MCM 55-2421 came unglued in a T18. What alternatives??

[Harley]

L clamps?? Got any pictures?

Leland has them

[But it Hertz]

Well Holy **** of ****ing god dam mother ****ing <enter expletive of choice here> poopy pants. That was a bar-steward of a job!!!!

Ever had that feeling that you are out of your depth, but can't stop? That was me today.

Here is the progress so far:

I had a practice baffle so I checked the clearance. Luckily it looks ideal.



Here's what I started with.



Cut away the old cover mounts and the driver goes in the hole... that was the easy part!



Playing with new router and I clean forgot about the screws!!! Drove the bit right into one. Sparks everywhere. So I took a little off the top until I could see the bondo and then dug it out of the screw head.



Then unscrew.



Here is the relief for the new cover. Not the prettiest routing job you will ever see here but I know where I went wrong now and learned loads in the process.

That painters tape made a really good drum. I admit to spending a couple of minutes pretending I was 12 years old... Bam Bam! Gives me a great idea for a musical instrument!



Marked out the new holes... second time lucky. I had to use tape to cover my first marks.... they were not central over the hole.



Right angled drill. I broke the bit in half in the vice with a hammer so it would fit in the hole.



This was the most difficult part. Turns out the bit I used was blunt and despite my best efforts wandered on 2 holes... so I was forced to oval them out to make the bolts fit. See the bolt right under the terminals? Yeah, it's not straight but at least it is held by epoxy that way.

I felt dirty doing it and vomited a little bit in my mouth. It was not a good moment.

Also check out the massive void, top left!! This is why we don't use cheap home depot plywood like me, OK?



Got a beer to celebrate an artistic shot. You can see how much the cover has grown relative to the box which is 18 x 18 inches.

Tried it on an amplifier and of course it leaks like a sieve. I was hoping to get away with it just for testing, but alas no!!



I'm kind of bored with wood work tonight so I made a quick & dirty cover. I'll make a proper one at some point.



I say I'm bored with wood but the postman bought me a new router accessory so I busted out a quick hole for for the speaker connections.



So this is the ugly picture. I'm not proud of it but it will be solid and straight when dressed up. Here you see I filled the old holes with epoxy. The two bolts you see sticking up are the 2 holes I had to oval. I covered them in grease, screwed them in and then filled the holes with epoxy.

Tomorrow I will remove them, clean the threads, smooth the surface and pretend like this never happened.



So no one appeared interested in the virgin versus burned in SPL chart... and to tell the truth I can't be bothered. But here are a couple of interesting pix taken of the driver at FS - 29.9Hz, 4 ohms. Compare this amount of movement with your 55-2421!!! This Infinity promises to be a beast!!

10v = 25 watts



20v = 100watts, and pretty much as the max the 55-2421 could cope with in free air. I could go as high as 22v (121 watts) in the T18 before it didn't sound too good (disclaimer - tried once just to see how it would sound..... don't want to attract the wrath of the BFM police - I'm learning as I go mmmmkay? Go easy on me dudes )



31.6v = the advertised 250w RMS. Just look at that range of movement! IIRC it looks waaaay more than the 55-2421 was capable of.... and it just sits there humming away quiet as a mouse.

I can't wait to get this in the box.



Stay tuned. Tomorrow I will be annoying the neighbours with a freshly broken in driver.

[But it Hertz]

Leland has them

Ehhhh. Yes I can see these would have come in handy today!!

[CoronaOperator]

31.6v = the advertised 250w RMS. Just look at that range of movement! IIRC it looks waaaay more than the 55-2421 was capable of.... and it just sits there humming away quiet as a mouse.



I can't wait to get this in the box.

If it lasts that long. You really, REALLY, REALLY, REALLY don't ever, EVER, EVER, EVER want to do that again with any driver being outside a box.

There are 2 ways to blow a driver. First way is too much power. I see your driver can handle 250 watts and you didn't give it anymore so your good right? Nope, second way to blow a driver is to exceed x-lim and physically damage the driver. It takes VERY LITTLE power to exceed x-lim at low frequencies when the driver is outside the box (no airspring to control excursion). Pray your driver is ok and you didn't bottom out and bend the voice coil former, tear the surround, or tear the spider.

[But it Hertz]

If it lasts that long. You really, REALLY, REALLY, REALLY don't ever, EVER, EVER, EVER want to do that again with any driver being outside a box.

I was just show boating briefly for the pic. One hand on the volume control, the other on the camera but point taken. Thanks. Much appreciated. Won't do it again. Promise.

I'm here to learn and this leads me to another topic for discussion....

I am led to believe that below certain frequencies in folded horns a driver becomes unloaded and can exceed mechanical limits fairly easily.

Should I be limiting the lower frequencies after a certain point. How far can I go when boosting the lower end to get flatter response before I am in danger of hurting the driver? How do I figure this out for a given sub when you can't see the driver??

[Gregory East]

It didn't make any nasty noises? Wow. Still, I wouldn't be surprised if it is shagged after that performance.

I was wondering how you were going to drill new holes. No doubt next time you'll be doing the L clamps after that escapade.

[biggerrigger]

Very nice recovery overall. Good work.

[shawn_g]

Nice work. I felt slightly responsible for your problems since I suggested the Infinity, but I'm glad you found a solution.

While testing out my Table Tuba, I momentarily hit 34 volts by accident during a loud part of a movie (at 2 ohms; ~578 watts), so I know these drivers can take a beating.

[But it Hertz]

It didn't make any nasty noises? Wow. Still, I wouldn't be surprised if it is shagged after that performance.

I was wondering how you were going to drill new holes. No doubt next time you'll be doing the L clamps after that escapade.

Surprisingly, no. It actually sounded OK. There won't be a next time! I'll stick with what ever speaker I start with!

Very nice recovery overall. Good work.

Thanks!

Nice work. I felt slightly responsible for your problems since I suggested the Infinity, but I'm glad you found a solution.

While testing out my Table Tuba, I momentarily hit 34 volts by accident during a loud part of a movie (at 2 ohms; ~578 watts), so I know these drivers can take a beating.

Yeah, look what you started!! I'm also going to argue that you indirectly (almost) caused me to suffer some kind of BFM social death by torturing this driver.

This speaker is aimed at the car scene. They have to idiot proof it up to a point. It has to be fairly tough...


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But look people. Lets put this into perspective. It's a $40 speaker. I just spent $800 on tools and a week making the T18... as much as I feel a bit silly for posting those pictures and I do really care about my reputation here....

I really don't give a sh*t at this point if I kill this speaker. I just spent the best part of 5 hours making it fit my T18 and I can now change it in 10 minutes flat.

Today I learned sooo much. I get it. Stupid. Baaaaaaaaaddddd. Won't someone think of the poor children (etc etc).

Try thinking of it this way: Now we all know this little $40 speaker can indeed put up with some fairly brainless abuse.

Lets move on please!

[shawn_g]

...
I am led to believe that below certain frequencies in folded horns a driver becomes unloaded and can exceed mechanical limits fairly easily.

Should I be limiting the lower frequencies after a certain point. How far can I go when boosting the lower end to get flatter response before I am in danger of hurting the driver? How do I figure this out for a given sub when you can't see the driver??

As I understand it, excursion increases very quickly and the driver will unload when pushed hard below the tuning frequency of the cab (I believe around 40hz for a T18). In my opinion, a high pass filter is only needed on a T18 if you like to push the limits. I personally run a 30hz high pass on my T18's. I wouldn't try to boost much (if any) under 40hz.

Yeah, look what you started!! I'm also going to argue that you indirectly (almost) caused me to suffer some kind of BFM social death by torturing this driver.

This speaker is aimed at the car scene. They have to idiot proof it up to a point. It has to be fairly tough...

[Radian]

You should get a medal for project "Rework of the month". I get frustrated from simply reading about your tribulation....anytime a see a picture of a drill or saw inside a finished cab, I get the chills. ~whew~

[Bill Fitzmaurice]

I am led to believe that below certain frequencies in folded horns a driver becomes unloaded and can exceed mechanical limits fairly easily.

Those who would lead you to believe that are without a clue. Folded horns have more excursion control than any other cabinet alignment.

[CoronaOperator]

Very nice recovery overall. Good work.

+1

Very nice work around . I wasn't trying to cause you any grief, just looking out for you.

[But it Hertz]

I am led to believe that below certain frequencies in folded horns a driver becomes unloaded and can exceed mechanical limits fairly easily.

Those who would lead you to believe that are without a clue. Folded horns have more excursion control than any other cabinet alignment.

OK. Thanks Bill. Just to check. I can EQ merrily away down at 30Hz to 40Hz (ish, what ever the numbers turn out to be) just for that little bit extra without fear of possible speaker damage? No need to high pass? If it sounds OK it probably is?

[Bill Fitzmaurice]

I am led to believe that below certain frequencies in folded horns a driver becomes unloaded and can exceed mechanical limits fairly easily.

Those who would lead you to believe that are without a clue. Folded horns have more excursion control than any other cabinet alignment.

OK. Thanks Bill. Just to check. I can EQ merrily away down at 30Hz to 40Hz (ish, what ever the numbers turn out to be) just for that little bit extra without fear of possible speaker damage? No need to high pass? If it sounds OK it probably is?

I didn't say you can push it with impunity. As frequency goes down excursion goes up, with any speaker, and as it's a 40Hz design that's as low as you should run it unless at low levels.