Emotiva: Shop Now

Notifications
Clear all

Emotiva: Shop Now

overcomplicated boombox build  

  RSS

RobinVC
(@robinvc)
Active Member Registered
Joined: 3 months ago
Posts: 5
19/08/2020 8:31 am  

Hi there,

First post here, thanks for having me :D. Anyhow, I'm designing a boombox with with two tcp115-4 woofers and two ND25FW-4 tweeters and I'm having trouble with them.
Because the tweeter sits in a waveguide, the phasing is hard to get right (I'm basically guessing the z-offset). This is the crossover I came up with:

crossover wave v1

 Which results in this frequency graph:

frequency wave v1

 I added a 0.5 inch offset to the woofer to achieve this phasing. The graph slopes down to accomodate baffle step loss, but I'm not sure what dimension I needed to account for since the boombox is technically two bookshelfs sandwiched together (so do I measure twice the baffle width?).
I'm also new to crossover design, so i'm not sure if my values make sense at all haha. If possible I'd like to keep the cost of components down by keeping their values low, but that seems very unlikely.
There is also the impedance that's worrying me a bit. I've used a zobel, but the woofer's impedance still climbs up drastically:

impedance wave v1

I'd like to add that i'm just using the supplied fdr and zma files. I've got no measuring equipment other than a small "diy" mic and some experience with REW. I'd like to first try "getting close" before ordering components 🙂

So to sum it all up; If someone has more info on the drivers or z-offset or thoughts about the crossover or project in general, please feel free to comment. Thanks!


Quote
123Toid
(@123toid)
Illustrious Member Admin
Joined: 3 years ago
Posts: 1071
20/08/2020 3:10 am  

Don't worry about the impedance going up unless you are using a tube amp to power it.  The only area to worry about with impedance is the 200hz range, but it looks to only dip to about 3.6 ohms, so it should be fine for a nominal 4 ohm amplifier.

As far as the z-offset, what waveguide are you using?  I can only guess without knowing the waveguide and with it for that matter.  But no matter waht, I wold venture it will be over 1/2"  But let us know the waveguide, so we can see if we can help with that at all. 

As far as the crossover goes, my main concern is you are dipping the high end down too much.  I personally would aim for it to be closer to 81-82db.  That way you can get that high end.  However this should be fairly easy to adjust with your resistor.  If I were you, I would try a few different itterations.


ReplyQuote

RobinVC
(@robinvc)
Active Member Registered
Joined: 3 months ago
Posts: 5
20/08/2020 4:56 am  

@123toid

Hey, thanks for the reply. I'm planning on using a TPA3116 based amp board, which should be 4ohm capable. As I said I was more worried about the rise, but i'm glad to hear that's less important.

As for the waveguide, I'm just using the stock one. (same tweeter of the C-note kits) link It's quite shallow, so I guessed there would be minimal z-offset....

After posting I tried a few itteration and bumbed up the highs a bit. But as you said, it would be easy to adjust the resistor afterwards if i'm not happy with the highs. Crossover point is slightly lower too now.
This is the new response:

frequency wave v2

I also tried raising the z-offset to 1.5inch and that gave less problems than I anticipated, lowering it to -1.5inch though gave me a dip on the xo-point.


ReplyQuote
123Toid
(@123toid)
Illustrious Member Admin
Joined: 3 years ago
Posts: 1071
27/08/2020 11:45 pm  

@robinvc

That;s good to know.  I was going to guesstimate about 1.5."  So I think you are probably pretty close via guesstimation.  The only real way to know would be to measure it.  THat frequency mockup looks great.  Looks like perfect phase alignment or close to it and a nice response. 


ReplyQuote

RobinVC
(@robinvc)
Active Member Registered
Joined: 3 months ago
Posts: 5
28/08/2020 10:22 am  

Jup, by now I've made about 3 variations of crossovers that all work. Just gotta pick my favorite 😀 . I also played around a bit in inventor, to get a feel for size and stuff. I might make the back of the boombox out of polycarbonate. I've recently built an ammo-can boombox and it is very fun to show the neat insides.

cad front
cad back

the only other dillemma i'm having is what color to paint it haha.


ReplyQuote

Newegg

Share:

Emotiva: Shop Now

%d bloggers like this: