Mark's new Alpair 12

[tinitus]

Originally Posted by markaudio

Hi Scott,
Thanks for the info.

Hi Tinitus,
I'll explain more about the Alp 12' mechanical properties ASAP.

Cheers,

Mark.

That would be nice, thanks

Scott, I understand perfectly well the advantages of wide BW
Whether its a fullrange or a woofer? Well, more like a cameleon that will do both
With the drawback of sitting between two chairs
Seems obvious to offer two versions with different specs

Im not negative. On the contrary. I think it has huge potential, or I wouldnt be here
But if theres a better way of showing respect, let me know
It shouldnt be perceived negative
But I will hold my breath until we know the price range

[GM]

Originally Posted by freddi

Beta 8CX "works" in k with Vas of ~20 liter -

-- does front chamber height have some control of response?

It also has a 20 Hz higher Fs while having a 'close enough' same Qts. Bottom line, when I double the 12's Vas, it sims as I expect it to, i.e. has the same BW/response slope as others with similar specs that I believe will work well in a K.

Its Vb dominates of course, but any strong enough eigenmodes will certainly modulate the diaphragm and weaker ones will comb filter with the driver's direct radiation, so for wide BW response it seems reasonable to me to minimize them as much as practical. Really, in the good ol' days, grill cloth was used to smooth/filter HF output and based on Dr. Geddes's research, finding the right density foam plug for the front cavity might be the next K tuning 'breakthrough'.

GM

[GM]

Originally Posted by markaudio

Is it OK to send you a message via the forum?.

Sure, it's why I don't have the feature blocked.

GM

[markaudio]

Mike's rightly pointed out a typo

Cms should be MM/N (0.750)

Thanks

Mark.

[Jozua]

Mark


Do you have an optimum enclosure design ready for the driver or must we wait for GM who seem to have done excellent work w.r.t. the Jordan drivers?

GM

I was tempted by your positive comments re the other 8" driver you recently tested but this one seems much better.



Regards


Jozua

[markaudio]

Hi Jozua,

I'd be most happy if Greg were to contribute some ideas if he has the time and is happy to do so. Other DIY members are gradually getting some ideas together that will become plans. This take time so keep a eye on this site in the coming weeks. I'm hoping DIYers will enjoy the Alp12's and illustrate their work in the months to come.

I will be posting some plans (thanks to Scott for a suggestion) in the coming weeks.

I'm busy getting ready to publish the Alpair 7 so it will take some time.

Cheers,

Mark.

[Scottmoose]

For sake of information, the aforementioned is as simple as it gets. Strictly 1940s era stuff (no bad thing). I just sketched out a traditional pre-T/S style BR tuned to 60Hz. After that, just stuff the box to taste to smooth things out. Job done.

It's not high tech., and it's not clever. But I bet it'll sound good. Big boxes = fun. Which is the point.

[markaudio]

Hi Tinitus,

I’ve received several requests to comment on the linear performance of the Alpair 12. So I’ve spent some time putting together some pics and thinking about how I can explain some of the mechanical properties involved. The forces involved in the execution of LF excursion are complex so I'll cover one aspect relating to spider design.

First, I tend to err on the conservative side of giving figures. Typically, following a convention of illustrating Xmax, the total mechanical movement for the Alpair = 18-mm and with retention of the winding within the motor’s influence, 1 X = 9-mm. Those that know my designs recognise this Alpair’s ability to make use of longer excursions while retaining linearity at low levels of distortion.

However, is is likely that anyone would drive a full range unit constantly at its Xmax? The answer is NO. At least I sincerely hope not. Apart from blowing ear drums to bits, the distortion would be unbearable, the potential damage to the driver’s suspensions and motor system will be significant.

As a rule of thumb, for any user wishing to operate a full range unit at high loads on a regular basis; I’d recommend not to exceed two thirds of the total available excursion, hence my 12-mm figure for the Alpair 12. This recommendation INCLUDES any running in period.

OK, now for the more important issue: How the Alpair 12 has a particular set of LF linear-mechanical properties. The primary component controlling the longer excursion on the Alpair 12 is the spider. The front suspension is secondary. Please take a look at the following:

1 - First, please study the pic titled “conventional spider”. Notice the profile of the spider is uniform. Each ridge is size proportional to the next and concentrically evenly distributed to the next.

2 - Now take a lok at the pic titled “ Alpair 12 spider”. You can observe that each ridge is non-proportional to the next, both in size and position.

The mechanical properties of the convention spider delivers a particular resistance proportional to a given X load point. This has some drawbacks. The first is a non-linear damping effort while overcoming the inertia of the power-train, particularly at the initiation of a LF oscillation. Makers jargon sometimes names this effect "rolling bounce". Second and more important is the design may offer little control towards the limit of excursion. Many of us have driven a woofer to a point where the coil has hit the back the the yolk plate. Most makers try to overcome these challenges by simply making a stiffer spider but this approach while partially solving the resistance challenge, creates others (sorry no time to go into this now).

The Alpair 12’s spider is different. It is designed with a specific resistance profile. There is moderate resistance on short X-LF loads. Going through the normal operational range, the resistance profile continues to be proportional to the loads, then stiffens near the limits of the excursive load. Since the front suspension is extremely soft compliance, the spider operates the significant part of the load damping and maintains the oscillational stability of the power-train.

This goes some way to explain why I was late delivering the Alpair 12, I wasn’t a happy bunny with conventional spiders. The alpair 7 also uses a special spider, more about that later. There’s a lot more reasons as to why I designed the Alpair 12 in this fashion but I’ve already written allot so will save for another time.

Finally, I know there’s a few fellas eager to run the Alpair 12 as a woofer. Please chaps, remember this is a full ranger. Use this driver for its intended full range purpose. You’ll get plenty of nice controlled bass by making a good optimal box for this driver. Henry has already asked me to design a woofer version, I’m happy to do so if demand is sufficient.

Have fun

Mark.

[tinitus]

Originally Posted by markaudio

Hi Tinitus,

and with retention of the winding within the motor’s influence, 1 X = 9-mm.

However, is is likely that anyone would drive a full range unit constantly at its Xmax? The answer is NO.

Please chaps, remember this is a full ranger. Use this driver for its intended full range purpose.

Henry has already asked me to design a woofer version, I’m happy to do so if demand is sufficient.

Mark.

[GM]

Originally Posted by Jozua

Mark
.........or must we wait for GM who seem to have done excellent work w.r.t. the Jordan drivers?

GM

I was tempted by your positive comments re the other 8" driver you recently tested but this one seems much better.

?? Link?

Sorry, no time to delve into potential alignments beyond the quick TTQWT sim to confirm what I assumed for my response to Freddy, i.e. low Qms, Vas = OB, sealed, aperiodic, compression horn, so performance wise, not hopeful in a super sized Jordan MLTL.

GM