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Author Topic: Mentally Preparing myself - a few q's  (Read 2182 times)

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Offline Aural Robert

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Mentally Preparing myself - a few q's
« on: June 09, 2010, 02:19:11 PM »
Well, I've gone and bought some vintage speakers in raw form, and now I'm thinking about building the cabinets. I bought JBL D208s, some Altec Bolero horns and one (yes only 1) xo.

I've built cabinets from plans but never from scratch before, so I thought I'd start here with a few questions and maybe pick up a few pointers. I know there are a lot of other resources out there in www land, but I respect the opinion of you folks on THIS board. That's why I'm posting here.

I posted on here a while back and PJ recommended a cabinet size of 1.64 cu ft with a port size of 2.4" diameter in 3/4" thick material. I've been drawing up the plans and a couple of thoughts occurred to me.

If I want to "mass load" the base with sand, should I increase the overall volume correspondingly?

The drivers are rear mounted. Therefore the hole I cut for the driver on the front panel should have a radius on it and not a square edge, for diffraction reasons, right?

Cabinet "tuning". I know this is a function of port area / depth. What if I want to use a commercially available port with a flare on it? I've read that's a better way to port. Anyone know somewhere I can learn more about this? I'm port-illiterate.

And lastly, does the box volume have to be dead-on? Of course I'm thinking of building it a bit bigger and then I just add solid wood inside to reduce the size if need be.

I'm really looking forward to putting these together and hearing what they sound like. Be interesting to contrast them with my FE166E's - blh in the main system, and Sexy's in the WAF zone.

More questions to come I'm sure.

Aural Robert
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Origin Live Calypso TT w String Theory arm & Shure V15VxMR, Eros or BH DAC -> BeePre -> Paramount 2A3s w JJ's => Blumestein Bamboo Tritons on Blumenstein Bamboo stands, AND Enhanced SEX w Sexy spkrs and subs in the WAF zone. DIY Belden 89259 w Eichmann interconnects throughout

Offline ssssly

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Re: Mentally Preparing myself - a few q's
« Reply #1 on: June 09, 2010, 05:11:01 PM »
If I want to "mass load" the base with sand, should I increase the overall volume correspondingly?

Yes, you must increase internal cabinet to accommodate for anything that you put in there. Bracing, sound absorption material, sand, everything. When building speakers from scratch one of the most common things people do is forget to account for the volume of the speaker itself.

The drivers are rear mounted. Therefore the hole I cut for the driver on the front panel should have a radius on it and not a square edge, for diffraction reasons, right?

You can route the corner down a bit if you wish but it is not critical.

Cabinet "tuning". I know this is a function of port area / depth. What if I want to use a commercially available port with a flare on it? I've read that's a better way to port. Anyone know somewhere I can learn more about this? I'm port-illiterate.

Port lengths are calculated differently for straight ports and flared ports. So make sure if you decide to go with flared ports you recalculate the port size and length. I use flared ports, but honestly only because I find them easier to mount and secure. I have never noticed an appreciable difference in sound.

And lastly, does the box volume have to be dead-on? Of course I'm thinking of building it a bit bigger and then I just add solid wood inside to reduce the size if need be.

No the volume does not have to be "dead on". Of course you want it as close as possible though. And your plan is a good one. For sealed or ported designs I build .5 liter too big and then deaden with sand to bring the volume back down to specs. Then I experiment with polyfil, sand, and wood blocks to adjust the volume to get the sound to my liking.