Downsize a BIB

[holdent]

Aahh - the path length is 160". I thought GZ meant 80". I'm at work until late tonight so I won't be able to re-run the sim until tomorrow (Friday) evening.

jrenkin - I'm using the latest version of Martin King's MathCad worksheets. I don't know if they're available for new users but was able to renew my license last April. You'll need a version of MathCad to run the worksheets.

[jrenkin]

Thanks, they are available. Last I had looked they weren't. Looks like a good deal for $25, but a learning curve. I will try and get it together to model my own, rather than ask more of you. Curious to see your results for this thread though.

I am doing this right though, aren't I? Build the speaker first, put the gigantic thing in the living room, hook it up, tweak it, then try and figure out what it does by simulation. Or do I have something backwards....

[holdent]

OK - got home earlier than I thought and re-ran the 160" BIB suggestion for the B20 from Godzilla. Here's the result:



zdriver = L*0.217 or 34.72 inches. No stuffing was used.

I haven't worked through what the in-room response simulation looks like for the 160" one but for the original it looks like this:



The BIB was simulated using 8ft ceilings, with the baffle of the B20 BIB 2 feet out from the side and back walls.

jrenkin - you might what to try varying the stuffing to tweak the sound. When 0.25 lbs/ft3 is added from behind the driver up to the closed end the in-room simulation looks like:



I prefer simulating first to get the design "into the ball park" then build and tweak it afterwards. Both in-room simulations above look they would be bass-heavy so I'd want to play with the design on my laptop rather than building first.

[holdent]

Now Godzilla's 160" BIB suggestion simulated in a room (assuming 8ft ceiling and baffle 2ft out from side and back walls as before), using 0.25 lbs/ft3 stuffing from back of driver to closed end:



This looks good!

I just realized why I made the mistake thinking that Godzilla was suggesting a 80" line length rather than a 160" line length. 160" is longer (ie. larger to me rather than smaller) than the original 138" length. He did suggest that the mouth be 144in2 rather than the original 200in2.

Godzilla - so the original has a shorter length (138" vs 160") but larger mouth (200in2 vs. 144in2) . Yes?

[jrenkin]

I gotta do some stuffin'!

I also don't have the full 8'ceiling.My room has an overhang at 8'over the speakers, but then it disappears and the room is vaulted. The bass is manageable, maybe a bit too diluted even.

I think a box of this size will be too much in a lower ceiling-ed room.

[danerius]

Originally Posted by holdent

Now Godzilla's 160" BIB suggestion simulated in a room (assuming 8ft ceiling and baffle 2ft out from side and back walls as before), using 0.25 lbs/ft3 stuffing from back of driver to closed end:



This looks good!

I just realized why I made the mistake thinking that Godzilla was suggesting a 80" line length rather than a 160" line length. 160" is longer (ie. larger to me rather than smaller) than the original 138" length. He did suggest that the mouth be 144in2 rather than the original 200in2.

Godzilla - so the original has a shorter length (138" vs 160") but larger mouth (200in2 vs. 144in2) . Yes?

Wow. Wish I knew Mathcad better. Tried it several times but its much too different from what Im used to working on. Im truly grateful for the sims ur providing

Ive cross checked different parameters for the BOFU and they differ a bit. Lowest Vas was 49 liters and highest 97. Fs ranges from 37 to 43. May be a good idea to wait til I have the units here, run them in and then check whatever specs Im able to check. Fs should be easy.

My room has a 9 foot ceiling, from what Ive gathered an eigentone at around 25Hz, speakers will be close to back wall ie 4-5 inches and 1 foot from walls. Would it be completely improbable with 8 x 12 inches internal dimensions? That size would solve a range of problems Height not so much an issue.

Best regards /Bo

[jrenkin]

I an no expert, but I would not ignore height. As the top of the box comes close to the ceiling, the ceiling becomes an extension of the horn mouth. Mine is less than a foot and a half from the overhang ceiling and standing under there the bass can be booming. I am saved by the open rest of the room. I would not like these for heavier rock or any bass heavy tunes if I had to sit undr that overhang.

[danerius]

Originally Posted by jrenkin

I an no expert, but I would not ignore height. As the top of the box comes close to the ceiling, the ceiling becomes an extension of the horn mouth. Mine is less than a foot and a half from the overhang ceiling and standing under there the bass can be booming. I am saved by the open rest of the room. I would not like these for heavier rock or any bass heavy tunes if I had to sit undr that overhang.

Im aiming to balance the smaller footprint cabinet with horn loading from ceiling + walls. The math behind it all is beyond me though. And the reason I started this thread

Regards /Bo

[danerius]

Lotsa recent changes regarding work has forced me to rethink my BIBs and cut costs. Getting the BOFUs to Sweden is gonna be $78 in shipping alone, smaller cabs will help in more ways than costs, etc. Im on post #1576 in the BIB post and Ive learned a bit more.

As the reprioritized plans are now its Monacor SPH-60X with the Dayton ND16FA. Scottmoose mentioned lowering Fs by (max) 0.707 in a post. Since I like a musical and convincing bass Im gonna go for that. Im guessing it will help with cone excursion as well? Wether I can trust Monacors specs is another matter.

Im gonna try a series filter as Ive found I like the sound of them. I have no idea why that is. If someone has an explanation for why that is. Please let me know. Gonna order filter parts in different values. Namely: 1R, 2R2, 4R7, 10R, 22R, 2.2μF, 15μF, 0.1mH so that I can try different series and parallell filter versions.

Attatching a screen dump of the spread sheet calcs plus the filter wich at this point is – at best, an ill informed sketch and a shot in the dark. Not sure if thats the correct way to dampen the tweeter or if the component values are feasible. Found this topology while googling for info on series filter and ran some calcs I found. Advice is greatly appriciated.

Yet another option is to skip the tweeter and filter, trust that the tonal balance will be okay without BSC. Peter Brorsson has this setup in the big BIB thread.

Best regards /Bo

PS. Ive also included an overlay I made of two different graphs for the Monacor SPH-60 and SPH-68. If someone other than me has a use for it. Awesome DS

[GM]

FWIW, the SPH60X is a drop in replacement in TC's RS 40-1354 BIB, so shouldn't need any BSC.

GM