Hi von Ah,
Not exactly a direct drop-in, but close.
The magnet bottoms out on the back-brace (if you have one) before the driver edge comes to rest on the baffle. The gap is (very) roughly 2-3mm. I did not measure it.
Dave recommended to go to home depot and buy a gasket to fill the gap. I went to both Home Depot and another store and neither had an appropriately sized gasket. I was referred to an industrial plumbing supply store, but I just headed home instead.
I ended up making my own gaskets out of cardboard. So right now the drivers are installed with a sandwich of stuff - The self-sticking 3M rubber gasket that comes with the drivers is installed on the drivers, the thin gaskets from the EL70s were left in place around the baffle holes, and the cardboard gaskets are sandwiched in between.
It is a temporary kludge, but it is invisible (my drivers are inset) and it works quite well. Well enough I might "take my time" finding suitable rubber gaskets.
Box tuning remains exactly the same.
My EL70s were wired in series, so I stuck with that - so ~ 10-12 ohm. I am running them on the 8 ohm taps of my SSE right now and it sounds good to me. I don't have my 16ohm taps wired to banana jacks on my amp, but I am going to change that soon, so I will be able to test on both the 8 and 16 ohm taps. With the 12 ohm load on 16 ohm taps, primary impedance of the OPTs will be about 3750 ohms. Plenty of people running their SSE with 3.2k ohm loads working fine.
Not exactly a direct drop-in, but close.
The magnet bottoms out on the back-brace (if you have one) before the driver edge comes to rest on the baffle. The gap is (very) roughly 2-3mm. I did not measure it.
Dave recommended to go to home depot and buy a gasket to fill the gap. I went to both Home Depot and another store and neither had an appropriately sized gasket. I was referred to an industrial plumbing supply store, but I just headed home instead.
I ended up making my own gaskets out of cardboard. So right now the drivers are installed with a sandwich of stuff - The self-sticking 3M rubber gasket that comes with the drivers is installed on the drivers, the thin gaskets from the EL70s were left in place around the baffle holes, and the cardboard gaskets are sandwiched in between.
It is a temporary kludge, but it is invisible (my drivers are inset) and it works quite well. Well enough I might "take my time" finding suitable rubber gaskets.
Box tuning remains exactly the same.
My EL70s were wired in series, so I stuck with that - so ~ 10-12 ohm. I am running them on the 8 ohm taps of my SSE right now and it sounds good to me. I don't have my 16ohm taps wired to banana jacks on my amp, but I am going to change that soon, so I will be able to test on both the 8 and 16 ohm taps. With the 12 ohm load on 16 ohm taps, primary impedance of the OPTs will be about 3750 ohms. Plenty of people running their SSE with 3.2k ohm loads working fine.
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Thanks for the clarification. Tricky considerations... I don’t have tube amps with specific taps, but a stout, updated Hafler DH-220C (Bob Cordell updated circuit) and a new TPA3255 class D amp with integrated SMPS (designed by drMordor).
I’m very intrigued by your results and may give it a shot with 12 Ohm first, then research 3 Ohm capability.
I’m very intrigued by your results and may give it a shot with 12 Ohm first, then research 3 Ohm capability.
I am guessing that a small change to the output filter on the TPA could be pretty easily made to compensate for the impedance change. I know with my TPA3118 "Wiener" it was only a matter of choosing a different inductor and/or cap value to get the right response from a specific speaker impedance (my brain is muddy on the details). In fact, I'll be looking to do this this very thing to my Wiener (summer amp) for these speakers.
No idea bout the Hafler. Sorry.
No idea bout the Hafler. Sorry.
Here is a visual representation of what this upgrade does. I have fairly accurately scaled and then overlaid the published response graphs of the EL70 and the P7.2HD, and threw in the microTower box for good measure.
Navy blue is P7.2HD, grey + dotted blue is EL70, red is microTower. The fork in the road at 5k says it all. The 12 to 20 decibel advantage from 10k up is both obvious and very welcome indeed.
Looking at it this way, it is pretty easy to see why I am hearing (to my surprise) slightly better bass from the new drivers than the EL70. All I was hoping for was that it be reasonably close.
It will likely become even more apparent when I start to put some power to them. Although something tells me that they will not take as much abuse as I have thrown at the EL70s over the years. That's okay. I'm mellowing out as I age.
Navy blue is P7.2HD, grey + dotted blue is EL70, red is microTower. The fork in the road at 5k says it all. The 12 to 20 decibel advantage from 10k up is both obvious and very welcome indeed.
Looking at it this way, it is pretty easy to see why I am hearing (to my surprise) slightly better bass from the new drivers than the EL70. All I was hoping for was that it be reasonably close.
It will likely become even more apparent when I start to put some power to them. Although something tells me that they will not take as much abuse as I have thrown at the EL70s over the years. That's okay. I'm mellowing out as I age.
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Nice work combining the graphs. Thanks for the output filter idea, too.
I know you’re overwhelmingly pleased with the result, but since I already have the EL70s, it naturally makes sense to me to experiment!
I wonder how a mix-n-match arrangement might work... P7HD on the top, EL70 on the bottom, as well as vice versa. That might be fun.
Here’s a general question: if a given full range driver has two variants, one 8Ohm, one 4Ohm (to keep it simple), what are the theoretical changes in how they affect the same solid state class AB amplifier? Is it just a matter of turning up the volume using the 8Ohm variant to reach the perceived level of the 4Ohm driver?
I know you’re overwhelmingly pleased with the result, but since I already have the EL70s, it naturally makes sense to me to experiment!
I wonder how a mix-n-match arrangement might work... P7HD on the top, EL70 on the bottom, as well as vice versa. That might be fun.
Here’s a general question: if a given full range driver has two variants, one 8Ohm, one 4Ohm (to keep it simple), what are the theoretical changes in how they affect the same solid state class AB amplifier? Is it just a matter of turning up the volume using the 8Ohm variant to reach the perceived level of the 4Ohm driver?
The mix-n-match idea occurred to me. I could try it since my 4 EL70s are just sitting in the P7 boxes doing nothing. Honestly, I am confused about how the drivers would behave electrically in this scenario and wonder what would happen in the box with 2 drivers with different resonant frequencies, etc. I thought about it for a while and decided it wasn't a great idea - but I could be wrong.
Regarding your general question about impedance and AB SS amps, I'll have to defer to someone more knowledgeable.
Regarding your general question about impedance and AB SS amps, I'll have to defer to someone more knowledgeable.
Well put, Dave. Extra EL70s sitting around is begging for a new project!
My general question, more direct, would be: Is it OK to just turn up an amp more if my microTowers are now 12Ohm instead of 8Ohm? Or would there be something missing by making the amp work a little bit harder for the same volume output?
My general question, more direct, would be: Is it OK to just turn up an amp more if my microTowers are now 12Ohm instead of 8Ohm? Or would there be something missing by making the amp work a little bit harder for the same volume output?
Dave,
I might do something really stupid like put all 4 of them in a box with a tube amp and use it as a practice amp for learning to play my new bass.
Seriously. I was using them for this anyway, in a roundabout way. I bought a Line 6 Amplifi TT which (among other things) allows me to plug in my bass and have line-out to any amp of my choice. I have it plugged into my Tubelab SSE and I was driving the EL70 microTowers, of course. It worked just fine.
I might also build some BLHs or BVRs with them. I am pretty familiar with the P10/Woden box library and all the options for the EL70.
I dunno. For now they'll sit in the boxes.
I might do something really stupid like put all 4 of them in a box with a tube amp and use it as a practice amp for learning to play my new bass.
Seriously. I was using them for this anyway, in a roundabout way. I bought a Line 6 Amplifi TT which (among other things) allows me to plug in my bass and have line-out to any amp of my choice. I have it plugged into my Tubelab SSE and I was driving the EL70 microTowers, of course. It worked just fine.
I might also build some BLHs or BVRs with them. I am pretty familiar with the P10/Woden box library and all the options for the EL70.
I dunno. For now they'll sit in the boxes.
I could always build a single EL70 ChubbyTower and power it with a mono amp. I've got a 25WPC EL34 P-P amp sitting doing nothing. I could modify it to take 1/4 inch guitar level input, disable one channel... That would be a giant, heavy practice bass amp!
Lots of project possibilities hidden in the dark corners of my house.
Lots of project possibilities hidden in the dark corners of my house.
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Once again I am not an authority on this topic whatsoever. All I can tell you is that I can barely tell any difference with 12 ohms on my 8 ohm taps. I though I would have to turn up the volume more, but it is negligible.
Impedance problems generally are more associated with have impedance that is too low for the amplifier in question. I feel like I have read that a lot more than problems with impedance that is a bit high.
Nice!
Prepare yourself for a very different listening experience. It isn't a subtle change. I started to turn up the volume a bit last night - let's say "medium" levels. The extra treble is astounding. I am thinking that at high volume it might even border on "too hot". This will depend a lot on everything else in the audio chain, of course. The point is, you won't ever be trying to squeeze detail out of them.
I feel like these drivers are revealing some of the warts in my system that I wasn't aware of (or as intensely aware of) with the EL70s. Some may see this as a downside, but I don't. I'll probably be hyper-focused on listening to my system (rather than just enjoying the music) for a while until I dial things in. I'm okay with that for a little while.
Prepare yourself for a very different listening experience. It isn't a subtle change. I started to turn up the volume a bit last night - let's say "medium" levels. The extra treble is astounding. I am thinking that at high volume it might even border on "too hot". This will depend a lot on everything else in the audio chain, of course. The point is, you won't ever be trying to squeeze detail out of them.
I feel like these drivers are revealing some of the warts in my system that I wasn't aware of (or as intensely aware of) with the EL70s. Some may see this as a downside, but I don't. I'll probably be hyper-focused on listening to my system (rather than just enjoying the music) for a while until I dial things in. I'm okay with that for a little while.
I’ve been very happy with my microTowers for 10 years, with a high-crossed tweeter stuck to the back. It will be interesting to experience more HF detail with the P7HDs. Especially since I typically do not listen at loud levels.
Also interesting to decide what to do with whichever 4 drivers don’t stay in the microTowers (and the extra tweeters, likely).
Also interesting to decide what to do with whichever 4 drivers don’t stay in the microTowers (and the extra tweeters, likely).
Ah, I see. I wasn't aware you had those tweeters in the mix. I assume they were there more as "super-tweeters" of sorts to add some "air"?
You definitely won't need them with the P7.2HDs, and the change for you won't be as dramatic as it was for me (I was just living with the EL70s' big roll-off).
You definitely won't need them with the P7.2HDs, and the change for you won't be as dramatic as it was for me (I was just living with the EL70s' big roll-off).