Single sheet TH challenge

[tb46]

Hi jbell,

What is the distance between boards H and E?

Regards,

[weltersys]

Originally Posted by r23d

We used 3 more sheets to make extensions for the 2x2 stacks, but for 4-8 db gain (curves for 1 box, 2 boxes and 2+extensions are attached), an extra 3/4 of a sheet per pox makes for a good sound to material ratio

They also unclip and pack flat...

It allows a pair of ss15s to hit a 45Hz corner, bumping up 40-45hz response by about 7-8db over a pair of subs with no extensions.

We came to the shape after a lot of experimentation with bits of ply and measurement mics, plus deciding on 600mm maximum extension from the front.

I can post sketches/plans if anyone else is keen, or just experiment yourself!

FYI, forum member Art Welter did something very similar with his keystone sub, and got equally impressive gains :

Richard

Richard,

Nice work!
Your extender adds more path length and is larger relative to mouth size than the ones I use, adding more gain and also lowering the Fb. Mine were designed to assist the low mid in my system, the extra 3 dB they provided down to Fb was a bit of a surprise.

The great thing about the added 4 dB (and lower frequency extension) an extender provides is it is not subject to power compression.

The SS15 has nearly 7 dB of power compression at 700 watt input compared to one watt, the extenders allow reaching a higher output level with a fraction of the power.

Did you happen to try the extender expanding from the full frontal area of the SS15, rather than just the mouth area as pictured?

Art

[CRESCENDO]

Originally Posted by jbell

PDC

Pretty Darn Cool

Ditto

Originally Posted by weltersys

Did you happen to try the extender expanding from the full frontal area of the SS15, rather than just the mouth area as pictured?

Art

I would also like to know

[Djim]

The only difference between extending the whole front instead of extending just the mouth is that if the cavity becomes large enough it can create its own resonance (peak in response).

[Djim]

Originally Posted by Djim

[jbell]

I'm not anywhere close to my shop, (it's graduation weekend for family member) but from memory.

The last ss15 layout I posted is 107" total path length. 3.5" to start at S1, 4.5" upper left, 6.5" upper right, 9.25" bottom right, 16" opening. Should be able to reverse engineer the hornresp inputs from there.

H and E are about 1" apart

[weltersys]

Originally Posted by Djim

The only difference between extending the whole front instead of extending just the mouth is that if the cavity becomes large enough it can create its own resonance (peak in response).

Djim,

Please show me your actual measured response showing a resonance peak being the only difference .

Until then, I'll await Richard's response to my inquiry.

Art

[r23d]

Originally Posted by tb46

Hi r23d,

Post #1518: "...I can post sketches/plans..."

Just the dimensions (size of the opening and depth of the extension) would be nice.

And, what was your measurement setup?

Regards,

The inside dimensions of the opening are 1110mm high by 1670mm wide, and the front edge is parallel with the box 600mm out.

The graph I posted should only be taken as a relative comparison, because we did not use an SPL meter to calibrate outputs to 1w/1m or anything so useful. For the graph posted, I used a behringer measurement mic (ecm8000 I think) about 2m away on the ground in my reasonably large backyard. I expect the results are a bit lumpier than we would get in a nice open area.

FYI we're using Room Eq Wizard v5 software to do sweeps - free download from Home Theater Forum - Home Theater Systems - HomeTheaterShack

To work out the best shape for extended response, I made some big guesses using hornresp, and then we expermented by sitting one sub on it's side with a board on top, placed side panels in at various angles and sat on them

Not hugely scientific I know, but we tried quite a few shapes quickly this way, and this setup gave us pretty good results.

Other tidbits :
- We wanted to keep the mouth open for simplicity and visual appeal, so I'm using aluminium channel to stiffen the edge.
- The top and bottom board do vibrate at bit much for my liking, so a brace is coming.
- The boards are butted up using adjustable over centre clamps with sponge rubber between to stop massive vibrations.
- Starting the flare at the horn exit gave us smoother results than using the full box width to start our extension from.
- From memory, the 170hz drop was less nasty with our test boards on a single box.
- We're using secondhand RCF lp200 drivers
- I didn't expect such a gain at the bottom from my guesses in hornresp, so will be testing in a park soon to see if this is a measurement anomoly from my backyard fence or something.

cheers all,

Richard

[r23d]

Originally Posted by tb46

Hi r23d,

Post #1518: "...I can post sketches/plans..."

And, what was your measurement setup?

Regards,

We did do a few measurements out bush when we dragged the rig out for my wife and friend's joint 40th - you may notice the improvised gas bottle stand in one photo. By then, the kegs were empty and we were sober, so the CO2 bottle got re-purposed...

Rich

[r23d]

Originally Posted by weltersys

Richard,

Did you happen to try the extender expanding from the full frontal area of the SS15, rather than just the mouth area as pictured?

Art

Yes Art, we did try using the full frontal area to start the extension from, and against my wishful thinking, the results weren't quite so good. Not as smooth, and not as much output, though I'm sorry I don't have any figures right now. I'll see if our audio guru Phil still has Holm impulse plots on his laptop.

I was really hoping it would make little difference, because building the extension would have been much easier, but the odd asymmetric shape has kind of grown on me.

We have almost finished the other pair, so soon will have plots of a matched set each side...

Richard