Mark Audio Alpair 10p Gen 3 - Tuning

JoeyGS

Member
2007-08-21 2:44 pm
Hi,

We have an Alpair 10p Gen 3 built with a Pensil box.

When compared with a CHR-70A Gen3 also in a Pensil box, the CHR-70A has better high frequency output than the Alpair 10p. Both of these drivers have extended high frequency capability.

Questions:
1. Is the CHR-70a really better than the 10p?
2. What could be wrong with the tuning of the 10p that would cause a less quality high frequency than the chr-70a? resonant baffle? over stuffing/dampening? inadequate stuffing/dampening?

Would appreciate insights from the experienced speaker builders.

Thanks in advance.
 
Questions:
1. Is the CHR-70a really better than the 10p?

That rather depends what you call 'better'. The CHR is a smaller driver with slightly more HF extension / output than the larger 10P. Having an alloy cone, its basic resonant characteristics are also somewhat different to the fiberglass-reinforced pulp cone of the 10P. Given that they both have relatively flat cone profiles, dispersion in practice will be quite similar, despite the size difference.

2. What could be wrong with the tuning of the 10p that would cause a less quality high frequency than the chr-70a? resonant baffle? over stuffing/dampening? inadequate stuffing/dampening?

Assuming that the enclosure is well-designed and built, what you're hearing is most likely just the differences between the drivers. A monopole speaker enclosure is only functional over a very narrow bandwidth, above which its sole job is to provide a solid mounting / platform for the direct radiation from the driver. As far as construction goes, too little damping can cause early reflections back through the cone; too much can mass-load the suspension & diaphragm, preventing them from moving / resonating as designed. Ideally you want to minimise edge diffraction etc. too, although that is typically less of an issue with FR driver types. Ideally bass enclosures should be as stiff as possible, which will raise the panel Fs to a point where it is unlikely to be excited and any minor resonances are easily killed.

As a general rule (there are exceptions), assuming similar driver types / qualities, a small wideband driver will tend to have a performance edge in the higher frequencies over a larger unit. Conversely, under the same conditions, the larger unit will typically have a performance edge over smaller drivers in the lower frequencies.
 
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Driver Comparison;
I have had both the CHR70 in Frugelhorns and 10P in Pensils, which is what I am using now. I recall that the CHR had a stronger and slightly harsh top end while the 10P's top frequencies are there, but cleaner and not exaggerated. Overall I am satisfied with the 10P treble response.
Stuffing;
My pensils are lightly stuffed from below the drivers to about 10 cm above the bottom of the cabinet. I also ended up adding some thick felt on the sides and back of the cabinet insides around the driver area to reduce back reflections to the cone, similar to what is recommended in the Frugel Horns. That helped clean up the upper midrange and treble response.
 
I would like to add some comments/questions on these issues - JoeyGS has the dual CHR-70 (seen in another thread by him) presumably side by side in the same room with the single Alpair 10P enclosures - that room in those images is acoustically treated, doesn't it mean that extra sound absorption perhaps balances things out for a brighter sounding cone? and leaves the more polite paper cone a bit shorter than expected...
Second of all 2xCHR70 = 100cm2 compared to 88cm2 for the Alpair 10P (extra 13% radiating surface) and Qts is higher (bassier) for CHRs - doesn't that mean extra bass output considering same type of enclosure?
I was going to ask JoeyGS for a long therm review of the dual CHR70 setup when I discovered this thread in which he questions the Alpair's performance rather than the CHR's - on paper this (CHR) seems to be the "better" option - more bass/highs & upper extension/better dispersion.