Thinking of building some Pensils - good idea? [Archive]

Martinh

19-03-2012, 19:42

Hi all,

I'm at the planning stage of my first DIY speaker build and have almost decided to make some Pensil 7s using a pair of Alpair 7.3s

I was hoping that someone here could advise me of the suitability for my room, which is 4 x 4m.

They need to be suitable for positioning at around 20cm from the wall in a corner setup without the bass getting too boomy.

Through my business I can get custom made mdf panels with decent quality vinyl wrapping in loads of different finishes, so I was thinking of going down that route to give me a perfect cabinet finish. Is mdf a good material to use?

Any advice would be gratefully received before I take the plunge.:rolleyes:

Cheers, martin

Reid Malenfant

19-03-2012, 19:53

I'm at the planning stage of my first DIY speaker build and have almost decided to make some Pensil 7s using a pair of Alpair 7.3s

I was hoping that someone here could advise me of the suitability for my room, which is 4 x 4m.

They need to be suitable for positioning at around 20cm from the wall in a corner setup without the bass getting too boomy.
Your room is about the same size as mine give or take a few cm :)

Perhaps if you can link to the speaker design & the driver specifications I may be of some use.

Also if you can be a little bit more comprehensive on the likely position of the speakers in relation to the rear & side walls it'd help a great deal (highlighted stuff).

Martinh

19-03-2012, 20:12

Hi Mark,

Here's the design from the MA website (i hope) http://www.markaudio.com/Plans/itemlist/category/22-Alpair-7-Gold it's the Dave and Scott Pensil design - click to download the design pdf.

Here is "my hifi corner" as my wife likes to call it:

http://www.chelsea-bathrooms.co.uk/IMG_7423.JPG

The room has 2 adjacent 4 x 4 m rooms forming an L with 6 foot wide square-shaped archways connecting them ( almost open plan). Hope this makes sense! Fully carpeted with sofa, curtains etc.

At the moment, my speakers have the ports closed off with rubber bungs to keep the bass under control.

Cheers, Martin

And this is the spec for the driver:

Alpair 7 Gen. 3 Data (with cover)
REVC 5.4 Ohm
Fo 70.90 Hz
Sd 5.02 K mm/2
Vas 4.58 Ltrs
Cms 1.27 uM/N
Mmd 3.74 g
Mms 3.95 g
BL 3.83 T*M
Qms 3.07
Qes 0.65
Qts 0.54
Levc 21.30 uH
No 0.24%
Spl
Spl
85.80 dB (with rear cover)
85.20 dB (rear cover removed)
Pwr 20w Nom.
X max 4.2 mm 1 way
Coil Dia 20-mm
Main tolerance +/- 1.5 Hz on mean Fo

Reid Malenfant

19-03-2012, 20:31

Hmmm, I guess they are called Pencils due to the slim design?

It's a bass reflex speaker. In my honest opinion I would never, ever use a driver that has a total Q (QTS) of above 0.4 in a reflex.

There isn't enough electromagnetic control from the amplifier to damp them enough & you will get overhang or wallowy boomy bass. If you built the speakers but without the port then they'd be clean as the enclosure is pretty big compared to the drivers VAS so enclosure total Q would be below 0.7.

You could probably get away with the port if you stuffed the enclosure to increase the damping on the driver. A secondary effect would be that the enclosure would appear to be bigger which may help in certain respects. You'd just need to keep the port clear of damping material. Something like those plastic net bags used to hold onions a few inches above the slot port, glued to the front & sides etc & above that stuffed with rockwool might be advantageous.

This is just my opinion, but I have formed it after nearly 30 years of designing loudspeakers :)

I'd be looking for a lower QTS driver though rather than using a plaster to fix things up. Anything below 0.4 would imho be much better in a reflex. If you have a valve power amp then simply don't even think about it as they tend to have a lower damping factor.

Toppsy

19-03-2012, 20:42

The Pensil range of speakers have been designed specific for the range of MA fullrange drivers. There are several in the range. Each cabinet designed for a specific driver in Mark Audio range. The designer of these speakers is well respected and has many a commercial and DIY design within his portfolio. http://www.wodendesign.com/

The cabinets are I believe MLTL's not bass reflex and are intended to be stuffed with Dacron or similar.

Many of these have been built and I know of no dissatisfied builders.

As a first DIY project they are perfect. If I was to build these I'd use good quality Baltic Birch Ply rather than MDF. However if you are on a budget then go for 18mm MDF.

Reid Malenfant

19-03-2012, 20:47

The cabinets are I believe MLTL's not bass reflex and are intended to be stuffed with Dacron or similar.
Well without stuffing they'd certainly be a bass reflex no?

Mass loaded transmission line... Maybe, but they are kind of short to be called a transmission line :eyebrows:

Me personally I still wouldn't entertain a driver of that high a Q except in a well stuffed sealed box, perhaps I'm just a perfectionist :scratch:

Martinh

19-03-2012, 20:53

Hi Mark, thanks for your help.

I think I undestand what you are saying - do you think that a sealed box design would suit my corner position better?

The Pensil design recommends leaving the back removable to allow for tuning, using filler material. It would also be very easy to close off the port as well, if required.

Do you know of any other designs that might be worth looking at?

Cheer for your help, martin

Reid Malenfant

19-03-2012, 20:55

How far from the back wall & from the side walls are the speakers likely to be positioned?

Martinh

19-03-2012, 21:01

How far from the back wall & from the side walls are the speakers likely to be positioned?

The 2 walls you can see in the photo are 1.5m long, so the diagonal is only 2m across - not ideal, but it's all i have :(

My seating position is about 3.2m away. I listen to all sorts fo music from pop, light rock to radio 2 type stuff :eek:

Martin

Toppsy

19-03-2012, 21:06

Don't trust to what I say :scratch:
If you are uncertain about this design or the observations expressed by Reid Malenfant then why don't you contact the designer through his web site posted above with your concerns?

You may be surprised by the amount of speaker design knowledge this guy has. I certainly trust his design prowess and knowledge as have many hundreds of DIYers and commercial builders.

As an alternative why not consider a pair of Frugal Horn Mk3 speakers with the same driver? Now I know these excel and have built many for clients as flat pack kits and full bespoke builds.

Martinh

19-03-2012, 21:09

As a first DIY project they are perfect. If I was to build these I'd use good quality Baltic Birch Ply rather than MDF. However if you are on a budget then go for 18mm MDF.

Hi Colin and thanks for your reply,

The ease of build and relatively low cost was what attracted me. Do you know if they are ok in a corner, near to the wall, like in my installation?

Also, there is a choice of the CHR 70 or Alpair 7.3 at 2 x the price - is it worth going for the Alpair? I can afford both and can they be purchased in the UK?

Sorry for all the questions.

Cheers,

Martin

Ali Tait

19-03-2012, 21:10

Yes agreed, Scott is an extremely knowlegeable designer.

Reid Malenfant

19-03-2012, 21:13

Ah, I see, should have taken more notice in reality :cool:

I'd suggest you look for some kind of kit that uses a low Q bass driver, say between 0.25 & 0.3 (if using small drivers) in a two way speaker with a pre built crossover. The reason I say this is because with a little bit of redesigning of the enclosure (if needed) you could end up with a speaker with an EBS (extended bass shelf) response & these tend to work very well when in proximity to walls :) The bass rolls off gradually as they go deeper & the proximity of the walls tends to flatten the response.

The important thing though is that the driver has a low Q, as then the amp that is driving it has vastly more control over the cone & thus the output!

Put it like this, Marco is using a pair of 15" in an EBS6 set of enclosures banged up against his rear walls & in a small room.

Martinh

19-03-2012, 21:15

As an alternative why not consider a pair of Frugal Horn Mk3 speakers with the same driver? Now I know these excel and have built many for clients as flat pack kits and full bespoke builds.

Hi Colin,

I saw the FH3 and like the style - the only problem is the bit at the back (not sure of the technical term) it wouldn't fit in my corner installation.

Could the bit at the back be chopped off to create a pensil type shape without ruining the sound?

Cheers, Martin

aquapiranha

19-03-2012, 21:28

Martin, the 'curve' at the rear of the FH3 is part of the horn, and integral and not optional. If you cannot accomodate the cabinet, I would not try to modify it but choose another design HTH.

moodybuilder

19-03-2012, 21:56

Reid Malenfant

19-03-2012, 22:06

hi
I have a pair of pensil super 12s which use the alpair 12 driver made from 25mm MDF these have the internal bracing, and are approx 1 quater filled for dampening and I can honestly say these are the best single cone drivers i have every heard, mine are approx 100mm from the rear wall and they work absolutly fine as i say these are a amazing speaker designed by scott (mouse) lindgren whos one of the most respected speaker designs around, female vocals are subline jazz sounds alive these are the real deal
Yes, now look at the driver specs....

QTS is low at 0.327 (http://www.madisound.com/store/manuals/Alpair-12-Specs.pdf)

Now while that won't affect the midrange it'll certainly have an effect on the bass & how clean it is ;) 9mm one way excursion, bloody hell - should be a killer in the bass stakes to :eyebrows:

Welder

19-03-2012, 22:22

Cant believe anyone has the front to call these full range drivers tbh. :rolleyes:

Martinh

19-03-2012, 22:45

Martin, the 'curve' at the rear of the FH3 is part of the horn, and integral and not optional. If you cannot accomodate the cabinet, I would not try to modify it but choose another design HTH.

That's what I thought. I have also been toying with the idea of filling in the whole room corner and building in some big horns - my semi could sound like the royal albert hall :eyebrows:

Martin

Martinh

19-03-2012, 23:01

Yes, now look at the driver specs....

QTS is low at 0.327 (http://www.madisound.com/store/manuals/Alpair-12-Specs.pdf)

Now while that won't affect the midrange it'll certainly have an effect on the bass & how clean it is ;) 9mm one way excursion, bloody hell - should be a killer in the bass stakes to :eyebrows:

Hi Mark and Phil,

I haven't got space for the 12s unfortunately. Do you think the difference in QTS between the 7s and 12s will make the two sizes sound/behave differently? The 12s sound like they are the business.

Martin

p.s. can't find the Alpair 12 on the MA website.

Reid Malenfant

19-03-2012, 23:09

Yes, the lower QTS Alpair 12 drivers can be used in just about any enclosure with minimal overhang. In other words they'll start & stop much better than the higher 0.54 drivers which an amp will have less control over.

Think about it like an american car... You must have seen a film where a big yank car pulls up to a stop & bobs back & forth for an age as it has crap damping! Yet a lighter car with the same suspension will stop & not do an impression of a jelly :eyebrows:

Clean bass comes from a well damped driver. You will get more bass from an underdamped driver but it'll sound bloated & unclean, overblown etc...

Not my cup of tea, but it might be yours...

Martinh

19-03-2012, 23:15

realysm42

20-03-2012, 08:22

Mark the drivers you linked, it says to gently run them in for 20 hours with no real bass and then gradually turn them up in the next 120 hours; is this the widely accepted manner of running them in?

Martinh

20-03-2012, 11:05

...and have built many for clients as flat pack kits and full bespoke builds.

Hi Colin,

Would you be interested in building me a pair of Pensil 7 enclosures either as flat pack ply or built and finished with walnut veneer? What sort of money are we looking at?

Cheers, Martin

Toppsy

20-03-2012, 12:14

Hi Colin,

Would you be interested in building me a pair of Pensil 7 enclosures either as flat pack ply or built and finished with walnut veneer? What sort of money are we looking at?

Cheers, Martin

Sure Martin,

Send me a PM and we'll exchange email addresses and phone numbers so we can then discuss specifics etc in private.

I'll answer your earlier posts and any queries there if that OK. At the moment I'm pushed for time building a couple pairs of my Edingdale speakers to be ready for collection this weekend.

Regards
Colin

Martinh

20-03-2012, 13:25

PM sent.

Reid Malenfant

20-03-2012, 17:44

Mark the drivers you linked, it says to gently run them in for 20 hours with no real bass and then gradually turn them up in the next 120 hours; is this the widely accepted manner of running them in?
Best to go on what the manufacturer recommends I reckon. It probably depends on the type of driver to, as it's a full range unit it's probably sound advice (pardon the pun :lol:).

Toppsy

20-03-2012, 18:21

I agree with Reid Malenfant with respect to this especially the Mark Audio aluminium coned drivers. These cones can be quite delecate and easily deformed so we warned. I would not recommend them if one has small children with probing fingers as they will damage these cones. Best to go for a paper coned FR in this case. You can abuse the paper coned FR drivers a little more.

However, I have found as long as you don't play music with heavy bass that will cause ther driver to move towards Xmas you should be OK playing them at your normal listening level for the first 30 or so hours.

keiths

20-03-2012, 19:24

I would not recommend them if one has small children with probing fingers as they will damage these cones. Best to go for a paper coned FR in this case. You can abuse the paper coned FR drivers a little more.

I must admit that the apparent fragility of most FR drivers does worry me a bit. No small children here, but my dad (who suffers from Alzheimers) does tend to 'prod' things - especially if they are new and unfamiliar. I think my FH3s with Mark Audio CHP-70s will have grilles for this very reason.

I plan to break in my CHP-70s by connecting them to an old Yamaha AV receiver I have (with the drive units just in the box they came in) playing very quiet and bass-reduced radio 24/7 for a few days and then gradually increase the volume and bass content (without being silly)