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CHR 70A Gen3 Dual Driver for Pensil

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Hi,

I plan to have a Pensil cabinet using dual CHR70A Gen3 drivers. I need help to direct me where I can find the Pensil plans with 2 CHR70A drivers as I need the dimensions where to exactly locate the drivers.

I will also try bi-amping the drivers or wiring them in series or parallel.

Thanks in advance for your help.

Regards,
JoeyGS
 
Thanks for your response Dave.

Yes I am using the Pensil R70.3 plans. Sorry am not too familiar with the the other terminologies as I am still starting in speaker building.

What is:
column's cross-section
terminus
Zd

I am placing the drivers on both faces. I am maintaining the distance of the top driver from the top of the box as per Pensil R70.3.

Appreciate your help.....

Regards,
JoeyGS
 
frugal-phile™
Joined 2001
Paid Member
So is it not feasible just to maintain the Pensil R70 baffle dimension with single driver and just add another single driver below the top driver?

You willlikely choke off the bass if you do not double the cross-section (WxD).

If you place both drivers on the front, then the average distance of the drivers from the closed end needs to be Zd.

Teminus is the slot at the bottom front.

dave
 
JoeyGS,

You can check out the Wessex MLTL at Dave's frugal-phile.com website - it's a design for Twin CHR-70. Drivers can be mounted on the narrow side also, making the speaker narrow and deep instead of wide and relatively shallow.

If a bigger cabinet agrees with you, there is the Mercia which should have a bit more low end oomph.
 
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Dave,

Thanks for the clarification.

Just saw Mark's thread:

http://www.diyaudio.com/forums/markaudio/224265-chr70-pensil-boxes-anechoic-measurments.html

..and thought that the R70.3 plans may work as-is and just add another driver......

Regards,
Joey


You willlikely choke off the bass if you do not double the cross-section (WxD).

If you place both drivers on the front, then the average distance of the drivers from the closed end needs to be Zd.

Teminus is the slot at the bottom front.

dave
 
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Joey - the microtowers were designed from the outset (by the same team as Pensils) with dual drivers in the calculus, so no modification to plans should be required.

I've built a total of 3 pairs, including two variants of the Castles. They certainly have a different soundstage presentation than the Pensils - even I imagine in dual driver configuration.
 
Bracing, Stuffing and Damping .....

As I move forward with a Pensil box design for the CHR-70.3 drivers, several things I need to be clear about bracing, stuffing and damping. When I back read the threads at the fullrange section I get confused as queries and responses are quite floating into bits and pieces......

1. Bracing - I understand that this would prevent resonance of the box walls. Without bracing on the the pensil boxes, is damping the alternative method? I understand damping to be absorbent materials that would prevent the box walls from resonating, am i correct?
2. Damping - What are the recommended damping materials for the Pensil boxes? Where will the damping materials be placed for the pensil box internal walls?
3. Stuffing - I understand that stuffing is used to fill the boxes to prevent standing waves, correct? Polyfills are examples of this as I understand. As stuffing is provided to tune the boxes, where should stuffing be placed? Entire box volume? Or what's the minimum requirement?
 
Re the questions:

1/ Bracing does not prevent resonance. It strengthens the box structure & moves the panel resonant modes to a higher frequency, where they are less likely to be excited. Panel damping (different sort of damping) can reduce the amplitude of panel resonance but unless you know exactly what you are doing, I wouldn't advise it with the pensil cabinets since it typically needs a different type of cabinet construction which was not assumed in the plans.

2/ Stated in the plans; Dacron hollow-fibre pillow stuffing material. The cabinets are not designed / assumed to be lined.

3/ Throughout & adjust density from the default quantity (also listed in the plans) to suit particular requirements / taste. That's why a removable back is specified / recommended
 
Great info Scott. Thanks.

Follow-up questions:

1. There were mention of providing damping materials behind the drivers so that reflections from the walls are prevented to affect the normal movement of the drivers. Are these apart from the specified stuffing material? If so, what type is recommended?

2. Whats the recommended optimum speaker wire gage for the mark audio drivers?

Thanks
 
1/ No. You can if you wish, but it's not a reqirement. If it was, it would be in the plans.

2/ There isn't one. Varies depending on system & personal choice. In general though, assuming you're not wanting to use the wire's LCR properties to shape the response, you want to be using something that keeps voltage drop to a minimum for the given length. That's not a major issue for internal wire; something like 20ga should do for that. It may for normal external runs from amplifer - speaker too for that matter, although slightly heavier is usually a good idea. Up to about 10ft runs, ~14ga should be fine. Some prefer much thinner wire, although resistance can get somewhat high there. A high output impedance amp i(e.g. a typical SET) is lusually less affected by this however. YMMV as always.
 
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