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Old 3rd August 2013, 09:14 PM   #21
tinitus is online now tinitus  Europe
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Robbintip

your project seem to be a 3way xo
is it relevant to the servo sub topic ?
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Old 3rd August 2013, 11:15 PM   #22
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Yes, one of the channels is a servo controlled sub channel.
It is a new version of the still popular Philips mfb or motional feedback speakers from the 1970's.
some diy people from Holland are giving the concept new life.
more info here:http://mfb.piratelogic.nl/data/docs/537.usermanual.pdf
there are even scanned original servicemanuals which explain the workings on the homepage of the forums I just posted.
This should help a lot.
They are currently sourcing customized accelerometers for use with any woofer. The originals are not availeble anymore.
I have 8 of the 8" mfb woofers laying here for my next project
I also have 2 pairs of working mfb 544 speakers.
I am now typing from my phone but if I read your posts tomorrow maybe I can help with translating some stuff that Google messes up in their transl.

greetings
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Old 4th August 2013, 04:58 PM   #23
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Here we go again (in Robbintip's link... as far as I'm able to read it), the usual MFB story: how to make poor and small drivers/enclosures produce OK bass.

That is a worthy challenge for Philips and audio businesses. I wish them luck.

But at DIYaudio, we're trying to take good speakers and make them better with MFB. So the techniques that can improve poor and small bass boxes may or may not be directly applicable here, except as inspirations.

Ben
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Old 4th August 2013, 06:49 PM   #24
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Quote:
Originally Posted by bentoronto View Post
But at DIYaudio, we're trying to take good speakers and make them better with MFB. So the techniques that can improve poor and small bass boxes may or may not be directly applicable here, except as inspirations.

Ben
When did they appoint you a director of R&D here?
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Old 4th August 2013, 07:13 PM   #25
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Quote:
Originally Posted by 454Casull View Post
When did they appoint you a director of R&D here?
Is there anything substantive and direct in the mildly-stated quote of mine that you'd like to comment on? Was I too harsh - even judgmental - in saying, "may or may not" or maybe you took serious offense when I suggested the work could be an inspiration to others?

Or do you just have a great need to surly ventilate today on this forum?

Well, I DEFINITELY and TRULY believe that work may or may not be useful and I DEFINITELY feel it might be inspirational. And I'll stick with those views.

Ben
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HiFi aspirations since 1956

Last edited by bentoronto; 4th August 2013 at 07:19 PM.
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Old 5th August 2013, 02:31 AM   #26
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Quote:
Originally Posted by bentoronto View Post
Is there anything substantive and direct in the mildly-stated quote of mine that you'd like to comment on? Was I too harsh - even judgmental - in saying, "may or may not" or maybe you took serious offense when I suggested the work could be an inspiration to others?

Or do you just have a great need to surly ventilate today on this forum?

Well, I DEFINITELY and TRULY believe that work may or may not be useful and I DEFINITELY feel it might be inspirational. And I'll stick with those views.

Ben
A totally pointless comment.

regards
Trev
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Old 5th August 2013, 04:57 PM   #27
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I understand that you are not able to completely understand the dutch text completely.
By saying MFB only makes small woofers sound OK, you are wrong.

MFB does a couple of things.
The first thing is making the woofer follow the exact input signal, and thus making it sound better than only the woofer being fed by an amplifier, in a normal way.
This is the part you want to use I understand, make the woofer replicate the exact input signal.

Then, to achieve monstrous bass from a small woofer, the input signal is corrected (before amplification) to compensate for the woofer's roll-of. Every woofer in a box has a roll-of at the low end. It doesn't matter if the box is too small or not, you will simply compensate more or less for this.
If a woofer has a -3db roll-off from 60 hz and down, you will essentially make a filter that adds +3db from 60Hz and down. This is the clever part that makes a small woofer sound big. To go more in detail, a rumble filter is needed, because it will try to produce even 2Hz signal at audible levels, frying your woofer by doing so.

The first part of the MFB workings, the correction circuit for the woofer making it duplicate the input signal rather than just having a go at it, is the part you would most likely use.

The second part however, is also interesting. When you modify the rumble filter of the newer 587 MFB's, you will get distortion-less (thus color-less) f3 25Hz sound. You see the 8" woofer in a 25L box (bigger than the 8L box of the first types) work very hard.
The result is astonishing. You can hear frequencies normally only produced by big 12" subs, played effortless, clean, and non-colorated. When you hear these speakers play, YOU WILL **** BRICKS!!! Really, if you haven't heard them, you don't know what I mean.
The limit is the Xmax and amp power.
If you for instances have high enough Xmax and power on a 12" subwoofer, you will be able to get the sound of a 21" sub. I am not joking, this is for real!
The sound produced is fast and clean because you will have a small mass, but still can reach deeper and cleaner then you would ever imagine coming out of your trusted speakers.
If used right, and not playing at extreme levels, you will get enough deep bass from 8" tower speakers to eliminate your 12" subs.

Then there is more.
MFB speakers are actively crossed over (full 3-way in the later series) and using a subtractive filter. They are fase corrected as well.

There is more to this speaker than just making a small woofer sound OK.
MFB 545 12" studio monitors for example produced the deepest sound from a 12" at that time without using ports/TL.

The deep bass then is not affected by the small box, because the correction circuitry simply makes the woofer follow input signal rather than be affected by box dimensions. Normally you would have the least colored sound at the tuning frequency of the box. This is not so with MFB, it doesn't have colored sound at low frequencies at all.
The advantage of this is you can have correct sounding bass at low frequencies, without having to use a port or a TL with their disadvantages such as steep roll-of, muddied, less tighter bass, coloration, name it all.
The disadvantage is that you will at some time reach your Xmax when tuning them lower and lower.

I have seen that one set of MFB's, old style (8" woofer in 8L cabinet) can vibrate my wall and dropping my pictures/clocks/paintings from it, while the bass was to low to actually hear. You really have to hear them to understand what I mean.
By saying it is just sounding OK, you are undermining it. I have never heard ANY sub (and I heard a lot) producing cleaner bass than controlled woofers like MFB.
If you refer to the whole speaker as sounding just OK, you are right. Over 150Hz, MFB woofers can sound colorated (hey, 1976...) also, the mids, tweets and the high amp are not top notch. This has several causes, first, it was 1976, second, they were made to not be expensive speakers that no one could afford. They were made for men that wanted big speakers sound, but had wifes that only would take small speakers in their living room. The speakers are therefore full of compromises.
By eliminating WAF, going past the compromises and use todays drivers and technology, you can create something that simply no company offers.

Philips is no small fish in the audio world. The only thing is that they made their stuff for regular consumers, not for audiophile, piles of money spending people. They had B&O to do that for them back then, also Marantz originated a lot of equipment from them back than, as were lots of others.

Phlips first mass produced the light bulb, but also made the first Hi-Fi speaker. They invented dome tweeters, dome midranges, they were first at producing a speaker with correction circuit for the woofer at mass production, they invented the compact cassette, the CD, the DVD, and lots of other stuff you use on daily basis.

I'm not saying Philips is the best, I only highly recommend to dive in a little deeper on these MFB speakers. They do exactly what you want (and a little more as well). I see you are open minded about this, that is why I regret it so much that all this information is in Dutch, as it is difficult to translate.

When you hear a corrected woofer play for the first time, you will be blown away! I sincerely hope you will finish your project and come to a nice result.

I would strongly advice you to buy a set of these speakers second hand (revised ones!!) and hear for yourself. If you even remotely like it, I would suggest going on with your project, and believe me, you will.

Greetings.
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Old 5th August 2013, 05:59 PM   #28
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1. No one is a bigger or more frequent advocate for MFB than me, as you may have noticed over the past few years. I experimented with it first around 1967 and had MFB in my woofers for many decades although not recently. But thanks for your sermon anyway.

2. Yes, Philips are swell folks.

3. I am glad your results with little drivers are so encouraging. Of course, that kind of "progress" making small speakers better with MFB has been published for half a century or more, if you will check your history. I hope will all will live to hear rooms shaking from an 8-inch driver. It would be wonderful to have more excellent small speakers of the sort you advocate and the sort that experimenters on this forum typically use for initial testing. I actually believe MFB R&D should be especially focused on extra-small drivers (making 2-inch drivers listenable).

4. Judging as best as I can from close attention to purposes of posts at DIYaudio, I continue to think people here want to see some R&D making large good-quality woofers even better, not small speakers tolerable (as has been proven for half a century already....). Please.

Ben
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Old 6th August 2013, 05:57 AM   #29
superR is offline superR  Netherlands
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Quote:
Originally Posted by bentoronto View Post
4. Judging as best as I can from close attention to purposes of posts at DIYaudio, I continue to think people here want to see some R&D making large good-quality woofers even better, not small speakers tolerable (as has been proven for half a century already....). Please.
I think MFB is great for BOTH small 6 inch woofers AND >10 inch (sub)woofer usage.
If you push a 6 inch woofer to the limit to get some 30-40 Hz SPL, this will cause distortion. What does MFB do? Attempt to lower that distortion, because it is a disturbance compared to the reference.
If you push a 12 inch sub to the limit to get some 15-20 Hz SPL, the same holds.

Anyway; Back on-topic!
Armand, any news?

Last edited by superR; 6th August 2013 at 06:12 AM.
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Old 6th August 2013, 10:36 AM   #30
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Hi Armand,

This is Jac Brown who you referred to in the first post regarding the audioexpress article. I have been hanging around diyAudio forums as lehmanhill.

I stumbled across your thread while searching for something else. I'm no expert, but maybe I can contribute some of my experience with servo subwoofers to this thread. I am just back in town from a trip, so I need to do some catching up with life and your thread, but I will check back in when I catch up.
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