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Old 18th June 2004, 04:25 AM   #1
Kittle is offline Kittle  United States
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Default Driver selection advice

Howdy all.

One nite I realized my mains were puting out more low end than my sub - so I set out on a project to replace it.

ive got an existing 3.0 cu/ft box that I can use for tests, and I recently got one of these NHT 1259 drivers, and a KG 5230 Plate amp from Madisound. Cramming everything into my existing box and some work with winISD's signal generator and a SPL meter gave me a Major spike at 65hz and a dropout at 40hz. Room gain issues? could be.

But that brings me to other questions.. It seems I dont have the right driver for what im after, as Ive seen several comments saying the NHT driver is NOT for a ported box, and after trying one for myself -- I agree.

My aims for the sub are as follows:
Used for both HT and music listening.
Powered by the above amp.
up 6-8 cu/ft box with flat response BELOW 20hz.
And im willing to pay for the proper driver.

So far the Scanspeak 23W/4557T00 driver meets these specs - but after a little fiddling with winISD I can see there will be big issues with port noise. (120ft/sec @ 20hz), then I look into a passive radiator, but nothing out there seems to have models or software on how to use one of these.

But also there are many many other drivers out there.

Suggestions & advice are much appreciated.
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Old 18th June 2004, 01:18 PM   #2
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The NHT is perfectly fine in a 3 cu ft box; tune it to 10 Hz. Trouble is in a 3 cu ft box that will take a 6 inch duct 244 inches long. Just seal the box and you'll get an F3 at 30 Hz, which should be quite adequate.

Your spike and null are both room derived and no driver or box can fix that. A spike at 65Hz indicates a boundary 8.6 feet away while a null at 40 Hz is from a boundary 7 feet away.
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Old 18th June 2004, 04:19 PM   #3
Kittle is offline Kittle  United States
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okay, thanks for confirming my suspicions on the room gain problems -- I'll find another way to deal with that.

244inch long port? Sounds like a canidate for a PR. The only (working) program ive found so far for a PR is WinISD, but the results and response graphs I get dont make sense to me. Mabye a link to PR theory and design issues would be the answer.
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Old 18th June 2004, 05:52 PM   #4
rabbitz is offline rabbitz  Australia
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I agree with Bill that sealed would be the best choice for NHT1259. If you want to go lower you can always use a Linkwitz transformer.

Like this: http://sound.westhost.com/project71.htm

A ported or PR with the driver is going to be more trouble than what it's worth IMO.
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Old 18th June 2004, 05:58 PM   #5
Kittle is offline Kittle  United States
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okay --- so any suggestions on other drivers? .. ie that Scanspeak ?

or.. what have others used that you like?
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Old 18th June 2004, 06:52 PM   #6
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by Kittle
okay, thanks for confirming my suspicions on the room gain problems -- I'll find another way to deal with that.

244inch long port? Sounds like a canidate for a PR. The only (working) program ive found so far for a PR is WinISD, but the results and response graphs I get dont make sense to me. Mabye a link to PR theory and design issues would be the answer.

You use a port the PR's diameter and consequent huge length.

You then convert the air mass to the PR mass, only goes
wrong if the PR's compliance comes into the equation.

http://www.diysubwoofers.org/prd/

sreten.
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