Hi WaxhawFive!
You've made a mistake in your calculation using the Hutton formula.
You have subtracted the 0.182 instead of adding it!
The resistive vent area for a 1.0 cu ft cab works out to be 6.67 sq in.
For 1.2 cu ft, as recommended by the speaker manufacturer, the area is 8.00 sq in.
I think it is well worth experimenting with a resistive vent. To me, the sound is more open than with a totally sealed box. You can always block off the vent permanently if you find the sealed box to be preferable.
If you don't give it a try you may always wonder what you're missing!
P.S. The DP alternative to a single 8 sq in stuffed opening is four rows of ten 1/2" diameter holes. These are covered internally by Black Melton fabric, a heavyweight fabric used to make winter overcoats.
You've made a mistake in your calculation using the Hutton formula.
You have subtracted the 0.182 instead of adding it!
The resistive vent area for a 1.0 cu ft cab works out to be 6.67 sq in.
For 1.2 cu ft, as recommended by the speaker manufacturer, the area is 8.00 sq in.
I think it is well worth experimenting with a resistive vent. To me, the sound is more open than with a totally sealed box. You can always block off the vent permanently if you find the sealed box to be preferable.
If you don't give it a try you may always wonder what you're missing!
P.S. The DP alternative to a single 8 sq in stuffed opening is four rows of ten 1/2" diameter holes. These are covered internally by Black Melton fabric, a heavyweight fabric used to make winter overcoats.
Thank you for the correction!
I just ordered the Melton fabric and will try the "leaky box" tuning. I may be able to find time to start on the enclosures this weekend. I really look forward to it, it's been about 26 years since I made my last pair. It'll be a basic rectangular box, deeper than usual to keep the front dimensions smaller, with the Heil "great" AMT just sitting on top.
I just ordered the Melton fabric and will try the "leaky box" tuning. I may be able to find time to start on the enclosures this weekend. I really look forward to it, it's been about 26 years since I made my last pair. It'll be a basic rectangular box, deeper than usual to keep the front dimensions smaller, with the Heil "great" AMT just sitting on top.
So you have helped me determine the volume for the enclosure, and now I'm playing around with the box dimensions, and have fallen into another deep hole of "research" (meaning reading articles on-line). How to size the front panel dimension. I honestly didn't think it mattered, but there are topics about the "baffle edge diffraction" and other effects of this front panel dimension. I've seen recommendations and designs demonstrating both extremes; with some designs having a front baffle barely large enough to fit width of the driver, to the exact opposite where the front baffle dwarfs the driver. Can anyone offer some advice on how I should go about sizing my front face box dimension? Should this be a new topic?
I suggest that a good starting point would be to adopt the 'Golden Ratio' and tweak the enclosure dimensions from there.
The Golden Ratio of height to width to depth is 2.5 : 1.6 : 1.0.
Baffle edge diffraction is worthy of a separate topic but has probably been done to death on this forum!
Personally, I'm from the old school which says "If it looks good, then it'll probably sound good"!
The Golden Ratio of height to width to depth is 2.5 : 1.6 : 1.0.
Baffle edge diffraction is worthy of a separate topic but has probably been done to death on this forum!
Personally, I'm from the old school which says "If it looks good, then it'll probably sound good"!
Sometimes I see designs with the driver not centered left-right, what's up with that? Just styling, or an attempt to cancel some undesirable effect of being centered?
Also, I'm starting to realize that a 30-liter box is larger than I had envisioned for this "bookshelf" speaker. I may shoot for the lower side of the manufacturers recommended volume, which would be 20 liters, especially since I understand that the aperiodic vent will make the box "appear" to be a little larger. In WinISD I see the small hump that shows up with the smaller box (when changing from 30L to 20L). Do the aperiodic vents help tame that hump, or is that not how it works?
Also, I'm starting to realize that a 30-liter box is larger than I had envisioned for this "bookshelf" speaker. I may shoot for the lower side of the manufacturers recommended volume, which would be 20 liters, especially since I understand that the aperiodic vent will make the box "appear" to be a little larger. In WinISD I see the small hump that shows up with the smaller box (when changing from 30L to 20L). Do the aperiodic vents help tame that hump, or is that not how it works?
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Have just seen your edit.
Since the aperiodic loading acts to reduce the system Q then it is likely to tame the hump (although you may prefer the bass reproduction with the hump!).
The beauty of your project is in the fact that you can compare DP with sealed simply by blocking off the vent with a wooden board!
Since the aperiodic loading acts to reduce the system Q then it is likely to tame the hump (although you may prefer the bass reproduction with the hump!).
The beauty of your project is in the fact that you can compare DP with sealed simply by blocking off the vent with a wooden board!
Using the numbers 0.612:1:1.612 is better for clearly showing the relationship.
One gets the required size by taking the cube root of the volume and then dividing by 1.612 and by multiplying be 1.612 to get the desired dimensions.
This is an example:
The driver is offset from the centre so as to distribute the set distances to the edges broader and make the edge diffraction and baffle step diffraction smoother.
The choice of baffle width is one of choosing your compromises, choices have a set of advantages and disadvantages. There is no perfect shape. There are some really bad ones thou.
dave
Divide by 1.612 then multiply by 1.612?
Would you please illustrate by giving an example calculation based on a 20 litre enclosure?
cube root 20,000 = 27.144 cm
27.144 / 1.612 = 16.839 cm
27.144 * 1.612 = 43.756 cm
So internal dimensions of 272 x 438 x 168 mm (wxhxd). (round up width, round down depth)
27.2 x 43.8 x 16.8 cm = 20,015 cm3 = 20 litres
Then one has to iterate for braces and anything else that eats up internal volume, and if one is targeting golden ratio external dimensions.
dave
27.144 / 1.612 = 16.839 cm
27.144 * 1.612 = 43.756 cm
So internal dimensions of 272 x 438 x 168 mm (wxhxd). (round up width, round down depth)
27.2 x 43.8 x 16.8 cm = 20,015 cm3 = 20 litres
Then one has to iterate for braces and anything else that eats up internal volume, and if one is targeting golden ratio external dimensions.
dave
Dave, hope you won't mind if I summarise your method of calculation for future reference.
How to obtain the 'Golden Ratio' dimensions of a loudspeaker enclosure
1. Width (in cm) equals the cube root of the enclosure volume (in millilitres).
2. Height equals width multiplied by 1.612.
3. Depth equals width divided by 1.612.
Thank you for this information which will be of great use to the OP.
How to obtain the 'Golden Ratio' dimensions of a loudspeaker enclosure
1. Width (in cm) equals the cube root of the enclosure volume (in millilitres).
2. Height equals width multiplied by 1.612.
3. Depth equals width divided by 1.612.
Thank you for this information which will be of great use to the OP.
Great document
I just noticed how great that PDF is. Some documents I have already seen were included, but they were well combined in this PDF, supporting each other and especially the speaker design. Also the highlighted text samples are good.
I just noticed how great that PDF is. Some documents I have already seen were included, but they were well combined in this PDF, supporting each other and especially the speaker design. Also the highlighted text samples are good.
Correctomundo
, though as usual, no clue about the math, but for those that can, can rearrange this formula:
https://speakerwizard.co.uk/driver-ts-parameters-fs-free-air-resonance/