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 http://www.madisound.com or http://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 site?
This site was created through group discussions on the http://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.

The site is not a commerical site 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 website 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 http://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.