Bass bins for 12" drivers

Frode

Member
2003-05-04 8:49 am
Bergen
I'm not quite sure why I bought them, but I have 4 cheap 12" drivers: http://www.mamut.net/homepages/Norway/1/18/dynabel/pa1250-1000-web.jpg

My plan is to cross them over to a horn in the 300-500Hz region. Depending on the chosen design, lower crossover will be maybe 40-100Hz. I don't have room for 4 50Hz horns. The speakers will be used in a ~7.5mx4mx2.5m room(~25ftx13ftx8ft).

How would you suggest I should use these drivers?

Frode
 
I'm not quite sure why I bought them, but I have 4 cheap 12" drivers: http://www.mamut.net/homepages/Norway/1/18/dynabel/pa1250-1000-web.jpg

My plan is to cross them over to a horn in the 300-500Hz region. Depending on the chosen design, lower crossover will be maybe 40-100Hz. I don't have room for 4 50Hz horns. The speakers will be used in a ~7.5mx4mx2.5m room(~25ftx13ftx8ft).

How would you suggest I should use these drivers?

Frode

Hi Frode,

Suggestions: Use two for a dedicated Sub and the other ones: in closed boxes to 300-500Hz.

b:)
 

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That might work! Is your design a TH with decreasing area towards the open end?

Frode

Yes it has, but thats where any other resemblance cease because a T-TQWT is always stuffed and is loaded more evenly on both the summed diaphragm sides( similar summed amplitudes too).

The generated SPL terminates into a smaller port area that also is insensitive for external boundary impacts.

A T-TQWT have more in common with a traditional TL where the driver(s) are placed very close to the floor and the terminus is placed close, next to the driver front side.

If such a TL is blocked max a couple of cm away from the driver cone and terminus, the SPL sums in the near-field instead of far-field like for a T-TQWT.

A T-TQWT trades SPL for BW opposed to a TH that trades BW for SPL.

Like a TL a T-TQWT accepts a wider range of driver TS(Qts) parameters unlike a TH does.

b:)
 
Now I see you've put 2 drivers into the sim. I thought I had to double the size if using both in the same box. Actually a nice and small sub. Is 120Hz your recommendtion regarding max upper crossover point? Highpass at 40Hz?

Frode

Hi Frode,

The T-TQWT uses two paralleled drivers in the proposed volume= ~167L.

I forgot to mention to consider the design of a detachable lid that should cover the front side of the drivers for easy access to the drivers.

If this lid is removed the T-TQWT turns into an OD-TL (Offset Driver-TL) with a sloping FR as for a TL, perfect for corner loading in a room that have low air leaks to eventual other surrounding environments.

Maybe you can stretch the upper FR bound for the T-TQWT a bit further but it all depends on how much gldy/ amplitude ripple that remains at your chosen XO point and if the box stuffings is chosen with care.

I would start designing two closed boxes(stands for your top Horns?) that suits your needs of mid bass extension down below 100 Hz or ported down to 55-65 Hz.

It looks like if you choose a closed volume between 20-53 L the f-6dB roll-off would be about 86-72 Hz, i.e. the XO can be acoustic overlapping to the Sub that needs an separate dedicated amp(LR 12-24 dB/octave HP).

In case you care for flexibility(I would) and choose a 53 L ported box for the mid basses ,you should use an active HP XO= 12 dB/octave set no lower than ~60 Hz(f-3dB ported =~51 Hz) due to the acoustic gldy.

If you close the port the box reverts into a Qtc= 0.5 system with a f-3dB of ~72 Hz.

For a T-TQWT XO:ed at 80 Hz or below I would choose a 12dB LP filter but if stretching up to 120 Hz I would use >= 24 dB LR filter to ensure not to add localization cues to appear from the sub, that is not happening if 250 Hz is lower than ~-20 dB.

b

PS: I ran my post into Google translate to check if my written language could be understandable. Using a foreign language can sometimes be puzzling: Look at the submitted picture!
 

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Frode

Member
2003-05-04 8:49 am
Bergen
Thank you for your help!

My initial plan was to use the drivers in push-pull slot loaded BR after djk's recipe, but I'm worried about how high they would be able to go. I also played around with volumes around 50L per driver tuned to ~50Hz, and that seems to work well. Maybe that's a good plan to start with.

As for crossover, I use Audiolense XO from Juice HiFi. The standard setup gives an overlap of 2 octaves, which means that a high passed driver doesn't receive any signal lower than one octave below XO, and vice versa for a low passed driver. This can of course be changed, but it's possible to make quite steep filters.

Frode