What do measurements say about SET’s
- Thread starter Rensselaer
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Active crossovers are larger more complicated and usually digital. The less bits between source and speaker coil the better
Look at Marchand tube active crossovers. All those passive components do a lot of damage.
Even an active crossover needs the same number of passive components - you can't do a filter without passive components. I've run simple R/C line level passive crossovers (as opposed to traditional speaker-level crossovers), and that is literally the cleanest way it can be done. An active crossover has to have those same passive components plus and active stage which can carry it's own problems such as noise. A 2 pole passive crossover consists of only two resistors and two capacitors for the woofer and HF horn.
Passive filters carry with them level loss, but that's expected and has no impact on the signal as long as enough gain exists elsewhere in the system to still provide enough voltage to drive the power amplifiers.
Beyond that, off-the-shelf active crossovers still need additional components to provide the necessary voicing, especially that needed by the Altec compression drivers since their native frequency response is nowhere near flat enough for HiFi use.
Suggest a design then, if you would please, with parts and values and I will solder it up.
You can Google "passive line level crossover" and get many suggestions like this one, which has circuits for 1 pole and 2 pole (2 pole is what you're interested in for Altecs).
You'll have to find someone to build it for you anyway, so I would go with their advise, however building something like this is trivial. Of more concern is the voicing circuit needed for the HF horn. This is something you're not likely to find on the web.
As long as those are 12dB per octave, then they would work, provided the input and output impedances of the outboard gear are correct. If the source and load impedances aren't right, the crossover point will be shifted. That just needs to be taken into consideration.
That still leaves the voicing filter......
Sure, a line level passive may work in some cases better than an active xover but directly hooking the amp to the speakers without a filter in between has noticeable benefit in dynamics.
You can try it, but without a sensible frequency response measurement of the two drivers it is usually doomed to failure anyway. Sometimes you have luck
This is why I work with well behaved drivers that need little to corrections to sound good. There are some high sensitivity drivers that actually fit that description !You can try it, but without a sensible frequency response measurement of the two drivers it is usually doomed to failure anyway. Sometimes you have luck
First he has to tell us whether the original drivers are still there, 806a & 416a or others.
Most A7 are modified
Most A7 are modified
My amp(s) have volume controls and are used sans preamps.
What I am looking for is a small passive device that I can place between the phono stage and two amplifiers. The device will necessarily split the phono stage output to two pathways, one pair having passive high pass (@ 500 Hz and above) filters to left and right output jacks to feed the 300B SET stereo amp (with volume pots), the other pair through low pass filters (500Hz and below) to feed the 211 SET stereo amp (with volume pots). Balancing will be done with the volume pots on the amplifiers. I assume small value parts placed there will do the trick without reducing the signal too much but don’t know that.
It has been suggested that because the compression drivers in my Altec A7’s are not flat they will need varable resistors to “voice” the treble.
Oh, it's not that hopeless.You can try it, but without a sensible frequency response measurement of the two drivers it is usually doomed to failure anyway. Sometimes you have luck
The responses of the drivers in an A7 system are well known. I wouldn't try plugging in these in-line crossover plugs without some way to measure that they're doing what is intended. Sending too much low frequency information to the compression drivers is guaranteed to ruin your day, with the original Altec diaphragms being unobtanium if you blow one.
Like I mentioned earlier, that still leaves the problem of voicing the HF driver. Really, the basic crossover is simple - the voicing filter is way more involved comparatively, and that's why having someone who knows these speakers intimately and is willing to build what is required is necessary.
Most high frequency compression drivers have an excess of energy in the 1kHz region, even modern ones. Can you post a link to a raw frequency response of a driver you consider 'well behaved'? The Altecs are really no better or worse than anything else out there in this respect.
The response of the different drivers were all basically the same and need the same basic voicing. More important for the high frequency compression drivers is the particular diaphragm installed. Ideally the drivers have the original Altec 34647 diaphragm, which was the usual one for "HiFi" use. The 16 ohm diaphragms have more limited high frequency extension due to the extra weight of the voice coil. Others such as the "Symbotik" were designed for PA type work and have more limited high frequency extension due to the higher weight of the voice coil and diaphragm. They do have greatly increased power ratings though, however this is useless for home listening. Great Plains Acoustics used to offer copies of the 34647 which were OK but suffered from lack of consistency of frequency response.First he has to tell us whether the original drivers are still there, 806a & 416a or others.
Most A7 are modified
The currently available Radian Engineering diaphragms are more similar to the Altec "Symbotik" types and are really more suitable for PA work.
I think it's more the horn, here is a tad 2001 in that horn it makes a peak too 1- 2khz. tad is smooth flat in other horns. I would damp the horn with greytak outside before i start with other things.
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No question the HF horns need to be well damped - in my case (picture below) I cover the entire surface with a thick application of Aquaplas which makes them completely inert. Bondo automotive putty also works well.
Running these Altec horns without adequate damping is a fool's errand.
I use modeling clay (car), it is very easy to shape and has a high level of cushioning. If necessary, it can be removed without leaving any residue if you sell the speaker later.No question the HF horns need to be well damped - in my case (picture below) I cover the entire surface with a thick application of Aquaplas which makes them completely inert. Bondo automotive putty also works well.
Running these Altec horns without adequate damping is a fool's errand.
View attachment 139829
Takes me back to the seventies when I completely covered the backside of my Klipsch LaScalas with Plasticine modeling clay. Really smoothed a peaky hardness right out of them. There were additional smaller gains to be had covering the driver itself YMMV.No question the HF horns need to be well damped - in my case (picture below) I cover the entire surface with a thick application of Aquaplas which makes them completely inert. Bondo automotive putty also works well.
Running these Altec horns without adequate damping is a fool's errand.
View attachment 139829
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