Lumped element vrs speaker phase properties in Time coherent systems

HBombToo · July 2003

Ok gents... The twin is not here yet but trying and would really enjoy all your thoughts on the phase properties of Polk tweeters and woofers. I have spent a little bit of time regarding this matter but am very lazy and would appreciate a collective array of thoughts.

Image stability, accuracy in reproduction and impacts on spl and efficiency are great starters but I'm just shooten in the dark.

Come on boys lets give it a wack???

HBomb

HBombToo · July 2003

pretty soon I'll delete this rant. I really thought it would draw more response.

Twin

gidrah · July 2003

Point source.

HBombToo · July 2003

here is a little tidbit I found that is a pretty easy read.

http://www.meadowlarkaudio.com/TC1.htm

Tour2ma · July 2003

I liked the "array of thoughts" pun.... the rest just made my head hurt...

amulford · July 2003

HUH???

gidrah · July 2003

With the rare exception of single driver speakers

That's what I said. Point source.

VR3 · July 2003

So Bose, is Time INcoherent?

BTW, all Rectangle speakers are........hmmmmmmmm

Lee Bailey · July 2003

You are wondering how can Polk speakers be accurate when the drivers are not aligned for time delay? Very few manufacturer's are today. Could it be that most listener's are just not sensitive enough to the effect? Or, is the time delay and phase adjusting just another way to hype your product? Even though it is measurable with equipment, one's senses are different from individual to individual.

The delays would have to built into the crossover network when one is building speakers that do not time align the drivers physically. I don't think you're gonna see this happen for the prices of mass produced products today. Nor will most people notice the difference.

HBombToo · July 2003

Originally posted by Lee Bailey
Could it be that most listener's are just not sensitive enough to the effect? Or, is the time delay and phase adjusting just another way to hype your product? Even though it is measurable with equipment, one's senses are different from individual to individual.

Lee you nailed it! Gidrah, point source is what I'm curious about. It seems logical that 2 point sources would give the greatest stereo image possible.

I have the chance here within the next year to bag a pair of Thiels and am wondering if its all worth it?

Goes back to my view on wire I guess? Why spend the cash if I'm not going to realize a huge difference. Kinda like me going from the Polk PSW350 to the SVS line... Orders of magnitude different if you catch my drift. I don't want subtle changes I'm in this hobby for the biggest bang.

Thanks
HBomb

[Deleted User] · July 2003

Forum members,
Here is a copy of a response Matthew Polk once gave concerning this subject, I thought you might enjoy it:
"Ken -

Although some of the message is difficult to follow, the basic idea is correct. Getting the sound from the various drivers to arrive at the listeners ears at the same time will improve the blending of those different drive units, reduce cancellations and improve overall coherence. This is true for all types of audio systems; home, car or professional.

As usual its not quite that simple. First of all, all frequencies travel through the air at the same speed. The bass is not slow, nor are the high frequencies fast. However, the filters used to roll off the high frequency response of woofers do introduce time delays which means that the low frequencies start out a little behind the higher frequencies. The lower the crossover point, the greater the delay, but even for a very low crossover point, say around 150Hz, the delay would be less than 1 millisecond. Sound travels about 1 foot per millisecond. So, to physically compensate for a 1 millisecond delay you would place the mid-range about a foot further away from the listener than the woofer meaning that sound from the midrange would take about a millisecond extra to reach the listeners ears.

There effect of having sound arrive at different times is to shift the phase and change the frequency response. For example, a 1 millisecond delay at 200Hz between two equal strength signals would cause a phase shift of less than 35 degrees and a change in frequency response of much less than 1db. However, at 500Hz because the wave length is shorter, the phase shift would be 180 degrees with a very deep notch in frequency response.

Typically, phase response is only important in the range from 200Hz to about 1,500Hz. Above and below that range it is frequency response that matters. The major benefit of time-aligning the drive units (physically or using electronic delays) is to get a smooth overall frequency response. This also is more difficult than it seems mainly because sound in a car bounces off a lot of other surfaces and those delayed reflections have as much effect on the frequency response as the direct sound. For this reason even with a box to dial in time delays for each driver (not cheap or easy to find) it would be very difficult to get things right without also doing very sophisticated in-car frequency response measurements. It is often easier to get things to sound good by manipulating cross over points and characteristics using much more readily available electronic cross-overs to get a smooth overall frequency response.

So, its not that it doesnt matter. In fact, its very important. However, there is no stock solution and there are easier methods than using time-delays.

-msp"

Lumped element vrs speaker phase properties in Time coherent systems

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