Proac 2.5 clone , really good speaker?

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I dont really see any major flaws in the speaker, and it looks to be a great project for a two way. However, the speakers aren't very high efficiency, and they are 8 ohms, so your current amp may not put out as much juice as they would into, say, a 4 ohm speaker. If you're looking for something with a bit higher efficiency, the VSS Eros project from SpeakerBuilder uses and MTM design with Vifa and Scanspeak drivers, and can be built for less than that of the Proac clone. There are a number of Ariel speaker projects on the net which have excellent results as well. But if you have your heart set on the Proac clone, you cant really go wrong for less than $1000 dollars in parts.

(The Dayton IV Veritas project on speakerbuilder also has me intrigued, I can't wait to check it out!)

The VSS Eros can be found here:

Good Luck!
You could do that, but then again, it would defy the purpose of building the ProAc clone in the first place. Aside from similar appearance, if you change the crossovers and drivers, you are basically designing an entirely different speaker, which is likely to sound very different from the clone seen on the site. Designing the clone the way the site tells you all saves a good deal of time and testing. As I said, if you like the design, go for it. However, don't expect to be driving these fairly inefficient speakers with 6 wpc amps. Does lower efficiency mean its a poor speaker? All designs have tradeoffs, and in this case, its the need to be driven hard with a good deal of power.


By the way, the plans for the eros speaker can be found at the url I gave earlier. The title is something along the lines of 'The VSS Eros'
*first post!!! 8) *


I think proacs are of fantatic imaging, soundstaging and transparency should be a complicated design with really customed drivers.

I suspect the enclosure isn't as simple as your avg crossbraced box and that good dampening materials are used.
Anyone opened one up and peeked inside?

Perhaps whoever is attempting this project should a deal more attention to the enclosure design. Added bracing, reducing the amount of parallel surfaces and good dampening stuff like blackhole5, etc.
I owned two sets of Proac's before I discovered DIY and I was amazed at how simple the cabinet was, no bracing, 18mm MDF and simple foam and bituminized felt damping.

And the crossovers were built with fairly cheesy parts, for me it was an excellent example of "it's not what you use but how you use it" at work.

It was also left me with the opinion that a lot of commercial 'speakers are very poor return for the dollar spent and that it is possible to do as good or better with a well designed DIY project for much less.

A friend of mine has built the 2.5 Clone and he tells me that they are amazing for the money and by the way you can get the drivers from Rolph at for much less than anywhere else and I have dealt with him several times and can recommend him with no reservations.

Have Fun.

Tony D.
Ew, so the Proac response enclosures are really that simple huh, there goes my faith in another hifi manufacuturer...

I reccomend using some good dampening material like Blackhole 5, using thicker (3" is good) enclosure as well as real wood veneer both inside and out. Not to mention higher grade crossover components and internal wiring.. should beat the original at 1/4 the price :)
T-S model .vs. real response?

I have been working on my own design for some time when I saw this thread. I immediately wondered how the theoretical performance of these compared to my own design. I plugged the T-S parameters for the bass driver into WinISD. No matter what I do with box size or tuning I cannot get the f3 anywhere the 20Hz quoted by ProAc for the real 2.5. The "ideal" enclosure gives an f3 of about 35Hz.

Anyone care to comment of the possible reasons for this?

The possibilities that come to mind are:
- The model is flawed
- The software is flawed
- The driver is not as "good" as the ProAc
- The real 2.5 does not really have an f3 of 20Hz


Not being familiar with the 2.5 myself, there are a few things that I can think of. One of them, as you mentioned, is that the driver is not as good. Although an additional 15 hz seems rather steep. Another possibilty which may get you slightly lower is the type of enclosure used, such as a bandpass design or alternative design for the bass chamber, though I doubt any 6 1/2 inch or 8 inch driver would have 'usable' bass down to 20 hz. In my opinion, there are several speakers that may reach down to 20 hz, but with output levels of but being down so many db's at that frequency that its not even audible. Odds are more than likely that the 2.5's ratings were quite exaggerated. Rarely if ever can a well design 10 inch driver reach 20 hz without being down well in excess of 6 db's, yet alone a 6 1/2 inch driver...
Yeah, there is no way the 2.5 bass response goes down to a usable 20 Hertz in my opinion. I have heard the original with excellent electronics and bearing in mind the room etc. they just don't have that bottom octave ompf.

But still amazing bass for such a small mid-bass.

Tony D.
No loudspeaker in this size goes down to 20Hz.
But who asks for 20Hz ?
That is no bass anymore, just a deep rumble, virtually no record has significant energy in that region for a good reason, because it is musically complete irrelevant and it just sucking energy from the amplifier.
Bass, real bass, is at least an octave or more higher, and can be reproduced by reasonable sized or constructed loudspeakers.
If ProAc claims 20Hz for their speakers they are either liars or it is technical babble by somebody who just wrote the leaflet...

I heard the ProAc 2.5, and I think it is a capable design.
The parts from ScanSpeak are surely one of the best available, and most of all the HighEnd manufacturers in the world use them in theír better designs.
But they are expensive, nothing just to tinker with.

There is much more needed to make a good loudspeaker. Why do you think all these manufacturers have all this costly equipment for testing, do you know how many premature designs are tried and rejected ?
If you find a trusted plan, or you have the possiblility to hear the loudspeaker first, stick to it as close as possible. Any modifications can be a deadly path (Listen to an experienced man !). For example, changing the loudspeakers from 8Ohms to 4Ohms changes everything completely, mostly because the loudspeakers are not similar and have a different Qts, etc.
And the perfect and balanced mechanical construction is as important as the parts used. (I have seen many "over"done loudspeakers, good looking but awful or lifeless sounding...)

Did you know that NaimAudio uses (ore used) relativly cheap MordauntShort parts for their smaller speakers ? But they are modified cleverly (with resonating dampers) and they are put into a complex box. The first SBL was made with a bass speaker which was also used by MS for their own humble design, the MS20. But the SBL was (with a clever decoupled ScanSpeak tweeeter) sounding so much better, there was no comparison ! (It was - alas - also a lot more expensive...)

If you are in doubt, search the net, there are some more designs with ScanSpeak chassis. This speakers are mostly used in the classic way of small and heavyly damped boxes, with low efficency (the opposite to light open high efficient tube friendly designs).
You will need very good transistor amplifiers to get a ProAc (or a good clone) to life !

But you can try!

Best wishes
*Raises hand*

I, for one, am one of those in search of deep, deep bass. It all depends on your musical preferences. If you are like Grey, for example, you experience nearly orgasmic levels of excitement when hearing and feeling the lowest note of a pipe organ in all its glory (as he does with his 12, 12" drivers). Some may view it as a rumble, others, with properly designed subs, view it as much, much more. There is more to music than 40hz+ if you aren't devoted to vinyl...

As for the ScanSpeak drivers, I couldn't agree more. Their carbon fiber filled paper midrange drivers are probably the best midrange driver available in cone form (as not to offend any ribbon folks, but sorry, I'm a coney as far as bass and midrange go :)). You can find them in the majority of high end speakers nowadays, including Wilson, and even Sonus Faber is using them now. Are they expensive? Yes, are they worth it? Yes, if you can integrate it properly...
Bass ends an octave above 20Hz?
I'm cross-eyed, not knowing where to start.
Okay, let's say dynamics, just for fun.
Any and every waveform begins at 0Hz, no matter whether it's an organ pedal or a ride cymbal. There's no such thing as an instantaneous rise from no sound whatsoever. If you begin at 0V, and begin any arbitrary signal, there will be a ramp-up period as the waveform begins. The frequencies will rise from 0Hz on up to the supersonic depending on the instrument. If you want an easy example, use a bass drum, which will have strong information content well into the infrasonic regions.
Okay, so what about pitch?
These days a goodly number of bass players use 5 and 6 string basses with the lowest string tuned to a low B...30.8Hz. Synthesizers are routinely pressed into service for low frequencies. Large organs go to 16Hz without batting an eye.
Just for fun, read up on Fourier analysis of waveforms. Every waveform, no matter how complex, can be broken down into a combination of sine waves. Some of surprisingly low frequency.

I have built several speakers using scanspeak. I dont think the carbonmids are scanspeaks best, try the 8546 a kevlarunit. In a 15 Liter box, 6 db. xover and the best scanspeaktweeter you can afford, its avesome! And the db is a bit higher than the carbon units...I agree with making the box as solid as you possible can. Try building it double wall with sand inbetween...
Sorry, folks, I did not want to rise a quarrel. Let us stay "on the carpet". I surely did not mean that bass ends at 40Hz.

But we are talking about the ProAc 2.5 here, aren't we?
I was talking about a clean and linear frequency response down to 20Hz, which is definitely a impossible thing for a 18cm Loudspeaker. It will move or waffle (also because it is a bass reflex speaker), but the actual sound emmission will be non existent.
Of course there is (or can be) musical information below 40Hz. But your speakers will have to move a lot of air to reproduce this frequencies properly, and you can do that only with big loudspeakers (12 inch and more), either horn loaded or highpowerded.

Grey, let us talk about the "grey-zone" (!) of bass frequencies here.
You mentioned the deepest organ pipe, with 16Hz, but you mostly hear the first harmonic, even live in the church. I even suspect that one can hear the louder second harmonic even more, thats why this pipes often sound strangely "out of tune".
It is the same with the deepest note of a bass, you will hear also or even stronger the first harmonic and the whack of the beginning of the sound, which is obviously much higher. That is the main reason, why bass players tune their preamps and amps with treble and midrange controls. It is a matter of balance and control.

If you have access to a computer equipped with a professional soundcard, try some examples with your amp and speakers:
Create a few sinusoidal signals below 30Hz f.e., or a quarter-octave wobbled sinus below 30Hz.
Listen to that: You will hear your loudspeakers membrans moving (a distortion maybe with some harmonics), some resonances in the room, maybe you hear the wind of the bass reflex ports.
Try to create impulses with low repetiton rates. You will hear the quality of the impulse (the frequency response of an ideal impulse is equal for the whole frequency band).
Continue and create a littel melody with sinus tones below 40Hz:
Can you follow the tune ? Can you tell if the melody is right or not ?

I am a composer and audio professional for a long time now, I actually did a lot of hearing and a lot of acoustic measurements too.
When I was composing a part of "TIDE" (for eight channels 1995,CD 1998) I used a special granular synthesis technic to transform sounds. For a part in the piece I created a slow glissando downwards, the sound went down to the lowest octaves till it was vanishing. An interesting experience: In the studio I was using big Genelec active monitors. When the sounds reached the lowest possible frequencies I could only hear the air coming from the bass reflex ports, I could actually fell the wind in my face. In the (big room) concert situation I played this piece once via big Klipschhorn loudspeakers and the audience could feel the sound dissolving "into thin air". But this was "air" (harmonics) and "wind" (low rumble), no definite pitches anymore, the glissando effect was continued "in the mind".
On a normal hifi setup this effect is much less present.

You might guess now that I really DO like the deepest frequencies too. But - to come back to the ProAc - you will need BIG loudspeakers for that.


ps: Grey, you are right about the fourier analysis. But it proofs that the opposite you said is true too - there is no sound without another, harmonics starting upwards from the lowest or the loudest frequencies. Bells (or drums) have also subharmonics, but they are always less loud than the main frequency.
But: "Any and every waveform begins at 0Hz..." So what? There is a difference between a ramp and a periodic waveform. And what does that have to do with dynamics ? Here I cannot follow your thought.
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