LLT/EBS sub design help

[scathontiphat]

Hello all. Came across this section of the site while looking for information about EBS style alignments. I was happy to find out about this group and it's interest in the LLT alignments.

Anyhow, I have a bunch of Elemental Design EHQS12 drivers and I'd like to try them out in an isobaric LLT type alignment.

I was looking at using one isobaric clamshell pair in a 5 ft^3 enclosure tuned to 15Hz. Planning to use a 4" Port with a 3/4" roundover on the MDF side.

How does that look to you guys? Would you suggest any changes to the volume or tuning?

One question about the port, does it matter in which direction the port is firing (I'm looking at top versus front)?

thanks in advance for any help

[Warmon]

Hello scathontiphat,

That's an interesting idea you have of combining isobaric loading with EBS / LLT. Are you trying to get the benefit of EBS / LLT is a smaller package?

[Mike P.]

DS-21 wrote:

To get the port length right, you'll either have to do a folded slot (no huge deal, but extremely hard to turn thereafter, so unless you can measure your individual drivers before you cut anything I probably wouldn't go that route), or an external port. Or use PRs, though that defeats the purpose of using inexpensive drivers.

5 cubic feet tuned to 15 hz with a 4 inch port = 28 inches long. No external port required.

[scathontiphat]

Warmon wrote:

That's an interesting idea you have of combining isobaric loading with EBS / LLT. Are you trying to get the benefit of EBS / LLT is a smaller package?

Basically yeah. Also, I have 8 of these drivers, so I'm just trying to figure out ways to use them (already built a big tapped horn which was fun, but didn't go as low as I'd like and is a giant eye sore). I figured since I have so many, I could try this LLT alignment without taking up too much space by using isobaric pairs. If it works out well, i'd probably continue to build 4 of these enclosures.

I know the harmonic distortion canceling effects of isobaric loading are debatable, but maybe I could reap some benefit from that. I think the two biggest con's I've read about isobaric loading are the loss of efficiency and increased group delay. But I already have a QSC USA900 amp to drive what ever I build (ends up being ~112 watts/driver if I use all 8) so I'm not too worried about efficiency. As for group delay, looking at the WinISD group delay model, it doesn't seem too bad to me (<10ms until 24hz, 16ms @ 20Hz). It gets pretty bad below 20Hz, but I don't know if one can really hear a difference that low anyways.

[Warmon]

scathontiphat wrote:

If it works out well, i'd probably continue to build 4 of these enclosures.

From what Mike P. says about port length, it looks very doable. Go for it - nobody else is doing anything along these lines. My only suggestion is to go pull pull or push push - only because I don't like the look of the back of a speak hanging out of the box...

[SLP113]

My only suggestion is to go pull pull or push push - only because I don't like the look of the back of a speak hanging out of the box...

But doesn't Isobaric work best when the volume between the 2 drivers is minimized? I seem to recall reading that somewhere. Anyway, it would seem to me face to face mounting would minimize the volume between drivers. Also the main point of going isobaric is to reduce enclosure size. It would seem to me that any other mounting arrangement other than face to face would also result in a larger enclosure because of the resulting additional volume of the isobaric chamber which would take away some volume from the enclosure meaning it would have to be a bit larger to attain the same net volume. So if one is going isobaric to reduce enclosure size why waist volume just for cosmetic reasons. Also another question that comes to mind is that if one used back to back mounting wouldn't there be some cancellation of the magnetic fields similar to that produced by a bucking magnet? Would that affect the parameters of the drivers? If so that might be another reason to go with a face to face mounting configuration.

[Mike P.]

As far as I know true isobaric loading that results in half the vas, is when the drivers are in a clamshell arrangement with minimum space between the drivers. As for your port question, it doesn't matter which direction the port is firing.

[SteveCallas]

You'll definitely need all four subs, cause output from a single one looks very weak.

[Warmon]

SLP113 wrote:

So if one is going isobaric to reduce enclosure size why waist volume just for cosmetic reasons.

I'm considering an isobaric for my next project and that's the exact same delimma I'm facing - that and porting such a small volume negates the benefits even more...a whole bunch of ** to save 2/3 CF on a final size. Cosmetics are important when you are trying to incorparate a sub into a piece of furniture or need SAF. Otherwise, I agree with you.

IMO, isobaric only makes sense with drivers that are inexpensive and I think scathontiphat's idea is a good one

[Mike P.]

In my opinion 4 cubic feet tuned to 18hz would be a better combination. You would gain 30% better power handling and 4db of spl. Maximum excursion would be ar 24 and 16hz. This would be a face to face mounting of the subs with minimum volume between them, just as it shows in WinISD under the "Driver" tab.

[thxgoon]

Neat idea! Here's a pic of the 18hz 4ft^3 option with a normal vented alignment (yellow) with 2 woofers vs an isobaric vented alignment (green). Pretty impressive I think.


sorry the graph goes to 1khz, for some reason winisd wouldn't let me change it...

[scathontiphat]

4 ft^3 with 18Hz tuning definitely looks good in my sims (not sure if i'm doing it right though, as it looks significantly different than thxgoon's plot).

Couple questions on it.
1) what are the ill-effects of this higher tuning?
2) Is the tuning low enough to get away without using a high-pass filter? Or do I need to worry about the woofers unloading?
3) With 4 ft^3/18Hz, group delay crosses 10ms at ~28Hz, and it's up to 27.5ms at 20hz. Is that still okay?

attached are my plots for 5ft^3/15hz (grey) and 4ft^3/18Hz (blue).

thanks for the help guys! Can't wait to get to some building!

[thxgoon]

Looks like I screwed up. I edited the post with the correct graph.

[Mike P.]

scathontiphat wrote:

4 ft^3 with 18Hz tuning definitely looks good in my sims (not sure if i'm doing it right though, as it looks significantly different than plot).

Couple questions on it.
1) what are the ill-effects of this higher tuning?
2) Is the tuning low enough to get away without using a high-pass filter? Or do I need to worry about the woofers unloading?
3) With 4 ft^3/18Hz, group delay crosses 10ms at ~28Hz, and it's up to 27.5ms at 20hz. Is that still okay?

attached are my plots for 5ft^3/15hz (grey) and 4ft^3/18Hz (blue).

thanks for the help guys! Can't wait to get to some building!

My plot looks the same as thxgoon's. Check the parameters you entered in WinISD and verify that they are correct.
1) A higher tuning is a trade off. You're gaining more Spl at the expense of lower output. With a sub with only 9.1 mm xmax, you can't have both.
2) A high pass filter is required at 18hz to protect the driver from over excursion while maintaining the maximun Spl this alignment is capable of.
3) Group delay shouldn't be a problem.
When you do build this, post some pics!

[SteveCallas]

One thing to realize here is that you won't get very good results with either tuning using only one of these subs, there just won't be enough output, and you'll have lots of compression and/or bottoming. At the very minimum, even just for the sake of testing, you'll want to build two subs (4 drivers), and even that won't be all that great. Just want to make sure you are aware of that.

To give you an idea, with all four subs (8 drivers) and ~1200 watts, you'll only then be approaching the neighborhood of the capabilities of a single high excursion 15" driver LLT.

If you are up for different options, then I'd raise the tuning even a bit higher, say 18 cubes, 20hz tuning, a 16hz highpass, and ~2000 watts. That way they will at least be able to handle 20hz+ competently.

[thxgoon]

Going off of what Steve said and considering the additional cost and time to build 4 boxes, would these drivers fetch enough on the used market to get you one or two high excursion 15's?

If not, I'm sure you'll be thrilled with the performance if you've never had anything like this before. While you may not get Steve's level of output I bet it'll put a big grin on your face

[Warmon]

Can you guys post a SPL graph? I would like to see what it looks like. What about another option? - stay with the design goal, but go 2 isobaric pairs in two boxes. Wouldn't he be able to just double the Vb - 8cf and stick with 18hz on the tune?

[SteveCallas]

thxgoon wrote:

Going off of what Steve said and considering the additional cost and time to build 4 boxes, would these drivers fetch enough on the used market to get you one or two high excursion 15's?

Now that's an idea.

[scathontiphat]

Thanks for the comments guys!

I paid ~$110 for all 8 of these drivers. Not sure I can get that much for them if i tried to sell them. Also I've got 3 sheets of 4'x8' 3/4" MDF sitting around, so that should be enough for at least 2 if not 3 enclosures. As for time... lol, if I didn't love spending tons of time screwing around building stuff, why on earth would I be on a DIY audio forum?

I'm pretty sure even if these aren't super amazing high output, i'll still be happy, especially if I build all 4 of them (at least for a short period of time, until i want more). Previous "sub" before the horn i just built was a tiny Yamaha HTiB sub that looks like it has a single 6" driver. The horn, which was also done with a single isobaric pair of these 12" drivers, was fun and had pretty good output above 25Hz (super strong around 60Hz), but output pretty much nothing below 25Hz. And for something so big, i wanted to at least play solid down to 20Hz, maybe a even lower if that's possible, although it's becoming apparent that going below 20Hz probably isn't going to happen with these drivers, even with 8 of them.

I've never built a large ported enclosure. How much bracing do they generally need? Should I line the walls with anything or use any stuffing?

thanks again for the help

[Mike P.]

One of the designs for these subs was from Elemental Designs in a thread called "Cheapest Way To Get 20Hz".

http://www.icixsound.com/vb/showthread.php?t=39744

I'd try a couple of them just to see the results. Who knows, you might be suprised!