I got the idea to build a large, DSP controlled 3 driver 3 way speaker by using a 18" woofer (namely the Faital Pro 18FX600). The midrange driver needs to be used from 400 Hz, otherwise it's distortion is high. My initial problem is the 18" seems to resonate/distort if I run a sine-sweep in free-air mode. My Eminence Kappalite 3012LF doesn't acts like this. But recently read somewhere a similar problem, and when the 18" was secured to a baffle/box, the distortion had gone.
The 18FX600 is a relative low Mms 18" with not too high Le, so I thought it may be usable up to 500 Hz, where it not beams yet, according to the factory off-axis response.
Does anyone have experience with large woofer free-air distortion that gone away when the driver is secured to a box?
I tried the smaller brother 15FX560 which have very good reputation amongst builders and that woofer also sounded distorted in free-air.
Any replies appreciated!
The 18FX600 is a relative low Mms 18" with not too high Le, so I thought it may be usable up to 500 Hz, where it not beams yet, according to the factory off-axis response.
Does anyone have experience with large woofer free-air distortion that gone away when the driver is secured to a box?
I tried the smaller brother 15FX560 which have very good reputation amongst builders and that woofer also sounded distorted in free-air.
Any replies appreciated!
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Many 18s can work that high but consider box resonances\nodes. Here's a calculator: http://mh-audio.nl/Calculators/standingwaveinbox.html
You'll want to crossover below the first node. For an 18 in a 6-10 cubic foot box that'll probably be below 400hz.
You'll want to crossover below the first node. For an 18 in a 6-10 cubic foot box that'll probably be below 400hz.
Yes, but the woofer would be placed exactly halfway of the largest box dimension, so the first mode would not be a problem. The other modes are about 400 Hz and these can be mitigated with adequate damping material.
Ohh, btw the woofer would be placed exactly at the halfway of the box width, so the second mode would be not a problem. Only the mode of the smallest dimension would be a problem, but that would be over 400 Hz.
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The box only loads the driver to its upper mass corner (Fhm) where T/S theory peters out, i.e. 40 Hz Fs, 400 Hz Fhm:
Qts': 2*Fs/Fhm = 2*40/400 = 0.2 Qts', so after factoring in VC heating its Qts' might can only come close with a huge field coil motor and/or need a low inductance for wide range.
(Qts'): (Qts) + any added series resistance (Rs)
Qts': 2*Fs/Fhm = 2*40/400 = 0.2 Qts', so after factoring in VC heating its Qts' might can only come close with a huge field coil motor and/or need a low inductance for wide range.
(Qts'): (Qts) + any added series resistance (Rs)
While the "motor strength" is not exceptioally high, it is adequate.
What it does have is the low TCR" voice coil wire to significantly reduce the effect of voice coil temperature/ power compression. Along with the increased cooling area of dual coils.
The effect is visble in the M2, 4367 and S4700's impressive power compression measurements.
And well behaved impedance control comes from the differential drive.
Along witha fairly low inductance.
The M2's bottom end is eq'd. The S4700 is more representative of the woofers low end performance without a digital boost on the low end.
As for a 18" taken high, the old big clasic JBL monitors used the 2245H up to 290hz. Design wise is worth a look.
Faital's 18FH500 does perfrom well fairly high.
TAD TL-1801.
JBL 2245H, 2241H does okay.
AE TD18H is frequently mentioned for the use, bottom might need some EQ.
Beyma has some woofers with low" inductance, and a very linear imepdance curve, along with fairly well behaved response.
Cant talk about the 18FX as i am not familiar with it.
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It was just an example for you/folks to either find the necessary Qt' or calc the chosen driver's FHM such as the JBL and it doesn't have box loading to 800 Hz either; to the 1st approximation it will be whatever its Fhm is, but what it does have is sufficiently low inductance for its design.
Okay, it seems the Faital 18FX600 is noisy. It's not as bad as when the voice coil is rubbing but similar, even at 1-2 mm excursion. The noise comes from the motor and/or spider, not from the cone. The noise is like rustling combined with some rattling, although this is still in free-air without box.
Does anyone experienced similar phenomenon with other woofers? I bought these brand new by the way and I didn't damaged them. Might even be VC rubbing from the factory?
Does anyone experienced similar phenomenon with other woofers? I bought these brand new by the way and I didn't damaged them. Might even be VC rubbing from the factory?
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Could be forced air cooling causing the noise. Some woofers aren't suited for open baffle because of this.
B&C 18PS76 is very quiet in open air....Eminence NSW6021 has lots of noise outside the box.
I use manual sweeps starting at 1hz when trying to narrow down noise sources.
B&C 18PS76 is very quiet in open air....Eminence NSW6021 has lots of noise outside the box.
I use manual sweeps starting at 1hz when trying to narrow down noise sources.
Have about the same plan for my project, but not using DSP and "only" up to 300-320 hz if it works.
Was thinking on using Faital Pro 18XL1600 driver because i have 4 of them in sub´s i don´t even use.
But don't know if they can play up to about 300-320 hz well enough and it´s a 13 kg beastdriver.
Wanted a driver with a little softer suspensionand (rms) and about max power about 5-600 watt, but don´t afford new drivers.
Regards John
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I think that woofer can be used up to 300 Hz or even higher, inductance is not high, frequency response is acceptable for passive filtering.
I almost sure, that noice will not leave the box, and stuffing eat that noice easy.
Regards John
I did some tests with the two 18FX600. It seems like not just the cooling produces noise, but also something else, maybe the spider. This is different than the air whistle noise and not generated by high excursion but high frequency. Here is a short recording, 20 cm in front of the cone, 500 Hz LR4 low-pass, woofer in free-air, all electrical connections are secure, the noise is coming from the woofer, not from the environment.
https://drive.google.com/file/d/1DqhJi1q3rB1YJJLXHdG3xNSKzcrtLaJD/view?usp=drive_link
What do you think, would a box block this noise?
With 100 Hz LR4 low-pass, the noise is much quieter.
https://drive.google.com/file/d/1DqhJi1q3rB1YJJLXHdG3xNSKzcrtLaJD/view?usp=drive_link
What do you think, would a box block this noise?
With 100 Hz LR4 low-pass, the noise is much quieter.
Once you install a woofer in an enclosure, the airflow noise should greatly drop and remain low down to the lower cutoff, where it unloads and noise / HD increases again. The lack of pressure balance in the VC gap, when a driver is played in free air, is the source of most excursion induced noise. Decrease in pressure difference means lower airflow velocity, hence less noise. There are very few drivers which are very quiet in free air. The ones which are quiet in free air usually have higher Qts, thanks to a wider VC gap.
400 - 500 hz is no problem for most 18" woofers. The only issues you may encounter running it that high are enclosure resonances, which can be hard to tame, especially port noise, modes and midrange leakage out of the ports.
Thanks profiguy!
So the airflow noise of the cooling is probably not an issue once the driver is in box.
But what about the high frequency induced buzz/rattle? This probably comes from the spider and it's slightly louder and than the airflow noise. This will not comes through the cone if the driver is boxed in?
Other than these noises in free-air, the driver sounds and measures good.
So the airflow noise of the cooling is probably not an issue once the driver is in box.
But what about the high frequency induced buzz/rattle? This probably comes from the spider and it's slightly louder and than the airflow noise. This will not comes through the cone if the driver is boxed in?
Other than these noises in free-air, the driver sounds and measures good.
I did a temporary enclosure for the woofer, filled with fiberglass damping mat and it seems like the noise (not the cooling airflow noise) comes through the cone, although maybe not as loud as in free-air mode. I also gently wiggled the lead-in wires, but it didn't make any difference.
Btw did anyone listened the recording from post #17? The noise is similar like when an electrical connection is unsure. It's very annoying, especially because I can't detect where it originates. The trigger isn't the high excursions, but the higher frequencies, and to my ears it doesn't change linearly with volume change.
What this could be?
Btw did anyone listened the recording from post #17? The noise is similar like when an electrical connection is unsure. It's very annoying, especially because I can't detect where it originates. The trigger isn't the high excursions, but the higher frequencies, and to my ears it doesn't change linearly with volume change.
What this could be?
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