Pensil 7 need advice

So I built the Pensil 7 cabinets thinking I would use the MA Alpair 7 speakers, then realized that the Alpair 7 is in generation 3 (7.3) and there is a different Pensil for it...so what driver should I use for the Pensil 7? Don't want to drop in something willy nilly...(hoping the CHN-70 will work, I like the price...)
Thanks!
 
(hoping the CHN-70 will work, I like the price...)

FWIW, in Hornresp sims, technically the cab is too small same as with the 7.3, though of the two, the 7.3 is a bit better fit with less [mid]bass roll-off, though how obvious the difference in bass response would be between the three drivers is hard to say since the room dominates down low.

Note that with either driver, adding some series resistance will flatten them out with up to a ~3 dB loss of efficiency unless driven with a SET amp, but for the apps these drivers are designed for it's probably not a deal breaker.

Anyway, these are Scott's designs that were done using MJK's software, which back when I was using it didn't line up too well with HR, so best to wait and see what he says as well as give me a clue as to how this much more feature filled current version of HR lines up with it.

GM
 
'Sounds' like pretty close. :) Greg, I'll crank them through MJK with / without damping & email the plots etc. over to you, which might help comparisons between the software.

In terms of the boxes, what GM said. Overall it's a bit small for the CHN or the 7.3 although both will go in and work reasonably, with the 7.3 being a touch closer in to the original.

The first Pensil 7 box was actually a touch under-sized compared to the Vb alignment I normally use for the pensils, as I was trying to tickle the response somewhat to balance off the respective gain BWs & blend into a ~'typical' room response. It kind-of worked, but I decided to stick more or less to my usual Vb alignment for subsequent pensil boxes as it gives builders more room (literally) for tweaking to their preference, and within reason I tend to prefer big boxes anyway. You may need to trim the damping a bit, but that's part of the design intention, hence the removable back. To quote my favourite musician, 'I'm a bit old-fashioned in that way, but it suits me very well!'

Attached: top = original A7, middle 7.3, bottom CHN. You can see the latter two have a little less gain through the midbass, notably the CHN as GM notes, although like him, I suspect in practice the differences will probably be swamped out by room effects. As a rule I take all modelled damping assumptions with a pinch of salt given the variability that can exist, so the densities are really just a default / ballpark starting point. Most people seem to find they only need about 1/2 the nominal density, and it's best to keep it a little way from the driver to avoid mass-loading the suspension / cone. YMMV as always, and, as GM also points out, this will also vary somewhat with the amplifier output impedance or any other series R.
 

Attachments

  • Comparisons.png
    Comparisons.png
    24.8 KB · Views: 296
Thanks a million for the info. I wouldn't say I have a trained ear so the CHN-70 should be fine. As for damping, I am using unfaced fiberglass insulation. Lined the top around the driver area by stapling in about 1/2 inch of material and then stuffed the bottom with 0.7 lbs, using dowels to keep it above the vent. Let me know if you think that is a good starting point or should I reduce the amount. Thank again, can't wait to hear how they sound. I'll post pictures if I can figure out how to upload. PS- I'm using an Elekit TU-8200 in pentode mode (about 6 watts/channel) with TU-8500 pre-amp.
 
OK, so I put the CHN-70's in my Alpair 7 cabinets, broke them in as long as I could possibly stand it (two full weeks at medium levels). Can these little 4 inch speakers be sounding as good as I think they are...WOW...at $27 a piece I'm one happy camper...
One quick question on damping. I've got 0.7lbs of fiberglass insulation in each, if I reduce this would I expect more or less bass. Thanks...
 
Chn-70 in Pensil 7

OK, so I built the Pensil 7 cabinets and put the Chn-70 speakers in it...been listening at medium levels for about a month or so for break in...Elekit Tu-8200 and 8500, giving it some time to break in. I'm just starting to crank it up, WOW...tonite I put it about 7 and I'm blown away (in a very good way), my question is can I hurt these speakers with over driving with my amp (6 watts)...Thanks...
 
It's always been opinion that the spectral content ( i.e. high orders of harmonics) of a hard clipping under-powered amp can be more damaging to speakers - most particularly tweeters and any crossover attenuation components - than when playing at the same volume with a much more powerful amp. A great laboratory for this type of failure mode is the mobile audio environment.

There are of course those who will opine that the "softer clipping" / compression of a vacuum tube amp would mitigate this somewhat, and you are talking about a full-range driver with no filters / protection described, but caution is always advised.

short answer: "careful with that axe, Eugene"