Scan Speak project 3way

[cadman]

All Scan speaks drivers
Tweeter D2905/9500 6 ohms Qty 1
MId D3806/8200 8 ohms Qty 1
Woofer 18W/8531G-00 8 ohms Qty 2

box size
All 1 inch MDF
H= 42.5
W= 7.75
L = 15.00
vent inside dia
3 X 5 long F3 40Hz

http://www.ht-audio.com/default.htm

I made a crossover 2th order
Lp 1200
Bp 1200 to 5000
Hp 5000

but I am not to happy with crossover I need Help
I am using X-over ver 3 Pro and all solen parts
plots from Mfg.

http://pages.videotron.com/diloreto/

[ThomasW]

Do you have frequency response plots of your drivers measured in your baffle?

[JonMarsh]

I'm also not sure what the crossover program you're using- is this from the same folks that do Bass Box Pro?

Putting these drivers together with "classic" straight filters from a text book or program, without having measurement of the driver impedance and response in your cabinet will not work well. It won't reflect the interaction between the crossover filter, and the driver impedance, so the filter slopes will change, as well as the Q at the crossover point.

Additionally, if you want a crossover having a seoond order acoustical function, you have to consider the driver response in the crossover region, and this plus the network response should equal the acoustical target.

To put this into concrete concepts, look at the response of your dome mid. It already rolls off at 12 dB per octave around 1 kHz. So, making a true 2nd order crossover at 1200 Hz will give hardle any power roll off to the dome mid. On the other hand, if you just put a conventional 2nd order text book network at 1200 Hz, (probably what comes from Crossover Pro), the net acoustical response will be more like 4th order Bessel. Lookin at your mid woofer, it has the classic Scan Speak rising reponse from 800 Hz to 2 kHz. So, if you put a textbook 2nd order filter on it, it won't even have a 2nd order roll off- especially not if you don't have impedance zobels to control the inductive rise of the woofer.

Last point, did your crossover design include baffle step compensation, for the transistion between 2 pi space radiation in the midrage (1200 Hz crossover) to 4 pi space in LF? This normally requires a 5-6 dB net downward slope between 200 Hz and 600Hz to 1 kHz, depending on the baffle width. This would be taken into account if you have measurements of the drivers at one meter in your own box. Textbook published curves like the Scan Speak curves you show are measured on a large IEC standard baffle, and won't show the effects of box mounting- you can't use these for designing a seaker, UNLESS you use the FRD tracing program, then use Baffle Diffraction simulator on that data to model the response on the panel, then use the resulting data to develop the required acoustical transfer function of your crossover.

There's too many simulation stages in their for my comfort, but it's possible to get tolerably good results that way, using the resultant data in a free program like Speaker Workshop to do the design. That's the only way I know of to get a workable design without your own measurements.

Also, classic SS drivers have that tiltup above 800 Hz so that you can use a single pole in the crossover around 250 and not have to play as fancy an impedance control tricks to put a zero in the response to stop the BSC - hence the 800 Hz rise. It can simplify the crossover. BUT, one side effect is that the cone's first mode is at 800 Hz, creating a coloration. I used to use these SS drivers in the early 90's, but haven't for a long time- I find I prefer pistonic performance to beyond the crossover region- midrange is clearer.

Let us know if you have more questions....

~Jon

Best regards,

Jon

[cadman]

to JonMarsh

I apreciate what you wrote but I am new at all this if you could do a crossover and post it for me I would apreciate it (also I am working on a 4th order but still all this is new to me) there is a lot to learn from the pros

I saw some of your work and wow way above me (but i do learn fast)

so some of the terms you use I am no familiare with (sorry)

[JonMarsh]

If you're not in a rush I can probably do what one would need to do working only from the factory data- but it might take me a couple of weeks to finish it all- run the ScanSpeak data through tracing and Hilbert transform (to get the phase info, then do a crossover design. I've got some time off right now, but I've got a huge backlog of other projects with high priority- some from early 2003! If that timetable is OK with you, then you can count on some help from us.


I'm also taking off around the 10th of Janaury, and for certain in that week I could do a design working backwards from the manufacturer's data and your cabinet dimensions.

What are the driver positions on the baffle, from the top? Just give me the distance from top edge to driver center for each driver. I'll need that also to model the baffle loading behavior.

What I'll do with this is post an example for our HT Guide Mission Possible of how to do this kind of a design without measurements- not a recommended approach, but possible to get in the ball park. There are a lot of folks in that position for DIY, not having their own measurement capability, but wanting to do something different from an existing kit. I'm sure we can improve considerably on the performance of "textbook" crossovers.

One other point to raise- becuase you have two midwoofers, and a relatively high crossover frequency, and a "fixed" baffle location (I'm sure you don't want to re-do your front panels) It may be best to make this into a 3.5 way system- using one midwoofer up to the dome midrange, and using the other with a tapered network to provide baffle step. I'll give some thought into how that might be combined without using too many components...

~Jon

[Dennis H]

Edit: I should have read Jon's reply more carefully.

[cadman]

to Jon

Jon that would be awesome

for your info I do have a mesuring mic and trueRTA 3.1.1
I do not know if any good but it looks good

http://www.trueaudio.com/rta_abt1.htm