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Old 1st October 2013, 09:18 PM   #1011
chrisb is offline chrisb  Canada
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one man's opinion(s):

- If you can at all swing the budget toward A7.3 you won't regret it
- Decent quality high density plywood ( aka "Baltic" / "Russian" birch, etc)
- Applying paper backed veneer isn't particularly difficult, although the shape of the FH3 does require some planning around the grain figuring pattern of the chosen species, and they will consume the best part of a full 4x8 sheet. Although not to quite the same degree, but similar to painting, the key to a clean veneer job is preparation, patience, and practice working with the materials.
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Old 1st October 2013, 09:59 PM   #1012
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Originally Posted by chrisgoeslive View Post
I see several people recommending ch70.1 , are they still available. is the a7 preferred to the ch70?
CHP70 is still listed by rumoh CHP-70 Gen1 (pair) - RumoH - Caps, coils and speakers

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Also, though I am toying with the idea of building the FHs from scratch does anyone know if there are any flat packs available in the UK?
Frugal Horn Mk3 Flat pack DIY full range speaker kit ideal for 4" fostex alpair

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I see that birch ply is the preferred material, is it a complete no no to use solid wood?
Good ply is with less long term issues, but if you know what you are doing they can -- and have been -- built from solid.

dave
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Old 1st October 2013, 10:27 PM   #1013
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Quote:
Originally Posted by cbiern View Post
Found a source of 15mm BB in Northern VA.
Could I laminate a piece of 1/8" (5mm) Baltic Birch to the top back of a 15mm front baffle to get the necessary thickness for an A7.3? Or do I need to buy a half sheet 0f 18mm to make the baffle.
Well, you will always find a use for the rest of the 18mm sheet!

I tend to use 12mm material, which makes the problem worse. I just double the baffle or portion of the baffle, giving me 24mm material. Using 15mm material, I would double the area behind the driver. As long as you chamfer the driver hole, all will be well. laminating two 15's is a lot easier than laminating a 15 and a 5.

Bob
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Old 1st October 2013, 10:53 PM   #1014
chrisb is offline chrisb  Canada
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chrisgoeslive - if you do go for the flat pak and either the CHP or Alpair, make sure the supplier (Customcans?) can machine for rebating of the driver flange. While arguably not essential for Fostex drivers, due to their thin metal flanges, that's not the case for the Mark Audio units, and the two of those do not share the same dimensions - further complicated by the optional bezel ring on the A7s. Unless each kit is cut to specific order, this certainly creates an interesting inventory challenge

edit - to answer one of your questions, I think most who've heard both would definitely prefer the performance of the Alpair over any of the CH drivers (paper or metal) - they do cost more, though
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Old 1st October 2013, 11:19 PM   #1015
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Default many thanks

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Originally Posted by chrisb View Post
chrisgoeslive - if you do go for the flat pak and either the CHP or Alpair, make sure the supplier (Customcans?) can machine for rebating of the driver flange. While arguably not essential for Fostex drivers, due to their thin metal flanges, that's not the case for the Mark Audio units, and the two of those do not share the same dimensions - further complicated by the optional bezel ring on the A7s. Unless each kit is cut to specific order, this certainly creates an interesting inventory challenge

edit - to answer one of your questions, I think most who've heard both would definitely prefer the performance of the Alpair over any of the CH drivers (paper or metal) - they do cost more, though
many thanks for all the replies.

I think I will go for the alpairs it is a little extra, but seems worth it. i have already contacted custom cans about rebating the driver hole to suit. perhaps it is possible to do this myself with a router? I was not aware there was an optional bezel ring though. aside from custom cans are there any other sources for FH flat paks? Is colin topps still producing them?
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Old 2nd October 2013, 05:59 AM   #1016
chrisb is offline chrisb  Canada
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Originally Posted by chrisgoeslive View Post
many thanks for all the replies.

I think I will go for the alpairs it is a little extra, but seems worth it. i have already contacted custom cans about rebating the driver hole to suit. perhaps it is possible to do this myself with a router? I was not aware there was an optional bezel ring though. aside from custom cans are there any other sources for FH flat paks? Is colin topps still producing them?

The issue that I found the couple of times I've had to hand-bomb a set of baffles for the A7s is that the width of flange didn't exactly match any of the combinations of rabbeting bits and bearing from a stacked set that I had on hand. For example, with the optional bezel ring, the width of flange rebate would need to be 16mm / 9.9mm deep, and without the extra ring - 13.5mm / 8.5mm deep. After struggling with some very tight fits, I also like to add a "thick red one" for ease of driver installation and removal.

As to the question of the "optional" flange, I know that Mark has his reasons which I don't want to second guess. FWIW I've used both and without exhaustive blind testing, etc, can't say that I can hear the difference. Not using them does simplify the baffle rebate - I'll come out of the closet and admit that more than once, I've used an 15mm baffle rebated for no extra ring, and simply not chamfered the rear side of through hole - I wouldn't recommend that with the 10s or 12s.

I'm not sure about Colin, but I think he's still active on the forums, so it shouldn't take long to get an answer.
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Old 2nd October 2013, 06:12 AM   #1017
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Is colin topps still producing them?
Last time i asked, no. He'd possibly do a finished set thou.

dave
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Old 2nd October 2013, 09:43 AM   #1018
jemraid is offline jemraid  United Kingdom
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Hello Chris GL,

It is possible with the most basic tools to make a pair from scratch.

If you lived fairly near to M1 Ju29 and wanted to have a listen you would be very welcome.

Cheers - Jim

Link below
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Old 2nd October 2013, 12:00 PM   #1019
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Quote:
Originally Posted by chrisgoeslive View Post
many thanks for all the replies.

I think I will go for the alpairs it is a little extra, but seems worth it. i have already contacted custom cans about rebating the driver hole to suit. perhaps it is possible to do this myself with a router? I was not aware there was an optional bezel ring though. aside from custom cans are there any other sources for FH flat paks? Is colin topps still producing them?
Howdy chrisgoeslive - Jason here from custom cans.
We have kits with 96mm, 102mm and 105mm cut outs as standard to fit a lot of the 4" and 5" drivers but can not offer rebating and recessing of drivers yet.
It may be something we can offer in the future but we are just keeping it simple at the moment
If you can't find anywhere else selling the flat packs you could just contact a CNC company with your requirements and get them to cut the panels and router out all the bits you need - it should not cost too much more and you will get them just how you want them
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Old 2nd October 2013, 05:12 PM   #1020
chrisb is offline chrisb  Canada
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Of course it's possible the machine the rebated opening by hand - it's rather more laborious, but I've done it myself numerous times by either of the methods describe below.

Note that either of these methods require tooling & bits that not all DIYers would have in their kit, and finding a local CNC shop could be more cost effective and accurate.


Whichever method is employed, unless you're supremely confident in your set up and measurements, always test on scraps first, and machine the holes in baffle before assembly - it's much easier to clamp a flat workpiece securely than the assembled FH3 enclosure.

1) In two steps with circle cutting jigs - either shop made or something like the Jasper Jig.

It does take some time and set-up to get the concentric holes each the right size, and since most DIYers wouldn't likely have a plunge router bit of sufficient diameter to cut the rebate in a single pass ( at least 13.5mm without the extra ring, and 16mm), it'd take at least 2 passes just for the rebate. Machine the outside hole first, then the through hole.

2) Mortise bit and separate pattern diameter of flange

- cut the 103mm through hole in the baffle, test fit driver
- in a piece of scrap create a "negative pattern" hole the outside diameter of the flange you've decided to use (allow a slight margin none is the trade as a "certain letter" hair - otherwise you might great fun if you ever need to get the driver out)
- elevate the baffle on scrap 2x4 etc, align driver square on baffle and pilot drill mounting holes, and temporarily install at least 2 screws
- place the outside pattern over the driver and clamp firmly to bench
- remove the driver
- using a top bearing mortising bit with depth of cut set to the thickness of the pattern + the depth of rebate, carefully follow the inside of the pattern

Click the image to open in full size.


- as this type of mortising bit is available in diameters much greater than the maximum 16mm required for Alpair7, only a single pass would be required.



I tend to use the second method, but then in a supply of offcuts, I have several CNC machined baffles that can be converted to the required patterns, and after many scores of enclosures, I'll take the lazy approach any chance I can.



Jim: your blog page didn't indicate how you rebated the driver cut out - if so, what method did you use?
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Last edited by chrisb; 2nd October 2013 at 05:16 PM.
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