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Old 23rd June 2012, 02:59 PM   #11
tvrgeek is offline tvrgeek  United States
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Quote:
Originally Posted by samadhi View Post
I thought the acoustic slope was what counted? Third order acoustic is third order crossover regardless of the components used to get there, no?
No. Not for power, distortion, or staying away from resonance and breakup modes. You have to meet all of these requirements.

I was just testing my most recent set. It uses second order electric in combination with the natural roll offs for effective 4th order at only 1700. (modification to the Zaph SR-71). At my listening levels, it works. I would not push it really hard though.
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Old 23rd June 2012, 04:54 PM   #12
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Originally Posted by theaudiophile View Post
hi,

Often its said that 1st order crossovers do not provide sufficient protection especially for the tweeter. I have read that signals down to 100hz get through at almost full power. That sounds pretty tough for a tweeter to cope with. How do you make a design like that work? I have seen that B&W used 1st order slopes on a number of their models, how do their metal dome nautilus tweeters cope with all that energy?
A lot depends on how loud your 'normal' playing will be. I used 1st order elect on the design at the link below:

Introducing the "INTIMATES" (high WAF & quality sound)
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Old 1st August 2013, 12:42 PM   #13
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with the Dayton DC28 and RS28, what are the lowest recommended 1st order x/o points? with the impedance rise from around 1khz to fs, do u have to cross higher to compensate for a rise in output?
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Old 1st August 2013, 03:06 PM   #14
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Originally Posted by norman bates View Post
well, usually the tweeter impedance shoots really high at its resonance, the resistance is so high there that instead of the tweeter rolling off 6db at say 3khz, it goes fairly flat down to say 1.5khz. Then you get carried away with the volume, then oops, why is the tweeter goings schhh, schhhhh on voices ?

And yes, A lot of power gets through a 6db filter. A driver moves 4 times farther as you drop an octave, even a tweeter. And you tend to get more and more power the lower you go in music on the freq spectrum. I think a 6db filter barely counteracts this.

You can build a rugged tweeter with a low resonance. I think rule of thumb is to cross 2-3 octaves above its resonance (for a 6db).

I've been wanting to play with 6db tweets (then you can get time aligned) but havn't yet.

Norman
When companies like Dynaudio and Thiel use first order slopes, they use a network to flatten out the impedance curve. If they didn't do this, the *acoustic* slope would not be first order, due to the problem you describe. Due to all these components, the crossovers are actually quite complex and expensive, despite only having one cap in series with the tweeter. (IE the impedance compensation network is more costly and expensive than everything else.)

I know that Danley uses phase coherent crossovers in the Synergy horn, and he's discussed how they work, but I've never figured it out. As I understand it, the Danley xover is phase coherent but it's NOT first order. These days I'm leaning towards MiniDSP as it's so cheap and so simple to use.

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Old 1st August 2013, 06:33 PM   #15
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I may be mistaken, but I think the deal with Danely's horns is simply like this:
1. Take a few drivers, and make a system with filters that result in the usual 180 or 360 degree phase difference between drivers (assuming they are time-aligned to start with).
2. Offset them in space to bring the phase difference back to 0.
3. Now everything's fixed, but wait, now nothing works right off-axis because your offsets don't stay constant when you move! Enter the synergy horn.

Last edited by dumptruck; 1st August 2013 at 06:35 PM.
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Old 1st August 2013, 06:38 PM   #16
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Originally Posted by dumptruck View Post
I may be mistaken, but I think the deal with Danely's horns is simply like this:
1. Take a few drivers, and make a system with filters that result in the usual 180 or 360 degree phase difference between drivers.
2. Offset them in space to bring the phase difference back to 0.
3. Now everything's fixed, but wait, now nothing works right off-axis because your offsets don't stay constant when you move! Enter the synergy horn.
If I'm not mistaken, Bill Waslo and Jason Winslow have a grasp on how the crossovers work in the Synergy horn. They've posted some things that detail how the filters work, but it's over my head. I understand horns quite well, but phase is something that I'm slooooowly learning.

It's definitely an important part of the sound; I've always noticed that Dynaudio and Thiel speakers have a type of imaging and articulation that sounds different than typical speakers with high order crossovers.
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Old 2nd August 2013, 08:18 AM   #17
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I always use 1st order slopes on my tweeters. You need decent quality tweeters, preferably underhung with good Xmax but generally it's no drama if you deal with the impedance resonance.

Typical average power is <1W for most listening.
Power is not much of an issue. Say you have 1st order at 4kHz and feed it 2.83V RMS at various frequencies:

4 kHz : -3dB => 0.5W
2kHz : -6 dB => 0.25W
1 kHz : -12dB => 0.06W
500Hz : -18dB => .015W

Nowhere close to frying a tweeter especially since the majority of music energy is below 500Hz.

As for excursion, a decent 25mm with first order at 4kHz will stay within it's linear range below 100W. The other drivers in the system will be distorting before the tweeter does.

Here's my 4way system's displacement limited power handling. The tweeter is the Seas Magnum (T29MF)

Click the image to open in full size.

Last edited by David Gatti; 2nd August 2013 at 08:23 AM.
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Old 2nd August 2013, 12:17 PM   #18
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Hi David, at 4khz are you just using a single cap or still needing to add components to flatten the impedance?
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Old 2nd August 2013, 01:56 PM   #19
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The impedance needs to be flattened or you won't have a true 6dB rolloff.
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Old 2nd August 2013, 02:47 PM   #20
Jsixis is offline Jsixis  United States
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when I started building speakers I use to use the capacitor at the crossover frequency 4.7uf and I lost a lot of tweeters.
Then when I was taking consoles apart I noticed that 90% of every tweeter had caps in the 2uf range.
I started using 2uf's and I quit burning out tweeters and as a plus I normally did not need a resistor to drop the volume.
I am also a fan of adding light bulbs in series to protect the tweeters. Some claim they can hear that but I doubt it.
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