Stupid Idea or Revelation?

[cogitech]

As many of you know already, I have been toying with the idea of adding a tweeter to my P-10 "Castle" microTowers for a little more "air" up top and I appreciate all the input I have recieved on that. I still might do it at some point, but... I have just had a bit of a "eureka" moment and thought that it made more sense to start a new thread.

I just looked at the frequency response graph for the CHR-70c and noticed that it's top end is significantly "hotter" than the rolled off top end of the EL70. It also appears that the form factor of these two drivers is nearly identical except for the shallower "depth" of the CHR.

So, my "big" idea is, replace the two "front" EL70 drivers on my Castle microTowers with CHR-70c drivers, and leave the top EL70 drivers in place.

Stupid?

The biggest challenge (for me) is how to deal with the impedance. EL70 is 4ohms and CHR-70 is 8ohms. Is there an easy way to deal with this (my amp will only go down to 4ohms). Perhaps add something in the chain to make the EL70 8ohms and then wire them parallel to the CHR-70 for a total 4ohm load?

Any other issues that are not obvious to me?

[zman01]

Cogitech,

The tonal balance of the two drivers is likely to be different - I have CHR-70.2s and can attest to that they sound different vs EL-70.

The other thing is driver T&S and tuning - CHR-70.3 is different - please note that port length is slightly different for Micro Tower with CHR-70.

I tried mixing CHP-70 (gen 1) and CHR-70.2eN - didn't sound too good in the Lotus^2 cabinet. The timing was kind of off IIRC. Logic was same as your's - bass and midrange richness of paper cone, top end of aluminum cone.

One thing you can do is get the CHR-70.3 and run them in parallel and run one of the drivers as a .5 driver by (capacitor trick - not just 90 degree offset). I am not sure if top driver gives a full .5 driver effect - I rather enjoyed the headroom the top driver provided in my old Micro Tower. It might be noted that I had made it with 15 degree angle, so probably some of the dispersion was forward too. I was actually firing the driver on the front baffle towards the wall. No shortage of treble with the CHR-70 though and it's quite a powerhouse for its size. However I like the EL-70 more.

If you want to increased the liveliness of the EL-70 you can try placing a handful of acosutastuf (dense type) just beneath the drivers - different stuffing material has different effects on sound and I've found that some materials tend to suck midrange/top richness while others can enhance it. Of course, the amount matters too.

[cogitech]

Originally Posted by zman01

Cogitech,

The tonal balance of the two drivers is likely to be different - I have CHR-70.2s and can attest to that they sound different vs EL-70.

Can these differences ever be "complimentary" or is this always a "bad thing"?

The other thing is driver T&S and tuning - CHR-70.3 is different - please note that port length is slightly different for Micro Tower with CHR-70.

I did consider this, however based on my own experience tweaking the ports on my microTowers (which I have not been completely "open" about ) I have to simply say that there seems to be (for my needs) considerable flexibility in the tuning of this port, and I can easily do so if I feel that it is necessary.

I tried mixing CHP-70 (gen 1) and CHR-70.2eN - didn't sound too good in the Lotus^2 cabinet. The timing was kind of off IIRC. Logic was same as your's - bass and midrange richness of paper cone, top end of aluminum cone.

Hmmm... I am not familiar with the Lotus^2. Is it a "Castle" style with one driver on top? I am thinking the Castle configuration may be rather forgiving, since a slight timing delay is what makes it work the way it does, with much of the signal of the top driver travelling up to the ceiling and then back down to your ears, while the signal from the front driver takes a shorter path (AFAIK).

One thing you can do is get the CHR-70.3 and run them in parallel and run one of the drivers as a .5 driver by (capacitor trick - not just 90 degree offset). I am not sure if top driver gives a full .5 driver effect - I rather enjoyed the headroom the top driver provided in my old Micro Tower. It might be noted that I had made it with 15 degree angle, so probably some of the dispersion was forward too. I was actually firing the driver on the front baffle towards the wall. No shortage of treble with the CHR-70 though and it's quite a powerhouse for its size. However I like the EL-70 more.

Well, that is a new idea entirely, which would require changing out all the EL70s for CHR-70.3. Not sure I want to go that far.

If you want to increased the liveliness of the EL-70 you can try placing a handful of acosutastuf (dense type) just beneath the drivers - different stuffing material has different effects on sound and I've found that some materials tend to suck midrange/top richness while others can enhance it. Of course, the amount matters too.

Interesting. My microTowers are pretty well stuffed for me as far as bass response goes, but I never considered the impact of stuffing on the treble. Thanks for the tip!

[zman01]

Originally Posted by cogitech

Interesting. My microTowers are pretty well stuffed for me as far as bass response goes, but I never considered the impact of stuffing on the treble. Thanks for the tip!

Whatever you do, make sure you can make the stuffing amount "right" again. IIRC you have a removable bottom, so taking the stuffing in and out should be easier.

Disclaimer: I shall not be held responsible if you manage to screw up the sound.

[cogitech]

I have just been doing some more research and it seems easy enough to add a 3.9ohm 10w resistor to the top EL70s and then run them parallel to the CHR70s.

I might just order two CHR-70c drivers and do this as an experiment. Worst case scenario I have a pair of CHR-70c for my next project

[cogitech]

Originally Posted by zman01

Whatever you do, make sure you can make the stuffing amount "right" again. IIRC you have a removable bottom, so taking the stuffing in and out should be easier.

Disclaimer: I shall not be held responsible if you manage to screw up the sound.

LOL

I will be very careful and put any removed stuffing into separate bags for each speaker. Or, perhaps I will just add some acoustistuff behind/below the drivers and leave everthing else in place...

[jimbro]

I had a similar idea using el70s front and chp70s top where their rolled off treble might be an advantage?

[fastbike1]

I don't think the TS differences are different enough to make a huge change in tuning. I've measure the EL70 and CHR70.3's that I have and the Fs are w/i 2 Hz, QTS are very close (.625 / .659), as are Vas 3.7/ 3.2l).

It's an easy enough change to try. I'd just temporaily wire them in series and give it a go.

Originally Posted by zman01

Cogitech,

The tonal balance of the two drivers is likely to be different - I have CHR-70.2s and can attest to that they sound different vs EL-70.

The other thing is driver T&S and tuning - CHR-70.3 is different - please note that port length is slightly different for Micro Tower with CHR-70.

I tried mixing CHP-70 (gen 1) and CHR-70.2eN - didn't sound too good in the Lotus^2 cabinet. The timing was kind of off IIRC. Logic was same as your's - bass and midrange richness of paper cone, top end of aluminum cone.

One thing you can do is get the CHR-70.3 and run them in parallel and run one of the drivers as a .5 driver by (capacitor trick - not just 90 degree offset). I am not sure if top driver gives a full .5 driver effect - I rather enjoyed the headroom the top driver provided in my old Micro Tower. It might be noted that I had made it with 15 degree angle, so probably some of the dispersion was forward too. I was actually firing the driver on the front baffle towards the wall. No shortage of treble with the CHR-70 though and it's quite a powerhouse for its size. However I like the EL-70 more.

If you want to increased the liveliness of the EL-70 you can try placing a handful of acosutastuf (dense type) just beneath the drivers - different stuffing material has different effects on sound and I've found that some materials tend to suck midrange/top richness while others can enhance it. Of course, the amount matters too.

[cogitech]

Originally Posted by fastbike1

I don't think the TS differences are different enough to make a huge change in tuning. I've measure the EL70 and CHR70.3's that I have and the Fs are w/i 2 Hz, QTS are very close (.625 / .659), as are Vas 3.7/ 3.2l).

It's an easy enough change to try. I'd just temporaily wire them in series and give it a go.

I was thinking sort of the same thing, and I have easy, direct access to my ports via removable bottom panels, so if I have to adjust tuning it is a no-brainer.

Hmmmm. And I did just get some Christmas money from my folks... I feel a CSS order in my near future

[chrisb]

what amp again?

almost any SS or even tube amp would have no issue with driving the series wiring load, but a lot might run into problems with the under 3ohms of the parallel load

a notable exception to the latter would be the Decware Zen amp - claimed to be stable @ 1 ohm (certainly was the case with Steve's OEM transformers, I'm not so sure about the latest sans part "kit" version in which a more conventional Edcor is recommended)