Hi all, I have been playing around with 2.5way crossover design. I am relatively happy with my desired flat modeled response. But, I am a little concerned with the crossover point for the lower driver. It crosses the tweeter at ~1110hz. The Fs of the tweeter is 710hz. This is a 2nd order lowpass, so the crossover should be no lower than 1420hz for this tweeter. However, this is a 2.5way design, so I am wondering if I am safe since the lower drivers lower cross won't be an issue since it is at much lower spl, and the higher driver crosses at 1646hz, which well above that 2x rule.
Any thoughts?
Any thoughts?
Looking at your graph, I'm not sure that the crossover point is so low, it seems a bit higher than what you think. Invert the tweeter and post again.
Anyway, Fs of a tweeter isn't the sole characteristics for deciding a crossover point, it also depends on the acoustic slope, the SPL needed (in other words, attenuation needed), and distortion profile. What tweeter are we talking about?
Ralf
Anyway, Fs of a tweeter isn't the sole characteristics for deciding a crossover point, it also depends on the acoustic slope, the SPL needed (in other words, attenuation needed), and distortion profile. What tweeter are we talking about?
Ralf
Did you take baffle step into account? Possibly made measurements of the drivers in the enclosure?
the lower (green) driver does technically also cross over to the tweeter, but the main and relevant crossover point is between midbass (blue) and tweeter, thus around 1,7 kHz which should be ok if you don't push the speaker hard.
If this is supposed to be a true 2.5 way design, then you should try placing a single coil between the two woofers and have it tandem off for the upper crossover point. This will be a whole lot easier to blend in Phase wise. Giving the second woofer its own crossover uses more parts and isn't as effective.
You don't want to skimp on the first LP inductor in line feeding both drivers, as this one tends to be a cored inductor which will see alot of current and be subject to inducing early saturation distortion at higher playback levels.
I did start the lower woofer fade starting at the calculated baffle step. I am still in the planning stage and have yet top take measurements of the speaker in the enclosure. This is more of a theory question for 2.5way MTM setups on what is too low for the low driver to crossover.
That is good to know. But what do you mean if I push it too hard? I would like to have the capability of pushing the speaker as far as reasonable, and I thought being more than 2x the Fs of the tweeter (710hz) I should be in the green. Is that not so?
I am not as familiar with what to look out for with phase. The main thing I know to look for is that all phase reversals should fall within the crossover area. Which I believe these are. Anything else to watch for?
Is there a reason to try for 1st order cross with the lower driver over a 2nd?
I did try to start the fade of the lower driver at around 530hz which is what I calculated the baffle step to be. (I have not taken enclosure measurments yet, I am more looking to get the theory of 2.5way MTM down first).
I do have have an inductor for each driver. I am a newbie here, so am I missing something? I do plan on using closer to mid grade components if the budget will allow if thats what you mean.
Below is with the tweeter inverted and it shows a large drop over the crossover point which I believe means the phase is aligned well, correct? I am using DA RST28F-4 tweeter.
I am unsure of what you mean by this design wise. I have searched as much as I could for crossover design and can't seem to find what you mean. Can you give me an example so I can understand better?
Historically -35 dB @ Fs for high power apps (no clue WRT today's mega power apps) with HIFI/HT 'high power' apps 'just' -24 dB IIRC: 2x Fs/4th, 4x/2nd, 7.1x/3rd, 16x/1st.
re:'reason to try for 1st order cross with the lower driver" - it's easier & cheaper - the purpose of the lower woofer is usually to deal with baffle step, above that it simply doubles the top woofer, so 2nd order is to be avoided.
re: Wolf's placement of inductor, there are two places it can go, directly off the input, or following the inductor to the top woofer, which allows a smaller inductor to be used (the lower has the value of the top inductor subtracted), but I doubt you'd save much, so prefer the first way.
re:'theory of 2.5way MTM' - it's either a 2.5 way OR an MTM, a 2.5 way MTM would have 2 mids AND at least one extra woofer, so my '2.5way MTM' has 2x6" mid-woofers in the MTM section, and 2x6" woofers in the .5 way section. I suspect that trying to do it with only 2 mid-woofers will stuff up the MTM lobing.
re: Wolf's placement of inductor, there are two places it can go, directly off the input, or following the inductor to the top woofer, which allows a smaller inductor to be used (the lower has the value of the top inductor subtracted), but I doubt you'd save much, so prefer the first way.
re:'theory of 2.5way MTM' - it's either a 2.5 way OR an MTM, a 2.5 way MTM would have 2 mids AND at least one extra woofer, so my '2.5way MTM' has 2x6" mid-woofers in the MTM section, and 2x6" woofers in the .5 way section. I suspect that trying to do it with only 2 mid-woofers will stuff up the MTM lobing.
You are not taking the baffle into account. It shows because your upper cross should not have the 4dB peak at the knee inposed by the filter. If in testing you would be aiming for a reverse baffle shape, or alternately faking the baffle step in the driver responses or simulating it or measuring it.
Tweeters usually have tight thermal and mechanical limits due to small thermal mass and small diaphragm combined with low xmax. In addition tweeters usually only have a single suspension (surround, no additional spider), as far as i know this is the reason why they should not be driven near fs to avoid wobbling motion.
when getting near the mechanical limit distorsion will rise rapidly, so you should be able to hear it.