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Yet Another SEOS/TD12M Build

post #1 of 23
Thread Starter 
Think I should start building my TD12M speaker. Looking at Bunny's build keep giving me the itch. smile.gif

I'll be putting it all in a 1.5cf BB box, with a vertical/horizontal brace. My woodworking skills are pretty amateurish, so my builds are quite simple.

The box will be tuned to around 49hz with an f3 at roughly 62hz using a 3" round port tube 3" in length.

Attached, is my crack at WinISD.

Could you guys glance over and see let me know if you have suggestions (changes)?

As far as port tubes go, what do you recommend?




winisp1.jpg
post #2 of 23
ideally, you want your -3db point to be right around your crossover point because your receiver will slap a 2nd order highpass and a 4th order low pass on that point.

-3 natural rolloff + -3 from the crossover give -6db for the tops. -6db from the crossover gives -6db at the crossover point for the bottom.

decreasing cab volume to about 1.25 moves the f3 to 80hz, if that is what you intend to use for a crossover point.

since you have good subs, if you have a separate crossover for the subs, you could run the mains in sealed 0.75 cubic feet "full range" and put a second order low pass on the subs, flip the polarity, and have something similar to what bag end does (which minimizes group delay, thus keeping as much sound as possible all in phase).

now that i think about it, dr. geddes also employs this same approach.
post #3 of 23
Thread Starter 
Thanks LT,

I do like the sealed boxes. Much simpler to build and easier to integrate with the rest of the system.

However, I heard that it's better to put the TD12M in a ported box?

I've adjusted the port length and diameter (3" by 8" length) to get it tuned to 35hz with f3 at 80hz while keeping the box volume at 1.5cf.

I am afraid a smaller box won't have enough room for both the waveguide and woofer. Unless I want the waveguide outside, or a completely separate chamber within the box for the woofer.



Photobucket
post #4 of 23
I understand the theoretical -3db for a -6db point. But it's always easier to reduce output than increase it. If the box size is fine, I wouldn't throw away SPL. Also, -6db cross overs are bad in theory in the bass range IMO. Ya, I'll disagree with Dolby and thx and bag end. I'm more interested in sound power at those frequencies. Not phase and direct sound level. I'm not sure in a multi sub system you can ever be sure you'll be in phase by doing the model a certain way. For a speaker, I use -6db cross overs 99% of the time. For subs, I maximize output on both the sub and speaker, then start working in the room taking measurements and adjustments until I get a flat response at the LP, while avoiding any boost.

I do agree running mains full range ain't such a bad idea IF sealed and IF it won't run out of xmax. Geddes does do this, but not cause of any phase kind of thing afaik. He uses badpass subs doesn't he? Bag end... I'm not familiar with their philosophy. I'd appreciate a link or something about that LTD.
post #5 of 23
"Geddes does do this, but not cause of any phase kind of thing afaik. He uses badpass subs doesn't he?"

the slope of a sealed enclosure is 12db/oct from the mains.

he uses bandpass subs which have a natural 12db/oct low pass slope on the subs.

12db/oct slopes give a lower group delay as the transition is made from the mids to the bass.

"Bag end... I'm not familiar with their philosophy. I'd appreciate a link or something about that LTD."

i don't have one off hand. i just recall that they use a similar approach, in their case 2nd order slopes crossed in at 90hz. a reviewer mentioned that while it didn't seem 'louder' per se, it seemed to hit harder configured this way.

part of the magic of the danley horns is minimizing phase changes across the bandwidth. to the extent that dr. g's approach and bag end's approach also minimizes phase changes, i'm inclined to believe that there may be an effect there.
post #6 of 23
Quote:
Originally Posted by LTD02 View Post

ideally, you want your -3db point to be right around your crossover point because your receiver will slap a 2nd order highpass and a 4th order low pass on that point.

The chances of the actual in-room -3 dB freq being the same as predicted by modeling is fairly remote, so I wouldn't base design decisions on that expectation.

And I expect EQ wilo be available to smooth things out.
post #7 of 23
"The chances of the actual in-room -3 dB freq being the same as predicted by modeling is fairly remote, so I wouldn't base design decisions on that expectation."

i agree. however, the electronics in almost every receiver make the assumption about the speakers that i was referencing. if you build to another specification and it works for you, great, and many have. i was just going on the stanard thx model for what they call sattelites and subs, but around here what we would call mains and subs.
post #8 of 23
Thread Starter 
Anyone know the complete T/S parameters for the TD12M?

Trying to enter them into Jeff B. Excel spreadsheet. Thanks
post #9 of 23
TD12M - 8ohm
Fs: 38.1Hz
Qms: 2.99
Qes: .27
Qts: .25
Vas: 140L
Cms: .35mm/N
Mms: 50g
Sd: 531sqcm
Rms: 4kg/s
Bl: 17Tm
Re: 6.6
Le: .2mH
Z: 8ohm
Pe: 500W

1W SPL: 96.5dB
Xmax: 6mm
post #10 of 23
Thread Starter 
Question on slot port.

If I cut a 1" height by 10" wide port opening in the baffle, but then I have a 2" height by 10" deep inside the box.

Does my port count as 2" x 10" x 10" because my port en-closer is 2" tall?

Or would it be counted as 1" x 10" x 10" because the port opening is 1"?

The reason I ask is that I wan to cut a 1" tall slot port, 1" above the bottom so my port won't sit all the way at the bottom of baffle.

Does this make sense?
post #11 of 23
i understand what you are asking and do not think that it is a good idea. you are effectively just blocking off half your port. that will create lots of turbulence and i'm not even sure how to calculate the tuning that you would end up with.
post #12 of 23
Thread Starter 
thanks.

perhaps i should stick with round port. or perhaps sealed just to make things easier.
post #13 of 23
Just place a piece of 3/4" plywood or MDF on the bottom and locate the slot flush with the 3/4" material. If you have to have it up 1", then tack a piece of 1/4" material on each end of the 3/4" plywood or MDF false bottom. Lots of easy ways to accomplish what you want to do. it does cost you some interior volume.
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post #14 of 23
^^^ a reasonable solution.
post #15 of 23
What's wrong with a sealed box?
post #16 of 23
Thread Starter 
Don't feel like building 2 separate chambers. tongue.gif

Or I have to work on a mounting bracket to mount the waveguide above the box.
post #17 of 23
The piece to separate the two chambers will also act as a brace.
post #18 of 23
Building the box with two sealed sections is the easiest build. You need to have a brace any way and placing it between the woofer and tweeter is a logical place to put it. Making it solid is easier than building a brace. Once again, it costs you internal volume for the mid-woofer.
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post #19 of 23
Quote:
Originally Posted by AV Science Sales 5 View Post

Building the box with two sealed sections is the easiest build. You need to have a brace any way and placing it between the woofer and tweeter is a logical place to put it. Making it solid is easier than building a brace. Once again, it costs you internal volume for the mid-woofer.

Going off on a tangent here...no need to seal the horn section. Leaving it open in the back is an easy way to make the crossover accessible for future tweaking.
post #20 of 23
Quote:
Originally Posted by mobeer4don View Post

Going off on a tangent here...no need to seal the horn section. Leaving it open in the back is an easy way to make the crossover accessible for future tweaking.
I wouldn't leave it open, due to the possibly of cabinet resonances. Sealed with a removable back would be a better approach.
post #21 of 23
or you can insulate it with Mortite or something similar. thats what i used on my Fatail Pro LTH142's and it seemed to work well.
post #22 of 23
Thread Starter 
Ok...I am going sealed.

0.71ft^3 for a qtc value of 0.702 f3 at about 110hz

need to pick up a 5x5 sheet BB to start going.




post #23 of 23
Thread Starter 
Well, it's about time I get going on this.

X-over parts ordered.





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