2 Tuba HTs

[logan74k]

Here are two THTs I'm working on, I ended up getting pressed for time to make an event date and had to focus on one rather than building them simultaneously.

I started with all the rough cuts for both per the cutlist in the instructions. Protip: I naively discovered the included cutlist with the instructions doesn't include any of the wood needed for the braces. After I went back to the lumberyard for the extra sheet I ended up using one 4x8 and 5 5x5's with very little waste, thanks to Cutlist (the program)



Because I didn't have a lot of time and don't have much patience for fixing warp in every panel, I went with Baltic Birch ply. There is quite a premium over 'regular' plywood, but BB is so clean and flat, and the material price for two giant subs is still 'only' about $300, it was a no-brainer for me.



After everything was rough cut, I started assembly on Sub 1, doing final angle and size cuts to the panels for both as I went.




As I mentioned, I had a big rush to get a sub done so built the first sub over 2 days, running into the extended set time of the PL as a major damper on the speed of assembly. I used a finish nailer to lock down the interior panels as I went, but shied away from nailing the perimeter as I wanted to put a decent radius on the finished edges. From a speed perspective, I was a little dissapointed in PL in terms of how long it requires to develop 'grab' and strength. It seems to go from wet to brittle over a number of hours before it really sets and gets a good hold, which made me nervous about shifting and flipping the cabinet as I went to nail the interior panels to the broad face.



One issue I've seen elsewhere on this forum and I managed to duplicate in my haste is the flip flopping of which end of Panel 4 the driver is skewed towards. I haven't seen any replies as to how this screwup may affect the output of the sub. In my case with limited unscientific measuring of the finished first sub, output is still pretty decent.

Thanks to DJPhatman for the heads up on the iNuke being loud for home theater use. I spent a little time early on opening mine up and quieting it down with a silent fan, and adding heatsinks to the different chips to make up for the reduced airflow. I also painted it black... as it should have been from the start... IMO.



I am a little curious about my output and will have to do more tests. It just doesn't seem like I've had the 'I almost shook my house down at 1/4 volume' experience that a lot of builders seem to have. I get plenty of output for my needs, I'm just curious to see what exactly makes the difference. I did check the cab for airtight and found no issues. I suspect it may be a basic question of power input from the amplifier as a lot of folks seem to have more substantial units, while the iNuke 1000 doesn't have a huge max RMS output, and I don't have a multimeter just yet to measure exactly what voltage is being output. Could also have to do with the driver position screwup. I'm pretty committed so will have to live with where it's at in Sub 1, but happily I still have time to correct it for Sub 2.

[Bill Fitzmaurice]

One issue I've seen elsewhere on this forum and I managed to duplicate in my haste is the flip flopping of which end of Panel 4 the driver is skewed towards.

That's one of the reasons why I provide Sketchup models, and include the instruction The driver hole is drawn 9½ inches on center from the end that joins to panel 5.
It's set towards panel 5 as that's where the chamber is higher. With a deeper driver it may not fit if it's set towards panel 1.

I was a little dissapointed in PL in terms of how long it requires to develop 'grab' and strength. It seems to go from wet to brittle over a number of hours before it really sets and gets a good hold

That's another example where haste makes waste. There's no points given for speed, so take your time and do only a couple of panels a day.

[Grant Bunter]

I ended up getting pressed for time to make an event date and had to focus on one rather than building them simultaneously.

This has made me curious.
What "event"?

[logan74k]

This has made me curious.
What "event"?

Ah, nothing grand. Just a scheduled movie night at my place that snuck up on me and which I couldn't bear to A:cancel or B: conduct sub-less! I'd already sold my two bag end Infrasub-18's to fund these! A personality flaw maybe

I have the RSS390HF-4 and they fit with plenty of headroom in the box as constructed, but I still intend to revise my pre-cut panel for the second sub to match the plans. The sketchup model is excellent reference, unfortunately it's not on a big screen in my workshop while I'm building. Still can't believe I glossed over the line in the plans that calls out the orientation, i got the 9.5" dimension down pat though!

[jimbo7]

Did you print out the plans to full scale?

[logan74k]

Haha, I did. Rather than measuring and plotting out points on both square sides (I'm mirroring the second sub) I printed out the schematic at 100%. I cut out the intersections of the panels so I could use it as a stencil, then connected the lines to show me exactly how the panels should lay out. I figured the breadth of the enlarged lines was within an acceptable margin of error. I did then drill the centers of the panel intersections as bill describes in the plans to map the nailing guides on the exterior of the panels - printing the plans just seemed faster to get the initial layout with guide lines on inside and outside of each panel as they go in.

Probably a holdover from bandsaw/hotwire sculpting where I'd print 3 ortho views of a model, trace it onto 3 sides of a block and then cut from each angle to quickly get to a rough form that was accurate in 3 dimensions.

[David Raehn]

It's a risky practice to print out the plans and work from them...

In technical drawing, DIMENSIONING is king.

The actual lines take a back seat to the accuracy of the specified dimensions and angles.

[Bill Fitzmaurice]

It's a risky practice to print out the plans and work from them...

Not really, they're pulled from the Sketchup model, so they're perfect. Too perfect, actually, as unlike with plywood a half-inch really is a half-inch. You still have to take into account the actual material thickness.

[logan74k]

This birch ply mics out to .485, if the thickness of a piece of cardstock is enough to throw off response appreciably, count me surprised. I appreciate the concern for absolute accuracy in printing out the plans though, and if this was a jet engine I'm sure I'd be a little more precise.

Using the plans with their broad enlarged lines it's certainly possible I've got error someplace in the box up to 1/8", however, everything's square, sealed, and the angles are correct. I was under the impression these were the most important factors. I've been wrong before.

[DJPhatman]

...and if this was a jet engine I'm sure I'd be a little more precise.

It's not a jet engine, per say, but it will make about as much noise as one!

Build is looking good so far!

[Radian]

I did check the cab for airtight and found no issues. I suspect it may be a basic question of power input from the amplifier as a lot of folks seem to have more substantial units, while the iNuke 1000 doesn't have a huge max RMS output, and I don't have a multimeter just yet to measure exactly what voltage is being output. Could also have to do with the driver position screwup.

Very nice build!

Couple of tips:

1. I know you checked cab, but double-check the gasket around the driver for leaks with a signal ~15-20 Hz. It's not uncommon for the drivers to develop a leak there after a day or so when the gasket finally sets. First hand experience.

2. Try to get that multimeter you spoke of, ASAP.

3. Triple check the settings on the iNuke or inside its DSP program. A DIP switch set unknowingly or an erroneous value entered in some wrong spot is all that it takes to mess up the signal to the point of completely trashing performance. There's a lot going on underneath the hood there.

Once again, nice work!

[logan74k]

Thanks Radian! Working on the multimeter, and I didn't see anything questionable in the inuke. Driver seal is good. Thanks for the tips! Ill post voltage as soon as I get it.

Can somebody enlighten me on the best initial corner alignment for a THT if corner loading is the goal? I've read against one wall, 18" from the adjacent wall, but this is a little vague if one is unfamiliar. Is the opening 18" from the wall, or is it closer, with the 36" square side 18" away from the adjacent? Basically, where does the mouth point?

[jimbo7]

http://billfitzmaurice.info/forum/viewt ... f=10&t=398

This might help. Also, against the wall firing down the length is acceptable (had to do this in a garage ). Really depends on the room abd what you're working with.

[logan74k]

Good link thanks! I'm reading conflicting information on sub configuration and placement - whether to couple 2 THTs in one place or spread them out for coverage and smoothing response. Personally I'm getting sufficient dB output from the single finished sub, and would prefer if I can make separate placement work to even out the bass once his sister comes out. Anybody having luck with spread out subs? The room is about 30x25 and there are no good placement options in front of the listening position. In spite of all the people I've seen spreading out subwoofers, it sounds like something that should never be done due to the size of the waves interfering in the room.

While I get that audibly bass isn't localizable, it seems like I can feel where it's coming from, and I want to spread that out if I can. Ill have to do a sub crawl again with these monsters.

I'm also about to dive into REW which will probably help me with this next new question, but here goes... Anybody find the need to delay their mains to match the sub output? I've seen this mentioned elsewhere, that due to the horn length the speaker distance is technically more than where the sub physically sits, requiring a certain delay so the subs hit in sync. Very interested to hear any stories on this! Anecdotally, it does occasionally seem to me that the bass is 'behind'.

[Grant Bunter]

Good link thanks! I'm reading conflicting information on sub configuration and placement - whether to couple 2 THTs in one place or spread them out for coverage and smoothing response. Personally I'm getting sufficient dB output from the single finished sub, and would prefer if I can make separate placement work to even out the bass once his sister comes out. Anybody having luck with spread out subs? The room is about 30x25 and there are no good placement options in front of the listening position. In spite of all the people I've seen spreading out subwoofers, it sounds like something that should never be done due to the size of the waves interfering in the room.

While I get that audibly bass isn't localizable, it seems like I can feel where it's coming from, and I want to spread that out if I can. Ill have to do a sub crawl again with these monsters.

I'm also about to dive into REW which will probably help me with this next new question, but here goes... Anybody find the need to delay their mains to match the sub output? I've seen this mentioned elsewhere, that due to the horn length the speaker distance is technically more than where the sub physically sits, requiring a certain delay so the subs hit in sync. Very interested to hear any stories on this! Anecdotally, it does occasionally seem to me that the bass is 'behind'.

Fear not!
The sub placement sticky helps those who have been previously clueless (like myself), or can learn something and gain some free output by wall or corner loading.
Wall or corner loading are applicable to all environments, the rest of the sub sticky more relates to live sound.
The one environment that suffers critically from room nodes/modes (frequency cancellations and nulls) is the home theatre/music environment.

It is reasonably well known that, in the home theatre type environment, it is not at all unusual to require two subs in different positions in order to address room nodes/modes.
Sometimes it even requires 4 subs, one on each wall, roughly on centre, of the wall length.

In HT it more often than not works out that 2 subs should be placed on opposing walls, and that kinda fits in your case as you say it's not possible to do so in front of the listening position.
So opposing long side walls could fit your requirements. Other options could be behind the LP for example.
Sometimes, again, any options that actually work best for best response, may not be the most pleasing options aesthetically. In which case you have to do the work that arrives at a compromise between aesthetics and function. Or, if you have no one else to consider, damn the aesthetics!

If your subs lead to some content being able to be "felt" in a source sense, what's your crossover point?
Anything below 80 Hz is omnidirectional, up to 100Hz pretty much the same, and after that, becomes more and more locatable. So it can depend on crossover point and may be frequency dependant.

Delaying mains? Well, if you have the ability to mess with that, then no probs, try it out.
Work on roughly 1msec per foot of horn length.

Generally though, it's a much better thing for mains to be leading bass, than the other way around.

REW is a great way to go. Wait till you have both sub cabs.
With REW, you stop guessing, and actually measure.
You still may have to mess around a lot positioning wise to get it all "just right", measuring again, and so on, though...