JX92S and baffle step compensation

Status
Not open for further replies.
Jump to Latest
#2
In a normal-shaped speaker box, high frequencies behave as if radiating into half-space, and low frequencies behave as if radiating into full-space. Low frequencies have such long wavelengths that they don't "see" the speaker's front baffle and act like a point source. High frequencies have such short wavelengths that the front baffle acts like an infinite plane, so high freqs act like a point source radiating into only one side of that plane. [Actually, the radiation pattern at mid/high frequencies is more complicated because of beaming and diffraction effects, but put that aside for the moment.]

So if you placed this speaker box into an anechoic chamber, high frequencies would have a 6dB boost compared to low frequencies.

Here's a longer discussion:
http://www.quarter-wave.com/General/BSC_Sizing.pdf

One way to eliminate baffle step effects is to place speakers directly against a wall, because the wall extends the speaker's baffle. Here is what Ted Jordan has to say on the matter (although he doesn't specifically address baffle step effects).

"[D]espite convention, there is strong argument in favour of placing the loudspeakers as close to the wall as possible. This reduces the time lag between the direct sound and the reflection from the 'virtual images' and substantially improves coherence and spatiality. (The ideal, but usually impractical, solution, is to mount the drivers in the wall where there would be no virtual image)."
http://www.ejjordan.co.uk/basics.html

BTW baffle step applies to multi-way speakers as well as single-drivers. Most commercial speakers have some sort of baffle step compensation built into the crossover circuit. The speakers are "voiced" for an assumed listening environment; note how higher-end speakers have some sort of recommendation for where they should be placed, i.e. "at least three feet from any wall" or what have you.
 
#5
neil_kaye said:
dumbass thanks for the brilliant response.
Looking at teds site i would need the following circuit:
Resistor: 4.0 ohms
Inductor: 2mH

Where would i find these parts and how are tehy wired?
Click to expand...
http://madisound.com/pdf/capcoil.pdf

I am 95% certain that the resistor and coil are in parallel to each other, but in series w.r.t. the speaker terminals, like L_bsc and R_parallel in figure 3 from the whitepaper I linked. The copy on the Jordan website is a bit confusing to me.
 
#7
Jordan Mini-monitor Baffle Step

At the 2001 Washington, DC DIY Loudspeaker event, Dennis Murphy measured the performance of my Jordan JX92S mini-monitors which had won the Atlanta DIY Loudspeaker event a month or so earlier. Note the in-room response with and without baffle step compensation at the link. The 'with BSC' data yields a much flatter and better sounding response vs. the 'without BSC' case.

The BSC for the mini-monitor speakers was a 1.5 mH inductor and a 4 ohms resistor connected in parallel and then that network placed in series with the positive lead of the speaker. While this type of BSC network does decrease the sensitivity of the speaker by 3 dB, the better balanced frequency response are well worth it. Other two-way designs that I have used (for instance with the JX92S with a ribbon tweeter) are designed to achieve BSC inherently within the crossover circuit so no additional components are needed.

Scroll down the DC DIY2001 results and measurements to see the Jordan mini-monitor data near the end of the page.

http://murphyblaster.com/content.php?f=DIY_2001.html
 
#8
Planet10,
Thanks for the link, but i am still not sure how to wire a passive BS compensation circuit. Do you have a link to a circuit diagram?
What manufactueres would you recommend to go with the Jordans?
How difficult would it be to fabricate a passive line level circuit for a 3886 chip amp? Would this even be recommended?
 
#10
Jim,
The resistor that you used, what make and wattage was it?

Did you find a sound difference between using an air-core or a copper coil inductor and if so how does the gage of the copper foil play into the results assuming the same mH across the board?

You actually mentioned to me in a recent email about a BCS and i just glossed over it, now with more research it is like "duhhh" of course
Thanks for the help
 
#11
Neil,

I typically use Mills 12 watts non-inductive resistors for most speakers. Only for higher power speakers would I use multiple resistors to increase the power handling.

On coils I typically use 14 to 16 gauge air cored units for such individual BSC cricuits. For tight packaging I might use laminated core inductors for the most inductance in the smallest package.

Jim
 
#12
Dumbass said:
....Most commercial speakers have some sort of baffle step compensation built into the crossover circuit. The speakers are "voiced" for an assumed listening environment; note how higher-end speakers have some sort of recommendation for where they should be placed, i.e. "at least three feet from any wall" or what have you.
Click to expand...

Are you sure ?

Neither the Spendor speakers I use now, nor the B&W speakers I used previously have any such compensation. They just have standard cross-over networks, with a small amount of impedance compensation, to allow for the rising voice coil impedance of each driver.

Neither of these speakers sounds particularly bass-light, quite the reverse in fact !
 
#13
cs said:
Are you sure ?

Neither the Spendor speakers I use now, nor the B&W speakers I used previously have any such compensation. They just have standard cross-over networks, with a small amount of impedance compensation, to allow for the rising voice coil impedance of each driver.

Neither of these speakers sounds particularly bass-light, quite the reverse in fact !
Click to expand...
Could also be compensated for in the tuning of the cabinet, if not in the crossover circuit. It all comprises a system, and manufacturers will be doing in-room measurements, multiple prototypes, etc etc, to make the speaker sound the way they want it to.
 
Status
Not open for further replies.
Top Bottom