What to look for in an OB driver?

Javachip · 6th September 2006, 04:21 PM

What T/S parameters or other specifications would predict good performance with an open baffle? I have read that Qts and EBP can be used to predict suitability for a sealed or vented enclosure. Are there any similar rules of thumb for selecting OB drivers? Thank you.

inrank · 6th September 2006, 05:19 PM

my understanding is mainly QTS, the higher the better for more bass, if you want to go loud you will need reasonable senstivity and X-max, and bigger cones generally do better (not gospel though)

more experienced people, please correct me if i am wrong...

badman · 6th September 2006, 05:47 PM

A higher Qts will tend to give you more bass energy. It also tends to correlate with a somewhat lower level of 'control', and if you're going to equalize anyway, lower Qts might work for you. Lots of displacement- either a lot of cones, or one (or several) large cones. High excursion is a bonus, if you can't get the output you want from less excursion, but higher excursion drivers usually aren't as high fidelity as lower. A large surface area moving very gently is what you want for best results.

planet10 · 6th September 2006, 09:10 PM

A large enuff open baffle basically brings the system Q to the same as that of the driver. So a driver of Q 0.5 to 0.7 on an arbitrarily large baffle will work well. If the Q is less you need EQ to bring the system Q up.

If you use a higher Q driver, then you can shrink the baffle size and use the dipole rolloff of the small baffle to bring the system Q down into the 0.5 -0.8 region that is ideal.

dave

Javachip · 7th September 2006, 07:09 AM

Thanks for the good info. To rephrase my question a bit, are there any drivers to stay away from for OB? For example, the air behind an OB driver is not pressurized and does not act as a spring to limit cone excursion, as might be the case in a box. Would certain drivers be at particular risk for reaching the limit of their excursion and bottoming out on an open baffle, compared to the same driver in a box?

planet10 · 7th September 2006, 07:27 AM

Quote:

Originally posted by Javachip
Thanks for the good info. To rephrase my question a bit, are there any drivers to stay away from for OB? For example, the air behind an OB driver is not pressurized and does not act as a spring to limit cone excursion, as might be the case in a box. Would certain drivers be at particular risk for reaching the limit of their excursion and bottoming out on an open baffle, compared to the same driver in a box?

Yes that is a real concern...

dave

Rudolf · 7th September 2006, 07:32 AM

Some more things to consider, which you will not find in the specs:

The driver should be sufficiently vented. Excessive noise from the pole vent for example will not bother in a closed box, but in OB it will.

If you are considering dipole for the midrange too, you should look for an "open" basket and a rather unobstrusive magnet. So you will not compromise the radiation to the back.

Rudolf

6th September 2006, 04:21 PM	#1
Javachip diyAudio Member Join Date: Dec 2005 Location: CA	What to look for in an OB driver? What T/S parameters or other specifications would predict good performance with an open baffle? I have read that Qts and EBP can be used to predict suitability for a sealed or vented enclosure. Are there any similar rules of thumb for selecting OB drivers? Thank you.

6th September 2006, 05:47 PM	#3
badman Custom Title diyAudio Member Join Date: Sep 2003 Location: Sunny Tustin, SoCal	A higher Qts will tend to give you more bass energy. It also tends to correlate with a somewhat lower level of 'control', and if you're going to equalize anyway, lower Qts might work for you. Lots of displacement- either a lot of cones, or one (or several) large cones. High excursion is a bonus, if you can't get the output you want from less excursion, but higher excursion drivers usually aren't as high fidelity as lower. A large surface area moving very gently is what you want for best results. __________________ I write for www.enjoythemusic.com in the DIY section. You may find yourself getting a preview of a project in-progress. Be warned!

6th September 2006, 09:10 PM	#4
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 4	A large enuff open baffle basically brings the system Q to the same as that of the driver. So a driver of Q 0.5 to 0.7 on an arbitrarily large baffle will work well. If the Q is less you need EQ to bring the system Q up. If you use a higher Q driver, then you can shrink the baffle size and use the dipole rolloff of the small baffle to bring the system Q down into the 0.5 -0.8 region that is ideal. dave __________________ community sites t-linespeakers.org, frugal-horn.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

7th September 2006, 07:32 AM	#7
Rudolf diyAudio Member Join Date: Mar 2003 Location: Germany	Some more things to consider, which you will not find in the specs: The driver should be sufficiently vented. Excessive noise from the pole vent for example will not bother in a closed box, but in OB it will. If you are considering dipole for the midrange too, you should look for an "open" basket and a rather unobstrusive magnet. So you will not compromise the radiation to the back. Rudolf __________________ www.dipolplus.de

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6th September 2006, 05:19 PM	#2
inrank diyAudio Member Join Date: Oct 2005	my understanding is mainly QTS, the higher the better for more bass, if you want to go loud you will need reasonable senstivity and X-max, and bigger cones generally do better (not gospel though) more experienced people, please correct me if i am wrong...

7th September 2006, 07:09 AM	#5
Javachip diyAudio Member Join Date: Dec 2005 Location: CA	Thanks for the good info. To rephrase my question a bit, are there any drivers to stay away from for OB? For example, the air behind an OB driver is not pressurized and does not act as a spring to limit cone excursion, as might be the case in a box. Would certain drivers be at particular risk for reaching the limit of their excursion and bottoming out on an open baffle, compared to the same driver in a box?

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