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Old 24th July 2004, 01:07 PM   #11
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Quote:
Originally posted by Vikash
Hi Zaph, I may have to rethink my design then. What is the net effect of bad group delay? sloppy bass? Group Delay is one of those graphs I've ignored up until now.

Perhaps my six drivers would be better made into sealed monitors for a HT setup. Hmmm.
Group delay -- the nemesis of filter builders -- in audio it can cause voices to blur or spread out and pianos to sound very unnatural -- i think that the voice and piano are the two great devices for listening tests.

The speaker, its box (and all the dimensions therein) or the alignment are all a "physical filter" -- the great advance that theile-small did was to transform the physical aspects into electrical aspects which could be modeled.
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Old 24th July 2004, 02:06 PM   #12
Zaph is offline Zaph  United States
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Originally posted by jackinnj


Group delay -- the nemesis of filter builders -- in audio it can cause voices to blur or spread out and pianos to sound very unnatural -- i think that the voice and piano are the two great devices for listening tests.
That's exactly right. Unnatural is the word that describes it best. Basically, the harmonics don't properly line up with the fundamental, and the result is slop. It's easier to hear it with high tuned, high Qts woofers because they will sound fine until the bass player hits that note at the tuning frequency. It will stand out like a sore thumb. Or worse yet, the music has a beat and that beat is at the tuning frquency. Honk honk honk. It may measure flat with a sine wave, but it's still going to sound like one-note bass.

I like vented enclosures, but in general I prefer them with lower Qts woofers, and the tuning frequency lower and out of the primary musical spectrum. Like tuned 35-40hz or lower. Or I bend that rule occasionally with different woofers, such as very low Qts small woofers, or larger slightly high Qts woofers that can make use of a very low tuning frequnecy.

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Old 24th July 2004, 02:36 PM   #13
Vikash is offline Vikash  United Kingdom
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What's the scientific explanation for it (in layman terms)? And what do you consider acceptable GD figures generally speaking?
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Old 24th July 2004, 03:50 PM   #14
Zaph is offline Zaph  United States
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Quote:
Originally posted by Vikash
What's the scientific explanation for it (in layman terms)? And what do you consider acceptable GD figures generally speaking?

Well, lets pick an instrument, say a kick drum. The primary tone (fundamental) that comes out of it is 60hz. But the kick drum also has harmonics all over the spectrum. probably some at 120 hz, some at 1500hz and even higher. If there were no harmonics, it would just be a simple sine wave.

If there is 20 ms group delay at 60hz, the fundamental is going to be slightly delayed in comparison to the harmonics, resulting in an unnatural sound. For higher frequencies, jackinnj's description fits well. At lower frequencies it can be described as sloppy and undefined.

Large kick drums are usually centered on 60hz, and the lowest string of a bass guitar is around 40hz. There are fewer harmonics in a bass guitar than a kick drum however. In general, I think you can get away with higher group delay as you move further away from the music spectrum. If I had to put a number on it, I'd say under 10 ms at 50 hz and under 12 or 14 ms at 40 hz.

This is often hard to do with a vented alignment, and I often chose a non-optimum box size for vented. I still prefer vented over sealed, but only with larger woofers. I rarely vent any drivers under 5".

See this thread over at the mad forum for an idea about non-optimum enclosures and group delay.
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