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Old 19th February 2004, 03:39 AM   #1
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Question Clonus Faber Crossover

Hello all, I hate to burden with just a simple crossover question, but I will admit to my utter ignorance in the art of good crossover design. My plan is the following:
I like very much the looks and sound of the Sonus Faber Concerto stand mouted speaker, its a relatively simple looking 2 way using what appears to be a modified Vifa Xt woofer and some Scan Speak or Vifa Soft dome. I have decided that rather than plopping down 2K on a set, I would try my hand at building something that may outperform them and keep the asthetics that I find very appealing. The cabinet will be an almost exact clone, with some added size to accomidate the bump up to 16L internal volume. I would like to use the Scan Speak 8545K00 for the mid/woofer in place of the Vifa, and the Scan Speak 9700 in place of the tweeter that the Sonus uses. It is my hope that the better drivers will help to bring a higher degree of accuracy to the table than the original. Sonus has a very engaging sound, but it needs some work tonally in my humble... As both seem to hold quite a degree of regard, and look good on paper, I have confidence they will serve me well in this purpose.
I've run some preliminary simulations in Winisd and settled on a 16L cabinet tuned to 33Hz, the roll-off seems to be well suited for room gain and group delays and etc. are well within the acceptable limits. Any input on the cabinet size or tuning would be appreciated as well.
The crossover is where I run into the problem. I would like to run an even order network to minimize phase problems. I am unsure though in the ability of a 12db slope to alleviate the nasty peak at around 3K that the woofer has. But, on the other hand, I am concerned that a 24db slope will be too steep and will sound somehow unnatural in the end. I would like to keep the crossover point at 2K or lower to mimize beaming and to move away from the peak the woofer shows up higher.
Any and all help or input or fresh ideas would be greatly appreciated. If any more info is needed, please feel free to ask as this project is just in the first planning stages.
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Old 19th February 2004, 10:49 PM   #2
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Well, I hoped somebody would have at least something to say. I've been searching through many different crossover tutorial pages but I still am about as clear as mud on what I need in this project. I've seen second order on the woofer fourth on the tweeter, second order on both, fourth on both, all possiblities, but I don't understand how to make that decision. Please guys, anything would help.

Another thing I don't get is the L-pad attenuation and how it ineracts with the crossover design. Do I need to adjust the values I plug into the calculator to accomidate the 2db's of attenuation I need on the tweeter or is that a seperate circuit?
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Old 19th February 2004, 11:24 PM   #3
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I've used 24db/octave slopes (that's 24 dB/octave acoustic, not electrical!) for my last 4 or 5 projects, after spending many years before that trying to overcome the disadvantages of 6dB/octave xovers. IMO, it's one of the best ways to go for power handling, insensitivity to driver offsets, and low distortion. It seems to give better polar patterns as well. The downside is that you don't get nice-looking square waves.

The keys are understanding the difference between acoustic and electric slopes and going into battle with the right weapons- frequency response and impedance measurement capability and software that lets you model crossovers with the experimental data you get from the drivers.
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Old 20th February 2004, 03:39 AM   #4
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Thats my problem SY, my slopes will be practically entirely electrical as the response of the 8545 hit a rise at 3200 and the inductance limit at a little over 4K from the looks of the graph, 4K is a full octave above the crossover point of 2k +/-. The tweeter doesn't begin rolling off until down in the 500-600hz region. My real concern is the peak at 3200 from the woofer, how can I keep that from making my speaker sound nasal or too forward? I was thinking 4th order on the woofer and 2nd order on the tweeter. From my understanding of phase relationships, this should put me 180 out of phase allowing me to just reverse the polarity of one of the drivers and I am back at 0. Is this correct?

Does anyone have any recommendations for alternate crossover points or slopes that may yield a better result? My emphasis here is mainly on good horizontal dispersion as imaging and depth are really what I'm looking for in this project. I can live with a little bit of compromise on the frequency response as long as the speaker is engaging in the soundstage.
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Old 20th February 2004, 02:48 PM   #5
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Quote:
Originally posted by Seth Smith

Does anyone have any recommendations for alternate crossover points or slopes that may yield a better result? My emphasis here is mainly on good horizontal dispersion as imaging and depth are really what I'm looking for in this project. I can live with a little bit of compromise on the frequency response as long as the speaker is engaging in the soundstage.
I was wondering if you have any measurement equipment, and the ability to export those measurements to a crossover design program? If you don't then all of your planning regarding phase and slopes of the crossover point may be wasted. Any formula derived crossover will have errors from the ideal due to baffle diffraction, driver response variations, etc.

I think your driver choice is excellent, but I wouldn't be so quick to rule out the Vifa XT series woofers as serious contendors. They are quite linear, do very well on IMD tests and have a great sound. I like them a lot! Both the XT wood pulp and the Scan Speak woofers have cone breakup modes in the 3K-5K region so crossovers often need a little extra attention by ear.

Scott Hinson
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Old 20th February 2004, 04:39 PM   #6
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I don't have any measurement soft or hardware as I'm completely new to the serious DIY hobby. I would like this to be a one time project, so, an investment of 300+ dollars in computational aid for one pair of speakers is a bit much I think. What is the least I can get by with? I figure $70.00 for a mic, and another $70 for software at the bare minimum. Is this about accurate?

The XT isn't a bad driver and is in fact my second choice if the Scan Speak's large 3K peak can't be dealt with. It trades a bit of off axis dispersion for its smoothness though and I am concerned this may collapse the soundfield. Any thoughts on that possiblity?
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Old 20th February 2004, 06:17 PM   #7
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There are a lot of issues here. Not the least of which is your use of a terms "serious" and "one time". SoundEasy can be had for $225, a mic can be built for about $5, a mic preamp is around $50. Or you can go with Speaker Workshop and save the cost of SoundEasy.

Puting a cap and an inductor on a driver does not result in a 2nd order crossover in most all cases. It's the total electrical and acoustic slope that determines the order.


Russ
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Old 20th February 2004, 07:01 PM   #8
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Quote:
Originally posted by russbryant
There are a lot of issues here. Not the least of which is your use of a terms "serious" and "one time". SoundEasy can be had for $225, a mic can be built for about $5, a mic preamp is around $50. Or you can go with Speaker Workshop and save the cost of SoundEasy.

Puting a cap and an inductor on a driver does not result in a 2nd order crossover in most all cases. It's the total electrical and acoustic slope that determines the order.


Russ
I totally agree. If you think about the amount of money you're planning on spending on the drivers you've selected, and the amount of time you'll invest a SoundEasy puchase may be the way to go. It's not an easy program to learn (at least last time I used it it was't...I haven't upgraded in a while so I don't know what it's like right now.) but it will do the job.


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Old 20th February 2004, 10:03 PM   #9
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Quote:
Originally posted by russbryant
There are a lot of issues here. Not the least of which is your use of a terms "serious" and "one time". Russ
Not exactly sure what that was supposed to mean

Considering the Sonus Concerto can be had new for 1400, the project's cost is already at roughly 1100 in materials alone. The addition of another 300-350 for software puts me dead even in dollars spent and my time and frustration hasn't even been considered yet. While I'm confident that the DIY result will outperform the Concerto, it makes the decision more difficult in determining what is the most cost efficient route to take when all things are considered. I still need to buy a larger 2 channel amp, stereo pre with high resolution DAC, and CD Transport. That being said, the budget alotted for the speakers is not to exceed $1600.

As this system upgrade is going to cost close to 5K after all is said and done, another DIY project will not be undertaken for quite some time to come, especially if these monitors turn out as well as I hope they will. Now do we understand each other on my hesitance to pay for soft and hardware that will be essentially a one time use? If it is necessary, then there is no avoidinig it, but if there is an effective cheaper way out, I would much prefer it.

Quote:
Puting a cap and an inductor on a driver does not result in a 2nd order crossover in most all cases. It's the total electrical and acoustic slope that determines the order.
I understand the concept of summed slopes, but at the 2K crossover point, why is there an acoustical roll-off in the equation, the woofer does not hit its inductance limit for another octave, and the tweeter does not roll off until below Fs (500Hz). Do these figures somehow change when put into an enclosure? I can understand low end limit on the woofer, but not high. Please elighten if you will.
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Old 20th February 2004, 10:46 PM   #10
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Quote:
Originally posted by Seth Smith


Not exactly sure what that was supposed to mean

Ohhh! Please don't be upset in any way! I can't speak for Russ, but I'm trying to help out a local guy who asked for some advice. If I've offened you in any way I apologize, I'm just trying to clear up some confusion that I see!

Quote:
Originally posted by Seth Smith


Considering the Sonus Concerto can be had new for 1400, the project's cost is already at roughly 1100 in materials alone. The addition of another 300-350 for software puts me dead even in dollars spent and my time and frustration hasn't even been considered yet.
Keep in mind that the least expensive commercial speakers using the 8545 SS woofer listed in the LDSG are the Meadolark Shearwater for $2400 a pair. (There is a Norh kit that's cheaper but I'm only looking at completed speakers.) So yes, it's getting close parts wise to the Sonus Concerto, but they are more expensive parts than are what in the Sonus speaker.


Quote:
Originally posted by Seth Smith

While I'm confident that the DIY result will outperform the Concerto, it makes the decision more difficult in determining what is the most cost efficient route to take when all things are considered.
If you factor in the time you'll spend on the project (which should be fun) then the DIY route is vastly more expensive.


Quote:
Originally posted by Seth Smith

I understand the concept of summed slopes, but at the 2K crossover point, why is there an acoustical roll-off in the equation, the woofer does not hit its inductance limit for another octave, and the tweeter does not roll off until below Fs (500Hz). Do these figures somehow change when put into an enclosure? I can understand low end limit on the woofer, but not high. Please elighten if you will.

The frequency response of the drivers will change drastically when placed into an enclosure. Vifa tests their speakers on an essentially infinite baffle in 2-pi space. (According to their web site)

The plot below shows what can happen with a driver in a speaker. The red line is the frequency response of a Seas 27TDC with a 3kHz textbook 2'nd order crossover. The grey line is the ideal Butterworth 2'nd order 3kHz crossover. There is a pretty big difference, mostly due to response variations caused by cabinet diffraction. In fact for this speaker I spent quite a bit of time minimizing the effects of diffraction, so the error for most applications might be even more.

Scott Hinson
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