CHR-70 GENERATION 3 - COMING SOON

[skeeter99]

I'm now thinking of picking up a pair of these for surrounds in my setup and want to make a large bookshelf speaker I can mount to some nice stands I already have. These will be crossed over at 80hz so I don't need them to go this low but a bigger cabinet doesn't bother me and I could use them for 2-channel later on if tuned lower. I will be making them with threaded inserts so they can physically bolt to the stands (no way for little ones to knock them over this way) as well as for threaded spikes. I plugged in the data into WinISD and came up with these specs for the box (using 3/4" material):

VOLUME: .509 ft^3 or 14.4L
WIDTH: 8.5"
HEIGHT: 15.5"
DEPTH: 10.47"
PORT: 1"H X 4"W X 7.32"D
TUNING FREQ: 47.63HZ

How does this look given what other people are doing? Is this roughly the right size cabinet? Attached is the plot and data and its all very smooth so I'd think I should be good.

Scott

[planet10]

I'd tune it a bit higher (or a slightly smaller box. i ended up at no bigger than 10 litre) to avoid the dip you have 50-80 hz.

dave

[skeeter99]

Originally Posted by planet10

I'd tune it a bit higher (or a slightly smaller box. i ended up at no bigger than 10 litre) to avoid the dip you have 50-80 hz.

dave

Hmm, that dip is -.13db at 64.29hz which is pretty small. What tuning frequency did you use on a 10 litre box? If I change to 10L with a 60hz tune this is my response with a 2.25db boost at 75.72hz with a 1x4x6.48" slot port.

[planet10]

I like to avoid the 1st derivative of the curve crossing zero more than once. Seems to affect tuneful bass.

With a restricted (hiZ/high aspect ratio) vent, the tuning in your 2nd sim looks better and should work well (the R in the vents will take the hump out). If you are planning on a plumbing pipe port, a little lower tuning to flatten out the hump a bit more.

dave

[skeeter99]

Originally Posted by planet10

I like to avoid the 1st derivative of the curve crossing zero more than once. Seems to affect tuneful bass.

With a restricted (hiZ/high aspect ratio) vent, the tuning in your 2nd sim looks better and should work well (the R in the vents will take the hump out). If you are planning on a plumbing pipe port, a little lower tuning to flatten out the hump a bit more.

dave

Got ya on the tuning. So with the smaller box, how would I restrict the vent? I was planning on doing a slot port similar to what's in a couple of your box designs as well as the one we're working on together.

Scott

[planet10]

Just the act of creating a high aspect ratio on the vent adds the R. If it is not suffiicent some open cel foam in the vent (can be tuned by the depth of the blockage)

dave

[skeeter99]

Originally Posted by planet10

Just the act of creating a high aspect ratio on the vent adds the R. If it is not suffiicent some open cel foam in the vent (can be tuned by the depth of the blockage)

dave

Ok so I'm learning, what do you mean by a high aspect ratio vent? Would the 1x4x6.48 port I have modeled be a high aspect ratio vent?

[planet10]

Aspect ratio should be climbing above 6, the original FonkenPrime was about 50:1 and some of the newer ones are even more radical.

dave

[skeeter99]

Originally Posted by planet10

Aspect ration should be climbing above 6, the original FonkenPrime was about 50:1 and some of the newer ones are even more radical.

dave

How do you find the aspect ratio of the vent? What is the formula? We can take this to another thread to keep this one clear ...

Scott

[planet10]

aspect ratio = width of vent / height of vent with w>h

dave