SPICA TC-50 Restoration and Measurements

[Pete B]

I am working on a pair of later SPICA TC-50s and have confirmed that the bright top end that was mentioned in several reviews is very strongly a function of listening height. Thought this page documenting the work might be of interest:

http://baselaudiolabs.googlepages.com/MR-TC50-REB.html

I certainly expected the TC-50's to be sensitive as far as listening height is concerned however the measurements show how extreme it really is. I was also able to confirm the mid band (approximately) linear phase response with SPICA's marketing literature.

[Carlspeak]

Pete, I did one set of scans during my restoration project which included placing my Behringer mic pointed straight down at the tweeter. The attached 1/6 oct. smoothed response plots show blue (on axis with the speaker & no felt), red (on axis with the speaker with felt added) and green directly above the speaker pointing down perpendicular to the front baffle board and finally, the black curve is a close mic of the bass/mid.

I found the same thing you did with regard to an elevated listening position and increased highs. The green curve shows some serious peaks in the 6-8 kHz range and again at about 15 kHz. I guess those tweeters are particularly beamy.

NOTE: These measurements were taken BEFORE the restoration and with the original tweeter.

[Pete B]

Pete, I did one set of scans during my restoration project which included placing my Behringer mic pointed straight down at the tweeter. The attached 1/6 oct. smoothed response plots show blue (on axis with the speaker & no felt), red (on axis with the speaker with felt added) and green directly above the speaker pointing down perpendicular to the front baffle board and finally, the black curve is a close mic of the bass/mid.

I found the same thing you did with regard to an elevated listening position and increased highs. The green curve shows some serious peaks in the 6-8 kHz range and again at about 15 kHz. I guess those tweeters are particularly beamy.

NOTE: These measurements were taken BEFORE the restoration and with the original tweeter.

Interesting Carl. especially since those were the earlier version. I take it by on axis you mean on the tweeter axis?

Because, I found that the out of phase condition around the crossover area improves with a lower measurement point.

I also wonder why they made the felt opening so small in the newer version.

[Pete B]

I mention in the writeup that one system is more efficient than the other and found that one of the woofers had been replaced. The B system has an S3.8-10 woofer, and it must have been replaced at some point, it should be an H3.7-8 woofer. The best solution would be to replace it with the correct service code, or at least and H spec woofer.

Anyone have a spare H3.7-8 for sale? Or a close one.

The other system has the correct woofer.

[Carlspeak]

Model TC50i measurements with different tweeter diffraction products installed. Summary report attached.

Interesting study. The ATB PC software/Behringer mic combination does a good job of showing the different results with the different products I tried.

The Spica felts opened my eyes to how important thickness is in getting attenuation results. This led me to run these trials with some old tweeter attenuation products I had laying around which didn't impress me in the past. Now, I can see the startling difference in these SPL charts.

Results should be applicable to most any brand of speaker with an overly bright tweeter.

Tweeter_felt_diffraction_product_trials.pdf

[Guest Francksoy]

Great info, thanks Carl

Looks like felt does really help removing those nasty "honky" sounds from high-mids baffle reflections. I'll perform a couple of auditive and curve tests with my current restoration job with AR10Pi's, which I find significantly agressive in the 3k-8k area (but the capacitors are still the original ones, this maybe explaining that).