Film-Tech Forum ARCHIVE: Our Sound System

This is topic Our Sound System - Your thoughts ? in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=16;t=003718

Posted by Dan Judge (Member # 8175) on 06-17-2019, 10:19 AM:

Since i started leading on our small one screen university cinema i have always been a little 'unsure' around the technical set up. Especially on the audio side.

The audio set up consists of :-

Dolby CP650 + DMA8Plus – Dolby Digital 5.1
Denon DN500AV Pro Cinema Amp

3 x Crown XLS1500 Power Amps

https://www.crownaudio.com/en/products/xls-1500

Speakers

Front L/R and Centre: JBL 3677 (250W)
Surround (x10): JBL Control 28 (87W)
Subwoofer: JBL 3635 (300W)

So the concern are the 5 x Control 28s (surrounds) in parallel 8 / 5 = 1.6ohms and 435W. I now see the amp handles 775W per channel at 2ohms. Nothing to worry about?

The sub is 300W and the amp provides 300W @ 8ohms. The stage speakers (L/C/R) only need 250W so fair better with the 300W available.

I am guessing i should be looking at :-

- Sub amp should provide more headroom (450w?)
- Stage speakers also could do with more headroom?
- Surrounds also need more headroom / rewire?

It had been set up this way for around 10 years and working ok so this is why no one has looked further into revisiting the set up.

Any advice?

Posted by Sam D. Chavez (Member # 1841) on 06-17-2019, 11:00 AM:

Others may come along and give more exact advice but here is mine to start things off. First, look at the speaker sensitivity and work from there. This is quoted or listed on the spec sheet as loudness at One Meter/One Watt. Next look at the length of the room and calculate the loudness at 2/3rds back in the room. This will tell you if you have enough power from the amplifier or if the speaker will withstand the power of any amp at the typical seating position. Bear in mind, you double the distance, you double the power required. Two Meters/Two Watts, Four Meters/Four Watts, etc. This is the direct sound, forget about room gain/reverb.

As to the surrounds, you can probably get away with a 1.6 Ohm load, depending on the speaker wiring garage and length of the wire run.

Posted by Michal Matys (Member # 8614) on 06-17-2019, 02:16 PM:

how big is your room? I have basically the same setup (different surrounds only) on 8,5 x 12,5m hall and it plays just fine, as long as the sound is calibrated properly there should not be issue.

It is not recommended to go under 2 ohm, meaning you should do 4 speakers in paralel max, but I have seen sites with 5 or more and it worked, there is a slight risk in damaging the amplifier. You can consider wiring serial but if it plays ok for years now as you say, I guess there is no need to touch it.

Posted by Marco Giustini (Member # 4544) on 06-17-2019, 05:08 PM:

What Sam said.
You’ll have to calculate if the speakers/amp are properly dimensioned for the given room.

That subwoofer in digital sound is probably inadequate even for a living room unfortunately - unless you run your films at 4.0.

I worked with the Control 28 a couple of times and the response was horrible - not sure whether it was due to the acoustic.

Posted by Mark Gulbrandsen (Member # 72) on 06-18-2019, 08:17 AM:

I would seriously ditch the Crown amps. They are famous for expelling DC into your voice coils when they fail.

Mark

Posted by Scott Norwood (Member # 30) on 06-18-2019, 01:29 PM:

There are other people here who know far more about sound systems than I do (some of whom have posted in this thread), but the simplest question is this: does it sound good? Does it? If so, great. If not, you might have an equipment problem, a room treatment problem, or an installation problem.

I don't personally see the point of upgrading stuff just to upgrade it. If the current system has been in place for a decade, anything that is likely to fail would have already done so. If something sounds bad, then it is probably best to call in a service technician to take measurements and figure out what is wrong or worthy of being upgraded.

Posted by Marco Giustini (Member # 4544) on 06-18-2019, 01:51 PM:

I feel that that question (does it sound good) should only be answered by a professional otherwise you’ll likely to get a positive answer as long as there is sound playing.

Posted by Mark Gulbrandsen (Member # 72) on 06-18-2019, 02:19 PM:

quote: Marco Giustini
I feel that that question (does it sound good) should only be answered by a professional otherwise you’ll likely to get a positive answer as long as there is sound playing.

Exactly! An experienced tech will be very subjective.

Posted by James Biggins (Member # 8574) on 06-18-2019, 03:58 PM:

quote: Mark Gulbrandsen
Exactly! An experienced tech will be very subjective.

Don't you mean 'objective'?

Posted by Jarod Reddig (Member # 6363) on 06-18-2019, 09:13 PM:

He surely meant objective.

Posted by Marcel Birgelen (Member # 6801) on 06-19-2019, 12:47 AM:

Maybe it was sarcastic?

Nobody listens to sound in a totally objective way, that's simply not how our hearing works.

Posted by Marco Giustini (Member # 4544) on 06-19-2019, 04:31 AM:

I hope it meant objective. [Smile]

Indeed there is an amount of subjectivity when it comes to sound. Picture is easier: if your colours, contrast, uniformity and brightness are right, you're good to do and nobody can claim otherwise.

Sound cannot really be easily measured - there are many tools of course but it's not as easy as a colour meter pointing at screen.

It also depends on the person who is looking to upgrade. If they run movies at very low volume, chances are it won't matter. But at higher volumes - not necessarily 7.0 - speakers will start straining and that is not 'black and white', meaning that speakers will slowly begin to distort and compress in a way that won't sound very obvious... until you upgrade!

Also, as it's been said, acoustic plays a HUGE role in here. I've upgraded a poorly-treated room in the past from a basic 2-way system to a massive QSC 3-ways system (wasn't my decision) and it did not really improve much. In fact, the extra power was triggering the poor acoustic even more, making the sound potentially worse.

Finally, it's the technician installing it. Take the best system in the best room and give it to the average guy who place a single mike on a stick, dials the curve and walks away and you've wasted your money.

All I can say from here about your system is what I said above.

Posted by Marcel Birgelen (Member # 6801) on 06-19-2019, 06:12 PM:

Help us, Obi Mark Gulbinobi, you're our only @#%^jective hope!

Posted by Jarod Reddig (Member # 6363) on 06-19-2019, 08:19 PM:

Knowing Mark is was meant sarcastic ya lol. Meaning each tech will have his subjective point of view for why this or that needs changed.

I think beefing up the sub-bass more would help just from having worked with that particular sub before. It doesn't go very low at all. Wether he plays at low levels or reference upgrading the subwoofer/amp would make a difference.

Posted by Mark Gulbrandsen (Member # 72) on 06-20-2019, 11:08 AM:

What Jarod said! Figured I'd let them hang a while [Big Grin]

Posted by Jarod Reddig (Member # 6363) on 06-21-2019, 05:04 PM:

Nice one Mark. [Smile]