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Day 268 - Feb 22 - Home

**** Sound Nerd Speak (with a little bit of Drum Nerd Speak) ****

A little bit about resonance and damping. There are many types of speaker enclosure designs but for the most part they can all be distilled down to two basic types. Loudspeaker enclosures that have a hole somewhere in them that leads to the outside world and enclosures that do not. Some of these designers can be very complex with maze of chambers while others are truly just a hole in the box or a hole so big that there is not even a box per se. Secondly, speaker boxes can be made out of a wide variety of materials ranging from woods, plastics, metals or even concrete. Finally, inside of these loudspeaker enclosures, the creators often put some sort of filling like fiberglass or foam or felt product. While there are many other factors, all of the above choices have significant effect on the low frequency response and how damped or resonant the enclosure/loudspeaker combination will be.

To visualize what is meant by resonant, think of a bell. A highly resonant bell will ring for a long time after being struck. Now stuff a sock in it and though the tone is the same, it does not ring at all, "dink." Loudspeakers in enclosures act much the same way and just as changing the size and shape of the bell will alter its tone, so does the size and shape of a loudspeaker enclosure.

So like the bell, a loudspeaker can be designed to "dink" or "rrrrring" depending on the size of the hole, the amount and type of filler and the size of the enclosure and many other factors. Ok, Acme Speaker Maker has designed what they believe to be a super cool floor monitor. Sounds great, tests great, it is loud and not so resonant that it sounds overly bongy but not so damped that it sounds thuddy. Acme Speaker found during the design phase that if they tuned the wedge at 50HZ with a well designed port (the hole) and duct (little tube attached to the hole), and used no filler that they could extend the low end of the box flat, a bit further. They release it and sell it and Roadrunner Sound buys a big pile of them. Off they head to the first rock show in a high school gym for a gig with local heavy metal band, The Falling Anvil.

First they play some music through them and they sound pretty good. Out comes the vocal mic, check one two, turn it up, check one two, turn it up and "blooooooooo" a low end feedback is everywhere. Heading over to the EQ, Roadrunner sound finds a whole bunch of 50 HZ needs to be taken out. It is everywhere. Everything sounds muddy but hey, what what happened? Not only that, they have to take out so much low end that the monitors now sound thin. It is like they only have a choice between thin and muddy. They sounded fine when we listened to them in the carpeted demo room back at Acme Music store. Plus, Roadrunner Sound even went to the factory where they had all kinds of really expensive test gear that showed how perfect the monitors were. The big room with all the padding on the walls was way cool. What the heck happened?

Well, this scenario is pretty much the norm for an incredibly high percentage of pro audio speaker products. Manufacturers test in anechoic chambers (rooms without reflected sound), often using test tones and signals focusing on flat response and max volume. The sound companies quite often use the products in rooms with lots of echo and the real issue is that some of the sound from the monitor speakers gets back into the mic and then comes out the monitor and back to the mic, round and round. If the amount is increasing, it is called feedback, screech! or Wooooo!, but if it is there but not enough to regenerate, then it just makes things more resonant sounding. These two things, room resonance and regeneration, combine in the live environment to increase the resonance of the loudspeakers in real world use.

Now comes along another manufacturer, Clever Sound, that designs loudspeaker systems specifically to be used in the real world. Knowing that a bulk of the market they shoot for is either going to be on amplified stages or resonant rooms, they design their cabinets to be under damped. To achieve this they tune them lower and the box begins to roll off at 60HZ yet is still usable down to 40HZ but it requires a bit of EQ. Also, they stuff the box with lots of filler which gives it a very tight thud sound when it is not in a resonant room with an amplified stage. With music in the anechoic chamber, the loudspeaker sounds a bit dead but with a mic it seems to liven up a bit.

Unfortunately though, because Clever's monitors are over damped, the specs show that they are lower volume and lower efficiency than the resonant ones. Unfortunately, Acme's resonant wedges sound louder and even though the extra volume is fairly useless is many of the real world shows because it needs to be EQ'ed out, it is still enough to increase sales.

This resonance vs damped situation also exists with drum kits. In the studio in a non amplified environment that is acoustically controllable for resonance, it is quite common to use ringy drums with no damping. The puzzled drummer then queries, "what is wrong with these live, they sound great in the studio, that is the sound I want." Aha, but in the studio you did not have a drumfill blasting, or a bass guitar rig three feet away wiggling all the drum heads or a PA system thumping and the the room in the studio had all those cool rolling sound panels. "OK, tell ya what, if turn off your drumfill, move you way over there away from the bass player and PA and surround your with acoustic panels, then you can play this kit all ringy like that. But I have a have a better idea because no one will see your stick twirls over there, how about we deaden the drums a bit and then crank the drumfill and PA till it brings them back to life? Then we do a rock show!

All that frustration with tuning drum monitors and ringy drums applies to tuning monitors. It is too bad though that drums are fairly easy to re tune and damp down mechanically while monitors, subwoofers and main PA speakers it is often integral to the design of the system.

**** End Sound Nerd Speak ****

The scratching my head,

Dave Rat


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Mike Eiseman on :


marco (yespa) on :

great! but you forgot the dynamite in the acme speaker...

Richie P on :

This is definitely my favorite sound nerd speak. Awesome!

Greg Cameron on :

Maybe ACME could use some Liquid Hole® for their monitors to fall into ;-) Good read as usual. Is that going to be a submission for one of the trade mags? Greg

Mikey B on :

Could this mean there is a market for movable dampning in enclosures. Being able to tune boxes like a good drummer tunes heads?? Rat Scabies would tune his drums to the system with no strip EQ or inserts. Just by tuning the heads. If anyone can brain this type of thing out, it's you Dave!!

Matt Uecker on :

And the moral to the story is...? :) I sense some real world business learnings here...maybe from the micro wedges? Good read Dave...keep 'em rockin'. Matt

Anonymous on :

Thank you! Thank you! From time to time I'm asked to do "Sound 101" lessons to the tech students at a local High School. You've just written next week's lesson for me! Bob

Sander on :

Hey Dave! Good story again! BTW: I managed to get tickets for the upcoming Peppers in the Park that you will be playing in the Netherlands on June 24. I assume that it will be a seperate show without the usual rig? Especially since Pearl Jam is doing the same location 4 days later ... (they did a similiar thing with 2 festivals 2 years ago and shared all the facilities) Looking forward to it! (although FoH is probably to high up to even wave :-) )

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