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Old 25th July 2005, 05:52 AM   #1
Nm2285 is offline Nm2285  United States
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Default Driver Alignment

A few questions regarding a large, 2-way bookshelf design:

1) When offsetting the two drivers from a vertical alignment in a bookshelf speaker, is there any standard or best practice method of determining the amount of offset?

2)What are the advantages of inverting the woofer and tweeter? When should this be done

3) Is there any method for determining the optimal vertical distance between the woofer and tweeter? I have a tall front baffle and am not sure how far apart to place them.


As a note, I'm using the Vifa XT19 and the Peerless 850122.

Thanks for your assistance!
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Old 25th July 2005, 07:51 AM   #2
simon5 is offline simon5  Canada
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2) Inverting the tweeter or woofer can be done if you use a 2nd order crossover on both drivers, or some situations like that.

3) As close as you can is better. Tweeter at ear level.
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Old 25th July 2005, 08:54 AM   #3
morbo is offline morbo  Canada
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Quote:
1) When offsetting the two drivers from a vertical alignment in a bookshelf speaker, is there any standard or best practice method of determining the amount of offset?
IIRC, the idea is to have the tweeter at uneven distances from all 3 nearby baffle edges (top, right, left). So for a start, make sure your offset doesnt end up making one of the side distances to be equal to the top distance.

I do recall some mention of the ideal ratio of these 3 distances, but I can't for the life of me remember when I saw it. Maybe the golden ratio?
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Old 25th July 2005, 12:48 PM   #4
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hehe It's funny how different people can interpret the same questions differently. The only one I had an answer for was 3, which Simon already answered

1. I thought the question was regarding time alignment, ie +ve or negative displacement of the tweeter in the vertical plane....

2. I thought the question was regarding invertion physically rather than electrically, ie tweeter on the bottom woofer on the top

Tony.

edit: if you want to model the effects of driver displacement left on the baffle (and have excel) then you should have a look at http://www.pvconsultants.com/audio/d...ownloadbds.htm
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Old 25th July 2005, 03:17 PM   #5
rabbitz is offline rabbitz  Australia
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Have a look at this thread as it might help on confuse you further

Time Alignment on a flat baffle.....

1. Use the centre of the voice coil, mid point of the driver's front plate is close enough.
2. Used in odd order crossovers, 1st and 3rd, to compensate for the downward polar tilt. Reverse the tweeter polarity for 3rd order.
3. Keep the driver centres less than the wavelength of the crossover frequency.... wavelength in metres=345/Hz. Have the tweeter at about ear level in your listening position.

BTW, nice choice of woofer as the 850122 is a freak of nature.... really special.

Cheers
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Old 25th July 2005, 03:53 PM   #6
Nm2285 is offline Nm2285  United States
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Thanks for the replies.

Question 2 actually was about physical inversion (tweeter below woofer rather than the usual on-top).

I'll have to take a look around for the ratio of top-left-right distances. Let me know if you have them.
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Old 25th July 2005, 04:01 PM   #7
rabbitz is offline rabbitz  Australia
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Quote:
Originally posted by Nm2285
Question 2 actually was about physical inversion (tweeter below woofer rather than the usual on-top).
Yep... that's what I was referring to.... inverted drivers...... woofer on top. The polarity only comes into it for 3rd order tweeters.

There's a program around called "The Edge" which can help on location of drivers..... do a search on this forum.
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Old 25th July 2005, 04:16 PM   #8
Nm2285 is offline Nm2285  United States
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One other question:

Since the drivers should be close together, I'll have a lot of extra space on the front baffle. It doesn't matter if I put them at the top, middle, or bottom, does it? I figure I'll just put them wherever ear level would be.
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Old 25th July 2005, 04:31 PM   #9
rabbitz is offline rabbitz  Australia
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As a suggestion, put the drivers close to the top of the cabinet and have a look at the picture in that link I provided. I tend to put the drivers in the centre of the baffle left to right even though it's frowned upon.

Have a look around what others are doing and also commercial speaker websites.
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Old 25th July 2005, 11:12 PM   #10
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Quote:
Originally posted by Nm2285
One other question:

Since the drivers should be close together, I'll have a lot of extra space on the front baffle. It doesn't matter if I put them at the top, middle, or bottom, does it? I figure I'll just put them wherever ear level would be.

David Weems suggests putting the woofer 1/5 of the way down from the top when you have a tall skinny cabinet. This is to help stop pipe resonances from memory.

Tony.
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