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Used JBL 2426J in PI? [message #43666]

Thu, 15 January 2004 11:10

GarMan
Messages: 960
Registered: May 2009

Illuminati (2nd Degree)

Is there anything I should be aware of when buying a set of used JBL 2426? I found a pro-systems place in town that's selling used units for a very good price. Also, the units that are available are the 2426J, 16 ohm versions. Are these usable in the 4PI configuration? X-over values would probably need to be adjusted.

thanks,
Gar.

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Also want to know about 2370A Flare [message #43669 is a reply to message #43666]

Thu, 15 January 2004 12:24

GarMan
Messages: 960
Registered: May 2009

Illuminati (2nd Degree)

Forgot to ask. Is there a substantial difference between the Eminence H290 flare and JBL's 2370A? Both are 90x40 and are designed to accept 1" throats. Is $100 USD a good deals for a used pair of the JBLs? This would still be $40 more than a new pair of H290.

thanks,
gar.

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Re: Also want to know about 2370A Flare [message #43672 is a reply to message #43669]

Thu, 15 January 2004 14:58

Wayne Parham
Messages: 18686
Registered: January 2001

Illuminati (33rd Degree)

Used 2426's can sometimes have damaged or second-source diaphragms. You can use 16 ohm versions, although as you've noted, the crossover was designed for 8 ohm devices. We discussed the values here, so you might try a search. I'll rummage around and see if I can find this information too. As for the horn flare, the H290 is much smaller and shouldn't be used below 1kHz. I'd keep 'em above 1.2kHz, which is OK since the PSD2002 really needs to be crossed higher too. The JBL 2370 is a much larger horn and can be used down to 800Hz.

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16 ohm vs 8 ohm drivers [message #43675 is a reply to message #43672]

Thu, 15 January 2004 15:26

GarMan
Messages: 960
Registered: May 2009

Illuminati (2nd Degree)

I did a quick search and I think I can gather enough information on XO values if I decide to go for the 16 ohm drivers.

However, wouldn't mind if I can be briefed on the advantages or disadvantages of using 16 ohms vs 8 ohms. Isn't a higher nominal impedence desirable for tube amps?

Gar.

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Re: 16 ohm vs 8 ohm drivers [message #43677 is a reply to message #43675]

Thu, 15 January 2004 16:38

Wayne Parham
Messages: 18686
Registered: January 2001

Illuminati (33rd Degree)

Honestly - It's best to model the circuit in Spice. Most online documents about crossovers and the difference between 8 and 16 ohm drivers are going to talk about the crossovers as if the load were resistive. They may mention a Zobel, which would then make the load impedance act more linearly, like a resistance. But the response curve of the π compensation network is shelved, with rising response at higher frequencies. It does this by using the voice coil reactance as part of the filter. So model the circuit with Spice to determine your values of R1, R2 and C1 when using a 16 ohm driver.

16 ohm π compensation network

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Re: 16 ohm vs 8 ohm drivers [message #43681 is a reply to message #43677]

Thu, 15 January 2004 21:25

GarMan
Messages: 960
Registered: May 2009

Illuminati (2nd Degree)

Wayne, I did a search under the H.Eff Speaker forum at the "other place" and found your post about 8 ohm vs 16 ohm speakers, and the need to match the impedence tap of the output transformer for maximum power transfer. Seems to make sense.

However, my question now is, if the two drivers in a 2-way are connected in parallel, wouldn't you need two 16 ohm drivers to build an 8 ohm speaker?

Gar.

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Re: 16 ohm vs 8 ohm drivers [message #43682 is a reply to message #43681]

Thu, 15 January 2004 21:58

Wayne Parham
Messages: 18686
Registered: January 2001

Illuminati (33rd Degree)

In a loudspeaker, the crossover prevents adjacent subsystems from being on-line at the same time. When a driver is making sound, it is being presented as a load to the amplifier. But when it isn't, the impedance of that leg of the circuit is very high, approaching an open circuit. The idea is that only the driver playing presents a load, and in the overlap region where both adjacent subsystems are transitioning, they both present a partial, medium-impedance load. So the overall impedance curve is rarely flat, but it does approach the advertised impedance in most cases.

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