Room EQing

[Ryan Gallagher]

I'd like to add something here.

As much as I appreciate the OP's intentions, sound is not like image where if the colour meter reads 0.314x0.351 you're all set (* ok, Laser have messed that up too!).
Sticking one - or multiple - mikes in a room and dial the "X curve" is only part of the game.

Yes, it will probably give you a baseline where to start from but as I said above, the Equaliser is only a player in the outcome - and a bad one, that is, you'd rather not have it!

I don't mean to discourage you from learning your way - just be aware that when it comes to sound things are a bit more complicated - the X curve was designed as an approximation to give cinema technicians around the world a baseline but the outcome is dependant on the acoustic. An RTA is "time blind". There are more tools today but none is the ultimate one. Probably - never worked with one - the Ovation is the closest to that, I'd imagine!

In short: be aware that sticking multiple mikes in the auditorium and dial the X-curve is not the ultimate goal.

I'd say that's true based on my observations too. We have the luxury here of having a Dolby tech tune our room once a year ahead of the big festival. Every time it's someone different they are always making adjustments. If it was just a matter of putting their mics in the same location and hitting an X-curve target, I doubt anyone would touch much year to year. But each tech has their own ears and way of being satisfied.

Last year the tech was excellent, and actually helped us in more ways than obligated by the festival. Took some extra time to tune for 7.1 separately and give us an updated EQ for that format.

[Ryan Gallagher]

Related question:

As an operator in a single screen venue that still employs projectionists. What day to day is good practice to implement to "catch" issues with the sound components?

My current practice is to run a "checkout" SPL top of my call that includes both Channel ID and Channel PinkNoise as well as my target patterns for adjusting masking. I go out into the upper balcony when I play the audio tests. I figure if something major broke I might be able to hear a difference and investigate further. But perhaps there are some better audio test CPLs to include in the battery of listening tests? Sweepey? etc. Maybe a trailer I become intimately familiar with would be a good addition?

As far as measuring. There is a SPL handheld meter in the booth that could be utilized. There is an antiquated 8-band RTA and tiny mic hung outside one of the portholes (a relic of the film era) that is always "on" and showing levels. I don't trust the placement of the mic to really produce anything repeatable though.

Beyond that the venue does own a mic array and SMAART license, though I'm not trained up enough to really utilize it in a meaningful way for tuning a room. Would it be silly to leave one of those calibrated mics in a position at the edge of the balcony and patched to the booth so that perhaps a more measured baseline could be compared day to day or week to week? Just for catching changes? That much I could manage.

My checkout now also includes a doremi macro driven fade-out sequence. We learned a couple festivals ago that our AP20 likes to have some sort of memory-leak issue crop up over time that causes networked commands to take in the UI, but fails to take at the outputs (in the house). Having some fader macros involved in a checkout sequence allows me to catch it and do a reboot. The interval between needed reboots appears to be about 2-3 months. They weren't using many audio automation macros before I started, so wasn't an issue before.

[Harold Hallikainen]

I think a single microphone and looking for changes is a valid way to detect component failure (such as amplifiers, drivers, etc.). This is the approach taken with the LSS-200. In a typical installation, a test show is run once each day. The test show includes a slow flash sequence at the beginning of the show that triggers the LSS to run a script that makes the measurements. The measurements start with screen luminance and chromaticity. Then, each audio channel is driven with band limited pink noise. The pink noise is broken up into one, two, three, or four bands to test multiway speaker systems. This provides a gross frequency response measurement. Changes in frequency response are visible on the graphs generated by the system. We typically also included an SPL measurement of silence. With these tests, we found changes in the high frequency response of left and right channels due to masking moves. We also found a failure in the air conditioning system due to increased SPL during the "silence" measurement.

Summarizing, I think a one microphone measurement with you watching for changes is valid (and certainly better than nothing). It's nice to have the tests automated.

Harold

[Marco Giustini]

Even with proper equipment the "absolute number" of the SPL meter has limited importance. This is also why it's recommended to look at "A weighted" values now but looking at the curve is also important.

What I want to say is: please don't adjust a system using an SPL meter without the ability to see the curve and without having properly evaluated the system.

The best tool for you are your ears and test content. Make sure you have

- Channel ID (both 5.1 and 7.1)
- Pink noise ID (both 5.1 and 7.1)
- Sync
- Surround delay
- Some content you are familiar with

Running a weekly/monthly check will detect 90% of the issues. Nobody will notice if your HF is down 1dB but might notice if your HF driver is not working
Minor changes in SPL or tone should really be left to a dedicated person with appropriate tools and enough time (I am not saying you are not that person BTW!).

[Ryan Gallagher]

Thanks for the input, for sure I was not considering making any adjustments with my current level of knowledge when an anomalous change is detected, just considering how to up our game for a more accurate repeatable way to listen for defects (perhaps assisted by measurements).

For example, the smaller room had a surround driver fail and it was not caught until Dolby was back for the festival. I never get to run films in that space or I might have noticed with my existing checkout habits.

[Juan Carlos]

Hola, saludos para todos desde argentina! Soy una persona mayor, y en mi juventud fui operador y técnico en la cinematografía. Hoy quisiera compartir aquí con ustedes, un analizador de espectros que diseñe y construí de forma artesanal en mi hogar (Homemade), allá por el año 1984, dado el alto costo de este tipo de equipo y la inexistencia en mi país, tuve que fabricarlo yo mismo para poder ecualizar salas de cine. El desarrollo y la construcción del mismo me llevó mucho tiempo. Para su ajuste fue calibrado comparando junto con un analizador profesional: INOVONIC 500
Quise compartirlo con ustedes solo a título de curiosidad como algo vintage.
El equipo mide en ⅓ de octavas en pasos de 1y3dB SPL, con una escala que va desde los 54dB a 125db, también mide banda ancha para poder ajustar los niveles de distintos canales del auditorio, posee su propio generador de ruido rosa, salida para osciloscopio, entrada de micrófono y de línea en su paste trasera.
Saludos para todos.

https://photos.fife.usercontent.goog...-gm?authuser=0

[Marco Giustini]

Juan

The link does not show anything to me unfortunately.
Yes, back then spectrum analysers were expensive and software analysers were expensive and/or slow and required good hardware. WinRTA was the first one which was doing a good job even on a small netbook.

To be fair, RTA software are still expensive - Smaart is great but it's not cheap. That said, Smaart gives you a lot of features!

[Juan Carlos]

Juan

The link does not show anything to me unfortunately.
Yes, back then spectrum analysers were expensive and software analysers were expensive and/or slow and required good hardware. WinRTA was the first one which was doing a good job even on a small netbook.

To be fair, RTA software are still expensive - Smaart is great but it's not cheap. That said, Smaart gives you a lot of features!

Hola, muchas gracias por su respuesta! Le pido disculpas por el link que no funciona, no se cómo subir las imágenes, no entiendo el cuadro de diálogo que me pide la URL de esta página. Subí en sitios de internet las imágenes para obtener la URL pero el cuadro de diálogo de esta página me da error, no se como funciona, necesitaría ayuda con ello. Voy a seguir intentando a ver si consigo subir las imágenes.
Es una lástima, porque la fabricación del analizador fue algo que me costó mucho esfuerzo y lo quería compartir.
También mis disculpas por escribir en castellano! No domino el idioma ingles, y tengo miedo de usar el traductor y que resulte en una mala traducción. Saludos desde argentina

Aquí intenté otra vez

https://drive.google.com/drive/folders/172K2_TpGs4_L7PIHuCyOKklv1p1a5DyX?usp=sharing

[Marco Giustini]

it's a beauty!

[Lyle Romer]

One of the things that the LSS-200 will show is how the EQ changes throughout the year. I was rather surprised when noting that the HF response is pretty significantly different in the summer/humid months versus the winter/dry months. This seems to be particularly true when using just a single mic reference, like the LSS-200.

Using my preferred analyzer, the D2, I can tell when the person used the D2 because the response will almost always be the same, within +/- 3dB. I find that analyzer/mic system to be the most consistent of them all.

When THX was a thing, I had a few rooms and would do the annual "recertifications." In one screening room, in particular, I could track the decay of the HF response over time. That is, it went down a couple of dB on the very high end (16KHz) over 15-years.

Until you posted this I never really thought about the temp and humidity. Now that I read your post my thought is "of course the tuning changes with changing temperature and humidity."

[Juan Carlos]

it's a beauty!

Thank you! Also in those years I designed and built a processor that replaces the Dolby CP-50. Regards

¡Gracias! También en esos años diseñé y construí un procesador que reemplaza al Dolby CP-50. Saludos

https://photos.google.com/share/AF1QipOLQG-gRZUOIDdRzq_nwrdx8Keu3IR5G2zFwhs9g1Ni5Y_1YCGybu7r8EgXsLu7kw?key=ay1vT0JMWC1KRVlKQ1pCakRuVndrWmFfYzd3MjFR

[Gordon McLeod]

Thank you! Also in those years I designed and built a processor that replaces the Dolby CP-50. Regards

¡Gracias! También en esos años diseñé y construí un procesador que reemplaza al Dolby CP-50. Saludos


https://photos.google.com/share/AF1Q...drWmFfYzd3MjFR

Very nice layout