BIB's, what did I do wrong?

[Rick J. B.]

Hello,

My first post, great set of forums.

About 4 years ago I built a pair of BIB enclosures for my Lowther DX-3's.

I must have done something wrong because the bass response in almost non existent.

I know little of speaker design so I probably screwed up the dimensions.



Mine are 86" tall, 11" wide & 14" deep. These are the OD
dimensions.



Z Driver dimension is 43.00" (top of cabinet to center of driver)

L - line length = 6.62" for A, B, & C.

Sm (terminus area) = 135.81"



So where did I screw up?

Thanks for any and all replies.

Rick

[JORGETronic]

Hi,
I am not an expert, but if you check the design that GM has done for the DX3 you are a litle far from the suggested dims..

Dims suggested for your driver are:
L=120"
Zdriver=25.2" from closed end
Sm= 220in2

And you have:
L=86"(tall)x 2= 172"...seems too long
Z= dont see that in your post, but seems to be larger that recommended

Sm= 11" wide x 14" deep =154, too small compared with the suggested 220..

Iwuld try the suggested Dims by GM with some cheap wood, then you can choose..
Hope this heps!!

[Scottmoose]

Hi Rick

First up, many congratulations on the quality of your construction. Looks great.

OK, Lowther DX3. Well, contrary to Lowther's claims, Fs is actually up in the high 50Hz regions (Martin's measured around 60Hz for his drivers), not the claimed 36Hz. FWIW, my suspicion is that a lot of Lowther owners are unhappy because their cabinets have been designed to the factory specifications, and the resultant mis-match is the reason they're getting duff sound.

Greg's done a couple of BIB designs for Lowthers, as have I, as suggested above.

So, what's gone wrong? Well, as noted, currently, line length is too great. You've accidentally tuned far too low, which has the result that the midbass and under goes walkabout. Zdriver seems to be out as well. You have roughly 172in line length here. Ideally, Zdriver for that length wants to be 37.5in (37.324 actually, but let's not split hairs ) Let's see what we can do as an alternative.

Greg's works, that's for sure. As an alternative, so will this (driver specs from Martin King's accurate measurements):

Line length = 128in
Zdriver = 27.75in
Sl = 126in^2.

Ideally WxD dimensions want to be in proportion of 1:1.4142, or rounded to the nearest sensible figure. Graph shows 1/2 space response, no stuffing assumed. Corner loaded, should be ~flat to 30Hz, and much smoothed out thanks to the room boosting the resistive portion of the acoustic impedence and increasing the effective size of the mouth by a factor of 8. Stuff the point above the driver lightly, and place an inch or so of damping material on the base of the cabinet.

Why the big difference in mouth area between GM's and mine? Different approach -all the BIB simulations on the zillaspeak pages Jeff so kindly hosts were done by Greg or myself, but we have subtly different takes on the subject. Greg favours a larger mouth than I do, and bringing the response flat with some series resistance, while I will often tend to go for a smaller terminus, and usually a fractionally longer line without the resistance. End result is usually a happy builder in both cases, so up to you really!

Good luck & let us know if we can help
Scott

[gychang]

Originally posted by Rick J. B.
Hello,

About 4 years ago I built a pair of BIB enclosures for my Lowther DX-3's.

I must have done something wrong because the bass response in almost non existent.

So where did I screw up?

Thanks for any and all replies.

Rick

I built 2 BIBs with different speakers and both sets are excellent in the base. I agree there is a mistake, speakers look great, and hope u get to use the proper dimensions and not give up on BIB...

http://www.zillaspeak.com/bib-lowther.asp

gychang

[Rick J. B.]

I sketched this quick so pardon the poor drafting.

Do these dimensions look right for my DX-3's?

[djQUAN]

or you could have wired the speakers in opposite polarity.

[BHD]

Those cabinets are gorgeous. It's a shame the lowthers don't work in them. I'd say try to find a driver (Fostex?) that will fit the dimensions of your current cabinet.

[Rick J. B.]

Surely I couldn't have wired both wrong?

No I was very careful not to do just that. Since I soldered all connections I double and triple checked everything.

[Scottmoose]

Should do the job nicely. Remember to calculate the thickness of the internal baffle when cutting -it's easy to forget! So, assuming 3/4in material, your cabinet should be, externally, 64.75in tall (including a base), 10.5in wide, and 16.25in deep.

Use a fairly high resistance speaker cable if possible, which should also help keep the LF up a bit: magnet wire is ideal for this purpose, or a pair of 24AWG conductors extracted from a run of Cat5. Make sure that there's some damping material on the front of the internal baffle directly behind the driver as well. A piece of felt for example. That should help prevent reflections back through the cone.

Drop a pair of Fostex FE206E in your existing cabinets BTW & either keep them for parties, or sell them on. Bass should not be lacking.

Best
Scott

[Rick J. B.]

Thanks Scott.

So the Fostex FE206E will work in the dimensions of my current enclosures? Man if that's the case I could put them in and sell them to finance the next set of cabinets!

Of course I'd have to sell them to someone close. These mothers are huge & heavy.

Rick