Going back to sealed from LLT

**thxgoon** · **10-11-08, 08:26 PM**

Well guys, as much fun as the LLT's have been, they are just too big in my new room. You have to turn sideways to fit between the subs and the couch to get into the room, literally. No good. So I thought I'd throw some ideas out and see what you all thought.

TC Sounds 15" TC1000's X2
EP 2500
BFD 1124

Originally, I'd noped to build a smaller vented enclosure similar to avaserfi's Infinity build, but with these drivers the box would have to be too big to get decent results. In a sealed design with both drivers mounted in 8 cu ft gives a Qtc of about .7. Power handling is right at 800 watts per driver before exceeding xmax (power compression not withstanding) so the design appears to be amp limited.

I took some REW sweeps of current locations vs new location and compared it with WinISD models. It appears that I should be able to get to within 1db of max ouput with a sealed design in a new location at the front of the room as compared to the LLT's at 20hz. This is thanks to the ability to co-locate the two drivers as well as better response from the new location.

Has anyone used an LT circuit? I'd like to reduce the box size to 6 cubes and this seems a good way to make up for lost performance. (max spl stays within 1 db of 8 cubes) Good idea? Bad idea? Is there any difference between an LT circuit and using external eq?

What do you guys think?

**Mike P.** · **10-11-08, 09:30 PM**

Have you tried modeling the 15" TC1000 in a sealed and also with a LT and compared them?

**thxgoon** · **10-11-08, 09:49 PM**

Yes. When I get home later I'll try to post some plots, but on the work puter that's not doable

Max SPL between 6 and 8 cubes is the same and this all I'm really considering given that any response irregularities can be tuned via eq.

There are 2 things I don't know:

1 - Whether LT circuit and external eq behave exactly the same
2 - How much power compression will become a factor in the design. Smaller box needing more power.
3 - How accurate WinISD is at predicting air spring related roll off. Oddly, response doesn't seem to be affected much until it gets below 1 cu ft per driver. And at infinitely large boxes, response drops to zero.

Okay, so that's 3

**Mike P.** · **10-11-08, 10:03 PM**

How can the SPL between the two be the same if a LT boosts the low end?

**thxgoon** · **10-11-08, 10:43 PM**

Quote:

Mike P. wrote:

How can the SPL between the two be the same if a LT boosts the low end?

The thought is that I can apply the same boost with the BFD.

Max SPL is a function of xmax or power as I understand it. So eq aside, the max spl is dependent on excursion, power handling, and available power. More power is needed in a smaller box for the same output. Between 6 and 8 cubes (according to WinISD) there is no substantial difference.

**Mike P.** · **10-11-08, 11:39 PM**

Quote:

The thought is that I can apply the same boost with the BFD.

Ok, gotcha.

**avaserfi** · **10-11-08, 11:56 PM**

Quote:

thxgoon wrote:

1 - Whether LT circuit and external eq behave exactly the same

If given a choice between passive (LT) and active equalization (BFD) I would recommend active equalization virtually everytime. Ideally, you could just build a circuit and you would have your desired response, but because of room interaction this will never be the case at these frequencies.

The LT will already be using valuable headroom from the sub, couple this with the equalization required to get the desired response and you are potentially wasting headroom between the two. Now, if you have no LT, you can still achieve the same low end response while allowing for room interaction. Furthermore when you attempt to equalize you will have no issues with trying to defeat passive method electronically (wasting headroom). If you really want to try the LT out do it externally such that you can remove it at will and measure which method allows more headroom.

Quote:

2 - How much power compression will become a factor in the design. Smaller box needing more power.

This will be largely driver dependant. You do have extremely high quality drivers at your disposal so I would expect less compression than typical.

Quote:

3 - How accurate WinISD is at predicting air spring related roll off. Oddly, response doesn't seem to be affected much until it gets below 1 cu ft per driver. And at infinitely large boxes, response drops to zero.

Low frequency modeling is fairly accurate, but not 100% so. I have never seen or bothered trying to verify the full accuracy of air-spring roll off as modeled before so I cannot sufficiently comment on this statement.

If you post the T/S for the driver and your goals for size, output and reach I would be more than willing to model it for you with for maximizing these aspects while minimizing size. This method would allow for maximized performance above tuning when compared to a sealed model.

-Andrew

**thxgoon** · **10-12-08, 03:15 AM**

Quote:

avaserfi wrote:

If given a choice between passive (LT) and active equalization (BFD) I would recommend active equalization virtually everytime.

Excellent! That's what I was thinking. WinISD must not take power into account for the filters when it calculates response and excursion for an input signal. It was telling me that only 350 watts were needed for a given output at 20hz with LT vs 1600 watts without. Some kind of voodoo magic...

Here are the T/S parameters:

Qes .381
Qms 3.820
Fs 15.6
Vas 393 l
Mms 238 g
Re 3.66
Xmax 27 mm

I'd like to maintain the performance I currently have if possible. I took room sweeps using REW of the 2 locations of the LLT's currently and the new location. I did this by placing one sub at the listening position and measuring all of the sub locations. The purple line is the new location and the yellow and green lines are the present locations of the subs.

From the looks of things, I gain 3 db down low from the location and should gain another 3 db by co-locating the subs. This should offset my losses of removing the ports. I'm not opposed to a vented design, as long as I don't lose 20hz extension.

Ideally I'd like to maintain over 110 db at 20hz from the sub before room gain and if possible keep as much sub 20hz output as possible. I would not be opposed to losing the sub-sonic stuff for lower distortion or higher output. The box needs to house both drivers, and be in the neighborhood of 24" by 28" by 30". At the moment I'm thinking 8 cubs sealed is the best bet but I'm open to any ideas.

Thanks for your help!

**Mike P.** · **10-12-08, 07:35 AM**

It sounds like active equalization together with REW will produce a sealed sub optimized for a specific location which should out perform a sealed sub with a LT applied and then being equalized for the best performance. Looking forward to seeing how this develops.

**avaserfi** · **10-12-08, 11:20 AM**

The size you gave is only about 7 cubic feet, but since you are thinking about 8 I went with that for extra performance

.

Below is the model of a 2x drivers in 8 cubes sealed (yellow) and 2x drivers in 7 cubes with a 12" x 3" x 50" port (16Hz tune total port volume is about 1 cube) (gray) both are with 1400 watts input assuming 4 ohms nominal being powered by an EP2500, 1 sub per channel:

Max SPL:

Cone excursion:

Port airspeed:

As you can see the ported enclosure will have about 3-4dB more output. Both units easily clear your 110dB request before room gain (it is safe to presume these drivers will be linear even at high output/power due to their extreme design). The main reason to go ported is the huge headroom you will have if you ever decide to get some more power. It isn't even close to reaching its limits yet.

With the recommended port there will be no issues with compression or chuffing. Due to its length port resonance will occur at about 130Hz, this is not even a remote issue if a 4th order crossover is used at 80Hz.

I would go ported without question.

-Andrew

**thxgoon** · **10-12-08, 02:25 PM**

Thank Andrew! I never thought to port so low in a smaller enclosure. The difference isn't as substantial as I'd thought between the sealed and ported designs but you're right about the power. I'm just not sure how much more power I can dump into the drivers without them melting

I like this design for several reasons, but especially that at 7 cubes, it behaves just like 8 cubes if both designs are sealed. This would give me the option of plugging the port for experimentation which is something I've always wanted to do.

Now on to some sketchup

I had a question about your slot port. When you bend the port, did you route any edges or just leave them sharp?

**avaserfi** · **10-12-08, 03:01 PM**

Quote:

thxgoon wrote:

Thank Andrew! I never thought to port so low in a smaller enclosure. The difference isn't as substantial as I'd thought between the sealed and ported designs but you're right about the power. I'm just not sure how much more power I can dump into the drivers without them melting

During music/movie playback I would expect these drivers to be able to handle 3000 watts a piece without any issue. Remember, the sine wave testing Ilkka uses is far more demanding than required for actual playback. Also, typical power ratings for drivers are done in a way that is not representative of typical domestic use.

Quote:

I had a question about your slot port. When you bend the port, did you route any edges or just leave them sharp?

I rounded all internal corners that could impede airflow to 0.75" radii.

-Andrew

**Mike P.** · **10-12-08, 03:10 PM**

Well then, so much for the sealed actively equalized low end experiment.

Nice pics of the slot port, Andrew. Definitely a reference for anyone wanting to know how a slot port should be built.

**thxgoon** · **10-12-08, 04:26 PM**

Quote:

Mike P. wrote:

Well then, so much for the sealed actively equalized low end experiment.

Well there won't be an LT circuit but I'll definitely experiment with plugging the ports and eq'ing

Thanks for those pics Andrew! Here's some preliminary designs from sketchup.

A little ugly, but functional

This one ends up being really looonnngggggg. 2nd driver on the other end.

A little tall but I could make it fit. Slot port on the back

And final design ala M&K, slot port out the back.

**thxgoon** · **11-18-08, 03:26 AM**

Sorry to resurrect this thread from the dead... With Thanksgiving break coming up I might actually have some time to work on this. Turns out that my space constraint is a bit tighter than originally thought, so as a compromise from Andrew's suggestions I have the following...

Looks like about 2db less than originally planned but I think I can deal with that. Final volume is 5.5 cubes tuned to 17.7 hz. What do you guys think? Drivers in Push Pull for experimentation and intend to experiment between ported and sealed with this design too

**Mike P.** · **11-18-08, 06:13 AM**

I love the design. Nice CAD work! What amp will you be using?

**thxgoon** · **11-18-08, 01:48 PM**

Thanks Mike! I'll be using the EP2500. From the looks of things though I may need more power

**toddbagwell** · **11-18-08, 02:17 PM**

WinISD must not take power into account for the filters when it calculates response and excursion for an input signal. It was telling me that only 350 watts were needed for a given output at 20hz with LT vs 1600 watts without. Some kind of voodoo magic...

----

Just my two cents, but if you use the Amplifier Apparent power (VA) tab in winisd (where you change from spl to excursion etc) you'll see that the LT really jacks up the power requirements down below Fs.

Sorry to add in so late in your thread. Enjoy your build. I'm mid-boxes, waiting on my brother-in-law's and my schedules to coincide again

todd

**Ricci** · **11-18-08, 02:20 PM**

Looks like a cool and unique design. The only thing that I'll say is that you are giving up a wee bit of volume by trying to go push/pull and it looks like you could use every bit of volume you can get with this box.

**tenzip** · **11-18-08, 08:20 PM**

One comment/suggestion on your box design, if you want the port in the middle of the box for looks, that's fine, but if you put it to one side, using the side of the enclosure for the side of the port, you'll save yourself some MDF, cutting, and a bit of internal volume.

Just a thought.

**thxgoon** · **11-18-08, 08:26 PM**

That's a good thought. I had also considered laying the port down in the area behind the second woofer and porting out of the side. In the end they all end up pretty close in terms of volume.

Ricci - The outer dimensions are pretty much fixed so push pull is the only way I can get the drivers to be on the same face. I could mount them opposite each other but I just don't like the idea. Total loss is only about a half cube when you account for the motor structure.

**Ricci** · **11-18-08, 08:39 PM**

.5 ft

Isn't that like 1/12th of the total enclosure volume? JK man. Dual opposed was what I was thinking. How is the enclosure going to be oriented in use? Port firing up?

**thxgoon** · **11-18-08, 10:39 PM**

Port firing out bottom back. I was thinking dual opposed too... Maybe I'll model that up

**Aaron Gilbert** · **11-19-08, 05:11 AM**

Quote:

thxgoon wrote:

Sorry to resurrect this thread from the dead... With Thanksgiving break coming up I might actually have some time to work on this. Turns out that my space constraint is a bit tighter than originally thought, so as a compromise from Andrew's suggestions I have the following...

...
Looks like about 2db less than originally planned but I think I can deal with that. Final volume is 5.5 cubes tuned to 17.7 hz. What do you guys think? Drivers in Push Pull for experimentation and intend to experiment between ported and sealed with this design too

That looks great! I really like it. One question: How do you install/remove the inner/lower woofer? I don't see any removable panels. Without that, I'd say the best option is to put captive through bolts on the interior baffle, then slide the woofer over those from the bottom, and a second set of nuts under the driver. That's not quite how M & K does it, but it would work. If you're just screwing straight up through the driver, that will be no fun to mount and unmount, unless you have a helper and a right angle drill. If you're mounting the lower woofer from the top, I don't see how it's ever coming out except via saw or sledgehammer.

**thxgoon** · **11-19-08, 04:20 PM**

I was thinking of using some kind of baffle between the driver and bottom of the cabinet. I could put the driver in, set the baffle over the hole and lower the driver into place. That make sense? Or just make the bottom panel removable and mount from the bottom. I don't think there'd be any harm in it.

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