Celestion HF1000 replacement tweeter?

[DarrenHW]

It wont measure 4.8 Ohms Darren, as you're confusing voicecoil DC resistance with frequency dependant impedance.

Yes I am How's this for a simpler plan, record the frequency response of a stock UL8:

install the new tweeter and manipulate the crossover values until the two charts match?

[Reffc]

Thats not a bad shout Darren but better if your did it for tweeter and woofer separately to measure individual response in room first, and that way you can see what the actual roll off slopes are, then try them together. You will of course be picking up all room reflections so this still wont achieve the accuracy needed but it's better than trying to calculate a filter. It won't tell you if correct phase response has been achieved but perhaps inverting the polarity of the woofer or the tweeter to see if you get a dip will be a help there. The bigger the dip with one out of phase, the closer the phase match when you re-invert.

[DarrenHW]

Thanks for sticking with me Paul!

Tweeter & woofer connected. Mic 150mm centred between tweeter and woofer:


Tweeter only. Mic 150mm centred on tweeter:


Woofer only. Mic 150mm centred on woofer:


As stock the polarity of the tweeter is reversed, is it worth rewiring this and taking another measurement?

According to the Celestion documentation the crossover frequency is at 2k which I guess is the dip circled in blue, any idea what the dip circled in red is?

[Reffc]

The best way to take the readings if in-room Darren is with one speaker positioned in the centre of the room and the mic at 1m from the speaker, level with the tweeter (which is where your ear level normally is when listening). I'd re-do the measurements for that. The dips could be due to room interaction or comb filtering caused by the cabinet design, so are likely null or cancellation points. However, the filter design might be partly responsible too and almost certainly is a significant factor for the first dip (read on...).

The tweeter's polarity being reversed as standard as with some 2 pole designs, indicates the designer thought it the best phase response using that polarity. What you can glean from the in room measurements is that the tweeter acoustic roll off with the standard filter is a steep 24dB/Octave between 1 and 2KHz and that the woofer starts rolling off at 1KHz with an approximate 18dB roll off (ie 3rd order acoustic) by 2KHz. This will give an uneven transfer function acoustically which is partly why you see that dip at approx 1.6KHz. The tweeter response is also far from smooth on axis with a notable rising output. I wont draw any firm conclusions from in room measurement though especially with the mic and speakers perhaps not ideally placed. Also, your measurements would have been taken slightly off axis. Whilst this wont have a significant impact on the result you see in your measurements, they would still benefit from being checked with just one speaker connected and situated as far from boundaries as you can get it, using a pink noise burst for measurement and gating the response if your software has that functionality.

[DarrenHW]

The best way to take the readings if in-room Darren is with one speaker positioned in the centre of the room and the mic at 1m from the speaker, level with the tweeter (which is where your ear level normally is when listening). I'd re-do the measurements for that. The dips could be due to room interaction or comb filtering caused by the cabinet design, so are likely null or cancellation points. However, the filter design might be partly responsible too and almost certainly is a significant factor for the first dip (read on...).

It will take me a couple of days but I can do that, I'll upload more charts once I have.

The tweeter's polarity being reversed as standard as with some 2 pole designs, indicates the designer thought it the best phase response using that polarity. What you can glean from the in room measurements is that the tweeter acoustic roll off with the standard filter is a steep 24dB/Octave between 1 and 2KHz and that the woofer starts rolling off at 1KHz with an approximate 18dB roll off (ie 3rd order acoustic) by 2KHz. This will give an uneven transfer function acoustically which is partly why you see that dip at approx 1.6KHz. The tweeter response is also far from smooth on axis with a notable rising output. I wont draw any firm conclusions from in room measurement though especially with the mic and speakers perhaps not ideally placed. Also, your measurements would have been taken slightly off axis. Whilst this wont have a significant impact on the result you see in your measurements, they would still benefit from being checked with just one speaker connected and situated as far from boundaries as you can get it, using a pink noise burst for measurement and gating the response if your software has that functionality.

I'm glad you agree the tweeter uses a 3rd order 18db crossover this was the only calculator that returned similar values to those used in the original crossover. Thanks again for all the help, I have more questions but I'll hold fire until I can upload more charts .

[Reffc]

It will take me a couple of days but I can do that, I'll upload more charts once I have.




I'm glad you agree the tweeter uses a 3rd order 18db crossover this was the only calculator that returned similar values to those used in the original crossover. Thanks again for all the help, I have more questions but I'll hold fire until I can upload more charts .

errrr...the tweeter response is acoustically 24dB/Octave (ie acoustic 4th order) judging by the in room response (the woofer looks like 3rd order acoustic). Once you can remeasure as suggested, and measure more on axis, that may well change the result and we can then better assess the filter requirements. Its nigh on impossible doing this by forum correspondence though! I'm really only trying to provide a few tips to point you in the right direction.

[tiguan]

Thread became a very usefull compact diy speaker guide and good lesson for me. Thank you Paul and Darren...

[DarrenHW]

errrr...the tweeter response is acoustically 24dB/Octave (ie acoustic 4th order) judging by the in room response (the woofer looks like 3rd order acoustic).

And there I was thinking I was getting my head around it The reason I thought the Tweeter was 3rd Order 18db is because it is wired like this:
crossover.gif
and the calculator puts the capacitor values in the same region as those fitted.
I thought the LF was 2ND order 12db because it is wired like this:
lf crossover.gif
and the calculator also puts the capacitor values in the same region as those fitted.
I guess it's not that simple?

Its nigh on impossible doing this by forum correspondence though! I'm really only trying to provide a few tips to point you in the right direction.

I appreciate that and also appreciate the help although I guess you may feel like your banging your head against a brick wall. I've taken some more measurements as you suggested, please don't feel obliged to reply if you don't want to .

Some new measurements all taken at 1m in the most open space I have.

UL8 Tweeter & Woofer (Tweeter Reversed).


UL8 Tweeter & Woofer (Tweeter not Reversed).


UL8 Woofer.


UL8 Tweeter.

[Reffc]

The woofer measured from listening height exhibits closer to 2nd order acoustic (as expected)and the tweeter a steep 4th order still. As mentioned, 3rd order electrical does not always equate to the same acoustic...it depends on the drive unit and the crossover point. In this case it's because the tweeter is being crossed off low towards its natural roll off and that is steepening the filter transfer function, hence 4th order acoustic.

If you can super-impose the individual measurements on the same graph, that will tell you a little more, but it looks like no obvious 2KHz dip and it's difficult to establish if the crossover is phase accurate but I suspect not from what I see. (This is a crude attempt to look at what's going on when a more refined approach is really needed) and that is as a result of the individual driver phase at crossover point. You can also see the effects of comb filtering with the tweeter not reversed to its "normal polarity".

The easiest approach if you want to match how the speakers came from the factory is simply to get a replacement tweeter to match the tweeter curve you have, making very sure to level match, so take the tweeter measurement at a set level, leave the test gear in place and swap tweeters, tinkering with electrical HF filter until you match the "master" curve for the old tweeter at crossover. That assumes that there are no clapped out electrolytics in the original filter to start wih. Personally, I'd re-design it using a low self resonance tweeter of 500Hz or so and try to get a 2nd order acoustic at 2KHz for better phase matching. The filter values will not be calculable because if a flat baffle, time alignment within the filter is also required.

Just trying not to over complicate things for you, so have some fun with it and it would probably help you to do a little research to help you understand things like phase relationships.

This will be a useful link for you and I'd recommend it as good reading material:

http://sound.westhost.com/lr-passive.htm

Can't do too much more for you without doing the work myself (ie having the speakers here) but you'd not learn anything that way Darren, so once again, have a read of the above link and associated topics and just treat it as a bit of fun and learning and best of luck with it.

[DarrenHW]

The woofer measured from listening height exhibits closer to 2nd order acoustic (as expected)and the tweeter a steep 4th order still. As mentioned, 3rd order electrical does not always equate to the same acoustic...it depends on the drive unit and the crossover point. In this case it's because the tweeter is being crossed off low towards its natural roll off and that is steepening the filter transfer function, hence 4th order acoustic.

If you can super-impose the individual measurements on the same graph, that will tell you a little more, but it looks like no obvious 2KHz dip and it's difficult to establish if the crossover is phase accurate but I suspect not from what I see. (This is a crude attempt to look at what's going on when a more refined approach is really needed) and that is as a result of the individual driver phase at crossover point. You can also see the effects of comb filtering with the tweeter not reversed to its "normal polarity".

Well I'm glad it makes sense to you ! Unfortunately I cannot super-impose the individual measurements, I could manually enter the values and create a graph but this would be a very simplified representation.

The easiest approach if you want to match how the speakers came from the factory is simply to get a replacement tweeter to match the tweeter curve you have, making very sure to level match, so take the tweeter measurement at a set level, leave the test gear in place and swap tweeters, tinkering with electrical HF filter until you match the "master" curve for the old tweeter at crossover. That assumes that there are no clapped out electrolytics in the original filter to start wih.

Yes, I'm going to stick with this plan and no there are no clapped out lytics in the filter, I have recently recapped (like for like values) with Alcaps and have a stock of Alcaps to use modifying the crossover for the new tweeter.

Personally, I'd re-design it using a low self resonance tweeter of 500Hz or so and try to get a 2nd order acoustic at 2KHz for better phase matching. The filter values will not be calculable because if a flat baffle, time alignment within the filter is also required.

I'm pretty much set on the 27TDFC (Free Air Resonance 550 Hz, Recommended Frequency Range 1500Hz - 25000Hz) it seems to have a similar impedance to the HF1000 (based on assumption) and uses ferro fluid as does the HF1000, so (as read in Rod Elliott's article) negating the need for a Zobel Network, "Note that tweeters using ferro-fluid in the voicecoil gap will usually be very well damped, and may show little or no resonant peak. This means that no compensation circuit is needed."

Just trying not to over complicate things for you, so have some fun with it and it would probably help you to do a little research to help you understand things like phase relationships.

This will be a useful link for you and I'd recommend it as good reading material:

http://sound.westhost.com/lr-passive.htm

Can't do too much more for you without doing the work myself (ie having the speakers here) but you'd not learn anything that way Darren, so once again, have a read of the above link and associated topics and just treat it as a bit of fun and learning and best of luck with it.

Thanks for the link, I've read through it and although this has lead to further reading in an attempt to understand some of the principles covered it has confirmed some things I've heard but struggled to accept, things I've heard but seem to be juxtaposed with forum consensus and dispelled some forum based misinformation. Pretty much every project I undertake is a leap of faith based on internet reading so it's comforting to read articles in line with my own listening experience.

Yes, this project is intended to be an enjoyable educational experience, I'm a better (but a very long way from good) student with working examples. The UL8's are not my ultimate speaker choice but a speaker that fits into the space limitations I currently have to work with and integrate well as surround speakers with the Celestions I use as front speakers.