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Old 26th February 2011, 02:22 PM   #1
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Default Help with BR design for CHP70

Hello,
I just ordered a pair of Markaudio CHP70 and I want to build them a simple and cheap BR to begin with them. I found a lot of plan for their metal sisters CHR70 or for pencils etc, but not a single one for CHP 70 BR.

Could you help me with figures (Vb, and port lenght for 4,6 cm diameter ?)

Qts = 0.572 ; Vas = 5.0 l ; Fs = 66Hz ; Xmax = 4.2 mm

Thanks in advance !
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Old 26th February 2011, 06:18 PM   #2
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A quick look has 10 litre, 38mm port 98mm long, near optimal from my POV

Could be squeezed down to 6 litre 25mm port 83mm

dave
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Old 27th February 2011, 03:36 PM   #3
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Thanks dave,
Could you tell me which tool you use as many on line calculators give around 15 liters boxes and quite low alignment (Fb arounf 43 Hz) ?
I could also need to adapt port diameter from your initial figures.
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Old 27th February 2011, 04:34 PM   #4
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I use an ancient piece of software for Mac OS 9, MacSpeakerz. It has proven to be really good.

What size port do you have access to (i most often implement a slot port (just use the equivalent area) or if using a tube, plumbing pipe.

dave
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Old 27th February 2011, 04:46 PM   #5
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Here are the sims in post 2 plus a couple sealed (the small sealed would be fine for surrounds for instance -- if you can actually fir the driver in that small a box)

dave
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Old 27th February 2011, 07:01 PM   #6
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Thanks dave,
In fact what do you think the FR will really look like - i have drawned a few imaginary lines (see picture) ? Won't this kind of driver and port tuning have a dip in the 100 Hz region ?
(this doesn't take into account baffle step and voltage source effects)
For the port, I need to look in some shops because the classic 50mm (46 mm inside) I have access to is only 10cm long = will be too short
I am also thinking of making a hole in glued wood blocks with the correct thickness inside the box (I have drill of 38 mm, but this should make a shorter length than a classic tube port, isn't it ?)
By the way, is it exactly 10 liters ?

Your software is exactly the one I was remembering seeing on some site (was yours in fact!) with excursions charts etc !
Best regards
Eric
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Old 27th February 2011, 07:49 PM   #7
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Quote:
Originally Posted by mahleriana View Post
In fact what do you think the FR will really look like - i have drawned a few imaginary lines (see picture) ? Won't this kind of driver and port tuning have a dip in the 100 Hz region ?
It is hard to say. With the MA i like to add a bit of a bump up to help fill in where the built in BSC hump starts to fall off. This whole region thou is dominated by the room.

Quote:
I need to look in some shops because the classic 50mm (46 mm inside)
You don't have a shop that sells plumbing pipe?

A slot port would be easier than gluing blocks and drilling.

dave
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Old 27th February 2011, 09:24 PM   #8
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Quote:
Originally Posted by planet10 View Post
With the MA i like to add a bit of a bump up to help fill in where the built in BSC hump starts to fall off.
dave
How do you bump it up there : BSC ?

Quote:
Originally Posted by planet10 View Post
You don't have a shop that sells plumbing pipe?
A slot port would be easier than gluing blocks and drilling.
dave
It is just I am not sure plumbing pipe in a hole will look nice with a front firing box...
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Old 27th February 2011, 09:36 PM   #9
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Quote:
Originally Posted by mahleriana View Post
How do you bump it up there : BSC ?
you'll note the 1 dB lump on the bottom of most of those sims... (BSC = baffle step compensation)

Quote:
It is just I am not sure plumbing pipe in a hole will look nice with a front firing box...
Personally i like the look better than the typical store bought port. Also cheaper & stiffer.

Our finished boxes are typicallyveneered and 99.9% of the time have a slot port.

If you are concerned with the look, rebate the back of the baffle around a hole the same size as the inner diameter of the pipe.

dave
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Old 27th February 2011, 10:18 PM   #10
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Originally Posted by planet10 View Post
you'll note the 1 dB lump on the bottom of most of those sims... (BSC = baffle step compensation)
dave
I tried to imagine various effects on the driver : baffle step, voltage source (I use SET) etc
Some on a post proposed a notch filter around 2k rather than a BSC.
This could be rather flat, but still with a perhaps thin bass response, despite the + 1dB lump ?
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