box design n00b question

[only4fun]

Hey everyone.

Hope you don't mind putting up with me.

I'm rebuilding an old set of CV's. The woofers have been professionally reconed, the mid and high frequency drivers check out, the x-overs have yet to be tested, might or might not need rebuilt but not an issue.

The guts is good.

The cabinets, being vinyl wrapped particle board and 25 years old, are beat to heck hence the reason for this project, plus I need another set of speakers for a new room.


Here's my question:

How critical are the box dimensions and shape to the tuning of the cabinet?

The original is just a standard rectangular box, roughly 18x19x32, with two rear firing 4x10 tube ports. I'd like to make the box with a slightly smaller footprint but also taller. I originally thought the stage felt low so my wanting to raise the mids/highs. I might like to do some odd/custom shaping on parts of the box as well, just depends on what I come up with aesthetically.

How much leeway do I have in my box design keeping in mind the only spec information I can go by is the original box since CV has no records or information concerning the TS specs of their old drivers. Can I simply take the existing volume and port dimensions and do what I want shape wise or does that introduce wave problems inside?

I'm one of not many who actually like CV, their performance has never let me down and the bass response is, well, CV so keeping things sounding as original is important. I also think CV get a bit of a bum rap since these did a lot of varieties of music quite well, not just RR.

I'm a cabinet and furniture maker, plus have made a few speakers over the years just for fun so "complicated" isn't an issue, I hope to do something special here. I'll be using them in my new large painting/music studio when finished.

Any help getting me through the technicals is greatly appreciated. I see by reading through the postings there is some amazing cogitating going on so I'm just here to listen.

Thanks in advance and look forward to hearing your thoughts!

[Sydney]

How critical are the box dimensions and shape to the tuning of the cabinet? ... Can I simply take the existing volume and port dimensions and do what I want shape wise or does that introduce wave problems inside?

Maintain the same net internal volume ( after additional bracing etc ).
General recommendations are to avoid cubes and dimensions that are even multiples.
Extreme elongation would make it more tube like and favor a resonance in that dimension.
( BTW designed properly with that predominate resonance in mind and it becomes more like a transmission line design )

[mikejennens]

I'd say as long as you keep the internal volume and vent size the same, you should be good. There is a "golden ratio" for speaker boxes (.6:1:1.6), but that isn't the case with the original box, so it shouldn't matter. If you can get the tweeter to ear height as you're seated, that's a good place to start. Info about the distance between drivers can be found here Wolf's Blog.
Have fun...
Mike

[JimHRB]

Looks like the original box was tuned to about 32hz. If you change the internal volume a bit, just adjust the ports to give you the same tuning. And while its apart, change the caps on the crossovers if the're NPEs.

[only4fun]

Thanks for the answers.

I was figuring on replacing the x-over caps before the rebuild as they are so old, it's an easy and inexpensive job. Didn't need to see if the originals were still in good shape when I could just update them for more years of service.

As for the height I was wanting to get them up around 48" but had concerns about getting the boxes too narrow for performance issues as well as to fit the 15" LF driver.

There's always the option of partitioning off a too big box or retuning a too big box. I'd also thought about splitting them out with a separate MT section from the woofer but then I get into driver spacing issues.

I'm trying to get the x-over points from a CV fan website so I can determine more about this project ie. the driver placement. I'm sure with more electronic know how I could "read" the assembly and find out for myself but I'm afraid that's a bit of a pay grade above me.

Still in the planning stages so I'm sure I might have some more questions.

Thanks!

[tpremo55]

Changing the baffle width significantly might result in a peak or valley in response that was not there in the original. Now, I'm not sure that baffle step was even considered in the original design, but it's something to be aware of as well.