Beta 12LTA in a 3cf box - port size

[GM]

Hi GM.

Lots of numbers but I'm afraid I'm a learner. Can you dumb the info down a bit? I do understand the the specs, measurements & calculations can vary but other than that I'm stumped

Greets!

Hmm, can't figure out what needs 'dumbing down'. I mean all I did was a comparison with two different software programs and two different sets of specs (with 'published' being the same as GZ used) to 'fluff out' his basic WinISD alignments and rather surprised that WinISD's enhanced 'Pro' variant would be so far off compared to the one I've used since late '81 since it's vented alignments are very close.

Also, for whatever reason he chose to compare a bit more under-damped alignments, but I didn't notice it until after I'd done them using the 0.707 Qtc default alignment, so a slightly apples n' oranges' comparison between mine and his.

Anyway, short of designing based on measured specs of your drivers, best to build the biggest cabs you can 'afford', with ~9.7 ft^3 being the minimum I recommend for sealed and still have an adequate amount of tuning flexibility with varying stuffing density.

GM

 

[JRKO]

Hi GM. I'm a bit dopey sometimes, thats all. I've reread you post and it makes sense now. I am a bit surprised that such differing results were achieved but hey ho.

I'm gonna aim for a whopper of a box though - 11 ft^3 or so

 

[GM]

I resemble that remark! Yeah, that's a decent size. How you going to shape it? I mean it's large enough that unless it's well stuffed you need to think about its eigenmodes. Don't want any internal reflections modulating the driver.

GM

 

[Godzilla]

Thanks db! That was great of you to post! Your stock measurement is very consistent with the manufacturer's chart. My boxes will be a little smaller than what you have. Do you supplement the bass?

I agree with JRKO regarding the smoothing and phase plug. Wow, those are extremely helpful response curves for anyone working with the 12lta... and yes, they should work great with the Econowave now that you cut off the whizzer so all is not lost and you will end up with a great pair of speakers... perhaps even better than leaving the whizzer on. Personally, I want to retain as much of that 'wide range' sound, even if it's a little rough around the edges.

Great fun building big boxes! Thanks GM for your comments. I always appreciate your input. 11 cf (or even 9 cf) boxes will be BIG and the 12lta will look like little monitors adorning them. I don't think i can fit even one 11 cf box into my listening space. For now the H-frames should suffice. If home from work tomorrow, due to snow, i should have both (unfinished) boxes up and running... and maybe even one dustcap cut off. JRKO, GM has a good point about bracing those large cabinets. Have you given it any thought?

I'm psyched about the great information everyone is providing! I'm very excited about this project! I may have to consider even lower powered tube amps since my 30 watt Cary sounds way too powerful powering the 12lta's in my room.

Thanks!
Zilla

 

[GM]

I see some inconsistency below 1K that I attribute to my difficulty in deciding where to put the cut off point before the first reflection, but maybe some of you can gleam something useful from this - or tell me how to improve it. From listening I do know that I don't like the cupped sound and removing the whizzer did get rid of it. Most likely I'll build an econowave with my 12ltas.

Thanks for sharing!

It's a trial n' error thing since each room, etc. is different, so about all I can say is to use at least 1/6 octave smoothing since it's more in tune with our hearing acuity limit.

WRT the whizzer's 'cupped' sound, the $0.98 'foam around the whizzer' helps as does kneading the starch out of the whizzer to make it much better damped. This way you lose so much top end, though for mating to a horn, getting rid of it is best overall.

GM

 

[GM]

Great fun building big boxes! Thanks GM for your comments. I always appreciate your input.

11 cf (or even 9 cf) boxes will be BIG and the 12lta will look like little monitors adorning them.

I don't think i can fit even one 11 cf box into my listening space.

........my 30 watt Cary sounds way too powerful powering the 12lta's in my room.

You're welcome!

Hehe, this reminds me of the ~7 ft^3 MLTL cabs I use to do for a popular RS 8" woofer. Folks thought I was nuts putting a small woofer in such a big cab until a stereo pair tuned to 32 Hz pounded them with DSOTM!

Bummer. This implies that you have to sit in a very reverberant field.

That's just because the driver wants to 'feel' a very large cab tuned low.

GM

 

[JRKO]

I reckon something like 950mm tall x 700mm wide x 460mm deep should do it. Minus bracing etc is will be about 10 cf^3 which is just about right.

Question: How do you sneak a small tank of a speaker past your significant other

Answer: Ask her how she would like it finished!

Turns out that if the cabinets are painted in a classical, chalk based, slightly off white paint, she is good to go. She even suggested a panel of glass on the front held in by these

 

[JRKO]

How you going to shape it? I mean it's large enough that unless it's well stuffed you need to think about its eigenmodes. Don't want any internal reflections modulating the driver.

I want to go for individual cabs for each driver. This image has been haunting me - what do you think? Just imagine it a lot fatter

 

[Godzilla]

12lta sounds smoother and less resonant without the dustcap. I took it off just one and compared them carefully. Diana Krall sounds more natural. Without dustcap is better. Next i will add acousta stuff around whizzer (98 cent tweak) and when i get to home depot i will buy a dowel to make a phase plug. Also, FWIW, i think the speaker sounds better when it's more heavily stuffed. Sounds great!

JRKO, i had an idea (a sketch) for your speaker but can't share until i get in front of a scanner. Would you rather go wider or deeper? The Focal design is very cool too. Would you angle the boxes in the same way? I think it would be great to put the 12lta on top and angle it down like that.

A tip to cut dustcap off is to sit the driver on a table that you can smoothly spin it. Have a sharp Xacto knife ready and spin the driver as you carefully score the dustcap. Figure about 50 to 100 spins and the dustcap will eventually come off in a near perfect circle.

Zilla

 

[ThorstenL]

Hi,

12lta sounds smoother and less resonant without the dustcap. I took it off just one and compared them carefully. Diana Krall sounds more natural. Without dustcap is better.

I found the same with the Goodmans Axiom 201 I used.

Dustcap's are there for obvious reason (if I was a driver maker I'd put them on) but they mostly seem to be a "bad thing" that cannot avoided. Well, that's what they invented small stanley knifes for.

Ciao T

 

[db6546]

Zilla - I don't have a pair up and running. I built this box to use as a test mule.

GM - I tried the .98 tweak. It helped some, but it still had too much cupped sound for my taste. I also flexed that outer ring on the whizzer, but that didn't do much either. I guess should have tried kneading the whole whizzer before cutting.

Today I removed the driver and tested it with my WT3. Fs is now 74 Hz and Qts is .54. Based on the size of the box, and that I'll need help on both ends, I'm going to move on from this project.

 

[JRKO]

JRKO, i had an idea (a sketch) for your speaker but can't share until i get in front of a scanner. Would you rather go wider or deeper? The Focal design is very cool too. Would you angle the boxes in the same way? I think it would be great to put the 12lta on top and angle it down like that.

I'm going for wider that deep as this will better suit our lounge.

If I went the focal route then I would have the 12LTA angled down. I need to get spousal approval for that. If not then the tweeter will end up on one of those stands made of dowel that fostex show their more expensive horn tweets on

I'm very interested in your idea Zilla

 

[Godzilla]

Here's my sketch. I am not able to build complicated cabinets so i always think simple. Basically the sub acts as a shelf for the 'monitor' that is the 12lta + tweeter. This way you can angle the monitor to suit your listening tastes, have the internal volume needed for the sub and the whole thing looks integrated. If you have good wood working skills maybe something more interesting can be done. Feel free to accept, reject or modify.

My speakers are functionally complete. Both dustcaps were removed and i will eventually get around to the 98 cent tweak as well as adding phase plugs. The boxes are sanded but not yet stained. I will post pics tomorrow.

Listened to music until past midnight. The overall presentation is large, dynamic, detailed and simply awesome! If the above tweaks improve things then it will be a bit more awesome. I really enjoy the result.

Zilla

 

[GM]

I guess should have tried kneading the whole whizzer before cutting.

Today I removed the driver and tested it with my WT3. Fs is now 74 Hz and Qts is .54. Based on the size of the box, and that I'll need help on both ends, I'm going to move on from this project.

Yeah, you've got to work them pretty good to damp them all the way.

Gees, that seems like too big an increase based on a 45 Hz Fs, so what was it originally? Now, the B12 needs to be limited to a ~80 Hz XO.

GM

 

[JRKO]

I'll need help on both ends, I'm going to move on from this project.

Thats a shame but your ears like what they like and there is no changing it! I wish you acoustical joy in your next project.

I accepted before I bought that any 12" 'fullrange' driver was always going to need help at extremes of the range. The most important thing for me was not crossing over anywhere near the critical 'telephone band'. The 12lta is good from 100-200 thru 8k+ htz

With the ft17h its really good, but once the bass fridge's are complete I'll be doing nothing but smiling

 

[Godzilla]

Some more pics. Removing dustcap is easy and even makes the driver a bit more interesting to look at. I will fashion a phase plug in the coming days but don't really feel there is anything more to do to the driver since the sound is already very good. Additional tweaks will only make minor differences. It sounds the way it sounds and i enjoy it. The overall sound is big and bold. The last few days i've been enjoying all sorts of live recordings by Fleetwood Mac, Simon and Garfunkel, Bee Gees, Eric Clapton and James Taylor. For fun i've also been listening to Rocky Horror Picture Show and Wicked.

The 12lta may not be perfect but it does things other (smaller) drivers just can't. It gets very loud and remains clear. It's very detailed, dynamic, efficient and bristles with life. It's easy to match with a tweeter and woofer. I enjoyed it even before cutting the dustcap off but it sounds better (less rough and less reverberant) when it's gone. It has an easy, effortless presentation that's forward. It doesn't do pinpoint imaging but after listening to it i have some questions on that topic for future discussion. It really is like a V8 muscle car of the past. And even with their limitations those types of cars are still fun to drive and have their loyal fans.

As i tried larger drivers i continued to like the sound i was getting. I think one can argue that larger radiating surfaces present music with a more lifelike presentation than smaller ones. Don't try larger drivers unless you have the space. I love mine.

This project has me curious about other 12" full rangers... maybe one day i will even try a 15". When the weather gets nicer i will add four rubber feet and finish these off with some nice stain and poly.

 

[GM]

This driver really wants a small super tweeter stuck on its pole piece or at least suspended over it.

GM

 

[GM]

I think one can argue that larger radiating surfaces present music with a more lifelike presentation than smaller ones.

Duh! Why do you think I always say 15" is where one wants to start to go 'live'? RCA's Harry Olson worked through it mathematically and experimentally to arrive at this conclusion by the mid '30s and last I checked, the physics of the situation hasn't changed.

Admittedly, there's ways to get a more accurate reproduction over the ultra-wide BW available to us today, but 'on the cheap' WRT to getting vocals 'right' enough, a tweaked 15" 'FR' driver can be convincing for most folks. Unfortunately, I don't know of any inexpensive 'FR' 15" still in production.

GM

 

[GM]

Forgot to add this: "The single most important attribute of reproduced music is Tone" - Harry Olson

 

[Godzilla]

>>> Duh!

LOL! But so many enjoy 3" and 4" drivers (including me). Even with all its deficiencies, the 8" Pioneer B20 always had something over those smaller drivers that kept me listening. Even larger, the Beta 12lta excites a room with sound more effectively than any small driver i've come across leaving them sounding... small.

If i wasn't at work i'd be listening to music.