BillFitzmaurice.info

Yeah 35v should be deafening in that small a space. Sines especially.

I'm not sure I agree. A sine wave is a very specific frequency. It is not wide bandwidth bass, which would have much greater energy.

Me and OxonJohn tried it again this afternoon. There was no blow by through the gaps round the access covers. We figured if there was a leak in the smaller lab 12 chamber volume it would be discernable at the 1.5mm gap round the access covers, but there was nothing, absolutely nothing.

The whole issue of making the lab 12 panels air tight and then leak testing them is why I added in extra bits of wood to cover the 'tunnel' entrance (both of them).

I installed the bits of wood early on:


I installed ALL the flanges early on also, as I found after my first build that installing them toward the end of the build is a PITA! When the sub got turned up the other way, the result was this:


And then I slapped a 'sea' of gasket tape onto the 2 triangle-y bits.


Net result = no leaks

I will build ALL of my future T30s in this way, although I don't think it would be as easy to do it on the second side if you are building the T30s with dual access panels (as you are). I have found one access panel to be fine, although I do take care where the bolts are positioned to allow for this! I am also blessed (for this task, at least) with scrawny arms!! When I flex my arm muscles, I get a furrow, not a bulge!! It's one of the (many) reasons why I went with the lightweight BFM option!!

I'm hearing what you're saying Aidan.

Bolted joints are funny things, especially if theres compliant material in the joints. The stiffness of the joint components determines the local clamp (and therefore sealing) load. Large areas of gasket make that part stiff in comparison to the narrower strips down the side for the same pitch of screws. If all screws are torqued the same then the clamp/sealing load (if theres no leak paths) is a function of the number of screws per unit area of gasket plus also the bending stiffness and flatness of the access cover and hatch strips (glued in). Eg. for the same torque setting screws at the corner of a hatch cover will pull down more than screw along one side. Ask me how i know this? I ought to have backed them off.

I don't think i have any leaks. What I think is confusing matters is perceived expectation of how 'loud' the cab should sound with sine waves in a small space. i.e. When John arrived yesterday, the 25Hz at 10v was louder outside the garage than in. 70hz made speach/hearing sound wierd (like talking in front of a rotating fan) and 60Hz dropped right off, ...with corresponding behaviours at 120 and 140Hz. It was certainly not 'loud' at 40 to 50Hz. I'm going to drag it outside garage amd measure a few set points and see if they're anywhere near the curve. So, if I have the cab on the ground, 2:83v, how far away do i need to be with the meter? (and then add 6db per halving of distance, etc ....)

I failed to consider that there could have been an awful lot of cancellation going on. If it's really loud outside, then you're probably spot on!

sine waves should have more "energy" than musical content, as they have a crest factor of −3. no other signal (that is lopassed at 100) will have a lower crest factor.

the only reason music feels like it has "more energy" is because there are harmonics that are higher up than the root fundamental, and due to equal loudness curves, everything seems "louder". Play 80−100hz sine waves and you will get a similar effect

As has been mentioned on here many times before, these horns don't sound as loud as what you expect, until you try talking over the top of them or start walking away from them. The bass is so clean it doesn't actually sound that loud,.. But it is

Hi Charles,

It's likely the problems are due to reflections and cancellation, and pure sine waves will be more susceptible to this than broader band signals. 1/4 wavelength from a boundary could give you as much as a 24dB drop I believe. Have you dragged it outside yet?

John

Hi John,

No I haven't dragged it outside. I've taken the view all is ok, since the second one has come out the same, apart from a very minor leak round the driver perimeter to which I applied PL in a momentary faux pas, see photo. Should have used sealant.

Once high passed and limited with proper music (wider bandwidth) i think things will be different in terms of performance, placement caveats still applying.

Have finally got onto the v plate (looking for that 3dB ), which is quite badly warped. Have got it weighted down on the floor in the house so the underfloor heating can hopefully work its magic. In our house, the best place to leave one's clothes is on the floor (its a 'man feature') - nicely warmed in the morning. I've drawn up a little clamp bracket which can be made en masse on the table saw, so the cabs dont require holes through the mouth side pieces. I was looking for hand knob wheel type things like Aidan used but in the end got mightily irritated by the prices they think they should charge for something so simple. My idea uses coach bolts, large washers, wing nuts and these clamping feet, and hopefully doesn't present a trip hazard on top of the cabs. These days one could probably be sued for someone dancing where they shouldn't (probably even ones own off spring) and tripping over something you put there.

Time to fill my boots again. Good progress tonight.
Made said V plate clamps. Bought 10-off each of M8x50 coach screws, large washers and wing nuts from screwfix for just under 6 quid. Bargain. So wanted to get on with clamping feet to prove it would work.
Photos:
- raw material, 2 bits of 12mm scrap glued together.
- after a bit of 'machining'
- 6 clamping feet
- coach bolt and clamp in action
- rubber feet on.

I believe the plans say the v-plate doesn't have to be perfectly flat (although it must be )

That Tuff Cab looks really good. Looks nice and even in the pics. Makes me dread looking at my bare cab till I get the other built.

You'll probably want to put the wing nuts on top instead of below....it's a pain reaching under there for the back ones.

Nice v-plate clamps! Pretty ingenious. Make sure you use some rubber weather stripping on the edge of the vplate that sits on the cabs or you'll get rattle.

Good work on the clamps, Charles!