I've got some leftover parts and am itching to make a pair of poor-man's Spectra 11s: I plan to use Mk-121C non-medallion HF transformers alone driving 8" panels, along with a single Velodyne Impact-10 subwoofer. The sub has a claimed range up to 140 Hz but the control on the back goes from 50-200 Hz, so not sure what that's about. I was thinking of maybe splitting the panels in half, Spectra-style, and using 330K resistors to to drive the outer halves. To maintain the low-budget aspect, I'm going to use a single HV supply if I can find a surplus 500-1000V transformer to bias both left and right panels using 22ga 10kv wires.
I expect balancing the crossover frequencies to be the hardest part. If anybody has tried anything like this, or just has any suggestions, I'd love your input.
Or is the whole idea nuts?
I expect balancing the crossover frequencies to be the hardest part. If anybody has tried anything like this, or just has any suggestions, I'd love your input.
Or is the whole idea nuts?
I think you'd be disappointed with the results. The equalization provided by the MK-121, either in-full or from a portion thereof, would be all wrong for the Spectra technique. For Spectra, the HF drive needs to be 'hotter' due to the reduced area of the half-panel.
If you want to make a hybrid, single panel speaker, drive the panel with the full MK-121 interface, suitably crossed over to the woofer. The HF transformer alone does not go nearly low enough in frequency for the the scheme you describe. You can try crossing over in the 100-150 Hz range.
If you want to make a hybrid, single panel speaker, drive the panel with the full MK-121 interface, suitably crossed over to the woofer. The HF transformer alone does not go nearly low enough in frequency for the the scheme you describe. You can try crossing over in the 100-150 Hz range.
Last edited:
Thanks for the quick answer. I'm assuming that the graphs I've seen posted here showing the HF transformer covering all the way down to 20 Hz (in the pre-C version) relatively flatly are just the transformer output, not what the actual panel would reproduce due to the panel's EQ requirements to get flat output? And that deficit is made up by the LF transformer summing to bring it up closer to flat?
The HF transformer working to 20 Hz? Don't know where you saw that. Although the two transformers do overlap in their operation, the HF transformer isn't much good below midrange frequencies. Operation below that would result in distortion, including transformer saturation and even possible transformer damage. And transformer damage can often lead to amplifier damage. Just don't do it.
Post by bolserst: All Acoustat panels can give
Relevant plot:
https://www.diyaudio.com/forums/attachments/planars-and-exotics/538351d1458336772-acoustat-panels-mk-121_interface_results_02-png
Relevant plot:
https://www.diyaudio.com/forums/attachments/planars-and-exotics/538351d1458336772-acoustat-panels-mk-121_interface_results_02-png
Last edited:
It looks to me like the HF transformer is relatively flat down to 20 Hz, but to maintain actual flat response from the panel, it needs summing with the output of the LF transformer which itself is greater output than the HF below around 4 kHz. But in the "C" version, the equality point is about 1600 Hz.
Hi all!
A friend of mine and me both have Acoustat Spectra speakers. He has the Spectra 2200's, I have the 22's. We both play with more or less the same equipment, a Rotel RC972 preamplifier, two Rotel RB970BX mono amplifiers and Phantom Analogue cabling. Somehow his speakers always sound a lot warmer, for both cd/vinyl etc. Could this be a difference in the 2200 vs 22's? Or could it be something in the parts (resistors/capacitors) inside the MK2123? Or could it be that the electronics in his MK2123 are older/newer than mine? What I've noticed is that the LF resistors (100Kohm) are different than mine and my 2123 has a diode and capacitor extra. This has been done by a repair shop to get the bias up to spec again.
Kind regards,
Ron
A friend of mine and me both have Acoustat Spectra speakers. He has the Spectra 2200's, I have the 22's. We both play with more or less the same equipment, a Rotel RC972 preamplifier, two Rotel RB970BX mono amplifiers and Phantom Analogue cabling. Somehow his speakers always sound a lot warmer, for both cd/vinyl etc. Could this be a difference in the 2200 vs 22's? Or could it be something in the parts (resistors/capacitors) inside the MK2123? Or could it be that the electronics in his MK2123 are older/newer than mine? What I've noticed is that the LF resistors (100Kohm) are different than mine and my 2123 has a diode and capacitor extra. This has been done by a repair shop to get the bias up to spec again.
Kind regards,
Ron
"could it be that the electronics in his MK2123 are older/newer than mine? What I've noticed is that the LF resistors (100Kohm) are different than mine and my 2123 has a diode and capacitor extra. "
Yes the type/make of Big 100k resistors can make the sound brighter...
An a higher bias can also make the sound more rolled off..
I have found all things can/do make a diff with ESLs....not always better just diff. I have used a variac to back the voltage down on the bias, it gives a warmer sound you may start there....if warmer sound is what you wont.
All just one mans finding...
Yes the type/make of Big 100k resistors can make the sound brighter...
An a higher bias can also make the sound more rolled off..
I have found all things can/do make a diff with ESLs....not always better just diff. I have used a variac to back the voltage down on the bias, it gives a warmer sound you may start there....if warmer sound is what you wont.
All just one mans finding...
Spectra 33 Full Range Segment Reconfiguration
Hello! Long time Acoustat owner here but I'm somewhat new to the Spectra series.
Question: Has anyone here tried reconfiguring where the full-range segment is located within the arrays? From the factory my Spectra 33 speakers have the full-range segment on the inside half of the innermost panel. The factory spectra array looks like the diagram below across the three panels, right speaker pictured looking from the listening chair. The | symbol below represents the edges of the panels:
|midrange down, full range| |Midrange down, bass| |bass, bass|
I want to move the full range segment inward so the speakers look like this:
|bass, midrange down| |full range, midrange down| |bass, bass|
Does anyone foresee a problem with this change? It's an easy rewire. A bit of background: I have Spectra 33s in a very narrow room. Right now I'm getting the best sound by moving the speakers almost all of the way to the side wall. Other than looking funny it actually sounds very good! I'm thinking that moving the full-range segment inboard on the speaker should allow the same soundstage but will get the speaker away from the sidewall.
Thoughts? Thanks in advance for anyone that might have insight on this idea!
Hello! Long time Acoustat owner here but I'm somewhat new to the Spectra series.
Question: Has anyone here tried reconfiguring where the full-range segment is located within the arrays? From the factory my Spectra 33 speakers have the full-range segment on the inside half of the innermost panel. The factory spectra array looks like the diagram below across the three panels, right speaker pictured looking from the listening chair. The | symbol below represents the edges of the panels:
|midrange down, full range| |Midrange down, bass| |bass, bass|
I want to move the full range segment inward so the speakers look like this:
|bass, midrange down| |full range, midrange down| |bass, bass|
Does anyone foresee a problem with this change? It's an easy rewire. A bit of background: I have Spectra 33s in a very narrow room. Right now I'm getting the best sound by moving the speakers almost all of the way to the side wall. Other than looking funny it actually sounds very good! I'm thinking that moving the full-range segment inboard on the speaker should allow the same soundstage but will get the speaker away from the sidewall.
Thoughts? Thanks in advance for anyone that might have insight on this idea!
Yes they are the same all the way across on the Spectra 33. All are 9" 5-wire panels with the stator wires cut at the center so each half of the panel can do it's own thing.
The arrays are also configured completely flat, with all panels in the same plane, no angles between them.
My 3 same as the 33,3300 panel wise....in a smaller room ...the out side panel is run full range.1/2...1/2 mid....next mid 1/2 bass 1/2...next all bass ..... same biger room full range inside
but set them up what ever sounds right to you.
the stock setup dose put the outside/inside mid 1/2 first i think...thin the full range on inside
so we end up with 1/2 full range....2,1/2s mid 3 1/2s bass
but set them up what ever sounds right to you.
the stock setup dose put the outside/inside mid 1/2 first i think...thin the full range on inside
so we end up with 1/2 full range....2,1/2s mid 3 1/2s bass
Spectra Bi-Amp with Dual Interfaces per Channel
Hello again., I'm still playing with my Spectra 33s and I thought of something that might be pretty cool...
I have four MK-2123 interfaces available, four channels of amplification (Crown Macro Reference amps), and a MiniDSP preamp with four separate channels of output.
Does anyone know what frequency the midrange-down portions of the Spectra 33 Arrays are reproducing? I'm thinking I would use one interface for the full-range segment only, feeding it full range from my MiniDSP preamp. Then, for the second interface, I would roll-off the frequency to be midrange-down only. I could then eliminate the segment resistor ahead of the midrange-down segments of the panel but leave the bass-only resistor in place. I just don't know what frequency and/or slope to set on those channels.
Thanks in advance!
Hello again., I'm still playing with my Spectra 33s and I thought of something that might be pretty cool...
I have four MK-2123 interfaces available, four channels of amplification (Crown Macro Reference amps), and a MiniDSP preamp with four separate channels of output.
Does anyone know what frequency the midrange-down portions of the Spectra 33 Arrays are reproducing? I'm thinking I would use one interface for the full-range segment only, feeding it full range from my MiniDSP preamp. Then, for the second interface, I would roll-off the frequency to be midrange-down only. I could then eliminate the segment resistor ahead of the midrange-down segments of the panel but leave the bass-only resistor in place. I just don't know what frequency and/or slope to set on those channels.
Thanks in advance!
I've done that for many years! Mostly with Acoustat servo amps but also with MK-121 interfaces and Crown Macro Reference amps. Just briefly playing with the Spectra interface, I see some real promise here - easier room placement, more detailed soundstage, and seemingly better HF response to name some right off the top.
ferrstein-
I see no issue (that is, it won't cause any damage) with re-arranging the segments in a Spectra speaker. My only suggestion is that it be done in such a way that you can return it easily to the original factory configuration. You may find you don't like the result.
As for your idea of using twin interfaces - that's way too complicated for my tastes, with dubious advantages. There's about a 100 ways that could go wrong after a lot of work to make it happen. Why put all that extra 'stuff' between you and the music?
I see no issue (that is, it won't cause any damage) with re-arranging the segments in a Spectra speaker. My only suggestion is that it be done in such a way that you can return it easily to the original factory configuration. You may find you don't like the result.
As for your idea of using twin interfaces - that's way too complicated for my tastes, with dubious advantages. There's about a 100 ways that could go wrong after a lot of work to make it happen. Why put all that extra 'stuff' between you and the music?
The Spectra 22 and 2200 are identical, electrically speaking. It's only a difference of cosmetics.
But, age and minor parts differences may account for some of the differences you hear. The biggest factor will be interaction with the room - comparing two speakers in different rooms is really pointless.
If you are looking at component differences between the speakers, the fact that one has a modified bias supply should be the first point of attention. Although many will swear to the merits of adding another stage to the bias multiplier, I have never been in favor of this. Until both speakers are at least as-built from the factory, and in the same room, comparison is impossible.
And BTW, if your speaker was modified to compensate for low bias, then it has a root problem that should be addressed BEFORE any modifications are considered. See previous posts and instructions for checking/upgrading the Ultrasonic Bias Power Supply. This is NOT a sonic upgrade - the modification applies to an earlier design that suffered from low bias on some speakers.