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Old 5th December 2011, 19:59   #16
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Default Re: 8 Ohms Amp

Originally Posted by Sam Kapasi View Post
That would then be a sub-sonic filter. While I understand that technically, this too is a high-pass, it isn't what it is commonly referred to as HPF.

I was quick to misunderstand.

Yes there is a sub-sonic filter on the amplifier, effectively making the low pass into a band pass. But I'm rambling.
Thanks for clarifying. In car audio circles it is more often referred to as a subsonic filter from my readings.

Originally Posted by cranky View Post
Where you will have an issue with pro woofer is excursion capability.

OTOH, if you are not looking at puncturing some eardrums, what there is will be good enough. I see you are already reducing output below 40Hz, in which case the pro woofer should be sufficient. Car subwoofers are low sensitivity, high excursion, and high power handling (sometimes).

Of consequence is the higher sensitivity of pro woofers, which means you can get by with less power. A good choice which I was toying with once was the Eminence Lab12, very good performance even in small sealed box with gently reducing output down to 35Hz in cabin. With EQ, it was possible to get a clean enough output down to about 30, with usable power handling and still being reasonably sensitive after accounting for cabin gain.
Yes pro woofers usually have less excursion but in the intended pass band (60-150Hz) a driver is generally thermally limited rather than excursion limited, also as navin notes a pro woofer is often able to withstand some excursion beyond rated xmax. IMO there is no equal to a pro woofer above 30-40Hz, below that one needs high xmax low sensitivity drivers, this is assuming one is talking about traditional ported or sealed alignments.

Originally Posted by navin View Post
Just check the F3 and F10 you get in 2cu. ft. before you build the box. Remember in a car there is a road noise (tyres on road) in the 60-70Hz band so a pro woofer tht sounds nice at home might sound a tad weak in the car.

I never blew the 2245s. They was XOed to a floor standing MTM using Focal 8N515s and MDT. The system could be heard 250m away even if my windows were closed and the air con on. Each sub was powered by a bridged carver 1.5T the MTM was powered by a carver M1.0t and later by a 250W home brew amp (1200VA tranny, 60,000uf filters, and 6 Hitachi MOSFETS per channel). When my friends came over the first question was how much power (they were used to PMPO numbers in the thousands) so I say "30W". And they'd go "only 30W bah". Then I'd turn the system on and part their hair and re-arrange their brains

When my wife came we had to reduce the size of the system. Out went the 2245s and MTM and 1.5Ts. The M1.0t was used to power a pair of subs each using 2 ACI DV12s and new MTMs were built using the ScanSpeak 8546-9900. Still the system could max out my RAT-Shack SPL meter.

Now we are working on a more WAFed system but that is a long story.

The pass through would be considered an "All pass" na?

Ramble on, now's the time, the time is now, to sing your song
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and blessin' our ears, we'll 'drink' a thousand times, so Ramble on.

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This is something I was going to suggest. Given that 1420 was going to stuff the woofer in a small box he could use a bit of EQ like a Linkwitz ransform described below. Pro woofers have nice stuff surrounds and hence are better protected against damage from over-excursion so applying a bit of bass boost to them is safe.

Active Filters
I did check the frequency response and it is one of the primary reasons I am still debating a ported enclosure. The driver is intended for a ported enclosure and should perform very well in the right cab if all the listed specifications hold true. By the way at approximately what frequency will the cabin gain start in a Honda City? And is it about 12db/oct gain? Is there any link which shows the mentioned 60-70Hz tyre noise? It would be interesting to see any measurements of it.

I am sure the 2245s in the B460s were something special, I wish I could have a listen. You were hitting 126db peaks? or continuous on the Rat Shack meter? I assume C weighted and set to slow.

Appreciate all the responses everyone, thanks.
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Old 7th December 2011, 17:13   #17
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Default Re: 8 Ohms Amp

Originally Posted by 1420 View Post
Is there any link which shows the mentioned 60-70Hz tyre noise?
No my findings are emperical. The range is more like 60-150Hz but most sedans are in the lower end of that range.

Tire/road noise may have significant acoustic contribution at low frequencies, and especially around 200 Hz, where tire acoustic cavity modes are present. Since the tire/road noise is generally transmitted only through structural paths (tire-to-wheel-to-tie-rod-to-suspension-tobody) for frequencies up to 200 Hz
taken from this link
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