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Eminence BETA LTA in TL
Eminence BETA LTA in TL
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Old 7th September 2009, 03:40 PM   #1
thansaffel is offline thansaffel  United States
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Question Eminence BETA LTA in TL

Hi, I have checked out Thorsten Loesch's Afterburner files, but I am kind of interested in building a Hammer Dynamics-style box for the Eminence Beta LTA, which I now have on an open baffle while I decide what box to build. My goal for this project is to have a fullrange speaker that has a little more crispness an detail than I am currently getting with the OB, but supplemented by a supertweeter around 7 - 8k and a subwoofer somewhere around 100Hz.

I am not a math person - I am a graphic designer and computer savvy but formulae leave me blinking. I have a table saw and router, and am game to try anything that's not too complex - for example a back-loaded horn is beyond my patience if not skills.

From what I have read the Hammer box is a sort of TL with a pipe tuned to 50Hz (I saw it written somewhere as 500Hz - I think it was Dick Olsher - but I figured that was a typo).

Does anyone have a diagram of the Hammer enclosure they are willing to share just for info purposes? Or would this be considered uncool because it is a proprietary design.

Anybody else explored any other interesting boxes for this driver?

The main reason I like the Hammer box is that it gets the driver up nice and high, unlike the Afterburner, which needs a stand. For WAF purposes, I like the pedestal look.

I am also wondering whether I need the Zobel circuit if I am actively EQing this thing and actively crossing it over for the sub and the tweeter. I am using the Behringer DEQ and DCX 2496es to do so, with Bottlehead Paramour for the mids and miscellaneous solid state amps for the subs and tweeter.

Thanks,

Than
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Old 7th September 2009, 04:10 PM   #2
Scottmoose is offline Scottmoose  United Kingdom
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The Hammerdynamics cab. is an MLTL (Mass Loaded Transmission Line, or ML QWR [Mass Loaded Quarter Wave Resonator] if you prefer). There's nothing inside it, aside from the damping material.

Anyway, main issue is one of size: it needs a big box. How big a cab. can you handle?
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Old 7th September 2009, 07:03 PM   #3
Godzilla is offline Godzilla  United States
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I think the Hammer is a 4 cubic foot box. I thought this pdf from Eminence was interesting re. the 12lta

http://www.parts-express.com/pdf/290-409c.pdf

I think the 2 cubic foot box is interesting if designing the system to include a sub.

Godzilla
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Old 7th September 2009, 07:25 PM   #4
planet10 is offline planet10  Canada
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Eminence BETA LTA in TL
I did burn a set of Hammer Dynamics box, after the owner could not get them to sound satisfactory. IIRC they had a false base that raise them up..

dave
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Old 7th September 2009, 08:27 PM   #5
bassrogue is offline bassrogue  United States
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I built the 4' vented box in Godzilla's link. The bass doesn't get down real low but what does come out hits you in the chest like a hammer. A great party speaker.
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Old 8th September 2009, 03:48 PM   #6
thansaffel is offline thansaffel  United States
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Wow, guess Labor Day was the right time to post this query!

Scottmoose, thanks for verifying the Hammer box as a MLTL. Initally, I was at a loss as to how the MLTL differs from a bass reflex box, but a Google search took me to Martin King's excellent explanations of the similarities and differences.

http://www.quarter-wave.com/Project03/Project03.html
http://www.quarter-wave.com/Project0...re_Design.html

To quote the most relevant of his observations:

"In my opinion, one of the negative attributes of a bass reflex enclosure is that any strong standing wave resonances in the enclosure will not be sufficiently damped. The lack of fiber in the center of the air volume allows energy from the back of the driver to potentially excite resonances and produce unwanted acoustic output that escapes through the port opening. . . . The ML TL enclosure can be thought of as a form of transmission line where quarter wavelength standing waves are used to provide the spring for the mass of air in the port."

Since I want to use this box as the center of of an augmented fullrange system, the MLTL philosophy feels right to me, but I have no idea how to begin calculating

a) The dimensions of the box
b) The dimensions of the port
c) any necessary correction circuits

Regarding the correction circuits, since I am using this speaker in a digitally EQ'd system (I am using a power Mac G4 Cube as a digital signal source, going digital right up to the amp inputs, DACT-style stepped attenuators for volume control) do I need to worry about correction circuits?

Thanks for everybody's input so far.

Than
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Old 8th September 2009, 04:19 PM   #7
Scottmoose is offline Scottmoose  United Kingdom
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Actually, to be a 'real' BR / vented box requires a uniform air-particle density in the enclosure and no standing waves present. The transition from BR to MLTL /MLQWR occurs when standing waves present in the enclosure necessitate a change in vent tuning over what a pure helmholtz / reflex design states is needed.

Either way, I warned you it'd need to be big, right? Large mid-Q driver with a relatively high Vas = a big box.

Here's two; top = max-flat alignment; 48in, 400in^2 CSA, Zd = 21.375in, Zp 45in, vent = 6in diameter x 0.75in long. Line top, back & one sidewall 1in acoustic fibreglass or similar & adjust this & vent length to suit your own requirements. Bottom = borader-band PA style alignment tuned to Fs, Vp = Vas (rounded up slightly) 48in, Zd = 19.25in, CSA = 174in^2, Zp = 45in, vent 6in diameter x 4in long, same damping.
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Old 8th September 2009, 05:34 PM   #8
thansaffel is offline thansaffel  United States
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Default Hmmmmm

Scottmoose, I don't understand any of that! Sorry . . .
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Old 9th September 2009, 04:09 AM   #9
Godzilla is offline Godzilla  United States
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Scott, the top sim looks 'so flat' but i wonder if i might prefer the bottom design? Either way, it's amazing how a slightly bigger cab makes such a difference in measured performance. Thanks for the sims.

Godzilla
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Old 9th September 2009, 04:29 AM   #10
lousymusician is offline lousymusician  United States
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Quote:
Originally Posted by thansaffel View Post
Scottmoose, I don't understand any of that! Sorry . . .
Translation:

For the upper FR trace, the box is 48" tall, and 400 square inches in cross section (20 x 20, or some other dimensions to make the same area). The driver is centered 21-3/8 in from the top. The port is centered 45 inches from the top, and is 6in diameter x 0.75in long (i.e. a 6" hole in the front of the box, the thickness of the plywood is the length of the port). Big box indeed!

For homework, translate the specs for the other version!
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