18 inch mini scoop design (compact)

[Pabesco]

hello to all the dedicated knowledgable persons on these forums.
i just completed four mini scoops that are smaller than the usual ones. i tried posting a few pictures but obviously im doing something wrong.
i would like to ask the professionals opinions on these cabinets as i have no idea about tuning and the other technical stuff
all i know is what i need them for
please direct me how to post first then i will be able to go from there
thank you

 

[zettairyouiki]

You'll have to post more details about what you built. 'Mini scoop' in itself doesn't give much to work with.

If by "smaller than the usual ones", you mean you scaled down an existing design, you're probably stuck with some useless cabinets. Scoops are tuned to the size they're built to. Changing the size will drastically change its performance.

 

[Brian Steele]

What he said.

Of course, it's possible that you've ended up with what are basically Big Vent Reflex boxes, which can be more efficient around their resonance frequency. But you'll need to post up more information about your build for that to be determined.

 

[Pabesco]

Thank you for the reply. If you can tell me how to post pics I'll put them up so you will see exactly what I did. I tried uploading the pics but keep getting an error.

 

[zettairyouiki]

If you can't upload here, try imgur.com and share the links here

 

[Pabesco]

Hopefully these pics show this time

The dimensions overall are

24 INCHES WIDE
24 INCHES DEEP
33.5 INCHES HIGH (after top and bottom put on)

They are made of 3/4 inch birch

Sorry. I forgot the cut sheet

 

[Brian Steele]

Hopefully these pics show this time

That's going to be an interesting one to sim. It looks more like a BVR than an RLH, but even then there's a "pinch" at the last fold before the mouth, because the cutout at the bottom corner reduces the cross-sectional area in the middle of the bend.

Unfortunately I'm going to be occupied for the next few hours with another project, but if no-one else jumps in, I'll take a stab at doing a HornResp sim for you. In the interim, so you have a means of measuring its impedance curve?

 

[Pabesco]

Thank you and I really appreciate it. I will hopefully start to understand about the technical part of what you are saying. The only experience I have is building cabinets and trying to scale them down and experimenting with how they sound.
I am really Loki g forward to learning what I should know about this.
Thanks again.

 

[bitSmasher]

For the unfamiliar, here are some other "mini scoop" designs - scroll down a few posts
Best SPL acoustic box for FANE colossus 18XB - Speakerplans.com Forums

 

[Pabesco]

trying to rotate the picture

 

[Brian Steele]

Thank you and I really appreciate it. I will hopefully start to understand about the technical part of what you are saying. The only experience I have is building cabinets and trying to scale them down and experimenting with how they sound.
I am really Loki g forward to learning what I should know about this.
Thanks again.

Ok, I've put together a basic sim (using the B&C 18TBX100, because you didn't indicate which drivers you're actually using). The results are not too pretty - the boxes are very efficient, but the resonance frequency is too high for them to be called subwoofers. That's if the sim is correct, of course. If you measure the impedance curve, that could be used to determine whether or not the sim is accurate.

 

[sine143]

Brian that sim doesn't look correct for blh, swap your vrc and vtc values.

 

[Brian Steele]

Brian that sim doesn't look correct for blh, swap your vrc and vtc values.

Whoops- good catch! I should have picked that up from the schematic, grr.

Ok, here it is with the corrected chamber volumes. Looks quite a bit better now. And the impedance curve and displacement suggest BVR.

 

[zettairyouiki]

That looks pretty good. The OP had me a bit worried but yeah, that should sound quite proper.

 

[Pabesco]

Thank you guys very much. I'm not sure what I'm looking at because I have no knowledge of sound measurement and impedence curve. I'll do a lot mor reading so I would have a better understanding of what you just assisted me with.
And I am presently using 18 sound lw2400s right now but have tbx100s already ordered.

Another question if you don't mind,
Should I dampen any part of these cabs? If so where and what type of material is best to be used.

 

[Brian Steele]

And I am presently using 18 sound lw2400s right now but have tbx100s already ordered.

There's minimal difference in the sim when the 18TBX100 is replaced with the 18Sound LW2400.

And yes, getting a hang of how HornResp works and what the graphs mean is going to take a lot of guesswork out of your builds.

Another question if you don't mind,
Should I dampen any part of these cabs? If so where and what type of material is best to be used.

You could line the chamber with polyester fiberfill, but if you're crossing this over below 100 Hz, I wouldn't bother.

 

[Pabesco]

I will be going lower than 100hz. Somewhere around 40hz after getting the tbx100s.
Thanks for the advise.

 

[Pabesco]

Can you advise on the "best" driver for these cabs?

 

[sine143]

Pabesco, you will not be lopassing at 40hz.

The tbx is a worthless upgrade from the lw2400. In fact I like the lw2400 better lol.

 

[epa]

maybe the 18lw2500 wil be a better choice.
hpf @ 35hz assuming 24db