I have a pair of what I believe are the original version Spica TC-50 speakers. They are a matched pair with matching crossover codes. I have read that the codes indicate specifics of the exact measurements of the parts (i.e. they were matched tighter than the tolerance of the parts). I don't think they sound as coherent as they did 30 years ago when I was running them regularly, perhaps the electrolytics have drifted. I suppose I should measure them.
Here's my question: would it be possible to trim the capacitor values using just a decent quality condenser mic (I have AKG perception 220), a computer and audio interface? I remember that the speakers were designed to be particularly flat in frequency and phase response at the crossover region (somewhere around 1k or 2k if I remember right). In other words, can I measure the crossover accuracy without buying more equipment? (No problem acquiring / compiling open source software as needed.) Thanks for any help.
Here's my question: would it be possible to trim the capacitor values using just a decent quality condenser mic (I have AKG perception 220), a computer and audio interface? I remember that the speakers were designed to be particularly flat in frequency and phase response at the crossover region (somewhere around 1k or 2k if I remember right). In other words, can I measure the crossover accuracy without buying more equipment? (No problem acquiring / compiling open source software as needed.) Thanks for any help.
Those look rather nice!
https://www.stereophile.com/standloudspeakers/446/index.html
I can't help with your question, I'm afraid, but if you've been listening to other speakers with different sound character and quality over time, your memory of how the Spicas used to sound may be coloured by time, changes of listening room, etc.
Geoff
https://www.stereophile.com/standloudspeakers/446/index.html
I can't help with your question, I'm afraid, but if you've been listening to other speakers with different sound character and quality over time, your memory of how the Spicas used to sound may be coloured by time, changes of listening room, etc.
Geoff
That's true, my memory of their sound is certainly not accurate. I really should get in there and measure the caps.
Did it occur to you that the drive units themselves may have deteriorated in 40y time? Swapping caps won’t fix that.
On the mike, yes of course you can use it for loudspeaker measurements. But it is a bit rudimentary, the AKG has nonlinear behavior of itself and I’m not sure how it behaves in a free sound field.
Just try it and get acquainted with acoustic loudspeaker measurements. A decent microphone can be had for under $100. So you have upgrade options too, assuming you have budget for new caps.
On the mike, yes of course you can use it for loudspeaker measurements. But it is a bit rudimentary, the AKG has nonlinear behavior of itself and I’m not sure how it behaves in a free sound field.
Just try it and get acquainted with acoustic loudspeaker measurements. A decent microphone can be had for under $100. So you have upgrade options too, assuming you have budget for new caps.
I have a set of those woofers I bought years ago. Used to think they sounded pretty good, but recently I gave them a listen for a possible project. Honestly I was disappointed, they might have to go on the chopping block.
Another variable to consider concurrently with those already noted is that the ears have aged 30 years as well. And consider whether the room’s properties, speaker placement etc. play into the equation. My .02.
Upside - Measuring will be a good project and a chance for learning.
Upside - Measuring will be a good project and a chance for learning.
I suppose the surrounds and other moving parts may have stiffened up. I've never seen anything regarding how much of a problem aging parts in a speaker are, other than foam surrounds, which is not applicable here. My ears are definitely not what they used to be.
I thought this brand was exclusive to portable AM radios that were very famous here, in Argentina !!. Many football fans attended the stadiums equipped with their "Spicas", and followed the game's events by tuning into the broadcasts of their favorite announcer...
Sorry OT
Sorry OT
Attachments
It would be nice! 😳 Although I just looked up who it is, football is not my passion, tennis is, but unfortunately my knees have had enough, even for a double mixed ! 🙄
Really? That is cool. I absolutely loved my TC-50s. I bought a pair new in the 80s. Wish I had never sold them. There were something special indeed. I wish John had kept on designing.
I'm waking this thread up because I picked up another pair of original TC-50s at a house cleanout sale. Same version, different service codes however. This pair is in a little rougher shape, but the drivers look ok other than a dented woofer dust cap. I switched back and forth today on the same music a few times. This second pair is a bit brighter and splashier sounding. My original pair sounds a little recessed in the highs. The new pair has seen some damp air whereas the original pair has been kept in a dry environment. Still looking to figure out some measurement protocol with just a computer, interface and condenser mic.
I use a program called Arta to make measurements. It is now free https://artalabs.hr/download.htm The manual is excellent and tells you everything you need to know to make measurements. There is also a program Room EQ Wizard ( REW ). Your equipment will be perfectly fine for crossover work.
The Stereophile article mentions a first order crossover. So that's as simple as it gets. If there are electrolytics, replace them with new or get film or metalized polypropylene caps from Parts Express or other. Just buy the value that is printed on the old cap. You could buy a few different values and see what works best.
If you have lots of time to kill, like all winter, you could measure the tweeter and woofer separately, and design a new crossover by trial and error or learn to use crossover design software. For a passive crossover you would measure with the gain and phase with the microphone and then the impedance using a few cables and a resistor with Limp ( in the Arta suite of software).
The Stereophile article mentions a first order crossover. So that's as simple as it gets. If there are electrolytics, replace them with new or get film or metalized polypropylene caps from Parts Express or other. Just buy the value that is printed on the old cap. You could buy a few different values and see what works best.
If you have lots of time to kill, like all winter, you could measure the tweeter and woofer separately, and design a new crossover by trial and error or learn to use crossover design software. For a passive crossover you would measure with the gain and phase with the microphone and then the impedance using a few cables and a resistor with Limp ( in the Arta suite of software).
Last edited:
Your condenser mic is a cardioid and what you need is an omni with flat frequency response. You can buy one for pretty cheap.
https://www.behringer.com/product.html?modelCode=0506-AAA
Believe it or not, this is good enough for measuring a speaker. Use Room Equalization Wizard (REW) and a sound interface with phantom power. You can download a generic mic calibration file from their website that will correct for some typical inaccuracies in these mics - slight rise above 1-2k followed by a droop above 10-15k.
You can make a simple jig and measure impedance Thield small parameters and components with REW, as well.
olsond3:
The tweeter section only is first order, The woofer is a higher order rolloff I remember. I also remember a Jon Bau comment somewhere that the part values were selected to a higher precision than the nominal value of the parts. Now with the extra pair it will be less daunting to rip into it. A while back I had yet another pair that had absolutely trashed cabinets that I parted out. I remember the crossover board being bolted in not glued, so hopefully I can get it through the woofer opening. Thanks for the tip on Arta, I may go that route unless I can find something simpler (play a frequency sweep, record it, analyze that in Audacity or whatever).
The tweeter section only is first order, The woofer is a higher order rolloff I remember. I also remember a Jon Bau comment somewhere that the part values were selected to a higher precision than the nominal value of the parts. Now with the extra pair it will be less daunting to rip into it. A while back I had yet another pair that had absolutely trashed cabinets that I parted out. I remember the crossover board being bolted in not glued, so hopefully I can get it through the woofer opening. Thanks for the tip on Arta, I may go that route unless I can find something simpler (play a frequency sweep, record it, analyze that in Audacity or whatever).
Last edited:
Ron E:
That Behringer mic is way cheap, yeah. Last time I looked for measurement mics I thought the low end would be around $100. I'm not sure why I would want an omni, wouldn't I want to favor the direct sound? I'm thinking measure a foot to a few feet away, directly in front of the speaker at a height between the two drivers. I think that Behringer is for calibrating a PA system in a room, so that's why they make it an omni. But I'll admit to being a complete noob at speaker measurement.
That Behringer mic is way cheap, yeah. Last time I looked for measurement mics I thought the low end would be around $100. I'm not sure why I would want an omni, wouldn't I want to favor the direct sound? I'm thinking measure a foot to a few feet away, directly in front of the speaker at a height between the two drivers. I think that Behringer is for calibrating a PA system in a room, so that's why they make it an omni. But I'll admit to being a complete noob at speaker measurement.
Here's a short tutorial on Arta.
This assumes the setup has been done where you select the input and outputs from the sound interface. There is a little check box for "center impulse" that has to be checked but you can see that looking closely at his settings.
Measurement microphones have to have a ruler flat response down to 20Hz, that is why they invariably are omni’s.
For serious work you have to have them calibrated or at least have checked if your specific one needs slight corrections through the frequency band. Sonarworks has a cheap (under $100] but good microphone for this. The Cross Spectrum Dayton is a good alternative as long as it is available.
The woofers are low-passed with a Bessel acoustic target response, if I’m remembering correctly. Maybe fourth order? The tilted front baffle adjusts the timing of the tweeter relative to the woofer, to match the phase behavior of the high pass and low pass rolloffs. One of my all-time favorite speaker designs.
Few
Few