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Starting a new project out of a pair of 104ab's
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Mike G
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PostPosted: Sun Apr 05, 2009 11:29 pm    Post subject: Starting a new project out of a pair of 104ab's Reply with quote

This is my first post here so hi to all.

I have owned a pair of 104ab's for about ten years now. The tweeters have long since gone. Last week I realized that I had a pair of Kef Coda7's kicking around so the tweeters where moved to the 104's just for fun. They sound pretty good but are to loud due to sensitivity. The B200's and the passive radiator are in good shape and ready to go.

I have looked at the Wilmslow Audio page and they recommend the Scanspeak D2905/9500 as there hi end replacement driver for the T27. I did a little looking around and they seem to get positive feedback. Anyone here know of a driver that might work better? I read somewhere this week (can't remember where) that the B200 has nasty breakup frequencies. I only have a vague understanding of what this means but more importantly, if true can this be helped without replacing the driver? I have always liked the full sound of these speakers but I am a little worried about accuracy.

Aonther question has to do with the crossovers. Is there any reason I should replace any of the parts in them if they seem to be working ok? I am concerned that the frequency response is not as it should be due to aging parts.

I am not sure anymore as to how these sounded when I first got them but they seem very dished out in the mids (with the unintended tweeters this is). I remember them being a little shy in the mids but compared to the Adam A7's that I have them sitting beside it is so extreme that I wonder if there is a problem.

This could be a topic on it's own but I thought I would throw it in here. The fact that these speakers are not mirrored. This has always bothered me. I will eventually be using these as studio monitors for mixing music. They will be very close to me in my new studio due to space issues. I am worried about phase and sound stage issues. Are the woofers off center to help cancel standing waves within the cabinet? It is the only reason I can think of for this. I have been thinking that I might build new front panels to reconfigure the drivers into a mirrored configuration . I was also thinking that I may want to move the tweeter between the B200 and the passive radiator because I will need to have them on there sides and it would help balance the frequency response across the front surface. I am concerned that moving the B200 would cause phase issues with the passive radiator. Anyone Know if this would be the case?

I know that this is a big post with a lot of questions but I have been mulling all this around for quite some time. Thank you to all that reply. It is great to find this place.

EDIT: Made it easier to read Embarassed
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speakerguru
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PostPosted: Mon Apr 06, 2009 10:11 am    Post subject: Reply with quote

Hi Mike G, by a strange co-incidence the lead designer on the 104 and 104aB was Mike Gough!
The 104 was designed on the tweeter axis without the picture frame around the outside. Most design work was done indoors at 1m using B & K warble tone and when the weather was fine, additional measurements were done outdoors at the top of a 10m cherry picker pole with the mic at 2m. The high and low pass filters being third order Butterworth (acoustic NOT electrical), the woofer and tweeter only add up correctly (in quadrature) on the tweeter axis around 1 to 2m distance. If you go one way off axis you get a peak at crossover and if you go the other way you get a dip. If you re-arrange the B200 and tweeter all bets are off and you are on your own. The B200 and BD139 are close enough at low frequencies to do what you like.


Last edited by speakerguru on Fri Apr 10, 2009 11:05 am; edited 1 time in total
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Mike G
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PostPosted: Mon Apr 06, 2009 2:48 pm    Post subject: Reply with quote

Hi Speakerguru
Interesting about the name coincidence. Maybe that is why I like these things so much Smile
Thanks for your reply! I have to admit that much of what your saying is going over my head. I understand the measurement explanations interesting and good to know.
You loose me when you start explaining that the crossover is third Buttworth (acoustic NOT electrical). I understand filter curves from mixing audio. I do not understand however the crossover is acoustic not electrical, as well as quadrature.
Are you saying that where the T27 sits in relation to the axis to the B200, and beyond that the placement of the B200 in relation to the bass reflex is critical to the frequency response due to phase cancellations or some other factor that I am missing? Phew that is quite the sentence.

Let me put this in the form of a couple of questions. Two scenarios here. If you can tell me if I would encounter problems or not I would be VERY appreciative!
1. Make two new front panels with the exactly same layout except mirror the two speakers.
2. Create new front panels where the BD139 remains in the same place. The T27 moves to the middle but at the same point off axis as intended. Then move the B200 to the far end but keeping the same exact relationship to the T27 and the walls of the cabinet.

I hope that is clear. In essence I would like to flip the T27 and the B200 around but keep there relationship to the axis the same, mirrored.

Again thanks for your feedback.
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ColinR
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PostPosted: Tue Apr 07, 2009 1:42 pm    Post subject: Reply with quote

Scenario 1. making mirror image baffles would not encounter any problems other than potential splinters and solder burns Very Happy .

Scenario 2. making a Calinda lookalike with a 104 width baffle not to upset the TS parameters might also be a goer.

So why not make one split baffle so that you can rotate the B200/T27 bit through 180 degrees and have a listen, the only design inconvenience would be an additional wider stengthening divider to accomodate two screw/glue lines.

Find which orentation suits your application and do the other speaker.

Just a thought as the 104/104aB kits had the T27/B200 and crossover mounted on a piece of wood and the BD139s were loose.
Never seen the construction sheet for the 104/104aB, so I don't know if it contains any dire warnings about baffle orientation Very Happy .
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Mike G
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PostPosted: Wed Apr 08, 2009 1:40 am    Post subject: Reply with quote

Hi Colin

Thanks for your feedback. I am thinking that I will (at some point) move the b200 to "top" of the cabinet and leave it on it's current axis. I will move the T27 replacement to the model of the cabinet keeping it on it's current axis and the same distance from the B200. The only thing that I can see bunging me up with this is the relationship between the B200 and the BD139. I don't think that there would be a problem though as the cabinet uses no form of transmission line. The pressure should remain consistent throughout the cabinet, more or less. I could be wrong though. I wonder if speakerguru would have any input on this one, nudge nudge wink wink Smile

I was not aware of the the Calinda design. That is pretty much what I am doing. As for how the 104ab is put together. The B200 is just screwed in the front, easy to remove, the crossover is bolted to the switch on the front, Comes out easy. The BD139 also pops out with a screwdriver. All easy easy.

I have been starting to think about how I would do the baffle. I figure that I would not be able to get the existing baffle out without doing serious damage to the inside edge of the cabinet. Not something that I want to get into. I am thinking that I will simply cut out the existing baffle leaving a small amount in place for screwing in the new baffle. I would then have to fill in the space of the old baffle by having the new baffle be twice as thick. Where the top face would in essence be the "mounting face" and the inner being the "filler". I was toying around with filling the inner space with either plaster or concrete to attempt to kill surface resonance. I know there is a re-enforcement somewhere in there but I can't remember exactly where it is. I am going to take a look tonight.
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speakerguru
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PostPosted: Wed Apr 08, 2009 2:56 pm    Post subject: Reply with quote

Mike G wrote:
The pressure should remain consistent throughout the cabinet, more or less. I could be wrong though.

No, you're not wrong. Over the operating range of the passive radiator, the box is a pure acoustic compliance and so the pressure driving the PR will not change substantially with position.
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Mike G
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PostPosted: Wed Apr 08, 2009 7:17 pm    Post subject: Reply with quote

Thanks speakerguru, again appreciated. Can anyone tell me if the crossover in the 104 should be refurbished or not? I know some parts age and others are more stable.

I am also wondering if anyone would be willing to offer opinions on where they feel the B200 lands on the current driver market in terms of sound quality. What is compatible in todays market?
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speakerguru
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PostPosted: Sat Apr 11, 2009 10:13 am    Post subject: Reply with quote

The B200 SP1039 was a pretty special driver. It has the short coil, long gap motor magnet configuration. This costs more but gives low distortion. I don't know if anyone else makes such an 8" unit.

Bipolar electrolytic capacitors can change value and loss factor with age. Check with a meter first rather than change them willy-nilly. N.B. KEF used to match capacitors within 1% but up to 10% away from the printed value (so you may have to use multiples in parallel to get within 1% .) Don't replace with non-electrolytics unless you use equilvalent series resistance or are prepared to put up with the change in response.
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Wiesiek Lipowski
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PostPosted: Sat Apr 11, 2009 11:56 am    Post subject: Reply with quote

> speakerguru: Don't replace with non-electrolytics unless you use equilvalent series resistance or are prepared to put up with the change in response>'

I firmly second that opinion.

In my PRO9-TL's I removed all the Alcap electrolytics and put Solens/Teflons in their places. Even the shunt woofer caps are now of a film type.

I have ended up with no resistors in the tweeter sections and just 2.4R in the mid section.

None of the inductors have been changed.
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Mike G
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PostPosted: Sun Apr 12, 2009 5:20 am    Post subject: Reply with quote

Hey guys thanks for the feedback. I took the advice of taking readings. When I pulled out the crossovers I was a little surprised to find that some of the parts had been replaced already. I now remember that when I bought them I had been told but ten years ago I did not care.

This image shows what has been replaced, not sure that it matters.


I took pictures But I don't have them uploaded yet. I would love to get some feedback on the readings that got. I am a novice when it comes to this element of speakers so please bare with me.

The image (from this site, thanks!)is labeled with the values I got using a meter set to 200ohm. When there are two numbers for one of the caps it is representing the two crossovers. One value is given if they where a perfect match.



I have tried looking at the schematic to figure it out myself but at the moment it makes only a little sense. I hope that this is clear enough, it has been a very long day.

Thanks again for all the input. I want to bring these things back to life.


P.s Wiesiek, what are the tweeters in your DIY speakers? I took a look online and you where one of the first links! I am not stalking you Smile
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Wiesiek Lipowski
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PostPosted: Sun Apr 12, 2009 8:41 am    Post subject: Reply with quote

I built my PRO9 back in 1977. First the tweeters were Audax 12X9D25.

Then I tried Scan Speak 2010, Vifa D27, but was not satisfied with the sound. The treble was too metallic and hard INHO. I would have had to alter the crossover but did not want to get down to this.

Now I use Audax TW025A1. Old HD 100D25's also sound nice, but with TWO25 you can have a spare voice coil (RW025A0).
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speakerguru
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PostPosted: Sun Apr 12, 2009 10:06 am    Post subject: Reply with quote

Mike G wrote:
The image (from this site, thanks!)is labeled with the values I got using a meter set to 200ohm.

Does this mean you used a multimeter on its Ohms range? You need to measure capacitors with a capacitance meter, preferably one which measures loss factor as well as capacitance. An Ohmmeter won't do. Also you should unsolder and lift one leg of each component so that there are no other parallel paths when you make the measurement.
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Mike G
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PostPosted: Sun Apr 12, 2009 2:32 pm    Post subject: Reply with quote

Thanks Wiesiek for the information on the tweeters. I am looking at the Scanspeak D2905/9500 tweeters. It is very odd buying speakers that you ahve never heard. Just a lot of reading.

Speakerguru it is a shame that is the case as I do not own a capacitance meter. So I am walking in the dark at the moment.
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speakerguru
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PostPosted: Mon Apr 13, 2009 12:46 pm    Post subject: Reply with quote

http://www.maplin.co.uk/Module.aspx?ModuleNo=4393

http://www.maplin.co.uk/Module.aspx?ModuleNo=4404

http://cgi.ebay.co.uk/LCR-RCL-INDUCTANCE-CAPACITANCE-RESISTANCE-METER-T86_W0QQitemZ370186061520QQcmdZViewItemQQptZUK_BOI_Electrical_Test_Measurement_Equipment_ET?hash=item370186061520&_trksid=p3286.c0.m14&_trkparms=72%3A1688%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318
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proffski
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PostPosted: Tue Apr 14, 2009 11:39 am    Post subject: Reply with quote

I use a couple of Maplin meters I bought years ago as well as the Peak Atlas modules. Remarkably accurate considering the price!
They are calibrated every 12 months.

http://www.peakelec.co.uk/acatalog/jz_instruments.html
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