4th order bandpass enclosures, importance of a drivers' Q

Puggie · 16th October 2006, 03:33 PM

I'm trying to build a Unity style horn, the main difference is my mid drivers need to be compact and I intend to house them in 4th Order bandpass enclosures with the port firing into the throat of the horn. I'm looking at small drivers (typically 3"ish) with a Fs in the region of 150-300Hz. Most of these have a high Qt, am I right in thinking this will seriously reduce the bandwidth giving me somewhat of a one note wonder box?

Would it be feasable to vent the rear, sealed chamber of the bandpass box through an aperiodic vent to the outside, this lowering the Q of that part of the system, widening the bandwidth?

please tell me if this is stupid, I'm really just thinking out loud at the moment, My aim is to get from about 200Hz up out of these bandpassed mids, I'm hoping to cross them over to the compression driver at about 1400Hzish.

thanks for any advice.

richie00boy · 16th October 2006, 03:41 PM

Can you not used a fully sealed rear chamber? Will that not get you enough SPL you think? Although I wouldn't think box type would have much impact in the >200Hz range anyway, just as long as it's not overly small.

Puggie · 16th October 2006, 04:38 PM

Well I don't know hence I'm asking, most of what i have found has a Qt of 0.8-1.5 ish which seems very high, I wondered if there was a way to reduce this if its going to affect the width of the pass band.

I havn't found any closed back mids available in the uk for sensible money, I'm really at the testing stage so I'm looking in the sub £10 a driver bracket (Visaton FRS 7 etc from CPC). Eminence LA6s seem an obvious candidate but no one in the UK seems to be able to get them, only the Alpha 6s.

Please suggest anything that I can get in the UK cheap and easy.

richie00boy · 16th October 2006, 05:44 PM

I think a sealed box will be fine. I'm pretty sure that once you get above 200Hz any box effects are no longer there, as the cone is not really moving any great distance and the wavelengths get small.

Also high Qts is not a problem as long as the resonance is well down out of the passband.

16th October 2006, 03:33 PM	#1
Puggie diyAudio Member Join Date: Oct 2004	4th order bandpass enclosures, importance of a drivers' Q I'm trying to build a Unity style horn, the main difference is my mid drivers need to be compact and I intend to house them in 4th Order bandpass enclosures with the port firing into the throat of the horn. I'm looking at small drivers (typically 3"ish) with a Fs in the region of 150-300Hz. Most of these have a high Qt, am I right in thinking this will seriously reduce the bandwidth giving me somewhat of a one note wonder box? Would it be feasable to vent the rear, sealed chamber of the bandpass box through an aperiodic vent to the outside, this lowering the Q of that part of the system, widening the bandwidth? please tell me if this is stupid, I'm really just thinking out loud at the moment, My aim is to get from about 200Hz up out of these bandpassed mids, I'm hoping to cross them over to the compression driver at about 1400Hzish. thanks for any advice.

16th October 2006, 03:41 PM	#2
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	Can you not used a fully sealed rear chamber? Will that not get you enough SPL you think? Although I wouldn't think box type would have much impact in the >200Hz range anyway, just as long as it's not overly small. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

16th October 2006, 05:44 PM	#4
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	I think a sealed box will be fine. I'm pretty sure that once you get above 200Hz any box effects are no longer there, as the cone is not really moving any great distance and the wavelengths get small. Also high Qts is not a problem as long as the resonance is well down out of the passband. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

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16th October 2006, 04:38 PM	#3
Puggie diyAudio Member Join Date: Oct 2004	Well I don't know hence I'm asking, most of what i have found has a Qt of 0.8-1.5 ish which seems very high, I wondered if there was a way to reduce this if its going to affect the width of the pass band. I havn't found any closed back mids available in the uk for sensible money, I'm really at the testing stage so I'm looking in the sub £10 a driver bracket (Visaton FRS 7 etc from CPC). Eminence LA6s seem an obvious candidate but no one in the UK seems to be able to get them, only the Alpha 6s. Please suggest anything that I can get in the UK cheap and easy.

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