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Before and After results of a Real Multipurpose Hall

Posted by jdbsound on December 4, 2017

This is a before and after test results of a multipurpose room.  The room is a converter steel factory.  The purpose of the room is for multi use including banquets, acoustical and amplified musical performances, teaching and general meetings.  While the room has a fixed sound system, the  room performs equally well regardless of the orientation of the seating or event layout.

sandbox B-A results

From the graph, it shows the before and after.  Before the room had an average of 2.1 seconds of reverberation.  That said, at around 400 Hertz, the reverb time was 2.85 seconds. This made the room unacceptable for all uses.  It was hard to have a simple conversation with someone only 5 feet away.

The acoustical treatment in this case require 3 different acoustical system.  Tube Radiators were used for controlling sound from 200 to 2000 Hertz.  The tube radiators have only a profile depth of 4 and 6 inches and the idea that something so small can control sound down to 200 Hertz is amazing.  The tube radiators only covers 12% of the total wall space of the room.  

The second system was outround diffuser panels.  They covered another 10% of the available wall space.  These panels were used to manage sound from 100 to 500 Hertz.  By combining these two system with the limited wall space, we were able to cut the reverb time at 400 and 800 Hertz 1.8 seconds.  That is a massive amount considering that 400 Hertz is a wave length of about 33 inches long and 800 Hz is about 17 inches.

The third acoustical was a fiber absorber.  The fiber absorber covered 40% of the ceiling and 10% of the side walls.  The fiber panels covered the outrounds on the side walls.  It is rare to need absorption in such projects but when you have a concrete floor with no carpet, you have to replace the carpet with something similar.  Here is the thing about carpet.  Carpet, which is always within 4 to 7 feet of our ears works very efficiently.  The shallow angle of most sounds we hear in a large room event gives a 1/2 inch of carpet the acoustical performance of 2 inches of a typical wall panel absorber.  Since one of the requirements of this room is to include music that can reach 100dB, it was planned to have a reverb time of 1 second, +/- .2 tenths of a second.  That goal was met and the range it was met is typical of our acoustical fixes.  If you look at the before and after, the room now meets that goal from 150Hz to 4,000Hz.  Before, using the same criteria, the room had a average reverb time of 1.8 second with a +/- of 1.1 second variance.

percent alcons 4 sandbox

The critical question is, how does the room sound for speech, talking and for music.  For speech, the change was from 14% Alcon’s (rated as poor) to 4% Alcon’s.  At 4%, it means that you can talk to someone from end to end of the 55 ft long room with a slightly raise voice.  When you add a properly equalized sound system, you can better the speech intelligibility to 3.5%.  For talking across a table during banquet or social events is easy in this space.  You can talk to someone 15 ft away while the person next to you is talking to someone across the table without having to raise your voice to compete with other conversations.

As for music, so far, for the high energy high SPL events the room has been well received by musician and audience members.  That has meant fewer events with drum shields, fewer events with IEM (in ear monitors) and very little floor monitor spill that degrades the sound for the audience.

At the other end there have been a few recital type performances where the even was all acoustical.  One person who was a graduate of a royal conservatory of music remarked that the room was similar to recital rooms at a well known royal conservatory school in Toronto, Canada.  One violinist said that while she would have liked a longer reverb time, the quality of the sound of her expensive instrument was amazing.  The last time she heard her violin sound so great was at a high end recording studio that was  acoustical treated.  She was also stunned that it didn’t matter where in the room she performed, the violin sounded great.

There is one down side to the new room.  Since there is no carpet, when the room is empty, you do notice the reflection off the floor. This does make the room a little challenging for those who do rehearsals when the room empty and before any table and chairs are set up.  Once tables and chairs are setup, the room behaves well.

In the real world, there are a lot of rooms that are used as multi purposed spaces but perform poorly.  Most facility owners don’t worry about acoustics because they may have the only place in town that can accommodate such events.  That said, if they were to get 10 to 20% more bookings per year, they would recover the cost of investing in an acoustical fix in less than a year.  Furthermore, it would allow the facility owner to charge a hire fee if the place gets too busy.  There is no down side to having an acoustically friendly community center, convention hall, rental hall or banquet facility.

 

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Church Ceiling Height Chart

Posted by jdbsound on May 26, 2017

Churches these days are building lower and lower building.  I guess when so many churches have experienced only poor quality acoustics, many wonder what is the point of building a taller worship space.  As it turns out, existing worship space acoustics is doing fine and a lot of churches are are getting their acoustics fixed, sounding better today than they ever did before.

When a church builds a low ceiling, it limits congregational singing and it makes you more dependant on technology, but guess what!  The same things that limits congregational singing is what also limits the performance of all sound systems.  So, instead of getting 100% out of your high quality over priced expensive sound system, your getting only 40 to 60% of the sound systems true performance abilities.  It is actually cheaper to build higher than the added cost of audio technology to make up the difference.   The chart below should clear the air as to the minimum height your next church should be.  Also, a taller worship space does not mean being stuck with longer reverb times. A higher ceiling means natural room reverberation is adjustable and tuneable.  With a taller ceiling you can change the frequency response of the whole room without needing a sound system or equalizer.

Minimum Church Ceiling height Chart.JPG

Church height is important for a worship space.  One of the biggest parts of worship is singing.  Congregational singing to be specific.  When singing as a group, several elements are required for a good and healthy worship experience.  There is chorusing, harmony, sound volume or loudness of the singing and being able to hear yourself as well as the people around you.  When all of these elements are in balance, the worship experience is like no other.  The majority of people get a lot of satisfaction from the singing experience during worshiping in rooms that have ceiling heights that matches the size of the seating capacity of the worship space. The above chart are minimum heights.  If you want to build higher, you can as the singing experience gets even better but the improvement is more subtle.
High ceilings allow better and less expensive sound systems to be used.  Higher ceiling permit better gain before feedback and it becomes easier to isolate drums and floor monitor. The performance of the sound system is much better too when that is coupled with a good quality acoustical management system.
There are economic advantages too.  The higher the ceiling, the cheaper it is to heat and cool when using a vertical displacement HVAC type system which is specifically designed for large gathering spaces for people.  Such systems cost less to install, they use smaller HVAC components and cost about 30 to 40% less to operate.  In addition, the cooling systems last 2 to 3 times longer before needing to be replaced.
Another thing to consider. If building new, don’t build a flat ceiling that is parallel to the floor. (and it doesn’t count of you put in a sloping floor.)  Many churches that are moving into commercial buildings are learning the hard way that flat ceilings limit the quality of live musical performances and congregational singing.  Sure, there are acoustical panels that can slightly improve the room for amplified sound, but the cost doesn’t justify the returns.  There is little that can help congregational singing even if you have the height. Vertical standing waves are hard to manage than horizontal standing wave. If you know what you are doing, horizontal standing waves can be controlled to create an outstanding room.  It is part of the formula for the almost perfect worship space.  Funny though, most concert musicians that perform in a church that I have fixed, they often make comments like, “I wish our concert hall sounded and performed as well.”  That is almost like saying, “concert halls make for lousy worship space but worship spaces can perform better than a concert hall.”
*Note* In any country that has freedom of religion laws, the worship space portion of a church building has no roof heights limits regardless of local city building height restrictions. 

**Note** The data is based on 2800 churches from North America, Europe, Philippines and Central America. 

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Pastor Guide To Acoustics

Posted by jdbsound on December 20, 2012

Here is an article I recommend reading.  It sings the same story share at this website.  Don’t know about the results but if it is similar, it would be amazing.

Pastor’s Guide to Acoustics
link: http://www.worshipfacilities.com/go.php/editorial/19635

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