Group dealy of overdamped BR boxes

[Guss]

Gday fellows, I worry about the group delays of my speaker as I'm looking for musical sounding units... A too high group delay would make the bass loose and I want it tight. I don't want to go for sealed enclosures with small drivers but I'd like to reach 40-45hz with ease so I'm going abit overdamped... I heard 18ms was the border line, then I read it was arround 20ms. What is my response should look like at fb? 14ms is good enough? Is there any existing way to lower it mechanically or electrically?

[Ron E]

There is no conclusive evidence by which you may formulate some sort of limit below which group delay is not a problem. In fact, there is no conclusive evidence that group delay can even be detected under normal circumstances. I believe most of the studies that have been done used headphones and signals that simulated changes in group delay.

Under real world circumstances with complications introduced by room resonances, I would suggest it is wishful thinking to use the value of group delay alone as a barometer to specify sound quality. While it is true that systems with higher group delay (relative to other systems with the same cutoff frequency) tend to have poorer transient response, that does not mean that all systems with high group delay have relatively poor transient response. Any speaker system with a deeper low bass response will tend to have a higher group delay.

I would suggest to you that spectrum response is much more important than group delay. Design your system so that it has a response with no peaks, and you will have satisfactory transient response. Whether or not it matches well withyour room will have a stronger affect on your perceived sound quality. That is the art of audio.

[sreten]

Any speaker system with a deeper low bass response will tend to have a higher group delay.

This is absolutely true. Bass with delay you can hear is better
than frequencies with good delay but you can't hear them.

Note the overdamped case has better delay down to 30Hz.

Flat delay at low frequencies = bass roll off.

sreten.

[sreten]

And heres the equivalent frequency responses :

sreten.

[kelticwizard]

It should be pointed out, though, that although the group delay is larger in the box tuned to 27 Hz than in the box tuned to 38 Hz in terms of milliseconds, the group delay of the 27 Hz tuned box is only 1.54 of the time interval of the wavelength. With the 38 Hz tuned box, the group delay is 1.75 the time interval. So in a sense, the delay of the 27 Hz box is actually less, wavelength wise, than in the 38 Hz tuned box even though the milliseconds are less.

t = 1/Hz

t = 1/27 = 37 milliseconds
t = 1/38 = 26 milliseconds

Am I making any sense at all?

[Guss]

Am I making any sense at all?

If you meant that it's normal to get higher delays in the bass region because a low wave is slower than an higher freq wave, than I got it...

[sreten]

think we are all on the same page, just point out
group delay divided by wavelength, we are really
talking about the slope of the phase response,
and the frequency of the slope.

Low phase slopes give good group delay.

Here are the phase responses of the above cases.

If You want low GD in the bass you need a sealed
alignment with the necessary low phase angles,
and therefore low phase angle slopes.

Here you can see the slope of the overdamped case
is lower until below 30Hz.

And why it has a higher maximum GD, as the slope is
maximum at a lower frequency.
What should be obvious is phase response is better
for the overdamped case, at all frequencies.

This is a powerful arguement against just
considering maximum group delay values.


sreten.

[DeonC]

Hi guys

I can't really add to the technical part of this discussion- I can only my own personal experience. I have a pair of Tannoy 15" dual-concentrics in an over-damped cabinet (Berkley). I must say that they have some of the most detailed bass I have ever heard. It really hit home one time when I was listening to a song on my system, a song I might add that I had heard several times on other systems (car, headphones, and others). Suddenly a bassline that had been previously totally obscured, appeared, clear as day. This was a real eye opener The bass is maybe not the most powerful around, but it is accurate So, I for one am a firm believer in over-damped systems

Enjoy,
Deon

[Guss]

Even if overdamping helps in getting deeper bass, there are some contraints... I don't know about your setup Sreten but mine doesn't allow much nice port length finding ( 1:10 ratio is the best I can get )...

But you were right, the group delay corespond to the phase response. But than again, I don't think I need to have a flat group delay down to 40hz as the bass becomes less punchy down there.

My main problem is finding a good port ratio, at least, I don't want to end up with a 3x30inch folded and refolded port inside the box. My concerns are : getting down to 50hz flat - detailed/articulated bass. I know winsids just a kind of forecast but there might be a solution. Please point out another configuraton to me...

[kelticwizard]

Guss:

How large is your box?

There is an alternative to longer ports. A port with flares at both ends reputedly is equal to an unflared port twice it's cross sectional area-not twice it's diameter.

So a 2 inch flared port (3.14 sq in area) is appoximately equal to a 3 inch port, (7 square inches), in terms of noise, etc. Yet it only has to be as long as a 2 inch unflared port to tune the box correctly. Just add a tiny little bit extra for the flares.

Similarly, a 3 inch flared port, (7 sq inches) is approximately equal to a 4 inch unflared port, (12 sq inches), in terms of noise, etc. Yet it only has to be as long as an unflared 3 inch port to get the box to the correct tuning.

So that is one option to shrink port length to execute the underdamped response.