"Crossover Design for New Project"

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Originally Posted by GM

I see you decided to use the restrictive window braces anyway. Hope they don't negate much of the cab's 1/4 WL ability to load/shorten the vents.

GM

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Yeah I did.I was pressed for time.I located them were you suggested.I just thought with a cabinet this BIG I really needed to brace it thoroughly.I still have braces that need to go from top to bottom in between those window braces the holes in them are large the picture doesn't do them justice.GM if they don't work I will cut them out.Front baffle is removable until cab is right then I will install them permanently.

While these aren't truly large cabs acoustically for the driver loading, they are still big enough that the pressure pulses on the walls aren't that great plus being a relatively high aspect ratio, the major pulses are concentrated vertically, so only a very rigid top/bottom is required.

The floor adds it to the bottom and ideally a slab of slate, granite or similar finishes the top off, even a heavy potted plant can audibly tighten up its tone (one professional engineer stacked all his old vinyl on his Voigt pipes to prove me full of BS and couldn't believe how much it improved their subjective performance). This puts the vertical walls in tension, so all that's needed is some vertical bracing with a tie bar or three to ensure the walls can't bow out over time.

With a horn perched on top, either multiple thickness top plates or massive horn sled will work well plus the vertical window/'holey' bracing like I referenced in a previous post to tie the top and bottom together finishes it off.

Anyway, not having compared what appears to be a significant blocking of the TL modes Vs very little, I speak only from theory as I understand it, so it will be interesting to see how much, if any, loss of loading occurs.

GM

Quote:

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Originally Posted by GM

While these aren't truly large cabs acoustically for the driver loading, they are still big enough that the pressure pulses on the walls aren't that great plus being a relatively high aspect ratio, the major pulses are concentrated vertically, so only a very rigid top/bottom is required.

The floor adds it to the bottom and ideally a slab of slate, granite or similar finishes the top off, even a heavy potted plant can audibly tighten up its tone (one professional engineer stacked all his old vinyl on his Voigt pipes to prove me full of BS and couldn't believe how much it improved their subjective performance). This puts the vertical walls in tension, so all that's needed is some vertical bracing with a tie bar or three to ensure the walls can't bow out over time.

With a horn perched on top, either multiple thickness top plates or massive horn sled will work well plus the vertical window/'holey' bracing like I referenced in a previous post to tie the top and bottom together finishes it off.

Anyway, not having compared what appears to be a significant blocking of the TL modes Vs very little, I speak only from theory as I understand it, so it will be interesting to see how much, if any, loss of loading occurs.

GM

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So if I have to do some minor tweaking that's OK.I have plenty of power tools with blades & bits.:D That is the fun part isn't it.Adjusting until getting it just right.:2thumbsup: Thanks GM for all of your gracious Help. :thankU:

Have been doing some more testing now that I think I have the measuring issues ironed out ! Software Issue ! But anyway I need to design a new sled and am wondering if i should keep the front of the horn low or raise it up a little bit. The one they are on now was just thrown together for measuring the 288's and 511E's.As in these photo's

http://www.hostboard.com/forums/hbmc...2010/11/43.jpg



http://www.hostboard.com/forums/hbmc...2010/11/44.jpg


http://www.hostboard.com/forums/hbmc...2010/11/45.jpg

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Originally Posted by Altec Best

So if I have to do some minor tweaking that's OK.I have plenty of power tools with blades & bits.:D That is the fun part isn't it.Adjusting until getting it just right.:2thumbsup: Thanks GM for all of your gracious Help. :thankU:

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You're welcome! The one of the points of helping you was to try and keep cab tweaks to a minimum, especially of the sawdust kind, since it's already paid for. Anyway, I'm really curious how much, if any, the braces may affect vent tuning, so hopefully we'll get something positive from this 'failure to communicate'.

GM

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Originally Posted by Altec Best

But anyway I need to design a new sled and am wondering if i should keep the front of the horn low or raise it up a little bit.

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Well, the main reason for putting the drivers as high up as practical in the cab is to keep their acoustic centers as close as practical to the HF driver, so jacking it up pretty much negates the effort, a bummer since ideally the woofers should have been down about 1/3 down from the top for the theoretically smoothest response, though in reality all it amounts to is the ability to use a bit less internal damping, a big deal with small 'FR' drivers, but not so much with big (mid) bass woofers.

You will need some fairly dense damping between the horn, cab though for best overall performance and personally, prefer a full perimeter foam horn extension since they are hard into the corners. Really, packing the whole corner around the horns is best to attenuate all its cavity resonances.

GM

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Originally Posted by GM

The one of the points of helping you was to try and keep cab tweaks to a minimum, so hopefully we'll get something positive from this 'failure to communicate'.

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All I said was if it doesn't work the (window braces) then I will have to fix it (Not a problem).I could have built them myself but I wanted to get them done sooner,I would have only been doing on the weekends.

Quote:

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Originally Posted by GM

Well, the main reason for putting the drivers as high up as practical in the cab is to keep their acoustic centers as close as practical to the HF driver, so jacking it up pretty much negates the effort, a bummer since ideally the woofers should have been down about 1/3 down from the top for the theoretically smoothest response, though in reality all it amounts to is the ability to use a bit less internal damping, a big deal with small 'FR' drivers, but not so much with big (mid) bass woofers.

You will need some fairly dense damping between the horn, cab though for best overall performance and personally, prefer a full perimeter foam horn extension since they are hard into the corners. Really, packing the whole corner around the horns is best to attenuate all its cavity resonances.

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I was talking about tilting the front of the horn up or down not really moving it up high there really isn't a whole lot to do with a sled. The brackets I have on the back of the horn are kinda small and was wondering about using a longer bracket to tilt them down a bit into the listening room. Heck i can use the same sled i have now I just have to cut the back corners off to fit it in the corner.So I can slide up or back to time align.

Well they are Finally home ! More pictures to follow once I get settled in with them. The size, well let's just say pictures don't explain the whole picture. :eek:

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Originally Posted by Altec Best

Well they are Finally home ! More pictures to follow once I get settled in with them. The size, well let's just say pictures don't explain the whole picture. :eek:

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Hey AB, thanks for keeping this thread going to the finish, I'll be waiting on those "glamour shots" when you post them.

FWIW, these build threads with the accompanying discussion of the various design decisions are like gold, IMO. Thanks to all that have contributed!

Your Welcome ! I'm looking forward to finishing them and then measuring them up.Will follow through. ;)