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Old 12th July 2005, 03:37 PM   #1
bigwill is offline bigwill  United Kingdom
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Default TL freq response

Ok, so I've got a driver, and I've looked at Martin King's TL alignment tables. It's a cheapo driver, and I don't know all its parameters. The ones I do know:

Sensitivity: 90dB

Qts: 0.27

Vas: 4.20

Fs: 26

I know these parameters are limited, but that's what I get for buying cheapy 18 woofers.

The geometry of the line I've chosen, according to the alignment tables yeilds a tuning of about 25Hz

Sl/So: 0.333
Line length: 106.8 inches

The problem is I don't know what the response will be like, and according to the document it says that drivers with a lowish Qts will have a peaky responce in a TL and the remedy is to tune it 5-10Hz higher. Is it worth doing this, and if so, will I lose any low end response? OR, is it worth keeping the tuning to the Fs of my driver?

Thanks for reading
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Old 13th July 2005, 02:35 AM   #2
GM is offline GM  United States
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Greets!

For my records, what make/model driver is this? Listed on a website? Overall diameter, any other details?

Yes, without some series resistance to 'fill' the cab/flatten out the response (lowering efficiency as the trade-off) it will indeed be 'peaky', with no real LF output.

With this low a Qts, it's basically a midbass driver if no series resistance is used, so tuning it up around 3*Fs would be 'best' and forget getting any real LF out of it. If lowered efficiency is OK, then design based on whatever Qp you want, such as 0.5, and add series R as required once built to flatten it in-room.

GM
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Old 13th July 2005, 11:46 AM   #3
bigwill is offline bigwill  United Kingdom
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It's an MCM driver, model 55-1480. It's a 10" driver and marketed as a woofer
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Old 13th July 2005, 12:11 PM   #4
bigwill is offline bigwill  United Kingdom
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I might try these woofers in a wicked one enclosure
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Old 13th July 2005, 01:41 PM   #5
GM is offline GM  United States
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Greets!

Historically, house brand MCM published specs are for whatever reason completely bogus, so without measuring them there's no telling what an optimum cab would be, so what most folks use to do back before measuring drivers became 'de riguer' was to put them in the largest acceptable box and tune them somewhere around 40 Hz since back then there were few tapes/records with content below it, using some form of EQ to balance out the response if too bass shy (overdamped) or 'boomy' (underdamped) in -room. Hardly optimum, yet they always got the job done.

GM
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Old 13th July 2005, 02:07 PM   #6
bigwill is offline bigwill  United Kingdom
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Why must it be so hard to get decent cheap woofers in the UK!
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Old 13th July 2005, 07:02 PM   #7
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Quote:
Originally posted by bigwill
Why must it be so hard to get decent cheap woofers in the UK!
Decent and cheap are almost mutually exclusive terms here in the UK. Its like saying 'fresh breath' and 'coffee drinker'

Generally it pays to spend a little more than 18 but it doesn't have to be silly money. There are some good woofers around the 40-50 price mark here in the UK.
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