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New Crossovers for old speakers (Pioneer Elite TZ7

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rchamlen View Drop Down
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    Posted: 26 November 2019 at 5:38pm
At the risk of being clear that I am not at all of yours level in specific knowledge, I am going right to the Advanced forum as I believe my chance of getting right to a quick answer will be higher here.

I have a very old set of speakers (Pioneer Elite TZ-7), 3-way, dual woofers, label claimed cabinet impedance is 4 ohm).  The drivers were custom mfg by pioneer and are not explicitly labeled with their impedance.   I have measured the RESISTANCE of the woofer(s) and midrange, and they come up as ~6.7 and 4.7 ohms respectively.

Here is the question: looks like one cabinet one of the crossovers (there are two) is dead (no signal to bass).  I would like to replace all crossovers with new ones, but I am not sure what to do in terms of impedances. 

First - the drivers.  My expectation is that the actual impedances should be HIGHER than the measured resistance.  So ... given the measured resistance, my initial belief was that the impedance of these drivers is 8 ohm (built back in ~1995 when most speakers were 8 ohm I believe????).   But (again, my understanding) is that it is bad practice to design crossovers with different imput and output impedances - would Pioneer really have done that?????   

Given my resistance measurements, is there any reason to believe that these drivers really are 4 ohm, or is it much more likely that they are 8 ohm?

Second - if they really are 4 ohm drivers ... so far in my search for off-the-shelf drivers, I have only seen circuits with 8 ohm output ratings (assume the drivers are 8 ohms).  Do any of you know of 3-way passive crossovers that accept 4 ohm output loads? (I know - I have the option of parallel or series wiring for the woofers - but I am stuck with the single midrange with its defined impedance).

I have been soldering circuits since I was about 8 ... so I am not against building my own crossovers (given a circuit design) ... but would rather go off the shelf.   Hopefully that is enough info to drive this thread for now.  let me know if you need/want anything more?

(I know I could  potentially repair the existing crossovers - but between the four cabinets there are two crossovers, and the wiring is extremely badly marked.  I dont trust the caps all the way around in circuits this old ... and I might never get the things wired back up the way they need to be  :-(

Thank you for your help!
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Conanski View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 27 November 2019 at 4:59am
Originally posted by rchamlen rchamlen wrote:

I have a very old set of speakers (Pioneer Elite TZ-7), 3-way, dual woofers, label claimed cabinet impedance is 4 ohm).  The drivers were custom mfg by pioneer and are not explicitly labeled with their impedance.   I have measured the RESISTANCE of the woofer(s) and midrange, and they come up as ~6.7 and 4.7 ohms respectively.

First - the drivers.  My expectation is that the actual impedances should be HIGHER than the measured resistance. 
Generally true but since this is a "nominal" rating it can go both ways. 6.7ohms DC is common for an 8ohm driver and 2 drivers in parallel gives you a 4 ohm load, while 4.7ohms DC could very well be a 4ohm driver.

Originally posted by rchamlen rchamlen wrote:

But (again, my understanding) is that it is bad practice to design crossovers with different imput and output impedances - would Pioneer really have done that????? 
No such thing as input and output impedances for a crossover only what speaker load it is designed for, and the amplifier just sees 1 combined load of drivers and passive filters. Additionally the low frequency section dominates so it almost doesn't matter what impedance the mid and hi drivers are,  and that means there is no problem using different impedance drivers for the upper frequencies as long as the passive crossover is properly designed for them.

Originally posted by rchamlen rchamlen wrote:

Second - if they really are 4 ohm drivers ... so far in my search for off-the-shelf drivers, I have only seen circuits with 8 ohm output ratings (assume the drivers are 8 ohms).  Do any of you know of 3-way passive crossovers that accept 4 ohm output loads?
4 ohm crossovers are not very common so you may have to build custom circuits, even if you did find some they will probably need to be modified.

Originally posted by rchamlen rchamlen wrote:

(I know I could  potentially repair the existing crossovers - but between the four cabinets there are two crossovers, and the wiring is extremely badly marked.  I dont trust the caps all the way around in circuits this old ... and I might never get the things wired back up the way they need to be  :-(
Post up some pictures, they may not be as complicated as it first appears.




Edited by Conanski - 27 November 2019 at 5:04am
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Xoc1 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Xoc1 Quote  Post ReplyReply Direct Link To This Post Posted: 27 November 2019 at 1:24pm
Impedance of the driver is frequency dependent
The crossover values should be to suit the impedance at the crossover frequency.
Otherwise a zobel network can be used to stop the impedance seen by the crossover from rising with frequency.
A cheap Inductance & capacitance meter can be very helpful when trying to service old crossovers.
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rchamlen View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rchamlen Quote  Post ReplyReply Direct Link To This Post Posted: 27 November 2019 at 5:28pm
thank you for the responses.  I could not figure out how to execute selective/partial quotes on this interface  :-( ...so will just need to reply free-form.

Yeah - the impedance of the input to the crossover is the result of the entire circuit (including speakers) ... sorry, stupid question based on some quick reading on the web  :-(

Understood that the low pass section dominates overall impedance.  My concern is that if the midrange is indeed 4 ohm, though I can find crossovers out there that allow selection between 4 and 8 ohm woofers, they all seem to assume 8 ohms on the mid and high range.  Maybe that is what you are getting at when you say "4 ohm crossovers are not that common"??

I mis-spoke in the first post: each cabinet has TWO "crossovers" - one board (card really) appears to three simple crossovers wired up in parallel.. Interesting though that the circuit for the front woofer is a traditional LC "L" circuit, whereas the circuit for the rear woofer is different - just a simple series L low pass only (not sure whey they designed with two different circuits - phase  concerns maybe?  (that is beyond me with base knowledge).   the high pass for the tweeter I cant quite trace without pulling the card - it ALMOST looks like it could be a basic RC high pass, but does not seem to be quite wired right for that - as the load is not clearly wired across the resistor (unless there is a wire I am not seeing). The midrange bandpass filter is a totally separate board - and is tucked up high enough I can not get a good look at it.  Picture of the low/high pass section is below.  Front an center is the electrolytic cap I have been thinking is the failed component ... but now that I am analyzing this circuit in more detail - I wonder if it is the cap that is bad - as both woofers do not work, but the filters appear to be in parallel to each other.....   I did try to check the ground wire from  board to connector, and it seemed ok.  But now I am thinking I need to pull the board and more accurately check those connections.  MY main concern so far has been that with one cap failed (IF that is indeed the case), then the others will remain suspect - and I would prefer not to go through this tear-down at random during the next several years!  Anyway - lots of thoughts ... will post the picture for now.

(QUESTION: tried to paste in a photo, but could not do so.  does this forum only allow uploading of links???   I do not maintain a photobucket or similar account.  any way to just paste in a photo??)

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Xoc1 Quote  Post ReplyReply Direct Link To This Post Posted: 27 November 2019 at 8:20pm
 Looked up the speakers on Google and found a couple of pictures.
The speakers have a front and rear facing bass driver so that probably accounts for the 4 ohm nominal rating of the cabinet.
The speakers look to be fair quality items. I would probably advise you to service the existing crossovers rather than try to replace them, or find all the values used & make upgraded clones.
Even then the crossover circuit may even account for the resistances of the coils and the ESR values of the capacitors and changing the components can change the balance of the speaker.
Passive crossovers from scratch are not easy, You have to consider the crossover frequencies and slopes to suit the drivers, level matching, any EQ to suit the drivers response, & the mechanical roll off frequencies of the drivers.
The crossover circuit will be made to suit the impedance of each driver at the crossover frequency not at the nominal impedance.
I have restored a couple of old speaker crossovers recently and usually any electrolytic capacitors are what fail. Having said that you say you have no output from the bass drivers which would not usually be caused by a capacitor failure.

I used a cheap LC meter bought on ebay and verified against some known value capacitors & inductors to measure the crossovers I rebuilt.

From your description the tweeter might be a first order cap with the resistor in series to reduce the level to match.


OMG my Daughter has gone prog rock!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rchamlen Quote  Post ReplyReply Direct Link To This Post Posted: 27 November 2019 at 8:53pm
From your description the tweeter might be a first order cap with the resistor in series to reduce the level to match
that probably makes sense - but there is also an inductor kicking around in the vicinity of the circuit that I can not see exactly how it is wired.

how do I get images uploaded to  the site - cant seem to just paste them???

You have to consider the crossover frequencies and slopes to suit the drivers...

Yeah - I know.  The best I was hoping for was to use a frequency generator (windows has one!!!!) to scan the "good" speaker and try to estimate crossover points, then buy an off the shelf crossover with approximately the same crossover points (or at least one within the capability of the drivers) ... but I was going to ignore dropoff slopes.   

You are probably right, that the best approach is going to be to replace the caps on all the crossovers (the coils and power resistors should be pretty much bullet proof over time - right????).  The drivers all appear to be in really good shape - so it is probably worth taking this approach (I guess I was just being lazy).  I know electrolytic caps age out .... but looks like there are some non-electrolytics in there also - do they age out also??? (I dont know about that...)

Yeah - the speakers are pretty darned good.  There are better out there, but these are nothing to sneeze at.  MY son (21 years old) has been using them ... and apparently all the folks that come over to his apartment (he is at the university - minnesota) rave about them.   Me..... I just had my hearing checked, and my ears are rolling off pretty badly starting at 1 kHz - so I dont benefit from them at all (Man ... and I remember when I could hear 20kHz  :-(   .

Please advise me on how to post pics and I will get some up here....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 27 November 2019 at 9:13pm
For uploading images, you need to be using the full reply editor then use the "upload Images" button to access the right dialogue box.
https://imgur.com/a/PQymLyo
The forum will however compress your images (to save drive space I presume) so if you want decent detail to be clear it's better to host offsite and paste in links to your posts. There are plenty sites that allow you to upload without an account, if you're only going to use the images once (like a forum reply) and won't care about finding them again later.
Imgur, like I've used above, is one popular one.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote rchamlen Quote  Post ReplyReply Direct Link To This Post Posted: 27 November 2019 at 9:33pm
I did try the full editor - but will try again....

No luck ... all I get is a "insert image" button, and when I click on it, I only have an option to choose a file from /uploads/public (I have no idea where that goes - and it has photos that have nothing to do with my computer) - and no option for changing the path.  I dont see any way to change the path to reflect choosing a file on my computer.

I am using Chrome - do you folks find that compatible with this site?????   Sorry if I am just doing something stupid....


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Post Options Post Options   Thanks (0) Thanks(0)   Quote BJtheDJ Quote  Post ReplyReply Direct Link To This Post Posted: 27 November 2019 at 9:45pm
Originally posted by rchamlen rchamlen wrote:

I did try the full editor - but will try again....

No luck ... all I get is a "insert image" button, and when I click on it, I only have an option to choose a file from /uploads/public (I have no idea where that goes - and it has photos that have nothing to do with my computer) - and no option for changing the path.  I dont see any way to change the path to reflect choosing a file on my computer.

I am using Chrome - do you folks find that compatible with this site?????   Sorry if I am just doing something stupid....

Once you have more than 10 rep points (you have 5 right now) you will be able to upload pictures to the site.

Clicking the tree icon takes you to the upload facility, and toward the bottom left corner you'll see a Browse button; the rest will be common sense.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote rchamlen Quote  Post ReplyReply Direct Link To This Post Posted: 27 November 2019 at 9:48pm
Ok ... so all I need to do is post a series of four more "nonsense" messages?????  Smile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Xoc1 Quote  Post ReplyReply Direct Link To This Post Posted: 27 November 2019 at 9:52pm
Insert image button,
Browse button - select local image file
Upload Image button.
Image should appear in your image properties list and should be preselected, or can be selected from the list to appear in the preview window.
Click On OK to put the image in your post.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote rchamlen Quote  Post ReplyReply Direct Link To This Post Posted: 27 November 2019 at 9:55pm
ok sorry about this folks ... I am going to post a series of nonsense messages to get my reps to 10 so that browse button appears....
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