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Or are the manufacturer's specs in most cases exact enough to base a design on them?
The Panny is putting out 100 watts per channel and has clock upgrades in it. The amp is driving the woofers beautifullly.So far this is really really nice! More on that later.Jeff
Explanation comes via doing and listening, because SPL plots tell you zilch about acoustic phase and relative group delays.
Quote from: John_E_Janowitz on 25 Sep 2008, 02:55 pm Another nice thing is that in the active system you can passively flatten the impedance curve first. Then work with your xover and EQ. You can end up with a nearly resistive load to each channel of amplification. Hi John,My grey cells also lit up when I read that; but I let it ride.Your links and explanation of this in post #48 above are good, and illustrate an aspect often forgotten by those who use passive crossovers. What caught my attention however, was your mention of this in the same paragraph as 'active' filters with implied direct LS to amplifier connection, where, if the amplifier is good and a normal SS type, those impedance correction circuits could not have any influence upon the drive to the LS itself within its own circuit, no matter how accurately the amplifier is being loaded.I much appreciate reading your explanations though.Cheers ...... Graham.
Another nice thing is that in the active system you can passively flatten the impedance curve first. Then work with your xover and EQ. You can end up with a nearly resistive load to each channel of amplification.
QuoteExplanation comes via doing and listening, because SPL plots tell you zilch about acoustic phase and relative group delays.And this is where Alpha 15 significantly outperforms OB15? C`mon, while Alpha 15 is a great value and performs nice, OB15 is pushing limits of what can be done, albeit at a higher price. What you get in return is probably state of the art in current woofer production. The mechanical losses of this driver are the best I`ve seen so far in a 15 inch driver (heck, it`s even better than in many 5 inchers), which promises a "lively" (for the lack of better term) low frequency reproduction. AESpeakers OB15 Fs: 33.8HzQms: 19.4Qes 0.86Qts 0.82Vas 311 LitersCms 0.3 mm/NMms 74 gramsSd 855 cm2Rms .81 Kg/SBl: 7.5 T/mRe: 3.1ohmsZ 4 ohmsLe 0.0375 mHPe (max) 100 WattsPe (transient) 250 Watts1WSpl: 93.5 dB2.83V: 97.6dBLinear Xmax 9 mm (peak)Mech Xsus 12 mm (peak)Quote from: Graham Maynard on 3 Oct 2008, 08:24 amQuote from: John_E_Janowitz on 25 Sep 2008, 02:55 pm Another nice thing is that in the active system you can passively flatten the impedance curve first. Then work with your xover and EQ. You can end up with a nearly resistive load to each channel of amplification. Hi John,My grey cells also lit up when I read that; but I let it ride.Your links and explanation of this in post #48 above are good, and illustrate an aspect often forgotten by those who use passive crossovers. What caught my attention however, was your mention of this in the same paragraph as 'active' filters with implied direct LS to amplifier connection, where, if the amplifier is good and a normal SS type, those impedance correction circuits could not have any influence upon the drive to the LS itself within its own circuit, no matter how accurately the amplifier is being loaded.I much appreciate reading your explanations though.Cheers ...... Graham.Try to use impedance correction circuits in an active (or passive) sytem once and listen to the difference, or just play an MLS signal through the compensated and uncompensated loudspeaker to hear the effects, you`ll be surprised. Cheers, Mirohttp://www.loudspeakers.we.bs/
Each user/designer will have to consider whether the additional money spent is well worth the improvement, consider thisAE driver = $259Alpha 15" = $65
Quote from: ttan98 on 2 Nov 2008, 07:12 amEach user/designer will have to consider whether the additional money spent is well worth the improvement, consider thisAE driver = $259Alpha 15" = $65Last i saw, the OB15 (a variant of the IB15) was $179/ea or $600 for four. The IB15 is $129/ea or $400 for four. Your price is for the Dipole 10, a very different driver.
Some TSPs even change with ambient temperature and humidity
After building we play a 10Hz break-in tone for about 30 sec to break in each woofer. All the breakin required is to stretch the the surround and spider to their limits a few times. This is 95% of all break-in and you won't see much change in parameters after that.
My research has shown that playing them hard for about 30 seconds doesn't contribute to more than 4 to 5% of the total change that you get from an extended burn in period. However, the heat in the voice coil from playing it hard will shift the T/S parameters much further and simulate 50 to 80% of the change that will come from extended burn in. If you really want to see the change in the suspension compliance then you need to let it cool for a couple of hours before checking it.
John, I noticed your new drivers and they look very good. You seem to favor a sealed box method for testing the T/S parameters. Is this the method you use on those woofers with the solid Aluminum phase plug?
This means reaching the excursion limits of the driver. We do it with 10Hz in an open baffle which requires very little power for most drivers to reach the limits. The change we look for is simply the change in Fs.
In the IB15 for example we often times see a 19-20hz Fs, then after the 30sec tone we see it at 16.3Hz or so. Playing the 10hz breakin tone overnight and checking again the next day showed a drop to 16.1Hz.
The only thing to break in on a woofer is the suspension.
Fs is simply a function of mass and compliance so whether the coil heats or not will not have any affect on that anyway.
Measuring an impedance curve before and after the break in tone shows no visible change, other than the shift in Fs.
Measuring the parameters on the drivers with phase plugs is a little tricky. Due to the way a driver like this is designed, there is a small air passage on the ID of the coil.
We can use this known value and apply a correction factor to get valid results. Then we can double check to verify our correction factor by taking a dust capped driver with identical mass and compliance.
Well, 10Hz wavelengths are fairly long and will quickly generate a lot of heat even at low power, and that will change the Fs.
Yep, I believe that. That is about right. However, the change you see after 30 seconds is NOT a result in the change in suspension compliance. At least not all of it. It is mostly from the heat change. Run your 30 second blast then let it cool for several hours and you'll see the difference in compliance change and change from heat. My guess is that you'll see the Fs drop back into the 19Hz range.
No, there are two things changing. There is a mechanical and an electrical change. Both will change over time.
No, that is not true either. Part of the damping is the field strength around the voice coil. Just increase motor strength and and Fs will come up. Decrease it and Fs will drop. Heat it up and Fs will drop. Cool it off and Fs will come up. You might also note that the DCR will change after your 30 seconds of hard play. Try measuring the DCR before and after heating it. Also, if you don't adjust for the change in DCR after heating it then it will also alter the parameters.
I wouldn't expect it to show much else, would you? If you look real close you might see the slight change in the minimum impedance area due to the changed DCR. It may be pretty hard to see on an impedance sweep though.
But you are going to see more differences in parameters by having to allow for and calculate the air loss of the box or the differences between different drivers than you will see from simply using the added mass method to get the measured parameters. So I wouldn't be to hard on the added mass method. If done correctly it too can be very accurate.
