JBL 2155H In Open Baffle

Status
Not open for further replies.
Jump to Latest
G

Gungnir

Member
Joined 2013
#1
So, I got a pair of these (new in the box) at an estate sale a while back and they have been sitting around begging to be used.

I have never heard an open baffle and I noticed that these were [briefly] mentioned in the JE Labs open baffle shoot out, but no mention as to how they sounded (maybe they sucked).

I want to use these in a JE Labs style open baffle with a 45 (or mayber a 71a) SET amp. The room is fairly large, but with a nice rectangular shape.

I noticed these coaxials are very effecient @ 102 db per 1 w, but the qts seems a little low @ 0.47.

I guess I am not out much if I just build it as I only paid like $20 US for the pair 😀
 
#3
As an infinite baffle...

attachment.php


OB will roll off sooner so it would need EQ but only has 2.5mm Xmax so probably would not take well to that.

However I really like its potential as a transmission line...

attachment.php
 

Attachments

  • JBLcoaxIB.png
    JBLcoaxIB.png
    15.4 KB · Views: 746
  • JBLcoaxTL.png
    JBLcoaxTL.png
    17.3 KB · Views: 691
#7
Gungnir said:
I want to use these in a JE Labs style open baffle with a 45 (or mayber a 71a) SET amp.

I noticed these coaxials are very effecient @ 102 db per 1 w, but the qts seems a little low @ 0.47.
Click to expand...

Note that the amp will have a high output impedance plus wiring will add a bit too, so effective Qts' will be higher, so needs to included in the design. Factor in that it's common for drivers to have a bit higher Qts than published, its Qts' could be 2x or more higher: Qts' = Qts + any added series resistance: mh-audio.nl - Home

GM
 
#9
GM said:
Note that the amp will have a high output impedance plus wiring will add a bit too, so effective Qts' will be higher, so needs to included in the design. Factor in that it's common for drivers to have a bit higher Qts than published, its Qts' could be 2x or more higher: Qts' = Qts + any added series resistance: mh-audio.nl - Home

GM
Click to expand...

That's good info, thanks! I'm gonna go ahead and build these, just didnt want to spend $50 and a Saturday if they were going to sound like crap. I noticed the Altec 604's have somewhat similar specs and those are have been used in OB (with helper woofer).
 
#10
You're welcome! Don't know how optimum the baffle is, but you can take a cheap 25 ohm pot in series to dial in any low Qt driver to maximize bass relative to the mids, then add a suitable power resistor. This of course may make the highs too muted, requiring a bit more complex XO, though in your case you should be able to adjust/tweak the horn's XO.

GM
 
#12
Yes, the cab will be too small due to the high Qts' and due to how a SET amp 'tracks' the impedance it ideally would need a larger cab tuned to Fs, so add 4-8 ohms of 'Rg' and alter tuning to see how it impacts your design.

GM
 
Status
Not open for further replies.
Top Bottom