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Old 22nd September 2014, 05:34 AM   #1
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Default Reviving vintage JBL cabinets

I have a pair of old JBL reference 502vx cabinets.

http://www.jbl.com/images/media/502VX%20ts.pdf link for reference.

I want to put new drivers in it. The crossover is very simple. first order low pass and second order high pass. Is it worth trying to drop in new drivers with the existing crossover or should I go ahead and select some drivers and design my own crossover for them.

the box is approx 1.54cube and has a 2" by 5" long port.

Either way I could use some help in selecting drivers and ultimately the design of my crossover. My first question is for the tweeter. The hole for the tweeter is actually 3" Is it desirable to go with a 3" speaker that could be crossed lower... say around 500-600 so the woofer can be crossed lower or stick with a tweeter in the 2k+ range? I realize I'll need to enclose the speaker to isolate it from the woofer.

If making a crossover I'm going to stick with a 2nd order for both low pass and high pass basically following the guide in the sticky.

This is my first diy and I'm just looking to salvage these cabs my roomate was going to throw away. Id like to keep this under 150USD which seems easily doable via partsexpress.

Last edited by MichaelM86; 24th September 2014 at 07:17 PM.
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Old 24th September 2014, 07:16 PM   #2
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I guess I was a little too vague in my first post. I've decided to go for a new 2-way and trying my hand at making a crossover. I'm looking at the following drivers.

Dayton dc28f tweeter.
http://www.daytonaudio.com/media/res...ions-46121.pdf

mcm 55-2950 8" woofer.

http://www.mcmelectronics.com/conten...ts/55-2950.pdf

following the crossover without measurements guide I have come up with the following values for a crossover at 2500hz.

these are calculated and ill need to closest avail part.
to flatten woofer impedance a resistor of 9ohm and a capacitor of 13uf

woofer inductor .51mH inductor.

use a 20hm resistor to flatten tweeter.

tweeter crossover using approx. 6.88uF cap and .59mH inductor....

I don't have a resistor in series and so I used the 20ohm instead of 10ohm resistor to prevent too low of an impedance. I did this because the woofer is rated at 94 db and the tweeter at only 89..

Is this okay? can this be a bit of a baffle step? Or do I really need to figure out a different combination with a tweeter that has a higher spl that I can then bring down. This seems to be a popular tweeter on parts express so maybe someone can chime in.

theres a 89 db woofer on mcms site, but its vas is a whopping 98 liters with a qts of .4529.... My box is only about 1.54cubes... ported.

Last edited by MichaelM86; 24th September 2014 at 07:42 PM.
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Old 24th September 2014, 09:06 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

I'd wouldn't take MCM's specs sheets too seriously.
That 8" is a PA drivers and wont match the cabinets well.

If the box really is 43L internal then its tuned to ~ 30Hz.
Looking at the only picture I can find it doesn't seem that big.

Choice of the bassmid is critical, and sadly not many
genuine 8" bassmids are made nowadays, most can't
do mids, and the ones that can are not cheap, using
all your budget and more in most cases.

Best guess :
https://www.madisoundspeakerstore.co...m-8-wool-cone/
Tweeter possibly : (basically just great value)
https://www.madisoundspeakerstore.co...116-mm-flange/
see : http://www.zaphaudio.com/tweetermishmash/compare.html for curves.

And yes your modelling must include baffle diffraction and some BSC.

rgds, sreten.

http://audio.claub.net/Simple%20Loud...ign%20ver2.pdf
FRD Consortium tools guide
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Last edited by sreten; 24th September 2014 at 09:34 PM.
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Old 24th September 2014, 11:50 PM   #4
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understood on the woofer. I figured 10 bucks was too good to be true lol. Any particular reason for that tweeter over the Dayton? what If I upped my budget and went with say...

http://www.parts-express.com/pedocs/...ions-46942.pdf

It matches the Dayton tweeter spl and has a vas 1.51 cubes which is close to my box. My understanding is if your around the .4qts mark a vented enclosure should be around the vas volume and larger for higher qts values or smaller for lower qts values. I realize this is very crude, but this is my first diy.

The woofer aside is their anything inherently wrong with my crossover calculations for the tweeter? With the lower spl Dayton woofer that leaves me room to change the resistors around depending on how it sounds.

Also I believe 24w of resister for the zobel is fine for the woofer and 10w in parallel with the tweeter is fine. The sony receiver is rated at 100w and I don't listen to this very loud.

also yes the cab is 1.54 or very close. The pdf in my first post has the actual box dimensions although it will not load now.

21.5" x 13.5" x 11.1875" I accounted for what looks to be .5" for the cab and 3/4" for the baffle.
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Old 25th September 2014, 08:17 PM   #5
system7 is offline system7  United Kingdom
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Let's do a proper job here. Download this; Downloads.

Now try the below circuit in a suitable cabinet (which you set up) with the following drivers:
Visaton W200S-8 8" Woofer with Treated Paper Cone 8 Ohm
Phenolic Ring Tweeter 8 Ohm

Your reflex bass loading will be 33Hz on 50L:
W 200 S - 8 Ohm

It'll look a bit like the below photo.
Attached Images
File Type: png MichaelM86 JBL Refit.PNG (7.3 KB, 153 views)
File Type: jpg Modified_MA-R300MD_HT22-8.jpg (79.0 KB, 152 views)
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Old 25th September 2014, 08:43 PM   #6
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by system7 View Post
Let's do a proper job here.
Hi,

You never really do a proper job, you over simplify it
using a simulator that cannot use proper driver data.

rgds, sreten.
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Last edited by sreten; 25th September 2014 at 09:09 PM.
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Old 25th September 2014, 09:08 PM   #7
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by MichaelM86 View Post
understood on the woofer. I figured 10 bucks was too good to be true lol. Any particular reason for that tweeter over the Dayton? what If I upped my budget and went with say...

http://www.parts-express.com/pedocs/...ions-46942.pdf

It matches the Dayton tweeter spl and has a vas 1.51 cubes which is close to my box. My understanding is if your around the .4qts mark a vented enclosure should be around the vas volume and larger for higher qts values or smaller for lower qts values. I realize this is very crude, but this is my first diy.

The woofer aside is their anything inherently wrong with my crossover calculations for the tweeter? With the lower spl Dayton woofer that leaves me room to change the resistors around depending on how it sounds.

Also I believe 24w of resister for the zobel is fine for the woofer and 10w in parallel with the tweeter is fine. The sony receiver is rated at 100w and I don't listen to this very loud.

also yes the cab is 1.54 or very close. The pdf in my first post has the actual box dimensions although it will not load now.

21.5" x 13.5" x 11.1875" I accounted for what looks to be .5" for the cab and 3/4" for the baffle.
Hi,

The designing without measurement post is OK, but
takes zobels far too seriously, they are not needed.
look at the designs here : zaph|audio

The PE 8" would seem a fine choice but I'm really at a loss
sometimes about their published specifications, e.g. compare :
http://www.parts-express.com/pedocs/...ions-46154.pdf
To :
Click the image to open in full size.

Its not good for modelling without measurements.

FWIW if Seas can't make a metal 8" good for a 2 way,
nobody can, and they can't, and I think nobody can.

On a budget I'd tend towards a FAST.

rgds, sreten.
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Old 25th September 2014, 10:30 PM   #8
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Quote:
Originally Posted by sreten View Post
You never really do a proper job, you over simplify it
using a simulator that cannot use proper driver data.
Whatever system7 does or doesn't do, Boxsim can use proper driver data just fine if you have such data, and use the corresponding settings.

Quote:
Originally Posted by sreten View Post
I'm really at a loss
sometimes about their published specifications, e.g. compare :
http://www.parts-express.com/pedocs/...ions-46154.pdf
To : http://www.zaphaudio.com/6.5test/DA175-8-FR.gif
I don't know why you're at a loss because that's not exactly worlds apart. Scales matched, overlayed, stated invalid portions of each cropped off:
Click the image to open in full size.

But...
Quote:
Originally Posted by sreten View Post
Its not good for modelling without measurements.
I agree.
Attached Images
File Type: gif temp.gif (36.4 KB, 144 views)
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Old 26th September 2014, 01:39 AM   #9
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Ok I toyed around with boxism and its def cool, but I don't have any measuring equipment. this is all best guess. That parts express driver isn't listed in the visaton drivers obviously and I don't even have all the values to try and input my own data such as fas. I looked up a visaton tsweeter but its vas was like 1900 and didn't seem to match up well to that visaton woofer you posted.....
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Old 26th September 2014, 02:20 AM   #10
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I love this stuff.

I consider it an upgrade for any speaker. Why not be better than ever?
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