A few questions about a system redesign.

[chris661]

Ladies and Gentlemen,

As some of you may know, I'll probably be going to university in September.
I know its a way off, but I realise that the rooms there are fairly small: certainly too small for my tapped horns (even just one of them).

So, I started thinking of other ways I could use the drivers I have (namely a pair of TB W6-1139SG, and a pair of Fostex FE126eN). Amplification will be a reasonably powerful amplifier for the subwoofers (currently 120w/ch), and an amp6b from 41Hz (good for 10w/ch into 8ohm).

I'd like to keep the amplifiers the same, but was thinking of making the subwoofers into midbasses, crossing over at more like 150-250Hz, and applying a Linkwitz Transform to the woofers to make them go low in a small box.

I was thinking of keeping the ML-Voigt pipes for the Fostexes, making a cabinet of similar size for the tapped horns, then stacking them so the Fostex cabinets are sideways. This would keep the centre-to-centre spacing nice and small.
However, this is not mandatory: a sealed box for the Fostexes yields a 2nd order rolloff, f3 of ~220Hz, which is handy.

My thoughts are that a higher crossover point would yield more headroom for the Fostexes and tripath amp, and a sealed cabinet with eq for the bass drivers would allow a degree of choice of bass extension.

So, the questions I have for you guys (feel free to ask questions of your own) are...

1 - has anyone tried the W6-1139SG (or other - SI, SH, etc) up to ~200Hz? Did it work well?
2 - any opinions on going sealed instead of the more popular ported choice for these drivers (passive radiators are unlikely to be an option)?

Thanks in advance

Chris

[mdocod]

When going sealed with these drivers, it's very easy to run out of thermal Pe long before running out of Xmax if the box is too small, which would be a real shame... My suggestion is model up the box size such that Pe and Xmax both cap out at the lowest frequency you intend to transform the system flat to.

The tiny box LT setups work best with drivers with enormous thermal Pe, the 1139 series don't really fall into that category.

[chris661]

You make a good point.

Running winISD, the Apparent Amplifier Power shoots well over 100w, despite excursion staying small - this was with the recommended ~5L cabinet.
Going to ~15L each (larger than a ported box) means the excursion gets large (>11mm one-way) at 100w.
The eq is set for Q=0.7, f3 of 18Hz.
There's also a 2nd order highpass set to 18Hz.
When the power handling limit is reached, the overall SPL is in the mid-90s of decibels.

This seems like a reasonable compromise: very good low-end extension, not much SPL available, but for a university dorm room (ie, nearfield), I would expect the mid-90s figure to suffice.

F3 = 23Hz, f6 = 18Hz, f10=15Hz. Not bad.

Chris

[mdocod]

Keep in mind that the "calculated" vented box would actually be much larger, since the vent has to be enormous to get the low tuning and handle the air velocity, in fact, modeling a vented enclosure for a driver with these characteristics may not be the best thing anyways, as such an enclosure would embark on TL theory pretty heavily. It would be interesting to see the variation in simulation from a TL simulation to a vented box simulation with equal box and "port" (line) dimensions.

[bjorno]

I'd like to keep the amplifiers the same, but was thinking of making the subwoofers into midbasses, crossing over at more like 150-250Hz, and applying a Linkwitz Transform to the woofers to make them go low in a small box.

Hi Chris,

If you avoid power-lossy approaches: You might try to build a T-QWBR using 2xTB-W6-1139SG drivers instead.
This Tapped-Quarter-Wave -Bass-Reflex -Sub will have a large usable BW from 22 to 145Hz.
If using a LR4 XO at 145Hz the level at 250 Hz will be 20 dB down =

Maximum allowable XO- frequency that can be used that is not drawing attention from the main-speaker dominant phantom LF localization cues that defines the in heard/visual height lower boundary of a sound-stage reproduction.


b

[mdocod]

Hey b,

That's really cool. never realized hornresp could do so much! Going to have to tinker more with it!

Eric

[chris661]

I have to admit, the form factor is rather nice.
I don't know how you keep churning out these pages, bjorno, but you're an asset to the forum.

The plan was to have the woofers and Fostexes on the same baffle, so that a more traditional crossover may be used - I'd be able to crossover up to 1kHz (though the woofers have a step in the response there: I'd rather go to ~300Hz) - this would take some stress away from the Fostexes: while some use them as full-range, dedicated subwoofer drivers are much better for bass.

While I'm not sure that the above design would facilitate such use, it is a very cool design, and I've stored it away so I can build it at a later date.

Best regards
Chris

[chris661]

Having pondered this for a while, I've decided that perhaps a ported design would be best as general purpose: after all, when used sealed, the Xmax and Pe run out at the same time at around 15L.
This is about right for a ported cabinet for these drivers, so I'm considering...

- Having the port blockable so the cabinet will be sealed
- Having a switchable LT circuit to extend the low end of the sealed cabinet way down.

The cabinet itself works out neatly as a 13" by 13" by 9" (hwd) box, including the 2L internal volume for the Fostex driver.

I could use some help on the crossover, though.

The Fostex rolls off (sealed) at 200Hz, 2nd order (Qtc = 0.707). If I added a 2nd order electrical crossover, would I then need a 4th order crossover on the woofers to maintain symmetry? Is a symmetrical crossover needed?

Thanks for any help in advance.

Chris

[mdocod]

I'm of the belief that symmetry is only important if it benefits the end result. Many successful speakers systems use a smattering of different effective roll-offs in order to achieve a desired final result. As I recall, the 1139 has a light roll off as well as it reaches into higher frequency so that may help balance things out. Personally I would be tempted to see about something as simple as a 1st order on the woofer and moving the x-over point higher. Maybe you can get some degree of BSC through simple attenuation of the high frequency driver and a shallow slope on the low pass.

With any luck, someone with more experience than myself will chime in on the matter.

Eric

[jerome69]

Mister Chris,

Go to bass reflex cabinet ... Less boxy sound and more quiet for your future neighbors.

To minimize space, mini-monitor + separate sub
You could hide the sub. You can do 2.1 or 2.2, i think one sub per channel is better. Don't need to complexify thing, you don't need a low pass for the monitor. Perhaps if you want do do a parties, a crossover will be useful.

10.5L@61Hz Fostex docs
http://www.fostexinternational.com/d...e126e_encl.pdf

Sub with W6-1139SG 12L@38Hz
Crossover frequency 60Hz.

Your can go further in the concept, a true 2 ways monitor + sub.
Fostex FE126E +
Perhaps with this setup you will not need for a sub in a small room ?

Regards.