Realistic Nova 8b Rebuild & Crossover Re-Design

[Elliot Thompson]

I have a pair of 5's (not b) and I may be interested in this mod. I'd have to check to make sure the drivers are the same as the 8b (I'm pretty sure the woofer is). My problems are:

1. The tweeters on mine are dead- currently using some vifa domes. Would the vifa's work in this case or should I hunt for the original tweeters?

2. I've never assembled a cross-over before so I would need a lot of hand-holding.

3. If they sound as good as you say I would have to re-laminate my cabinets as they look pretty bad now (my problem).

I have to say with the new capacitors and the vifa tweeters I put in these Optimus 5's they sound pretty good. If they improve as you say then sounds like they are one heck of a speaker after the mods.

Tiga

Hi.

I own the Nova 5 which are used for computer speakers.

The original tweeter offered a frequency response of 20,000 kHz. Providing your Vifa tweeters offer the same frequency response, they should be fine.

I would not recomend getting caught up in looking for tweeters that offer a higher response than 20,000 kHz if your Vifa tweeters cannot achieve 20,000 kHz.

There needs to be a proper balance between the woofer and tweeter which the frequency response amongst both drivers play a factor on the overall sound.

If you prefer the original tweeters, try searching Ebay for some Nova 5 speakers. I believe I picked up mine for $15.00 in 2002.

Best Regards,

 

[videolady201]

About Drivers

I have a pair of 5's (not b) and I may be interested in this mod. I'd have to check to make sure the drivers are the same as the 8b (I'm pretty sure the woofer is). My problems are:

1. The tweeters on mine are dead- currently using some vifa domes. Would the vifa's work in this case or should I hunt for the original tweeters?

2. I've never assembled a cross-over before so I would need a lot of hand-holding.

3. If they sound as good as you say I would have to re-laminate my cabinets as they look pretty bad now (my problem).

I have to say with the new capacitors and the vifa tweeters I put in these Optimus 5's they sound pretty good. If they improve as you say then sounds like they are one heck of a speaker after the mods.

Tiga

1.. You would need to check and make sure your drivers are the same. I think the 5bs are but I don't know about the 5s. The crossover may work for the Vifa but not likely. You really need a crossover design for a given set of drivers. If all the drivers are the same I would try and find original tweeters and then build the crossovers.

2.. I think the main changes in the B versions of the Optimus 5 and the Nova 7 & 8s were the woofers. If you have the original tweeter and mids from one of these models they may work fine.

3.. Also, it would help everyone here if you could check the impedance listed and the # stamped on the back of your mids and your blown tweeters, if you still have them. Better would be some images of each!

 

[videolady201]

About the Stock Tweeter

I like the stock tweeter for a few reasons.

1..It is what came with the unit, no mods required for mounting, etc.

2..It has an FS of around 420Hz! This is very important as it has no resonance in the usable range or no harmonics an octave up that enters into the usable band of operations making it very neutral!

3..It has a very large rear chamber that you will not find on the newer models, domes, etc, allowing more harmonic detail. While it does not have the power handling and the newest materials it does have many very important features for very good performance! It also has very good dispersion with the new crossover.

These features are important enough that I would recommend finding working models of the originals to go with the new crossover. I would love to see a modern production of a tweeter like this with these same features!!! Also the unit as you can see in the charts, goes out above 20khz. They started to roll off at 23khz!:yes:

 

[Elliot Thompson]

1.. You would need to check and make sure your drivers are the same. I think the 5bs are but I don't know about the 5s. The crossover may work for the Vifa but not likely. You really need a crossover design for a given set of drivers. If all the drivers are the same I would try and find original tweeters and then build the crossovers.

Hi.

The Nova 5 is a very simplisitic 2-way design. The only means of crossover is a capacitor for the tweeter. There is no need for a crossover on a woofer unless you want to bring forth more distortion by having chokes, and resistors between the amplifier and the loudspeakers when driven at high SPL.

It is a good sounding box on it's own which (from my ears) does not need any modifications.

Best Regards,

 

[tiga]

I would love to see a modern production of a tweeter like this with these same features!!! Also the unit as you can see in the charts, goes out above 20khz. They started to roll off at 23khz!:yes:

Well I think this proves that the drivers in the 5 are different than the 8b. I distinctly remember my 5 tweeter had a rating to 15khz stamped on the back and was a 4ohm model. I'll check the mids and woofers (hopefully tonight) and report back.

 

[videolady201]

Optimus 5s not the Nova 5s

Hi.

The Nova 5 is a very simplisitic 2-way design. The only means of crossover is a capacitor for the tweeter. There is no need for a crossover on a woofer unless you want to bring forth more distortion by having chokes, and resistors between the amplifier and the loudspeakers when driven at high SPL.

It is a good sounding box on it's own which (from my ears) does not need any modifications.

Best Regards,

This is where we have to be careful. In the text above I mentioned the Optimus 5s and the Optimus 5bs. I was not referring to the Nova 5s. I guess I should of said Optimus 5s each time instead of 5s. I know the Nova 5s are completely different speakers. However, the Optimus 5bs should be the same as the Nova 8bs and the Optimus 5 should have the same mid & tweeter as the b versions and this crossover should apply to them as well. See posting above: "ABOUT DRIVERS"
See attached image...!

 

[va3ux]

I recently saw a picture of the Optimus 5B with the grill off. It *looks* identical to the Nova 8B in the pictures in this thread. How close are they to each other ? Or how different are they from each other ? Could the modified Nova 8B crossover be used on the Optimus 5B ?

Thanks VL for the excellent contribution.

 

[videolady201]

Optimus 5b / Nova 8b

I recently saw a picture of the Optimus 5B with the grill off. It *looks* identical to the Nova 8B in the pictures in this thread. How close are they to each other ? Or how different are they from each other ? Could the modified Nova 8B crossover be used on the Optimus 5B ?

Thanks VL for the excellent contribution.

I believe they are the exact same speaker in every way other than the cabinet and the grill cover!! If I had a pair of the Optimus 5bs I would put this new crossover in it in a heart beat!!:yes:

 

[videolady201]

Cross Overs on a Woofer?

Hi.

The Nova 5 is a very simplisitic 2-way design. The only means of crossover is a capacitor for the tweeter. There is no need for a crossover on a woofer unless you want to bring forth more distortion by having chokes, and resistors between the amplifier and the loudspeakers when driven at high SPL.

It is a good sounding box on it's own which (from my ears) does not need any modifications.

Best Regards,

Sometimes it is better for the woofer to have a crossover and it reduces distortion and other times it does not. The damping factor is usually better without a crossover. However, many woofers have modulation issues when driven at high power. Also, we now have inductors with DCRs into the low range of .05 ohms, so it is not as big of an issue as it once was. Speakers are reactive loads and a lot of parameters swing as it is being driven. If the woofers' response is allowed to operate into the higher frequencies distortion can occur. This is also due to Doppler effect as well as other parameters filtering the smaller current of the higher frequencies. If you filter the higher frequencies from the woofer at the proper point, modulation distortion is reduced or even removed. It is driver/design dependant! :scratch2:

 

[RayW]

Looks like a nice response curve. Bravo, VL!

 

[videolady201]

Response Curve

Looks like a nice response curve. Bravo, VL!

Thank You. I goofed up a bit in the thread. I didn't make it clear enough that we are talking about Optimus 5s & 5bs and Nova 8s & 8bs, both three way speakers. Radio Shack also made the Nova 5s, a two way system and some here are confused by some of the postings... S O R R Y.

On another note, this is a impressive speaker!! Nice woofers!:yes:

 

[tiga]

Ok here is the information from the Optimus 5 drivers.

Tweeter (I kept the blown tweeters that were in there) - 4 ohm, 0705AC, 2k-15khz, 9D12D.

Mids - 4 ohm, 0710Aa, 9D03A (no frequency range spec).

Woofer - 8ohm, 3007a.

I've posted pictures of them as well.

I wonder if this was the original tweeter for this model.:scratch2:

 

[videolady201]

Driver Info

:scratch2:

Ok here is the information from the Optimus 5 drivers.

Tweeter (I kept the blown tweeters that were in there) - 4 ohm, 0705AC, 2k-15khz, 9D12D.

Mids - 4 ohm, 0710Aa, 9D03A (no frequency range spec).

Woofer - 8ohm, 3007a.

I've posted pictures of them as well.

I wonder if this was the original tweeter for this model.:scratch2:

The mid range drivers are the same! I think that tweeter came from another speaker, where someone had replaced them before. Maybe a Nova 7 or 7b. It does have a different #. I have some 7bs here I will pull a tweeter and see if the number matches your tweeters. Since yours are blown and your midranges are the same, you could just try to find a pair of the 8b tweeters. The number is: 725ac 1D24D. Radio Shack still sales a new replacement tweeter for the Nova 8B! I will let you know what I find.:scratch2:

 

[rmeade]

I have a pair of 5b tweeters that I am willing to donate to the cause. I just disassembled a pair of 5b's. They are Model 0725Ac 8 Ohms; 350Khz to 18KHz. they are yours for a clear parts list and wiring diagram (posted here of course). PM me and I will send them off.

 

[Elliot Thompson]

Sometimes it is better for the woofer to have a crossover and it reduces distortion and other times it does not. The damping factor is usually better without a crossover. However, many woofers have modulation issues when driven at high power. Also, we now have inductors with DCRs into the low range of .05 ohms, so it is not as big of an issue as it once was. Speakers are reactive loads and a lot of parameters swing as it is being driven. If the woofers' response is allowed to operate into the higher frequencies distortion can occur. This is also due to Doppler effect as well as other parameters filtering the smaller current of the higher frequencies. If you filter the higher frequencies from the woofer at the proper point, modulation distortion is reduced or even removed. It is driver/design dependant! :scratch2:

Bear in mind woofers by design will automatically roll off the upper frequencies. This is based on the voice coil winding and how much of the coil is sitting within the magnetic gap.

Impedance fluctuations are based on the cabinet tuning and how the woofer reacts in the enclosure at the given frequency. All loudspeakers offer reactive loads, which cannot be prevented.

Most crossovers will focus primarily on the midrange driver and tweeter since they have a higher chance of driver damage instantaneously than the woofer.

Building passive crossovers under high power conditions bring forth more cons (Chokes burn, components melt) than pros, which is why many just abandon the idea and move towards electronic crossovers if they need a lot of power.


Best Regards,

 

[videolady201]

Woofer Crossovers

Bear in mind woofers by design will automatically roll off the upper frequencies. This is based on the voice coil winding and how much of the coil is sitting within the magnetic gap.

Impedance fluctuations are based on the cabinet tuning and how the woofer reacts in the enclosure at the given frequency. All loudspeakers offer reactive loads, which cannot be prevented.

Most crossovers will focus primarily on the midrange driver and tweeter since they have a higher chance of driver damage instantaneously than the woofer.

Building passive crossovers under high power conditions bring forth more cons (Chokes burn, components melt) than pros, which is why many just abandon the idea and move towards electronic crossovers if they need a lot of power.


Best Regards,

In the pro industry what you have said is true for more than one reason. Part is the cost and the other power handling. Our company has produced Hi-End speakers for the last 25 years. In our industry, Hi-End audio, I know of no one in the industry that builds current production products without a crossover on the low frequencey driver. I am sure there may be some, but none of the names I know. As we are in the industry, I know many and their products well. Burning inductors in the type speaker we are talking about just don't happen. The drivers can't handle that kind of power. Most inductors today handle any where for 400 to 700 watts RMS. That's why we have so many different speakers of all flavors, each has his own ideas about sound and what works! I haven't found a woofer yet that can't be helped with a crossover, as most have a stepped response. In a perfect world if we could design the driver and hit the target we were after, there would be no crossover on any woofer. It's just to hard to get the T/S parameters and have the power handling and roll off + roll rate we are looking for.:yes:

 

[videolady201]

Parts List

I have been asked by some for a parts list. The circuit diagram has the parts listed but may be hard to read. Attached is a parts list. It is just for a single speaker. Be sure to repeat this list for each additional speaker you are going to order parts for.:thmbsp: I will try to add the wiring diagram tomorrow!

 

[Elliot Thompson]

In the pro industry what you have said is true for more than one reason. Part is the cost and the other power handling. Our company has produced Hi-End speakers for the last 25 years. In our industry, Hi-End audio, I know of no one in the industry that builds current production products without a crossover on the low frequencey driver. I am sure there may be some, but none of the names I know. As we are in the industry, I know many and their products well. Burning inductors in the type speaker we are talking about just don't happen. The drivers can't handle that kind of power. Most inductors today handle any where for 400 to 700 watts RMS. That's why we have so many different speakers of all flavors, each has his own ideas about sound and what works! I haven't found a woofer yet that can't be helped with a crossover, as most have a stepped response. In a perfect world if we could design the driver and hit the target we were after, there would be no crossover on any woofer. It's just to hard to get the T/S parameters and have the power handling and roll off + roll rate we are looking for.:yes:

The difference you may be facing from manufactures than choose not to use a choke on a woofer is voice coil size/length. For as we know, the smaller the coil/xmax the greater the high frequency response. Not to mention some tweeters are crossed high so, I would imagine crossing the woofer at a particular frequency is necessary to equalise the sound.

I built a pair of small 84 litres (which is large by some) subs for my mum’s home theatre in 2004. Since amplifiers are plentiful based on my line of work, I have a pair of 8’s residing on an 800-watt amplifier. I merely used an equaliser to boost the lower end of (40 Hz downward) and that’s it.

I believe the voice coils are only 2 inches however they claim the xmax is 8 mm. These drivers roll-off severely above 300 Hz.

Best Regards,

 

[terra1]

I have been asked by some for a parts list. The circuit diagram has the parts listed but may be hard to read. Attached is a parts list. It is just for a single speaker. Be sure to repeat this list for each additional speaker you are going to order parts for.:thmbsp: I will try to add the wiring diagram tomorrow!

Thanks.
I have an Optimus 5B.

If the wiring diagram shows how to wire in parallel etc. I may give it a shot.
Some remedial skilled noobs like me don't know how to read a schematic.

thanks

 

[terra1]

Thank You. I goofed up a bit in the thread. I didn't make it clear enough that we are talking about Optimus 5s & 5bs and Nova 8s & 8bs, both three way speakers. Radio Shack also made the Nova 5s, a two way system and some here are confused by some of the postings... S O R R Y.

On another note, this is a impressive speaker!! Nice woofers!:yes:

Here's another interesting quote about the crossovers:
http://www.audiokarma.org/forums/showpost.php?p=3172168&postcount=104

I had the Nova 8B 12" woofer 2 midranges and another acting as a tweeter. The Optimus 5 has the same configuration but I never had the pleasure of listening to them, but they are highly regarded.

the main difference between the nova 8b & the optimus 5 besides furniture appointments, was the crossover
the Nova 8 crossed over lower from woofer to mid speakers, and the Optimus 5 had a higher crossover point, making it a little dryer .
The rock crowd seemed to go for the Optimus while the easy listening and classical crowd seem to flock to the Nova
Other than that they are identical .

Rob

I assume this shouldn't be a problem whether 5 or 5b?