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Old 1st March 2006, 09:48 AM   #1
rabw is offline rabw  United Kingdom
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Default Inductance + Subwoofers

Hi everyone,

I need to build a sub (although it will have to work up to around 200Hz) to partner a front horn.

I was wondering if anyone could answer some of the questions I have about 'fast' bass. I've read the PDF by Adire Audio on inductance and subwoofer drivers, so I guess I should be looking for a driver with low inductance. I dont care about movies, this thing has to be able to do music.

I picked this up from another thread - the Audio Atlas 15 has a low inductance of 0.86mH - unfortunately I've never seen this driver and doubt its availible over here in the UK or EU. I was looking at an Adire Tempest 15D8, it has an inductance of 3mH per voice coil - this looks high, but would I be right in thinking that when both coils are wired in parallel the inductance would be just 1.5mH, which doesnt seem so bad.

Also the Tempest 15D4 has an inductance of 1.9mH per voice coil, so I assume that gives you an inductance of under 1mH with both coils in parallel (unfortunately I think this driver will kill my plate amp when wired in parallel).

I was looking at 15" PA drivers as these are reported to be fast and dynamic (well they play high anyway) but to my suprise the inductance of a Kappa Pro 15 LF for example is over 1mH, not much or any better than the previously mentioned subwoofer drivers appear (and doesnt go low in a sealed box either).

One last question - I've heard of people complaining about the Adire Shiva rolling off at higher frequancies because of its high inductance. Do you think this will be a problem for me with my target upper rolloff?

Cheers, Richard.
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Old 1st March 2006, 01:28 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

regarding "fast" bass I'd ignore any article that grossly simplifies the issue.

You need a good bass driver, good to ~ 400Hz, not a subwoofer driver.

Presumably your going to have an active crossover ?

And much more bass amplifier power than horn amplifier power ?

If not your also going to need a high sensitivity driver.
Which will effectively preclude sealed box loading,
you'll need reflex for decent bass extension.

With a horn midrange/treble the most important capability for
the bass driver you should be looking at is low distortion.
As ever the bigger the driver usually the better.

/sreten.
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Old 1st March 2006, 01:36 PM   #3
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Agree with all of sreten's comments.

'Fast' bass comes from more that just inductance, it the synergy of a load of factors.

Seems to me to be a bit bonkers trying to partner a box-loaded bass bin to a midrange horn. Bass is what eats watts and is where you need to concentrate on efficiency.

Are you wanting a PA or home application?
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Old 1st March 2006, 01:47 PM   #4
rabw is offline rabw  United Kingdom
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Hi,

Sorry I failed to mention that it is active, I will be using this plate amp - link Which I have had modified so the filter is variable between 40-240Hz.

Quote:
Are you wanting a PA or home application?
This is for home use.

I was previously going to use the Eminence Magnum 15LF as it seemed to fit my requirements perfectly however they decided to discontinue it in the EU, and to get it from the US would mean 33% tax ontop. So if anyone knows where i can get this over here, please let me know!

Here's a link to a rendering I did last week of how I hope my project to turn out - link

Thanks for the replys, Richard.
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Old 1st March 2006, 02:36 PM   #5
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I see, interesting concept. I think there is another Loughborough student designing a speaker system on here, Matt somebody.

I assume the system is more for music than films? Just curious why you are going for horn mids. Also if you can give us a target low cutoff and box size it might be that there are other drivers that are suitable or even better than PA ones.
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Old 1st March 2006, 02:51 PM   #6
rabw is offline rabw  United Kingdom
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Hi, yes you're right, my friend Matt is also designing a speaker for his final year project

Yes this system is also intended more for music. The Horn has a cutoff of 150Hz, with decent output from about 204Hz (predicted). I have GRP'd one horn so far and given it a try and the 200Hz prediction seems about right.

I went for horn mids as I've experimented with the Fostex FE206e in a backhorn and liked the sound (after driver tweaks). Reviews of oris horns etc seem to indicate more of the same so I thought it'd be interesting and different (my lecturers certainly seem to think its different) to try out.

Once the driver I've brought to uni with me had warmed up the 1 front horn sounded very very promising, voices very much more real than I have experienced before, so I'm pleased and want to make sure I do a decent job of the bass unit.

I know I should've sorted it out months ago, but I thought I had with the Magnum 15LF, and have been messed around since october by a shop in London that had 'the only pair in the UK' - long story. Now it looks like these drivers are out of the window, so I really really need to find something else soon.

I have around 120-130L to play with and about 400UKP ~ $701.46 for a pair of bass drivers.
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Old 1st March 2006, 03:04 PM   #7
sumit is offline sumit  India
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Default woofer inductance

Try peerless xls serise. Or better try some woofers rather than subwoofers. Decent woofers (10*2 or 12*1) can reach 30Hz easily.
Every manufacturer has some point to show off. Fast bass in case of subwoofers is basically meaning less. There is no fast bass. Actually its the matching of the woofer with the midrange which creates the sensation of fast bass or transients. The better the match the faster the bass it appears. Lower L helps but xbl tech. does not come cheap.

For a 4ohm woofer with 1mH inductance the impedance(Z) at 200Hz is about 5.256.
Z=R+2*3.1428*f*L if i can remember correctly.

Roughly speaking a 4ohm woofer would become 5.256ohm at 200hz.

Shiva has about 4.2mH per coil, and would cause some trouble at 200hz. But after all its a LCSG sub woofer.
Yes parall. coils reduces inductance by half.
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Old 1st March 2006, 03:11 PM   #8
rabw is offline rabw  United Kingdom
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Hi, thanks very much for the reply. I agree a woofer would be more suited than a subwoofer.

I've asked one of the moderators to remove the other copy of this thread, hopefully they can do that...

Sorry for the confusion, Richard.
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Old 1st March 2006, 03:22 PM   #9
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Old 1st March 2006, 03:25 PM   #10
rabw is offline rabw  United Kingdom
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Thanks very much.
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