Need help tuning

[Sandor the hun]

Hello, I have a 2226 in a 3.6 cubic foot box and would greatly appreciate it if someone could help figure out the port dimensions.
Thank you

[RMC]

Hi Sandor,

Assuming your 3.6 cu.ft. is NET volume and the usual QL 7 box loss, then Winspeakerz box design software gives the following:

Tuning the box at 40 hz is too low giving a dropping LF response from 125 hz down (- 3-4 db @ 50 hz). Tuning the box at 50 hz is much better since it gives you pretty flat LF response and an F3 of 48 hz.

As for the vent dimensions needed to achieve that tuning frequency and response, here are some suggestions in relation to cabinet size:

The software recommends a min. 42 sq. in. vent area (equivalent to a 7.3" tube), and suggests 2 X 6" tubes (56.55 sq. in.) with a length of 10.8".

However, to make it easier on you and give you more vent options re box size, you may be able to use somewhat smaller vents IF YOU WILL NOT drive the woofer at full capacity of 600 Watts. IF THAT IS THE CASE, then you may be able to use 2 X 5" vents (39.3 sq. in.) with a length of 6.642" or even 3 X 4" vents (37.7 sq. in.) with a length of 6.274", depending on input power...

The larger the vent area the better, but in practice this has to be appreciated in relation to box size [i.e. space available for vent(s)] and expected power input...

Regards,

Richard

[Sandor the hun]

Thank you.

[robertg]

Why does a 4350 have 6x3" ports, shouldn't they be larger? I have dual 2226 drivers in an 8 cubic foot box with 6x3" ports and it works fine. I have a 500w amp, but it doesn't get played loud very often and when it does, I don't do it for long.


Hi Sandor,

Assuming your 3.6 cu.ft. is NET volume and the usual QL 7 box loss, then Winspeakerz box design software gives the following:

Tuning the box at 40 hz is too low giving a dropping LF response from 125 hz down (- 3-4 db @ 50 hz). Tuning the box at 50 hz is much better since it gives you pretty flat LF response and an F3 of 48 hz.

As for the vent dimensions needed to achieve that tuning frequency and response, here are some suggestions in relation to cabinet size:

The software recommends a min. 42 sq. in. vent area (equivalent to a 7.3" tube), and suggests 2 X 6" tubes (56.55 sq. in.) with a length of 10.8".

However, to make it easier on you and give you more vent options re box size, you may be able to use somewhat smaller vents IF YOU WILL NOT drive the woofer at full capacity of 600 Watts. IF THAT IS THE CASE, then you may be able to use 2 X 5" vents (39.3 sq. in.) with a length of 6.642" or even 3 X 4" vents (37.7 sq. in.) with a length of 6.274", depending on input power...

The larger the vent area the better, but in practice this has to be appreciated in relation to box size [i.e. space available for vent(s)] and expected power input...

Regards,

Richard

[RMC]

Hi Robert,

RE: "Why does a 4350 have 6x3" ports, shouldn't they be larger?" They don't necessarily have to be larger individually. Total vent area is what counts to avoid port noise. And that's what YOU have.

JBL's extensive research into vents (e.g. for the 1996-7 HLA series, my all-time favorite for many reasons btw, even if it may sound crazy to some), has led them to insist on the usefulness/necessity of the larger vent area, the better, particularly at high power.

In designing the 4350 system the design engineer compensated for the smaller diameter vents by multiplying their number. Probably for reasons of space available, though sometimes its done for marketing reasons (i.e. appearance or look).

A 3" port has almost 7.1 sq. in. of area. Multiply this by 6 such ports = 42.4 sq. in. or the equivalent of a 7.35" tube. So what you have in reality is like a 7.35" vent. Looking at pictures of the 4350B's baffle, I don't see much space where a 7.35" vent would have fitted properly. Since design engineers are smart fellows they used a number of smaller vents that have an equivalent area to 7.35"! Such size reduction, though, doesn't imply one can easily use a pile of straws to do the same job... Then you'd get hit by other issues one of which is mentioned below.

When multiple vents are used (more wall area) there is a vent length fine tuning or correction that needs to be done which you may or may not have done on your DIY box. This is covered in some JBL papers, and its related to increased "... air friction on the greater wall surface area."

In theory, JBL could have utilized the unused baffle space top right or top left on 4350 that is reserved for horn/lens and tweeter mounting, depending on right or left mounting of these two, but then they'd have no more left or right mounting option remaining for the high frequency drivers, if one such space is occupied by a large vent.

I'm not claiming this is the reason for the 4350, but lets not forget there is also an important marketing aspect in relation to commercially sold speakers. A large/huge hole in a box doesn't look good either to sell. In several ways, Yes "marketing is king" when it comes to having to sell as many as possible). The DIY fellows do not necessarily have this major constraint.

Regards,

Richard

[robertg]

Thanks, I was under the impression that if you have two drivers you have to double you port area.

[RMC]

Hi Robert,

RE: "Thanks, I was under the impression that if you have two drivers you have to double you port area."

Just to avoid any misunderstandings.

Note that I have not commented on the suitability or not of a vent area of 42.4 sq. in. (equivalent to a 7.35" tube given as e.g.) for a 2 X 2226 box, powered by 500 or 600 W or more, since I have not modeled it, plus the intended tuning frequency was not mentioned, and I didn't want to spend time guessing Fb without Lv.

A 4350 using double 2231, 2234 or 2235 (with continuous program ratings from 100 to 300 w depending on each driver) VS a double 2226 box with each driver rated at 600 W AES continuous pink noise, it may be a different ball game in terms of required vent area at such high power. The lower the Fb and/or the higher the input power, the worst it gets if too small a vent area...

Going from one 2226 in a 4 cu. ft. box to two 2226 in a 8 cu.ft. box does require doubling of vent area for same tuning. The rule being: compared to a single woofer box, double identical woofers in double the box volume requires double the vent area, but with the same vent length as for the single woofer box.

"500w amp, but it doesn't get played loud very often and when it does, I don't do it for long." Not pushing it does play in one's favor if too small a vent area, however if one does beat the hell out of the box sometimes its another matter at that point... Regards,

Richard

[Ian Mackenzie]

FWIW the 4355 uses two 5 3/8 inch ports (see enclosure plans in reference section)

[RMC]

RE: two 5 3/8 inch ports for 4355

This is relatively consistent with the 4350's 6 X 3" vents.

A 5 3/8" vent has 22.7 sq. in., so two of these = 45.4 sq. in. (equivalent to a 7.6" tube)

The six vents on 4350 represent an area of 42.4 sq. in. (equivalent to a 7.35" tube)

So not a big difference here, only 3 sq. in. in favor of 4355. And this slight increase may be explained.

4350B (2231H, 200 w cont. prog. each), 4355 (2235H, 300 w cont. prog. each). The higher woofer(s) power input capability logically leads to that little larger vent area.

But there's more to it if we "look under the hood".

In both boxes (4350B/4355) the bass reflex chamber volume is the same, given as 9.5 cu.ft. However, a place where they're also different, in the low end, is box tuning frequency:

4350B: "Proper loading to 25 hz is accomplished by a distributed port consisting of six openings." (Spec sheet)

4355: "Proper loading to 32 hz is accomplished by a distributed port consisting of two large curved tubes." (Spec sheet)

So JBL not only changed the woofers but also the tuning frequency, while keeping same chamber volume.

Tuning a little higher puts less strain on a woofer in terms of VLF reproduction, plus requires a little less vent area. At the same time, the boxes' rated LF input capability increased from 200 w cont. sine wave (4350B) to 300 w cont. sine wave (4355). Therefore, continuous program material capability goes from 400 to 600 W. The latter requiring a little more vent area. So there's a balancing act that was done here...

Going down from 32hz to 25hz may not seem like a big challenge for some, but it would have been a tough job for such a woofer at these newer higher power levels. Moreover, then the red light gets on: larger vent area required!

But there's only a limited amount of space available on the baffle panel where JBL gathered the stuff re wall mounting in large studios. The design engineer sure knew what he'd be faced with when he modeled the box and decided on Fb 32 hz, and two 5 3/8" vent tubes. Note the LF response of the 4355 has a slight bump around 50 hz whereas the 4350B is flat at that point. Could be the result of the little higher tuning and balancing act...

Richard

[Sandor the hun]

Thank you all for your help

[Ian Mackenzie]

The 2216 was used in the prototype 4350.


“Walter Dick placed responsibility for the development of what would eventually become the 4350 in the hands of a recently hired engineer named Pat Everidge. Ed May would be re- sponsible for the development of a brand-new bass driver for this system, the 2230. This was JBL’s first 15" driver to utilize a cone damping treatment that JBL named Aquaplas to lower the driver’s resonant frequency and extend deep bass response. Ed also developed a new 12" driver, the 2202, specifically for application as the mid-bass transducer for this system. The pre-existing 2440 and 2405 filled out the driver lineup.”

Ref Stereo Sound article

Edit reason incorrect reference

[Robh3606]

The 2230 woofer that was developed for the prototype 4350 was the first JBL short gap long coil woofer designed for higher power, deeper box in smaller enclosures than the LE15.


Hello Ian

IDK The Le-14A has the same power handling and is also a long coil short gap and much earlier. Also the same bandwidth in about 4 cubic ft.

Rob :)

[Ian Mackenzie]

Quote

“The development of these systems was made possible by Ed May’s design for a new bass driver which would evolve to become the standard for JBL’s large format monitors for the next two decades. This driver was the 2231, with its con-
sumer counterpart designated as the 136A. Prior to the de- velopment of the 4350, JBL’s standard 15" driver for both monitors and home speakers was the 2215/LE15A. This transducer had an outstanding reputation for accurate re- sponse, but was limited in power handling. The 2230 that Ed May developed for the 4350 was the first JBL driver to use a very long coil, short gap topology. The longer coil handled more power and dissipated heat more effectively. It also allowed for greater cone excursion which increased dynamic range and output.

To fill out the monitor lineup, Pat Everidge took on the de- sign of the 4340/41 in 1973. This was a scaled down version of the 4-way concept introduced with the 4350 that em- ployed a single 2230 (later replaced with the 2231) with smaller mid-bass and compression drivers. This design had the wide, linear bandwidth of the 4350 with only a small reduction in maximum acoustic levels. It proved to be a very popular monitor and, in updated versions, would gain unex- pected demand as a home speaker, particularly in the Japa- nese market.

As previously stated, the 2230 was coated with Aquaplas to enhance its low-frequency extension. While this worked very effectively in the 4350 with its low 250-Hz crossover, it was found to be problematic with the higher crossover points needed for two- and three-way designs. The heavy, damped cone proved to have an uneven and falling response in the upper mid-bass region. To address this, Ed May came up with the unique solution of a mass control ring. This was a metal ring affixed at the junction of the cone and the coil former. It provided the mass needed for low-frequency ex- tension while permitting the use of a stiff, lighter cone for extended mid-bass response. This revised transducer would be employed in all of JBL’s new 15"-driver monitors, in- cluding an updated version of the 4350. Its domestic coun- terpart, the 136A, would find its way into the L200B and L300.”

Ref Stereo Sound article

[Ian Mackenzie]

Hello Ian

IDK The Le-14A has the same power handling and is also a long coil short gap and much earlier. Also the same bandwidth in about 4 cubic ft.

Rob :)

I think my initial reference was a little inaccurate.

Anyway it’s a great read on what led to the development of the 2231A. I have a 2231A driver which has since been reconed with a 2235H kit.

At the time the 2231A was the latest development and an impressive woofer which l used in my diy 4343.

[ivica]

I think my initial reference was a little inaccurate.

Anyway it’s a great read on what led to the development of the 2231A. I have a 2231A driver which has since been reconed with a 2235H kit.

At the time the 2231A was the latest development and an impressive woofer which l used in my diy 4343.

Hi Ian,
I think that changing suspension on 2231a would have been better solution then C2235 recon kit...
As 2231a is very nice sounding bass driver on my opinion relative to 2235...

Maybe i am wrong, VC height on 2231 is about 15mm ( 3/5"), but on 2235 VC height is about 19mm ( 3/4")
Regards
Ivica

[Robh3606]

I think my initial reference was a little inaccurate.

Anyway it’s a great read on what led to the development of the 2231A. I have a 2231A driver which has since been reconed with a 2235H kit.

At the time the 2231A was the latest development and an impressive woofer which l used in my diy 4343.


Agreed they are really nice woofers! If look at the T/S tables you can see that the 2231A and Le-14A have the same Re/Le/X-Max/Fd and Pe so it looks like common coil and pots.

[Ian Mackenzie]

I think it’s in context of being a 15 inch driver as used in all the pro monitors which used a 2215-2216 used previously.

[Ian Mackenzie]

Hi Ivica,

It wasn’t a consideration 30 years ago.

At the time it was all about reliability.

[Ian Mackenzie]

Anyway the reason for raising the 2230 was the 4350. As you know they put 2235H’s in the 4355.

Regards the LE14 or the more recent iterations l don’t think anyone is claiming is not a long v.c driver. The LE14 might be subjectively a better woofer for domestic hifi (as in the L250) and maybe the guys over in JBL Pro were not talking to the guys JBL Consumer. That sort of culture was/is part of the American business model.