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Old 4th June 2008, 07:49 AM   #1
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Default Gauges for inductor components in 2-way speaker with impedance correction

I have designed the following 2-way crossover for a woofer+mid bass guitar cab:

Series Inductor on Woofer: 1.9mH (2nd order Butterworth)
Parallel Cap on Woofer: 22uF

Series Cap on Midrange: 22uF (2nd order Butterworth)
Parallel Inductor on Mid: 2mH

Series RC Parallel to Midrange: 10uF and 8.2ohms (Zobel)
Series RL Parallel to Midrange: 0.6mH and 3.3ohms (Resonance peak correction)

I expect the speaker to be used with amps up to 1000W though that kind of power is very unlikely to be sustained due to the dynamic nature of bass guitar and live music. Maybe the cab will see 50-100W average with peaks up to 1000W+.

I'm intending to use a 15 gauge P-core plus discs inductor in series with the woofer but I'm don't know how low a gauge I can safely use on the two shunt inductors on the midrange. Any answers?

Thanks,

Alex
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Old 5th June 2008, 02:06 PM   #2
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Anyone?

Thanks!

Alex
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Old 5th June 2008, 02:35 PM   #3
pjpoes is offline pjpoes  United States
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For that kind of power you will want to stay with 15-12 guage. I would stay away from standard iron core because of core saturation, but would consider something like a pcore, Erse Super Q, or the C-core toroidal inductors. All of which will not saturate as easily and can handle considerable power. None are rated for 1000 watts, but as you say, the speakers will likely never see 1000 watts sustained, so it isn't a big issue. I would mount the crossovers externally though, as it will make repairs quicker in the event that an inductor does get fried. It also allows air to circulate around the components better.
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Old 5th June 2008, 04:44 PM   #4
sreten is offline sreten  United Kingdom
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Hi,

All those parallel components on the midrange do sound like a good
idea, especially the RL with R=3.3R. The Zobel on the midrange is
not needed, whilst omitting it for the bass unit means the "textbook"
2nd order c/o function will not be accurate for it.


There is a lot to be said for a simple 1st order series crossover
with just 2 components for this application - as it is resilient
to driver impedance variation, cheap and does not waste power.

Values for 1khz / 8ohm are 1.3mH and 20uF.


/sreten.
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Old 9th June 2008, 11:38 AM   #5
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Quote:
Originally posted by sreten
There is a lot to be said for a simple 1st order series crossover
with just 2 components for this application - as it is resilient
to driver impedance variation, cheap and does not waste power.

Values for 1khz / 8ohm are 1.3mH and 20uF.
Thanks, that's very interesting. Have done some experimenting with this and it seems to work rather well in theory...

Is there anything in particular I should be aware of with such a 1st order series design?

Alex
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Old 9th June 2008, 11:47 AM   #6
sreten is offline sreten  United Kingdom
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Hi,

It depends on the intended c/o point and the details of the two drivers.

/sreten.
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Old 9th June 2008, 01:01 PM   #7
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Quote:
Originally posted by sreten
Hi,

It depends on the intended c/o point and the details of the two drivers.

/sreten.
The drivers in question are the Eminence 3015LF 15" woofer and the Beyma 605Nd 6.5" midrange. The crossover point needs to be high enough for the midrange to be safe from overexcursion/overpowering but low enough for the off-axis respons to be relatively smooth. With a 24dB active filter you can cross as low as 500Hz without problems but with a shallower slope ~1kHz seems wiser.

Alex
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Old 9th June 2008, 04:56 PM   #8
sreten is offline sreten  United Kingdom
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Hi,

With ~ 6dB slopes the midrange will still increase in excursion until
it hits its its bass roll-off, in other words it should be tuned to a Qts
of at least 0.7, or possibly somewhat higher, up to 0.95 (1dB ripple)
to maximise the frequency where excursion will begin decreasing.

I'm not sure what the best arrangement is for those two drivers,
or that they are a particulary good combination, the Eminence
has issues around 1.5 kHz that sort of implies it will mess up
the midrange of a separate unit if a simple c/o is used.

The Deltalite for example looks easier to crossover.

/sreten.
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Old 9th June 2008, 07:15 PM   #9
badman is offline badman  United States
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Quote:
Originally posted by alexclaber


The drivers in question are the Eminence 3015LF 15" woofer and the Beyma 605Nd 6.5" midrange. The crossover point needs to be high enough for the midrange to be safe from overexcursion/overpowering but low enough for the off-axis respons to be relatively smooth. With a 24dB active filter you can cross as low as 500Hz without problems but with a shallower slope ~1kHz seems wiser.

Alex

Jeeze man! That's a heck of a high crossover point for a 6.5", high efficiency prostyle or not. The 15" will be well into breakup at 1kHz, and will have beaming and off axis lobing like crazy. Even the .5mm Xmax Audax PR17OMO has recommended XO to a midbass transducer at around 500 (or lower) with a 12dB slope.

Headroom is a lovely thing to have, but I think you're taking the power handling requirements very extremely.
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Old 10th June 2008, 07:24 AM   #10
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Quote:
Originally posted by sreten
Hi,

With ~ 6dB slopes the midrange will still increase in excursion until
it hits its its bass roll-off, in other words it should be tuned to a Qts
of at least 0.7, or possibly somewhat higher, up to 0.95 (1dB ripple)
to maximise the frequency where excursion will begin decreasing.
Good point. I've reduced the midrange enclosure size to raise the Qts and raise the bass roll-off which gives usefully more output higher up too.

Quote:
Originally posted by sreten
I'm not sure what the best arrangement is for those two drivers,
or that they are a particulary good combination, the Eminence
has issues around 1.5 kHz that sort of implies it will mess up
the midrange of a separate unit if a simple c/o is used.

The Deltalite for example looks easier to crossover.
Right, I'll make sure the output is reduced more before the break-up peak. The 3015LF is outstanding when it comes to moving air - huge Vd, which means it can keep up with a whole array of generic 10" bass guitar woofers, so it's worth having to deal with crossover challenges.

Quote:
Originally posted by badman
Jeeze man! That's a heck of a high crossover point for a 6.5", high efficiency prostyle or not. The 15" will be well into breakup at 1kHz, and will have beaming and off axis lobing like crazy. Even the .5mm Xmax Audax PR17OMO has recommended XO to a midbass transducer at around 500 (or lower) with a 12dB slope.

Headroom is a lovely thing to have, but I think you're taking the power handling requirements very extremely.
Ok, thanks, advice taken on board!

I'm now experimenting with a conventional 2nd order crossover with full impedance correction. Due to the output of the midrange diminishing as it goes lower it seems very difficult to get the woofer/mid output to acoustically cross lower than 1kHz even though for this version of the crossover I have the woofer lowpass at ~800Hz and the mid highpass at ~500Hz.

Alex
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