Hi-Vi/Zaph/SB 3-way MTM build thread
 

Hi all, haven't posted ehre in a while. I finally decided on a project to replace my Peerless/Morel 2-ways. I am doing a 3-way MTM with a Hi-Vi M12 woofer, two Zaph Audio ZA14W08 mids in parallel, and a SB Acoustics ring radiator tweeter. Since I don't have the measuring equipment at home to properly design a crossover, I decided to have Madisound design it for me. I should receive that in a few days. In the meantime, here are the drivers which I received in the mail today:

http://www.madisound.com/catalog/pro...oducts_id=1513

http://www.madisound.com/catalog/pro...oducts_id=8643

http://www.madisound.com/catalog/pro...oducts_id=8540

First impressions: Massive woofers. The surrounds and cones are extremely stiff, but they give way when driven hard. The woofer has no venting under the spider, but the spider is "air-transparent" and there is a small hole through the pole piece. I decided to drive these in open air and gave them a good amount of power. Good: they rattle everything. Bad: they rattle. I can hear a pretty loud whistling noise through the pole piece vent at about half of x-max. It needs more venting, but I think the sound will be masked when they're in their boxes.

The Zaph drivers are great construction, sturdy, lots of venting everywhere, and copper in the motor. x-max is limited, but that is a good thing in my application because the short coil/gap combination means less Le and less harmonic distortion. They look like they are much more expensive, and because they match the Seas Excel W15s ($160) in performance, they should be.

Tweeters look interesting. Very large surrounds and the center of each dome is fixed to the pole piece, so they are ring radiators. They are better than the Vifa XT25 according to Zaph's tests.

Pictures:

http://h.imagehost.org/view/0718/DSC00895

http://h.imagehost.org/view/0126/DSC00898

http://h.imagehost.org/view/0881/DSC00897

I just received measurements and a crossover from Madisound.

http://a.imagehost.org/0688/driver_responses.jpg

http://a.imagehost.org/0483/frequency_response.jpg

http://a.imagehost.org/0289/impedance_response.jpg

http://a.imagehost.org/0672/crossover.jpg

Many thanks to the Madisound designer for these, as I could not have done them by myself.

Comments on the above:

At first, the response looks far too bass-heavy, but it doesn't look like baffle step was taken into account. In this case, the response is just right, as the baffle step frequency for the bass box will be at about 300Hz. Final sensitivity should be 89-90 dB. The lowpass filter is a simple first order with a Zobel for impedance correction. Midrange is more complicated with Zobel, notch filter tuned to 8760 Hz, and a steeper low-end rolloff. The tweeter circuit is a simple second-order filter with padding.

I will need to fix the 3 kHz impedance peak, though, with a series notch filter. I might be using a tube amp with these.

Hmm... my kinda speaker! So hurry up and build it already! ;)

Nice set of drivers there! Crossover design seems good, with the BSC basically implemented into it by nature.

Am suprised the M12 woofers have much motor noise. I have used the M8a woofers and when testing in free air found them to be exceptionally quiet up to the Xmax limit.

This kind of response reminds of a house curve. Such should be the balance from a pair in the far field in order to sound naturally tilted by the acoustics blending with the power response.

If it is 1m gated and spliced at 300Hz with very close field, chances are that the pair is going to sound heavy at 3m in a normal indoors environment.

Yes, it's unfortunate. The noise is whistling from the pole piece vent, which should have been larger. There should be far less noise when the drivers are in their boxes.

I will have to see how it sounds because I don't know exactly how Madisound sets up their measurement mics. I did specify to them that I wanted some BSC, though, so it looks like they catered to my needs. If I see that the sound far too heavy, then I will either play with crossover values or EQ it down.

Does anyone have any idea how to select values for the series notch to get rid of the 3 kHz impedance peak? All the series notch calculators I've found ask for Qms and Qes, which is not helpful.

Once it stops raining over here and things dry up, I'll stock up on MDF and the building will commence.