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Jus Lukin

Give me a hand yanking my horn?

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I have a sealed cab with a poorly tweeter, an Ashdown AAA-115t. The tweeter works, but appears to be leaking air, causing a chuffing sound at all but the quietest volumes. I have Hi-Fi cabs for when needed so I'm happy to pull the HF driver and keep the cab old-school, sealing the hole with a piece of MDF. From very a rough try with a test tone, the components don't appear to be crossed over as the woofer goes plenty high enough with the tweeter off, but there does appear to be a capacitor, presumably to bleed lows from the input to the tweeter.

Ashdown have been their usual very helpful selves, but I don't want to keep pestering them. They've said that it is probably fine to just unsolder the the tweeter from the PCB and seal the hole, but I'd like to double check before I go ahead as the cab will be used mainly with valve amps.

Will that cap likely cause issue with the tweeter removed, or will it just sit there unused and trouble free? I could also remove the cap, or try to unsolder the whole PCB from the input, link out, and tweeter switch, and fix the woofer direct to the input, but my soldering isn't the finest, and I'm (quite obviously!) looking for the simplest option!

Any advice gratefully recieved!

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Thanks Bill, I'm pretty sure there is no coil, just the cap and a couple of resistors for the 3-position tweeter attenuator switch.

I'll double check once I'm back in there, but sounds like I'm good to go! Cheers, Andy

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Why not diagnose what the problem actually is before pulling the tweeter and finding the chuff still there.

Remember pulling it too often makes you go blind! LOL

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11 minutes ago, BassmanPaul said:

Why not diagnose what the problem actually is before pulling the tweeter and finding the chuff still there.

Remember pulling it too often makes you go blind! LOL

😃

I did take the grill off to check all the screws were tight- the tweeter has obviously taken a knock at some point as there is a small chip on it, and the chuffing is coming from a vent in the centre- I could stop it by... uh... putting my finger on the hole!

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If it's physically broken then that's another matter. Why not just replace the horn? Resale would be better that way.

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Well, it's a pretty cheap cab which I got as part of a deal on an amp. I have large and small Barefaced boxes for Hi-Fi sounds, so I was going to use this for cranking lower powered valve amps through- of course, I could do that through the BFs with the horn down, but the Ashdown matches my CTM-30 so nicely!

I'll make a patch of MDF with a foam rubber backing which will fix over the gap with the existing screw-holes, so it will be completely reversible if I change my mind in future.

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If it's of any interest or use to anyone, here is a snap of the patch I made to cover the hole left by the tweeter. 4mm MDF with a square of yoga mat glued to the back! Works a treat, the cab is now well behaved and sounding great. There is no wadding so I'll add some later, but I'm pleased with the results so far.

20200429_215332.thumb.jpg.c298bed9f538d4b511fc3ea4d875852b.jpg

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On 26/04/2020 at 19:40, Bill Fitzmaurice said:

Blind? No. Carpal tunnel? Yes.

The voice of experience there!

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1 hour ago, Bill Fitzmaurice said:

Unbelievable.

Makes for a nice project for me, at least!

I was planning to use polyester wadding, a little of which I have left over and some which I was going to take back out of a 4x12" (which sounds great, but I have other plans for the drivers), but it turns out that my loft wasn't insulated very effectively. The wool is in good condition but was cut too narrow for the joists and will need replacing, which will give me plenty spare. I'm not sure if it is glass or rock, although I think I have a mixture of both types. Is there any preference in terms of material?

My gut feeling is that rock or glass wool would be more effective but less stable, being denser but more brittle- but that is certainly conjecture!

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The best material is rigid Type 700 fiberglass boards, but it's not easy to come by. Next best are open cell foam and polyester batts. Fiberglass blankets, as used in home insulation, doesn't work as well, and it fractures easily. I never use it. Rockwool works well.

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2 hours ago, Bill Fitzmaurice said:

The best material is rigid Type 700 fiberglass boards, but it's not easy to come by. Next best are open cell foam and polyester batts. Fiberglass blankets, as used in home insulation, doesn't work as well, and it fractures easily. I never use it. Rockwool works well.

Thanks Bill. I'm pretty sure I can tell the difference between glass and Rockwool by the look, but to be safe I think I'll have to be patient and wait until I have the polyester back in my hands! The insulation can always go towards broadband absorbers and bass traps.

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Posted (edited)

See if you can nick an old pillow from Mum. Just be sure it's not filled with feathers.

Edited by Bill Fitzmaurice

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Posted (edited)

Actually, I was eyeing up a polyester filled one just today, there might even be two in the cupboard I could pinch! The wife builds a strange little nest next to me to sleep in, and we've ended up with about ten pillows around the house. 😄

Do you leave the wadding in the case? Air does pass through it, but I wouldn't say it was completely resistance-free when I blew through it.

Edited by Jus Lukin

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You could leave it in the case, but then it's probably thicker than  you need. My wife also collected pillows, and bowls, and umbrellas, and more shoes than a centipede could make use of.

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Oh man, if unworn shoes had a good absorption coefficient I'd be laughing!

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Posted (edited)
9 hours ago, Dan Dare said:

Polyester toy stuffing worth a try? eBay has plenty.

I've got lots of options knocking about already- the poly is in a cab which is stored elsewhere (at my Mum's, funnily enough!). I just need to pop up and get it, but was being impatient, I suppose! No money needs spending for this particular job. 🙂

Edited by Jus Lukin

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22 hours ago, Bill Fitzmaurice said:

You could leave it in the case, but then it's probably thicker than  you need. My wife also collected pillows, and bowls, and umbrellas, and more shoes than a centipede could make use of.

Bill. Could I pick your brains, please? Is there a straightforward way to work out how much wadding a cab needs, or is it a case of suck it and see? Is it best to allow for the wadding when calculating cab volumes? Thanks.

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I finally got around to adding the wadding to this cab, two inches of poly wadding all round, but forgot to take any photos while I was at it.

I didn't do any testing or even an A/B, but it seems to be more detailed in the mid range and the tight low end response I associate (rightly or wrongly) with sealed cabs seems all the more so, and that's trying with an EB-0!

Regardless, for a budget item this thing looks and sounds great for a 'vintage' style cab.

Thanks for the help everyone.

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On 03/05/2020 at 15:24, Dan Dare said:

Bill. Could I pick your brains, please? Is there a straightforward way to work out how much wadding a cab needs, or is it a case of suck it and see? Is it best to allow for the wadding when calculating cab volumes? Thanks.

You can model the effect on the lows in WinISD 0.7 by changing the Qa value. The effect on the mids and highs is fully reached with only an inch or two. Damping does not occupy acoustic volume, so you don't compensate for it.

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