First speaker design - please comment

[sobazz]

I'm currently working on my very first speaker project. Designing and calculating is a very tough process for me, since I'm really a newbie in this buisness.

The result is supposed to be a sealed 2-way standmount with an internal netto volume of around 6l (approx. 0.212 ft^3). So far I've chosen the Scan Speak 8530K01 for bass and midrange. I've not yet decided which tweeter to use. Any recommendations?



Cone excursion at 1w


Cone excursion at 5w


Max SPL


The enclosure will be a plain MDF (19, maybe 22mm for front and back) box. Later I may want to make a better one. Are there any specific relationship between the sides I should stick to?

Please comment.

[sobazz]

Hmm... why is there a sharp edge at around 100hz (last graph)?

[Kanga]

Hi Sobazz. The mid-woofers you have chosen are very inefficient. How much amp power do you have, and what king of bass extension and loudness are you looking for?

Dennis Murhpy has an MTM design using this driver (bringing the efficiency up), paired with a Hiquphon OW1 tweeter. http://murphyblaster.com/content.php?f=revowlator.html

He also has a design using the driver with a HiVi research ribbon tweeter, but he says that he doesn't actually recommend that you build such a speaker, because its too insensitive and is not good value.
http://murphyblaster.com/content.php?f=revelator.html

Mick

[sobazz]

My amp is a Harman/Kardon HK680 (85w nom.). I'm thinking about building a class-d amp using LC Audio's circuits, but for now I'm fine with. The HK680 is capable of putting out a serious amount of power into both 2 and 1 ohm loads, and it's current capabilities are pretty impressive too.

The speaker has to be small - like this one: http://www.danskaudioteknik.dk/sites/icon.htm

[Ron E]

The sharp edge is the boundary between two important regimes.
The driver is excursion limited below the edge and thermally llimited above the edge.

Below that edge, the driver cannot theoretically handle the amount of power (based on predicted cone excursion) used to generate the graph, and above that frequency it can.

In reality, a loudspeakers suspension is nonlinear (ggets stiffer with greater excursion) and a well designed loudspeaker will handle more power than an excursion estimate would indicate, but at the cost of increased distortion.

[sobazz]

At what power should I calculate the excursion in order to get a usable result?

[sobazz]

Ok... I've reconsidered. The projekt will be way too expensive if it fails. I've decided for another speaker. It is actually very different from the above.

3L netto volume, vented, tuning freq. 74hz
Vifa 4½ TC11SG49-08 bass/midrange
Peeless 811435 neodymium tweeter
Vent diameter 35mm, length 149.6mm
Sides in ½" MDF, front and back 3/4"


Here's a drawing. As you can see, I haven't spend much time on it...

[navin]

why not use vifa TC tweeter as well.

[sobazz]

I would like to. But the space is tight, and so is the budget. Space limits my options to neodymium tweeters, and Vifa's neo tweeter retails for approx. 2½ times the price of Peerless'.

[Ron E]

Any small speaker is going to have excursion issues in the bass range unless it is very inefficient. There was nothing wrong with your initial design - I was just explaining what the sharp edge was.

The power where the excursion prediction meets the Xmax spec is the theoretical mechanical power handling for the woofer, but a well designed woofer will often handle 2 to 4 times the predicted power before mechanical damage happens, because of the suspension nonlinearity. When the mechanical powerhandling is less than the thermal, it just means that at those frequencies, the speaker will bottom before the coil overheats.

Remember also that power handling depends on what kind of music you listen to - you aren't going to be bottoming many woofers with violin concertos

Cheers...