track that has been recorded to the Dolby refence level. What us HTfers do is use the parameters set forth for theaters to achieve the same spl levels in your HT area.

In numbers this means a surround channel max of 105 dbs is obtainable at the prime seat and an LFE spl max of 115-121 dbs at the prime seat. From that point there are many if's but essentially, if (big if) the soundtrack is recorded properly and if (big if) your system is capable and calibrated and if (another big if) your room is eq'd or treated for a flat response then you could play the movie so that the sound in your room would be near identical to the sound levels in the theater.

It's been a while since I've been to a movie theater but no one know's for sure if the theaters are actually playing the movie at the max dolby volume setting or a few dbs below the setting. Or if the Movie theaters subwoofers can actually play a 20 Hz tone at 115 dbs at your seat.

Most people find Dolby reference levels to loud to comfortably watch an entire movie but we occasionally enjoy cranking the volume to reference levels for scenes that have lots of low bass for kicks or to see if our system can play the movie that loud.

Because max Dolby reference levels are very demanding, a soundtrack that is recorded a couple of dbs above the reference standard can damage or break your equipment.

When it comes to DVD mastering the reference or standards seem to be open to artistic interpretation. I generally find DTS to be a bigger mastering culprit than Dolby labs. For example in my room, the DTS version of Gladiator is 7-8 dbs louder than the Dolby Digital track and Casper is 5-6dbs above the Dolby Digital track. However, without strict adherence to the Dolby refernce standards it's hard to know if the Dolby Digital versions of these two flicks are mastered to low, just right or to high. In other words the DTS tracks could be correct and the Dolby tracks incorrect. Either way, the inconsistency between DTS and Dolby means that someone is probably not doing it right.

If you are interested in calibrating your system, pick up the Avia DVD guide to home theater and an spl meter and you can get under way.

 

[Doug Montgomery]

For example in my room, the DTS version of Gladiator is 7-8 dbs louder than the Dolby Digital track

Whew...2-3 times LOUDER than Dolby...now that's volume

 

[Dave Moritz]

mmmmmmm I guess I really need to pick up a decible meter to check what decibles my Altec A-7 crank out :b

But after I build my custom center channel with dual 12" JBL with a HF horn and dual 15" subs. I will need to play AOTC and LOTR and see how much plaster falls from the ceiling.

 

[Doug Montgomery]

Have an umbrella handy

 

[Edward J M]

When it comes to DVD mastering the reference or standards seem to be open to artistic interpretation. I generally find DTS to be a bigger mastering culprit than Dolby labs. For example in my room, the DTS version of Gladiator is 7-8 dbs louder than the Dolby Digital track and Casper is 5-6dbs above the Dolby Digital track. However, without strict adherence to the Dolby refernce standards it's hard to know if the Dolby Digital versions of these two flicks are mastered to low, just right or to high. In other words the DTS tracks could be correct and the Dolby tracks incorrect. Either way, the inconsistency between DTS and Dolby means that someone is probably not doing it right.

Zack clearly "gets it".

We all should be calibrated to "Reference Level" at a given Master Volume setting with a calibration DVD like Avia or DVE or S&V.

But playing a DVD at that Master Volume setting is certainly NO guarantee that your system will be playing at Dolby Reference Level (105 surrounds and 115 LFE).

Zack nailed it - the variable in the equation is the DVD mastering level - they are all over the board from mild to wild.

So while I am indeed calibrated to "Reference Level" at Master Volume 00 on my 3803, I find that achieving true Dolby Reference Level playback (105/115) is best accomplished with a sound level meter (using correction factors) at the listening position than by trusting an arbitrary volume setting.

Regards,

Ed