Author Topic: ProAc 2.5 speaker inspire  (Read 6069 times)

jb

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ProAc 2.5 speaker inspire
« on: August 16, 2016, 02:26:22 PM »
This speaker is all time favourite of many users here. I happen to have two original ProAc 2.5 woofer speaker laying around the house, so thinking of doing this project..and so happen another user in another forum already started this project. So will be interesting to learn of his project experience and share the knowledge. Here is his project link.. http://myoldvintagehifi.blogspot.sg/
another link with technical info to built the ProAc 2.5 spk..  http://www.justblair.co.uk/blog/137-diy-proac-response-25.html

I have done a circuit simulation of the ProAc 2.5 crossover circuit using the Agilent ADS to look at the crossover frequency point and phase response. But will redo this exercise as a new project.. Next is to find a cheap source of the speaker box and crossover circuit parts and scan speak tweeter.

The original ProAc 2.5 use some kind of 'tar like wood pieces' to lay inside the speaker cabinet wall beside using the glass fiber, so the voicing of original speaker may be different due to the damping material, may have to experiment more to get the final voicing.



« Last Edit: July 16, 2017, 02:57:39 PM by jb »

watchdog

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Re: ProAc 2.5 speaker inspire
« Reply #1 on: August 16, 2016, 10:06:37 PM »
Oh, this post brings back plenty of memories. This was my second DIY project after a TQWT Fostex FE103.

At that time, Troels guide was the definitive resource for information.

A word of advice, it doesn't make sense to me to stinge on crossover parts. The finished product will surprise you with the performance possible. Mine was made using Sonic Cap capacitors, Solen aircore inductors and Mill non-inductive resistors. Not sure whether mine still works though - the 18W/8535 driver has a nasty habit of failing in our humid weather. I've replaced mine twice over already.

To simulate the bituminous pads used by Proac, you can paste roofing bitumen sheets on the inside of the cabinet. The original Proac crossovers will surprise you - cheap plastic and electrolytic caps, but they sound marvelous.

jb

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Re: ProAc 2.5 speaker inspire
« Reply #2 on: August 19, 2016, 04:49:27 PM »
Thanks for the info, will keep that in mind when I source for the crossover parts. Yes the bitumen sheets may just do the job and will need to source this from hardware store. For the speaker box , did you source the MDF board locally and get it cut locally? or you purchase the speaker box from china source? Anyway when I actual start the project will need more info from you as you have past experience in building this speaker, for now I am reading up the design info before proceed to build it.

jb

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Re: ProAc 2.5 speaker inspire
« Reply #3 on: August 20, 2016, 02:13:12 PM »
Today, will try to simulated the crossover circuit frequency and phase response and crossover frequency point. A good LT spice tool can be found here : http://www.linear.com/designtools/software/#LTspice


watchdog

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Re: ProAc 2.5 speaker inspire
« Reply #4 on: August 20, 2016, 06:45:18 PM »
Thanks for the info, will keep that in mind when I source for the crossover parts. Yes the bitumen sheets may just do the job and will need to source this from hardware store. For the speaker box , did you source the MDF board locally and get it cut locally? or you purchase the speaker box from china source? Anyway when I actual start the project will need more info from you as you have past experience in building this speaker, for now I am reading up the design info before proceed to build it.

You have a few options on the speaker cabinet,

1. DIY

You can get MDF sheets of various thickness from Ban Heng Long in Syed Alwi Road. They will cut to size for a small fee, and also sell veneers. The biggest obstacle for this route is routing - you are on your own here. If you have no experience in making your own cabinet, or veneering, I can understand that this option is a bit daunting.

2. Martin Electronics

Auntie Martin has some carpenter contacts to make cabinets for her. Warning, he isn't cheap and neither is he incredibly enthusiastic about taking on assignments. I suppose it depends on how busy he is.

3. Our enthusiastic audiophiles

I know that Synthesis does cabinets for people, and is happy to also do up the crossover too while he is at it.

I took option 2. When I built this project (This was at least 10 years or more ago), there weren't any cost effective ways of shipping the China cabinets over. Feel free to let me know if you have any other questions on this project. Drop me your e-mail via PM and I'll send you a PDF guide on this project. Many of us used this as a bible and has a number of variants of the crossover for you to try.

jb

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Re: ProAc 2.5 speaker inspire
« Reply #5 on: August 20, 2016, 08:25:08 PM »
Thanks for the info, I would consider the option to take when making the box cabinet. likely i would choose option 1 as have friend that have machine to do the routing.

jb

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Re: ProAc 2.5 speaker inspire
« Reply #6 on: August 21, 2016, 10:50:24 PM »
This is the preliminary simulation of the Proac 2.5 crossover circuit simulation, for now all the component use assume perfect without parasitic stray impedance.

The crossover schematic:

« Last Edit: July 15, 2017, 09:28:44 PM by jb »

jb

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Re: ProAc 2.5 speaker inspire
« Reply #7 on: August 21, 2016, 10:52:31 PM »
The crossover circuit frequency crossover point plot: crossover frequency at about 2.9 KHz



« Last Edit: July 16, 2017, 02:58:35 PM by jb »

jb

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Re: ProAc 2.5 speaker inspire
« Reply #8 on: August 21, 2016, 10:54:45 PM »
The bass low pass filter -3dB roll off plot: -3dB frequency at about 600 Hz



« Last Edit: July 16, 2017, 03:02:13 PM by jb »

jb

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Re: ProAc 2.5 speaker inspire
« Reply #9 on: August 21, 2016, 10:59:11 PM »
The tweeter high pass filter  -3dB roll off frequency at about 3.3HKz, do noted that the tweeter has a -6dB insertion loss due to the series 5 ohm resistor, so you can change this resistor value if you need higher gain for high frequency amplitude.

« Last Edit: July 16, 2017, 03:02:28 PM by jb »

jb

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Re: ProAc 2.5 speaker inspire
« Reply #10 on: August 22, 2016, 02:40:16 PM »
Proac 2.5 crossover actual circuit

I have noticed most published proac 2.5 crossover circuit is different from circuit taken at actual speaker unit that I traced, not sure whether they have make changes to their crossover routing. The tweeter is wire in reverse phase indeed. Anyway will be able to measure the frequency response once the crossover circuit is build. May be some users can comment on this... here is how the actual circuit look like...



« Last Edit: July 15, 2017, 09:31:00 PM by jb »

watchdog

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Re: ProAc 2.5 speaker inspire
« Reply #11 on: August 22, 2016, 09:55:28 PM »
The DCR of L2 and L3 need to be taken into account. Crossovers are quite tricky, it may be better to leave it externally and assembled using alligator clips before you start soldering the components in. Yes, leaving the crossover out affects internal volume, but nothing to lose sleep over.

R1's value is a matter of taste and depends on how "brilliant" you like the HF, and the amount of attenuation you need. I found my Cloneac 2.5 to be quite warm and smooth, so allowing the D2010 to be quite prominent helps balance out the sound, and give a bit of "air".

I am hoping that Synthesis registers an account and helps you out here. He has more experience building speakers in his little finger than I have in my whole body !

jb

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Re: ProAc 2.5 speaker inspire
« Reply #12 on: August 22, 2016, 10:26:51 PM »
Ya, the DCR of L2 and L3 will increase the bass insertion loss but don't think will shift the low pass filter frequency response a lot. I will put those number into the simulation model when I purchase those inductors component and measure it then get a more accurate simulation plot.

I guess all this pre- work is just to get us to within the target zone, the final value tweaking still have to be measured using REW software with Mic, and tuning those value to suit our taste. My bass woofer is from the original Proac 2.5 spk that I had before so hopefully the final crossover component value does not change too much.

looking at the crossover circuit, look like R2, R4 47 Ohm is more for tuning the phase delay response than for frequency. I guess our ear is sensitive to phase delay of sound, it will be a great task if proac can tune the LF and HF phase delay to be minimum at the sweet spot listen position.

yes, I saw Synthesis can design nice speaker with very good mechanical skill and experience. He will be a big plus to our DIY community in Singapore.

jb

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Re: ProAc 2.5 speaker inspire
« Reply #13 on: April 28, 2017, 11:28:35 AM »
Will be using this speaker box dimension to cut the MDF board...

« Last Edit: July 15, 2017, 09:31:25 PM by jb »