CSS 3 way bookshelf speakers

[sam xt]

Hello everyone, I have been reading these forums for a while but this is my first post.

So for some time I have been toying with the idea of a bookshelf speaker made with the following drivers from CSS, SDX7, FR125, and the RT1. My idea is to arrange in a mtw arrangement all sealed.

I have looked around and have planned to have the SDX7 in 7L sealed, the FR125 in a 9.4L sealed and the RT-1 in its own small compartment.

So now the question where I hope someone with more experience will come in - the crossover. To start will all be passive. The following pic shows what I have come up with for values. Crossover points are 500 and 4000 Hz.





The crossovers will all be wired in parallel. They are based on a butterworth arrangement, and the values for caps and inductors were calculated based on the impedance at the crossover frequency.

So if someone could help me out and have a look over, let me know if I'm way off base here. I'm also flexible to the crossover points and any other recommendations about my preliminary design.

Below is the plan for the speakers, curved sides, with a walnut veneer finish on sides and top, and a curved leather wrapped front baffle. Not a very good pic to start but I'll find another and post it soon.



I know it's a long first post, but I look forward to hearing your feedback and I'll be posting pics of it when I get it started.

Thanks again to everyone here!!

Sam

[gz76]

Wow, great diagram there... it always amazes me how people use Excel creatively to do diagrams. My sister-in-law uses it like graph paper to do floorplans and calculate areas!

I'm sure the original designers of the software only ever thought it would be used for dealing with boring stuff like numbers!

[planet10]

Originally posted by sam xt
So for some time I have been toying with the idea of a bookshelf speaker made with the following drivers from CSS, SDX7, FR125, and the RT1. My idea is to arrange in a mtw arrangement all sealed.

I have looked around and have planned to have the SDX7 in 7L sealed, the FR125 in a 9.4L sealed and the RT-1 in its own small compartment.

I'd allocate the volume somewhat differently... the RT1 doesn't need any enclosure as it is sealed from the back. I'd put the FR125 in no more than 7 litre, I'd actually use 5-6 litres and vent it aperiodically out the back. The SDX7 can work in pretty small sealed box, but if possible i like to get it up to at least 14 litre, where it really shines.

Also the SDX7 really benefits from 1st order cone treatment to tie the carbon fibres together.

XOs i try to stay away from. On all 3 of the speakers i have with SDX7 i cross-over actively. With the extended range upward of the (treated) SDX7 and the ability of the FR125 to go low, you could away with a pretty simple 1st order PLLXO -- i'd also push the XO lower than 500 Hz to take advantage of the FR's FR capabilities.

Tweeter to mid is a bit trickier. RAW had his XO a bit higher 4250 IIRC, i'd give a try to just a single cap on the RT1 as a starting place (XO up at 10-12k) just to see what that does.

dave

[sam xt]

Thanks for the help Dave,

Here is what I have now for the crossover.



The main changes are:
Crossover between mid and bass is now a first order at 360Hz
Upper crossover point has been raised to 7200 Hz and only has a cap on the tweeter.

I'm revising my box plan now to allow the volumes you recommended.

[sreten]

Hi,

Your going to need two SDX7's to match the FR125S.
(look up baffle step compensation).
The SDX7 in 7L sealed works, but venrted low is much better.
Shown are graphs for 2 SDX7's, which coulds be mounted
in force cancellling mode like the AudioPhysics Virgo.

See : http://rjbaudio.com/Extremis/extremis.html

/sreten.

[sreten]

http://www.rjbaudio.com/Audiofiles/FRDtools.html
http://www.geocities.com/woove99/Spk...esigningXO.htm

http://www.zaphaudio.com/
http://www.rjbaudio.com/projects.html
http://www.geocities.com/woove99/Spkrbldg/
http://www.troelsgravesen.dk/Diy_Lou...r_Projects.htm
http://htguide.com/forum/forumdisplay.php4?f=39
http://www.humblehomemadehifi.com/

/sreten.

[planet10]

Originally posted by sreten
The SDX7 in 7L sealed works, but venrted low is much better.

It may model better, but the sound of an SDX7 hitting its stops is not pleasant... i'm sticking with the sealed air spring to help prevent that.

dave

[sreten]

Originally posted by planet10


It may model better, but the sound of an SDX7 hitting its stops is not
pleasant... i'm sticking with the sealed air spring to help prevent that.

dave

Hi,

And your point is ? Other than stating the obvious ?
What so special about the SDX7 than means sealed is better than vented ?
Unless you just saying sealed is best .... which it is not .... is this case ....

/sreten.

[planet10]

Originally posted by sreten
And your point is ? Other than stating the obvious ?
What so special about the SDX7 than means sealed is better than vented ?
Unless you just saying sealed is best .... which it is not .... is this case ....

Every non-sealed box i've tried for these has had to have the port stuffed to aperiodic to keep them from bottoming out. For this woofer, i eould indeed say sealed is better.

dave

[sreten]

Originally posted by planet10


Every non-sealed box i've tried for these has had to have the
port stuffed to aperiodic to keep them from bottoming out.
For this woofer, i eould indeed say sealed is better.

dave

Hmmmm..........

Triumph of claimed experience over engineering ?

On paper there is absolutely no reason why they should bottom
out. Vas is not excessive for a 6.5" driver which means that the
surround is quite stiff, the low Fs coming from the cone weight.

Only if the driver is badly designed (see klippels papers) will
it be prone to "bottoming" out / jumping out of the gap, and
for that case lower Vbox will linearise a dodgy suspension.

This should be very unlikely for an XBL motor, Zaphs analysis of
long throw 6.5" drivers indicates that excursion is suspension
rather than motor limited.

I've never read anything anywhere else that implies the SDX7 and
its precursor the Extremis is not suitable for vented loading. Noting
a vented single driver is the same as four sealed drivers at the port
frequency two drivers in 30L tuned to 30Hz looks very good for a
full range (no sub) design, and it should do at > $200 a pair.

And like all vented designs if using vinyl a rumble filter is mandatory
if you intend to use the driver near up to its maximum capability.

/sreten.