[jwr159]

Hi all:

Have been using my Fertin full range field coil drivers in a JE Labs configuration for several years now. The overall sound is superb, but lacking in the lower end.

I am planning to add a pair of subwoofer drivers in a new OB configuration. The low end drivers have a high end frequency of 300Hz. The Fertins are 8 inch drivers.

I would like to (1) make sure the Fertins are integrated with the low end drivers and (2) limit the width of the OB to as small as practical.

What would be the ideal width?

Will 16 inches work?

Is there a formula for calculating the natural roll off frequency of a full range driver for a given width?

Appreciate any response. Thanks


 

[Rudolf]

Is there a formula for calculating the natural roll off frequency of a full range driver for a given width?

There are two different roll offs: The driver roll off, which is defined by its Qts value, and the baffle roll off, which can be simulated with www.tolvan.com/edge or calculated following http://www.musicanddesign.com/Equivalent_Baffles.html.

The diagram shows the roll of for some Qts values from 0.1 to 10:



1.00 on the x axis is Fs, 2.00 means 2 x Fs, 0.5 means half Fs etc.

You need to add the dB values of both to get the resulting combined roll off.

Rudolf

[nullspace]

I am planning to add a pair of subwoofer drivers in a new OB configuration. The low end drivers have a high end frequency of 300Hz. The Fertins are 8 inch drivers.

Do you have a link to the low-end woofers you have in mind? That would be very helpful in terms of us making some suggestions.

Also, any thoughts to how you'd like to crossover from the Fertin to the helper woofer? And, how about amplification? Are you planning on using a separate amp for the helper woofers?

Regards,
John

[jwr159]

Thank you kindly for the replies.

For amplification, I will be using the Transcendent Sound SE OTL for the Fertins. I was planning to NOT use a cross over for the Fertins.

I have a pair of Reckhorn A-401 amplifiers, which have an adjustable subsonic filter that ranges from 15Hz to 300Hz.

The low end drivers I plan on using are the 10 inch Augies from Hawthorne Audio.

My plan is to figure out the roll off for the Fertins and then integrate with the Augies by adjusting the sub filter on the Reckhorn amps. I am new to all of this so I am not sure if my "design" is stupid/unworkable or simple/elegant.

My listening room is very small. So the narrower the baffle w/o compromising performance, the better.

SPECS FOR AUGIES: 

10" low frequency augmentation driver

Ideal for bass augmentation in open baffle and infinite baffle configurations

Particularly well suited for small to medium sized rooms

Heavy cast basket

Santo Edge

Cast frame

Reinforced Paper cone w/ Mass plug

Knurled binding post factory installed

Cutout                         9 1/8"
Outside Diameter          10 1/4"
Power handling: 150 watts RMS.

Impedance: 8 Ohms

SPL: 88.7 dB 1w/1m

Qt:   0.65

Fs: 33.0 Hz

Magnet weight: 67ounces

[nullspace]

Since you plan to biamp and have some eq available via the sub amps, you can use as narrow baffle as you wish, strictly speaking. But, there are certainly trade-offs -- as the baffle gets more and more narrow, you'll need to add more and more eq, taxing both the amplifer and driver. Off the cuff, I don't think you'd want something more narrow than 24" or so, generally. Maybe 18" but that's definitely pushing it.

10" drivers are generally on the small side displacement-wise. If you haven't yet purchased them, you might consider the 15" Auggies. Certainly people have had good luck with one of the 15" per side on a narrow baffle. If it were up to me, I'd prefer to see 2x15" per side. I would think the Reckhorn won't have any issues with the 4ohm load, and the additional displacement is a nice thing. I have a relatively small room, 13'x18', and I don't feel the 2x15" AE OB15 per side are overkill at all.

Regards,
John