Small Sub with 10" Ciare HS251 -- some questions

Hello there,

I have now received a pair of the Ciare HS251 subwoofers. They look nice, magnets are bigger than I expected. For now I stuffed them into a big box, connected to an amp driven with a LSP crossover plugin up to 110 Hz... just to "burn" in a bit.

For my box calculation I used Unibox by Kristian Ougaard. It's available on Charlie Laub's website

I ended up with a 72 liter box with a port of about 170mm length (inside diameter of port is 74mm). That's a bit long... not sure if that should be a concern. I decided to put it onto the back of the box. My concept for this built is to use corner blocks and also blocks along some length as seen here:


I have build a huge 2 x 15 bass instrument speaker like that and it worked out great... less trouble clamping etc.

Anyway, my question is if this port length seems odd? I also have the program "Basta" installed, and there I am getting quite a different length suggestion (82mm).

Any idea why these values don't line up?
Any suggestions regarding the box design? There will be two of these... placed behind my desk.


Thanks :)
Just a quick comment on rear ports plus your planned position behind a desk; make sure you have enough space to avoid having the ports choked up against a wall or any other boundary that may be back there, else they won't do any good at all.
I'm not familiar with either of the modelling programs you've used but Win ISD predicts approx 28Hz tuning for the 174mm long version of your port, that assumes the internal end of the port tube is well away from any boundaries within the box, ie it's not tucked right into a corner. It might be worth checking in Basta to see if there is any adjustment made to the end correction, as that is one way that different port positions are accounted for and will give different port lengths as a result.

Edit PS: Depending on how loud you expect to listen, that 74mm vent diameter may be a little low - check the vent airspeed graphs to confirm after setting input power to your expected listening level to be sure.

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OK, so I just downloaded Basta to see what it offered wrt End Correction etc, when I specify 72litres tuned to 28Hz, I get a predicted vent length of 164.7mm, only ~3% different than your Unibox prediction.
Is there any chance you left the default 35Hz tuning in place in Basta? That does give approx 83mm length....
Thanks for your responses.

Regarding the space behind the port, there will be about 30 cm of breathing space. Maybe a little more.
I am planning to put the subwoofers sideways, firing to the center, away from the side walls... there is only about 50 cm of space between the desk the back wall, hence the idea to put them sideways.

About the port length:
I am pretty sure I forgot to change the desired Fb Basta, great catch! I don't use Basta very often, not too familiar with all the parameters.

Should I move the port a bit more towards the center? Is it sitting too far in the corner?

The reason for the 74mm port size is a) I already have this size tube and b) Unibox recommends a minimum diameter of 68mm. I am sure I could find a smaller diameter tube, but I also assume there is a good reason why Unibox suggests a minimum diameter of 68mm... I suppose?
30cm space should be fine, no worries.
The rough rule of thumb for port placement within the box is to keep it at least one diameter away from any surface; you look to be right around that w.r.t. the side wall of the box so a small adjustment there might help it behave a little closer to the prediction.
Minimum port size is always a trade off between keeping vent airspeed low enough to avoid it causing extraneous noise and on the other hand avoiding impractically long vents. Again, using rough rules of thumb, we want vent airspeed to be below ~17m/s for highest fidelity applications; for lower fidelity some people get away with up to double that.
WinISD predicts you'll get about 100-101dB per box at the lower airspeed, using your 74mm pipe, rising to 106-107dB per box at the upper limit.
Unless you really want to push these as loud as possible, you'll probably be OK.
That should be plenty of dBs... I don't think I'm gonna sit at my desk and crank it up to +100 dB.

I have now found the Fb field in Basta, and that was indeed the mistake I made. What's interesting is also, that Unibox will also adjust the port length for you if you change the port ends... possible values are "one flared end", "one flush end", "two flush ends" and so on. Having both ends flush yields a a port length of 164.6 mm.

I did flare the end of a port before, it was actually fairly easy to do. I am thinking I could do that for the interior side... but I am not sure if it's worth it.

Today I managed to get some 18mm Poplar plywood. It's disappointing how difficult it is to get some good plywood in my area (I live one hour from Paris now). I don't like messing with MDF, the only other choice in most stores is "Okume" Plywood, which is terribly soft and bends easily. Birch Plywood is nowhere to be found here, but with some luck Poplar plywood is availble, which is not bad at all.

I'll start making some cuts this week and report back ;)
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Gettin' there. I had a big pile of oak sticks lying around which I used all along the inside edges. Everything is glued, clamped, and nailed (brad nailer). The oak sticks already tame any resonances, and the inner brace should do the rest. I think whatever resonances are left are out of the frequency range that this subwoofer will play at anyway.

I will add some padding on the walls though, for good measure.

The protective grill I bought won't fit, too shallow :( I guess it works only if the speaker is mounted from the inside. Maybe I'll find another good grid later.

Some progress pictures:

Gotta know when to add what...


You can never have enough clamps.


Pretty close the the drawing ;)

Painted them with Milk Paint in "Barn Red". Kind of a cool color, in my opinion ;)

Added some simple terminals, that's good enough for me:

And some simple feet as well:

Applied Bees Wax after two coats of milk paint:


Next time I'll choose a black pipe... will look a bit neater.

The sound is fantastic. I wired each one in series, they are plenty loud enough. I am currently using an old Adcom GFA-545 to drive them.

"On Top" I am running two Altec 403A drivers as mids with a FaitalPro 3FE22 as tweeter, all "naked" without a box or baffle. These are driven by a Sony TA-F5000. Everything was measured with REW and EQ values calculated, which I then setup with the LSP plugins. I also use the LSP Crossover Plugin to divide between the subwoofer and the "top end" (the top end has a simple 1st order crossover at 600 Hz).

I am currently crossing the subs at 90 Hz.

Overall very happy with this system, as weird as it may sound... it's so crystal clear, it's just marvelous, and now it has plenty of punch in the lower octaves, which was missing. I also sit just 3 feet from the speakers... which definitely adds to the realism.

This was a fun project, thanks for everyone who helped out!
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Please someone correct me if I'm wrong:

If I now want to use an inductor to create a 90 Hz low-pass filter (1st order), I would need a 28 mH inductor, is that correct?

And since these are hard to find, I can connect two 14 mH inductors in series to achieve the same result I assume?

Each driver is wired in series, and should therefore be 16 Ohms.

Thanks ;)
A passive subwoofer crossover is almost always a bad idea. The inductors will be large and lossy, and it's still only a shallow slope. There's also the matter of matching the sensitivity to the rest of the system.

If those things aren't a concern, then 2x 14mH in series will do what you're looking for.

Thanks Chris.

So an active crossover would be a better choice if not using software? Is that simple to construct?

My reason for wanting to go passive or analog active is, that I prefer using the volume knob of my amp rather than hunting down the software dial...