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Alternative explanation for subjective preference of sealed boxes

Posted by Duke (D) on December 23, 2009 at 13:13:21

In Reply to: Because cabinets are skinny now posted by Presto on December 23, 2009 at 11:18:50:

"Sealed box subs sound more musical to me anyways. The improved transient response is quite audible IMO."

I read a paper in the Journal of the Audio Engineering Society that investigated the audibility of group delay (transient distortion) on the order of what we would find in a decent vented box. Group delay was found to be barely audible on test tones, but not audible on music program material. This implies that a subjective preference for sealed boxes is probably not caused by their superior bass transient response.

In a home listening environment, the room itself is a huge factor in the perceived bass. Because of boundary reinforcement, rooms tend to boost the low frequencies. The deeper we go in the bass region, the more room boundaries will be within 1/4 wavelength of the speaker and the more bass reinforcement we get. A term that some writers have used for this is "room gain", and I've seen charts created by two different authors which suggest that typical room gain is +3 dB per octave below 100 Hz or so.

A vented box tends to be "flat" anechoic down to a much lower frequency than a sealed box, while the latter tends to have a more gentle rolloff characteristic. Factoring in room gain, a vented box that is "flat" to the 25 Hz will be +6 dB at 25 Hz in-room, which will sound bloated and slow. On the other hand a sealed box that's gently rolling off to -9 dB anechoic at 25 Hz will be -3 dB at that frequency in-room, and will sound quick and tight. In other words, the net result of vented box + room gain is likely to result in excess bass energy which is perceived as poor transient response, while the net result of sealed box + room gain is not.

I'll admit that the above is a rather extreme example, but the principle it illustrates is valid. And relative to group delay, differences in the in-room frequency response are vastly more audible.

So I don't dispute your observation, Presto, but the actual cause may be something else.

Ironically, achieving an un-equalized response that is the approximate inverse of typical room gain is easier with a vented box than with a sealed box. I've been doing it for years, and I'm sure others did so long before me.

Duke
Me being a dealer makes you leery?? It gets worse... I'm a manufacturer too.

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