Question for Dr. Spec about yogurt

burdette · March 2003

No, of course it isn't about yogurt.

You know I'm on track to build the EBS sonosub for the AV12. Because I either have or will end up with enough material anyway, I've decided to build a practice sub before going after the actual sit-in-the-living-room sub. That will be the place I learn the lessons and make mistakes.

I was going to make the optimum flat alignment (about 64 liters), which has a -3dB of about 23 Hz... but then checked the box that matches the driver's Vas.. 88 liters. That has an Fb and an F3 of 21 Hz (the driver's Fs).... but the graph looks sort of like the EBS alignment, and if you take the portion up to about 50-60Hz as reference, then -3dB is actually about 19 Hz. Just means I turn the amp up a little.

I've read basically nothing on making a cabinet exactly at Vas and tuning to exactly Fs... do you have an opinion on which of these (Vas or "optimally flat") is more likely to succeed? Is there anything inherently wrong with Vb = Vas? and Fb = Fs?? I thought if I'm going to make a practice sub, it will still function (if I want to change over the driver), so I might as well make (sort of) the opposite of the EBS.

I'd appreciate any thoughts.

Oh, there is a good chance that either of these will have to have some of the port outside the box.. probably sticking out the top, or it won't fit. From what I've read at several "reputable" DIY subwoofer sites, that should still work just fine (just don't include extra volume for the part of the port outside the box).

Thanks. Got plans with a buddy from work to use his truck this week to get the sonotube. Have to buy the 12' size... but it is only $1.95 per foot.

Dr. Spec · March 2003

I'll do this tomorrow - too tired tonight. Check out the fun over in the Speakers forum - Stryke Force has landed.

Dr. Spec · March 2003

I'm not sure what you mean by "most likely to succeed".

It all boils down to what kind of in-room FR you are looking for and what you want the sub to actually do for you.

If you build the optimally flat unit at 64 liters, it may exhibit at least some degree of boom due to boundary gain and of course it will not dig as deeply - but it will play loud.

I see nothing wrong with an 88 liter enclosure that happens to be tuned to the T/S paramters (i.e., Vb = Vas & Fb = Fs).

I think your original 95 liter was a good compromise too.

Bottom line - you said you wanted the deepest possible extension in favor of volume, and that means an EBS or quasi-EBS enclosure. With that said, there is absolutely nothing wrong with going after a higher tune with your practice sub and seeing how it actually performs in your room with a FR sweep.

Remember - anechoic and in-room will look different. Look at the Styke Force - a nearly 10 dB GAIN peaking at 16 Hz. WinISD never predicted that. But that's what happens when you tune for subsonic and room gain happens to interact right at the same point. If he shortens the ports a hair, he might be able to move that hump closer to 20 Hz instead of 16. Either way - he got a KILLER low end in the subsonic region.

burdette · March 2003

I suppose 'likely to succeed" means .... does one have design issues that you have to hit pretty much ON the money or performance goes to ****.. in other words, is one more forgiving in the design?

I just hadn't read much about making an enclosure that was exactly Vas, and didn't know if there was a (or some) design issues that make it hard to be successful.

Not sure I'm going to bother, anyway. I got most of the small wooden enclosure for the amp done this weekend (that was all I could work on until I get the actual tube). It went well, so I may just jump in, and I know how I'm going to cut large circles w/o investing in an expensive jig.

The amp enclosure rides outboard of the tube, sitting on a little 'wing' that will extend from the baffle board on the bottom of the tube. Easily removed for transport or repair or to use with a different sub/enclosure. Actually.. a very slick design that I am quite happy with.

Sides of amp box are 1" thick hardwood, front panel is 3/4" plywood, and the top and back is 3/8" plywood. I'll use a speaker wire jumper of about 6" to connect the amp to the sub. I'm essentially building a passive sub, and happen to be using the PE amp at this point.

Thanks for all your help (thus far!) on this project. Hope to get the tube this week.

Dr. Spec · March 2003

Originally posted by burdette
I suppose 'likely to succeed" means .... does one have design issues that you have to hit pretty much ON the money or performance goes to ****.. in other words, is one more forgiving in the design?

I just hadn't read much about making an enclosure that was exactly Vas, and didn't know if there was a (or some) design issues that make it hard to be successful.

Naturally, tuned and vented enclosures are harder to hit right on than a sealed enclosure.

But you have the suggested alignments from Stryke, so it's hard to screw up. If you go vented they suggest the EBS alignment. If you go smaller, I think they suggested a PR alignment.

I noticed you've been posting over at the DIY subwoofer forum - good move. Those guys know this stuff better than I do. Nothing about the Vas issue gives me pause, but I would ask them to be sure.

With that said, I still recommend you run the final alignment past Styke to be sure.

goingganzo · March 2003

just play with the moddle till you are happy with it. do 3 or 4 sims with the same size and different tuneing fr and comepare results. if you buld a design is recomened by the maker of the sub it will work. and if you are off by like a 1/4 of a in on the tube lenth. it wont afect much unless you have mupitil ports. this is my first ish besides the 3/4 finished sono i bult and it turned out great just have to paint the box

burdette · March 2003

Originally posted by Dr. Spec
I noticed you've been posting over at the DIY subwoofer forum - good move. Those guys know this stuff better than I do. Nothing about the Vas issue gives me pause, but I would ask them to be sure.

With that said, I still recommend you run the final alignment past Styke to be sure.

Yes, I've posted on the DIYsub site.. and the PE site, and a little on the Madisound site, although that one didn't really impress me. I am a *very* firm believer in collecting as much information as possible. Longer process, but it does its part to ensure a happy ending.

My final design WILL be the EBS, pretty much what Stryke recommends and what I've come up with on WinISD (and 2-3 other software applications), and I've corroborated the results with good old number crunching in Excel.

If I remember correctly, I'll be cutting about 48" of 16" tube (volume in the 5+ ft3 range) and using a single 4" port (flared on both ends). With room gain, I'm thinking I should be around 16Hz at 3 dB down, with quite sufficient SPL capability. Not bad for under $300 plus my time, considering my driver is the AV12.

Dr. Spec · March 2003

Remember, you can still go with two 3" vents if you are now comfortable you can do your own pipe length.

Remember to go a little longer on the port length because you will be using flared ends - you can always cut it down a bit if absolutely necessary, but you can't stretch it.

Of course, remember to subtract volume driver and the ports and add volume for the polyfill lining before you make the enclosure cut.

I think you will be fine with the suggested EBS alignment and if the vent is flared on both ends, a single 4" will probably be fine for flow at all but the highest volumes.

Good luck!

mantis · March 2003

burdette,
due to the fact I'm hungry,
"Question for Dr. Spec about yogurt"
Dannon makes these cool smoothie yogurt drinks.I like the Peach,now I want one.

Question for Dr. Spec about yogurt

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