Little MTM speaker Fountek FR88EX

[BrechtVD]

Hi all,

Its been a wile sind I posted something (and then I mean really long). But I’m again in the mood to make a small MTM speaker
The drivers I want to use:
Fountek FR88EX-8

http://www.fountek.net/fr88ex.html

Off Axis response:

Harmonic distortion:

Because of the rise of the 2th order harmonic distortion at 3kHZ and the off axis-response I wanted to cross before 3kHz
So I wanted a tweeter that was small so I can place them close together. And a fs below 1000Hz

I went with the SB Acoustics SB26STCN-C000-4

http://www.sbacoustics.com/index.php/products/tweeters/dome/sb26stcn-c000-4/

For the enclosure I went with a vented box with a volume of approximately 5 liter. Then I have no problem with my max lineair extrusion at 10W (for one driver) and with a port with a diameter of 35mm the air speed is OK at 10W

The dimensions of the speaker: 12cmx32cmx24cm (with x height x depth) = [inch] 4.75x12.6x9.5.I am planning to use MDF 1.5cm = 0.6 inch
Next I messed around with the X-over and in that process I changed 2 times from tweeter and moved the tweeter more to the side for the baffle step peak.

This is what I ended up with:


Frequency response of the driver is derived from SPL Copy, so I didn’t measure it. I crossed at 2500Hz, it probably is the limit for this tweeter but that is where I am now at the moment. The phase alignment is pretty good (I think). I assumed that the offset of the 2 drivers is 0.3 inch (0.8cm). I can’t test this because I haven’t the drivers and measuring equipment.
The only thing I don’t like very much is the frequency response between 1kHz and 3kHz. Should I take a bigger inductor (now 720uH) to lower this a bit?

Furthermore what are the thoughts because I don’t have much experience. Just made a little full range speaker an that’s why this also stays small

Thanks in advance,
BrechtVD

[BrechtVD]

Also some pictures from the reverse polarity and the impedance of the speaker

[augerpro]

Those caps on the tweeter are huge. You should be able to get away with much smaller: https://sites.google.com/site/somasonus/Home/bbv2

[BrechtVD]

augerpro, thanks to post that link
Didn't know that I was using the same tweeter h:

I used your values from your xover and started again from there. And looked wich values resistors, capacitors and coils I can get.
This is what I have for the moment:




The only question I now have is. Does it pay off to lower (more flat) the impedance and phase of the speaker? Make it a bit easier for the amp.
For those components you can use cheap bipolarized electrolytic capacitors, ceramic resistors and small inductors. So why not? Or am I wrong?
This is what I get:

[BrechtVD]

Hi all,

They are done and I am really happy with the look and te sound!

First of all the build of the enclosure. I never build an enclosure and I really did not know how to begin. Cut it at 90° or 45°, big front baffle or not. That's why I googles and watched some things on Youtube.
And than I saw something I really liked.
I did the cuts under 45° ,lined the panels up and taped them together on the outside. So afterwards I just 'fold' it together. To my own suprise the tape did hold pretty well.
I used wegdes on my table and clamps on top. But first I had to make sure the wedges are aligned square.





At last I gleud top and bottom with a panel that was a little oversides

[BrechtVD]

Next I had to trim the top and bottom panel and need to know where exactly my drivers wil be to.
I draw my front baffle in CAD software and printed it 1:1 scale so I can gleu it to my baffle and begin to play around with router (for the first time...)


I build my own circle jig and it worked pretty well. But of course first always try on a scrap piese of wood!


Finished after I was done with my router and put a 45° cut to the side of the front baffle


I was so pleased with the raw look of the plywood I put clear varnish on it. Only down side is that you see where you sanded to much to get the wood glue of, but stil I like it!


Speaker next to a 2 liter bottle to see the size (same height)

[BrechtVD]

At last 2 pictures of the xover assembly.
Because it is not a really big spaeker, I made two panels. One for the Fountek's FR88 EX and one for the tweeter




I know that there are two inductors really close to each other. That are two inductors (same value) in serie, that's why I did not mind to do that.
I mounted the panels on the top and bottom inside my speaker.

A practicale question:
I completly glued my enclosure together and aftherwards I was really lucky that I could stil put my hand in through the hole of the Fountek speakers. If you guys build small speaker enclosures, do you make sure that you can disassemble one panel?
Thanks in advance!

[augerpro]

Nice work! First builds are always very satisfying, and you picked some good drivers so that helps.

On speakers like this I usually make the back panel removable.

[BrechtVD]

Thanks.

And how do you make the back panel removable, just with srews or with bolts and inserts in de wood?