Linkwitz Transform - Driver selection?

[mrwireless]

I'm selecting a mid-bass driver for a 3-way and plan to use it sealed with a Linkwitz Transform.

Normally i'd look for an EBP nearish 50 to get a naturally low response. I also am looking at a range of drivers with EBP up to and around 90. Theoretically the LT can correct equalise these within reasonable limits. i.e. no gains greater than 20 dB.

So my question is, how important is it to use a driver that is well suited to a sealed enclosure, when you intend to use a Linkwitz Transform?

[6.283]

Originally Posted by mrwireless

So my question is, how important is it to use a driver that is well suited to a sealed enclosure, when you intend to use a Linkwitz Transform?

Your question implies that the LT is only used to boost "LF". That is not the case. In some applications you even cut the lower end.
When boosting, you could say: The less a driver is suited for a CB the more equalisation is required (and power from the amp). Then you need to watch xmax and the distortion behavior.
BTW, EBP values are no sufficient criterion for CB vs. e.g. ventialted because EBP does not consider xmax. Classical woofers for a CB always have and require a higher xmax than the ones for ventilated enclosures.

[Michael Bean]

The Linkwitz biquad can be useful for reshaping the 2nd order HP response of just about any driver, but it's no panacea. Like 6.293 said, if you want to lower the Fs of a woofer, you need to cater to the Xmax and thermal limits of the driver, and you'll need a LOT more amplifier power. Take a look at Mr Linkwitz' and ESPs sites, lots of good info and guidance from both.

Active Filters

ESP - The Linkwitz Transform Circuit

Mike

[DualTriode]

More info see here
TA Speaker Topics - Designing a Linkwitz Transform

[mrwireless]

Thanks for the comments. What sparked my question was selecting between two scanspeak drivers, the 18W/8535 and 18W/4545. They're very similar, same Xmax. The 8535 however is "better" suited to a sealed enclosure, Q of .71 in 27 liters, f3 around 50Hz. The 4545 (which is only on the scene because i can get it cheap) needs 8 liters sealed for Q of 0.71, f3 around 75 Hz.

I need an enclosure nearer 15 liters, due to space contarints. So neither driver is optimised in this volume. Using the LT to equalise, both seem viable. So i am tempted to go for the 4545 even though it usually wouldn't be my choice at all, for a sealed enclosure.

Here's how they both look equalised in a 15 liter box:

18W/8535


18W/4545

[6.283]

...'am looking at the response graphs in the data sheets...do you want to share at what F you would like to cross to which drivers as well ?
And keep in mind that numbers for Q and Fs in data sheets are virtually never "correct"

Oliver

[mrwireless]

Originally Posted by 6.283

And keep in mind that numbers in data sheets are virtually never "correct"

Oliver

Ha, yes, that is another little problem. Let's not aim for perfection!

Scan-speak mid-bass will cross over at 800 Hz to an ATC midrange dome. Possibly lower, based on experimentation, but not lower than 400 Hz.

(I am not attached to the scan-speaks btw, open to suggestions)

[6.283]

Originally Posted by mrwireless

I'm selecting a mid-bass driver for a 3-way

So the Scan will be the bass and not the mid range. That was not 100% clear. Is there a data sheet for the mid dome ?

[mrwireless]

Yes, more bass than mid-range, but up to 800Hz, i cannot comfortably call it bass only anymore.

Planning to use ATC SM75-150S. No FR data for this driver from the manufacturer. Only the standard parameters:

http://www.atcloudspeakers.co.uk/dow...ions_sb.xl.zip

But Shin did do some measurements, not sure how accurate they were:



Resonance at 4.5k should be avoided by crossing over steeply at 4k, (probably to a ribbon).

All filtering to be implemented in miniDSP, including the LT.

[6.283]

hmmm, on this graph the mid rolls off at 700Hz. So crossign over at 800Hz will not quite work. But not sure how the data was recorded.
In case you need to reach higher than around 400...500Hz those Scans are not quite first choice because of the resonances around 700..800 Hz.
In that driver category there is a wealth of drivers. So many that it becomes difficult again. The Scan discovery series e.g. has a very good price/quality ratio.
Maybe CARLY could fit your 15l requirement.
The mid/woofer I am using is superb even in a CB. But too expensive if you don't use the midrange above 1KHz.
And finally, I would not push a 6.5" down to 25Hz as you did in the simulations. I'd rather stop at 30Hz.

Keep having fun !
Oliver