Two drivers one selaed box

[zeus_threat]

Hi could anyone please help on this:-

I am planning to build a sealed subwoofer with two drivers in it. The drivers share the same volume. The drivers will be equalized with a linkwitz transform circuit.

My question is how do i measure the Q parameters for the woofers in the sealed box for the linkwitz transform:

do i

1) Measure the parameter for one woofer and multiply the Vas by 2?

2) Or connect each woofer in parallel and measure the total Q values? ( Note that each driver will have its own amp and the amps are driven by a linkwitz 24 dB/Octave active low pass filter)

Thanks for the help

[MJL21193]

Hi,
Measure both driver and average the results. Use Unibox, set for two driver in either series or paralell, with the average parameters. Unibox will do the rest.

[zeus_threat]

Hi thanks for the reply i will try to look for unibox. But actually each driver is run by its own amp they are not connected together neither in parallel nor in series. So is it still valid to consider theT/S parameter of one driver only (measured in the box with both drivers present) and used these values for the linkwitz transform?

Thanks

[MJL21193]

Ok, first things first: You need the T/S specs to design the enclosure. I measure these with Speaker Workshop to get Fs (free air resonance), Qms, Qes, Qts and Vas. The driver needs to be measured in free air, not in the box. I mass load the cone to determine the Vas.

To design the enclosure with Unibox, two drivers in paralell or series electrically makes no difference to box volume or tuning. You need the Fb and the Qtc of the box to determine the values for the Linkwitz transform. Fb should be near the top of the desired frequency range of the sub, to drive the speakers below this resonant peak.
For example:
2 subs with Fs = 35 installed in a 40 litre box gives an Fb of 80Hz(this is just a for instance example, not real data).
Below 80Hz, impedance is flat, easy load for the amp to drive.
Having the box small enough to drive Fb up is one of the biggest advantages of the Linkwitz transform.

[y8s]

Originally posted by MJL21193
[B]Ok, first things first: You need the T/S specs to design the enclosure.

nah he doesn't need them prior to building if he's doing a linkwitz transform. Sure you need to be in the ballpark so your max gain isn't too high, but the point of the L-T is to make a random box behave like a better-than-perfect box. just measure the drivers in their box after it's all built and use that Q and Fs.

matt

[zeus_threat]

Hi thanks for your replies the steps you have mentionned have already been done. So to make it simpler with the two drivers in the same box do i connect only one driver and measure the Fs and Qts or both of them?

[y8s]

connect them as you would during normal use. you'll want the "system" response and that's how the system will be used.

the L-T will be fed into the amplifier driving the two drivers, correct?

[zeus_threat]

YEs Y8S the same linkwitztransform will be fed into both amps

So to sum up i put both woofers in the box. Connect only 1 woofer. Measure the T/S parameters and use the measure parameters in the linkwitz transform and it should work.

[y8s]

ohh two amps.

I would still do them together. both running, both measured. you're only making one linkwitz transform, correct?

source -> LT => amplifiers => woofers

the LT doesn't know how many woofers or amps there are, it just knows the system Q and Fs. Measure the system response with the same source into both amps and woofers and use that.

If you hook up only one woofer in a box with two woofers, the second "dead" woofer will interact and give you improper response curves.

[richie00boy]

If you are using an amp per woofer I would put a partition between the drivers to make two equal boxes. Then as you are using only one LT I would either measure each woofer individually and average the results to design the LT, or connect them in parallel or series and measure that way.

If you do not have a partition sealing each half you cannot only measure one woofer leaving the other unpowered. The results will be completely screwed as the undriven woofer tries to be a passive radiator.