Baffle Width and BSC

[mortron]

Hi there, I always worry I am in wrong subforum, so feel free to move if needed and apologies.

I am planning a 3 way using 2245, 2251J and a 1" yet to be determined. As it stands now, I have some 8 cubic foot ported cabs for the 2245, and am looking to put an enclosure into service for the 2251J soon. I need to determine a few things first on that. These will not necessarily be permanent and am considering what enclosure route to choose. I am not sure if I will use my DSP active system, or try to pursue a passive crossover yet, if that matters.

Is there any benefit to the all in one large wide cabinet like the 4345 uses? I'm guessing baffle size still plays some factor in low end response? Is utilizing separates like some others and Greg Timbers uses in his Array horned system better?

Reality is that I'll never make an exact 4345 replica for various reasons, but would like to know if it's worth pursuing a large all in one cabinet or separates? And what role of any baffle step would play in going from one large baffle to lower profile separates. Thanks in advance.

[Robh3606]

Interesting question

I have never used baffle step compensation on any DIY I have ever made. If you go through JBL schematics I have never seen it used even on the smallest systems like an L1 or L20T as an example. If you go with separate boxes depending on the size like a small cube as an example you might want to extend the baffle a bit depending on how much ripple you get in the drivers passband and to match the width of the lower cabinet.

The only modular work I have done is woofers with separate tops where they match the lower cabinets and are otherwise full baffle width. That's an L250 Jubilee top I had an MTM and a midrange waveguide as well and a HEIL too.

Rob

[RMC]

Weird? Don't think so, certainly unconventional compared to others. That said JBL doesn't have the monopoly on knowledge and designs. There's some advanced and patented electronic processing involved in the OWL system.

Can't reproduce Eargle's sketch and technical explanations about the system being copyrighted stuff. However,

"... a listener located on the primary axis of the system will localize left and right image sources slightly out-board of the loudspeakers, due to phasors created at the ears by the slight spacing between loudspeakers... As a result, the localization comes from two sets of complementary cues, resulting in a fairly large listening "sweet spot".

The Owl loudspeakers are primarily intended for use in postproduction spaces where the listening position of the remix engineer remains fairly consistent." (P. 383)

Different and interesting concept. Wide imaging for a stationary engineer...

[Eaulive]

Weird? Don't think so, certainly unconventional compared to others.

Well, that's what I meant basically, and I just realize now that it's in fact a stereo pair in a monolithic enclosure so it makes more sense.

Cool.

[Earl K]

@mortron

Troels Gravesen "The LoudSpeaker"

Troels thread ( which outlines a modern take on the 4345 & the design process for it ) is an excellent read and is highly recommended reading ( home-work ).

Note that he does dry-run "mock-ups" before committing to wood cutting.



Here's Troels Gravesen's measurement of a 2123h on a 30cm x 50 cm baffle ( set in the middle ) ;



Now here's the same 2123h on a larger baffle ( 65cm x 105cm ) > I assume with this larger baffle the JBL 10" was placed in the spot where his preferred 10" was located ;



One can quite easily see the response changes that 2 different baffle sizes ( and driver positioning ) actually make .


Obviously, making response measurements are critical to the whole process.

[RMC]

Since you're at design/testing phase no need to spend a lot for experiments:

RE wattage resistors, 10W Lynk metal oxide should suffice (Solen)

RE gauge coils, i posted elsewhere David Weems' recommendations for coils:

For inductances from .1 to .32 mH, use 24 ga wire. For .33 to .51 mH, use 22 ga wire. For .60 to 1.28 mH, use 20 ga wire. For 1.4 to 4.3 mH, use 18 ga wire. "Avoid using wire of smaller diameter than that listed for a choke if possible." (p. 175).

RE they have 4.7mH but not 4.8mH, check qcomponents.ca, maybe they have 4.8mH ?

RE use just cheap caps for now? Solen has a lineup of yellow color 160V 5% tolerance polyester caps, bought a bunch for a small project and measured half dozen sample to see how good/close. They were at 3% tolerance! better than spec and similar to some more expensive black ones (don't remember the black models number but they have 250V, 400V or 630V).

Again its for preliminary and testing no need to overspend at this phase, later you'll be spending enough dough

[Ian Mackenzie]

Hi Morton

I had a look at your previous posts on the 2251J (pro driver).

There are some consumer variations of this driver.

Based on the pro driver specs below using a simple simulation the sealed enclosure and the ported BB4 enclosure are very compact

If you are using the 2245H woofer you can operate to up to the 4345 crossover point without an issues. Notions of the 2245 not being accurate in the 100-250 hertz region are a myth once room boundary interference is addressed in your Drive Rack.

In this situation you will find a critically damped sealed enclosure quite satisfactory and the easiest to implement. You can use a LR 12 dB or LR 24 dB or 3rd order BW network on the high pass and low pass active crossover. Some manual adjustments of each crossover slope will yield a good phase null at the crossover point (280-350 hertz) with your spl test equipment and the integration will be seamless.

Vb 6 litres plus volume of the driver say 7 litres or 0.25 cu ft3
Fb 152 hertz
F3 236 hertz
Loose filled with fibre glass (not tightly packed)

http://www.audioheritage.org/vbullet...hp?17040-2251J

If you are looking at a full active crossover l suggest a 2nd order BW low pass electrical filter @800-1000 hertz on the 2251J, and a 3rd order BW on the horn as a starting points.

Pad back the horn with 6.2 R series and a 6.2 R shunt fixed LPad to reduce noise from the horn. This will also act to protect your compression driver from clicks and pops.

Crossover Primer

Depending on your horn some specific response shaping maybe required. That can be addressed once you assemble your initial mid/ high frequency enclosure.

Below are some screen dumps of some measurements you might expect.
These are indicative voltage drives and driver response measurements showing in phase and phase reversal of the woofer & midrange. Such measurements can quite readily be made with REW and implemented with your drive rack. Greg Timber’s is an advocate of REW and has made reference to REW in some of his LHF posts.

A point to note and a misnomer is that a loudspeaker driver on a baffle is not going to behave like a text book driver on a IEC test baffle under laboratory conditions. Therefore your Drive Rack text book filters will need some editing or application of PEQ filters to the raw driver response before application of your crossover filters.

In the passive crossover world response shaping can now be incorporated into the crossover filter design with powerful Cad tools or by making trial and error adjustments to the crossover values.

Good luck with your project

If you get stuck or need a sounding board for ideas we are here to assist where we can

[turnitdown]

Interesting question

I have never used baffle step compensation on any DIY I have ever made. If you go through JBL schematics I have never seen it used even on the smallest systems like an L1 or L20T as an example. If you go with separate boxes depending on the size like a small cube as an example you might want to extend the baffle a bit depending on how much ripple you get in the drivers passband and to match the width of the lower cabinet.

The only modular work I have done is woofers with separate tops where they match the lower cabinets and are otherwise full baffle width. That's an L250 Jubilee top I had an MTM and a midrange waveguide as well and a HEIL too.

Rob

That is pretty sporty cutting down L250s, but then I am considering the same with L7s. My guilt has been dialed down.

My speakers, my rules, I get it. Your 250s look like they belong that way.

[Robh3606]

That is pretty sporty cutting down L250s, but then I am considering the same with L7s. My guilt has been dialed down.

My speakers, my rules, I get it. Your 250s look like they belong that way.

Hello turnitdown

My goodness no! Those are scratch built tops. I used the measurements from the L250 and built those tops from there. Thanks for the compliment in the sense I was close enough you thought I cut up a pair. I would would love to own a pair of stock L250's!

Rob

[mortron]

If I understand correctly, you're saying that a sharp transition between two different widths will cause the ripple? I noticed the angles cut down on Greg's setup, and it would make sense seeing your tops and bottoms mate. If I have my 8cuft cabs vertical, there is less width to contend with, but getting the HF at an appropriate height becomes an issue. If I place the cab on its side, things will be lower but the baffle wider and more floor bounce. I'll have to take some measurements and see where things will line up.

It's interesting your mention of lack of BSC in most designs you've encountered. I wonder if not dealing with BSC is one way to keep sensitivity up without losing some to BSC. Then again, any X.5 way design can also compensate for baffle step, and they've used that in a few designs. Don't some of the bigger dual 15" speakers have a woofer that is crossed lower than the other?

[Robh3606]

If I understand correctly, you're saying that a sharp transition between two different widths will cause the ripple? I noticed the angles cut down on Greg's setup, and it would make sense seeing your tops and bottoms mate. If I have my 8cuft cabs vertical, there is less width to contend with, but getting the HF at an appropriate height becomes an issue. If I place the cab on its side, things will be lower but the baffle wider and more floor bounce. I'll have to take some measurements and see where things will line up. It's interesting your mention of lack of BSC in most designs you've encountered. I wonder if not dealing with BSC is one way to keep sensitivity up without losing some to BSC. Then again, any X.5 way design can also compensate for baffle step, and they've used that in a few designs. Don't some of the bigger dual 15" speakers have a woofer that is crossed lower than the other?

Hello Morton

Actually a combination of step and actual box size used for the midrange. If you look around on the net you can find simulations that show the ripple and the differences between a circular vs a rectangular box. The larger the baffle width the lower in frequency it occurs so you could make the step insignificant depending on your lower crossover point vs baffle size.

I would say you are correct on about loosing sensitivity. Both Everest 2 and the 4435 have helper woofers crossed lower, so do the Urie 813 and 815 monitors.

Take some measurements and see what you get. Some people wouldn't think about building a speaker without BSC so it's design choice.

Rob

[Eaulive]

I have to ask... and maybe I'll regret it but, what is BSC?

[RMC]

Thinking about this some more I'm still not convinced regarding woofer size (e.g. 18") making a difference here or that LF diffraction loss is a thing usually applicable to smaller drivers in narrow baffles (as if they were mostly the only ones). For sure it applies to small woofer/narrow cab but what about other larger combos?

Putting a small woofer in a narrow box or a large woofer in a narrow box basically looks the same issue. For example, an 8" driver in a 10" wide box or an 18" driver in a 20" wide box seems like a similar problem to me.

I don't see this as being a woofer diameter or box size ALONE as an explanation. I think its more a matter of LF driver size VS cab size used (proportion of one to the other).

Putting a smaller woofer in a larger size box is probably where LF diffraction loss might be reduced, assuming cab is not already directly on the floor (2Pi) for example.

Interestingly, the OWL speaker system side panels do appear to make a difference when comparing free field (4 Pi) and half space (2Pi) frequency response data shown on WorthPoint link posted:

"response free field: 62 - 20,000 Hz +/- 2 dB fc reponse in wall: 60 - 20,000 Hz +/- 1.5 dB"

The 2 hz and .5 db differences are probably in the tolerance range. Response is practically the same with quite different mounting, whereas in free field (no boundary) LF response should be down by 6 db and its not. So the side panels on the OWL do appear to make a notable difference.

Have not seen the mounting instructions for the OWL speakers, but i guess these could be side panels in action for free field mounting and panels folded or removed for in-wall installation.

Remains the question of is it worth the work, effort or cost to do the same? I guess its for users to decide based on their own situation.

My additional two cents...

[mortron]

Sorry... Baffle Step Compensation.

The way I understand is at a given width, a driver's low end rolls off (6db/Oct IIRC) and must be compensated for. This results in a loss of sensitivity. Less of an issue with a giant baffle or wall mounted stuff. Hopefully someone more eloquent and knowledgeable than I can chime in too.

[Eaulive]

Sorry... Baffle Step Compensation.

The way I understand is at a given width, a driver's low end rolls off (6db/Oct IIRC) and must be compensated for. This results in a loss of sensitivity. Less of an issue with a giant baffle or wall mounted stuff. Hopefully someone more eloquent and knowledgeable than I can chime in too.

Ok, gotcha. You're referring to half space, quarter space, eighth space speaker placement? I never heard about a crossover compensation for that except on some amplified studio monitors, but usually this is done in the final EQ after setup is finished.
I don't know about baffle itself because at low frequencies the wavelength is usually long enough not to be bothered with a couple of inches.

Then again, this is way above my pay grade