Question on PMC and changes done to + version

SashaV · 19th February 2006, 10:27 PM

Since there is a lot of DIYs here, I would think some would be able to comment on this.
I am considering to buy PMC FB1+ (new version with soft some tweeter), but could not hear it amywhere, only the older FB1 version.
From what I understand, FB1 had 3kHz crossover point and 2nd order crossover.
With FB1+, a new tweeter was introduced and crossover point was moved to 2kHz.
Does anyone know if the slope remained the same, or it is now 4rd order?
From what I have read, the new tweeter is not the best one out there (better then the old one, but still not capable of going to extreme lows), so I was wondering if the new tweeter is forced to run too low, and consequenty produces larger amount of distortions?
Is it possible that PMC had made modifications to achive better off-axis response at the expense of tweeter distortions?
I would think so, if crossover remained 2nd order, tweeter would be forced to work at too low frequences?
Should I stay away from it?

Tenson · 19th February 2006, 10:33 PM

A lower crossover point is better IMO. You get a more ideal point source, faster response etc...

I have the PMC AML1 (for sale actually, let me know if you are interested!) I find it works brilliantly using a crossover of 1.4KHz. It has the same 34mm tweeter they use in the active BB5 and MB2.

It has to be said though, not many commercial speakers use really good drivers. Especially tweeters. That doesn't mean they sound bad though.

SashaV · 20th February 2006, 02:10 AM

Tenson,

Thank you for the offer, but I think I will consider only FB1+ (if it does not turn out that my concerns are valid).
I found FB1 perfect in every way with the exception of that metal dome tweeter, so I was hoping that with FB1+ they did not mess things up by lowering crossover and keeping 16dB/oct..
It is interesting that AML1 is crossed at 1.4kHz, but then again it has 24dB/oct (4th order) crossover.

SashaV · 20th February 2006, 06:12 PM

Ok, here is the story.
Tweeter on paper has resonant FQ at 650Hz, but reportedly they measure around 900Hz to 1kHz.
So, is it good design to have such tweeter crossed at 2kHz with 12dB/oct crossover?

Tenson · 20th February 2006, 06:18 PM

Sounds perfectly fine to me. It is good practice to cross at least 1 octave before roll-off so it seems they have done this and with a 12dB per octave crossover that’s not too bad at all. A higher slope would probably be better but anything more than 2nd order is quite tricky to do passive so I am told.

19th February 2006, 10:27 PM	#1
SashaV diyAudio Member Join Date: Feb 2006 Location: Toronto	Question on PMC and changes done to + version Since there is a lot of DIYs here, I would think some would be able to comment on this. I am considering to buy PMC FB1+ (new version with soft some tweeter), but could not hear it amywhere, only the older FB1 version. From what I understand, FB1 had 3kHz crossover point and 2nd order crossover. With FB1+, a new tweeter was introduced and crossover point was moved to 2kHz. Does anyone know if the slope remained the same, or it is now 4rd order? From what I have read, the new tweeter is not the best one out there (better then the old one, but still not capable of going to extreme lows), so I was wondering if the new tweeter is forced to run too low, and consequenty produces larger amount of distortions? Is it possible that PMC had made modifications to achive better off-axis response at the expense of tweeter distortions? I would think so, if crossover remained 2nd order, tweeter would be forced to work at too low frequences? Should I stay away from it?

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19th February 2006, 10:33 PM	#2
Tenson diyAudio Member Join Date: Feb 2006 Location: Kent	A lower crossover point is better IMO. You get a more ideal point source, faster response etc... I have the PMC AML1 (for sale actually, let me know if you are interested!) I find it works brilliantly using a crossover of 1.4KHz. It has the same 34mm tweeter they use in the active BB5 and MB2. It has to be said though, not many commercial speakers use really good drivers. Especially tweeters. That doesn't mean they sound bad though.

20th February 2006, 02:10 AM	#3
SashaV diyAudio Member Join Date: Feb 2006 Location: Toronto	Tenson, Thank you for the offer, but I think I will consider only FB1+ (if it does not turn out that my concerns are valid). I found FB1 perfect in every way with the exception of that metal dome tweeter, so I was hoping that with FB1+ they did not mess things up by lowering crossover and keeping 16dB/oct.. It is interesting that AML1 is crossed at 1.4kHz, but then again it has 24dB/oct (4th order) crossover.

20th February 2006, 06:12 PM	#4
SashaV diyAudio Member Join Date: Feb 2006 Location: Toronto	Ok, here is the story. Tweeter on paper has resonant FQ at 650Hz, but reportedly they measure around 900Hz to 1kHz. So, is it good design to have such tweeter crossed at 2kHz with 12dB/oct crossover?

20th February 2006, 06:18 PM	#5
Tenson diyAudio Member Join Date: Feb 2006 Location: Kent	Sounds perfectly fine to me. It is good practice to cross at least 1 octave before roll-off so it seems they have done this and with a 12dB per octave crossover that’s not too bad at all. A higher slope would probably be better but anything more than 2nd order is quite tricky to do passive so I am told.