Crossover point for Scan-Speak Drivers - Opinions needed

[ShinOBIWAN]

Lo all,

I've just recently bought a pair of R2904-7000 ring radiators along with the 18W4531 Mid/Bass driver for use in an active 2-way design.

I'll be using a Linkwitz Riley 4th order 24dB/Octave network but would like to hear peoples thoughts on potential crossover points.

I was looking at around 2Khz personally but would value any input from others.

Here's the manufacturer response/impedance plots:

R2904:


18W4531:

[ShinOBIWAN]

Anyone?

[ScottG]

w/ 4th order 1.5

[Bill Fitzpatrick]

2750

[RobWells]

Hi Shinobiwan,

Bill's on the money with where the dispersion pattern is the closest for the 2 drivers. Best measure the drivers in the finished box to make sure though.

That mids' response is like my s-speak 8530's plot. Make sure you include a shelving low pass to lose the hump around 1 to 5k, otherwise they'll sound very bright. (to my ears anyway )

I take it you got bored with the Visatons ?

Cheers,

Rob

[5th element]

Bill is correct saying an xover of 2750.

The ringr will appreciate a higher xover having limited xmax and the mid/bass is sufficiently well behaved to handle 2750.

The bump in response can be managed with the lowpass.

You will require a shelving network to compensate for bafflestep though, linkwitz website details this and it works very well just using textbook maths.

You will also most probably require a delay circuit to bring the drivers into correct (or close enough) phase alignment to get the xover to sum well at 2750 and give you the notch on reverse polarity. Otherwise this should sound pretty darned good.

Tweeters are nice and easy just the filter network and a level adjuster, understand though that you probably will not need 4th order electrical filters on either the drivers to achieve 4th order acoustic.

Active filters are a little bit easier to design because you dont need to worry about impedance, but you still really need to measure the drivers in box, and use software to get the most out of them, especially with the delay network.

[ShinOBIWAN]

Scott:
You think the R2904 would handle that? What would distortion be like at that frequency. I know the 4th order would quickly roll off the response before real problem occured but wouldn't SQ be impaired at all?

Even with an FS of 520hz scan-speak recommend crossing over no lower than 2Khz.

Bill:
I was thinking that I should maybe move the crossover up to about 2.5-3Khz myself. What would be the most transparent point to crossover at?

Is it better reason that the R2904 is among the best HF drivers out there ATM so should be used to cover as much of the frequency range as it possible to do without impairing quality - my original reasoning behind the 2Khz point.

Or...

Move the crossover point out of the mid-range and upto around 3.5-4Khz. For the best midrange transparency.

Or...

Go with a different mid/bass all together! Whats passing off as one of the best mid/bass driver at the moment? What about PHL? The sensitivity looks like a great match for R2904.

As ever, any opinions greatly appreciated.

[ShinOBIWAN]

Originally posted by RobWells
Hi Shinobiwan,

Bill's on the money with where the dispersion pattern is the closest for the 2 drivers. Best measure the drivers in the finished box to make sure though.

That mids' response is like my s-speak 8530's plot. Make sure you include a shelving low pass to lose the hump around 1 to 5k, otherwise they'll sound very bright. (to my ears anyway )

I take it you got bored with the Visatons ?

Cheers,

Rob

Hi Rob,

I will of course take some measurement proper once the drivers are in the cabinets. At the moment I just want to throw as many ideas around as I can to get an idea of the directions I can head.

Regarding the hump, I agree whole heartedly with what you've said , since its going to be an active XO, shelving could be added at some point but I'm also strongly thinking about swapping the mid/bass out for something else.

Yep, the Vistatons went to another good home where I hope they are being enjoyed. That project was a great learning experience as far as cabinet building goes, so now I'm confident in that area I'd like to turn my attention to the electronics side and hence my reason for going with full active 2-way's with onboard XO's & bi-amping with dual mono power amps(based on something like the lateral MOSFET design by Rod Elliot).

[ShinOBIWAN]

@ Fifth Element

Wow!

Clearly I thought I was beginning to really understand loudspeaker design and then a few new topics get thrown in for good measure, cheers FE

If you don't mind I've got a couple of questions because my brain is hurting after reading that:

Originally posted by 5th element
Bill is correct saying an xover of 2750.

The ringr will appreciate a higher xover having limited xmax and the mid/bass is sufficiently well behaved to handle 2750.

The bump in response can be managed with the lowpass.

You will require a shelving network to compensate for bafflestep though, linkwitz website details this and it works very well just using textbook maths.

Cheers pretty much what I originally thought until madness set in after looking at driver frequency plots for too long.

The R2904 has a rising response anyway so what do you think bafflestep will add to this? Better still isn't there something on the linkwitz site to calculate it?

You will also most probably require a delay circuit to bring the drivers into correct (or close enough) phase alignment to get the xover to sum well at 2750 and give you the notch on reverse polarity. Otherwise this should sound pretty darned good.

This is the one I'm having trouble understanding. Help please!

Delay circuit? I was planning on using the cabinet design to time(phase) align the drivers. Am I being dumb in assuming this is enough or is their more to be done that I simply don't understand quite yet. I know that out of phase drivers usually results in drops/gains in the response but what would a delay offer that an offset tweeter wouldn't or is it an easier way to achieve the same thing?
What do you mean when you say 'give you the notch on reverse polarity'?
I've clearly still got lots to learn so any advice would certainly help me understand a little more.

Tweeters are nice and easy just the filter network and a level adjuster, understand though that you probably will not need 4th order electrical filters on either the drivers to achieve 4th order acoustic.

Yep I've allowed for variable cermet trimmers in the XO output buffer stage on both the HP and LP. What do you think the final acoustic order of rolloff will be, taking into account the HF drivers rolled off response?

Active filters are a little bit easier to design because you dont need to worry about impedance, but you still really need to measure the drivers in box, and use software to get the most out of them, especially with the delay network.

Will do once the cabinets have reach a suitable stage. I'm using a Behringer ECM8000 measurement mic along with TrueRTA with 1/24th octave measurements. Is this setup OK for measurements or do I need more accuracy?

[ShinOBIWAN]

Fifth Element:

Wilmslow Audio cocked my order up and sent me a 15W8530 instead of the 18W4531. So this is the perfect opportunity to swap to something else, maybe something better or something that doesn't have the nasty hump at 1-5Khz? All the Scanspeaks seem to do that strangely Maybe its the SD-1 motor tech?

What do you think about swapping the mid/bass for something like a Volt 2500.4 mid/bass driver? Effeciency is a little better but I'm concerned about using a 10" driver up at around 2.5Khz.

Hmmm... maybe not such a good idea. Always liked the Volt bass drivers though and for me they are unmatched for pure SQ, was wondering what there mid/bass's were like, anyone tried them?

Or what about something like a PHL or Seas Excel.