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Sub bass & bass Speakers with 18" Volt RV4564 drivers


MF 1000
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Interesting the comments here on secondary vibration of the baffle.  My speakers have a concrete baffle to overcome this issue. Details here

https://sites.google.com/site/matteisloudspeakers/home

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I agree with the principle/idea Dave …hence my heavily braced 51mm thick mdf/balau (vv dense hardwood) sandwich construction on the cabinets

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4 hours ago, MF 1000 said:

I agree with the principle/idea Dave …hence my heavily braced 51mm thick mdf/balau (vv dense hardwood) sandwich construction on the cabinets

That makes sense; making a bass cabinet "hard" moves the resonant frequencies above its operating range.

Edited by tuga
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Quite a few years ago I recall reading an article about speaker panel vibration/flexure which discussed the idea that even a tiny movement in any of the panels when stead across the area of the panel was equivalent to the more significant displacement in the speaker driver over an obviously smaller area.  This I guess is what we refer to a colouration in a speaker.

As far as my bass units are concerned it’s amazing that even with a 100 mm port the 18” driver creates quite a pressure inside it and forces air through any small gaps in the inner carcass and the cladding…..so if the cabinet wasn’t braced and of a thick sidewall etc  I’m sure I’d have far more vibration occurring.  Just writing this has got me thinking and I might now feed a pipe through the port length and set up a basic manometer to gauge the internal pressure created.

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2 minutes ago, MF 1000 said:

Just writing this has got me thinking and I might now feed a pipe through the port length and set up a basic manometer to gauge the internal pressure created.

A manonmeter will just show atmospheric pressure I think, due to averaging out the rapidly fluctuating pressure of the acoustic waves. Using your microphone would be the better way to go if you were really curious.

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One of the most hardcore money no object approaches to cabinet design I’ve seen so far is that of Rockport:

images?q=tbn:ANd9GcRCxQaduyMkQCxVTuYPYn-

Edited by tuga
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32 minutes ago, MartinC said:

A manonmeter will just show atmospheric pressure I think, due to averaging out the rapidly fluctuating pressure of the acoustic waves. Using your microphone would be the better way to go if you were really curious.

Absolutely - it won't give you any useful info. A mic is the way to go.

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With a 25Hz tone through the driver I can feel air escaping through a couple of panel gaps ….these will be filled/sealed as I now have time before March 22.  

I wasn’t suggesting that a pressure test could replace any other testing …..it was just out of my image curiosity to see how much pressure was created inside the cabinet to generate the air escaping from orifices other than the port - this has to be created by a pressure differential and they must have detrimental effect.

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26 minutes ago, tuga said:

One of the most hardcore money no object approaches to cabinet design I’ve seen so far is that of Rockport:

images?q=tbn:ANd9GcRCxQaduyMkQCxVTuYPYn-

Interesting. And a bargain at only $169,500 a pair for the Lyras :shock:.

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1 minute ago, MartinC said:

Interesting. And a bargain at only $169,500 a pair for the Lyras :shock:.

£200k in GB... :D

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3 minutes ago, MF 1000 said:

With a 25Hz tone through the driver I can feel air escaping through a couple of panel gaps ….these will be filled/sealed as I now have time before March 22.  

I wasn’t suggesting that a pressure test could replace any other testing …..it was just out of my image curiosity to see how much pressure was created inside the cabinet to generate the air escaping from orifices other than the port - they must have detrimental effect.

I was suggesting using a microphone to measure the pressure inside the speaker cabinet, by actually putting it inside the speaker. Although you might find the pressure levels exceed the maximum the micophone can be used for.

Edited by MartinC
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1 minute ago, MartinC said:

With a 25Hz tone through the driver I can feel air escaping through a couple of panel gaps ….

Oh, and at the risk of pointing out the obvious, be very cautious about playing about with tones at this sort of frequency as it's a good way to burn out a driver if you're not careful. 

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2 minutes ago, MartinC said:

I had a quick look but couldn't find anyone selling them!

Are these guys in your vicinity?

https://audiolounge.co.uk/brand/rockport-technologies/

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Julian - Bigrod gave me some great advice on finishes for the yellow balau, using tung oil so this weekend I decided to start on the hopefully final surface finish.  As you may recall it’s a tropical hardwood vv dense (30% more than Russian birch ply) with a very tight grain structure.

Trying to produce each panel from 140mm planks with biscuit joints etc was a challenge and the wood has ‘moved’/ cupped so I found a vintage Wolf belt sander off eBay than had the grunt to attack this wood.  
 

Two hours of sanding with 80 and 120 grit belts gave me a good flat surface and then as recommended by Julian, I hand sanded it down to 400 grit then a tack rag (to remove all the dust), wipe down with white spirit, then using a lint free cloth applied a 50/50 mix of pure tung oil & white spirit.

Wow the grain really stands out now …but this morning I flatted it off again and applied a 75/25 mix.  I’ll let this harden off for two weeks (mainly as I’m away with work next weekend) then it’s two more coats of 100% pure tung oil.

8BCBB19A-AA85-42F2-BDB9-E6FBDB64C5D2.jpeg.3cc9c5d63c2c57766e82dd499ab37a26.jpeg

AC1CC12D-5587-45A3-8EBD-E7A340D64101.jpeg.870a96a625e5f6792f9a8735da086952.jpeg

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