My 4520 project

[Lee in Montreal]

The reason why I bought these cheap $200 4520s despite their age and flaws was to study their construction. I haven't yet found the ideal location for a connecting plate. Also, I am surprised that JBL didn't include a brace on the center of the front panel up to the rear panel. Not much wood at the front and certainly a weak area, prone to vibrate. Originally, the rear panel wasn't even braced to the forward panel and only had two timbers to dampen the vibrations. Not to mention that I suspect that the enclosure's dimensions were partially dictated by JBL's bean counter wanting to put as much of the 4'x8' sheets in that box. Sides are 48" tall + 2 x 0.75", which means less cut, less waste, cheaper to produce. I would do the same if I were a business.

Basically, many mods have been made by people who have reproduced these cabinets in order to make the cabinet less resonant. So, an original 1970s 4520 might be great for collectors, but most likely, any other iteration from a third party is probably better constructed.

[jcrobso]

I used a pair of 4520s for a Church sound system as subs, loaded them 2226s and crossed them over at 100HZ if I remember correctly. I could shake the whole room with them.
If you want to use 12' speaker for a mid I would suggest a JBL 2206 it is an excellent speaker.
http://www.jblpro.com/pub/components/2206.pdf

[Eaulive]

More recones
http://www.flickr.com/photos/eaulive...th/5618187086/

[maxwedge]

You've got some work to do!

[Eaulive]

You've got some work to do!

Yup, and I still miss two baskets

[Lee in Montreal]

Yup, and I still miss two baskets

I have empty baskets ;-)

[Eaulive]

I have empty baskets ;-)

I know you do, don't tease me

[subwoof]

I have made hundreds of the single and doubles since 1980.

Yes there are numerous bracing and pathway mods that improve performance but remember that when the factory cabs were popular the majority of speakers and amplifiers were WAY below the 200 watt level so those parameters didn't come into play.

The most popular model I made was a single 18 variant of the 4520 - it could fit through normal doors, had a large mouth and went deep enough ( singularly ) for the SR guys who rented to raves.

sub

[Eaulive]

Nice weather today, I finished my midbass horn prototype, we'll see tomorrow if the weather allows some sweeps

Don't mind the quality of work, it's a rough prototype, unfinished and it's not for the living room.

I'm a butcher



Full set here: http://www.flickr.com/photos/eaulive...7626260334894/

[Lee in Montreal]

Nice.

100Hz to 800Hz?

[Eaulive]

Nice.

100Hz to 800Hz?

theorically the cut-off is 125Hz, we'll see after that how high it goes before going bezerk but I hope to reach 1k.
The driver goes flat to 4k according to specs but I doubt the construction allows it.

[Lee in Montreal]

2118j ?

[Eaulive]

2118j ?

Nope, B&C 12PE32, for lack of an E120 or a 2204H

[Lee in Montreal]

Hey Olivier.

Today I will reinforce the front baffle as it tends to vibrate (not buzz) even at medium output level. It think the front baffle is a very weak point. I will simply brace it with the baffle behind. Iptimally, it should be two 3/4" skins, or one HDF 1", still with bracing. I am very happy having purchased these cheap 4520s as it allows me to clearly see the weakness and improve the forthcoming units I will make.

[Eaulive]

Good!
Experimenting, I like it

I sweeped my midbass cabinets today but even outside there's a lot of reflections, first sweep gave me a sharp 20dB null at 400Hz, I almost put the box on the curb

The backyard is very small, around 16' between the house and the fence, so I tried different positions and I came up with this.

At first there was no damping in the back box, so I made some runs with no cover, with damping, etc.

This is the result I get, which is not so good but there's too much reflection in this back yard.



This is at 2m on-axis from the horn mouth, not the driver, with 4VRMS.
At 300Hz the SPL is 106.1dB, I checked it with my SPL meter for reference next to the microphone I use for the sweep.

Microphone Earthworks M30
Audio interface Lexicon Lambda
Software DSSF5E

So much for loading down to 125Hz but it should be useable from 150Hz to 1.5kHz with some EQ