Cardioid/Dipole woofer

[drchait]

I am planning on developing a system that uses a dipole or a Cardioid bass designed woofer. I want to try both designs around 1 woofer to see which one is preferable in my room and situation.
Ultimately what I would like is a woofer with specs that will work in both systems. This woofer should be capable of going up into the midrange frequencies e.g. above 600 hz. This limits a H-frame or U frame design, as those are not designed to go very high in frequency because of the type of cancelation of the dipole null. I will only be using this woofer down to about 50 hz, where a subwoofer will take over from there. So my design would incorporate a flat baffle designed dipole or a cardioid system as per the instructions available on this website. DIY archive of Kimmo Saunisto

My first choice in woofers is the AE Dipole18

Here are the specs

Dipole 18 dual 16ohm(coils in parallel)
Fs: 22.9Hz
Qms: 8.85
Vas: 885L
Cms: .42mm/N
Mms: 115g
Rms: 1.87kg/s
Xmax: 12mm
Sd: 1218sqcm
Qes: .89
Re: 6.8
Le: 1.4mH
Z: 8ohm
Bl: 12.2Tm
Pe: 200W
Qts: .80
1W SPL: 92.76dB

I love this woofer and it is definitely my first choice as long as it can work in both type of designs. I will use the cardioid type design with the venting on the side of the box with a closed box behind it.

I know this woofer will work in the flat baffle dipole design because it was made for it, but my question is can I also get it to work in the Cardioid design?

also:

Some designers say stick with a woofer that has a QTS of .5 or less for the most transient perfect bass and boost the roll off. I am afraid to use a low Q woofer because it may require extreme equalization of roll off and I am using a DCX 2496 for all equalization....comments?

Will a woofer with a QTS of .8 be optimum for a Cardioid design?

The web site above is excellent for design of a cardioid woofer, but it leaves out how large the box is supposed to be for that design. How do you figure box size for a cardioid speaker system?

Any help is extremely appreciated
This will be my first dipole or caroioid design and would like to get it to work out right

Thank you

John C.

 

[boris81]

I want to try a cardioid bass at some point as well so I will be following this thread with interest. You raise very good questions. I can't answer any of them with certainty but I will give my limited understanding so we can start a discussion.

DSP has limited amount of headroom before risking signal degradation. It was stated somewhere on this forum by the miniDSP Customer Support that they divide the incoming signal by 4 when they digitize it. That gives us 12dB of headroom. I can't comment on the DCX 2496 but I suspect they are more similar than different. Attenuating the high end might be a sensible alternative when you need to raise the low end by more than 12dB.

Assuming a 4th order LR crossover at 50Hz I think that you will be far enough from the Fs to worry about the high Qts. I think that you will be safe but my knowledge on the subject is limited. If you really want to get crazy about it there are amplifier designs that can use the input from the second voice coil for feedback and achieve very precise control over the cone travel. Rythmic Audio sells such amp plates that may or may not work with your woofer.
Rythmik Audio • Direct Servo - how it works


I don't think the box size is as important. The absorption material and volume, the size and spread of the holes, as well as the baffle size and distance from the woofer to the holes are the key parameters. We should try to put together a collection of some basic guidelines on this thread.