How to tune a JBL 4530 scoop???

[djnagle]

Hi All, I have a pair of JBL 4530 scoops with JBL 2225 drivers as bass bins in my main system. I think the bass should be a bit tighter. They sound looser than the ones from my memory. In the first back chamber is lined with semi-hard batting and that is all. If I add stuffing, will that tighten the sound up a bit? There also seems to be a 3 to 5db dip in the upper drum region. Will stuffing bring that up? Thanks in advance.

[Paul D]

Are you sure that the 2225's are fresh? The reason I ask is because a friend of mine had a pair of 2226's in bass cabinets that were used heavily for years. It was hard to tell that they were tired because visually they appeared to be perfect. He started to notice the same thing (lack of punch) so he reconed the 2226's and the difference was unbeleivable.
Apparently, the rigidity of the cone must have broken down or something.
I was surprised that this could happen without voice coil failure or at least some kind of visual clue!

[djnagle]

You might be onto something. These drivers are old and WELL worn. A friend of mine has a NIB pair of 2226 drivers. Maybe I can talk him into using them for a test.

I just looked at the plots for the 4530 here in the library and see a big dip in the 150hz range. Maybe that is what I am hearing...or not in this case. Is that what a notch filter is for?

Here is a link to the plot.

[FONT='Times New Roman','serif']http://www.jblpro.com/pub/obsolete/Low_Frequency_Enclosures2.pdf[/FONT]

[subwoof]

The stiffness of the spider and surround are important for the speakers to work correctly in the 4530. Old 2225's are going to be suspect. I suggest finding a pair of fresh 2226 or 2227 for the scoops.

As far as insulation, little difference was noted since we used them 150 and down in loud PA apps. I will be assembling a group of four with 2227 / 2397 / 2441 in the spring and will need to manage the crossover region ( 800 ) so the insulation issue will be important.

notch filters are almost always used to remove not add on passive networks.

sub

[Robh3606]

I just looked at the plots for the 4530 here in the library and see a big dip in the 150hz range. Maybe that is what I am hearing...or not in this case. Is that what a notch filter is for?

What matters is your in room response and you need to measure it to know what's going on. The measured response on the graph becomes useless below about 300hz or so where the room dominates what you hear. If you have a room mode issue no amount of EQ will bring a Null up. They act like black holes and trying to EQ them just sucks headroom out of your system. You can use EQ to tame peaks to some degree but not deep nulls. Your best bet is to find the best possible placement in the room first and then use EQ only if absolutely necessary and sparingly at that. If you look at any of the older "Room Correction" 1/3 Octave Eq's like a Urei 539 they are all cut only for that reason. Also remember that nulls are less audible than peaks but it depends on how wide or narrow, low or high Q, the notch is. Room nodes can be really narrow, high Q, especially in a basement with solid concrete walls as an example.

Rob

[djnagle]

Hi Rob, I just called a friend and left a message for him to bring over his measuring stuff so we can do just that. My experience in this room so far as not shown a null at that point with all the other speakers I've had in it. I've placed these scoops in five different locations with no real effect on the dip. I have four sliding glass doors with curtains over then. If I open all or some of then (effectively big bass traps) I get the same effect. The floor is carpeted, the ceiling has accoustic tiles and the back of the room "L" off to a larger room. By opening the bi-fold doors a bit behind the speakers into large closets, they also become bass traps. All to no avail....same problem. But the measurements will show where the problem actually lay. Also, If I run my two subs up to 180hz, they fill the dip in nicely but muddy up the lower signals. This one has really got me stumped.

[Robh3606]

Hello djnagle

Well that should help. What ever it turns out to be I hope you can find an easy fix for it. Keep us posted

Rob

[jcrobso]

Are they vertical or horizontal?

[djnagle]

Here is one, then the room shot.

[jcrobso]

The dip in response occurs when it switches from horn loading the bass to the direct radiation of the 15" speaker. I have a pair of home made C40 rear loading horns and they have a similar effect, but since the C40 is a little smaller it is not so pronounced. I used a graphic equalizer to help balance out the curve. Keep us posted.

[Eaulive]

Those are beautiful cabinets you have there! Not sure about that red horn though

[djnagle]

Those are beautiful cabinets you have there! Not sure about that red horn though

Hey, what can I say, I'm an artist: can't help myself.

[Flemming Skov]

Very nice speaker set-up! I'm also using the 4530 (E140 + 2240 sub's) in my living room and when measuring at the listening position I'm not in trouble with the inherent dip from rear loading. I think my room respons help flattering the natural dip at around 150Hz out!

How did it end up at your place?

Regards
Flemming