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Multi-Way Conventional loudspeakers with crossovers

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Old 22nd January 2009, 05:58 AM   #11
sardonx is offline sardonx  Canada
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I realize this is an older thread, but I've now read in several places people complaining about this hexagrid cover on the H1212. So I'll second ch83575 when he says you can remove it easily (and probably on other seas models). I remember starting to cut the grid around the edges with a pair of small wire cutters. A few seconds later i pulled on it accidentally and the whole thing just came off. So get yourself a pair or small cutters/needle nose pliers, or whatever will grab the cover and just take it out. Be careful and hold a firm grip because the dome (or the grid) is magnetized so the grid will be pulled back towards the dome.. no one likes dented tweeter domes!
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Old 22nd January 2009, 06:33 AM   #12
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I removed the grill on my tbfcg and then removed the phase disk, then replaced the grill for protection, The sound is better than stock, But it sound it's best without the grill.

I think this is one disadvantage of metal domes over soft domes, In that metal dome need the grill for protection, So far I have'nt heard a metal dome that did;nt improve in SQ when the grill is removed.

Another solution is to make a big hole on the center of the grill and then solder 2 thick arched shaped copper wire spaced from the center of the holed grill. Then paint. I tested this on my car audio tweeter , And it works, It protects the metal dome while being acoustically transparent.
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Old 22nd January 2009, 12:03 PM   #13
dlr is offline dlr  United States
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Quote:
Originally posted by marchel
I removed the grill on my tbfcg and then removed the phase disk, then replaced the grill for protection, The sound is better than stock, But it sound it's best without the grill.

I think this is one disadvantage of metal domes over soft domes, In that metal dome need the grill for protection, So far I have'nt heard a metal dome that did;nt improve in SQ when the grill is removed.

Another solution is to make a big hole on the center of the grill and then solder 2 thick arched shaped copper wire spaced from the center of the holed grill. Then paint. I tested this on my car audio tweeter , And it works, It protects the metal dome while being acoustically transparent.
Removing the phase shield is roughly equivalent to adding a slight droop at the top using the crossover. The top end still has the ultra-sonic peak at breakup, but then has the droop in response that had been corrected by the phase shield.

If you were to equalize the response after removing the phase shield to correct for the droop now put back in, the sound would likely be nearly the same as before removal of the shield. The system could easily be designed form the start with a slight slope at the top end without any changes to the tweeter and with similar sonic results.

Dave
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Old 22nd January 2009, 10:36 PM   #14
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Quote:
Originally posted by dlr

Removing the phase shield is roughly equivalent to adding a slight droop at the top using the crossover. The top end still has the ultra-sonic peak at breakup, but then has the droop in response that had been corrected by the phase shield.

If you were to equalize the response after removing the phase shield to correct for the droop now put back in, the sound would likely be nearly the same as before removal of the shield. The system could easily be designed form the start with a slight slope at the top end without any changes to the tweeter and with similar sonic results.

Dave

It doesnt matter and I dont care , All I care about is that It sounds better and more transparent without it.

Correct me if I'm wrong, In my understanding, The phase shield was there to reduce the ultrasonic peak. BUt it also affect the SQ, OTOH, some metal tweets dont have it, and they do fine.
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Old 23rd January 2009, 12:41 PM   #15
dlr is offline dlr  United States
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Join Date: Mar 2005
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Quote:
Originally posted by marchel
It doesnt matter and I dont care , All I care about is that It sounds better and more transparent without it.

Correct me if I'm wrong, In my understanding, The phase shield was there to reduce the ultrasonic peak. BUt it also affect the SQ, OTOH, some metal tweets dont have it, and they do fine.
That's a common misunderstanding. The purpose has nothing to do with the peak, although it does alter it.

The phase shield is in an attempt to reduce the droop in response at the top end of any hard domed driver (mid or tweeter) below the peak. Prior to breakup (below the peak), there is an increasing interference effect due to the time delay between the wave launched near the voice coil and that near the tip of the dome. Hard domes, unlike soft ones, have almost no damping to reduce the output near the tip at higher frequencies. At high frequencies, the short distance from former to tip is significant with regard to wavelength. The difference is a phase shift due to the time delay between the areas. As frequency increases, the constant time delay corresponds to increasing phase shift.

The end result is the droop caused by the increasingly destructive interference. The shield partially blocks the output near the tip, reducing the droop, thus the term phase shield.

Much of the perception of hard domes comes from older drivers and/or cheap ones that had a peak below 20K, not ultra-sonic. Removing the phase shield doesn't significantly alter the peak, but it does slightly roll off the top end, differently for each driver, of course. It is essentially adding EQ to the driver response, not much different than simply designing the crossover from the start to roll off or droop, something I often do even with some soft domes. I usually prefer about a 1db drop from 10K-20k. Flat response is not always preferred.

Also, the smaller the cone diameter and/or the more shallow, the less the effect of the phase delta at any given frequency. These domes have less need of a shield for the audible range.

Dave
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