So how would you explain if someone gets data that clearly resembles that of a manufacturer, such as peerless, and then in the exact conditions and methods finds the data of another manufacturer to be different from the manufacturer's data. And what if this is repeated many times across many manufacturers and among many DIY'er.
Would ground plane, or 5m off the ground be close enough to anechoic to you? Even an anechoic chamber has reflections. Outside though, there is only 1, the ground.
If the data we measureis similar to the manufacturers it means that the T/S curves of that driver are close to a horizontal line.
dave
Hi Tux (Guys),
For your first question, I've witnessed factory tests on several competitor makes including the one you mention that don't match. There are many variables that affect test outcomes. From the effectiveness of the anechoic isolation (chamber size and type), accuracy and working range of the mic, accuracy of the calibration, test equipment type and environmental conditions (temperature, humidity and barometric pressure) and so on.
Interestingly, Markaudio has a reasonable record on independent close data. I remembered some of the first independent tests and reviews done in Germany where 2 sets of tests using different equipment gave close results:
Markaudio Alpair 10 - ein Kurzbericht
Japan's MJ magazine did a large scale review of the Alpair 12 and got close results. But there's been a few guys who've got different results from my data, some spending their time complaining to me, or knocking my work down publicly on the net. Usually, those tests that close match mine are anechoic or near anechoic, done by guys who have good knowledge on driver construction, operation and have spent some time getting their test set-ups properly sorted. The point is its a random situation. There's bound to some results that will match and some that won't.
As I've said soooooo mannnnnny times: Until there's a comprehensive universal single standard that all use (pro and amature alike), there will always be variation.
2 - This is a more practical and useful question. For those guys who want to do full-range frequency testing at home (note the words "Full-Range"). Here's my advice: (Tux, note the positions, dimensions and foam isolation requirements):
A - Invest is a decent mic. Don't buy the cheapo mics that cost below US$300. They are fine for general set-up but Not for accurate testing below 50Hz and past 15-kHz. Take a look at the Earthworks measurement series, at the very least, their M23 but this is only good up to 20-kHz. Expect to pay around US$500 for a M23. You'll need the M30 or the M50 is you really want to find out more:
Measurement Series | Earthworks Audio
B - Try to get hold of hardware/software like Linear X V4, DAAS, MLSSA and similar test gear. There's also something available for Mac that Dave (Planet 10 uses - Dave please mention as I can't remember the name).
C - Beg, borrow (or steal) your wife's, granny's, friend's spare room, basement etc. and set about creating an isolation chamber within: see my sketch pic attached (dimensions = Metres).
Regarding the acoustic foam on the floor, you'l need to carefully cut large rectangles, treating them as mats to be lifted and put down during the measurement process. For siting the mic and driver, buy a small laser pen and place in the same clamp as the mic. Aim it directly at the centre of the driver's dust cap. Once aligned, carefully exchange it for the mic. Just 10-mm off alignment will create measurement error so take lots of practice to get it right.
Could be a great collective project for a group of audio buddies. Remember, this is an isolation chamber, unlikely to become anechoic, but at least its a reasonable opportunity to remove the worst of the external variables.
Phew.....I've got to go, its Easter day off and need a rest.
Cheers
Mark.
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Ah ha! The answer to one of my questions.You use a 1.5m square baffle with the driver centered. I know you know, but neophytes might not -- The shape of the roll-off below 200-300Hz is almost entirely dependent on the baffle. Some manufactures will put a sealed box behind the baffle and that totally changes the shape of the response curve.
Bob
Bob
Hi Bob,
Actually, we use large volume sealed box with interchangeable front mounts. Best I take some pics when time permits. I'm flat out busy at the moment.
Given that I'm suggesting a simple DIY isolation arrangement as possible, a large sealed test box needs +1 metre clearance around it, so will increase the size of the isolation chamber.
Cheers
Mark.
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Dave: 1inch would maybe change the response by less than 1db.
Mark: thanks for the feedback. I've coveted an ACO Pacific mic for a while and would love an earthworks m30. Pricey though. I suppose I'm only interested in 200 to 10,000hz. For this I go outside and use a gated impulse response. I am able to replicate many spec sheets to within a couple db (considering baffle effects), consistently. This is good enough for a DIYer. Thanks for the professional feedback.
I think Bob meant below the baffle effects there will be baffle step losses. You don't use an IB?
Sorry to derail a good thread. If there is interest I wouldn't mind a separate thread on this. I love measuring more than building
Nice to have feedback from a manufacturer.
Mark: thanks for the feedback. I've coveted an ACO Pacific mic for a while and would love an earthworks m30. Pricey though. I suppose I'm only interested in 200 to 10,000hz. For this I go outside and use a gated impulse response. I am able to replicate many spec sheets to within a couple db (considering baffle effects), consistently. This is good enough for a DIYer. Thanks for the professional feedback.
I think Bob meant below the baffle effects there will be baffle step losses. You don't use an IB?
Sorry to derail a good thread. If there is interest I wouldn't mind a separate thread on this. I love measuring more than building
Nice to have feedback from a manufacturer.
sorry, I couldn't help myself - sensitivity, proximity, efficiency of effort - you see where this is going
I have Alpair 10 Gen 1 in 21 litre infinite baffle columns. I have used a variety of amps, which I would place here in ascending order of satisfaction:
- 807 PP (triode) with 6SN7 drivers, choke loaded
- 6V6 PPP (triode) with 6SN7 drivers, choke loaded
- 300b with Lundahl LL1660/60mA OPTs and combination bias, 26 and 46 input
- 300b with Lundahl LL1660/80mA OPTs self bias, 26 and 46 input
- 2a3 PP with choke loaded 4P1L drivers and 26 input, O-netics OPTs
- 2a3 PP with 01A direct coupled to 31 then LL1660/PP to outputs (O-netics).
The 807 and 6V6 amps are indirectly heated - they have a rich and forward presentation which is good to listen to. Plenty of control. But with the DHT amps we get more detail and better timbre.
The 300b amps have the best midrange, SE DHTs all through with the 26 in choke loaded (2xHammond 156C) filament bias and the 46 coupled to outputs with Hammond 126C interstages. These amps are about as far as I could go with the 300b without getting exotic.
The drawback for me, despite the lovely liquid midrange, is the lower mids and bass which simply don't have the dynamics and attack of the 2a3 PP amps. The 300b stage needs to have at least 60mA current, preferably 80ma or more. I haven't totally optimised the amps, but they are pretty close. The 300b is also a warmer sound, 46 is neutral and 26 is warm. So sound is quite euphonic.
I turned to PP 2a3 not expecting it to better the 300b amps, but it did quite significantly in the lower mids and bass - cellos and basses in the orchestra came to life. This gave a better balance right through the frequency range, and overall there was more clarity and better control. I'm still experimenting here - the differential 4P1L stage is promising - it's choke loaded with the 90K side of a Hammond 124b which is surprisingly effective, and teflon FT-3 coupling caps. This is being driven with my 26 preamp. It's a really good combination.
The other 2a3 amp is all differential pairs - 01A direct coupled to 31 interstage coupled to the 2a3s. Now this is nice, very nice. It only just has enough gain from a CD player, and in fact I'm using it without a volume control. So there will be changes made, despite the fact that it's my amp of choice here. I've resistor loaded the 01A stage, so that's going to have a plate choke - 124b or Lundahl LL1667. I'll stick with direct coupling for now, though I could be using a LL1660/PP instead as an option. I'm thinking to substitute 26s for the 01As. The driver stage needs more gain. Choices here are 10Y, 46 and 4P1L. The 4P1L is a lot cheaper, though I have enough 46 and 10Y. It has the most gain as well. So this will be my first experiment. Right now the interstage is LL1660/PP but I'll also try LL1692 and LL1671.
I'm using standard Chinese 2a3s so I could move up to 2a3C tubes. I also have some Sovteks I can try. Then there are all the 6B4G and 6C4C types. But anyway, for now my conclusion is that a PP 2a3 amp is the way to go with these Alpair 10s. It's clean, clear, has good control and amazing detail, and is all-round musical and very satisfying. I'm pretty happy right now, and there is more optimisation to do yet!!
Andy
- 807 PP (triode) with 6SN7 drivers, choke loaded
- 6V6 PPP (triode) with 6SN7 drivers, choke loaded
- 300b with Lundahl LL1660/60mA OPTs and combination bias, 26 and 46 input
- 300b with Lundahl LL1660/80mA OPTs self bias, 26 and 46 input
- 2a3 PP with choke loaded 4P1L drivers and 26 input, O-netics OPTs
- 2a3 PP with 01A direct coupled to 31 then LL1660/PP to outputs (O-netics).
The 807 and 6V6 amps are indirectly heated - they have a rich and forward presentation which is good to listen to. Plenty of control. But with the DHT amps we get more detail and better timbre.
The 300b amps have the best midrange, SE DHTs all through with the 26 in choke loaded (2xHammond 156C) filament bias and the 46 coupled to outputs with Hammond 126C interstages. These amps are about as far as I could go with the 300b without getting exotic.
The drawback for me, despite the lovely liquid midrange, is the lower mids and bass which simply don't have the dynamics and attack of the 2a3 PP amps. The 300b stage needs to have at least 60mA current, preferably 80ma or more. I haven't totally optimised the amps, but they are pretty close. The 300b is also a warmer sound, 46 is neutral and 26 is warm. So sound is quite euphonic.
I turned to PP 2a3 not expecting it to better the 300b amps, but it did quite significantly in the lower mids and bass - cellos and basses in the orchestra came to life. This gave a better balance right through the frequency range, and overall there was more clarity and better control. I'm still experimenting here - the differential 4P1L stage is promising - it's choke loaded with the 90K side of a Hammond 124b which is surprisingly effective, and teflon FT-3 coupling caps. This is being driven with my 26 preamp. It's a really good combination.
The other 2a3 amp is all differential pairs - 01A direct coupled to 31 interstage coupled to the 2a3s. Now this is nice, very nice. It only just has enough gain from a CD player, and in fact I'm using it without a volume control. So there will be changes made, despite the fact that it's my amp of choice here. I've resistor loaded the 01A stage, so that's going to have a plate choke - 124b or Lundahl LL1667. I'll stick with direct coupling for now, though I could be using a LL1660/PP instead as an option. I'm thinking to substitute 26s for the 01As. The driver stage needs more gain. Choices here are 10Y, 46 and 4P1L. The 4P1L is a lot cheaper, though I have enough 46 and 10Y. It has the most gain as well. So this will be my first experiment. Right now the interstage is LL1660/PP but I'll also try LL1692 and LL1671.
I'm using standard Chinese 2a3s so I could move up to 2a3C tubes. I also have some Sovteks I can try. Then there are all the 6B4G and 6C4C types. But anyway, for now my conclusion is that a PP 2a3 amp is the way to go with these Alpair 10s. It's clean, clear, has good control and amazing detail, and is all-round musical and very satisfying. I'm pretty happy right now, and there is more optimisation to do yet!!
Andy
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Currently I use dual mono'd UCD180 with a little modding, driven from a Buffalo2/Legato3.1 (modded) to feed a signal to my Alpair 7.3s (grey cones, no voodoo- all that was in stock when I ordered).
The Alp7s are open baffle, 70cm from walls. In my current set up I am using them in FAST stylee with stereo TL subs. Because of this and in order to preserve the delicate suspension of the Alpairs and still get some spl going on, I have rolled off the balanced output of the I/V stage 6db/oct from about 180hz. A full range signal is taken from the SE circuit on the Legato to a mini-DSP which low passes and eq's a rough Linkwitz-Riley sub response fed to the much more robust subwoofers.
This gives me what I feel is a great compromise between the sweetness of the fullrange and the ability to feed the Alpairs enough juice to fill my (fairly small) listening room. This gives me great bass extension without forcing the little Alpair cones out of their comfort zone. Phase distortions are kept low (gentle filter slope) and out of the key pass band.
Still a WIP (the open baffles are cosmetically challenged for sure) but the match between the classD UCD180s and the Alpairs is very much to my liking.
Mark
The Alp7s are open baffle, 70cm from walls. In my current set up I am using them in FAST stylee with stereo TL subs. Because of this and in order to preserve the delicate suspension of the Alpairs and still get some spl going on, I have rolled off the balanced output of the I/V stage 6db/oct from about 180hz. A full range signal is taken from the SE circuit on the Legato to a mini-DSP which low passes and eq's a rough Linkwitz-Riley sub response fed to the much more robust subwoofers.
This gives me what I feel is a great compromise between the sweetness of the fullrange and the ability to feed the Alpairs enough juice to fill my (fairly small) listening room. This gives me great bass extension without forcing the little Alpair cones out of their comfort zone. Phase distortions are kept low (gentle filter slope) and out of the key pass band.
Still a WIP (the open baffles are cosmetically challenged for sure) but the match between the classD UCD180s and the Alpairs is very much to my liking.
Mark
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Update on my PP 2a3 amp. Tried the Sovteks and hated them - hard sound. My Chinese biplate Golden Dragons are actually a nice sound. I prefer Chinese 300b over Russian ones so I'm not surprised at the 2a3. Thorsten suggests running the Sovteks like 45s but I don't know that you'd get the power.
Anyway, I took out the resistor loads for the input 01A long tail pair and put in a 124b Hammond as plate choke (the 90K side with the centre tap). This is cheap but half nickel and sounds better as a plate choke than as an interstage to my ears. Got some more volume and much cleaner sound with more detail and dynamics - well worth while. This is direct coupled to the 31s, which have a LL1660/PP to the 2a3s. So far this is the best amp I've made. I'm looking forward to optimising it.
I tried the UcD 400 but could only get one of my two modules to work. Have you seen the UcD180 Hybrid thread on this site? You bypass the input stage with tubes and just use the output section. This has a balanced input impedence of 1.8K so needs a bit of thought about driving it. Guido Tent has working versions for sale. I'd be looking to use DHTs with a stepdown transformer.
Andy
Anyway, I took out the resistor loads for the input 01A long tail pair and put in a 124b Hammond as plate choke (the 90K side with the centre tap). This is cheap but half nickel and sounds better as a plate choke than as an interstage to my ears. Got some more volume and much cleaner sound with more detail and dynamics - well worth while. This is direct coupled to the 31s, which have a LL1660/PP to the 2a3s. So far this is the best amp I've made. I'm looking forward to optimising it.
I tried the UcD 400 but could only get one of my two modules to work. Have you seen the UcD180 Hybrid thread on this site? You bypass the input stage with tubes and just use the output section. This has a balanced input impedence of 1.8K so needs a bit of thought about driving it. Guido Tent has working versions for sale. I'd be looking to use DHTs with a stepdown transformer.
Andy
Hi Guys,
You might find this new thread interesting:
http://www.diyaudio.com/forums/markaudio/210283-alpair-12p-gen-2-paper-cone.html
Cheers
Mark.
You might find this new thread interesting:
http://www.diyaudio.com/forums/markaudio/210283-alpair-12p-gen-2-paper-cone.html
Cheers
Mark.
Using Alp 12 with Hypex UCD180HG modules. I am very happy. Very detailed and transparent midrange and airy top, plenty of treble extension. There is impressive bass weight in tracks that have it. Also trying Banglacx's MarKen7.3 this afternoon. Similar impressions - the amp matches well with these drivers.
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