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Old 2nd July 2012, 08:01 PM   #1
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Default Lotus^2 build advice

Hi all

After spending some time getting to grips with DIY electronics it's now time to finally look at building some speakers. I've decided on the Lotus^2, with one front and one side firing driver. I have the drivers already (BB4-AL variant of CHR-70), it's not a complex build, and they aren't going to annoy the lady of the house.

This will essentially be a "training" build for me. I've read all the threads I could find about the Lotuses, but I'd be grateful for some advice on the following:

1. The original plans are for 19mm material. We only get 18 and 25mm here, so I've redrawn plans for both thicknesses. The question is this: is there any real benefit from using 25 instead of 18mm? The cost is higher, but if the benefits are worth it I'm happy to spend the money.

2. Any advice on lining / stuffing? I've got a good amount of both Sonofil fluff as well as Visaton damping material. Which of these should I use? Or is there something else I should consider? By the time the side panels are on I'll probably have lost a couple fingers to the table saw, so I'd prefer to avoid taking them off again to mess about with the guts if at all possible... . I looked at the following pics:
Mark Audio CHR-70 Application Thread
Lotus^2 build and listening impressions
These look to be about the right amount of stuffing, yes? Should it be applied to the remaining side panel as well?

3. Should I place a cap inline with the side-mounted driver? Motosapien recommended 68uF to tame the highs - has anyone else tried this? The BB4-AL variant should have a slightly smoother top end.

4. and last, what to do with the bottom deflector? Should I stick with the stepped approach, or alternatively go with a flat panel and load the void behind it with sand? What kind if dispersion characteristics will each offer?

I'm a total n00b when it comes to speakers. Thank you very much !
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Old 2nd July 2012, 08:29 PM   #2
zman01 is offline zman01  Bangladesh
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Tachyon666,

Good to see a reference to my build thread in your post.

I'll try to answer a few of your queries - if I am wrong, the more learned and experienced folks can always correct me!

1. 25mm vs 18mm ply - 25 mm is probably too much, and too thick cabinet walls may not be ideal. So, 18mm will be good enough for the build.

2. Lining the desugnated areas inside the The Lotus^2 should be good enough, no need for stuffing. The lining material recommended is ~3/4" wool/receycled denim type felt material. IIRC fibreglass can also be used, but poses some health hazards - so I would not advise.

3. My guess is that cap will not be required for BB4.AL

4. the stepped deflector will add some mass to the bottom - in my expereince not required. But if you have small kids or pets, better to make the base as shown in the plans for stability.

Not to detract you from the Lotus^2 build, but there's another design for twin CHR-70/BB4.AL that grabbed my attention - the Woden Mercia - a large MLTL. Recently came across a thread where a forum member built a pair for HT duty and was very happy.

- Zia

Last edited by zman01; 2nd July 2012 at 08:32 PM.
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Old 2nd July 2012, 08:49 PM   #3
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Quote:
Originally Posted by zman01 View Post
Good to see a reference to my build thread in your post
Yup, I took some inspiration from your build

Quote:
Originally Posted by zman01 View Post
18mm will be good enough for the build.
Good to hear! Will save me some cash...

Quote:
Originally Posted by zman01 View Post
The lining material recommended is ~3/4" wool/receycled denim type felt material.
Hmm... the stuff I have is lightweight poly fibre. Possibly not dense enough?

Quote:
Originally Posted by zman01 View Post
the stepped deflector will add some mass to the bottom
No kids or pets, but I prefer a lower centre of gravity for safety's sake. If I go with the flat panel I'll fill behind it with sand or lead shot.

Quote:
Originally Posted by zman01 View Post
the Woden Mercia - a large MLTL
The Mercia seems pretty awesome, but I think the aesthetics of the Lotus will mean less hassle from the girlfriend . Plus I hate cutting circles - straight lines are fine, but circles just remind me of how much I suck at woodworking...
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Old 2nd July 2012, 10:30 PM   #4
zman01 is offline zman01  Bangladesh
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Quote:
Originally Posted by Tachyon666 View Post
Hmm... the stuff I have is lightweight poly fibre. Possibly not dense enough?
For lining if you are refering to "poly batting", I have found that these do not have the same effect as denim/cotton felt material. Another option is jute carpet underlay - 2-3 layers of 6 mm stuff should do the job.

Quote:
Originally Posted by Tachyon666 View Post
The Mercia seems pretty awesome, but I think the aesthetics of the Lotus will mean less hassle from the girlfriend . Plus I hate cutting circles - straight lines are fine, but circles just remind me of how much I suck at woodworking...
Yep, agree - among the big boxes, probably the Lotus^2 scores highest WAF wise with the narrow baffle and slanting top.

BTW, if you are intimidated by the holey bracing in the Mercia drawing, don't be - simpler bracing can be used, even if it doesn't result in the same degree of stiffness. If you ignore the bracing, Mercia will have fewer pieces and easier to build.

Before I forget, make sure you do a rebate for your drivers so they are flush-mount on the baffle, and you also need to do a chamfer/round over on the inside of the hole.
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Old 3rd July 2012, 02:28 AM   #5
jimbro is offline jimbro  United States
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I cut triangles and squares in my braces with a scroll saw but a sabre saw would work fine also. No circles needed. I just made sure there was about a 1" wide piece of uncut wood from the back of the driver to the back of the box.
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Old 3rd July 2012, 07:23 AM   #6
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The only comment i have is that i'd 1st try with no series cap on the side driver, play with room placement, and then only of you still can't get happy with them, try the cap.

dave
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Old 5th July 2012, 03:48 PM   #7
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The circles in the braces are typically cut w/ a hole saw. Not so bad.



Quote:
Originally Posted by Tachyon666 View Post
Yup, I took some inspiration from your build


Good to hear! Will save me some cash...


Hmm... the stuff I have is lightweight poly fibre. Possibly not dense enough?


No kids or pets, but I prefer a lower centre of gravity for safety's sake. If I go with the flat panel I'll fill behind it with sand or lead shot.


The Mercia seems pretty awesome, but I think the aesthetics of the Lotus will mean less hassle from the girlfriend . Plus I hate cutting circles - straight lines are fine, but circles just remind me of how much I suck at woodworking...
__________________
I was so much older then, I'm younger than that now.
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Old 6th July 2012, 01:37 PM   #8
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Thank you all for the great advice

Am really looking forward building these!
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Old 25th August 2012, 10:39 AM   #9
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Default Best CHR driver gen for lotus 2

Hello!
Which of the MA CHR-70 Gen (1,2 or 3) will work best in the lotus 2?
Thanks!
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Old 25th August 2012, 02:48 PM   #10
frugal-phile(tm)
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The ones you have

The specs on the CHRs didn't change much.

The tonal balance has changed abit thou.

dave
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