Sealed high pass subwoofer with high Qts woofers

[Hjalmar]

Hello all,

I am looking for some help on building a sub-woofer with a couple of Dynaudio 30W100 woofers I have.
The woofers have a Qtc of 0.61, Fs 24 Hz and a VAS of 269 liter according to the company specs.
I have one pair in a huge closed box speaker which has Variovents.

Now I want to build a sub-woofer which can fit in our smaller living room and has a bit higher WAF.
When I did some quick calculations I noticed a closed box was going to be huge with this speaker.
As I have one pair I thought about using them in a compound set-up, thereby nearly halving the required box volume. Which is alas still humongous....

So, I then thought about going for a high pass filtered speaker box, this will decrease the box volume considerably as a Qb of around 1.0 can be used.

Does anybody have experience with building a high-pass filtered sub-woofer or with building a sub-woofer with the Dynaudio 30W100 units?

Regards,

Hjalmar Dijkstra

[LQ1Z34]

If youre talking about running a LARGE cap before the sealed sub then I think Phil has done this to good success.

[Jeff B.]

Hello all,

I am looking for some help on building a sub-woofer with a couple of Dynaudio 30W100 woofers I have.
The woofers have a Qtc of 0.61, Fs 24 Hz and a VAS of 269 liter according to the company specs.
I have one pair in a huge closed box speaker which has Variovents.

Now I want to build a sub-woofer which can fit in our smaller living room and has a bit higher WAF.
When I did some quick calculations I noticed a closed box was going to be huge with this speaker.
As I have one pair I thought about using them in a compound set-up, thereby nearly halving the required box volume. Which is alas still humongous....

So, I then thought about going for a high pass filtered speaker box, this will decrease the box volume considerably as a Qb of around 1.0 can be used.

Does anybody have experience with building a high-pass filtered sub-woofer or with building a sub-woofer with the Dynaudio 30W100 units?

Regards,

Hjalmar Dijkstra

A Qtc of .7 with a woofer with a Qts of .6 will result in an enormous box, because Vab will approach infinity as Qtc approaches Qts. Dynaudio's method was to use these woofers in a box that resulted in a Qtc of around 1.1 to 1.2 and then use the variovent, which introduces leakage to the box to lower the effective Qtc. This leaky box technique works well with high Qts woofers; without them you are left with a response peak in the midbass.

The use of the capacitor will likely produce a peak in the bass response because it will interact with the woofer's box impedance peak. This can be tuned with the right cap value to help extend the bass, but it takes some modeling to do it right.

[Hjalmar]

A Qtc of .7 with a woofer with a Qts of .6 will result in an enormous box, because Vab will approach infinity as Qtc approaches Qts. Dynaudio's method was to use these woofers in a box that resulted in a Qtc of around 1.1 to 1.2 and then use the variovent, which introduces leakage to the box to lower the effective Qtc. This leaky box technique works well with high Qts woofers; without them you are left with a response peak in the midbass.

The use of the capacitor will likely produce a peak in the bass response because it will interact with the woofer's box impedance peak. This can be tuned with the right cap value to help extend the bass, but it takes some modeling to do it right.

Thanks Jeff,
I was not aware how Dynaudio modeled the speakers with the variovents.
This might be another option for me. I wonder if it works with compound speakers?

I found some information on sealed high pass design in the German Hobby-Hifi magazine, they call it GHP (Geschlossen Hoch Pass). The published a set of equations with which easily the Vb and the size of the capacitor Cb can be calculated. They published a few design, but none of them with such a high Qts woofer like the Dynaudio, which got me to ask around about experiences with this type of speakers.
So if any of you has experiences with this type of speaker I would like to hear.

thanks in advance,

Hjalmar Dijkstra

[Hjalmar]

A variovent works well with the Dynaudio 30W100's.
However the speakerbox is still considered very large to pass WAF.

In the mean time I found a pretty old, well that's what you get if you use extinct woofers, design for a 50L closed box.
The trick is to compensate the diminishing woofer output at low frequencies by boosting the heavily around 30Hz. To reduce physical overload of the woofer they also used a very sharp sub-sonic filterin the design.
The design was published in the French L'Audiophile magazine (alas long gone).

I might give this a try, unless I'll go for the iso-baric solution with variovents.

Wish I could find a drawing of the large commercially produced Dynaudio Isobaric Compound 5 design.

If any of you have any experience with the above please let me know.

Best regards,

Hjalmar Dijkstra

[MarkL]

Would two single-driver subs be more managable?

[philiparcario]

A variovent works well with the Dynaudio 30W100's.
However the speakerbox is still considered very large to pass WAF.

In the mean time I found a pretty old, well that's what you get if you use extinct woofers, design for a 50L closed box.
The trick is to compensate the diminishing woofer output at low frequencies by boosting the heavily around 30Hz. To reduce physical overload of the woofer they also used a very sharp sub-sonic filterin the design.
The design was published in the French L'Audiophile magazine (alas long gone).

I might give this a try, unless I'll go for the iso-baric solution with variovents.

Wish I could find a drawing of the large commercially produced Dynaudio Isobaric Compound 5 design.

If any of you have any experience with the above please let me know.

Best regards,

Hjalmar Dijkstra

yeah that is what I did with an IB. a big cap resistors and a subsonic filter.

your woofers could be iBs due to high qts and hi vas you would need to protect them from over excursion with a good subsonic filter.

problem with iB subs are they can't be moved you need the right room for them. cult of the infinite baffle has a lot of ideas on making them.

[GranteedEV]

I believe woofers like this will work very well with a pair in U frame open baffles. That is what I would do. Add a miniDSP to equalize and protect the driver accordingly.

An added advantage of a U-frame would be that as long as you sit on axis, you should excite less room problems compared to sealdd and the ones you do excite are random.

Since it is not a huge room, a good box in this case is no box

[dfaulds]

Another option would be to sell the Dynaudios and use the money to buy something that will work within your constraints. I'm sure there is still a market for them, and you should get enough from them to buy a pretty nice sub driver.