First multi-way build

[theyoungone]

Hi all

I have recently completed a few full range builds and I am now wanting to have a go at designing and constructing a multi way speaker system.

I am going to use a Monacor SPH-8M as the bass driver and a Fostex FF105WK as the high/mid frequency driver and crossing it over at about 600hz.

My question is whether it would benefit from an impedance equalization circuit being integrated into the crossover? If so how do I compensate for the change in impedance of the drivers when designing the rest of the crossover?

Many thanks

Alex

 

[sreten]

Hi,

This still really belongs in the FR forum as a FAST.

However seeing your here lets get rigourous :

http://audio.claub.net/Simple Loudspeaker Design ver2.pdf
FRD Consortium tools guide
http://web.archive.org/web/20090902124715/http://geocities.com/woove99/Spkrbldg/DesigningXO.htm

You should be able to work out if you don't want to slug
the Fostex too much your going to need a ~ 92dB bass
driver, or a couple of 8 ohms 86dB drivers in parallel,
for 4 ohms bass, 8 ohms mid treble.

The crossover has to take into account box diffraction,
and may be 2.5 way or 2 way depending on the x/o
point you choose, whatever you choose the target
should be 2nd order L/R acoustic, and mildy
assymetric to tilt up the main polar response.

rgds, sreten.

 

[theyoungone]

Hi Sreten

Thank you for your quick response and the attachments.

I have been looking at the problem with the SPL of the bass driver. I am finding it difficult to find a sensible sized bass driver (at a reasonable price) around the 92db sensitivity, without having to use another full range as a bass driver. The closest I can find after a quick look is 90db. As with the dual driver arrangement you suggested, this looks good if I am right in thinking that wiring in parallel should add 6db to the sensitivities?

As with the 2 or 2.5 way crossover if I integrate a baffle step compensation circuit into the crossover wont this remove the need for the 2.5 way crossover (and therefore a third driver)?

Thanks, Alex

 

[Richidoo]

They look like a good match to me, with bass a little stronger for baffle step correction.

You don't need the impedance of the drivers to match, you just need the SPL to match at crossover. If you run a tube amp you'll want flattish overall impedance curve, but they are both 8ohm coils so that won't be hard.

At 600Hz you can safely try a 1st order, they sometimes work, but it's so hard using normal drivers like these. The challenge is as sreten says the Fostex will play too low for loud passages and the woofer will muddy up the mids. Steeper crossover cures both problems and LR2 still sounds very good if good parts are used. You'll get the woofer out of the midrange, and you can use the added sensitivity of the woofer to correct for baffle step if you put the crossover closer to the baffle step rolloff as determined by your box width.
https://www.trueaudio.com/st_diff1.htm

 

[theyoungone]

Hi Richidoo

I have modeled the baffle diffraction response both for the Fostex and the bass woofer on a 10 inch wide baffle (please see attachments).

From this please can you advise what would be the most appropriate cross over point?

Thanks

Alex

 

[theyoungone]

I have looked around at other bass drivers and came across the Seas CA22RNY.

http://www.seas.no/index.php?option=com_content&view=article&id=173&Itemid=165

I have modeled an enclosure on UniBox (for the first time) which came out to be a 33 liter enclosure tuned to an F3 of 48.31Hz which come out with a relatively flat response. I then put it into WinISD (what I normally use) to check this and it shows a 0.8 dB rise above 0dB. Will this slight rise cause any problems or will it be ok?

Thanks

Alex

 

[Richidoo]

John Murphy's baffle step formula (in the link I posted) puts F3 baffle step at about 450Hz, so put your crossover there. Start with 3dB of correction and adjust to taste, depending on your room size, genre preference, bass feel preference, presence of dancing ladies, etc.

The slight bump in FR in WinISD is insignificant. The box vibrations and the room reflections will skew FR much more than that small bump. Designing bass is much more an art than a science predictable by computer. But they help get you in the ballpark.

Consider sealed cabinets. You might find them much easier to make sound good playing music than ported designs on your first design project. The reflex formulas rarely sound good for music, better for HT type subs. If you want ported, try to find a ported design for the driver you choose, maybe contact the driver mfg for advice on ported box design. Point the port exit in the opposite direction from your listening seat. There's a lot to learn about reflex design, good luck and take deep breaths, get a stress ball...

 

[theyoungone]

Thanks for the information and I will certainly look into sealed cabinets.

 

[sreten]

if I am right in thinking that wiring in parallel should add 6db to the sensitivities?

Hi, Yes it does, rgds, sreten.

Vented is your best bet if subs are not involved.