I recently bought some unclaimed drivers from a local re-cone shop. I have two JBL 2220's and a JBL 2240. I also have some PSD 2002's with flares left over from another project. Any suggestions on how best to use these ?

Thanks

Dave

For a seven π cornerhorn, you'll want to make the motor cabinet 2ft3 tuned to 80Hz. A 5.5" diameter hole cut through a 3/4" baffle will tune it nicely. But since you also have 2240's, you might build subwoofers from them, and then just put the 2220's in sealed or bass-reflex cabinets for midbass duty. I'd probably still go with PiAlign recommendations, and use a 2ft3 tuned to 80Hz for the 2220's. I'd probably run an EBS alignment and use the same subwoofer cabinet as I normally recommend for other JBL 224x 18" woofers. So I'd say put the 2240's in an 8-10ft3 cabinet tuned to 30-35Hz.

The PSD2002's will do nicely for tweeters, but if the 2220's are like the 2205's, you'll need a midrange subsystem. I think JBL is still selling 2123's, so that would work out just great.

I was wondering about the term EBS alignment. I have (mis)understood that the point of reflex tuning is to tune the enclosure at the Fs of the driver, to limit the cone excursion at resonance.

I thought that an EBS alignment essentially said "let the driver look out for itself, I'm tuning this thing as low as I possibly can".

You indicated an EBS alignment for the 2240 was 8-10 ft^3 at 30-35 Hz. Since the Fs of the 2240 is nominally 30Hz this would seem to be "normal" reflex tuning.

Can you help me understand this terminology better?

Thanks

Response from EBS alignment

You can see where the alignment gets its name. Bass response is extended from peaking at very low frequency, and a region of lower output is formed - an "extended bass shelf."

This and other alignments are shown on the post called "Response curves of closed vs. vented systems."

In answer to your comment about tuning the enclosure to Fs to limit cone excursion at resonance consider the following: the only maximally flat acoustic (i.e., without electronic compensation) BR alignment with Fb equal to Fs is for drivers with a Qt of 0.383. Drivers with a lower Qt have Fb greater than Fs, while those with higher Qt's have Fb below Fs. The resonant blurring of the sound is easily avoided by using alignments with minimal peaking from below maximally flat and to above maximally flat. For each driver there is not one unique alignment that will produce high quality bass, but a continuum of alignments that can produce good results, from a minimally peaked EBS thru maximally flat up to those with a db or so of rise above flat.

With respect to the need to damp the drivers resonance consider the following:
1) Once enclosed in a BR cabinet the driver no longer resonates at Fs. The cabinet and driver interact, producing two resonances (Fl and Fh). The cabinet is generally tuned to produce bass extension with minimal peaking-whatever Fb is required to do this. Note that a response with minimal peaking is only possible over a relatively limited range of cabinet volumes. To (over?) simplify, the nearest analog to Fs in a BR is Fh, where the cabinet air stiffness is added to that of the driver raising its resonant frequency. Its resonant frequency has been moved upward due to interaction with the cabinet resonant system (mainly air stiffness), and - the new resonant frequency is Fh. At Fl, the port air mass has been added to that of the driver, producing a lower resonance. Hence the twin impedance peaks characteristic of BR's. This is somewhat of an over simplification but it does provide some insight into what is happening. The breakthrough of T & S was to quantitatively analyze the system as coupled resonant circuits via analog filter theory, allowing the accurate modeling of system response.

With respect to damping of Fs, and the resonant booming and total distortion chaos that result when Fs is undamped consider that some very fine sounding low frequency systems have been designed using open baffles and drivers with high Qts. This is very similar to an IB of large volume. For most well designed drivers, if you stay within Xmax, distortion will not be a major problem.

The only BRs I have heard that had resonance problems (and were properly located in the room) were those with fairly large peaking. I recall a Cerwin Vega that developed a low frequency howl when fed white noise (not all CV's did this). The salesman about lost it.

Hope some of this is helpful.

Regards,

AstroSonic

Thank you *very* much.