Question about building Lowther DX3 BIBs

[gnugear]

I got this info off of Godzilla's site:

L = (Line length) 120"
Zdriver = Driver 25.2" down from sealed end of cabinet
Sm = 220in^2

Is this for the 8" or 6" driver?

Also, what does "with 4 ohm series R" mean?

[TerryO]

Originally posted by gnugear
I got this info off of Godzilla's site:

L = (Line length) 120"
Zdriver = Driver 25.2" down from sealed end of cabinet
Sm = 220in^2

Is this for the 8" or 6" driver?

Also, what does "with 4 ohm series R" mean?

Gnu,

Six or Eight inches? If it came off of Zilla's site, maybe you should ask him. The beauty of these forums is the ability to go to the source.

The "with 4 ohm series R" means that you would have a 4 ohm resistor in series (soldered inline with) with the positive lead of the driver's wire.


Best Regards,
TerryO

[gnugear]

I tried to get in touch with him (been bugging him a lot!) but haven't been able to do so yet.

What's the purpose of changing the resistance?

[Scottmoose]

Both. It works with the 8in & the C45. The 8in units IIRC do not require the additional resistance, the purpose of which is to artifically lift the Qe of the driver (amongst other things).

[gnugear]

Great, so I can simply install the driver and let it rip? I'll double check my math and get some feedback.

[gnugear]

Wow, the enclosure is big! I'm not sure if I can fit it into my room unless I make it taller. Is there a way to use the calculator to increase the height and reduce the width/depth?

[giantstairs]

use gm's calculator found on zilla's page.

play with the Fs to alter the height but i don't think you want to tune it too low. yes, they are BIG cabinets.

[GM]

Originally posted by Scottmoose

The 8in units IIRC do not require the additional resistance...........

DX3, DX4 & C45 with 4 ohms series resistance: http://www.diyaudio.com/forums/showt...948#post951948

DX2 with 2 ohm series resistance: http://www.diyaudio.com/forums/showt...958#post951958

So, if no series resistance is used and driven with a very low output impedance such as a typical SS amp and sufficiently large gage wire, then a smaller footprint BIB is desirable due to the lower Qts, but bass and driver protection may suffer if bass heavy material such as Brian Bromberg, Pink Floyd, and especially pipe organ symphonies, is played at room filling SPLs with a powerful enough amp to keep it from clipping.

Note that unless you plan to floor load it I don't recommend shortening the pipe and while lengthening it will make a smaller footprint and tune it lower, I don't recommend going too long as it allows the driver to unload too much in the critical mid-bass.

GM

[Godzilla]

gnugear is very serious about purchasing the Lowthers. Can someone check and offer suggested dims for him. There seem to be varying opinions for BIB sizes. The calculator is great as a starting point but maybe there are some nuances for this one and varying Lowther specs worry me. Also, other than a BIB or a Voigt Pipe, are there any other recommendations using the DX3?

Since the drivers are so expensive it's a good idea to measure twice (or more) for this design IMO. Let's help gnugear build the best design he can since he is making such a large investment in drivers. He's already built BIBs for the 168ez and feels it's better than the Stereophile Class A rated Paradigm speakers he owns. It's exciting to know that we can all build something for hundreds that sounds like thousands! The Lowther BIB could become a reference BIB.

Peace,
Godzilla

[gnugear]

Thanks Zilla!

Hey Scott, I found this quote from you in the archives and was wondering if you could confirm whether or not these specs are still accurate (the thread was old and refering to a Lowther built BIB that was built to the wrong dimensions). My room is small 10x13 so I can't really accomodate the specs currently on Godzilla's site. These new specs appear doable if they're correct.

QUOTE:
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!