Would something like a SEOS Fusion / Alpha/ karma DIY work well in a baffle wall ??? - AVS Forum
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Old 08-30-2013, 09:46 AM - Thread Starter
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Mostly looking at something with DNA360

Thoughts?

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Old 08-30-2013, 11:52 AM
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yes. any good driver with a well integrated crossover network will be fine.

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Old 08-30-2013, 12:37 PM
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Wouldn't it be necessary to install the waveguides in the wall so that they're toed in at 45 degrees for optimum performance?
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Old 08-30-2013, 12:53 PM - Thread Starter
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I guess I need to learn more about baffle walls. I was going some reading and I am weighting the false screen wall versus a full baffle wall. Just wondering about that...

If I build a full SEOS style speaker would I just mount it or incorporate it into the baffle wall ? Or do you cut a whole in the baffle wall that the speaker fits into and mounts flush ? Does it matter?

I guess I need to do some more research.

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Old 08-30-2013, 12:57 PM
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"Wouldn't it be necessary to install the waveguides in the wall so that they're toed in at 45 degrees for optimum performance?"

yes. it wouldn't have to be exactly 45 degrees, but some sort of toe in.

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Old 08-30-2013, 12:59 PM
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"If I build a full SEOS style speaker would I just mount it or incorporate it into the baffle wall ?"

either way.

some speakers have "baffle step correction" built into the crossover. this reduces the top end sensitivity to make the bottom end seem more balanced. when put in or on a baffle wall, such correction isn't really needed, particularly if you are doing it right and have eq anyways.

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Old 08-30-2013, 01:29 PM - Thread Starter
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Old 08-30-2013, 01:31 PM - Thread Starter
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I think I understand the point of a baffle wall...

But I am not certain if a baffle wall is for a specific speaker like a Procella or a in wall Triad type- or if you can use any speaker with a baffle wall and get the benefits of a baffle wall?

Could I build a baffle wall- cut out an exact size hole for a SEOS- and mount a totally stock built SEOS into it and get the proper result ? Or would I need to re-design the parts or crossovers or cabinets ?

Better to skip a baffle wall and just use a false screen wall ?

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Old 08-30-2013, 01:47 PM
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i'm not sure how much baffle step correction is built into each different seos crossover design. at worst, you build the wall, put your speaker in it and have to apply a little bit of eq. no biggie.

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Old 08-30-2013, 02:09 PM
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here is a bit on bsc: http://www.salksound.com/wp/?p=42

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Old 08-30-2013, 02:22 PM
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Old 08-30-2013, 02:46 PM - Thread Starter
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Thanks for this !
http://www.salksound.com/wp/?p=42
Quote:

BSC made simple (and why it may be important to you)

by JIM SALK
in SPEAKER DESIGN
While baffle step compensation (BSC) sounds complicated, it is really quite simple once you understand what happens when sound waves emanate from a speaker. Here is a slightly over-simplified explanation:

the nature of sound
Sound, by its very nature, wants to travel in all directions. When sound is generated by the woofer in a speaker, for example, that sound not only projects forward to the listening position, but also travels around to the rear of the speaker.

You can confirm this with a simple experiment. Stand behind a speaker and you will still hear sound, although note that the highs will be lacking.

Congratulations, you have just unlocked the key to understanding the mystery of BSC! Let’s look at what is happening here.

details
What happened to the high frequency sounds? In short, they were reflected forward when they bounced off of the front baffle of the speaker.

This phenomenon is related to the wavelength of the sound at various frequencies. Just so you don’t have to do any math, here is a rough table (bear with it…this will not get too technical):

Frequency
Approx. Wavelength
20,000 Hz
.67″
10,000 Hz
1.35 “
5,000 Hz
2.7 “
1,500 Hz
9 “
1,000 Hz
13 “
750 Hz
18″
440 Hz
(A above middle C)
30 “
I have highlighted two entries in the above table. We will see why in a moment. And you will understand the theory behind BSC when that moment arrives!

baffle width and BSC
Let’s take a look at what happens when sound is generated by speaker drivers that are mounted in the middle of a baffle that is 9″ wide.

When the 20,000 Hz signal in the table is generated by the tweeter, it tries to move in all directions. But after one wavelength, it has traveled only .67 inches. So although a portion of the energy tries to move to the rear of the speaker, it can’t. It hits the front baffle and is reflected forward towards the listener. The same is true of the 10,000 Hz and 5,000 Hz signals in the table.

The 1,500 Hz signal (highlighted), on the other hand, has a wavelength of 9″ and reaches the edge of our 9″ baffle where diffraction can actually cause a slight rise in response levels at the listening position. At 750 Hz (also highlighted), the sound actually begins to travel around to the rear of the speaker.

So basically, any frequency lower than 750 Hz will be able to travel around the speaker (creating a roll-off of 3db for two octaves at the listening position), while frequencies above that will not. You heard this in the listening experiment above.

Note that increasing the width of the baffle will simply reduce the frequency where this behavior difference occurs. So BSC must be designed for the specific baffle in question.

the problem
OK. So, in our example, most of the sound at frequencies above 750Hz is directed forward toward the listener. Sounds at lower frequencies are not only directed forward, but also pass around the speaker to the rear. In fact, nearly half of the sound pressure is lost to the rear of the speaker.

So think about this: if the tweeter and woofer generate the same volume, high frequencies will be twice as loud as low frequencies at the listening position. (While this sounds like a huge difference, keep in mind that a doubling of sound pressure is about the smallest volume differential humans can detect.)

At any rate, the result at the listening position is sound that will be thin and lacking in the bottom end.

the solution – BSC
The solution is to design a circuit in the crossover that shapes the sound to compensate. It basically rolls off the higher frequencies so that they are in line, volume-wise, with the lower frequencies at the listening position. Baffle step compensation saves the day!

You should now understand the theory behind baffle step compensation. Congratulations!

but…
What happens when you mount this speaker in a wall?

Well, you have now increased the width of the front baffle. It now becomes the entire wall surface, so you have essentially created a baffle of infinite width. In this case, even the low frequencies cannot move to the rear of the speaker.

Since you rolled off the highs with BSC, you will now have too much low frequency energy directed forward. The result will be a boomy, uncontrolled bottom end.

The same would be true, although perhaps to a lesser extent, if you backed the speaker up to the wall. In both cases, an excess of bass energy (in relation to higher frequencies) is directed at the listening position.

This is why speakers designed to be free-standing (which require BSC) should not be mounted in a wall.

congratulations!
You now have a working understanding of baffle step compensation. Your friends are bound to be impressed, but as to whether that is in a positive or negative fashion remains to be seen. You are now officially a “speaker geek.”

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Old 08-30-2013, 02:46 PM - Thread Starter
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I was thinking more build the full speaker (the box too) and just mount the front of the speaker flush with the wall. No ?

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Old 08-30-2013, 03:24 PM
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Originally Posted by LTD02 View Post

here is a bit on bsc: http://www.salksound.com/wp/?p=42

One of my bookmarks for sure, good description and well written imo.

Hey, Mfusick. Just wait till you hear a set of SEOS designs, they're awesome. Build a pair and then you can decide how far you want to take it. I love mine!

Anyway, linwitz's definition of diffraction is simple: "diffraction is about the transition between an acoustic wave propagating from one space first into another space of different volume."

http://www.linkwitzlab.com/faq.htm#Q8

A simulation will show a full 6db loss at the given frequency when it travels across the edge and sides, but it'll change when we're in 4pi space. Most of these SEOS designs' xo's are between 1200Hz-1500Hz and would occur at a shorter wavelength hence the 14.5-17.25" baffles. If there was any compensation added, a wall might cause an unwanted rise in response right around crossover frequency. Check out Bagby's Diffraction and Boundary simulator to see this happen in 2pi. If had to develop a bsc circuit, though, I would start at 2db and work up in values (parallel resistor and inductor in series). Measure-repeat. There are many variables depending on the crossover order, but ultimately this has to be attained through driver's frequency response in the final system.

So, ya, you'd probably need to redesign if doing a baffle wall. smile.gif Build a pair and stick them behind an acoustic transparent screen...
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Old 08-30-2013, 05:17 PM
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You're going to change the tonal balance putting it into a wall. Even a baffle wall. You can correct with eq, but you'll have to measure the response to know how. What I did to my wall is no different than a baffle wall. A dedicated XO will extract the most from your plan and reduce the amount of eq required. But can be bandaided with eq if you must use an existing design.
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Old 08-30-2013, 05:36 PM
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Quote:
Originally Posted by robotbunny View Post

A simulation will show a full 6db loss at the given frequency when it travels across the edge and sides, ..
True, but most of that comes back off the rear wall as a reflection, so it's not truly lost unless there is no real wall. Just as much of a consideration is Allison Effect, where the baffle is 1/4 wavelength from the rear wall, and the reflection meets the original wave 180 degrees out of phase, causing a cancellation notch. One benefit to flush mounting is that there is no Allison Effect. But you do have to be sure that if you're going to flush mount that you don't incorporate BSC into the design.
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Old 08-30-2013, 08:32 PM
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Quote:
Originally Posted by robotbunny View Post

One of my bookmarks for sure, good description and well written imo.

Hey, Mfusick. Just wait till you hear a set of SEOS designs, they're awesome. Build a pair and then you can decide how far you want to take it. I love mine!

Anyway, linwitz's definition of diffraction is simple: "diffraction is about the transition between an acoustic wave propagating from one space first into another space of different volume."

http://www.linkwitzlab.com/faq.htm#Q8

A simulation will show a full 6db loss at the given frequency when it travels across the edge and sides, but it'll change when we're in 4pi space. Most of these SEOS designs' xo's are between 1200Hz-1500Hz and would occur at a shorter wavelength hence the 14.5-17.25" baffles. If there was any compensation added, a wall might cause an unwanted rise in response right around crossover frequency. Check out Bagby's Diffraction and Boundary simulator to see this happen in 2pi. If had to develop a bsc circuit, though, I would start at 2db and work up in values (parallel resistor and inductor in series). Measure-repeat. There are many variables depending on the crossover order, but ultimately this has to be attained through driver's frequency response in the final system.

So, ya, you'd probably need to redesign if doing a baffle wall. smile.gif Build a pair and stick them behind an acoustic transparent screen...

I believe Bill did not design any baffle step in his crossover designs for the SEOS.

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Old 08-31-2013, 08:44 AM - Thread Starter
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Originally Posted by AV Science Sales 5 View Post

I believe Bill did not design any baffle step in his crossover designs for the SEOS.

What type of correction is appropriate ?

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Old 08-31-2013, 10:17 AM
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"What type of correction is appropriate ?"

none is required, but it is a personal preference.

a smooth and slightly downward sloping response across the entire frequency spectrum is what many folks prefer, but not everybody.

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Old 08-31-2013, 10:57 AM
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It also depends on the baffle size and whether subs are used. On a little stand mount TM with a 8x12" baffle without subs, pulled away from the walls 5' or more, you're going to want 6db of baffle step compensation. That makes for an inefficient speaker.

If a large speaker with subs taking care of the sub 80hz then the amount of baffle step required wont be much, and if none is used, it won't be that audible depending on the room.
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