DIY ProAc Response 2.5

mvc-004s This is a do-it-yourself (DIY) version of the ProAc Response 2.5 which was one of the most famous speakers in its class made from around 1996 to 2003. This model was replaced by a new model around 2003 called the Response D25, which uses different driver units but still in a similar two-way floostanding concept.

The Response 2.5 is considered to be one of ProAc's most successful and famous designs and is a modern testament to the skill and voicing of it's designer Stewart Tyler of ProAc. It is perhaps among the most full range 2-way floorstanding conventional cone loudspeakers in it's class and is still an excellent sounding speaker even by current standards.

Introduction

This is a "textbook bass reflex design" using good quality Scan-Speak drivers. The drivers used in the design may not be Scan-Speak's top line drivers, but they have been integrated in a very special way to provide the best possible sound. The original ProAc Response 2.5 sound is characterised as very musical, sweet, coherent, tuneful, lush, and with a very bullet proof bass (for its size). What it may lack in extreme microdynamic detail in the midrange and treble, it makes up for this by simple tonal enjoyment, which even many larger and more complex speakers are unable to provide.

The design will provide a ProAc Response 2.5-like or better sound depending on your choice of crossover parts. Try it and you will not be disappointed. For further information, reviews and answers to many questions please refer to the FAQ section, website links and builder comments at the end of this article.

Mid-Woofers Please note that this articles main purpose is to provide a speaker project that is close to the original design in terms of sound character and voicing. After reading this article you may think this is the only DIY speaker project to build because it is well documented and reviewed.

Please remember that all speaker choices have advantages and disadvantages and should be matched to your sound tastes, room environment and equipment. There are many other DIY projects to equally consider to suit your situation some of which can be found in the links to this website.

The information in this article is now over 8 years old, I will need to amend some of the advice in regard to what this website has highlighted (that new SS driver specs have changed making the crossover less accurate)  https://www.hi-end.tk/

The 2.5 clone information will still be relevant if older drivers are found.

Special mention is due to the other authors Ben C & Fred K.

-Al M.

Disclaimer:
These speakers are only meant to emulate the excellent qualities of the ProAc Response 2.5s, and all of the information contained in this site was culled from the public domain. We strongly recommend this project be used for only personal use and not for commercial production.

Dimensions

(.PDF)

mvc-005s Width: 225mm

Height: 1020 mm

Depth: 255mm

Compensate for any major internal volume (2 litres or more) changes if adding extensive bracing.

Approximate weight of finished speaker should be around 24kg/53lb, however choice of lighter weight materials may not affect the sound.

Port is 140mm long by 75mm internal diameter and located about 350mm from top of cabinet, and if desired with internal flanges placed at both port ends inside the cabinet to reduce air turbulence (use either 100 x 100mm square MDF which can also brace side walls or PVC pipe flange)

Tweeter positioned 50mm from top of cabinet and off set 35mm from side edge (Note: CAD drawing mistake should read 84mm from side of cabinet not 74mm), with 10mm gap between drivers. Woofer located 25mm from side edges or centred in middle of cabinet and 160mm from top. Both drivers are recessed into the cabinet. 

Cabinet material and bracing: 25mm medium density fibreboard (MDF) front and back, 18mm sides/top and bottom, single 150mm wide brace around the port or none at all.

It appears some ProAc 2.5 models were braced while others are not and the choice is entirely yours to make. Reports from builders indicate both sound very good. CAD drawing brace shown is positioned under the port in the middle of the cabinet height. 

mvc-007s Cabinet lining is 3-5mm bituminous felt damping or similar mass loaded material, 30-50mm polyester (Dacron 200g/m2 density) stuffing/lining. Wall lining and damping is added to all internal walls, except the front wall. It is important not to over specify or use too much lining so the correct amount and density of lining is used in order to maintain the same voice balance of the speaker. This can have more effect on the sound than other over specified and expensive crossover parts (capacitors and inductors). Over stuffed cabinets will result in undesirable and constrained sounding speakers with less bass and midrange voicing. If you cannot find the correct density or thickness, simply peel away estimated amounts of lining. 

Cabinet internal volume is 34 litres after wall damping is inserted. However, up to 38 litres volume have been reported to offer deeper bass extension. Changes to cabinet dimensions for this should be done by increasing the depth and keeping the front baffle dimension the same at 225mm. 

Install 25mm thick plinth that overlaps by 20mm on all sides, on spikes which improves stability and bass response.

1

ss8535factcustomDrivers

Tweeters
Scan-Speak D2010/8513-00 19mm (3/4") dome, 150W

Woofers
Scan-Speak 18W/8535-00 and shielded type, Carbon fiber paper, 178mm (7"), 70W

Speaker sensitivity 86dB (1W/m)

Impedance load 8 ohms

The internal cable is Bandridge Superflex OFC LC 7403 which is used in original Proacs. This product appears only to be available in Europe unless ordered internationally.

SS8535factorycustom2Crossover

(courtesy of Ben on Madisound Discussion Board, who obtained it from a friend who saw it in Audiophile Magazine in Hong Kong).

 proac_response25_xover

The DCR of inductors in the commercial ProAc 2.5 is unknown, but the lowest possible DCR is recommended around 0.2-0.4 ohm for all inductors."

The original 1996 Stereophile magazine review and technical assessment indicates the tweeter and woofer are out of phase with each other and your final tweeter crossover should reflect this. This is shown differently in the original Chinese magazine crossover, however it is now unanimously accepted and proven by both listening tests and measurements that reversing the polarity of the tweeter on the Hong Kong crossover circuit is correct (see final crossover in the next image).

The internal cable is Bandridge Superflex OFC LC 7403. https://www.bandridge.nl/index2.htm

Thanks to Jacq from Madisound discussion board, measurements have been done using the standard non-customised drivers 18W/8535-00 and shielded 18W/S8535-00, which have slightly different physical parameters to commercial ProAcs but do not affect the sound (See FAQs). 

Using the Chinese magazine crossover with standard drivers produces a slight to moderately audible 2khz peak, which can be reduced by changing the woofer crossover inductor from 1.5mH to 1.8mH and capacitor from 8.5uf to 7uf as recommended by Jacq and preferred by many. Most of the early successful reviews are based on the original Chinese magazine crossover with tweeter polarity inverted.

The differences in sound between the crossovers are moderate but significant. TroelsmodifiedcrossoverSo the Jacq modified crossover is still largely preferred by many who know the original sound of the ProAc 2.5 even to that of other modifications suggested by Troels G. and others who have done much valued further work on producing a more neutral sounding 2.5 clone version, which is a very different sounding speaker (see his site in the linklist). If you seek a more neutral sound or application of the Scan Speak 9500 tweeter his recommendations are highly recommended by many.

The final recommended crossover schematic, which includes all the modifications is depicted in the image to the right…

Thanks to Treols G. for the schematic.

Parts List

Part    Qty. Total
Scan-Speak 18W/8535 2 $266
Scan-Speak D2010/8513 2 $104
Cabinets 2 $100-300
3.4 µf capacitor 2 $50-100
4.7 µf capacitor 2  
7 uf (8.5 µf Chinese crossover) capacitor 2  
47 ohm / 5 W resistor 4  
5-9 ohm / 5 W resistor 2  
0.25 mH inductor (air core) 2 $50-100
0.82 or 0.83 mH inductor (air core) 2  
1.8mH (1.5 mH Chinese crossover) inductor (air core) 2  
Spikes 1 Set $20
Terminal jacks, internal cabling   $50
Total Project Price   US$640-940

Setup

mvc-010s Speaker positioning

Speakers are best heard sitting 2.5-4m/7-12' away from you, situated away from the rear wall and corners due to rear port (front 0.6-1.2m/2-4"away from rear and side walls, space permitting) and toed in pointing at your shoulders. This will improve imaging greatly and reduce excessive bass.

Amplification and source

Any good CD or turntable, solid state (20W plus) or valve amplifiers (10W plus). Speaker will thrive on good healthy solid state power, or do better on nice valve amps to produce a smoother sound. More neutral sounding equipment with less pronounced treble brightness and deeper bass is generally preferred.

Recommended music

It will play many styles of music nicely, but its stated character suit wind instruments (flutes, panpipes, trumpets), female vocals, dance, reggae, country rock, flamenco and others. Here are some recommended CDs that the speakers are matched for (* very good):

Chris Isaak – country rock (vocals, guitars, bass): 1. San Fransicso Days; 2. Baja Sessions*; 3. Forever Blue; 4. Wicked Game*

Andean Legacy – South American Indian music (flutes, panpipes, guitars) Narada Collection *

Armik – flamenco music (Spanish guitars): 1. Gypsy Flame; 2. Rain Dancer

Robert Michaels – flamenco Paradiso *

Eva Cassidy – Blues, country, jazz vocals * Eva by Heart

Nelly Furtado – pop Whoa Nelly

Black Sorrows – rock, country * Lucky Charm

The Fureys – Irish folk music * When you were sweet sixteen

Mary Black – Irish country vocals * Self titled album/CD

Patriot Games – movie soundtrack, Irish folk/dramatic

Enya – Irish female folk * Shepherd Moons

Maire Brennan – Irish folk Whisper to the wild river *

Sweet blue midnights – WA jazz vocals This years kisses *

Gloria Estafan – Latin pop vocals Mi Tierra

Gypsy Kings – flamenco Mosaique

Celine Dion – pop Falling into you *

Eric Clapton Unplugged *

Jennifer Warnes – vocals, pop, country The Hunter *

Aaron Neville – country Warm your heart *

Tracy Chapman Self title *

Medwyn Goodall – new world music, South American Indian panpipes Kingdom of the sun god

Vince Jones & Grace Night – jazz vocals Come in spinner *

Optional Modifications/Tweaks

Flared port;
Hi-end internal cabling like Nordost Blue Heaven, Audioquest etc;
Driver gaskets, (added routing depth required)
Air-core inductors of 12-13 gauge copper
Audiophile capacitors like Crescendo, Aeon, Solen etc. To save the cost of using full uf value higher quality metal film capacitors you can simply connect a low value 0.1uf capacity in parallel with a lower quality capacitor to improve sound quality. This is highly recommended in the tweeter crossover section.

Builders' Comments

from Steve:

For what its worth, just a few Supratek style review comments on your speakers. Firstly, it's a very good speaker...probably in the top 5 that we've owned or evaluated. Coherency is right up there with the best, and you get the impression the sound is probably the best you're going to get from the driver compliment used. Imaging is excellent and better than the original Proac 2.5 which had a softer presentation. The players in the soundstage lock-in nicely in their respective positions and do not waiver. I would have to rank this image locking-in ability as 1). Quad ESL; 2). W.A.R Reference One; 3). VAF-i66 &  4). DIY Proac 2.5 .

The whole sound is very audiophilish and you don't need to make apologies for it. Even the treble which could be characterised as 'raspy' at times, is very special. It has the right amount of attack to make the music interesting at all times, and there's a nice musical harmonic texture to the treble tones. For example, having heard the Proac Response 3.0 with its different tweeter and the Scanspeak 9500 tweeter you have used in other designs, I still feel there is something special about the 2.5 tweeter. These others don't seem to capture your imagination as well.  I also prefer the bass of the 2.5 to most other speakers I've heard. It fills (& energises) the room nicely, and has that soft low extended texture that we like.

All in all, a truly audiophile speaker like the Reference One with its exotic Raven ribbon tweeter and ceramic Accuton mid, still beats the DIY 2.5 (but not by much!) . In the end, there's no substitute for super hi-end drivers which give you ultimate refinement and microdynamic detail. However, I'm not sure that most people have the ancilliary equipment to reveal these small differences - so they are better off (financially) going for the DIY 2.5 which will do 95% of what the expensive Reference Ones are doing.

Having said this, the DIY Proac 2.5 makes you re-evaluate your hi-fi priorities. For $1,100AUS you get a $10,000 sound...I mean you can't even buy second-hand at the $1,100 price point to get anywhere the overall sound quality of the DIY Proac 2.5 !

 

from Draki

"Yes , I just finished mine ... Crossover with ferrite coils and SCR caps ( with ansar by-pass ), box with triple bracing : and YES , they do perform as expected ! Very revealing , details (for instance , incredibly true stringed instruments ) , highs very pleasant , wide sound stage, vocals "out of the box" . The first couple of hours were "thin" , and it is probably several weeks away from full-scale bass . IMO , extremely good value - for the money and in absolute terms ! Thanks to all who helped by posting details on the system .

P.S. driven by Tripath digital amp - a very nice match!

Draki"

"Posted By: Draki

Date: 8/14/2001 05:00

To all interested , I am glad to report that the speakers ( now with over 100 hours in them ) are just getting better ! The bass is all there , and it sounds like a genuine full-range system , of course if used in a suitable room (mine is 25M2). Now that the bass developed , it comes out so naturally that one takes it for granted. As a result , I am amazed that it is the MID-range that cleared up significantly too -they just sound natural , which is the strongest compliment one can assign to a speaker ... It simply involves you into the music."

An excellent system - thanks again to (Al.M) for sharing it with us .

from LeeB

"In addition to Al.M's post on this thread, I can understand your trepidation at investing in a 'new' project such as the ProAc 2.5 clone.

You can be sure however that this is something that has proved to be very very special!

With the help of Al.M and other friends here on this board, I'm enjoying my music far more now than ever before with my 2.5 clones!!

The financial outlay IMHO is far outweighed by the results you will get if you follow the design with the correct drivers and XO as detailed on the DIY 2.5 site. I guess everyone has a different taste in speakers, however after owning many many different speakers, the 2.5 clones are by far the best sounding boxes I've used. Incidentally, I have in the past owned real ProAc response 2.5's and the clone design is pretty damn close. Maybe I enjoy the clones more as I built them and they cost me a hell of a lot less than the real McCoy's. (to build they might cost you only 25% as much for near enough the same speaker!)

Good luck and keep us posted on whatever you decide to build first!!

Regards

Lee B

Gloucester UK"

from Al.M 

"As some will know I have tried my own previous DIY clones of these speakers, and this is by far better and is the real one. The sound is very very close (95%) to the real Proac 2.5 I owned a few years ago. Take note everyone, if you have been looking for a special sounding DIY speaker in this category, this is the one to build, all the hard work has been done. You can build this with a high degree of confidence. For experienced DIY builders it is also a chance to find out what is possible in terms of getting the best results from such a 2-way driver combination in terms of coherence and musicality."

from anonymous

FYI, This is a e-mail I recieved this afternoon from a friend who helped his cousin build a pair of the proac clones for a home recording studio. He is an avid DIY'r and has the usual stash of drivers around the house (some eton's, focals, etc). I preface this by saying I have not heard the speakers nor have I had a chance to measure them so I am in no way to offer any advice or guidance. As they used to say on Dragnet..."only the names have been changed" 
P***,

The clone ProAcs kick-butt!!!!!!!!!!! Deep-deep bass, incredibly 
natural/smooth tonal balance and super-fine midrange detail, huge soundstage......etc. Sounds just like the real thing, meeting the description as stated in Stereophile.

This is the best 2-way system I've ever heard and definitely does not sound like a typical project piece. The first CD we listened to was Beck-O'delay. Good-God, who needs a subwoofer with these things???? All the minute details in the mastering of the CD were there; the analog punch-in noise, instrument noise, etc. I can't wait to hear what they sound like after the break-in period.

G*** is blown away. After the maiden voyage, I went home and listened to Beck on my Missions......They have got to go, now. Screw the Etons, for now, I've got to build some of these ProAcs."

FAQ

davesspks Please take your time to read this site thoroughly as all the information needed to successfully build the speakers is here.  Questions not answered on this site are otherwise welcomed or can be answered by other recent builders on the https://www.madisound.com or https://www.diyaudio.com discussion forums. But please make sure you read the website information before emailing questions as they can often be unnecessary. Please remember to search the website forum archives for answers to your intended question/s.

What is the nature of this Article?

This Article was created through group discussions on the https://www.madisound.com discussion board. It became apparent that much of the key information to build the Proac 2.5 clone was available in the public domain in the form of published material and a DIY site was made possible through the group effort of several core persons and the many contributors. Thank you very much to all those involved.

This article was origionally published as a geocities website.  After 8 years, Yahoo decided to close Geocities and the article was transferred to www.justblair.co.uk

The project is not commerical and is intended for private use only. Therefore, no kits are available and commercial production is not recommended.

Is this the real ProAc Response 2.5 design?

The design has not been copied directly from a commercial ProAc for obvious legal and ethical reasons, however there is a very strong belief through information gathered in the public domain that the design is very close to the real thing.  Comparisons have been made by builders and many report the DIY speaker to be very close, as good or better in sound quality to the real ProAcs depending on the final execution of the design and parts used.  One builder in particular, Jacq, indicates there are small differences in the woofer cone material composition in the form of less carbon fibre used in the customised original ProAcs, which result in a moderately audible 2000Hz peak in the DIY speaker.   

Consensus from many builders on this issue indicate the Jacq modified crossover modifications are very effective and should be implemented to achieve a closer result to the orignal ProAc sound. Furthermore, the addition of the extensive crossover work by Troels G. (see JPO linklist article) to further control the 2000hz peak is valued by those who seek further changes in the sound to for their own tastes and is also recommended for a more neutral sound.

How different are the drivers (tweeter and woofer) between DIY available and commercial customised ProAcs?

The DIY speaker is the closest possible attempt at replicating the ProAc 2.5 given the lack of public access to the ProAc customised Scan Speak 18W/8535 woofer that is used. But with Jacq's crossover modifications and your chosen better quality parts it is believed the difference can be compensated or exceeded. Reported and measured differences of the commercial ProAc 18W/8535 type woofer and those available from Scan Speak to the public appear to be minimal. Visually the customised woofer has about 20% less rough fibre lumps on the cone surface, and basic measurements show approximately 5 dB higher response in the 2500-3000hz region for the non-customised woofer.

Approach to this project for beginners?

This article is not intended to be a step by step guide for every action and decision you need to take.  Any one who has done some woodwork and electronic soldering can easily build the speaker.  So please feel free to improvise and be creative in your choice of materials and methods.  Your approach to this project will depend on your skills in basic wood working, electronics soldering, finishing and sourcing of materials in your local area. 

If you believe you have none of these skills it may be best to find help from a professional cabinet maker and electronics person or avoid such projects altogether.  However, the project is not difficult and any one who is willing to learn and apply themselves will be successful.  It is suggested that you take your time, learn and research as much as possible the links to the site, books such as Vance Dickason’s Speaker Design Cookbook, JPO, LDSG and other website links. The project can take more than 40-50 hours of work depending on your expected level of finish, quality and skills. Unless you are an advanced or experienced speaker builder a simple approach to the project is recommeded.

It is very easy to become obsessed with minor but complicated and expensive choices of materials with little or no sound benifit at the end. In order of importance for this design are: correct density cabinet stuffing, good capacitors (polypropylene or metal film), large gauge air-core(1.8mm diameter/ 13 gauge copper wire) inductors and series resistors in an MDF (medium density fibre sheet) cabinet on spiked feet plinths. Some may argue, but of less importance are: expensive exotic stuffing and wall damping, port flares, bracing, over-specified inductors and capacitors, cabinet edge diffraction round-overs etc. Keep to the recommended design in terms of cabinet size and driver components as you will have enough to do anyway.

Your basic plan approach to this project should be:

1. Source the parts in your area
2. Build cabinet
3. Build crossover
4. Install parts
5. Allow adequate run-in time for drivers and parts

Be imaginative in choosing and obtaining materials. Most of it will be available in some form or another in local stores and shops.  More of this later.

Where can I obtain the materials and parts?

Here is a brief list of places to start looking for materials and parts: Home Depot or wood product specialists for MDF (medium density fibreboard), PVA or similar wood glue, chipboard screws, wood putty, PVC plumbing ports, veneer or paint. DIY audio parts shops or similar places for speaker drivers, capacitors, resistors, inductors, wall damping, insulation, floor spikes, connectors and others.  See website links and your local shop listings. Fabric suppliers or furniture material shops for dacron insulation. Audio parts shops, car repair or rubber material suppliers for the bitumised felt (roofing felt), rubberised lead impregnated or other material for wall damping. Sign writers or cabinet making shops for computer routed recessing to the speaker driver holes or use plunge router machine with circle jig attachment.

Where do I find non-standard value inductors and should I use iron core or air core inductors?

Either have the inductors custom wound to the specification or use standard higher value inductors and unwind enough coil length until the correct mH value is measured with an accurate multimeter. Inductor values of less than 0.01-0.03 mH or even 5% variation apparently make no difference to the sound. The original design uses ferrite core inductors to satisfy lower production costs and maintain low DC resistance. Many builders have used air core inductors with low DCR to achieve theoretically lower distortion over iron core inductors and report good or better sound performance results. 

What is the DC resistance of the crossover inductors?

The DCR has not been measured but it is assumed the lowest possible DCR value of around 0.2-0.4 ohm should be used. The original ProAcs used ferrite core inductors which have low DCR but higher theoretical distortion.  Many builders have used air-core inductors successfully and report audible benefits in midrange and treble detail. Air-core inductors for the woofer will need to be at least 1.8mm diameter coil wire (13 gauge). If you wish to remain close to the original ProAc specifications then use thin gauge (0.6mm diameter or less) ferrite core inductors.

Can different Scan-Speak drivers be used on the speaker crossover?

It is tempting to think this can be done successfully using the 18W/8545 mid-bass woofer and D2905/9500 tweeter but this should not be done without redesigning the whole crossover and changing values, which means it is no longer a ProAc 2.5 clone. The tonal balance of the 18W/8535 and D2010/8513 drivers have been carefully matched and the success of different driver combinations can not be assured. This site can not offer you any further design suggestions, except referral to Troels G. website offering the use of the Scan Speak 9500 tweeter and associated modifications. If you must have different specification drivers we suggest you try North Creek and the various links for commercial kits and other DIY designs.

Should 25mm (1”) MDF be used on all walls?

The choice is yours but the original ProAcs used 18mm (3/4”) side walls, which is believed to take advantage of lower cabinet resonance and assist the voicing of the speaker. ProAc’s choice of “varying wall thicknesses” appears to allow for a slim and elegant design, yet maximising internal volume for bass extension. 

What internal cabinet bracing is used?

It appears that some original ProAc models used a small (125mm wide) single MDF brace fitted around the port attached to the side walls, while others did not use any at all.Your choice will depend on whether you believe that the bracing is desirable or not.

What crossover parts should be used?

Good quality polypropylene or better capacitors (tin foil capacitors) and large gauge (1.8mm dia/13gauge) air-core inductors should be used.  Builders have commented that comparisons between original ProAcs and DIYProac25 speakers indicate there is significant improvement in sound quality in terms of clearer treble, imaging and detail when using the higher quality parts in the DIY speaker.  Any of the premium range of quality parts from each manufacturer will probably be satisfactory. Some common high quality brands include Hovland, Aeon, Solen and MIT.

Where can the bitumised felt wall damping be found, if not what are substitutes?

In Europe it is commonly found in building supply centres, USA (roofing felt) at some Home Depots, and in Australasia it appears difficult.  Substitutes may include other speaker damping products such as Blackhole, lead or barium impregnated rubber or vinyl sheeting found at car repair suppliers, rubber shops and DIY audio/electronics centres.  Commercial floor vinyl has also been suggested and acoustic engineering suppliers have various products such as Deci-damp vinyl sheeting.  Sticky-back, bitumised and lead lined car panel damping sheets are highly recommended and cost effective.  The objective is to use a mass loaded material to absorb vibration, providing about 4kg/9lb additional weight to each speaker cabinet.

Damping and insulating walls?

The bitumised or similar material damping is applied by self adhesive or gluing (rubberised bathroom tile adhesive) and stapling to all inside walls, except the front, which is according to the original design. Remember to maintain the desired thickness of approximately 5mm wall damping to ensure the internal cabinet volume is constant. 

Recessing driver holes and mirror imaging of speakers?

Both the tweeter and woofer are recessed so they sit flush with the front cabinet, which has audible benefits as it reduces edge diffraction problems. Recessing can be difficult unless you have a specialised circle jig to fit onto a router machine. If this is the only speaker project you will ever build it may be cheaper to computer route with a professional cabinet maker or sign writer instead of purchasing additional equipment. A circle jig can cost approximately $30 (see website links) and routers $60. Recessing should be done after the cabinet has been built and surfaces finished to obtain clean edges. Mirror imaging of the tweeters on each speaker means that they are positioned close to the inside edge of left and right side speakers relative to the listeners centre position, which aids imaging.

Driver matching and selection?

Driver matching at the shop can be done by some shops but is an additional cost. If you chose not to match drivers you can request that the drivers supplied are within the closest production batch numbers of each other. Scan-Speak drivers are high quality and the problem of un-matched units is unlikely. Most builders have not gone to the trouble of using matched drivers and still report good results. Reports by one builder of "new" 18W/8535 drivers produced by Scan Speak in early 2003 do not appear to be substantiated on a wider level as described by the darker rear cone coating appearance and measurement of one sample of drivers. Scan Speak has not published new specifications or confirmed this. Other builders do not agree that any new driver exists after as many as 8 pairs have been observed in one case. It is understood that the air drying process during driver manufacture has resulted in slight visual differences.

Crossover design looks the wrong way around?

The crossover polarities on the inputs and drivers are unconventionally laid out but this is the correct way.  The design appears odd but this is what makes the sound so special. Listening tests have shown that a conventional layout in this design does not enhance performance. In fact the opposite occurs with the loss of coherence and imaging.

How long will it take for the drivers and crossover parts to run-in or cure?

Unless you have run the drivers in for at least 72 hours by playing them constantly before listening they will not sound their best. This is because the rubber woofer surround and spider will be less compliant and sound constrained with inadequate bass extension.  If you plan ahead while the speakers are being constructed and run the drivers in they will be ready for you to judge them by the time you listen to the finished speaker. Over a period of 1-3 months or more the drivers and crossover parts will run-in further, sounding much sweeter with more extended bass and clearer midrange.

Further crossover tweaks suggested by Eric Chan at Audioreview.com ProAc Response 2.5 comments?

Eric refers to a local Hong Kong audio magazine that suggested the crossover parts of commercial ProAcs be upgraded using higher quality capacitors, inductors and resistors.  A lower value 4 ohm series resistor is also suggested on the tweeter, which increases treble intensity.  While the use of higher quality parts has merits, the modification of the treble intensity is very system dependant and should be tried with caution.  On bright sounding systems or equipment it may not be appropriate.

Many builders have already chosen to use premium quality crossover parts (large gauge aircore inductors and tin foil capacitors) and are reporting significant sound improvements, but have not chosen to modify the treble intensity as they feel the treble balance is adequate. However, if you find the treble intensity excessive higher value 8-9 ohm resistors can be used in the tweeter crossover to reduce the intensity.

Placement of crossover?

Positioning of the crossover inside the speaker is according to your own preference. Some builders prefer externally located crossovers while most place them internally. Internal crossover placement can be done directly behind the drivers above the rear port, which is simple and easy while reducing internal cable length, or at the base of cabinet further away from percieved or real magnetic affects of the drivers. Each has advantages and disadvantages. If using the Troels G. notch filter on the woofer driver remember to position the LCR filter within 50-70mm of the woofer to reduce the impedance effect of greater lengths of internal wire on the LCR circuit.

Is there a discussion forum for this project?

You can ask any other questions on the Madisound discussion board or at the https://www.diyaudio.com forum, particularly for local suppliers of parts, alternative materials and system matching. If your questions can not be answered contact this website’s email. However, please remember to read all the website imformation to avoid repetitive questions that may be found in this website, on other forum discussion archives and many ClonAc websites on JPO. Many questions will already have been discussed and answered in the past. If you are new to forum discussions please remember to be civil and polite to all members and considerate to everyone's different experiences, opinions and views.

Home theatre centre design

Several people appear to have successfully redesigned and built centre speakers based on the same drivers, crossover, cabinet volume and port size. Feel free to improvise on this concept to suit your own requirements.

Front port design

Several people have reported building these speakers with a front mounted port for reasons such as limited rear room space to control excess bass, while retaining much of the sound quality.

Links

General
ProAc Official website. .
Sterephile review 1996
Troels Gravesen project website and Proac 2.5 clone variation papers
Madisound
DIYaudio.com loudspeaker discussion forum
Parts Express
Speaker City
Scan-Speak

Cabinet Manufacturers
Designs by Derwood
Sonic Craft

Miscellaneous
https://www.cantech.net.au/~supra/
  Beautiful cottage industry valve amps
Pass Labs DIY site

  Solid state amps DIY from Nelson Pass of Pass Labs
Bandridge Cables
Audio Components
  Parts suppliers in Europe.
Audioreview.com
  ProAc speaker reviews.
LDSG
  LDSG guide to speaker building
Stephan's ProAc clone site
JPO Speakerbuilding Linklist
  Lots of links to speaker building sites