BillFitzmaurice.info

Last night's update:

Installed panel 6 in the 2nd T30. The wood had big warp in it (actually, it may have been a small warp, but it has been my first warped panel - it was about 1/2" off at the top. Managed to use clamps and screws to force it back into shape.


Then cut the phase plugs for the Otop. I cut the first with a jigsaw and then roughly cut the other 2 and used the flush trim bit to make them all the same. Routers kick ass! Also cut an extra plug, so that I can just use it to route round to create the final 2 I will need for the 2nd Otop. Then looked into cutting a woofer spacer, but realised that I couldn't without the woofer It was then that I discovered that the 2 spacers that I messed up when building my 2nd T30 may well fit the bill with minimal adjustment. The Lab12's baffle cutout (according to Eminence) is 10.98" and the 2512's is 11.06". That extra 0.08" will probably mean that I can use the scrap spacers on the Otops. I cut the hole on the scrap spacers fractionally too big (maybe 1/32") - it would have worked, but I wasn't happy with it, so did it again... and again! May well pay dividends now (or it may not!)... only way to know is when I get the 2512s through the post in a week or so and check the measurements against a speaker. Neither the plugs or the woofer have been glued btw I'll now move onto the 2nd Otop tonight.


Thought I'd include some photos of jigs and stuff, to keep the interest going! Firstly, my 'any angle' jig. Note the 45° block at the top of the pic. I had to use a bit of scrap wood to create a 12mm high 'leg' for the jig, and came across a woofer spacer cutoff, which gave me the idea of running it at 45°. Don't know if I'll use it!


2nd is my 4" 45° bevel cut jig for the throat reflectors. Notice the tiny overhang... trying to get that 45° cut without this jig would be nigh on impossible, and the rubbish 'exterior ply' that I had to use for the first sub


My wood pile is slowly decreasing:

Much better wood 2nd time around


Finally a gratituous shot of my powertools

escapemcp wrote:

Don't forget to get some braces in the horn path there. The wood looks a lot better indeed.

Last night had a bad night The warp on panel 6 which I spoke about the night before last has caused me untold problems when installing the braces. I think after several clamps and straight boards I have managed to get it close enough, (89° at the base), but I am still not happy. It bows out in the middle (half way between the braces), so will use a guideboard tonight to see if it moves so that I can squeeze that last bit of warp out before panel 7 goes on. Note to self: next time, just cut another bit of wood if the original bit is badly warped and use the warped panel for braces or something similar - would have saved me ages!

Oh, can anyone explain to me about this rule:


They are both lined up at 0mm, but the 500mm is different. It is the shorter rule that is 'wrong' - it has 4 millimetre scales on it, 2 on each side, and they are ALL different. Is this a special rule or something... I only just noticed it last night... it had messed me up a few times when I had to remeasure things - luckily the 'measure thrice and cut once' rule saved me repeatedly!

I can tell you that one of them needs to go in the recycling bin.

biggerrigger wrote:I can tell you that one of them needs to go in the recycling bin.

I think it is by design, as the smaller one has 500mm marked in SEVERAL different places. I was just wondering what it would be used for. I don't tend to use it anyway, as it doesn't have inches on it.

Oh, and I just contacted Monacor direct about the MPT-016:

I can do these for £2.64 each ex VAT plus a £10.00 next day delivery charge

Delivery can be with you Monday but we will need payment up front via card or a BACs transfer.

Please email me your delivery address if you would like to go ahead.

£2.64+VAT is £3.17

I was asking for the price on 40 of them, as I figure I will need 12 in each Otop, plus about 8 in the WH10 = 32, plus 8 for spares/duds/me cocking up the cuts!. I figured going direct for this amount may well be the better option, which it is - next cheapest is £3.46/ea+£2.95 P&P - this would be cheaper for smaller quantities - up to 24 tweets. 25 and over - go to Monacor!)

escapemcp wrote: Oh, can anyone explain to me about this rule:

If you used an on-line convertor, you would find that 50 cm = 19.7 in, which is 19 3/4" .

Payday tomorrow. So before I get spending I have a few quick questions.

1) When attaching the driver to the spacer to the baffle, should I drill the spacer holes bigger (so that the screw slips right through), so that tightening these screws will pull the baffle and the spacer tight to each other?

2) Is this all right for the xovers (lickable clink):


HPF components first.

3) On the LPF for the woofer, there was no mention of whether I should use a higher current inductor - in the HPF it says to use "air core of smallest gauge available as it carries almost no current", but there is no mention of what size to use with the LPF - as it is stuck there right in the way of the current, I was thinking it may need to be a bit more beefcake. Should I buy a higher power one?

4) I have provided 2 options for the 4Ω resistor - either 2x2Ω or 1x3.9Ω - should I spend the extra 81p and hit the 4Ω bang on?

I have tended to opt for the tighter tolerance items (2% rather than 5% or 10%). I know that Bill has mentioned elsewhere that this is not necessary, but I don't want all my values to be off and the xovers are crossing over too high or low. For a couple of quid, the peace of mind is huge, and I'll never be wondering "what if" if I think the speakers don't sound quite right (ok, ok, it's v.v. doubtful that they will sound off!) I am just keen to do things as good as I can - "buy once" or whatever it is

Many thanks in advance for your assistance

A

While a slight variation in crossover component values won't hurt anything, you can never go wrong using the exact value/part specified. The coil/inductor for the woofer definitely needs to be beefier than the inductor for the highpass. IIRC it's either 16 or 18-gauge; I'll defer to others for the exact specs. I ordered the "hi-power" LP crossover parts from Leland and the capacitor is rated at 100 volts. I'd go with that value if you can find it.

I'm not sure about the "ceramic wire wound" resistors. "Wire wound" to me sounds like they will behave somewhat like an inductor as well. For crossover resistors you would need non-inductive resistors. Those with more in depth knowledge may correct me on that though.

Regarding the spacer, in my DR250 and WH8 plans, it says, when trial fitting the driver etc, to PL the spacer to the baffle, using the driver mounting screws to hold it in place until the PL is set.
Then take the screws out.
It won't hurt to do it that way and means you don't overdrill the spacer, more "meat" for the screws to bite into.
I notice this is not in my copy of the Otop12 plans.

In some older plans it stated the woofer inductor should be 14 to 16 g.
Recently there was another thread (in part) about the inductors.
Bill commented in that thread that the inductor should be solid cored, as these inductors have lower DC resistance or DCR. If the inductor you're looking at doesn't have a DCR value of 0.4ohms or less (at least for an 8ohm driver), then you should find one that does.
I notice this is not in my Otop12 plans either.
He did also say in the thread that the gauge is less important than the DCR value.
Try as I might, I couldn't find a solid cored inductor with the exact value of 0.6mH, only 0.5x and 0.6x.

Given Anton's post above, the big white resistors you see from Leland etc are ceramic wire wound and are fine.

Hope this helps...

Sorry for lack of posts. Have been hard at work! The 1st T30 is almost complete... it only requires a few licks of paint in the horn and touching up a little (just like Stuart Hall does ):



Those removable castors are very good. Small footprint so you can install them without having to drive any screws through the 'pressurized' section of the horn. Use them to roll the thing about and then simply remove them once the sub is in place to avoid those nasty rattles.

I then moved onto the Otops. I have managed to cock one of them up by not making the spacer hole small enough, so that any bolts driven through are far to close to the rim of the spacer. I therefore concentrated on the 2nd Otop (which has far fewer mistakes on it anyway!). I did make a slight cock up by PLing on one side and only then deciding that I wanted to use T-nuts, which I then couldn't get access to. My solution was to attach the T-nut to a seperate small block of wood, and then PL this block in place, using the M6 bolt to pull it tight to the baffle.



After a bit more cutting and PLing, it was onto the tweeter array. Making a jig was easy - mine looked like this:



I did cut the tweeters a little too much, which means I now have a 7 tweeter array, but I think this shouldn't cause any major issues. The impedance will drop slightly (although it will still be very high, when compared to the woofer. They will still all receive the same voltage, so as far as I can tell, it should all be ok. It fits far more snugly into the OT as well - I never liked the gap that the 6x2x2" melded array had, so by trimming a little more off of each tweeter, the gap is no more!



After that it was all pretty easy stuff, except the soldering. I had always had an iron and solder, but never really soldered anything before. It was good practice soldering all those tweeters and the crossover (although the crossover is a bit of a mess!). By the end, I was getting right into it and am looking forward to hooking up array #2. A bit of foam later and I was left with something that looked like this:



I cut the back piece and attached it, but had to wait for the next day to properly test.



The next day came and I FINALLY heard what a BFM system should sound like. VERY happy. The sub properly pumps with really tight bass, the likes of which I have not heard before I was expecting a bit more from the top. It sounds very clear and I have heard things in some tunes that I had not heard before, but it was not as 'night and day' (when compared to 'normal' speakers) as the sub is. I still have to EQ (without an RTA or measurement mic ), so that will improve the sound of the OT, so hopefully that will provide the OT with as much as a WOW factor as the T30.

The last couple of nights I have gone back to working on the 2nd T30 and last night, I got all the structural pieces in place. I now only have to install the speaker wire and sand down any panels that are a little too long, and then the side is being PLed on to that sub. Then it is all the fun stuff left like rounding over and duratexing.

The 2nd OT is a little wonky. I have been thinking as I write this that I may well build another.



Notice on the pic above how the horn panels are wonky, is joins perfectly on the left hand side of the pic, but goes wildly off on the RHS join. This was caused by overconfidence after building the T30 The 2nd one (which is the one I have now completed) was built with a little more care. I think I have the wood to rebuild, so I think restarting it is the sensible thing to do.

So that is you all up to date. I will try to post some vids shortly so quench your speaker porn fetish, but I am sure that what I have posted so far is enough for you to crack on with!

EQ changes the sound of the OTs an awful lot. They sound 'odd' when EQd, very clear...

88h88 wrote:EQ changes the sound of the OTs an awful lot. They sound 'odd' when EQd, very clear...

Am getting there! Sorry for lack of posts, but have been head down to hit my deadline of next Saturday. And just to compound my troubles, I am thinking of building a flightcase for CDJ's and mixer also in time for the 25th (Thx Bill for your speaker building woodwork course. I feel like I can tackle these other things now )

I have been trying to get my Otop sounding right (2nd one being rebuilt after I wasn't happy with my first attempt at it). Without any EQ, they seem far too bright on the tweeter array. And when I use a graphic EQ on my phone (OK, not the best idea, but it does tally with what I am hearing and it does have a calibrate option which suggests something more than a 'gimmick' app), everything above 2k is way higher - there is also a small dip at 2kHz - I have tried reversing the polarity of the tweets which has made this dip smaller. One thing I did do wrong in my haste, was to solder up the tweeter array without checking polarity, but if I did have some round the wrong polarity, then surely they would cancel to create a reduced sound rather than a too bright sound? I have to build the next array tonight, so I will check those as I go and then compare the array I know is all correct with my one I have already built. Another thought is that I have been testing at low level, would this make the tweets overly bright?

I am using 14 tweeters, rather than the recommended 12 (to avoid any gap at the top or bottom which I wasn't happy with), but I don't see this causing such a major change. If doubling the speakers will add 6dB, then adding 2 to a compliment of 12 wouldn't even change it by 1dB - which would be almost (if not) inaudible. Any thoughts?

Anyway, here's where I am at:


Finally, I have a dynamic EQ on my iNuke amp. Is it worth getting this involved to EQ for different sound levels (e.g. to reduce or nullify the effect on the sound of power compression?)

If it were me, I'd be using every opportunity to play with eq (until it measured audibly flat) but it is definitely not necessary to use the dynamic EQ.