First speaker build - Alpair 10p

[hankhill]

Hi All,

I was originally turned on to the 10p by reading a thread here using the Pencil design, so I went ahead and ordered up a pair of drivers and some terminals.

However, my primary use for these will be while working at a desk, and after putting a bit more thought into it, Pencils on the floor most likely won't give a clear line of sight from my ear to the drivers, and setting them on the desk doesn't seem like a good option either.

I've since been looking at either Planet10's CGR, or the Mar-Ken10.

Can anyone comment on any characteristic differences between these? Or any other suggestions? I notice the CGR design specifies variations for the 10.3 vs 10p driver, while the Mar-Ken does not (older design I presume).

If the material I use to construct is of a different thickness than specified in the plans (.75 in/19mm vs 18 or 15 mm), should I just adjust dimensions to maintain the same interior measurements? Or will the difference be insignificant? I plan to use 3/4" MDF, and likely add some type of veneer later on for aesthetic purposes.

Thanks!

 

[zman01]

I have built both types (for other drivers, not Alpair 10P) and found them good.

P10 has made available the CGR Mar-Ken designs free for DIYers; most of the Mar-Ken (non-CGR) plans are part of paid plan-sets.

You need to maintain interior measurements. Dave and Chrisb both recommend use of quality plywood for their designs.

 

[planet10]

Thanx Zia,

The CGRs, rectangular miniOnken, trapezoidal miniOnken, and, if the volume is sufficient, the Compact Floorstander all use the same tuning with variations in the box shape aimed at suiting a user's particular needs. While they do not sound exactly the same (mostly due to diffraction signature) they are very similar. To get the best diffraction signature (which helps reduce the ability to "hear" the speaker) takes the hardest to build boxes.

A full planset costs a modest amount of money. http://www.diyaudio.com/forums/plan...10-hifi-minionken-plan-set-subscriptions.html

I typically put one of the plans out for free use -- usually a CGR -- as a teaser. The paid plansets are more complete with many more design variations (the A10x plan set is now over 60 pages)

The Mar-Ken10 is for the original Alpair 10. There are variations of the "same" box for both A10p and A10.3. For the A10p there is also a series of slightly larger boxes.

dave

 

[chrisb]

hank - a couple of thoughts;

- Full floor length designs (Pensil/ Bob Brines' MLTL, FHXL) will deliver much more of the LF extension and "punch" of which these drivers are capable. I have a pair of the compact floorstanders that Dave mentioned in one of my own systems (7.1 video system) and they work quite well.


- At the risk of opening up that can of worms again, would your budget have room to use BB or Apple Ply? Whatever your final choice of material, it'd be the internal dimensions that you'd want to maintain, but yes, the minor fractions of inch or 1 mm would be a problem. I've been using 15mm BB ply for the cases, and 18mm for the fronts on most of my builds for years. Thinner 12mm would be fine for the smaller drivers such as A5.2 and the new CHS70. Also note that the cast composite resin frames on all Alpair drivers are thick enough to require between 9- 10mm of rebate for flush mounting. While others might disagree, I'm of the opinion that with the high ply density of BB that leaves more than enough core when using 18mm for carefully tapped holes for supplied screws to do their job. These drivers aren't heavy and don't need to torqued with the same pressure as say a JBL 15 woofer.

 

[hankhill]

Thanks for the input!

Dave - I'll shoot you a PM about plansets.

Chris - regarding LF extension, I should add that I do have a 15" powered sub... so as long as the main drivers can reach down to ~50-60Hz I think that will be plenty. My hesitation with one of the floor standing designs is that if I set each speaker on the floor on either side of my desk, I'd be afraid that the desk itself (currently about 28" high, but I another project I have been contemplating is to raise it up a bit and use as a standing desk) would interfere with sound waves.

As far as construction material, I had been thinking MDF because it's stocked at all the local home improvement stores, and because I was under the impression that its uniform density was ideal for speaker construction... Would BB or Apple Ply be preferred for strength reasons? Or acoustic properties?

I hadn't previously looked into ordering BB online... It looks like that might be feasible, but once I sit down to do the math on how many pieces to order it will likely take me some extra time to come up with the funds to make it happen.

 

[chrisb]

hank - re engaging in a conversation on the merits of various construction materials / bracing schemes, et al - careful what you wish for

I've been a proponent of BB / Apple ply over MDF for sonics for well over a decade. It's not something that is necessarily stocked at local building supply ("big box") stores, and not all plywoods are created equal.

You're probably the best to judge whether a desk-top sized enclosure is the right solution for your case, and the A10s could definitely reach in the the mid 50s in a small well designed enclosure. I've built enough boxes that I can't recall if I've done one of the smaller CGR types for this model - the notable successes or failures usually don;t escape my recollection.

 

[hankhill]

Thanks for all the info so far! I ended up going with Baltic Birch and one of the trapezoidal Mar-Ken designs, and am mid-way through the assembly stage.

One (hopefully) last question... When applying felt to the interior surfaces, should the felt cover the passages to the side vents? I searched and found an older thread in which it was explained to only apply felt to one side of the brace, and that holes in the brace should be covered.

 

[planet10]

You want to ensure that the felt lining does not impede the vent entrances.

dave

 

[matt_garman]

I'm using the Slim CGR dMark-Ken7.3 speakers on my desk, listening as I type this. I ordered a flatpack and the treated Alpair 7.3eN from Planet10. Finished in Duratex, I posted pics in this thread (which can easily be found by doing a google search for "skookum computer speakers").

I haven't heard the Alpair 10.3 or 10P, but I suspect they are not terribly different than the 7.3s. No complaints! While they are not bass monsters, I feel they put out a surprising amount of bass given the size of the driver and enclosure. I couldn't host a rave, but for a nearfield application I don't find myself wanting for bass.

 

[waxx]

I'm using the Slim CGR dMark-Ken7.3 speakers on my desk, listening as I type this. I ordered a flatpack and the treated Alpair 7.3eN from Planet10. Finished in Duratex, I posted pics in this thread (which can easily be found by doing a google search for "skookum computer speakers").

I haven't heard the Alpair 10.3 or 10P, but I suspect they are not terribly different than the 7.3s. No complaints! While they are not bass monsters, I feel they put out a surprising amount of bass given the size of the driver and enclosure. I couldn't host a rave, but for a nearfield application I don't find myself wanting for bass.

Cosign, my 10M gen 3 in ported boxes give plenty of bass on low volume. I listen a lot to dub (where subbass is very important and goes easely in the low 30's), and never got the impression i was missing something on those...

 

[hankhill]

Thanks for all the feedback so far! Very helpful... progress has been a bit slow (kids, work, travel, kids...), but they're coming along.

You want to ensure that the felt lining does not impede the vent entrances.

dave

On that same note - should the felt cover the entire back wall? Or should there be a gap so as not to "restrict" airfow into the vent entrances?

In the pictures below, if I cut felt wide enough to completely cover the back wall between the brace and the side wall, the gap between the felt on the left side wall and the felt on the back wall will only be about 1/2"... is that what I should have?

Also... it occurs to me that it would have been smart to apply felt to the back before the sides

 

[hankhill]

Well... ended up covering the entire back wall in felt.... I figured that the vents themselves were only 9mm wide, so there shouldn't be a need to have more space than that between the felt on the side wall and that of the back wall.

Finished construction last week, added a single coat of danish oil, and did a break-in over the weekend.

I don't know that I've got the vocabulary to describe them, but I will say that I'm very happy with the way they sound! Very clear, and great imaging.

One "problem" that I'm running into now that I didn't have with my previous cheap bookshelves is that even with the XO on my sub set at 50Hz (as low as it will go), there seems to be a bit of overlap between the sub and the mains. I might try to resolve that in the short term by adding a pair of basic HPFs.

Next project I think will be a Firstwatt F5.

 

[chrisb]

It never hurts to high pass a full range, or even small multi-way system when there's a competent sub in the mix. Eliminating the heavy lifting from the mains will yield improvements in dynamics, higher attainable SPLs, and reduced lower midrange distortion. You can easily go as high as 80-100Hz in most rooms . Much above that and stereo woofers would be suggested, in which case you're now essentially talking about a "FAST" system. I still cringe when I read / type that, but it is a bit of shorthand that most builders here generally understand.

 

[Bigun]

Those look really nice speaker there Hank!

 

[matt_garman]

...
Finished construction last week, added a single coat of danish oil, and did a break-in over the weekend.
...
One "problem" that I'm running into now that I didn't have with my previous cheap bookshelves is that even with the XO on my sub set at 50Hz (as low as it will go), there seems to be a bit of overlap between the sub and the mains. I might try to resolve that in the short term by adding a pair of basic HPFs.

They look great, thanks for posting the picture!

What size monitor is that, just so we can have a sense of scale? Also, how big is your desk?

I have a similar setup, see this post. I'm using the Alpair 7.3 in Planet10's Slim-CGR enclosure. I have dual 20" widescreen monitors on a desk that is approximately 30x60.

With the bigger Alpair 10 drivers, you speakers must be 9ish inches wide? yet nothing looks out of place to me!

Have you tried running without the sub at all? You might find the fullrangers are "good enough" without a sub, particularly for near-field listening. I don't run a sub, and don't find myself wanting for bass.

You might also see about raising those speakers off the desk a bit. I use yoga blocks to prop mine up (cheap and they match the "utilitarian" look I have going on).

 

[chrisb]

matt - you commented on that earlier post about the "long time" it took to complete the duratex paint job on those little boxes - can you remember the total number of days that was?

are those yoga blocks organic rubber?

 

[hankhill]

Thanks guys!

Matt - monitor is a 25". The cabinets end up just shy of 10" wide. The "desk" (really just a sheet of melamine) is about 70" x 30".

I have tried running without the sub, and it's really not bad at all. If I didn't already have it I probably wouldn't feel the need to find one, but since I've already got it I'll most likely keep using it. I played around a bit with a sweep tone generator, and with the sub turned off, I can still hear down to about 40Hz from the Alpairs (though the response is down significantly from say, 60Hz).

I do need to find something to raise them of the desk though... that's on the short list of things to do

 

[planet10]

The trapezoial Mar-Kens for the Alpair 10s fit into a range of sizes & shapes.

dave

 

[matt_garman]

matt - you commented on that earlier post about the "long time" it took to complete the duratex paint job on those little boxes - can you remember the total number of days that was?

In general, Duratex doesn't need that long. I can't remember the guidelines, but I'm pretty sure you don't have to wait more than a few hours for one one coat to dry before applying a second coat (assuming reasonable temperature and humidity conditions). And for home use like this (i.e. not abusive road conditions), two coats is probably overkill, one is likely more than enough. The final curing to be "truly" dry is around a week I believe, but I think the wood can be handled after a few hours.

All that is from very bad memory, please consult the documentation if you're thinking of using it!

Mine took a long time only because work and "daddy" duties take up most of my time, so I had to wait a day or more between coats to actually find the time to work on them. Furthermore, I ended up with a lot of coats (I don't even remember how many) because I kept changing my mind about how I wanted the final finish to look.

The biggest lesson I learned was to first practice on some scrap wood to get a feel for how the product works. Which of course is obvious, and recommended by anyone who's ever used any product ever.

are those yoga blocks organic rubber?

I don't know. That wasn't a consideration at the time I bought them. I just wanted something quick, cheap, and boring-looking. Those blocks met those requirements exactly.