QTS/OB explanation needed

[MJK]

OK, I understand your question now. Adding fiber to a closed box will increase its apparent volume slightly, I tend to believe a 10% increase if it is really packed. This increases Vb which impacts alpha and thus Qtc, it reduces the spring of the box and really does not provide any damping of the driver.

 

[InclinedPlane]

Oh, heh I just noticed your location. I just moved from Cohoes back to Maine last year, but I knew Clifton Park well.

 

[MJK]

Cohoes to Maine, you upgraded significantly!

I live at Exit 8 off I-87, one exit north of Cohoes. Been to Cohoes many times, nice old city with some interesting looking buildings which were probably pretty spectacular in their prime.

 

[voltcontrol]

If my question is not correct, please tell so;

can the Q(ts) of a driver be to high for OB/Dipole use?
And if yes what and why this limitation?

 

[v-bro]

There is hardly a need for a specific Qts because the driver needs correction anyway, at least when it is too low a damping factor you can always add a series resistor. I have used from PA up to car woofers in OB with great results... For low bass extension a low Fs can be useful... I can't imagine it can be too high, what value are we speaking about anyway?

 

[voltcontrol]

Data is scarce on these cheap units (about 15/25 Euro's a piece) i'm looking at..


Outdoor and basket-Ø: 300 mm
Max. load (music): 200 W
Sine: 120 W
Mounting-Ø: 280 mm
Installation depth: 110 mm
Frequency: 26-4600 Hz
Impedance: 4 Ω
Resonance Frequency: 33 Hz
Noise: 89 dB
Qts: 2.14
Vas: 425 l
Weight: 1940 g

Or

Outdoor and basket-Ø: 380 mm
Max. load (music): 250 W
Sine: 150 W
Mounting-Ø: 350 mm
Installation depth: 130 mm
Frequency response: 20-4000 Hz
Impedance: 4 Ω
Resonance Frequency: 35 Hz
Noise: 88.6 dB
Qts: 1.63
Vas: 697 l
Weight: 2910 g

The idea is to (test) setup a cheap linkwith-like dipole sub before i start pouring a lot of money into this kind of enclosure. I want to know if i like the results and experience what the (construction/calculation) difficulties with this kind enclosure are..

(Third option Perhaps?)
*Power handling: 150 watts RMS/300 watts max *VCdia: 1-1/2" *Le: 2.64 mH *Impedance: 8 ohms *Re: 5.62 ohms *Frequency response: 24-1,000 Hz *Fs: 24 Hz *SPL: 93 dB 1W/1m *Vas: 14.98 cu. ft. *Qms: 3.71 *Qes: 0.37 *Qts: 0.34 *Xmax: 4 mm *Dimensions: A: 15-1/8", B: 14", C: 6".

Groeten uit Kerkrade/Waalwijk btw (I see that you're Dutch 🙂 )

Ps I'll use active correction, no passive components.

 

[preiter]

This is an awesome thread. I've been working on trying to develop a more intuitive understanding of driver Q for a while and these are the best explanations I have seen.

Open baffle bass is tough to beat. Once you hear it, "bass" stops being this separate entity and just blends in with the rest of the music.

 

[InclinedPlane]

I recommend avoiding drivers with a Q over 1.0 for the simple fact that the motor tends to be too weak to control the cone very well.

 

[Rudolf]

I recommend avoiding drivers with a Q over 1.0 for the simple fact that the motor tends to be too weak to control the cone very well.

Lets assume a dipole driver with Qts = 2 and another one with Qts = 0,25. Both with Fs = 50 Hz. At Fs the first driver will be 6 dB above its nominal SPL level, the second driver will be 12 dB below. You have to push the low Q driver 18 dB at 50 Hz to follow the SPL curve of the high Q driver. In other words: You have to increase the sound pressure almost tenfold, meaning you have to throw about 70 times the energy at the low Q driver than at its nominal level. At the same frequency the high Q driver works with the same energy as at its nominal level.

Forcing 70 times the energy through the low Q driver means reducing its control over the cone to the seventieth part of the original control.

I know that this is a very rough comparison, but control is not a constant value.

 

[GM]

......can the Q(ts) of a driver be to high for OB/Dipole use?

Yes, once the Qts is high enough that the driver IS the baffle, i.e. needs no baffle, then this is the practical limit. Carver's Amazing Loudspeaker woofer array used custom woofers with a ~3.5 Qts IIRC: Stereophile: Carver Amazing Loudspeaker (Platinum Edition)

GM

 

[GM]

I recommend avoiding drivers with a Q over 1.0 for the simple fact that the motor tends to be too weak to control the cone very well.

For a wide BW use, I agree, but (mid) woofer systems, not so much since if the correct baffle loading is chosen its roll off will damp the driver(s) somewhat.

GM

 

[GM]

Forcing 70 times the energy through the low Q driver means reducing its control over the cone to the seventieth part of the original control.

Viewed another way, an OB is the inverse of a high gain TL, so as the long TL that only has the same pipe area as the driver's effective piston area (Sd) wants a strong motor (low Qts), the unfolded TL (OB) wants a proportionally weaker motor (higher Qts) and smaller baffle.

GM

 

[Don Hills]

So underdamped systems produce more bass with less power, but roll off quickly and have a resonant peak at F3. Hum hum hum--and equalization can flatten the total amount of energy, but can't stop the overhang/humming.

I think you will find that equalisation does stop the overhang/humming. The secret is to match the equalisation to the resonance. If you have, say, a 6 dB peak at 50 Hz with a Q of 1.2, then applying a 6 dB dip at 50 Hz with a Q of 1.2 will correct it, both in frequency (continuous) and time (impulse) measurements.

 

[InclinedPlane]

Well I should have said '.6-1.0 seems to be the range that provides the best sound to my humble ear'.

 

[rjbond3rd]

Viewed another way, an OB is the inverse of a high gain TL, so as the long TL that only has the same pipe area as the driver's effective piston area (Sd) wants a strong motor (low Qts), the unfolded TL (OB) wants a proportionally weaker motor (higher Qts) and smaller baffle.

My head just exploded 🙂

 

[GM]

Hope it didn't hurt for long. 😉

GM

 

[brookbh]

So after reading this read and many others on OB over the past year or so, there seems to be several basic implementations of open baffle woofers:

1) high qts drivers like the alpha 15s, goldwoods, other in-exspensive drivers
2) low fs, high sensitivity pro drivers with a q around .3 to .5, higher x-max than alpha 15s or goldwood 18,15,etc..
3) drivers like the augie or AE dipole

So here is my noob question,I have seen a few members here and other sites suggest the sigma pro 18, how would go about implementing a low q driver such as this in a standard flat open baffle?