JBL Compression Drivers 8 and 16 Ohm

[Bubo]

Any driver I bought off eBay I would buy with the assumption that it's going to need new diaphragms. These are pro drivers, and may not have led a sheltered life in a home stereo setting. When I bought my 2360s, they had 2450s mounted and were from a church. I bought them for the drivers, the horns were physically too large for my home, but they are nice sounding horns - basically the top of the butt cheek line. Elephant butt cheeks.

That said, 2450s are generally plentiful on eBay, there's a pair of 2450J on there for $450 now. Neo magnet, newer phase plug (that the 2446 also has IIRC). Slap some 8 ohm 'phragms in there and go to town.

The likely reason the sheets match the 2446/2360 is just because they are from the same era, not any inherent synergy.

The Horns are toooooo-large for my home too, but I just got the call that my 4 2360s are ready for pick up, so I'm off to rent a van...........

The low-cost used-drivers that I hoped to score formerly lived in a THX movie theater, I suspect that they had a strenuous daily workout.....for years.

I have to play with my spreadsheet some more, dropping a resistor across the leads to a 16 Ohm driver bringing it down to 8 Ohms may be a good thing in several ways.......that I haven't quite grasped yet...........I may have to activate my second, and only remaining, brain cell.

I know that phase plugs have cult-followings, Altec Tangerine comes to mind. I'll have to study the JBL ones to even know their names.

Then there is the whole AlNico, Ceramic, and Rare Earth Magnets discussion...............

A brief video of my research facility.....

 

[Bubo]

Certainly, it can be wired in the signal chain, and some of it's functions used in that manner. But in your 2.0 setup scenario it won't be acting as a crossover. In any configuration it can only split the signal ahead of the amplifier stage.

The real question would be whether the filters for any single output will swing far enough to create an essentially full range pass band.

There is no place like a bench, there is no place like a bench, there is no place like a bench.

 

[1audiohack]

The impedance rating is the an average "resistance" of the coil to an AC voltage signal usually over the majority of the linear range of use of the driver. This is not measured by an Ohm meter which uses a measured amount of DC.

Barry.

 

[Bubo]

Four 2360s arrived, I would say VG++ or NM if they were records. One nick on the L bottom lip.

Still have to inspect the other two, and the four adjustable mounts and flanges.

Will probably look a little tall on top of a LaScala 1 cabinet.

Surface is grainy or rough, perhaps to keep the reflections at a min.

I'll have to see how they balance out on a plywood base, given that I want them to extend 12in to the rear.

They are huge, but smaller than expected. I was actually relieved when I went to pick them up.

The small box on the R has my K-55V drivers that I need to sample first, while I finalize what I am doing with the drivers, crossovers and coin to pay for it.

 

[GordonW]

There's so much magnet strength in these compression drivers. that the back EMF from the voice coil movement, increases the effective impedance the amp "sees", to a MUCH greater degree than with woofers. So, a compression driver with 8-10 ohms DC, will EASILY act like the same effective AC impedance as a woofer with a 12-14 ohm DC resistance (normal for 16 ohm woofers).

Regards,
Gordon.

 

[VolvoHeretic]

Do you need four more? There are some that look just like those 60 miles away from me for $200 each.

http://www.bismanonline.com/rugby_nd/jbl_large_format_horn_speaker_works_great_new_t

 

[Bubo]

I'm a marketing guy, so I'm comfortable at component and systems level, design is new, even a simple one.

All constructive input welcome.

If its not constructive, please make it humorous.



Crossover Design

Goal: keep it simple and low cost, and preferably sounds good.

Off the shelf 8 Ohm Crossover: Eminence PXB-2 500Hz, 2-way ($40 x 2 = $80)

Match 4 ohm Woofer to 8 Ohm Amp
Existing LaScala Bass K-33 4 Ohm produces 105db @ 1W 1M
- Use a Crites Autoformer to match at 8 Ohms, cost $35x2= $70
- The 4 Ohm driver is already matched to 8 ohms in the Klipsch Design, so I am assume no change in output specs (hopefully I am correct).
- Since Klipsch doesn't have any dual woofer designs I can think of, I don't know why the K-33 was selected as 4 Ohms?

Match 16 Ohm Compression Driver to 8 Ohm Amp
JBL 2in Compression Driver and 2360 Horn: 118db @ 500 Hz rolling off above 10K
- If I go with the 16 Ohm version and run it parallel with 20 Ohm (100W?) resistor, it pulls it down to 8.9 Ohm = increase of 2.7db @ 500Hz to 120.7db (118 + 2.66).
- 16Ohm + 20 Ohm = 0.0625 + 0.05 = 8.8888888889 Ohm
- Playing with my spread sheet, the addition of the 20 Ohm resistor to the 16 Ohm Driver does two good things, it creates an 8 Ohm load, and it cuts the variance in the resistance at frequencies to a range between 7.5 and 10 Ohms, instead of 12 to 18. (2.5 vs 6 Ohm variance). This from looking at the little chart on the spec sheet, not exactly scientific, more like darts.

Matching the 2 Driver Outputs to 105db
So the question becomes how best to match the Compression Driver at 120.7db to the Woofer at 105db at 500 Hz?
I have two options, use an auto-former in 1db increments, or an L-pad?
The autoformers sold by Crites max out at -12db, and it appears that I need -15 16db est.
This leaves the L-Pad at $25x2 = $50
I believe that this is where JBL and Altec on ended up on their designs.


Crossovers... $80
Autoformers .$70
L-Pads..........$50

Total............$200

Some terminal strips, or connectors, and a little bit of wire, some boards and a few screws.

Maybe some paint if I want to go all out.

Estimate $300 for the compression drivers, if I'm lucky.
New Aluminum Diaphragms, if I don't like the factory Ti....add $200-230

 

[Bubo]

Do you need four more? There are some that look just like those 60 miles away from me for $200 each.

http://www.bismanonline.com/rugby_nd/jbl_large_format_horn_speaker_works_great_new_t

Looks like they are in N Dakota.

I wonder which drivers are on there, and if he is including them for the $200.00 each.

I was told that the ones I purchased with the throats and mounts came out of a Theater that went belly up.

At 200 with the drivers, they are a pretty good deal when you take the driver and shipping into account.

I purchased 4 with mounts and flanges, 4 more than I need...... but I couldn't stop myself.....

 

[toddalin]

Four 2360s arrived, I would say VG++ or NM if they were records. One nick on the L bottom lip.


Match 16 Ohm Compression Driver to 8 Ohm Amp
JBL 2in Compression Driver and 2360 Horn: 118db @ 500 Hz rolling off above 10K
- If I go with the 16 Ohm version and run it parallel with 20 Ohm (100W?) resistor, it pulls it down to 8.9 Ohm = increase of 2.7db @ 500Hz to 120.7db (118 + 2.66).

No you wouldn't increase the volume and in fact could decrease it a bit. While you've reduced the impedience thereby using more power, this power is dissipated as heat through the resistor and not as more volume to the horn.

JBL uses 10 watt resistors for this. I used 12 watt Mills pieces. Remember that after the signal goes through the crossover, the horn actually receives very little power. And if the resistor is 20 ohms and the speaker is 16 ohms, the speaker gets more power than the resistor by virtue of its reduced resistance.

The 20 ohms resistor is not really intended to lower the impedience, but to serve as a "buffer" to stabilize the changes in impedience with frequency.

 

[toddalin]

Looks like they are in N Dakota.

I wonder which drivers are on there, and if he is including them for the $200.00 each.

I was told that the ones I purchased with the throats and mounts came out of a Theater that went belly up.

At 200 with the drivers, they are a pretty good deal when you take the driver and shipping into account.

I purchased 4 with mounts and flanges, 4 more than I need...... but I couldn't stop myself.....

If you are on a "spree," there are four available in So Cal with 2445Js for $1K for all. No affiliation.

http://www.recycler.com/details/63421281/speakers-professional-jbl

 

[bowtie427ss]

I don't want to sound too crazy here, or sound like a broken record. But, it seems as though a fella that had 4 of these puppies at his disposal might be able to liquidate a pair to offset the cost of enough DSP and amplification to do a proper bi-amp set-up.

There are really sweet sounding reasons that a few of us keep mentioning "bi-amp" and "DSP".

 

[bowtie427ss]

please delete dupli-post

 

[Bubo]

I don't want to sound too crazy here, or sound like a broken record. But, it seems as though a fella that had 4 of these puppies at his disposal might be able to liquidate a pair to offset the cost of enough DSP and amplification to do a proper bi-amp set-up.

There are really sweet sounding reasons that a few of us keep mentioning "bi-amp" and "DSP".

My house looks like an amp museum, Yamaha.

The concern I have the with DBXs of the world is that they don't publish a SN number for their units.

Also if you are trying to be an analog purist, aka vinyl to speaker, introducing quantinization error violates this.

If I find the coin, I may yet get one to play with, always wanted to jack my sub into the LaScala Mac rack.

 

[donprice]

Also if you are trying to be an analog purist, aka vinyl to speaker, introducing quantinization error violates this.

If I find the coin, I may yet get one to play with, always wanted to jack my sub into the LaScala Mac rack.

Be a rebel! Drop $125 for the the 2x4 miniDSP and use it to work out the crossover in the digital domain and then use those results to as a model to have someone try to work up a passive filter design for analog purity. You can use the same unit to experiment with adding the subwoofer and/or super-tweeter by running it as 3 or 4-way mono.

You can experiment a little without getting hooked on the digital dope