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KIH #34 – Any port in a storm

  • One man’s ‘Ode to Joy’ by Louis van Beethoven becomes another’s ‘Node to Oi’ by Lewis von Beathaufen. He uses ‘Oi’ as shorthand for obnoxious irritant. This forwards us from prêt-à-porter, ready to wear in French, at fret-à-ports, ready to swear at ports. In speakers, they’re virtually omnipresent. For every sealed or transmission-line speaker, there must be 100s with one, two or three holes attached to which are pipes of a certain length. Those act as resonators to enhance low- frequency reach and power. Depending on which direction they aim at (front, back or down), to what frequency they’re tuned and whether they’re high or low Q, ports can come with side effects which aren’t that often discussed.

    There’s the notion that good sound only matters in the sweet spot. That’s rooted in how stereo works. The perfect stereo illusion demands perfect symmetry by way of path-length equality between the left/right speakers and your ears. Anything outside that spot is sub optimal by definition. Why should a card-carrying audiophile care what happens outside his small comfort zone, there at the apex of our tribe’s sacred stereo triangle?

    I could think of two reasons. The first is social not asocial enjoyment. If one could do so without liabilities, why not make better sound in more seats or areas? Two, the sweet spot isn’t an island in a vacuum. It’s influenced by what else happens in the room. The air connects everything within it.

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    Do a little experiment. Play some music containing substantial bass. Walk around your room. Stand in each front corner. Walk along the side walls. Stand to either side of the central chair as though there were more seats on each side. Walk up and down the virtual centre aisle. Map the entire space like a chequered table cloth. Unless you’re very lucky; or very good at setup; or simply happen to own one of the rare non-ported speakers… you should have noted rather uneven sound depending on your location. Particularly, you should have noticed how certain notes or bunches of them “went off” like a bell or debris from a mortar hit. This boom and associated wooliness could make listening in any of those spots most annoying indeed.

    Granted, you’ll never sit in the front corners. Why give a toss about those? If you’re not inclined to share, you might feel the same about any spot other than your hot seat. And that’s certainly a valid position to take. Even so, it still overlooks that if your shoe is too tight, it’s not only your foot that hurts. Your mood sours, your gait changes, your attention keeps getting diverted and so forth.

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    The same is true for a room. “Faraway” bass pressure zones compress far finer more fragile HF which want to pass through them as reflections. Less pressurization, better treble. Also, high pressure zones create acoustic stress which our nervous system registers whether we’re aware of it or not. This leads to sooner fatigue. The proof is in the pudding. Temporarily stuff your ports with tightly rolled- up kitchen towels or anything else suitable. Repeat the walkabout. Not only should you notice less “room mode crap” (which that experiment proved was in fact a lot of port-induced crappola), you should also notice better easier more even sound in the hot seat. (Of course you’ll also have less bass power and perhaps even extension since you disabled that particular speaker’s innate tuning.)

    Without massive room treatments, certain peaks and troughs are unavoidable. Acoustic energy distribution below 200Hz will activate certain room modes based on placement and architectural geometry. Good setup simply insures that the seat doesn’t coincide with either a peak or trough though a cut will be less offensive.

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    Just how big the before/after effect will be between open and closed ports depends on their tuning frequency, Q and your room. In my experience, the worst offenders are rear-firing ports whose tuning sits below 50Hz. I touched on this subject in the recent Æquo Audio Ensis loudspeaker review for my site. As a rarer sealed design, I compared it directly to a 2-way monitor with two rear ports per channel. Where the Ensis performed far less lumpy all around and likewise in the hot seat, the Kroma Audio Julieta was unlistenable in a rocking chair along the sidewall where it boomed like a juvenile truck. In the same spot, the Ensis performed unblemished. Ditto for more areas like my work desk, our dining table and others. While the Julieta was brilliant in the sweet spot, it was really fussy outside of it.

    Ports are popular because software can easily calculate their length and diameter for a given box volume and response goal. They allow more bass from smaller boxes with smaller woofers. Since small is popular, ports are, too. What few people tell you is that many ported designs will cause acoustic hot spots which are very easily mistaken for room modes, i.e. effects one thinks are endemic to the room and thus must be put up with. Not. It’s when one experiments with ported vs. sealed designs of similar bandwidth, in the same room, each optimized by precise location, that the penny begins to drop about self-inflicted pain. Invariably the sealed speaker will cause less “room” issues. It’ll sound better, more even and less lumpy in more places (a benefit on the social scale) and because of that, will sound better in the hot seat (a benefit on the asocial scale).

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    If you’re invested in a ported speaker you love, never mind. You’ll have figured out how to best accommodate it. This article is for those who aren’t committed; who are still shopping for their next ‘serious’ speaker. It’s to those people that I recommend sealed speakers or transmission lines. If not you, then your significant other who does all her listening anywhere but in the sweet spot might just thank me. Actually, I’m certain you’ll be as well. Removing or minimizing port-induced issues really does have a demonstrable effect on the listening experience even in the ‘perfect’ spot. For good sport and to wrap up, obviously there are worse and lesser port offenders; and combinations of those and given rooms that will show up these interactions to varying degrees. But I’d still ask myself. Why buy into ‘less’ when one could avoid stepping into the muck altogether? Ode to Joy and all that…

    You can read more of Srajan’s supremely erudite audio coverage over at his own 6moons.

    Srajan Ebaen

    Written by Srajan Ebaen

    Srajan is the owner and publisher of 6moons. He used to play clarinet at the conservatory. Later he worked in audio retail, then marketing for three different hifi manufacturers. Writing about hifi and music came next, then launching his own mag. Today he lives with his wife Ivette and Nori and Chai the Bengal cats in a very small village on Ireland’s west coast, between the holy mountain Croagh Patrick and the Atlantic ocean of Clew Bay in County Mayo’s Westport area. Srajan derives his income from the ad revenues of 6moons but contributes to Darko.Audio pro bono.

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