Beta 12LTA in a 3cf box - port size

[Godzilla]

I am going to purchase the Eminence Beta 12LTA this week and add another project to my list of projects. Currently, my office has two small speakers – both projects that are not shaping up as I hoped. They use Dayton drivers (inexpensive 6.5 and 5 inchers). Maybe I am just used to Fostex in BIBs or expensive TBs on open baffles with H-frames providing beautiful bass… but these little bookshelf speakers are NOT satisfying me these days. They just sound small, don’t do bass and become congested at higher volume levels. Sooo, the Beta 12LTA will be added to my collection.

This project will fit the space available. The driver seems optimal in a 4cf box like the Hammer Dynamics but I want to go smaller. 2cf does not seem to offer the performance I desire.

I decided to go with a 3cf box 12” x 12” x 36” inner dims and will top it off with a tweeter (pro sound with a small waveguide). Initial sims indicate simply cutting a 3” hole into the .75” wood for a tuning of around 40hz.

I plan on powering this speaker with the neat little Dayton T-amp I just got and using my Droid phone or iTouch as the source. I really enjoy both!

Can some of you check my sim and offer any suggestions on tuning the box before I cut wood?

Thanks!
Zilla

PS, I was up last night trying to find a way to do this with one 4 x 8 but without luck... will have to purchase two boards and cut some more wood for upcoming projects.

[vinylkid58]

This is what I get in WinISD with your tuning:

3" round vent would be 1.75" long.

2.25" x 2.0" square vent would be 0.76" long.

jeff

[Vix]

Jeff, it will be interesting to try another approach. Beta 12 LTA in ported box, or perhaps equalized sealed one, with a 1" compression driver/ waveguide on top. I mean something like this:
YouTube - Rev Up Your Vintage Speakers, Econowave Style
AK Design Collaborative - Econo-Waveguide Speaker - AudioKarma.org Home Audio Stereo Discussion Forums

[GM]

Originally Posted by Godzilla

I decided to go with a 3cf box 12” x 12” x 36” inner dims........Initial sims indicate simply cutting a 3” hole into the .75” wood for a tuning of around 40hz.

I plan on powering this speaker with the neat little Dayton T-amp.......

FWIW, ancient wisdom dictates a ~3.36 ft^3 net tuned to Fs as the 'ideal' minimum, so assuming only 10 'clean enough' watts available at Fb, I calc a ~3.5" dia. x 0.75" deep hole is required based on published specs, though WinISD Pro (WIP) says a 3.125" dia. (~42 Hz my way), so a range to work with.

For a 3 ft^3 gross/~2.9 ft^3 net then, its mid-bass 'bloom' will be a bit more peaky unless tuned down around the T/S max flat alignment's ~36 Hz which requires a 3" dia. x ~2.5" (~2.87"/WIP) long vent.

Regardless, a 3" dia. x 0.75" vent in ~2.9 ft^3 = ~44 Hz/(47 Hz).

GM

[Godzilla]

Thanks for the input guys! I will continue to play while the drivers are on their way! I wonder sometimes how this 12" compares to the Audio Nirvana 12"... has anyone compared them? Two totally different sounds i'm sure.

I know and like the idea of the Econowave! One day i will probably build a pair. But the reason i choose not to use it for this project is that the 12lta is much more 'wide range' than most 12" woofers and doesn't require a tweeter to go so low, the strength and reason for the very cool Econowave. So i can 'get away' with a smaller tweeter that can be crossed similar to the way i'd cross a super tweeter to a fostex or tb wide range driver. I've pretty much given up on complicated crossovers and enjoy finding more simple solutions that sound great. I hope the 12lta is up to par and the expensive TB and Fostex drivers i enjoy don't spoil things. The Eminence drivers seem built more purposeful and less esoteric or fancy. I also like the 97db eff rating and am hoping for an 'easy and mellow' presentation overall after voicing the tweeter. I want this to be a speaker i can enjoy all day long at the office and then turn up at night when everyone goes home.

I think i am just too curious about larger diameter drivers playing music and want to feel it as well as hear it.

[Godzilla]

Here are my sims for the 12lta.

3 cf box, 3" port:

.75", 2.5" and sealed. Seems you can't go too wrong. Since they will be in or close to corners i am going to split the difference and go with the 36hz tuning and the 2.5" length (thanks GM). If it's too boomy i will stuff the port. This driver might work best in aperiodic cab but i don't know how to sim that.

My hope is to tame the rising response of the 12lta simply by angling the speaker. The tweeter will sit on top of the box to be angled to taste separate from the main driver. It's all part of the fun and i am looking forward to experimenting!

Thanks again guys. Funny how i'm basically building the Afterburner from many years back. It's an oldie... but i hope it's a goodie!

Zilla

[db6546]

Zilla,

Ron Brady over on the Full Range Driver forum has done some work with this driver that you may find interesting.

I also have a pair of these drivers and thought about installing a coaxial tweeter, but may just try an Econowave design instead. I'm trying to decide how big a box I can live with.

Are you going to treat the cone with anything?

Keep us posted.

[Godzilla]

Thanks db, i will seek out Ron over at FullRangeDriver.com.

>>> I'm trying to decide how big a box I can live with.

I think a 2cf box will work with these drivers down to 65hz either sealed or ported depending on how much bloom in the bass you like. I think what kept me from buying these earlier was that the pioneer b20 went deeper in smaller cabs. But my recent experience with larger full rangers (8") has prompted me to go even larger! The 4 and 5 inchers out there are lovely but 8" provides some more impact and are easier on my ears. One day i will probably go back to the benefits of smaller drivers but for now i need to get my fill of these bigger ones lol... i am hoping for a system with impact and detail, power and drive, an easy on the ears, not too excitable, mellow sound and hope the 12lta provides that for me since the plan is to listen to them daily in my office. Power will be provided by a T-amp. I don't expect to modify the cone at all... i like things stock but appreciate the benefits of tweeking. Call me lazy.

Today i bought the 12lta along with the GRS 8" full rangers (not in stock), the little Lepai T-amp (also not in stock... for kicks since i just got the very cool aluminum Dayton and three of the plastic Dayton's), a bunch of caps ranging from .47 - 3.3uf to experiment with, a different pair of waveguides to try with my compression tweeters... some more piezos... i am excited just thinking about all the stuff! This weekend i plan on staining a pair of large open baffles for my son... Jamo buyout 15" woofers, B20 on OB and a pair of lemon squeezer piezos... how cheap! I bet it sounds great when it's done.

Sorry for the vent... i am just happy to have some fun projects to look forward to and learn from.

Zilla

PS, Saturday morning i go for my promotion test in krav maga. Just thought i'd throw that in.

[Godzilla]

LOL! The 12lta looks huge compared to ALL the other full range drivers i've had. They are propped in corners now without any box for bass support. I just wanted to make sure they worked... they do. Looks like a lot of cardboard to make that driver and its GIANT whizzer cone. They play much louder than the little dayton drivers. I can tell they will produce a huge soundstage... or at least make a lot of sound. I still have not made boxes for them. Just looking at them i can tell they were not designed for small rooms and i don't think they were designed to produce every nuance of sound based on how heavy and stiff they seem. The whizzer has little crinkles in the cardboard suggesting these are not precision made nor were they meant for close inspection. The TB 1808 is much more compliant, delicate and refined looking to be sure. They are built to the standards of the pioneer B20 and alpha 15's some of us are familiar with and look like a blunt instrument compared to fostex and tb. I am VERY excited to get these into boxes and connect a tweeter. They certainly need a tweeter! They do produce lots of sound even in free space. Their sound changes drastically moving them on and off axis so the 'sweet spot' will need to be defined. I am enjoying the noises they are making at this very moment and can't help but wonder how these will ultimately sound. I bet they will be fun to play with and listen to. Looking at them now makes me hungry for Chinese food. They would be the wok to cook everything in!

[Vix]