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Old 16th September 2010, 02:53 AM   #1
gmg733 is offline gmg733  United States
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Default Crossover Design Assistance Request

All,

Greetings! I am in need of some assistance to design a crossover for my 2-way project. I have MarkAudio Alpair 7 and Exodus Audio Anarchy 6.5 woofers. I want to design a minimalist crossover design based upon the following criteria:

Serial crossover design for 8 ohm impedance
Single order filters if applicable
Crossover frequency around 300-450hz

My enclosure is .75 cu ft. and houses the woofer and will be tuned to around 35Hz. The MA 7 enclosure is a sphere enclosure (about 10" in diameter) that is mounted to the top of the midwoofer enclosure (baffle width is 10").

I have toyed around with Speaker Workshop and find it a bit overwhelming for my skill set.

Info on the drivers can be found here:

Alpair 7 Driver | Markaudio

DIYCable.com : Intro Home Exodus Subwoofers

Any takers?

Thanks!
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Old 16th September 2010, 04:14 AM   #2
Fedess is offline Fedess  Argentina
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I think that even for the simplest 1st order cross-over you will need to do some measurements of the imedance (real impedance not nominal) of the woofer and tweeter... if you do not have enough tools for this task you can build the ARTA box which is very simple and you can do most (all) the measurements needed with the soundcard of your PC and an amp.

I have seen the Alpair 7 is 6ohm nominal impedance and I didn't found the woofer impedance in the link you posted, anyway I'll suggest you to measure them, because if you do not measure, the calculation of the capacitor and the coil won't match the desired frecquency cut...

How much power is your amplifier?? I find the freq. you want too low for the Alpair 7 with a 1st order filter... the link says it is "20 watts nom"... that should be something like 10 watts RMS.. (not sure).
Also a 6,5" mid-woofer shouldn't have any problem with higher freqs! So I find better going to at least 1500 or 2000Hz...
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Old 16th September 2010, 02:33 PM   #3
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Hi Gmg,
Interesting idea although I designed the Alpair 7 to run as a pure full-ranger.

Some points you need to consider:

1 - The Exodus Audio Anarchy 6.5 woofers have a rising response by some 6dB going from 2.5-kHz to around 5-kHz. You'll need to well suppress this part of the frequency output to give the Alp7 clear air. I'd suggest keeping the XO point below 1-kHz if your going 1st order. Your original idea of XO'ing around 450Hz is worth trying. The "Brit Telecoms" 400Hz/4-kHz (cross below or above but not in-between) XO guide is often worth considering if the drivers performance permits.

2 - The Alpair 7 is rated 4-Ohm (3.6 at the coil) not 6-Ohm. Given the differences in power-handling between these drivers, you'll need to add additional resistance into the feed to the Alpair 7, something around 4 to 6 Ohms maybe about right. This should balance to load on both circuits.

Cheers

Mark.

Last edited by markaudio; 16th September 2010 at 02:39 PM. Reason: additional info
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Old 16th September 2010, 09:02 PM   #4
gmg733 is offline gmg733  United States
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My reasoning for the x-over frequency was to keep it out of the voice range. I saw Occam Audio do this with an AP5 and Bob's woofer and thought what a great idea. However, I Occam did use a 2nd order filter.

I have a Class A amp capable of 100W per channel.

Thanks for the input. I'll check out your source Mark.
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Old 16th September 2010, 10:43 PM   #5
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Quote:
Originally Posted by gmg733 View Post
My reasoning for the x-over frequency was to keep it out of the voice range. I saw Occam Audio do this with an AP5 and Bob's woofer and thought what a great idea. However, I Occam did use a 2nd order filter.
I have a Class A amp capable of 100W per channel.
Thanks for the input. I'll check out your source Mark.
Glad to help. Yes, keeping the voice frequencies clean (400Hz to 4-kHz), free from XO has its merits. My worry for you is the rise in the woofs range. You might need a 2nd. order to suppress this part of its response.

I'd suggest experimentation, putting the XO in a small box outside the cabinet.

Your 100w class A is more than enough so please take extra care with the Vol. control. What's the make of the Amp? What source?

Cheers

Mark.
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Old 17th September 2010, 08:18 AM   #6
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Bell Labs defined our critical hearing bandwidth (nee midrange / telephone band) as 200Hz - 4KHz back in the 1920s - '30s. In an ideal world, you don't want an XO within an octave of either side of these limits & especially not within an octave either side of 2KHz, as this is the region where human hearing is at its most sensitive, as shown on a basic Fletcher-Munson or equal loudness curve. The XO frequency itself isn't the problem so much as the phase issues that can creep in to either side of it.

A reasonable compromise would be to cross at 500Hz, as this would ensure the midbass is handling the regions with the highest power / dynamic BW demands, while preserving most of the midband with the A7, so I'd say you're on the right lines. I'd want 4th order though. If you can go active rather than passive, so much the better.

Last edited by Scottmoose; 17th September 2010 at 08:20 AM.
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Old 17th September 2010, 05:47 PM   #7
chrisb is offline chrisb  Canada
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FWIW, the graph posted on Kevin's site for the Exodus woofer would indicate a nominal 8ohm rating

As for the Alpair 7 - having heard it in several different enclosure designs, its real world performance in the lower mid range/upper mid bass is such that I'd suggest experimenting with as low an XO point as you think you can get away with.
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Old 18th September 2010, 05:17 AM   #8
gmg733 is offline gmg733  United States
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Thanks all for the feedback. I do see the peak on the woofer. I made a computer speaker set of speakers and used one of these as the woofer. One word to describe it. Clean. I have it crossed over about 180Hz electronically.

I'll experiment with higher order filters to see what I can come up with.

The amp is a Gemstone and the receiver is a Marantz AV8003. All balanced inputs too.
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Old 18th September 2010, 08:06 AM   #9
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Quote:
Originally Posted by gmg733 View Post
I'll experiment with higher order filters to see what I can come up with.
The amp is a Gemstone and the receiver is a Marantz AV8003. All balanced inputs too.
The bulk of opinion suggests crossing low.

Interesting choice of amplification. Recently I've been playing the Alp10 and Alp6 Gen 2. prototypes on Accuphase DP67 CD and Accuphase 308 (100 watt a/b), then comparing with Tony's 300B and 6V6 tubes.

I tend to lean toward tubes with the Alp7 while Alp12 gets me going on the Accuphase. One of the local guys brought his vintage Sansui Mofset in recently, the Alp7's were silky sweet on this amp.

I still can't make my mind up on the amplification for the new Alp6's and Alp10's. To be fair, running Alp6 on solid state this size is total over-kill. I've already come close to blowing up a pair of the paper cones. So far, these drivers sound sweetest on tubes. Alp6 metal and Alp10 to my ears sound good on both solid and tube.

Either way, you've got loads of power so go easy on the Alp7. Best design a filter that can also balance the load.

I'm packing to leave for the assembly factory tomorrow.

Cheers

Mark.

Last edited by markaudio; 18th September 2010 at 08:13 AM. Reason: typo mending
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