Alpair 7 & cabinets - opinions sought

[roscoman]

Hi guys
I'm interested in a starting fullrange project and the Alpair 7 gen 3 look very interesting. However, I'm not keen on the Pensil cabinets, for two reasons. Firstly, I don't understand them I don't 'get' them; they don't seem to follow any of the basic cabinet patterns I've seen before (I am very much a novice here). Secondly and more importantly, I have a bit of an issue with vented designs because my experience of them is of 'sloppiness' and I really like a tight sound, especially in the midrange. The problem of course is that closed cabinets lack bass. I want my cake and eat it.

So I had an idea that I'd like to run past anyone who'd care to listen. I want to make a dual enclosure. Vented for the bass, closed for everything else. As I thought about this, I reasoned that if I used two identical fullrange drivers I could avoid having any crossover above 200Hz and also get near-perfect driver matching into the bargain. (There might also be cosmetic benefits of having two identical looking drivers and aesthetics are a consideration for me).

It might seem like a subversion of the fullrange ideal but that aside, does the idea have merit? Does anyone have any experience of dual enclosures?

Big thanks up front
Ross

[motosapien]

Starting from scratch on a box design is ambitious. I used two EL70's in my project wired in series with a 68uF cap across the second one which filters the highs away from it. Really brought the bass and highs into balance. Also makes for an 8 ohm load which is easier to drive.

You are not going to get serious bass from a 4" driver. Down to 50hz perhaps. You might try Scott's Maeshowe design with a sub and get the best of both worlds. Or planet 10's golden ratio design again with a sub. The Maeshowes would be lovely and majestic and the bass they do give would be taught and articulate I'd bet. Good luck!

Woden Design | Maeshowe

[woodturner-fran]

Frugal horn mk3 maybe?

[zman01]

Roscoman,

I have Alpair 12 in Super Pensil 12 - biggest Markaudio FR driver in biggest Pensil cabinet.

Bass - tight and nice! Not a hint of sloppiness. Actually all the FR drivers I've played around with have tighter bass and better mids (more natural, much more detail) vs a lot of 3 ways I've listened too. The Pensil design is a MLTL variant AFAIK.

I'm currently breaking in a pair of Alp 7.3 - too early for me to comment on listening experiences, but read that the Alp 7 (previous) gen had great mids and decent bass in a range of cabs - Mar-Ken, Maeshow, FH MK3, Pensil.

But pls note - FR drivers will not give you bass like subs or dedicated large woofers. As the saying goes - there's no replacement for displacement! But quality bass at moderate SPL levels in the 40s - yes, I get that and am happy with it.

What you talk about in your dual enclosure is akin to FAST (Full Range AssisTed) - a full range unit assisted by woofer or subwoofer. You can read more about that on the forums. Definitely a good way to enjoy best of both words.

[roscoman]

Thanks for the replies. I'm not desperate for big bass below 50Hz, just so long as it's all nice and tight. So maybe I should reconsider the Pensil design. I'm just uncomfortable with using a design I don't really understand. Maybe I'm making a mountain out of a molehill but when I use ISD online to model the Alpair 7 driver, the optimal vented cabinet volume is much smaller than the volume of the Pensil cabinet. And the vent doesn't seem to have a tube. My (limited) understanding of a vent was a tube of air that resonates with a frequency dependent upon the dimensions of the tube. A simple gap at the bottom of the baffle doesn't seem to operate this way to me. This leads me to think that the Pensil uses a totally different philosophy to the other patterns I've seen (sealed, vented, rear-loaded horn etc).

Could anyone explain it to me in fairly basic terms?

[chazdrumzalot]

There should be lots of info about the concept behind the pensils; As I understand it, they're a form of transmission line whereas your 'sloppy bass' impressions are more likely related to bass reflex enclosures. From everything I've heard, transmission lines produce very controlled and articulate bass and the pensils have been thoroughly tested and approved by numerous DIYers on this forum.

edit: have you read through any of the pensil threads in the mark audio forum?

[chrisb]

Originally Posted by roscoman

Thanks for the replies. I'm not desperate for big bass below 50Hz, just so long as it's all nice and tight. So maybe I should reconsider the Pensil design. I'm just uncomfortable with using a design I don't really understand. Maybe I'm making a mountain out of a molehill but when I use ISD online to model the Alpair 7 driver, the optimal vented cabinet volume is much smaller than the volume of the Pensil cabinet. And the vent doesn't seem to have a tube. My (limited) understanding of a vent was a tube of air that resonates with a frequency dependent upon the dimensions of the tube. A simple gap at the bottom of the baffle doesn't seem to operate this way to me. This leads me to think that the Pensil uses a totally different philosophy to the other patterns I've seen (sealed, vented, rear-loaded horn etc).

Could anyone explain it to me in fairly basic terms?

FWIW, the Pensil series were designed specifically for the Mark Audio drivers, there's nothing particularly foreign or revolutionary about their principle of operation, but I don't think you can compare it to an "optimal" conventional vented ( BR?) design.

More than a few (by now probably scores of) pairs of various sizes have been built and enjoyed by folks, including myself. I don't fully understand how my touch screen iPhone works, but it doesn't stop me from using it.

Someone, perhaps Scott if he has the time, could explain how (if) it's different from other types with which you're comfortable.

It wouldn't hurt to spend some time here:

Quarter Wavelength Loudspeaker Design


Martin is one of those guys to whom the DIY speaker building community owes a huge debt of gratitude, even those of us (like me) who get lost in the math after " see equation 1 below" .


As with many MLTL and other "1/4 wave" enclosures, the damping fill is an important part of the design, and when built following the instructions, and with fill adjusted by ear, the bass will not be lumpy or sloppy. I've heard far boomier LF performance from a couple of expensive commercial BR enclosures than the Alpair 7 Pensils or Maeshowe.

[mondogenerator]

agreed. the pensils arent conventional in the sense, but arent complex enough to hinder you should you wish to build them and have reasonable woodworking skills. Im terrible at woodworking (but great at sanding) and i have built several systems. since the design was made for the mark audio drivers and fostex in mind IIRC, i believe you can trust that they will perform as expected, as long as you dont expect the windows to rattle at 20hz

MJK site, who Chris linked is well worth a look, and will answer some questions. perhaps inspire more questions, as it did for me. I cant use Mathcad for toffee, but i was able to use the 'original' alignment tables and a scientific calculator to calculate an initial design for my own Tapered line. a little help from others who CAN use the worksheet software helped me out with the additional tweaking and simming. ive now got the task of FINISHING the project......

TQW lam build progress

still a work in progress, not enough hours in the day blah blah, but it may give you an idea what efforts new design could require. although the pensils are very well documented, if you search threads here youll turn up a whole plethora of results.

[vinylkid58]

Originally Posted by chrisb

I don't fully understand how my touch screen iPhone works, but it doesn't stop me from using it.

LOL!

[chrisb]

rosco - sometimes chrisb gets a little cranky / snarky - he's practicing the grumpy old man thing before "some-timers*" starts setting in

not all-ze-time, just some of ze time

he's also inclined to refer to himself in the 3rd person