I'm trying to make some speaker boxes for some 6.5" marine speakers. Just by experimenting with trial and error, I came up with a box that I rather like, it's internal volume is an 8" cube, it's made of 3/4" plywood glued at all seams. This calculates to 512Cu Inches or close to 0.3cu Ft, unfortunately it wouldn't fit in one of the locations where I want to install it.. these are going in the ceiling of my house before I drywall it. So I made a new box, also 512cu inches inside, this one the interior measures 6.75width x 13.192length x 5.75depth... I also offset the speaker to one side just to get it closer to the wall.. but it doesn't need to be that close... I just thought it would look good.
The new box just doesn't sound anywhere as good as the 8" cube, even though it has the same internal volume. identical speaker and both running off the same amplifier. The cube has a clean low frequency response that fills the room while the new box is just lacking substantially.
I'm trying to get my head around why this would be.... I've seen so much about box volume but not much regarding the actual shape of the box. I'm wondering if centering the speaker sounds better than having it offset, or perhaps it's just the shallow depth that's causing the issue. I would rather not build box after box just randomly trying things, so if anyone has any insight as to what is going on here it would save me hours of building boxes, while that is a bit of fun, I do have some work that could be done instead 🙂
The issue I'm having with the one location is there is a ventilation duct in the way, so I can't make this one box any wider than 6.75 (interior) so I'm wondering, should I make it deeper maybe go back to 8 instead of 5.75, or or should I go even further, making it even deeper to compensate for the narrow width.... or is the speaker just being off center causing the issue? Or... here's another possibility.. do I need to change the air space volume all together due to the new shape?
Any insight or thoughts on this would be appreciated
The new box just doesn't sound anywhere as good as the 8" cube, even though it has the same internal volume. identical speaker and both running off the same amplifier. The cube has a clean low frequency response that fills the room while the new box is just lacking substantially.
I'm trying to get my head around why this would be.... I've seen so much about box volume but not much regarding the actual shape of the box. I'm wondering if centering the speaker sounds better than having it offset, or perhaps it's just the shallow depth that's causing the issue. I would rather not build box after box just randomly trying things, so if anyone has any insight as to what is going on here it would save me hours of building boxes, while that is a bit of fun, I do have some work that could be done instead 🙂
The issue I'm having with the one location is there is a ventilation duct in the way, so I can't make this one box any wider than 6.75 (interior) so I'm wondering, should I make it deeper maybe go back to 8 instead of 5.75, or or should I go even further, making it even deeper to compensate for the narrow width.... or is the speaker just being off center causing the issue? Or... here's another possibility.. do I need to change the air space volume all together due to the new shape?
Any insight or thoughts on this would be appreciated
A cube is actually not the best as it has a strong resonant mode. With the rectangular box, it may not have this main resonance. Do you have stuffing inside? With sufficient stuffing they should aound similar.
Yes, I did make sure the polarity was the same, I also even switched speakers just to rule out the actual speakers, even though they are the same
I think I must have ended up with standing waves or some kind of resonant chamber on the cube, I'm just not sure if it's the shape all together or how far the back is from the speaker, or something else.. and if I can duplicate it with something a shape that will fit where I want to put it
I don't have any stuffing inside, I have some fiberglass insulation laying around, would that be suitable for stuffing or should it be something else?
I also have lots of scrap plywood, so I thought I might try some other configurations.. the only limiting dimension I have is the 6.75 on the one side. I'm not sure if I should try keeping the 8" on the depth and ending up with 6.75 width x 9.48 height x 8 depth or make it sideways so it's 6.75 width x 8 height x 9.48 depth.
I think I must have ended up with standing waves or some kind of resonant chamber on the cube, I'm just not sure if it's the shape all together or how far the back is from the speaker, or something else.. and if I can duplicate it with something a shape that will fit where I want to put it
I don't have any stuffing inside, I have some fiberglass insulation laying around, would that be suitable for stuffing or should it be something else?
I also have lots of scrap plywood, so I thought I might try some other configurations.. the only limiting dimension I have is the 6.75 on the one side. I'm not sure if I should try keeping the 8" on the depth and ending up with 6.75 width x 9.48 height x 8 depth or make it sideways so it's 6.75 width x 8 height x 9.48 depth.
Have you tried a wide range of track genres when judging that the cube sound best, say this because speakers have errors in their reproduced signal compared the signal they are feed, and it could be a coincidence on a certain track the cube have a colouring parameter that enhance the track to sound outstanding.
Moving away from the shallow depth is a good idea, whether it be 8" or 9.48" I doubt is going to matter.
Modes for 8" X 8" X 8" below: from mh-audio.nl
Tony.
Modes for 8" X 8" X 8" below: from mh-audio.nl
Tony.
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Possibly unrelated but your length is very close to being exactly double the width. In general, it's better to use some variant of "golden ratio" to avoid the modes from interacting (big sums and/or dips). For example (ignoring volume for the moment) if one dimension is 10", then the other two could be 6" and 16" (i.e., a ratio of .6 to 1 to 1.6 is one option).
Presumably you eliminated air leaks as a factor.
You might consider using test tones (e.g., step through the tones incrementally and see what's utterly lacking or exaggerated in one design vs. the other, and chances are a dimension is involved). There are plenty of tones on the Internet.
Regardless, it should be stuffed. Any differences are going to be minimal if it's full of fiberglass. It may be that the deeper depth of the cube is improving the sound in it's unstuffed state, because of fewer reflections bouncing from the back, or perhaps the resonance is adding a subjectively pleasant coloration. That won't matter if properly damped.
wow, all this has me thinking.. I didn't know there was so much involved with speakers!
I can't seem to get things right with the golden rule because I either end up with the short side smaller than my speaker or the large side too big to fit, but I noticed the website for calculating resonances mentions "cube root 2" ratio of 1.26 as another recommended ratio, My new box idea came close to that at 1.19, so I thought why not make it come out to 1.26 to see what happens, so I looked up how to implement this and it looks like if I make the middle side = X then X*0.7939 would be the short side and X*1.2599 would be the long side.. I decided to keep the same volume of 512 Cu Inches and did the math and figured that if I kept one side 8" then my short side would be 6.35" and the long side would be 10.08" This will make a box that will fit where I want to put it nicely, so I'll give it a try. This will also have the same internal volume as my last 2 boxes so I can try them all side by side by side... with and without stuffing and see what happens.
As far as stuffing it.. what am I trying to do here? Is the idea to create obstacles so standing waves can't develop in the box? how much fiberglass do I need or want? just a little around the speaker or packed full?
I can't seem to get things right with the golden rule because I either end up with the short side smaller than my speaker or the large side too big to fit, but I noticed the website for calculating resonances mentions "cube root 2" ratio of 1.26 as another recommended ratio, My new box idea came close to that at 1.19, so I thought why not make it come out to 1.26 to see what happens, so I looked up how to implement this and it looks like if I make the middle side = X then X*0.7939 would be the short side and X*1.2599 would be the long side.. I decided to keep the same volume of 512 Cu Inches and did the math and figured that if I kept one side 8" then my short side would be 6.35" and the long side would be 10.08" This will make a box that will fit where I want to put it nicely, so I'll give it a try. This will also have the same internal volume as my last 2 boxes so I can try them all side by side by side... with and without stuffing and see what happens.
As far as stuffing it.. what am I trying to do here? Is the idea to create obstacles so standing waves can't develop in the box? how much fiberglass do I need or want? just a little around the speaker or packed full?
The results are in! Yes, resonance seems to be what is happening. I went ahead and built the "cube root of 2" box and while it did not have the cool resonant sound I liked on the 8x8x8 box, it was much more consistent of the three. Apparently the resonant effects can either add to or subtract from the sound depending on the exact frequency. I got some fiberglass insulation, about 12"x16"x5" pieces of it and put it in all the boxes... don't really know what I'm doing, just randomly got some and put it in there... I was having the listen very hard to detect any difference at all between them then, and they all did sound pretty good. I had another box I made that was a lot smaller, 8x8x4, and no matter what I did to that one, the sound just seemed dull and muffled, it was probably not enough air space for the speaker to work right.
One other thing I noticed is that if I turned on any random two speakers, with or without stuffing, the two together sounded pretty good, even if I fed them both the same signal (both left channels for example) I guess whatever one box lacks is filled in by the other box. I wonder if it will be a big deal to use two different shape boxes even in the same room.. the boxes will never be seen, they are being attached to the rafters before the ceiling drywall goes up and only the speaker itself will be visible, this is why I'm trying so hard to get this right... after they are installed, I won't be able to change them... ever... they will be drywalled in between a space between the first and second floor and completely in-accessible. I have a few locations where there are plumbing pipes in the way, so I can't have a tall box, or other obstacles are making it so I can't have a wide box... If I use fiberglass to damp them then I'm hoping I can mix and match different shapes of boxes to make things work.
I appreciate the feedback and information, I find this all very educational indeed!
One other thing I noticed is that if I turned on any random two speakers, with or without stuffing, the two together sounded pretty good, even if I fed them both the same signal (both left channels for example) I guess whatever one box lacks is filled in by the other box. I wonder if it will be a big deal to use two different shape boxes even in the same room.. the boxes will never be seen, they are being attached to the rafters before the ceiling drywall goes up and only the speaker itself will be visible, this is why I'm trying so hard to get this right... after they are installed, I won't be able to change them... ever... they will be drywalled in between a space between the first and second floor and completely in-accessible. I have a few locations where there are plumbing pipes in the way, so I can't have a tall box, or other obstacles are making it so I can't have a wide box... If I use fiberglass to damp them then I'm hoping I can mix and match different shapes of boxes to make things work.
I appreciate the feedback and information, I find this all very educational indeed!
Zaaphod,
Mine sealed boxes nearly always end up full stuffed with loose fiberglass. Stuffing adds virtual volume seen from the driver think it's something like up to 30% volume stuffing can add, and can be measured looking at the resonance peak when drivers impedance is measured sitting in the box.
Add a picture of simulation to help understanding, the three plots is sealed box and have approx. 30% internal volume in difference, the one with overshoot and steepest cut off of low frequency is the smallest box volume, a spec where the smallest box win is it makes the best spring brake so the Xmax of cone movement is the least movement seen in red plot. The yellow plot show driver and box cooperation which makes a resonance spike where the one at right belong to the smallest volume, guess now you can figure out which data belongs to the others, and at the -3dB and -10dB lines you can see the largest box have the lowest frequency extension at these points.
Sound from back of cone is at opposite out of phase as from front of cone therefor in sealed box needs to be dampened/isolated out, in other box types the tech art is to mix low frequency front and back waves together in way they add correct instead of distort or cancel each other.
These good advises for stuffing sealed i got from xrk971 at a time, hope ok share here X 🙂:
Sealed is a good choice. If you can make your box with no parallel walls that will help. Just put lots of stuffing inside and line walls with open cell eggcrate foam. Fiberglass i am using with good success - need to be careful as it can be itchy on skin. I can also cannibalize old pillows that we don't use anymore. Check out the BASF phenolic foam - works great as sound absorber. They sell as household cleaning pads so can buy it anywhere. Kind of pricey but maybe 4 to 6 pads is all that is needed directly behind driver basket. Use open cell foam for rest. Link BASF phenolic Mr. Clean Magic Eraser S-14765 - Uline.
EDIT because they get a part of building for fire safety maybe best to use fiberglass.
Mine sealed boxes nearly always end up full stuffed with loose fiberglass. Stuffing adds virtual volume seen from the driver think it's something like up to 30% volume stuffing can add, and can be measured looking at the resonance peak when drivers impedance is measured sitting in the box.
Add a picture of simulation to help understanding, the three plots is sealed box and have approx. 30% internal volume in difference, the one with overshoot and steepest cut off of low frequency is the smallest box volume, a spec where the smallest box win is it makes the best spring brake so the Xmax of cone movement is the least movement seen in red plot. The yellow plot show driver and box cooperation which makes a resonance spike where the one at right belong to the smallest volume, guess now you can figure out which data belongs to the others, and at the -3dB and -10dB lines you can see the largest box have the lowest frequency extension at these points.
Sound from back of cone is at opposite out of phase as from front of cone therefor in sealed box needs to be dampened/isolated out, in other box types the tech art is to mix low frequency front and back waves together in way they add correct instead of distort or cancel each other.
These good advises for stuffing sealed i got from xrk971 at a time, hope ok share here X 🙂:
Sealed is a good choice. If you can make your box with no parallel walls that will help. Just put lots of stuffing inside and line walls with open cell eggcrate foam. Fiberglass i am using with good success - need to be careful as it can be itchy on skin. I can also cannibalize old pillows that we don't use anymore. Check out the BASF phenolic foam - works great as sound absorber. They sell as household cleaning pads so can buy it anywhere. Kind of pricey but maybe 4 to 6 pads is all that is needed directly behind driver basket. Use open cell foam for rest. Link BASF phenolic Mr. Clean Magic Eraser S-14765 - Uline.
EDIT because they get a part of building for fire safety maybe best to use fiberglass.
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That's good to know.. after these boxes, I have another project to make speaker boxes for a 5 sided room.. each corner is 108 degrees, not 90, so it's very hard to make any kind of box with parallel walls, my speaker boxes will end up having 7 sides and only the top and bottom will be parallel, but those will not be the same size or shape, because I want the speakers to angle down. I was concerned about the lack of parallel sides, but now it seems that will be a benefit!
I think I'll stick with the fiberglass, I have a LOT of it left over from the house, so I might as well use it for something
Great you go with a lot of crazy angles take a look here more crazy angle 🙂 http://www.diyaudio.com/forums/full-range/265915-hyperfast-hypercube-based-2-way.html.
Regarding fiberglass if you have some of the hard stuff often use for floors put 0,5 to 1" at walls inside and the airy normal fiberglass in middle to fill the box. This in my experience make box more dead, and know many use felt at the walls which we can say the hard stuff can replace.
If the "hard stuff" is closed cells type it'll only subtract volume from the box.
Some good hard stuff is lead : 1 or 1.5 mm thick it can be glued to the panels and make them stiffer and the added mass would make them vibrate less...
Felt is another thing as it is the only material that has proprietary acoustic characteristics nowhere else you can find. It is used in anechoic rooms...
Some good hard stuff is lead : 1 or 1.5 mm thick it can be glued to the panels and make them stiffer and the added mass would make them vibrate less...
Felt is another thing as it is the only material that has proprietary acoustic characteristics nowhere else you can find. It is used in anechoic rooms...
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