DIY JBL 4 Way Sound Reinforcement

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I have been looking at the posts in the loudspeaker forums, some very interesting projects and clever people out there.
Currently halfway through a large speaker project for my self, personally not so into home audio addictions but prefer something for a few more people to hear.
If anyone wants to know about this project and problems and good parts could they offer advice? If it is a turn off I will understand!

Thank you

Dave
 
JBL Sound Reinforcement more info.

4 of JBL 2226j low/sub bass vented enclosures

2 of JBL 2206h in top cab design, a pair of these cabs, also containing ( or loaded! don't you hate that pro audio term?) with 2380a horns (90x40 nominal coverage).

Attached to horns jbl 2446j 2 inch throat compression driver.

Very high frequency 2404h bi radial 100x100 coverage.

I am using crown K2 on bass. (2500w 4 ohms)
I am seaching for suitable mid amp. (1200w per side into 4 ohms needed).
Qsc ex 1250 on compression drivers. (300 a side 8 ohm).
H and H mx 250 on 2404 bi radials. (80 a side into * ohms).

This system will be stereo, currently testing with dreaded behringer cx 2300 in mono. Botom cabs have been made in mdf as a temporay test four seperate enclosures tuned to 40hz.

Top cabs are being made in birch ply by cabinet maker,should be going to see them tommorow. Details of bracing and port sizes not finalised. Calculations done on win isd.

I have a few concerns about the sound quality I could end up with, I have tried to steer clear of cheap and nasty bits.

Is this of any Interest?:)
 
Dave,

This is a breif on-the-run type post, which I'll add to later tonight. I'm very familiar with the 2226 and 2445/2446/2380A series' (I have 6 pairs of these).
How low and loud do you want this thing to go?

In the meantime, have you seen these?
http://www.audioheritage.org/html/perspectives/drews-clues/system.htm
http://www.audioheritage.org/html/perspectives/drews-clues/audiophile.htm (home system but interesting)
http://www.geocities.com/loudspeakerguru/ ( a LOT here in multiple pages. Jeff knows his stuff)

Tap Eric's brain, he's very experienced and knowledgable. But do it now as he's getting a bit old and senile. Reasonably nice too for a sandgroper.:D:D

hehehe
 
JBL Sound Reinforcement

How Loud and Low?

In a small to medium sized bar or club this ain't enough bass, will have to do on current budget.

I have used these bass cabs for a party once, here is a quote from a unknown guest.

Guest: How much 'k' have you got.
Lee (party helper): Well that amp is 2.5k (crown with ioc flashing)
Guest: Sounds more like 1.8
Lee:rolleyes:

Have had stern words with 'experts' who think these drivers are poor, of course low frequencys will be at the expense of volume to some degree, would like to lower fb and increase number of drivers in the future.

Wn isd gives 134db for four of these at one metre but that does not take into account power compresion, port losses and driver excursion. In fact that last statment might be total bs I have no measuring equipment bar a multimeter!

:)
 
From Downunder

"In a small to medium sized bar or club this ain't enough bass, will have to do on current budget. "

Hmmm, that sort of setup ought to cut it good enough and loud enough - it used to in the late eighties for pub rocknroll.
There is no real sustitute for lots of drivers and amplifiers if really high power lows is what is needed - only it gets costly.
Maybe hire some extra lows cabs for a show and see if this is the soloution.

IME to get the most and cleanest for all the audio bands is to use 4 wire power extension lead wired as star-quad, ala Canare loudspeaker cable.
This will help to get that extra dB or two clean, reduces driver dissipation, and reliability.
Be sure that all cables are wired in the same direction.
RC networks across the driver voicecoils will clean things up, allow amps to deliver more power, improve reliablity, and improve sonics overall.

Regards, Eric.

BTW - who is this Brett character ? :D
 
RC networks?

Will these prevent unwanted peaks damaging drivers?
Where could I find more information or details on design of these?

I presume star quad would be wired with neutral and live twisted together in pairs, not really used twisted pair speaker or line level cables as a rule.

I would like to post a picture of box design in the next few days, still waiting for cabinet maker.

Thanks Eric.

Dave
 
Electrical Tuning

Hi Dave,
The RC networks are to be found in 'Loudspeaker Design Cookbook' by Lance Dickason.
Voice coil inductance causes a rising impedence characteristic, and is magnetically stored energy.
By fitting a compensating RC network across the voicecoil, the amplifier is seeing a flat over frequency resistive load, as opposed to an inductive load.

This pays big dividends in reduction of distortion from both amp and speaker, reduces the amount of dynamic correction required of the amplifier, and this allows both the amplifier and voice coil to run cooler, and gives more dynamic headroom.

To choose correct values of R and C, a standard amplifier, oscillator, audio level meter, sensing resistor and ohm meter are required.
The RC shunt network will null the rising characteristic, and a shunt RLC network is required to null the driver resonance hump if desired.

Star quad configuration requires four wire cable, with the diametrically opposite wires in parallel, and this gives lower series inductance cable than any twin cable.
Again this will lower overall distortion, and allow greater dynamics.

Hope this helps, ask if you need more,
Regards, Eric.
 
Just been testing enclosure for general sound quality.

It is made from 13 ply baltic birch and is tuned around 50 hz with 2 six inch diameter ports.

I have braced the cabinet walls extensively and used 2x2 braces front to back. I have tried to keep the braces fairly random as detailed in the 'loudspeaker Cookbook'.

The cabinet with drivers now weighs 80kg!

I have a fairly pleasing bass kick output at present but the mid bass is boomy and coloured. This enclosure doesn,t need to produce low bass as it is subwoofer supported. I do need a nice midrange sound.

Would anyone use stick on bitumen type pads on the enclosure walls?

I have fibre glass resin and matting to reinforce if necessary.

Have not yet used quantitys of fibreglass insulation, to damp standing waves.

Are there any other causes of this colouration of sound?

Thanks again.

Dave G.
 
picture

Picture of box.
 

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Just Bloody Loud

Hello Dave Goodhew,
Congratulations on your new cabs.
In answer to your mid bass boominess and colouration questions -
Fitting RC networks will go a long way towards curing this.
The drivers you are using have always been a bit mid bass barky, so good damping is required.
Also damping wool inside the cabinet, but DO NOT EVER use fibre glass wool in a vented cabinet.
If you are to run such a cabinet in good lighting/sunlight you will see puffs of glass fibre shooting out the ports on bass, and this is a very hazardous material - Polyester pillow stuffing or sheeps wool is a much better soloution, and economical.
Also large diameter echoey port tubes will allow mid bass colour - these can be lined with a strip of thin carpet to reduce this.
Are you sure the 6 inch ports are not too big, or too short ?.
Also the class of LP filter controlling bass roll out will effect the mid bass character.
Also use the star-quad extension cable I mentioned above.
Also is the mid horn flare 'quiet/dead' ?.
If these are rattly/excitable much colouration is caused.
Glueing deadening material to the outside of the horn will help.


Regards, Eric.
 
Hello Eric

Since that photo I have added bracing to cabinets, have also reinforced insides with a bit of glassfibre resin and matting to make extra sure.

Have large amounts of self adivesive anti drumming sheets of the type used to prevent sheet metal ringing. Does anyone use these?

Appologes for speaker cable exit through port, a supreme bodge!
I have ordered neutrik eight way sockets and plugs to keep it tidy.

Have you seen Drew Daniels comments on fibreglass he thinks it is the best medium to use! I wouldn,t like it all over the place though. I think there are a few myths flying around with damping material.

He states that fibreglass increases virtual box volume?

It is quite annoying as I have a bail of synthetic wadding material as big as me. This is called 'luxbond' and is a fire retardant furniture stuffing I would think. I am sure some manufactures still use fibreglass but you would know more than me on such a matter.
I would think these matarials would have a similar effect I might do a A/B comparason.

The crossover slopes are 24 db per octave linkwitz reilly, according to behringer!

The ports are seven and half inches long, they are six inches in diameter.

The box air volume is approx 4.2 cu ft.

Coming back soon,
 
Back again:

I was wondering at what point would be ideal to tune the boxes to, would a higher tuning frequency tend to cause a resonance in up higher in say the 100-300hz range. is this range of frequency's in the bark or boom region?

What I am trying to say is should the box be tuned lower than the crossover frequency (say crossover at 80 hz) by a large margin to keep port tuning peak out of high output region,s?

Win isd does not show a large peak at tuning frequency but I know it is a basic program and will not show all parameters.

The ports need to be a bit longer (half inch) on paper but a do feel that the woofers are at minimum excuusion at the low 50 ish hz.

Is that a good enough method to get a idea of box tunning?

I use a test disc with tones and place my finger on the suround lightly, the point of peak impedance is also near to tuning frequency is it not?

I need to do these tests properly. I have Loudspeaker Cookbook (fifth edition). What would be the best way to progress from here? I need to submit some testing to third party with testgear.

The RC networks are the brainteaser!

Is it all worth doing, will these sound as good as something you can buy?

Have you had much sucess over the years with homebrew design's?

I can see why people don't give away designs for this type of project on the web. I have been planning and searching for unwanted JBL bits for months. You can only do so much planning but I have to go through the motions to learn the best way to get a decent sound.

I rate things such as Martin Wavefront, Funktion one and some JBL systems but often not other JBL systems!

What has impressed you Eric, over the years?

Thanks

Dave G.
 
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