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Old 8th September 2011, 01:28 AM   #1
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Join Date: Aug 2011
Default CHP70 concrete build

Hi everyone, ive been a member of the site for a few months now trying to learn as much as possable before starting my first serious speaker build.
I have built a few very rough speakers in the past, reboxing computer speakers in larger cabinets and similar stuff, but ive always had a hankering to try a set of concrete speakers. My first design was for a very small 2 liter bookshelf two way design reboxing some gale 1010s that I saw going cheap, but decided I could probably do better, so they never got off the drawng board, as well as looted the other week.
The last quality hifi set up I owened was a B1 amp powering a set of Castle Warik's
which also got looted, allthough not by so many people, several years back.
I hoped to build a pair of full range speakers that would be as good as they were, and this is what ive come up with.

Click the image to open in full size.

Click the image to open in full size.

The molds are now complete, and will be cast in the next day or two. Ive taken, Daves suggestion in another thread, and aimed for 10 liters with a br port which will be around the 100mm mark.
The baffel largly dictated the design which are a pair of 19mm thick bambo chopping blocks, set into the concrete giving the front face 30mm total thickness, while the other walls are 20mm thick. The back panel will be 18mm bp.
After studying long and hard I eventually chose the CHP70s first gen going cheap.
Tight budget, over the CHRs et al.
If ive done the math correctly they should come in at 16kg each not including stands.
Ive gone for a golden section design, but as you can see end ways on. All the internal corners are radiused mainly to minimise the chance of cracking,
I will post pics later, providing I dont end up with a pile of hard core, and would appreciate any tips and advise if anyone has tried similar projects.
The few areas im concerned about are internal wireing. Damping. Diffraction panel for the backpanel. Is driver basket bracing crucial. And anything else anyone can think of.
Thanks in advance. Fantastic site.
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Old 8th September 2011, 12:01 PM   #2
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Just to fill in a few missing details. I should have said the base port will be 35mm x 100mm or there abouts depending on listening tests. It may not be clear from the render but the vertical edges of the front face are rediused over. I have not put a radius on the horizontal edges due to asthetics as well as difficulties in construction while hopeing to maintain a clean finish. Im using general purpose concrete, with no mesh reinforcing, but I have purchased some 20mm polypropelene fibers which should suffice. I am going to add a small quantity of acrilic paint to the mix which I hope will act as a plastisizer as well as achive a more uniform colour.
From what I have read, I thaugh the latest thinking on internal cableing recomended using, I forget the cable name, but it seemed to be ethernet cable. Isent that a little thin.
As I have designed in a removable back panel, the front bamboo baffle will be bonded into the recess. With this I hope to prevent transmiting hf to the cabinate, and minimise the possability of ringing. Can anyone suggest a suitable cheap product for this. No more nails perhapse?
I am concerned about the location of the br ports closeness to the driver, and my thinking on this is I could add the triangular shaped foam to the back panel, or even a scaled down bbc block patturn diffuser.
Another approch could be a combined driver frame brace, cotinued down to form a deflector over the port mouth?
My current amp is simply the one the came in the computer speakers also reboxed into a aluminium hard drive caddy. This will be replaced with a T2020, or possably a T2050 when funds allow. Also the computer, my sole imput, may get treated to a new sound card.
Im hopeing that the combination of materials will avoid the dead sound that concrete speakers are often accused of.
Unfortunately I dont have any measuring equipment so I wont be able to post any graphs for now, but over the years I have spent 100s/1000s of hours tweaking junk to try and get it to sound better, and my current home brewed set up to my ears sounds better than the last set of commercial speakers/amp I owened. Tannoy Mercury's with a Tecknics amp.
Judgeing from the sound of the CHPs breaking in the cardboard shiping box, I am expecting really good things from these.
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Old 8th September 2011, 12:07 PM   #3
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Sorry to keep rambleing on, but I should say also, thanks to the furnature shop down the road that donated the scrap sheet of malamine backed chipboard free of charge that made the molds possable, and my favorite 3d software since ever Blender.
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Old 8th September 2011, 12:09 PM   #4
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Welcome Dave, very nice render!! Before you do the casting you might want to read this post This is a guide to using acoustic concrete.

Any intelligence I may appear to have is purely artificial!
Some of my photos
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Old 8th September 2011, 12:31 PM   #5
sayrum is offline sayrum  Germany
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nice design!
i like the warm look of the wood chopping block. goes well with the chp70 membran.

have a look at the point70.
afaik a great build for the chp70!
maybe use these dimensions (metric) with the trap circuit.

i hear it's preferable to not put the port on the front...

keep us updated.

Last edited by sayrum; 8th September 2011 at 12:34 PM.
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Old 8th September 2011, 02:56 PM   #6
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They look beautiful in the render. And so do the stands - I'd love the have a pair of these!

Wish you all the best. Sorry I couldn't help.

p.s. make sure the back panel is installed in a way it is well sealed.
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Old 9th September 2011, 12:48 AM   #7
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Thanks for the links and compliments. Some very usefull info.
sayrum Im glad someone is thinking along the same lines as me. My molds are already constructed so its to late to change, but the over all dimensions are similar, at 175x261x395 mm externaly.
I started with a pure 3d golden ratio box and scaled it in blender until I achieved as near the correct volume as possable while leaving space for the bamboo baffle.
Your right about the port, and I havent totaly decided on that yet.
In the origional small two way design that would have been space for the tweeter, with the port at the rear, or even sealed in a 2.1.
It is partly cosmetic, but also I have quite a small room with not much space behind the speakers. Even less with these deeper boxes, but we will see. Ive still got construct some sort of router table hole cutting jig thingy yet, while the concrete cures.
I dont know if it will be possable to reuse the molds, but if it is I may even cast a third box as a paturn for some proper fiberglass molds, allthough I dont know what shipping would cost.
Early days yet.
Anyway I will keep you updated. Should be casting today.

Last edited by Dave Holloway; 9th September 2011 at 12:53 AM.
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Old 9th September 2011, 07:39 AM   #8
sayrum is offline sayrum  Germany
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good morning everyone

dave you can also put the port on top or bottom...

what design are you talking about, that uses the chp70 with a tweeter?

good luck with the casting!
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Old 11th September 2011, 11:46 AM   #9
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I origionaly intended to make some small cabs for a broken very cheap 5.1 with a blown channel.
This was the design I came up with, using some plastic jugs for molds. I actually made just one as a proof of concept, and to try and discover the main pitfalls. Also so I could conduct side by side listening tests. I then started trying to source better quality doner speakers on ebay etc, but fell in love with CHPs. Hence the total redesign. I may well build a proper set of these later, with suitably matched drivers. The max internal volume is only around 1.5 liters.
One interesting point with the design is there is no "up". They can be rotated around to taste, allthough I have no idea how this would affect to sound, if at all.

Click the image to open in full size.

Click the image to open in full size.

Still not quite ready for casting. Friday turned into "make like a moose" day so it got put on hold for a bit. To be continued after the Grand Prix.
I did get a very good deal on binding posts, so I only have to source or construct the ports to complete the project.
I was hoping for some advise or opinions from older members about cableing and basket bracing.

Last edited by Dave Holloway; 11th September 2011 at 11:51 AM.
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Old 11th September 2011, 07:40 PM   #10
sayrum is offline sayrum  Germany
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beautiful design! love it.
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