How Much is Enough?

by Frank White with Anthony Grimani

Our latest for Grimani Systems, this comes from our list of the top 50 recurring problems in home theater systems - gathered over the last 25 years from more than 1,000 high-performance installation projects.

What the devil is this "headroom?"

You don't hear the term "headroom" in our industry much. Check out this case study:

Worked in a machine shop as project manager in the late 70s trying to fund our fledgling AV company. Had about 15 detail machinists, 10 welders, and 6 assemblers, all using pneumatic tools. The compressor was driven by an old '68 GM 350 2bbl delivering a realistic 170 or so horsepower.  That motor was well over a decade old and was run for 15 hours a day, 6 days a week. No one was ever short on air power. The 60 year old facilities guy kept the oil, coolant, and plugs changed and topped. That motor was run well under its capabilities - we call that "headroom". The objective of reliability was met. Heard from an old buddy... that motor lasted another 14 years.

To restate: The engine had much more capability than required. That is headroom.

How does headroom fit in today's problem? Let's unwrap this a bit. A great starting question would be: Do you have any idea how much amplifier power and cone area it really takes to drive sub-sonic frequencies in your client's theater room? Also, how do you know?

As your engineering DNA start to kick in, terms like total room volume, room dimensions, surfaces, reflections, resonances, seating placements, acoustic room isolation, and budget all compete for their proper prioritization in your design.

As Anthony Grimani tells it, he always brings a gun to a knife fight, so to speak. When it comes to subwoofer capability, he's most comfortable specifying more amp and speaker than most would think is necessary. 

When you default to that standard subwoofer that you've used 100 times in the past, you're under-addressing this point and missing out on what really sets you and your client's home theater apart. Furthermore, you're potentially missing out on a truly great opportunity to immerse listeners in the wonder, amazement, and magic that is delivered by music and great cinematic art. Not to mention word of mouth recommendations that come with a great experience!

At its basic core, it's simple. It takes at least 110 dB of clean and tight bass in a home theater to get listeners to crack a smile. True reference level requires 115 dB for LFE alone. Targeting 115-118 dB gives you sufficient headroom so that your subwoofers aren't straining or limiting at 110 dB. Many home theaters have plainly anemic bass that tops out at 90 dB at the needed frequencies - barely enough to get any reaction at all from the audience. Of course, it takes subwoofers that are powerful enough. Subs that appear on the surface to be similar can differ in bass delivery by a full 10 dB! Also, proper tuning can make huge differences. Properly setting the delay for the back pair of subwoofers in a four subwoofer configuration can eek out 12 dB of additional bass in the bottom octave just like that. You do need an outboard digital equalizer to make it all happen - but talk about a huge bang for the buck!

So here's our solution set: It takes horsepower and tuning to achieve sufficient bass headroom. You need enough cone area, enough amplifier power, and multiple subwoofers that are placed for maximized room gain efficiency. Then you need to carefully tune the relative delays, EQs, and levels of the subs until you squeeze out every little ounce of sound pressure from 20 Hz to 100 Hz. This cannot be done without the right spectrum analyzer, the right test signals, the right engineering talent, the right subwoofers, and the right amount of time to make it all happen.

While on the web, check out Anthony's new offerings at Grimani Systems.

Thanks for investing a few with us on this topic. We look forward to your success!

To ge hold for Frank, (I build compelling narrative around your message) - [email protected]