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> Put A Sock In It, small 2 way monitors
Saoirse O'Shea
post Jan 4 2012, 12:32 PM
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Fireball recently posted here that he got some new monitors for XMas and had put some socks in the port. Here's why it's a good idea for the majority of small 2 way studio monitors...

Most small 2 way mixing/recording studio monitors are ported - that is they have a hole cut in to the cabinet. The hole is there to supposedly help extend the bass response of the monitors. So, for example the monitor might have a moderately flat frequency response without a hold down to say 100Hz, at which point it will then start to attenuate from 100 down to 20Hz, often at something around 6dB per octave. A port hole allows this corner frequency so the response may now be reasonably flat down to say 60Hz before it starts to drop. What this means is that when you listen to the monitors with the port open the bass initially sounds better.

At this point everything sounds great and you'd be forgiven for thinking that you should leave the port open. So why has Fireball closed his and why do I agree with him? Well things might sound great initially but there are some problems with the bass produced by open ports on small, 2 way studio monitors.

1/ The bass response may have a lower corner frequency but it also attentuates severally. A closed port might attentuate say betqween 3-6dB per octave but an open port may easily attenuate at a rate between 18-30dB per octave. Every 6dB of attenuation is equivalent to halving the volume of the frequency. A closed port might start to attenuate at a higher frequency but it is not as severe as an open port. The level balance of a closed port is thus more accurate and more predictable than an open port and so it is much easier to hear and judge what the volume of the bass notes are and thus difficult to judge for frequency balance.

2/ Open ports usually suffer from an effect sometimes called 'ringing'. Ringing occurs when a note doesn't decay naturally but is instead made to sustain. This sustain means that a note is held for too long and so can still be heard even after the real sound has died away. The amount of sustain isn't the same for all notes but is rather erratic and can extend up into in to the mid range. All of this again makes it hard to judge a mix both for frequency balance and timing.

3/ Open ports are prone to distortion, comb filtering and other adverse issues. Most small 2 way monitors are designed to be placede close to a rear wall or a corner. What happens in these cases is that some of the sound is reflected back in to the port from these boundary walls in an unintended, unwanted and uncontrolled way. These reflected signals cause lots of problems including distortion, comb filtering, phase cancellation, time smearing, post ring echo and so on all of which result in audio that is hard to judge in terms of frequency balance, stereo width, depth and placement and timing.

You can reduce these problems - but not elimitate them - if you block the port on the monitors. You can block the port with acoustic foam but if you don't have any to hand you can still ameliorate some of the problems by using soft material - so a pair of socks will help do the job. You will have 'less' bass but it will be more accurate and more reproducible. So if you want to mix using small 2 way monitors - put a sock in it !

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Ivan Milenkovic
post Jan 4 2012, 04:47 PM
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Cool topic for reading, and it is written well

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