Dual hi-vi mini project

[BionicSniper]

ok i got everything yesterday.

13sqft of sound dampening stuff from elemental design (1$ a sqft!)
1lb of acousta stuff
then all the other parts for the speakers. I found a 1 7/16" hole saw that is the right size for the tweeter and if that doesn't work i can just make a super small hole jig for my router. I'll make a build thread tomorrow

 

[gtforme00]

My first impression was very good. The cast frame makes an enormous difference in the appearance. The foam gasket on the stamped frame guys is tacky (as all gaskets are to me). They are worth every penny more than the stamped frame versions for the looks alone.

I did some quick parameter measurements of my 55-3855's after an hour of break in at 45Hz.

Driver 1:
Fs: 54.2 Hz
Vas: 6.2 L
Qts: 0.50
Qms: 7.73
Qes: 0.53
Re: 7.5 ohm

Driver 2:
Fs: 58.9 Hz
Vas: 5.4 L
Qts: 0.47
Qms: 6.90
Qes: 0.51
Re: 7.3 ohm

MCM Published Specs:

•Power Capacity: 50W/100W RMS/peak
•Sensitivity: 87dB (W/M)
•Impedance: 8ohm
•Re: 6.0ohm
•Le: 1.83mH
•Frequency response: 55Hz~10KHz
•Fs: 55Hz
•Qts: 0.37
•Qes: 0.41
•Qms: 4.16
•Vas: 5.87 (liters)
•Xmax: 2.25mm

For comparisons sake here are the specs Zaph measured for the non-shielded version:

I have to admit I was a bit disappointed by the measurements. I spend extra for the shielded version because it modeled better in a small enclosure according to the published specs. The real specs measure as close to the non shielded woofer than they are to the published specs, meaning there is likely no advantage to the shielded version besides the shielding (which is not important to me anyways).

Aside from a larger enclosure than I was hoping for, I don't think I will be dissappointed in the performance. If they measure acoustically anywhere close to what Zaph tested, they will be some very sweet drivers.

I will be pairing them with a pair of Seas 25TAF/DTV tweeters I bought on buyout from Solen. Preliminary modeling using Zaphs frequency response data for the woofer and Seas datasheet (usually very honest) is extremely promising.

I will likely finish parameter testing tomorrow so that I can then design the box for these. It is very important to measure your own specs and design the box according to what you measure yourself, not what the manufacturer gives you.

The woofers are breaking in over night at my office. Hopefully the parameters will relax more into spec by tomorrow morning.

Regards,
David

 

[Jack Hidley]

David,

What type of meter are you using to measure Re with? I'm very surprised that there is a 20% difference between spec and your measurement. Any decent voice coil vendor can control this within +/-5%. This will affect the calculated Q values a fair amount.

 

[gtforme00]

Jack,

You caught that too huh? That bothered me a lot so I recalibrated Speaker Workshop.

Using a Fluke 29 I get a DC resistance of 6.8 Ohms on Driver 1 and 6.7 Ohms on Driver 2.

Here are the updated specs after recalibrating Speaker Workshop and after 12 hours of burn-in.

Driver 1

Fs: 54.3 Hz
Vas: 6.14 L
Qts: 0.386
Qms: 4.42
Qes: 0.423
Re: 6.79 Ohms

Driver 2

Fs: 60.3 Hz
Vas: 5.32 L
Qts: 0.392
Qms: 4.45
Qes: 0.430
Re: 6.74 Ohms

Much closer to the published spec. Do not place much value in the previous measurements, as Speaker Workshop relies on precise calibration. I also averaged these parameters over 10 runs.

I wish my Fs and Vas were more similar, but the Vas was measured with the added mass method and I am suspect of the absolute values until I can build a test box. The relative values still don't match up, so I guess chock this one up to production variation.

When I get into this build in more detail I'll start a new thread.

Thanks for checking my results Jack.

-David Malphurs