JBL 2245 : 10 or 12cft

[Lee in Montreal]

I 've been calculating a 4th order bass reflex cabinet at 10,1cft using Vb=(15)(Vas)(Qt2.87)

Then found F3 32,5Hz using F3=0.26(Fs)/(Qt1.4)

And Fb 27,3Hz (basically the port tuning) with Fb = 0.42(Fs)/Qt 0.9

What if I increased cabinet size to 12cft?
How lower will F3 be? Any drawback?

I want to build two cabinets to use up to 800Hz for home duty. No PA action here.

[ivica]

I 've been calculating a 4th order bass reflex cabinet at 10,1cft using Vb=(15)(Vas)(Qt2.87)

Then found F3 32,5Hz using F3=0.26(Fs)/(Qt1.4)

And Fb 27,3Hz (basically the port tuning) with Fb = 0.42(Fs)/Qt 0.9

What if I increased cabinet size to 12cft?
How lower will F3 be? Any drawback?

I want to build two cabinets to use up to 800Hz for home duty. No PA action here.

From some simulation program (BBox) minimal F3=32Hz, for 12cft (340 Lit) can be get for Fb=29Hz., while for 10cft box with Fb=27.3Hz, F3=35Hz.
So the differences from the calculated and simulated values I expect is
'coming' from the damping material influence.

The only drawback that I can see is maximal Xmax (cone displacement) is about 2mm greater for the same frequency, so limitation of about 9.5mm with the smaller box is reached at 16.9Hz, while for larger that is about 17.4Hz, all under 100W power 'applied' to the driver.
What would be the real solution depends mainly of the influence of the damping material applied in the box.

[Lee in Montreal]

Hi Ivica

Thanks for your insights. One subject I'd like to discuss with you as well as others is the port tuning. Some people will tune the ports to Fb (the cabinet's resonance), and others will tune to Fs (the driver's free air resonance in order to avoid phase cancellation at very low frequency. Myself, I would tune to Fs.

It is also my understanding that if a woofer runs lower than the port tuned frequency, it will "unload" and go into high excursion. Which is why I think that if Fs and port tuning are the same (20Hz in this case), then the driver could handle more power before reaching Xmas.

[Eaulive]

then the driver could handle more power before reaching Xmas.
The advantage here is if it doesn't handle the power and burns out before Xmas, you'll still have time to ask Santa for a new one :D

:leaving:

[Lee in Montreal]

BTW The intent of the project is to be flat fro 30Hz to 800Hz.

[Ruediger]

BTW The intent of the project is to be flat fro 30Hz to 800Hz.

... and end up at 22 Hz. You need an electronic xover which can give You the missing two orders: 4 orders come from the box, and two from electronic filtering.

See the Thiele papers.

Ruediger

[Lee in Montreal]

... and end up at 22 Hz. You need an electronic xover which can give You the missing two orders: 4 orders come from the box, and two from electronic filtering.

See the Thiele papers.

Ruediger

Hi Ruediger. You lost me here ;-) How will the 12db electronic crossover affect the lower end? Do you mean a small "bump" down there?

[Ruediger]

Hi Ruediger. You lost me here ;-) How will the 12db electronic crossover affect the lower end? Do you mean a small "bump" down there?

General Audio Discussions -> Technical References Thread -> Thiele Papers Part I -> Page 6 resp. 186: "Sixth-Order Butterworth Response". See also Figure 6 on page 8 resp. 188.

A filter of any order can be achieved by chaining filters of order one and two. Four orders will be supplied by the box, and two by the electronics.

You even have three choices, which two of the six orders You handle by electronics, and which four by the box. Not all of these choices will always lead to a good design.

There is a good design in the tables of that paper.

May I say "EV DX-38" again?

Ruediger

[ivica]

Hi Ivica

Thanks for your insights. One subject I'd like to discuss with you as well as others is the port tuning. Some people will tune the ports to Fb (the cabinet's resonance), and others will tune to Fs (the driver's free air resonance in order to avoid phase cancellation at very low frequency. Myself, I would tune to Fs.

It is also my understanding that if a woofer runs lower than the port tuned frequency, it will "unload" and go into high excursion. Which is why I think that if Fs and port tuning are the same (20Hz in this case), then the driver could handle more power before reaching Xmas.

From my point of understanding Fb is the frequency at which box+port make "resonance", where most of the sound is reproduced by port(s), and the depending of expect-able response of the whole system (driver+box+port) Fb is desired. My suggestion of tuning the system is based on "almost maximal flat response". That is usual tuning for "standard home or studio monitoring us", but, of course, the other more complicated solutions can be arranged. In such case ( flat-tuning) using "much" lower frequency then Fb is not suggest-able, mainly because of large cone excursion, and all the problems that are in relation with that.
You can find much more detail about in Thiele/Small papers or some presentation of their works.

On one place :


http://www.readresearch.co.uk/articles.php
http://www.readresearch.co.uk/thiele-small_papers/smalls_closed_box_article_1.pdf
http://www.readresearch.co.uk/thiele-small_papers/smalls_closed_box_article_2.pdf
http://www.readresearch.co.uk/thiele-small_papers/smalls_closed_box_article_3.pdf
http://www.readresearch.co.uk/thiele-small_papers/thieles_vented_box_article_1.pdf
http://www.readresearch.co.uk/thiele-small_papers/thieles_vented_box_article_2.pdf
http://www.readresearch.co.uk/thiele-small_papers/smalls_vented_box_article_1.pdf
http://www.readresearch.co.uk/thiele-small_papers/smalls_vented_box_article_2.pdf
http://www.readresearch.co.uk/thiele-small_papers/smalls_vented_box_article_3.pdf
http://www.readresearch.co.uk/thiele-small_papers/smalls_vented_box_article_4.pdf

http://www.readresearch.co.uk/loudspeaker_papers/klipsch_modulation_distortion_article_1.pdf
http://www.readresearch.co.uk/loudspeaker_papers/klipsch_modulation_distortion_article_2.pdf
http://www.readresearch.co.uk/loudspeaker_papers/klipsch_modulation_distortion_article_3.pdf

http://www.readresearch.co.uk/measuring_ts_1.php

[Ruediger]

From my point of understanding Fb is the frequency at which box+port make "cabinet resonance", and the depending of expect-able response of the whole system (driver+box+port) Fb is desired. My suggestion is based on "almost maximal flat response". In such case using lower frequency then Fn is not suggest-able.

When using the Thiele paper You start with Your drivers Qt. Locate an entry with the same Qt as that of Your speaker. If there is no exact match You need to interpolate. Read how Qt is influenced by DC resistance of cables and xover coils. Often You can adjust Qt by making it larger.

One column gives You f3/fs. Fs is that of Your speaker in air. F3 is the -3dB frequency of the whole system.

Another column gives You f3/fb. Fb is the box resonant frequency.

Yet another column gives You Cas/Cab which is equal to Vas/Vab. Vab is the box volume.

Ruediger

[yggdrasil]

BTW The intent of the project is to be flat fro 30Hz to 800Hz.

800Hz? IMO that will be stretching it.

[Allanvh5150]

JBL ran the 4430 and 4435 up to a 1K crossover with the 2235 and we all know how good they are. I have run the 2235 out to 1200hz and they sounded pretty good. Didn't do any real testing though, it was more of an experiment to compare them to a 2225 in the same cabinet. I also had a 2425 on top..

Allan.

[ivica]

After all, I think, for Lee_in_Montreal these links can be very use full:

http://www.lansingheritage.org/html/jbl/reference/technical/1983-subs.htm

http://www.audioheritage.org/vbulletin/showthread.php?24178-2245-Subwoofer-Box-12-Cubic-Ft





When using the Thiele paper You start with Your drivers Qt. Locate an entry with the same Qt as that of Your speaker. If there is no exact match You need to interpolate. Read how Qt is influenced by DC resistance of cables and xover coils. Often You can adjust Qt by making it larger.

One column gives You f3/fs. Fs is that of Your speaker in air. F3 is the -3dB frequency of the whole system.

Another column gives You f3/fb. Fb is the box resonant frequency.

Yet another column gives You Cas/Cab which is equal to Vas/Vab. Vab is the box volume.

Ruediger

I totally agree with you that all of the T/S are 'dependent' of other ambient things such, as: temperature, humidity, air pressure, amplifier output impedance, cable impedance, applied power, age of the driver, total operating hours etc, but keeping all of that in mind, T/S parameters are very good starting point for any loudspeaker project.

Some theoretical presentation of the influence of the T/S parameters variations in short, and nice presented in Dr.Keele publication:

http://www.xlrtechs.com/dbkeele.com/PDF/Keele%20(1973-05%20AES%20Published)Sensitivity%20of%20Alignments .pdf (http://www.xlrtechs.com/dbkeele.com/PDF/Keele%20%281973-05%20AES%20Published%29Sensitivity%20of%20Alignmen ts.pdf)


There are a lot off free calculating-predicting characteristics programs,
some short form formulas can be find:

http://www.audiogearreviews.com/tech/theory/enclosure_design/vented_enclosures.asp


examples:

http://www.randteam.de/_Software/AkAbak/Download-AkAbak.html

http://www.audiogrid.com/audio/avi(2).zip (http://www.audiogrid.com/audio/avi%282%29.zip)

http://image.ajdesigner.com/vc/ajvented.exe

and at the end, all of them suggest that, for 'bass-reflex' (Vented box) design make at list 30% LONGER port duct, and then, by "try-measure-and error" finally decide what would be acceptable duct(s) length.
From my point of view all of such measurements has to be done in appropriated "acoustical surroundings" (I suggest 'easier solution' would be open air at the roof-top, as we can see JBL did in early days), and has to be repeated in the real 'listening' room.

Concerning the project that would incorporate some kind of 'active" equalization Dr.Keele paper:

http://www.xlrtechs.com/dbkeele.com/PDF/Keele%20(1975-07%20AES%20Published)%20-%20New%20Set%20of%20VB%20Alignments.pdf (http://www.xlrtechs.com/dbkeele.com/PDF/Keele%20%281975-07%20AES%20Published%29%20-%20New%20Set%20of%20VB%20Alignments.pdf)

would be a good starting point, but as I remember there were some work "in that way" presented in upper mentioned:
http://www.lansingheritage.org/html/jbl/reference/technical/1983-subs.htm

May be some other use full links starting here:

http://en.wikibooks.org/wiki/Engineering_Acoustics/Bass_Reflex_Enclosure_Design#Introduction

[Robh3606]

Why are you guys making this harder than it has to be?? Run a simulation in a decent box program, tune for the desired frequency response and power handling and you are done.

Rob:)

[ivica]

Why are you guys making this harder than it has to be?? Run a simulation in a decent box program, tune for the desired frequency response and power handling and you are done.

Rob:)
I can agree with You if the intention is only "to make and forget", but if some kind of deeper understanding is the "goal", then more time has to be spent, and much, much more work too.

[Lee in Montreal]

800Hz? IMO that will be stretching it.

I don't think it is impossible. Look at the graph.

53654

[ivica]

I don't think it is impossible. Look at the graph.

53654
The "problem" is "dotted-line" which is usually 45 deg "off-axis" response, or better to say,
large driver tends to "beam". Under such you have -5dB on 800Hz

[Robh3606]

I don't think it is impossible. Look at the graph.

I think it would be better to look here:

http://www.audioheritage.org/vbulletin/showthread.php?10654-2245H

Rob:)

[JeffW]

I'm not sure about all the different models of speakers JBL made, but there's not many places the 2245 was used as anything but a subwoofer. The 4345 used a 2245, and crossed it out at 290Hz (I think, seems like 320Hz is another figure floating around in my head), but much lower than 800Hz.

[Robh3606]

Hello Jeff

Yes and if you look at the impedence curve in the referenced measurement you can see jogs at the dip and peak after 500Hz which is probaly why this is so.

Rob:)

[ivica]

I think it would be better to look here:

http://www.audioheritage.org/vbulletin/showthread.php?10654-2245H

Rob:)
Unfortunately, there is no "off-axis" response, but I think it is expect-able that over 500Hz, off-axis response stat to 'decline'

[1audiohack]

Build the 12 ft³ version, that way when you get your fingers out of your ears after your primary listening experience you will have the real-estate to add a dog box and a 10" or 12" driver. :p

[Allanvh5150]

I always find it odd that many people worry about off axis response but when they build a listening room, the seating position is always smack on axis.....:blink:

Allan

[Eaulive]

I always find it odd that many people worry about off axis response but when they build a listening room, the seating position is always smack on axis.....:blink:

Allan
Yes, swet spots sucks, and if the "direct / reflected of the walls" combination is important to you, then it becomes important.

[Allanvh5150]

Yes, swet spots sucks, and if the "direct / reflected of the walls" combination is important to you, then it becomes important.

Who mentioned a sweet spot? I just do not recall any listening rooms where the speakers are pointing at some angle.

Allan.

[ivica]

I always find it odd that many people worry about off axis response but when they build a listening room, the seating position is always smack on axis.....:blink:

Allan

May be for some other members it would be interesting to read Dr. Earl Geddes paper which is dealing with the Speaker Directivity

http://gedlee.com/downloads/directivity.pdf

and this too:

http://decoy.iki.fi/dsound/ambisonic/motherlode/source/Optimum%20loudspeaker%20directional%20patterns_Kat es_1980.pdf


For my personal experience: I do not like to "directiv" speakers

[Robh3606]

Who mentioned a sweet spot? I just do not recall any listening rooms where the speakers are pointing at some angle.



Do you mean facing straight ahead with no toe in towards the listener?? Mine sure are. I have toe in on all three of my fronts and my mains for the stereo rig.

Rob:)

[Lee in Montreal]

I just do not recall any listening rooms where the speakers are pointing at some angle.

I am surprised you haven't previously seen listening rooms with speakers angled toward the listener's seat. I've been doing it for the past 30 years and as far as I remember, I even think it is how most systems are installed. After all, isn't it what "on-axis" is about? :D

Back to the 10 vs 12cft topic, I managed to grab a simulation "software" to work on my Mac. Basically, nothing more than an Excel spreasheet but good enough. The difference between 10 and 12cft is not more than perhaps 2 Hz in F3 and Fb, reduced 50Hz SPL and increased excursion when feeding 350w.

[Robh3606]

I managed to grab a simulation "software" to work on my Mac.

That's the point I was making. It took you what 5 minutes if that to find the answer you were looking for.

Rob:)

[Lee in Montreal]

That's the point I was making. It took you what 5 minutes if that to find the answer you were looking for.

Actually, it gave me some clues, but didn't answer all my interrogations. Per exemple, the ports is de facto tuned to Fb. I can't find how to tune the port to the driver's Fs 20Hz, or somewhere between Fs and Fb.

So far it goes like that. 10cft vs 12 cft tuned at Fb 27,3Hz

Response. The thin green line is the gain/loss between 10 and 12 cft

53670

Excursion at 350w

53671

[ivica]

Actually, it gave me some clues, but didn't answer all my interrogations. Per exemple, the ports is de facto tuned to Fb. I can't find how to tune the port to the driver's Fs 20Hz, or somewhere between Fs and Fb.

So far it goes like that. 10cft vs 12 cft tuned at Fb 27,3Hz

Response

53670

Excursion at 350w

53671

Changing the size (typically the length) of the port-tube you can change "tuning of the WHOLE SYSTEM", (box+port resonant frequency Fb) and what would be the influence of such (tuning or changing) to the WHOLE SYSTEM RESPONSE, you can easily see using mentioned simulation programs.
Here are some examples:
it seems that "what-ever-you-do" you will get -6dB around 30Hz....
so it seems to me that optimum in maximal cone displacement "in band", and "out of band" would be the 'leading rule'.

[Lee in Montreal]

Changing the size (typically the length) of the port-tube you can change "tuning of the WHOLE SYSTEM", (box+port resonant frequency Fb) and what would be the influence of such (tuning or changing) to the WHOLE SYSTEM RESPONSE, you can easily see using mentioned simulation programs.

Yes. That I know. Only I haven't yet been able to find how to do it with the Excel simulator I have. ;)

[ivica]

Yes. That I know. Only I haven't yet been able to find how to do it with the Excel simulator I have. ;)
that depends on what are the INPUT and what are the OUTPUT variables to the program, and what kind of "constrains" are applied.

[Ruediger]

That's the point I was making. It took you what 5 minutes if that to find the answer you were looking for.

Rob:)

... such as Bessel, Butterworth, Cauer, Chebyshew and others.

These filters do have well defined properties and thus a predictable behaviour.

If You build *any* filter it will have *any* properties and *any* behaviour.

It is the merit of Mr. Thiele that he has made the design process rational. And You guys go back to the days when the punchcards were made from wood :)

Once You are used to the table in the Thiele paper it will take You less than a minute to understand what is possible with a certain drver, and what not.

Ruediger

[4313B]

Once You are used to the table in the Thiele paper it will take You less than a minute to understand what is possible with a certain drver, and what not.I personally use Bass Box Pro these days.

The tables were all we had back in the 70's and 80's. While simulation software has made using them all but obsolete I do think it's important to know that those tables are the basis for the simulation software.

An interesting side bar, one rather famous JBL engineer was an expert in theory but couldn't design a good sounding loudspeaker if his life depended on it. Another JBL engineer wasn't all that high on theory but he sure could design some great sounding systems. Both still work for Harman after all these years.

[jdelange]

Changing the size (typically the length) of the port-tube you can change "tuning of the WHOLE SYSTEM", (box+port resonant frequency Fb) and what would be the influence of such (tuning or changing) to the WHOLE SYSTEM RESPONSE, you can easily see using mentioned simulation programs.

I followed the subwoofer article by Kramer and Timbers (http://www.lansingheritage.org/html/jbl/reference/technical/1983-subs.htm). Installed a 12" (29 cm tube + part of baffle) port in an 8 foot cabinet which gave following response (Woofer Tester 2).

54214

This puts the system frequency (fm) at about 26 Hz which is as per the article.

Yet the fact that the impedance peaks of port and speaker do not match up as they should in a proper tuned system got me confused initially. Therefore I reduced the port length stepwise to get them aligned. It turned out the system requires a port length of about 9 cm + baffle (4"), resulting in a system frequency of 33.5 Hz, again as per the article.

54215

Re-reading the article I now understand that the BX63 filter, electronically compensates for the "error" of the longer port. Though I do not exactly grasp how the bass boost makes the impedance curves of port and speaker match.

[ivica]

I followed the subwoofer article by Kramer and Timbers (http://www.lansingheritage.org/html/jbl/reference/technical/1983-subs.htm). Installed a 12" (29 cm tube + part of baffle) port in an 8 foot cabinet which gave following response (Woofer Tester 2).

...............
Re-reading the article I now understand that the BX63 filter, electronically compensates for the "error" of the longer port. Though I do not exactly grasp how the bass boost makes the impedance curves of port and speaker match.

BX63 compensate (boost) lower frequency region taking care of mechanical driver limitations ( Xmax). It does not have any influences of the diver(in the box) impedance.

[Fort Knox]

Since you guys are so good at measuring woofer boxes......
How about getting busy and measuring the acoustic impedance
(and timing) mismatches a mid horn .. creates... in a flat baffle cone woof box;)

[grumpy]

I'm not sure what this has to do with a 2245 or about
a suitable cabinet... nor the purpose of the question
that appears to be more of a statement. Perhaps start
a new, direct thread.

[Fort Knox]

grumpy
I'm not sure what this has to do with a 2245 or about
a suitable cabinet... nor the purpose of the question
that appears to be more of a statement. Perhaps start
a new, direct thread.

I was just reading the last entry about "diver (in the box) impedance"
and that horn/cone imped. diff. thing ...popped .up in my head...?!!

[ivica]

BX63 compensate (boost) lower frequency region taking care of mechanical driver limitations ( Xmax). It does not have any influences of the diver(in the box) impedance.

More technical info about BX63 (a):
http://www.jblproservice.com/pdf/Vintage%20JBL-UREI%20Electronics/UREI-%20BX63A%20ts.pdf

[4313B]

Just buy one of these things and forget about it.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-811

It has a built-in 25 Hz bump filter (similar to the BX63 but with a lower Q) as well as an extra EQ feature, plus a bunch of power.

10. Bass Boost

Selects a bass boost filter with +3dB @ 25Hz, Q=1.4. Allows

the user to add boost to the low end response without using

the built-in parametric EQ. This leaves the parametric EQ

function to address room modes to cut out an excessively

loud room resonance.

11. Subsonic Filter

Selects a subsonic filter with -3dB @ 18Hz, Q=.8. Allows

the user to remove the subsonic information from the

signal and tighten the low end response of some

subwoofer systems.

[pathfindermwd]

Just buy one of these things and forget about it.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-811



I too had been contemplating a 2245 project. Thanks very much for posting this! :bouncy:

[rusty jefferson]

Just buy one of these things and forget about it.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-811




Do you have first hand experience with this amplifier? Is the high pass passive? Does it sound as good as the BX63-A?

Thanks

[Ian Mackenzie]

I 've been calculating a 4th order bass reflex cabinet at 10,1cft using Vb=(15)(Vas)(Qt2.87)

Then found F3 32,5Hz using F3=0.26(Fs)/(Qt1.4)

And Fb 27,3Hz (basically the port tuning) with Fb = 0.42(Fs)/Qt 0.9

What if I increased cabinet size to 12cft?
How lower will F3 be? Any drawback?

I want to build two cabinets to use up to 800Hz for home duty. No PA action here.


<What if I increased cabinet size to 12cft?

Asbolutely no advantage going from 10 to 12 cu ft with an un assisted alignment in a normal domestic situation.

>Any drawback?
Yes. Size of enclosure and what is known as group delay in the base response. JBL do not recommend this size enclosure operater above 80 hertz



Actually, it gave me some clues, but didn't answer all my interrogations. Per exemple, the ports is de facto tuned to Fb. I can't find how to tune the port to the driver's Fs 20Hz, or somewhere between Fs and Fb.

So far it goes like that. 10cft vs 12 cft tuned at Fb 27,3Hz

Response. The thin green line is the gain/loss between 10 and 12 cft



Your simuation is incomplete.

You need to know where the enclosures will be located and thw resulting effect of room gain in your room.

The effect of room gain is going to have a much greater impact on the overall reponse than incremental tuning differences.

When this is accounted for add the room gain to the driver/enclosure simulated response.

To give you a few clues if you are considering using the 2245 above 80 hertz you will want the smoothest bass in the pass bandband response from 35 - 300 hertz.

Otherwise use the assisted alignment as advised above for sub woofer applications below 80 hertz.

The effect of room gain is to create a hump that decends from 120 hertz to 40 hertz with the 2245 in 8 cu ft tuned to 28-29 hertz ie maximally flat response.

According to Witold Waldman a scientist in Aust who created Calsod the 1st system optimisor software written in DOS, the human ear is particularly sensitive to distortion and response flatness below 100 hertz.

If your amp has a bass tone control this is quite obvious.

The size of the hump will vary according to the enclosure location.

You can triangulate the Q and magnitude of the hump according the height of the woofer centre above the floor and distance from the wall boundary.

The 2245 has strong boundary reinforcement so it is desirable to have the woofer centre at least 15 inches above the floor level

Given the size of this enclosure you are not going to have too many placement options so we will assume its located against a floor / wall boundary. Corner placement will exagerate the size of the bass hump.

In other words it will sound more woolly and possibly boom.

The idea is to use the room gain to your advantage to extend the system response with minimal ripple or bass hump.

So how do we fix this without applying active equalization?

By moving to a larger box and a lower tuning frequency we can see the tilt in the response below 100 hertz which is advantagous to compensate for room gain.

To tune the system correctly you cannot however pick any combination of the enclosure size and FB and we refer the the formula below.

Sub optimal tuning will response in ripple in the passband. The effect of this is poor transient performance.

We also need to consider the dymanic performance and the displacement demands on the woofer in the 35-50 hertz range where the port is going to actively contribute the systems overall dynamic range.

If you tune too low you will loose some of the benefit of the port in the useful range of 35-50 hertz.

The un assisted tuning below is a very good balance of box size, bass extension in room and in room response flatness.

I have used this alignment with the 2245 and in practise ands its better for the above reasons than the 4345 box tuning.

The beauty of a diy project is you are free of marketing and manufacturing contraints and can design the system to suit you room and your needs.

Enjoy and have fun.

10,1cft using Vb=(15)(Vas)(Qt2.87)

F3 32,5Hz using F3=0.26(Fs)/(Qt1.4)

Fb 27,3Hz (basically the port tuning) with Fb = 0.42(Fs)/Qt 0.9

Remember the Vb is the net volume allowing for bracing, displacement volume of the woofer and effect fill which increases the virutal enclosure Volume due to frictional losses QL.

In an enclosure of this size the effect of normal fill ie 1 inch fibre glass will cancel out the volume subracted for the bracing and the woofer.

I recommend 3 four in ports and trim the length so fb is 27 hertz.

[4313B]

Do you have first hand experience with this amplifier?I'm thinking about buying one instead of the Tannoy iwSA 500 D. My only concern is that it might not have the kind of current output I like.
Is the high pass passive? Does it sound as good as the BX63-A?Doesn't matter, all that is handled by the surround sound processor these days and I'm not a big fan of subwoofers with two-channel systems, which is why I still can't get my head wrapped around what the HK 990 is for. I suspect it was probably designed with something like the JBL LS Series in mind :dont-know:.

So, this Parts Express amp/crossover has a 3 dB bump filter at 25 Hz (or you can use the EQ at ~25 Hz instead if you need more boost), the 1500 Array has a 4 dB bump filter at ~25 Hz and the BX63/BX63A has a 6 dB bump filter at ~25 Hz. Some people don't like any bump filters with their B380 or B460 (it is room dependent). My point is, this Parts Express offering has a bit more versatility. Some people/manufacturers use plate amps instead.

[Ruediger]

What if I increased cabinet size to 12cft?


If You pick a larger cabinet size Vb then the following formulas apply.

f3 = fs * sqrt( Vas/Vb)
fb = fs (Vas/Vb)**0.32

You will have a "ripple" (deviation from flat response):

R = 20 * log10(2.6 * Qts * (Vas/Vb)**0.35)

There is a missunderstanding about fb and the box resonant frequency, fb *IS* the box resonant frequency, this is when the system of air mass in the ports together with the air "spring" in the box does resonate.

If You build a passive xover then the Qt of Your speaker will change because of the DC resistance of the series coil in the xover. This has been explained several times here, and it is explained in the Thiele paper. See the technical references thread.

Ruediger

[kartsmart]

I see going larger than 10 cu ft but what happens when going smaller to the 8 cu ft box ? like what jbl has sold. what would be the trade off for 30 HZ to 340 HZ

[Ruediger]

I see going larger than 10 cu ft but what happens when going smaller to the 8 cu ft box ? like what jbl has sold. what would be the trade off for 30 HZ to 340 HZ

... see the Thiele paper. Many well-defined filters are possible, Butterworth of order 4 is just one possible choice, and even that only when the driver fits.

You may as well apply the formula given in my last response. The response will have a positive ripple, the response will be peaked somewhat. The corner frequency will be higher. In too small a box a smaller driver may be better than a larger one.

Ruediger

[Ian Mackenzie]

On the basis of responding to the context of the 1st post in this thread please find the simulation per my previous post of the D.B Keele pocket calculator formula.

The blue line is the woofer/ boxing system and the yellow line is with my customised room gain added.

The current trend in bass reflex systems for domestic use incl current JBL K 2 systems is to tune the system so that it can be located near a room boundary and get a reasonable smooth and extended response.

Your own room gain could well be less or more. In the case of a maximually flat tuning ie a smaller box Vb and higher tuning Fb where the system 40 hertz point is 0.00 db under room gain conditions this could be + 4 db or more leading to boomy bass.

On paper tunings of this type do not turn heads but they sound better in a typical domestic environment hence the banana curve.

In my own environment the in room response is -3 at 27 hertz with full power available at that frequency. For music this is excellent.

The original JBL vintage monitors and the current blue series are tunings for maximually flat response where the modest size enclosure has the Fb pushed up for an elbow curve.

In some cases the Fb of these systems is 32 hertz which make it sound quite aggressive as was the case when I heard them in Japan back in 2008.

The banana curve is perhaps more Hifi as is the case with the overall sound of the newer K2 systems.

On paper it looks impressive but like in a domestic situation it can be a PITA.

. This looks good on paper but is problematic for the user who must drag the system one foot or so out from the wall and or erect the system on stands which is somewhat impractical given the overall size and height of the enclosures.

[ivica]

On the basis of responding to the context of the 1st post in this thread please find the simulation per my previous post of the D.B Keele pocket calculator formula.

The blue line is the woofer/ boxing system and the yellow line is with my customised room gain added.

The current trend in bass reflex systems for domestic use incl current JBL K 2 systems is to tune the system so that it can be located near a room boundary and get a reasonable smooth and extended response.

Your own room gain could well be less or more. In the case of a maximually flat tuning ie a smaller box Vb and higher tuning Fb where the system 40 hertz point is 0.00 db under room gain conditions this could be + 4 db or more leading to boomy bass.

On paper tunings of this type do not turn heads but they sound better in a typical domestic environment hence the banana curve.

In my own environment the in room response is -3 at 27 hertz with full power available at that frequency. For music this is excellent.

The original JBL vintage monitors and the current blue series are tunings for maximually flat response where the modest size enclosure has the Fb pushed up for an elbow curve.

In some cases the Fb of these systems is 32 hertz which make it sound quite aggressive as was the case when I heard them in Japan back in 2008.

The banana curve is perhaps more Hifi as is the case with the overall sound of the newer K2 systems.

On paper it looks impressive but like in a domestic situation it can be a PITA.

. This looks good on paper but is problematic for the user who must drag the system one foot or so out from the wall and or erect the system on stands which is somewhat impractical given the overall size and height of the enclosures.

This is very nice presentation, but if bass driver is planned to bi used above 100Hz, then the problem of the influence of the "image cancellation" one has to be aware.

from: http://www.silcom.com/~aludwig/Physics/Main/Cavity_modes.html

or http://www.silcom.com/~aludwig/Room_acoustics.html



it can be seen that about +14 dB gain can be get at low frequency, but -5dB loss (or more) on the higher frequencycan be expected too.

Not to mention usual stereo arrangement.

Some responses presented: http://www.nousaine.com/pdfs/Stereo Bass.pdf

or in more detail: http://www.infinitysystems.com/home/technology/whitepapers/inf-rooms_3.pdf

or http://www.bodziosoftware.com.au/Article_7.pdf

From all mentioned above it is 'clear" that if we "want to introduce" the room acoustic in to the speaker response, then we would jump into the "deep mud" .

[Ian Mackenzie]

That goes for any room and any loudspeaker unless configured like the early the Alison systems or NHT 3.3 with the woofer placed at the wall / floor junction and the id 4 feet from the floor.

However, careful placement even small movement of the enclosure can provide an acceptable compromise.

The actual response below 400 hertz is normally swomped with room modes . This tends to be more of an issue in small rooms.

You can if you wish apply very modest equalization with parametric equaliser as some member have done but without suitable measuring kit and experience its best left well alone.

The point here is however that it is industrious to design the system for a balanced response where tuning and room gain can extend and smooth the broad humps that can otherwise ocurr in a typical domestic environment. Its is there broad humps that are most noticable to the ear.

[Lee in Montreal]

Reviving an old thread for everyone's benefit. It seems that an alignement of 5.7 is the golden rule for any woofer. Volume = 5.7*(Vas*(Qts^2)) which is around 12.5cft for the 2245. No early knee and no ripple.

[Champster]

So Lee, what did you build? As you know, I am just now getting my 2245's and planning to build them into a true subwoofer with an upper limit of about 80hz.

I really am tempted to build this 12cf cabinet (http://www.lansingheritage.org/html/jbl/reference/technical/1983-subs.htm) in this article. I am going DSP with fully active amplification, so the electronic boosting will be simple.

Has anyone built either of the cabinets in this article?

Thanks,
Paul

[Allanvh5150]

I think Greg Timbers always said that the 2245 would benefit from a 12cuft box. He also said the 4345 was always limited buy the box size.

Allan.

[svollmer]

So Lee, what did you build? As you know, I am just now getting my 2245's and planning to build them into a true subwoofer with an upper limit of about 60hz.

I really am tempted to build this 12cf cabinet (http://www.lansingheritage.org/html/jbl/reference/technical/1983-subs.htm) in this article. I am going DSP with fully active amplification, so the electronic boosting will be simple.

Has anyone built either of the cabinets in this article?

Thanks,
Paul

I built four of the 12cf models as described in Greg's article. I changed the dimensions to fit my space, but other than that, they're the same. I have them crossed over at 60Hz (18db/octave if I remember correctly) and they KILL! Mine are close to a corner stacked floor to ceiling.

If you do the 12 footers, I'm sure you will love them!

[Lee in Montreal]

The 2245 can use 8cft to 12cft depending on if you prefer underdamped to overdamped. 8cft will yeld a tighter bass. 12cft will go lower.

I made mine at around 10cft. with two 6" ports. Roughly 33" x 23.5" x 23.5" (or if you make a draft from an 8'x4' - make 36"x24" and 24"x24" panels, minus blade thickness)

http://img.photobucket.com/albums/v668/Lee_Vuong/JBL parts factory/DSCN2574_zpseea4a070.jpg

http://sphotos-a.ak.fbcdn.net/hphotos-ak-frc1/883153_564405090257530_411380388_o.jpg

[dkalsi]

I think Greg Timbers always said that the 2245 would benefit from a 12cuft box. He also said the 4345 was always limited buy the box size.

Allan.

That is why, when I built my JBL 4345 Clones, I made my enclosure a little deeper, so the internal volume of the enclosure (net of the dogbox) was around 12 cubic feet

[Champster]

Ok so I'm going with the 12cf box tuned to 20hz. When I put the vent into WinISD I get 2 - 4" vents about 11" long. What is vent mach? Does that sound right?
62069

[svollmer]

Ok so I'm going with the 12cf box tuned to 20hz. When I put the vent into WinISD I get 2 - 4" vents about 11" long. What is vent mach? Does that sound right?


I’m certainly no expert and many here would know for sure, butI thought Greg’s plans called for a large vent because of the high velocity of air produced by the sub.The larger the vent, the less “chuffing” occurs.The B460 used three vents to simulate one large vent because JBL was afraid that small animals could get into one large vent (or at least that’s what I’ve heard).I just copied Greg’s plans, but I altered the dimensions (same net volume) and I changed the round vent to a square vent.I think my vents are something like 8”x8”, or close to that (I'd have to measure them at home).I just calculated the area of the 9” vent described in the article and changed it to the proper dimensions for a square vent so the area was the same.


I chose the 20” version which is 25hz unassisted.I can verify that it will produce startling infrasonic frequencies with the subs near one corner and thorough bass traps in each corner.I use an Audio Control Richter Scale III xover/eq at 60Hz (sometimes 40) and I have never had to boost the lowest frequencies.I keep it flat and the bass is deep and tight.

[Champster]

Thank you svollmer for the excellent feedback! Does anyone else have an experience with the 12cf box & its vents?
Paul

[svollmer]

No problem. Just remember, we want to see pictures of what you build!J

Also, I had originally built two of a different version of the subs at my last house. I used different dimensions than my current boxes because I wanted them to match my main speakers’ height. I also obtained 9” round Sonotube for the vents. I can tell no audible difference between my last subs and these with different dimensions and square vents.

[Lee in Montreal]

Hi Champster

May I sugget you model the 12cft cabinet with 3 different tunings and see how it affects your two bottom octaves. Test tuning to 20Hz, 23Hz and 26Hz... When you tune to 20Hz, you will probably give away some of the "real life bass" around 30-50Hz.

Also, I don't think that two 4" tubes will be enough. Try a pair of 6" or three 4". May I also suggest you check how Onken cabinets use bracing to stiffen the panels and create vents at the same time.

Oh, and try 12,5cft internal volume (excluding vents, bracing and driver volume).
"Volume = 5.7*(Vas*(Qts^2)) which is around 12.5cft for the 2245. No early knee and no ripple."

http://nicolas.davidenko.perso.sfr.fr/plancaisse/mini-2.jpg

http://www.studiomsoft.com/audio/images/onken/onkenfig2small.gif

http://quarkconcept.online.fr/ONKEN_417.jpg