How bad is the combing effect using multiple mids?

swak · 17th August 2007, 05:45 PM

I have the plan to use 4 small (4.5") drivers per side spaced at 12.5cm from each other (center to center distance between each other, in two colums, each driver touching the others edge) and I was wondering at what frequency the combing effects could get me in to trouble. The drivers can go up to 9K, although I may not want to go that high. So, what should be the highest frequency of operation of the mids? How much do combing effects affect sound quality?

Svein_B · 17th August 2007, 06:00 PM

Download THE EDGE baffle difraction simulator from
http://www.tolvan.com/edge/help.htm
Then you can play with different configurations.

The [simulated] effects are most noticeable above around 5K

SveinB.

zobsky · 17th August 2007, 07:31 PM

Quote:

Originally posted by swak
I have the plan to use 4 small (4.5") drivers per side spaced at 12.5cm from each other (center to center distance between each other, in two colums, each driver touching the others edge) and I was wondering at what frequency the combing effects could get me in to trouble. The drivers can go up to 9K, although I may not want to go that high. So, what should be the highest frequency of operation of the mids? How much do combing effects affect sound quality?

wavelength = 340 / 0.125 = 2720 Hz
2 x wavelength = 5440 Hz

You want to cross over somewhere betwen these two frequencies (preferably closer to the lower number, though the actual value will depend on the actual degree of roll off from arraying them)

rcavictim · 18th August 2007, 04:07 AM

I advise against placing them in two closely spaced vertical columns of two drivers per column (or any other number). You will get azimuthal lobing. Place all four in one vertical clolumn as close together as you can get them. The actual characteristics of the driver will determine to a great extent how bad if at all the comb filtering will be.

swak · 18th August 2007, 12:31 PM

Thanks for your responses.

I have been playing with Egde,and I am a confused with it: increising the speaker source density high enough there is no more ripple/combing. The response changes drastically by increasing the number from 1 to 20.From what I see, 4 is renders the expected behavior.

RCAVICTIM:

thanks for your comment. How about a diagonal line of drivers going from one corner of the baffle (upper left) to another (lower right). This would allow for a shorter baffle. Acrually the response in Egde is better this way as configured in any vertical column.

there is also this arrangement which models very flat and has less open baffle peak. It looks like this:
___
....X|
.X...|
.X...|
__X|

There would e enough space to place the tweeter in the middle of the drivers, but then again this may lead to the problem rcavictim mentioned in the overlapping range, specially in low order crossovers are used.

swak · 18th August 2007, 01:06 PM

One more question: should I expect 3dB extra from each additional mid driver?

tinitus · 18th August 2007, 01:43 PM

No, there is a limit to it all ... I think it is 3db every time you double the amount of drivers

swak · 18th August 2007, 01:49 PM

So, I double the first, +3db. Then I double the pair, +3dB again for a total gain of 6 dB respect to the base sensitivity of the first driver, right?

darkfenriz · 18th August 2007, 01:58 PM

Combing should be no problem here, because distance from drivers to listener will vary only by single centimeters if the listener is on axis.

17th August 2007, 05:45 PM	#1
swak diyAudio Member Join Date: Jul 2003 Location: .	How bad is the combing effect using multiple mids? I have the plan to use 4 small (4.5") drivers per side spaced at 12.5cm from each other (center to center distance between each other, in two colums, each driver touching the others edge) and I was wondering at what frequency the combing effects could get me in to trouble. The drivers can go up to 9K, although I may not want to go that high. So, what should be the highest frequency of operation of the mids? How much do combing effects affect sound quality?

18th August 2007, 04:07 AM	#4
rcavictim diyAudio Member Join Date: Jun 2004 Location: Cool end of a soldering iron NW of Toronto	I advise against placing them in two closely spaced vertical columns of two drivers per column (or any other number). You will get azimuthal lobing. Place all four in one vertical clolumn as close together as you can get them. The actual characteristics of the driver will determine to a great extent how bad if at all the comb filtering will be. __________________ I.Q.Test. Have you ever purchased a recreational snowmobile?

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17th August 2007, 06:00 PM	#2
Svein_B diyAudio Member Join Date: Oct 2005	Download THE EDGE baffle difraction simulator from http://www.tolvan.com/edge/help.htm Then you can play with different configurations. The [simulated] effects are most noticeable above around 5K SveinB.

18th August 2007, 12:31 PM	#5
swak diyAudio Member Join Date: Jul 2003 Location: .	Thanks for your responses. I have been playing with Egde,and I am a confused with it: increising the speaker source density high enough there is no more ripple/combing. The response changes drastically by increasing the number from 1 to 20.From what I see, 4 is renders the expected behavior. RCAVICTIM: thanks for your comment. How about a diagonal line of drivers going from one corner of the baffle (upper left) to another (lower right). This would allow for a shorter baffle. Acrually the response in Egde is better this way as configured in any vertical column. there is also this arrangement which models very flat and has less open baffle peak. It looks like this: ___ ....X\| .X...\| .X...\| __X\| There would e enough space to place the tweeter in the middle of the drivers, but then again this may lead to the problem rcavictim mentioned in the overlapping range, specially in low order crossovers are used.

18th August 2007, 01:06 PM	#6
swak diyAudio Member Join Date: Jul 2003 Location: .	One more question: should I expect 3dB extra from each additional mid driver?

18th August 2007, 01:43 PM	#7
tinitus diyAudio Moderator Join Date: Nov 2005	No, there is a limit to it all ... I think it is 3db every time you double the amount of drivers

18th August 2007, 01:49 PM	#8
swak diyAudio Member Join Date: Jul 2003 Location: .	So, I double the first, +3db. Then I double the pair, +3dB again for a total gain of 6 dB respect to the base sensitivity of the first driver, right?

18th August 2007, 01:58 PM	#9
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	Combing should be no problem here, because distance from drivers to listener will vary only by single centimeters if the listener is on axis.

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