For a 3-way surround speaker, are there issues in a W-T/M layout? - AVS Forum
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post #1 of 9 Old 04-24-2013, 07:19 AM - Thread Starter
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I'm planning to upgrade my HT (and m-ch music) system from having coax 5.0 to 3-way speakers.

To do the surrounds in the same 3-way would result in a fairly tall rear speaker, which I'd like to avoid.

So two questions:

- are there any issues with a more horizontal layout (effectively removing one woofer from the centre)



- in the image the dark part is of course the slot port; with a couch against the back wall these will be placed to the side; what would be the best order for the layout (the image shows port next to wall, woofer next to port, T/M furthest)

Thanks smile.gif

edit: oops, meant to put this in DIY, but let's see what folks think here too.

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post #2 of 9 Old 04-24-2013, 08:42 AM
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Yes, there is an issue with a layout such as you suggest. There will be a range frequencies where both the woofer and mid range are making sound. This can create additions and cancellations, lobing, that will change as the listener moves horizontally. What these frequencies are depends on the choice of woofer, mid range, crossover frequency, and crossover slopes. Just how audible this might be depends on many details, including the distance between the listener and the surround speakers.

An alternative is a 2-way surround speaker where the drivers are in-line with each other vertically. Because you seem to want as much bass as possible from surround speakers, I think a 2-way with a suitable 6½" woofer could work well.

Both designs are compromises. In my opinion, a 2-way is less of a compromise than the 3-way you described.
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post #3 of 9 Old 04-24-2013, 08:48 AM - Thread Starter
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Quote:
Originally Posted by R Swerdlow View Post

Yes, there is an issue with a layout such as you suggest. There will be a range frequencies where both the woofer and mid range are making sound. This can create additions and cancellations, lobing, that will change as the listener moves horizontally. What these frequencies are depends on the choice of woofer, mid range, crossover frequency, and crossover slopes. Just how audible this might be depends on many details, including the distance between the listener and the surround speakers.

This shouldn't be much of an issue, as this is really 2/3 of the centre speaker with W-T/M-W layout, with W->M xo chosen such that the two woofers won't cause lobing (somewhere around 500Hz where the wavelength is 27.1", so driver CTC spacing would be way under this).

I think i have this right redface.gif

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post #4 of 9 Old 04-24-2013, 09:07 AM
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Quote:
Originally Posted by rick240 View Post

I think i have this right redface.gif

Why did you ask? Believe me, I don't wish to argue over this smile.gif.
Quote:
Originally Posted by rick240 View Post

This shouldn't be much of an issue, as this is really 2/3 of the centre speaker with W-T/M-W layout, with W->M xo chosen such that the two woofers won't cause lobing (somewhere around 500Hz where the wavelength is 27.1", so driver CTC spacing would be way under this).

The major questions involved in selecting a crossover frequency are the high frequency behavior of the woofer and the low frequency behavior of the mid range. Relative driver location, CTC spacing, is considered, but it isn't the primary factor.

I have seen others say that CTC spacing determines the crossover frequency for speakers. This is an oversimplification and has been known to sometimes result in bad speaker designs. If I've assumed incorrectly that this is behind your thinking, please forgive.
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post #5 of 9 Old 04-24-2013, 09:38 AM
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Quote:
Originally Posted by R Swerdlow View Post

The major questions involved in selecting a crossover frequency are the high frequency behavior of the woofer and the low frequency behavior of the mid range. Relative driver location, CTC spacing, is considered, but it isn't the primary factor.
In this case it is. Keeping the CTC less than one wavelength will mutually couple the woofer and midrange in the region of the crossover, so there will be no combing or lobing issues. Of course the drivers must be chosen so that they work well together, just as is the case with a vertical alignment. But in a vertical alignment combing and lobing aren't nearly as serious issues as they are with a horizontal alignment, and therefore one wavelength CTC in a vertical alignment is a secondary consideration and need not be strictly adhered to. In a horizontal alignment CTC spacing is a critical factor.

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post #6 of 9 Old 04-24-2013, 01:12 PM
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The wavelength corresponding to the crossover frequency between the w and m will almost certainly be much less then the CTC distance of the 2 drivers. I think the layout will be fine. Ideally, the drivers would be stacked, but you can't do that so your layout is probably the best you can do within reason. Unless you do what Kef does and put drivers inside of drivers.
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post #7 of 9 Old 04-24-2013, 02:57 PM
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are you gona be mounting these on the wall or stand?
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post #8 of 9 Old 04-24-2013, 04:15 PM - Thread Starter
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Originally Posted by RicardoJoa View Post

are you gona be mounting these on the wall or stand?

They are likely to be resting on furniture (tables or stands).

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post #9 of 9 Old 04-24-2013, 07:01 PM
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The reason i asked is because, if you are going to rest them on a stand and if this is going to be a custom job, might as well just go with a tower set up. It will take as much floor space and you dont have to worry about the horizontal layout between the woofer and mid. But it may not be as flexible, if you are resting them on a furniture, then may need some planing
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