Rules of thumb for thick baffles?

alanhuth

Some of you may have noticed this new guy, alanhuth, with an unnatural obsession for building Curt Campbell’s Halcyons. The only pair in existence, AFAIK, was Curt’s test set.  His and Jim’s friend, Wayne, built them with a double baffle (2 x 0.75”), which is not on the drawings. It was done for a reason, and I’m planning on doing the same. I’m trying to find out the implications of this change, if any, on the cabinet.  I’ve tried to go to the sources, but so far, no luck. I’m hoping that there are “standard” answers or procedures that I can follow in a pinch. Here are my questions:

1. Were the cabinet dimensions changed in any way to accommodate the speakers being moved 3/4” forward?  (Should they be?)

2. And what was done to the backside of the double baffle, if anything (conical cut, radius, step?) for woofers and full range? (What should be done?)  

I’m assuming the speakers will be flush-mounted to, essentially, a board that’s 1.5” thick.  Assuming the flanges are buried 1/4” for flush-mount, that leaves 1.25” of solid wood behind it. Is that a pure cylindrical cut or is it flared out or rounded or ??.  Would the same treatment be applied to each driver type?

Each cabinet will contain:

1 x Markaudio Alpair 10P 6" Paper Cone Full Range Driver

2 x SB Acoustics SB17NRXC35-8 6.5" Paper Cone Woofer

If anybody has general rules of thumb that you would recommend absent feedback from the authorities, I’d be most appreciative  

Thanks in advance. The help I’ve received from this group has been phenomenal. 

BrannigansLaw

general rules of thumb:

1. The internal volume must remain the same as the published design
2. The baffle width and placement of drivers on the baffle relative to each other and its edges must remain the same

This realistically leaves only depth (and possibly gross height) as variables that coudl be manipulated. So, if the baffle is twice as thick, you'd need to add .75" to the internal depth specified. To find out if the design as posted includes the double thick baffle, I'd ask Jim and Curt on the htguide forum, they seem to post there most. 

In terms of dealing with a thick baffle - the driver cutouts need to be chamfered on the backside for good airflow. This does make a real difference, particularly on fullrange drivers like you'er working with. Like so:

Kornbread

Generally when using thicker than specified materiel, the internal volume remains the same with the OD changing and a baffle will often be relieved on the back side to allow the driver to breathe.   

alanhuth

Thank you. 

BrannigansLaw:  Thanks for the great diagram. If I ever engage a builder, I’ll give him that.  Curt’s drawing did not include the double baffle, and he even commented that Wayne added the double baffle on his own. I will try to get feedback on htguide. Question:  What did you mean by “if the baffle is twice as thick, you need to add .75” to the internal depth specified”?  My guess is that you meant that if the outside dimensions are per drawing, but he used a double baffle, then the internal volume was reduced by .75” so it needs to be added back. Is that right?  My assumption (ass-u-me) was that he made it per drawing (single baffle) and then slapped another layer of baffle on it, making the box depth greater than the drawing by .75”. Are we on the same page?

Kornbread: Thanks.  Your comment helped me formulate the above for BrannigansLaw. Question for you: What do you mean by OD?  I assumed you meant outside diameter but now I’m thinking outside dimension. In effect you are agreeing with my assumption that he slapped another layer on, increasing the depth of the box?  

As I re-read this, I think I’m answering my own question, but I’ll leave it here just in case. 

alanhuth

I left Curt a message on htguide. Looks like his last visit was in September. Sigh. But, on the plus side, I think you guys have given me enough to get by. 

BrannigansLaw

Alan - Jim is usually the one who answers questions. If you post on this thread:

http://www.htguide.com/forum/showthread.php?43521-Posted-3-new-designs-on-my-website-Halcyon-Finalist-Monitor-MicroStatements&highlight=halcyon

I bet he'll answer. 

In terms of my comment re: adding .75 to the internal depth, you got it exactly right. 

ani_101

All i'll say is this. Keep the baffle width and height the same and increase the depth to account for the extra baffle thickness, but even if you don't, the tuning frequency will change due to the decrease in volume with the same port - but don't sweat it - a db up or down the tuning frequency would not have a great effect overall.

alanhuth

BrannigansLaw: Yes, I contacted Jim before this posting and he answered immediately.  He wasn't sure and suggested I contact Curt again.  

I'm pleased to say Curt did answer and he said what you guys predicted, so we're all good.  He was also very encouraging about the Halcyons, so I'm more excited than ever to get going on this.