Realistic Nova 8b Rebuild & Crossover Re-Design
- Thread starter videolady201
- Start date
videolady201
AK Member-Design Engineer
Measurement
You said the speaker reads 4 ohms. That's not right. You need to measure between the black and blue wire, with the blue disconnected from the crossover or pull the tweeter out and unhook it and measure that way. It would also be good to measure the mids between the black and white wire. Also, one of the wires should be disconnected as well. They both (tweeter & mids) should read right at 7 ohms each. If they don't we need to find out why. The mid drivers should be measured only from the black & white wire so the series is hooked together for the 7ohms reading.
You said the speaker reads 4 ohms. That's not right. You need to measure between the black and blue wire, with the blue disconnected from the crossover or pull the tweeter out and unhook it and measure that way. It would also be good to measure the mids between the black and white wire. Also, one of the wires should be disconnected as well. They both (tweeter & mids) should read right at 7 ohms each. If they don't we need to find out why. The mid drivers should be measured only from the black & white wire so the series is hooked together for the 7ohms reading.
Smorgy
Vinyl Junky Speakerhaulic
The speaker reads 4.0 ohms across the terminals when disconnected from the crossover. It is marked 4 ohms on the back. This is a Optimus 5B.
The mids sound ok, but I'll have to measure them (out of the cabinet) when I get home. Since the mids are in series and are 7 ohms, that should result in a 3.5 ohm load to the crossover.
//Smorgy
videolady201
AK Member-Design Engineer
First off a quote by rmeade
Then a quote from Smorgy
As I said in a post previous to this one, I didn't think you had an original tweeter. Rmeade says he has three pair and the number he has listed is the stock tweeter number and it is 8 ohms. Also, I am glad you found your loose wire on the tweeter that was keeping it from working.:yes:
Drivers in series doubles the impedance. Each of the Mids are 4 ohm units and the two in series should give you 8 ohms with a DCR of around 7 ohms. I am not sure where the 4 ohm tweeter unit came from, but again, I don't think it is an original driver based on what I have seen in the past and on rmeade's findings. That is why at the start of this thread I posted the pictures so one could see the driver numbers and impedance of each. This allows you to check that your drivers are the same that I designed the crossover for. The crossover may work ok with it but it will not perform as it would with the stock 8 ohm driver.
Then a quote from Smorgy
As I said in a post previous to this one, I didn't think you had an original tweeter. Rmeade says he has three pair and the number he has listed is the stock tweeter number and it is 8 ohms. Also, I am glad you found your loose wire on the tweeter that was keeping it from working.:yes:
Drivers in series doubles the impedance. Each of the Mids are 4 ohm units and the two in series should give you 8 ohms with a DCR of around 7 ohms. I am not sure where the 4 ohm tweeter unit came from, but again, I don't think it is an original driver based on what I have seen in the past and on rmeade's findings. That is why at the start of this thread I posted the pictures so one could see the driver numbers and impedance of each. This allows you to check that your drivers are the same that I designed the crossover for. The crossover may work ok with it but it will not perform as it would with the stock 8 ohm driver.
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Copa1934
My ears are bleeding
Is it me, or is there a stunning similarity between the Nova line and the Pioneer line (CS77/99 etc.) I just checked dimensions and they're almost spot on. The bevel fronts are the same. The lattice work, while common, is still very similar. The cuttout in the back appears to be the same dimensions, location and same/similar connections. Main difference is the drivers, though they all are accoustic suspension speakers. Yes I know RS was in bed with many brands, but I wasn't sure about the speakers.
Smorgy
Vinyl Junky Speakerhaulic
First off a quote by rmeade
Then a quote from Smorgy
As I said in a post previous to this one, I didn't think you had an original tweeter. Rmeade says he has three pair and the number he has listed is the stock tweeter number and it is 8 ohms. Also, I am glad you found your loose wire on the tweeter that was keeping it from working.:yes:
Drivers in series doubles the impedance. Each of the Mids are 4 ohm units and the two in series should give you 8 ohms with a DCR of around 7 ohms. I am not sure where the 4 ohm tweeter unit came from, but again, I don't think it is an original driver based on what I have seen in the past and on rmeade's findings. That is why at the start of this thread I posted the pictures so one could see the driver numbers and impedance of each. This allows you to check that your drivers are the same that I designed the crossover for. The crossover may work ok with it but it will not perform as it would with the stock 8 ohm driver.
For sure the tweeter has been swapped out, probably for a mid. I'm guessing since it is a 4ohm speaker and looks identical to the mids. It is not marked "midrange" like the others though.
I tried in vain to find a pair of correct tweeters online.
So, here is what I have:
Woofer 8 ohms (measures 7.0 ohms) 3007Aa Japan (Cast aluminum frame with oval slits from the mounting surface to the magnet, looks a bit art deco-ish)
Midranges 4 ohms (measures 7.6 ohms in series) 0710Aa Japan marked "midrange"
Tweeter just says 4 ohms
Grills say Optimus 5B
Rear of cabinet says Optimus 5 Cat No. 40-2002
So, shame on me for not detailing my parts list ahead of time.
Somebody, at some time in the past 25 years or so, swapped out the tweeters and the grills on the ones I have.
Assuming the tweeter circuit is correct (?) then all I really need is the correct tweeters to be able to close this one up - and start on the 2nd one!
//Smorgy
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videolady201
AK Member-Design Engineer
Woofers & Tweeters
I am 99 percent sure your woofers are from Optimus 5s and not the B version. Because it is 8 ohms, I think the crossover will be fine for it! I do think you need to have the right tweeters for the crossover to work like it should. The fact that your units have the l-pads to adjust mids and highs tells me your units are Optimus 5s. The Optimus 5bs had switches with low, normal and high positions only. However, I think the Optimus 5s with the stock drivers, are the same drivers for tweeter and midrange. The woofer is different but should still work nicely with the new crossover! Lower frequencies are less picky and the impedance of most woofers are pretty close. I think you have 5bs grills and probably mids put in the tweeters place as you had said. Let us know what you find when it's all said and done!!:yes:
I am 99 percent sure your woofers are from Optimus 5s and not the B version. Because it is 8 ohms, I think the crossover will be fine for it! I do think you need to have the right tweeters for the crossover to work like it should. The fact that your units have the l-pads to adjust mids and highs tells me your units are Optimus 5s. The Optimus 5bs had switches with low, normal and high positions only. However, I think the Optimus 5s with the stock drivers, are the same drivers for tweeter and midrange. The woofer is different but should still work nicely with the new crossover! Lower frequencies are less picky and the impedance of most woofers are pretty close. I think you have 5bs grills and probably mids put in the tweeters place as you had said. Let us know what you find when it's all said and done!!:yes:
Smorgy
Vinyl Junky Speakerhaulic
Did you find anything on these replacement tweeters from Radio Shack? I just spent an hour poking around their web site and didn't find these. If they are available, I would definately buy a pair.
//Smorgy
videolady201
AK Member-Design Engineer
New Tweeters
Based on what I have found, Radio Shack shows they still have replacement tweeters for the Nova 8b. :yes: The information to contact them is listed below:
To order parts call Radio Shack Order Line 1-800-843-7422
Catalog #: 11083698 SPEAKER,TWEETER NOVA 8B, 8 OHM L.T
New Part #: SP0266
Based on what I have found, Radio Shack shows they still have replacement tweeters for the Nova 8b. :yes: The information to contact them is listed below:
To order parts call Radio Shack Order Line 1-800-843-7422
Catalog #: 11083698 SPEAKER,TWEETER NOVA 8B, 8 OHM L.T
New Part #: SP0266
Copa1934
My ears are bleeding
When I worked for RS ordering parts was a breeze. Recently I tried to get a volume pot for my receiver and I was told to go to my local RS, who in turn told me I had to bring my receiver in and they would send it in for service. Right. And risk my otherwise good receiver getting busted up, or something else? Not sure the number you posted is the same one I used, but I'll give it a try tomorrow.
tiga
Super Member
My Optimus 5's (not B) have these exact same drivers. (check my post #32 for pics). Mine had 4 ohm tweeters as well. Either someone swapped grill badges with yours or possibly RS was rebadging their 5's as 5B's for a while.
A sign from above?!?
A Pawn Shop that I'm real familiar with just took in a pair of Optimus 5B's. I said if you don't put too much into 'em and price 'em cheap, somebody (wink-wink, nudge-nudge) will buy them. Oddly enough, I happen to have a pair of those 2.7mH P-Core inductors laying around. Is that a sign or what?
:scratch2:
P.S. I also have some 4-ohm Peerless dome tweeters too!
A Pawn Shop that I'm real familiar with just took in a pair of Optimus 5B's. I said if you don't put too much into 'em and price 'em cheap, somebody (wink-wink, nudge-nudge) will buy them. Oddly enough, I happen to have a pair of those 2.7mH P-Core inductors laying around. Is that a sign or what?
:scratch2:
P.S. I also have some 4-ohm Peerless dome tweeters too!
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videolady201
AK Member-Design Engineer
Upgrade Status
Anyone got your Nova 8bs or Optimus 5bs modded with all stock drivers yet?
Anyone got your Nova 8bs or Optimus 5bs modded with all stock drivers yet?
videolady201
AK Member-Design Engineer
Tweeters
No they are not. The optimus 5bs and the Nova 8bs should be. The 2b and Nova 7bs are different tweeters and will not work like they should.
No they are not. The optimus 5bs and the Nova 8bs should be. The 2b and Nova 7bs are different tweeters and will not work like they should.
absolve2525
Super Member
I opened up my Nova 8s to see what drivers are inside. They are and same as Smorgys Optimus speakers, with a 4 ohm tweeter and two 4 ohm midranges. The midranges have bigger magnets than the tweeter. I looked closely at the tweeter, and it looks the same as the 8ohm version found in the Nova 8B pictures, except it says "4 ohms" on the back. Is it possible to enter 4ohms into the tweeter crossover cap model and end up with (for the most part) the same sound?
videolady201
AK Member-Design Engineer
Tweeters???
I wish it was but LEAP is looking for the complex impedance data along with the acoustical output. The impedance and the spl are different at every single frequency, even if just by a small value. LEAP has to know this information for the modeling to work. One thing that did come to mind. I would like someone to measure that tweeter with an ohm meter. The 4029 mach 1 woofer says 6 ohms, but it is not, it's an 8 ohm. Maybe your tweeters that are marked 4 ohms could be an 8 ohm that is mislabled. If you could please check and post the results.:scratch2:
I wish it was but LEAP is looking for the complex impedance data along with the acoustical output. The impedance and the spl are different at every single frequency, even if just by a small value. LEAP has to know this information for the modeling to work. One thing that did come to mind. I would like someone to measure that tweeter with an ohm meter. The 4029 mach 1 woofer says 6 ohms, but it is not, it's an 8 ohm. Maybe your tweeters that are marked 4 ohms could be an 8 ohm that is mislabled. If you could please check and post the results.:scratch2: