I am currently designing and building a two way active studio monitor for a school project. I have been slowly building up my knowledge on different components, yet I am still unsure about impedance. I understand that speakers within a system do not need to have the same impedance, but I am not clear on the reasons why.
I am just wondering first of all whether it is easier to choose a woofer and tweeter with the same value of impedance?
Also if I were to have a woofer with an impedance value of 8 ohms, and a tweeter with an impedance value of 6 ohms, what things would I need to do differently within my monitor that I wouldn't have to if their impedances matched?
I am not very experienced with electronics so please try and reply as you would to a beginner, thanks!
I am just wondering first of all whether it is easier to choose a woofer and tweeter with the same value of impedance?
Also if I were to have a woofer with an impedance value of 8 ohms, and a tweeter with an impedance value of 6 ohms, what things would I need to do differently within my monitor that I wouldn't have to if their impedances matched?
I am not very experienced with electronics so please try and reply as you would to a beginner, thanks!
No, it's not necessary to use drivers of identical impedance. It doesn't make designing the crossover any easier (or harder) whatever the Re value is. The overall system (complete speaker of drivers and crossover) impedance will vary over the range. This is not a problem, providing the load doesn't dip to an excessively low level, or become excessively reactive.
Some caveats. Note: 'Re'. Ignore the nominal impedance, which means nothing useful, and do yourself a great favour and do not use on-line calculators to design the filter, or any textbook mathematical equations: these take no account for the actual acoustic response of the drivers, nor of their changing impedance loads with frequency. Use a proper crossover design programme.
Some caveats. Note: 'Re'. Ignore the nominal impedance, which means nothing useful, and do yourself a great favour and do not use on-line calculators to design the filter, or any textbook mathematical equations: these take no account for the actual acoustic response of the drivers, nor of their changing impedance loads with frequency. Use a proper crossover design programme.
The driver's natural roll off would.
Don't know about any active crossover design programmes.
Here is some reading material regarding active crossovers:
BiAmp (Bi-Amplification - Not Quite Magic, But Close) - Part 1
Don't know about any active crossover design programmes.
Here is some reading material regarding active crossovers:
BiAmp (Bi-Amplification - Not Quite Magic, But Close) - Part 1
The driver in the finished box's natural roll off and general frequency response that is. At least account for diffraction effects as these would likely be dominant in the x-o frequency range for a typical 2-way monitor.
It would have helped if I'd noticed the word 'active' in the original post...
the Active Crossover Designer web page
the Active Crossover Designer web page
If you want to get a good background to the subject, you could do worse than read Doug Self's book; The Design of Active Crossovers: The Design of Active Crossovers: Amazon.co.uk: Douglas Self: 9780240817385: Books
Hi, relative newbie here with a similar question:
I have a pair of infinity RS 3000's. I'm generally happy with them, just lack the really fine treble at the higher frequencies that the Infinity EMIT-Rs are capable of reproducing but the Polycells can't so I decided to replace the original tweeters with EMIT Rs that I really like.
I tried to figure out how to modify the crossovers, but I'm a beginner in electronics and trying to understand crossover design I quickly realized I was in way over my head... and all I'd like to do is replace the tweeters in these speakers (and modify the crossover to suit them) not become an expert in crossover design. I can build a crossover if I have the schematics, but I can't design it.
I found the crossover schematics for both the RS-3000 and another 3 way Infinity that uses the EMIT-R for starters:
RS-3000 (with Polycell): http://www.infinity-classics.de/technik/manuals/RS_3000_technical_sheet.pdf
CS-3006 (with EMIT-R): http://download.tigersea.com/portable/infinity/cs_3006/manuals_file/153649.pdf
If anyone could give me some pointers on how to modify the existing RS-3000 XO to make it work with the EMIT-Rs I would really appreciate it.
I have a pair of infinity RS 3000's. I'm generally happy with them, just lack the really fine treble at the higher frequencies that the Infinity EMIT-Rs are capable of reproducing but the Polycells can't so I decided to replace the original tweeters with EMIT Rs that I really like.
I tried to figure out how to modify the crossovers, but I'm a beginner in electronics and trying to understand crossover design I quickly realized I was in way over my head... and all I'd like to do is replace the tweeters in these speakers (and modify the crossover to suit them) not become an expert in crossover design. I can build a crossover if I have the schematics, but I can't design it.
I found the crossover schematics for both the RS-3000 and another 3 way Infinity that uses the EMIT-R for starters:
RS-3000 (with Polycell): http://www.infinity-classics.de/technik/manuals/RS_3000_technical_sheet.pdf
CS-3006 (with EMIT-R): http://download.tigersea.com/portable/infinity/cs_3006/manuals_file/153649.pdf
If anyone could give me some pointers on how to modify the existing RS-3000 XO to make it work with the EMIT-Rs I would really appreciate it.
Crossovers in three paragraphs...
The Infinity RS-3000 is an 8" polycone bass AFAIK, probably crossing near 3kHz. You should measure both type tweeters DC resistance to ensure they are around 6 ohms (AKA 8 ohm nominal). They ought to be safe to swap then. Levels may need adjusting.
The below modification will work better with the original tweeters. It fixes the hole in energy at 5kHz from a bass that rolls off steeply going to a shallower 2nd order tweeter crossover. Note that tweeter polarity is now reversed. The 22R 7W wirewound resistor will attenuate levels about 2dB if required.
The 6.8uF capacitor can be a regular 250V polypropylene.
The Infinity RS-3000 is an 8" polycone bass AFAIK, probably crossing near 3kHz. You should measure both type tweeters DC resistance to ensure they are around 6 ohms (AKA 8 ohm nominal). They ought to be safe to swap then. Levels may need adjusting.
The below modification will work better with the original tweeters. It fixes the hole in energy at 5kHz from a bass that rolls off steeply going to a shallower 2nd order tweeter crossover. Note that tweeter polarity is now reversed. The 22R 7W wirewound resistor will attenuate levels about 2dB if required.
The 6.8uF capacitor can be a regular 250V polypropylene.
Attachments
What makes you think so? Per Infinity's documentation, the Polycells and the EMIT-Rs are crossed over at the exact same frequency - 4kHz. If what you say was the case, wouldn't they use different xo frequencies?
1. Lspcad: Untitled
2. LinearX: LinearX Systems Inc - Welcome
Both programs are not cheap, but the result is very good.
This EMIT-R tweeter seems to be some sort of exotic ribbon type. Therefore DC testing would be dangerous and might damage it.
But that is not the issue for the poor treble sound of the RS-3000. It is the second order filter on the tweeter that needs correcting, as I said. A third order filter will increase treble energy above crossover. It will sound more lively. Simple as.
But that is not the issue for the poor treble sound of the RS-3000. It is the second order filter on the tweeter that needs correcting, as I said. A third order filter will increase treble energy above crossover. It will sound more lively. Simple as.
Crossovers in three paragraphs...
The Infinity RS-3000 is an 8" polycone bass AFAIK, probably crossing near 3kHz. You should measure both type tweeters DC resistance to ensure they are around 6 ohms (AKA 8 ohm nominal). They ought to be safe to swap then. Levels may need adjusting.
The below modification will work better with the original tweeters. It fixes the hole in energy at 5kHz from a bass that rolls off steeply going to a shallower 2nd order tweeter crossover. Note that tweeter polarity is now reversed. The 22R 7W wirewound resistor will attenuate levels about 2dB if required.
The 6.8uF capacitor can be a regular 250V polypropylene.
Thanks a lot! Just to make sure this is based on the right assumptions, here is what I know at this point (exact specs are not easy to find on these old boys...):
- Yes, woofers in the RS-3000 are the 8" polypropylene (translucent) cone ones
- Infinity lists the RS-3000 as 6 ohms nominal impedance
- The original Polycell used in the RS-3000 is the 902-2722. I removed one from the cabinet to measure the impedance, and it measured 7.2 ohms, so I assume it's an 8 ohm tweeter. It seems to be identical to this one: Infinity Polycell Tweeter 902-6758 (the RS-3000 is also listed as one of the speakers the driver is compatible with) so I'm pretty sure it's an 8 ohm tweeter.
- So that makes me think that in order to arrive at the 6 ohms of nominal impedance, the RS-3000 must have a 4 ohm woofer and an 8 ohm tweeter - does that sound right? I can also measure the impedance of one of the woofers to be sure if needed.
- The EMIT-R is 4 ohms, not 8 (I thought all EMIT-Rs were 4 ohms - aren't they?)
Thanks a lot - being a relative newbie and not really knowing the first thing about crossover design, I really appreciate your help!
The relative impedance of the woofer and tweeter really doesn't matter to a transistor amp.
Just give what I said a go. See if it works with the original RS-3000 tweeter. It won't be exact, because I've kept the mods to a minimum, but it will give you far more treble energy.
I'd keep that EMIT-R tweeter out of this. It's not the issue.
Just give what I said a go. See if it works with the original RS-3000 tweeter. It won't be exact, because I've kept the mods to a minimum, but it will give you far more treble energy.
I'd keep that EMIT-R tweeter out of this. It's not the issue.
Thanks Steve - I appreciate your help, but you may not completely understood my reasons and what and why I'm trying to do. Infinity's EMIT ribbon tweeters are vastly superior to their Polycell dome tweeters. The discussions confirming this on the net are legion - and I can attest to it, having listened to similar sized Infinity speakers that use the EMIT tweeters - they are in a different league entirely. I'm not trying to simply increase the treble level. The ribbon tweeters sound different, they have a much more refined quality to them. I am a beginner in electronics but being a musician and owner of many different types of speakers (mostly expensive, high end studio monitors) I know the difference when I hear it. I listened to hundreds of speakers using well known reference tracks that are selected specifically to test the finer, subtler aspects of speakers such as resolution in the highest frequencies, and there are HUGE differences. So I KNOW that the EMIT tweeters are way better than the original ones in the RS-3000 - that's why I want to upgrade the tweeters, and not tweak the inferior dome tweeters the RS-3000 came with.
This "project" started because one of the (original) Polycell tweeters has been damaged (torn) and to replace and upgrade it at the same time, I already purchased a pair of (matched - hard to find) EMIT-Rs. My goal is to upgrade the speakers with the ribbon tweeters that DO sound much better - I just need to modify the crossovers to match the new tweeters.
Re. impedance: I know the relative impedance doesn't matter to the amplifier, but if I change the tweeter from an 8 ohm to a 4 ohm one, then the overall impedance of the speaker will change. I also understand that I can't just drop in a 4 ohm tweeter to replace an 8 ohm one, because my understanding is that the different impedance would shift the crossover frequency designed for the 8 ohm tweeter, right?
Again, I appreciate your help - I provided the additional info so that you understand what I'm trying to do, which is that I'm determined to upgrade the tweeter. After paying for a vastly superior replacement for the tweeters (a matched pair of EMIT tweeters cost more than a pair of RS-3000s), there is no way I'm going back to the - inferior - original tweeter. In order to get really good sound, you need to start with a great driver. I'm sure the sound from the existing drivers could be improved with a better crossover, but you can't get sound out of a driver it's physically incapable of reproducing. My goal is to tweak the speakers for the highest quality (not volume - I rarely listen to loud music) and that's why I want to do this upgrade.
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