Testing and measuring Spirula shaped speakers based on Akamake's project designed by Ondra Chotovinsky.

[Walt B]

Hi Folks, this is my first post in here I hope I tailoret it to the right section.

I recently finished my last pair of custom made speakers based on Akamake's project designed by Ondra Chotovinsky.

These are the details:

Drivers: Mark Audio Alpair 7ms
Revc= 7.200 Ohm
Fo= 74.724 Hz
Sd= 50.270 cm²
Vas= 4.968 Ltr
Cms= 1.384m M/N
Mmd= 3.072m Kg
Mms= 3.277 g
BL= 3.859 TM
Qms= 2.350
Qes= 0.744
Qts= 0.565
Levc= 124.716u H
No= 0.270 %
SPLo= 86.324 dB
Xmax = 4.5mm 1 way mech
PWR= 15 Watts Nom

Box: Custom Spirula shaped printed in one piece using SLS printer using Nylon 12 material powder
Mass: 2,5 KG per unit
Supra Classic-2.5 Speaker wire (13 AWG) for internal connections
Dayton Audio BPP-SN Premium Binding Post
Dayton DSS3-SN speaker spikes

Actually I'm using a Fosi Audio BT20A PRO Class D amplifier powering these speakers. By the way I thing this is a great one from a respectable company.

This is how it looks like:

So basically, what I need is to take the measurements for:

- Frequency Response
- THD down to < 0,1% and THD at high SPL levels (up to drivers thermal or mechanical limit)
- Waterfall / spectral decay

Sumarizing what I need is:
Best affordable setup for reliable measures, what mic and what software do you recommend for entry level.

Just in case I have purchased a DaytonAudio iMM-6 mic, for tunning my daughter's violin, do you think is too basic?

I will appreciate any help you may provide.

Best regards,

Walt B.

 

[cyrano]

Looks good, if you're into that kind of thing. But how do these sound?

As long as you want to compare your measurements only with your own measurements and with what you're hearing, any decent mic will do.

After all, the room the speakers are in will produce more deviation than the difference between measurement mics. The low end is just a small diameter electret, as these are usually flat. They are a bit less noise wise, but that shouldn't affect frequency curve measurements.

When you start comparing your measurements with others', a UMIK BK1 is the first step up, since it's level calibrated. It is, however, a USB mic. It's easier to use a simple audio interface, with input and output from one device. Two or more devices might give some trouble when routing the IO to the software.

When it comes to software, REW (Room EQ Wizard) is probably the most used. It's very complete and free. It also has a very knowledgeable forum. There are others, like OpenSoundMeter (free) or ARTA. They have their own pros and cons, you have the choice...

 

[hamlet01]

Why you choose that drivers?
I was taking some calculations to find the best driver for the 2.2l volume of the akemake spirula and the best match is with the dyton audio RS100P
I don’t understand why deeptime use the Tang Band TB W4-2142 or you use the Mark Audio Alpair 7ms
I prefer mark audio o TB but Dayton do best result in my knowledge that is nothing, I’m totally new by in this.
I post the results and the specification of the drivers and please give me your opinion. I don’t know what driver finally use.

 

[hamlet01]

 

[k brown]

My first thought was that they would need a fair amount of baffle-step compensation; that's a lot of flat surface area with hard edges around the cones, and a perfect circle being pretty much the poorest shape for a baffle.

You see in the B&W Nautilus, a much better ratio of cone area to baffle area, with greatly rounded edges

 

[JohnRoberts]

That's interesting "looking"... how does it sound?

JR

 

[hamlet01]

What happen here??? I have printed it oversized??

 

[hamlet01]

I dont understand…
All of that drivers are 4” in the catalogue but the Dayton is much smaller
I have print the boxes to big for the Dayton but to small for the Mark audio or tand band

 

[k brown]

Well, not all 4-inchers have the same frame dimensions/geometry.

But post #7 looks to be for more like a 5.25".

 

[hamlet01]

I cant find a driver that fit my ******* print now
I think that I have to reprint it. Anyway I don’t know what driver will have the better response / quality

 

[Disco Volante]

Cut a nice piece of board to put between the driver and the flange...

 

[Disco Volante]

Using full-range drivers pointing upwards... the treble will be beaming heavily.. so a stereo listening position would place your armchair under the ceiling..
I suggest making it twice as long, make an opening in the narrow end so it becomes a transmission line. Then print a small version and mount it on top with a tweeter in it, making sure the tweeter sort of points to your preferred listening position. Do a bit of math and make a crossover, adjust it with the help of whatever mic you have available and the splendid REW software.. A DIY nautilus..

Interesting project!

 

[k brown]

Cut a nice piece of board to put between the driver and the flange...

See post #5.

 

[hamlet01]

See post #5.

 

[Paul W]

Is there an acoustic reason for this cabinet shape, or is it just for the looks?

 

[hamlet01]

 

[hamlet01]

 

[KrIVIUM2323]

Is there an acoustic reason for this cabinet shape, or is it just for the looks?

There is a reason! It's known as a closed transmission line. The idea behind it is to 'kill' (redirect) the backwave ( generated into the box) through the use of absorbing material along the spiral line. The length define the lower freq the line can reproduce (1/4 wavelength). Taper make it appear longer than the line really is.
That's one of the reasons B&W used different lines into the Nautilus.

The principle works but through experiments from fellow diyers you can manage 90% same effect through the use of a 5 sided kind of pyramidal shape stuffed as loading chamber. Of course it won't get as low as a spiral shape ( cancelation through line length) but for a mid enclosure it works very nice in 'killing' reflections in the mids ( high are absorbed). If you want sealed but 'box free' sound it's one working answer. Can work aperiodic too ( with a bass reflex aperture).

But like K Brown said there is compromise to be made with this kind of shell shape: diffraction behavior is not of the stealth one.
For BSC well... use a reflecting surface nearby could kind of counteract but a shelf eq is easier and better imho.

 

[k brown]

No shelf EQ can iron out the problems of a circular baffle pointed out in post #5.

Gotta figure out a way to reduce that baffle area to a minimum, and considerably round off the edges. Look closely at the pic of the Nautilus; it doesn't look like that for no reason.

A possible alternative is what Bau did on the Spica TC-50; surround the driver with 3/4" thick felt. This blocks sound waves from diffracting off the edge of the baffle. If foam is used, it has to be of the sound-absorbant type, not the sonically transparent kind used for microphone pop filters.

 

[hamlet01]

There is a reason! It's known as a closed transmission line. The idea behind it is to 'kill' (redirect) the backwave ( generated into the box) through the use of absorbing material along the spiral line. The length define the lower freq the line can reproduce (1/4 wavelength). Taper make it appear longer than the line really is.
That's one of the reasons B&W used different lines into the Nautilus.

The principle works but through experiments from fellow diyers you can manage 90% same effect through the use of a 5 sided kind of pyramidal shape stuffed as loading chamber. Of course it won't get as low as a spiral shape ( cancelation through line length) but for a mid enclosure it works very nice in 'killing' reflections in the mids ( high are absorbed). If you want sealed but 'box free' sound it's one working answer. Can work aperiodic too ( with a bass reflex aperture).

But like K Brown said there is compromise to be made with this kind of shell shape: diffraction behavior is not of the stealth one.
For BSC well... use a reflecting surface nearby could kind of counteract but a shelf eq is easier and better imho.

That is!