Pro midrangers - very low Q on modelled boxes ?

[RobWells]

Hi,

I've been modelling some pro 10" midrange drivers recently, and they've tended to produce very low Q sealed boxes. For example the Precision devices pd107 driver is showing a box of 1.1L for a Q of 0.71 - unacheivable

They recommend up to 35L boxes for it, but a 10L gives a Q of 0.308.


Will these drivers sound "overdamped" ? Will a Q of 0.308 produce a 'bad' sounding speaker ?

Other drivers are similar. I think I remember somebody talking about the Q changing with high power (as the voice coil heats up)


Cheers,

Rob

[454Casull]

How low will they be playing?

[Magnetar]

I've been modelling some pro 10" midrange drivers recently, and they've tended to produce very low Q sealed boxes. For example the Precision devices pd107 driver is showing a box of 1.1L for a Q of 0.71 - unacheivable

In my experience it's best to either load drivers like this one of two ways for home hifi. One is in a straight 100-200 cycle flare horn with a tuned back chamber. The second is on a proper open baffle that will give you baffle reinforcement all the way down to where you cross them to the bass. With either method I have yielded far better results than a traditional reflex or sealed box. Biamping also helps because of the high z of the low q driver/box near the crossover frequency.

[DSP_Geek]

Originally posted by RobWells
Hi,

I've been modelling some pro 10" midrange drivers recently, and they've tended to produce very low Q sealed boxes. For example the Precision devices pd107 driver is showing a box of 1.1L for a Q of 0.71 - unacheivable

They recommend up to 35L boxes for it, but a 10L gives a Q of 0.308.


Will these drivers sound "overdamped" ? Will a Q of 0.308 produce a 'bad' sounding speaker ?

Other drivers are similar. I think I remember somebody talking about the Q changing with high power (as the voice coil heats up)


Cheers,

Rob

And remember your Fb will increase with your Q, so bringing Q from 0.17 to 0.71 would also up your Fb from 75 Hz to over 300 Hz. You can always try for Q=0.5, then use a Q=0.9 to Q=1.0 high pass filter for the crossover - it'll be somewhat misaligned, but not too far from a Linkwitz-Riley fourth order. Box Q=0.5 also puts Fb around 200 Hz, which is close to the maximum energy density for music, so the crossover would split the power evenly between lows and mids.


Best of luck,
Francois.

[RobWells]

Thanks for the replies guys.

More info : I'm using the dcx2496 crossover for these speakers, planning on crossing 250 - 300 from the bass, and 1200 ish to some compression drivers (beyma 380) for the highs.

The plot here :

http://www.precision-devices.com/asp...s/super/13.pdf

Seems to suggest a better response than winISD does.

I was planning on dropping it in a box, eq'ing flat to 125Hz, then applying a 4th order LR high pass at 250 / 300 Hz.

It just struck me as interesting that the 'recommended' box sizes cannot fit the driver inside them.

I haven't got the space available to horn load at the moment, and they have to go in one place, so the OB idea may not work with my room.

Cheers,

Rob

[pinkmouse]

Originally posted by RobWells
It just struck me as interesting that the 'recommended' box sizes cannot fit the driver inside them

The Turbosound boxes that these were designed for are very compact. The "rear chamber" is literally a cardboard tube that just fits over the rear basket, leaving the mounting ring free, and extends just to about 2" behind the back of the magnet.

[RobWells]

Aaahh that explains a lot then Al

I'm probably going to try these as they seem very well put together, and pretty good value too. If they improve upon my scans then I'll probably add a pro 12" beneath to replace my existing bass units.

I love my present speakers but they just lose all dynamics at reference levels on film.

Cheers,

Rob

[RobWells]

Magnetar,

Even though I haven't got the space for midhorns at the moment, I'd still like to build one to have a listen. Would the 'pi speakers' midhorn here:

http://www.audioroundtable.com/PiSpe...ges/14408.html

Work OK for me ? The specs for my pd107 are not hugely different to the jbl2012 mentioned. I've got a beyma td250 90x40 horn for ~1000Hz and up, and only need to reach 250 / 300 on the bottom end.

I'd really like to hear what horn loading would do for the mids.

My pd107 specs here:

http://www.precision-devices.com/asp...s/super/13.pdf

And the jbl here:

http://www.jblpro.com/pages/pub/components/2012h.pdf


Cheers,

Rob.

[roddyama]

Hi Rob,

Here is a very good thread on the JBL 2012 (2122, 2123, LE10, ...) at the JBL Audio Heritage forum.

[RobWells]

Thanks Rodd,

The new speakers are working out well btw. Just measured all the drivers in box this week and am sloooowly getting the xo's tuned in ...

Very happy with the mids/highs, getting there with the midbass/subs...

Rob.