Dynaudio Aperiodic question

[dpaws]

Hi,

I'm considering the Dynaudio Sirius - however, I have a 17WLQ 8ohm driver, as opposed to the suggested 17W75 4ohm.

http://www.geocities.com/CapeCanaver...91/sirius.html
How do I need to alter the relative volumes of the two compartments to suit my driver?

Is Vas everything? Are aperiodics so vague that it will be close enough as a starting point?

http://www.gattiweb.com/images/dynaudio/17wLQ_data.pdf http://www.gattiweb.com/images/dynaudio/17w75_data.pdf

Vas of both drivers is the same, however, the original Qt is 0.7 and mine 0.4. I assume, therefore, that my upper enclosure would need to be smaller or more tightly vented to provide more air resistance/damping to override the drivers own better damping?

How do aperiodic enclosures and 0.4Qt drivers get on together?

Is an aperiodic simply not sensitive enough for my 24W of 845SE amplification?

All thoughts much appreciated

Cheers, Steve

[SY]

I don't know about the 17WLQ (never used one), but the specs on the 17W75 are pure fiction. I've used about a couple dozen of them and never had one even vaguely close to the ratings. Generally Qts and fs come out a chunk higher than ratings.

The high Qts (0.8 minimum, more often 0.9-1.0) of the 17W75 can be tamed somewhat with the resistive loading of an aperiodic or a TL; I'd suspect that this loading would dry up the bass on a Qts = 0.4 driver. But first, I'd want to see what the Qts really is...

[dpaws]

Many thanks SY - that's all I need, as if this game isn't hard enough without moving the goal posts!

However, a higher Qts may be a blessing - Northcreek have published their design based on a recommended Qts of 0.6. They suggest dimensions using Vas data only (0.3 x Vas for the top half, 1 x Vas for the bottom)

Anyone got a spare Qtsometer?

[SY]

If you have a soundcard, a small amp, and a resistor, you've got a Qtsometer.

[dpaws]

Originally posted by SY
If you have a soundcard, a small amp, and a resistor, you've got a Qtsometer.

Isn't the net a wonderful thing...

http://www.diysubwoofers.org/measure.htm

[Geoff H]

Hi Steve,
I have been doing a bit of experimentation with APs and other concepts of late. The APs are fairly broadband by nature.

What I have found to date, if the port size is tuned to give a box resonance at the point where the Z starts to rise, then damp the port, you'll be fairly close to the mark. For a start, mount the new drivers and have a listen.

Have a look at:
Aperiodic enclosures

I have done 3 cabs now. The latest one may be stretching it a bit far. 30Hz out of 0.8 ft3 with a 10" driver is the goal. I haven't finished with that yet.

[happy.gringo]

Geoff,
Could you give a specific example to help us 'special ed' students catch on? I am putting together some floor monitors for my band in boxes that are obviously too small, so I am wondering if I can go AP and get a bit smoother response.
Thanks

[Geoff H]

Hi Happy Gringo,

Sure thing. The floor monitors you talk off sound like what we know as "fold back" speakers. I am working on something right now, that at least look like foldbacks. Don't know if they'll do the SPL you might need. Keep an eye on the other thread. All going well I'll post results for the 0.8 ft^3 cabs next weekend.

Regards
Geoff