I have a shabby pair of B&O CX50 speakers here. For anyone not familiar they are a small 2 way in an extruded aluminium cabinet. A 100mm paper cone midwoofer and 27mm tweeter with a simple 1st order series Xover.
The Foam rots on these drivers and I'm considering a replacement driver rather than refoam, I don't give a monkeys' about originality. I'm probably going to load a small class D amp board (TPA3116 based in all likely hood, MA12070P or Icepower if I'm feeling fancy) into the back of the enclosure. These are aiming to be small portable speakers, so nearfield/desktop mainly, but with a bit of punch as they may occasionally be small room speakers (may end up in the kitchen to be honest). I'm not looking for 110dB critical listening though.
The cabinet is internally 110mm wide, 155mm deep and 190mm high, 4mm thick aluminium, so 3.25l. I'll chuck some pics up later. The main driver is 90mm dia cutout, 4x110pcd fixing (with some wiggle room) and a square chassis with 98mm sides and 124mm corners. The baffle is a steel bonded in affair so changing it is possible but not straight forward.
So without much thought, I'll probably start looking at:
The 4" dayton drivers RS100, ND105
The Tectonics 65mm BMR
Other drivers people could suggest? I'm happy to consider either full range or 2 way, sealed or ported alignments (for a full range I could port through the tweeter cutout with a suitable PVC tube).
Any thought on other drivers I should be considering, the Markaudios all seem to be for larger cabinets.
The Foam rots on these drivers and I'm considering a replacement driver rather than refoam, I don't give a monkeys' about originality. I'm probably going to load a small class D amp board (TPA3116 based in all likely hood, MA12070P or Icepower if I'm feeling fancy) into the back of the enclosure. These are aiming to be small portable speakers, so nearfield/desktop mainly, but with a bit of punch as they may occasionally be small room speakers (may end up in the kitchen to be honest). I'm not looking for 110dB critical listening though.
The cabinet is internally 110mm wide, 155mm deep and 190mm high, 4mm thick aluminium, so 3.25l. I'll chuck some pics up later. The main driver is 90mm dia cutout, 4x110pcd fixing (with some wiggle room) and a square chassis with 98mm sides and 124mm corners. The baffle is a steel bonded in affair so changing it is possible but not straight forward.
So without much thought, I'll probably start looking at:
The 4" dayton drivers RS100, ND105
The Tectonics 65mm BMR
Other drivers people could suggest? I'm happy to consider either full range or 2 way, sealed or ported alignments (for a full range I could port through the tweeter cutout with a suitable PVC tube).
Any thought on other drivers I should be considering, the Markaudios all seem to be for larger cabinets.
Almost perfect volume for the Mark Audio Alpair 6.2m. No XO needed. What is the diameter of the hole?
dave
An interesting project!
A SEAS 1" tweeter and some sort of 4" paper midbass. 90mm cutout, 110mm PCD on a square frame and 98mm width to work with. Something from 2L to 3.5L closed box. Best placed in a bookshelf for bass reinforcement apparently, though a corner might do.
Series filter, 0.33mH and 6.8uF. Positive polarity.
Bang & Olufsen Beovox CX50 Loudspeaker | Hi-Fi News
I would be interested to know the DC resistance of the two drivers, but shall get modelling. And looking for a driver and at your Dayton RS100 and ND105 prospects. 😎
A SEAS 1" tweeter and some sort of 4" paper midbass. 90mm cutout, 110mm PCD on a square frame and 98mm width to work with. Something from 2L to 3.5L closed box. Best placed in a bookshelf for bass reinforcement apparently, though a corner might do.
Series filter, 0.33mH and 6.8uF. Positive polarity.
Bang & Olufsen Beovox CX50 Loudspeaker | Hi-Fi News
I would be interested to know the DC resistance of the two drivers, but shall get modelling. And looking for a driver and at your Dayton RS100 and ND105 prospects. 😎
I'll leave the fullranger prospects and any crossovery to m'learned friend planet10, Dave. 🙂
I have located a splendid prospect here with the 4" Faital Pro 4FE32-8.
Faital Pro : Faital Pro 4FE32 8 Ohm Faston :: PS18.66
Looks to tick most of the boxes to me! I am sure there is room for a bit of drilling with the 115 mm mounting bolts. We have had a good time lately with Faital Pro drivers. Very efficient at 90dB, flattish frequency response, and the impedance is flatter than most.
I have located a splendid prospect here with the 4" Faital Pro 4FE32-8.
Faital Pro : Faital Pro 4FE32 8 Ohm Faston :: PS18.66
Looks to tick most of the boxes to me! I am sure there is room for a bit of drilling with the 115 mm mounting bolts. We have had a good time lately with Faital Pro drivers. Very efficient at 90dB, flattish frequency response, and the impedance is flatter than most.
I've done it with a pair of CX100 cabinets many moons ago, but honestly I can't remember how. I think I cut the baffles free with a slim blade (?).
Hole is 90mm, would need to shave a bit off/truncate the frame to get the width and height down a couple of mm, and locally increase the size of the mounting hole at the 4 spokes of the basket. But not a big deal to fit IMHO. Looks promising, not a cheap option though, not decided on a budget and no x-over means £££s saved there.
Yep think that would fit, would you go shallow xover and existing tweeter, I'll measure up some driver resistances tomorrow, doubt I will have time to get REW set up, just be stick a fluke on it.
I suspect as much. might bung them in the over at 200DegC for 20 mins and see how they fare. I could just powdercoat if they survive that ok. I'm tempted to sand back the dings and scotch the hell out of the faces to give a brushed look, then get them anodised something unsubtle (green maybe), but would need the baffles out first.
No love for DML driver here then? the Tectonics and Faitals both being about £15 a pop is tempting. Scanspeak Discovery 10s are another option I've not considered, from memory they have a nice (if not particularly cheap) full range driver.
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The problem is the cutout size. The baffles are recessed so the woofer has to fit between the inner walls of the alloy case.
The Dayton ND105 has perfectly placed mounting holes but the frame bulges out too much between them. They're cheap enough to cut the frame down if you're so inclined. I think the Faital 4" one may fit but have not verified. The other small Dayton (square flange) is IIRC too big for the grille to fit over.
The Dayton ND105 has perfectly placed mounting holes but the frame bulges out too much between them. They're cheap enough to cut the frame down if you're so inclined. I think the Faital 4" one may fit but have not verified. The other small Dayton (square flange) is IIRC too big for the grille to fit over.
We seem to be down to a few driver prospects now.
I was just revising the series filter idea. I have messed around with these things in modelling.
Usually got awful impedance when including bafflestep for standmounters. Much easier with wallmounters.
The late Jeff Bagby Filter table did all the maths years back.
These are for 8 ohms DC measurement. Most drivers are around 6 ohms.
All worked out rather well with Jeff's 3kHz crossover values. This was 8" bass and 1" tweeter. Big high inductance basses come with bafflestep largely built in. Bafflestep can be added with a passive RL circuit.
Flat Impedance and Flat Power response design.
I used impedance correction and time alignment there. But your 0.33mH and 6.8uF looks rather close to Jeff's values when converted to 6 ohms, so competent work by B&O.
I was just revising the series filter idea. I have messed around with these things in modelling.
Usually got awful impedance when including bafflestep for standmounters. Much easier with wallmounters.
The late Jeff Bagby Filter table did all the maths years back.
These are for 8 ohms DC measurement. Most drivers are around 6 ohms.
All worked out rather well with Jeff's 3kHz crossover values. This was 8" bass and 1" tweeter. Big high inductance basses come with bafflestep largely built in. Bafflestep can be added with a passive RL circuit.
Flat Impedance and Flat Power response design.
I used impedance correction and time alignment there. But your 0.33mH and 6.8uF looks rather close to Jeff's values when converted to 6 ohms, so competent work by B&O.
So the OE driver static resistances are:
Tweeter 6.0Ohm
Woofer 4.7Ohm
Now to add maximum frustration to your efforts, I'm moving the goal posts!
I've decided these are going to be my kitchen speakers. So good for bass as they will be sat pretty on top of the units pretty much in the corners, so they will have good loading. But it now means off axis response matters much more as they will typically be listened to around 20 Deg off axis (their angled baffles will help the woofers here).
Just to clarify, I'm not looking for originality, nor bothered about modifying driver frames etc. What I do care about is keeping the original look of the cabinets and grilles.
Thanks
Tweeter 6.0Ohm
Woofer 4.7Ohm
Now to add maximum frustration to your efforts, I'm moving the goal posts!
I've decided these are going to be my kitchen speakers. So good for bass as they will be sat pretty on top of the units pretty much in the corners, so they will have good loading. But it now means off axis response matters much more as they will typically be listened to around 20 Deg off axis (their angled baffles will help the woofers here).
Just to clarify, I'm not looking for originality, nor bothered about modifying driver frames etc. What I do care about is keeping the original look of the cabinets and grilles.
Thanks
I think Pallas has already decided the Dayton drivers will need much frame cutting.
I didn't find anything MarkAudio at KJF Audio (Hi Stefan!) that worked either:
Markaudio | KJF Audio
MarkAudio are usually about 4 ohms DC, as it goes, but its the frames that don't fit.
I noticed the Faital Pro 4FE32 has supply delays. The 4FE35 is more available at Blue Aran, but not so pretty on frequency response. That 8kHz peak looks a nuisance.
Faital Pro : Faital Pro 4FE35 8 Ohm Faston :: PS13.36 IN STOCK (29 Sep 2021)
Do you think you can get the Faital Pros to fit?
A small change in DCR from 4.7R to 6.5R won't mean much. I'd rather go higher than lower. Can't comment on 20 degrees off axis much. For sure the top end falls off a bit, but hardly a lot. These speakers seem to be overly bright at the top anyway.
I didn't find anything MarkAudio at KJF Audio (Hi Stefan!) that worked either:
Markaudio | KJF Audio
MarkAudio are usually about 4 ohms DC, as it goes, but its the frames that don't fit.
I noticed the Faital Pro 4FE32 has supply delays. The 4FE35 is more available at Blue Aran, but not so pretty on frequency response. That 8kHz peak looks a nuisance.
Faital Pro : Faital Pro 4FE35 8 Ohm Faston :: PS13.36 IN STOCK (29 Sep 2021)
Do you think you can get the Faital Pros to fit?
A small change in DCR from 4.7R to 6.5R won't mean much. I'd rather go higher than lower. Can't comment on 20 degrees off axis much. For sure the top end falls off a bit, but hardly a lot. These speakers seem to be overly bright at the top anyway.
The Alpair 6M gen 2 would need frame mods, but truncating the sides and taking a little out of the baffle for the spokes would be very possible.
Faital Pros would be snug as a bug in a rug, that has been on the cake all of lockdown, but yes they would fit with the mounting holes in the baffle (or basket) being re-pitched slightly.
I'm happy to alter the xover should it be needed, the cap is a bipolar electrolytic so swapping it out would be no hardship and the coil nothing special.
Also I have no issue with a 4ohm load for the speaker ultimately, I do not need to keep the impedance as the original.
Thinking about it, I'm in no rush, waiting 6 weeks for drivers is not really an issue. I'll just get the cabinets done in that time.
Faital Pros would be snug as a bug in a rug, that has been on the cake all of lockdown, but yes they would fit with the mounting holes in the baffle (or basket) being re-pitched slightly.
I'm happy to alter the xover should it be needed, the cap is a bipolar electrolytic so swapping it out would be no hardship and the coil nothing special.
Also I have no issue with a 4ohm load for the speaker ultimately, I do not need to keep the impedance as the original.
Thinking about it, I'm in no rush, waiting 6 weeks for drivers is not really an issue. I'll just get the cabinets done in that time.
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If that driver diagram is anything to go by, a needle file will take off 2mm on the mounting holes very quickly. I'd just tape a bag over everything else to stop iron filings flying into the magnetic parts.
Very nice people at Blue Aran. Swaythling near Southampton. I have been there and talked to them. They might even do the work for you... can only ask!
Anecdotally you want a very low resistance coil on the tweeter for rejection of low frequencies. A better polypropylene capacitor would only be a few pounds too.
But I haven't even simmed it yet... so I don't know exactly how it works out. It goes against my nature to dip below 6 ohms. That way cheap amps do fine.
Very nice people at Blue Aran. Swaythling near Southampton. I have been there and talked to them. They might even do the work for you... can only ask!
Anecdotally you want a very low resistance coil on the tweeter for rejection of low frequencies. A better polypropylene capacitor would only be a few pounds too.
But I haven't even simmed it yet... so I don't know exactly how it works out. It goes against my nature to dip below 6 ohms. That way cheap amps do fine.
I'm fine with 3-4Ohm final, The amp used with these is most likely 2Ohm stable. It will be going in the enclosure so no need to cater for anything else.
I'll measure the DCR of the coil tomorrow, its not a chunky wire so I expect the DCR is higher than ideal. I have a collection of caps and coils, probably something suitable in there. Failing that I have access to a coil winder.
I think looking at the drawings the driver frame could be notched for the existing mounting holes with relative ease. bag and tape it all up before starting to prevent and swarf getting anywhere it shouldn't and it would be no big deal. I'd rather wait for the better driver I think than try dealing with that peak.
I'll measure the DCR of the coil tomorrow, its not a chunky wire so I expect the DCR is higher than ideal. I have a collection of caps and coils, probably something suitable in there. Failing that I have access to a coil winder.
I think looking at the drawings the driver frame could be notched for the existing mounting holes with relative ease. bag and tape it all up before starting to prevent and swarf getting anywhere it shouldn't and it would be no big deal. I'd rather wait for the better driver I think than try dealing with that peak.
Progress... 4FE32s fitted. They sound quite toppy, need to break the drivers in before any real judgement. They did drop in with no mods though, just some big old M3 'c' washers to cover the mounting holes.
They will need a little material taking out at the sides and bottom. The sides just touch without fabric on the frames. The bottom edge does not fit on at all yet, but I think a bit of sanding to the frame and it should be OK.
Finally got these done.
The drivers settled down a bit with some hours on them. I started cleaning up the cabinets to powder coat, only to realise the previous owner had painted them black... rather badly. The Anodised aluminium underneath was in pretty decent nick really once the paint was removed. I had some melamine acoustic foam so redid the bits round the tweeters, the grilles were sanded a bit with a dremel to clear the driver frames and new grille cloth fitted with hotmelt glue.
Overall for my £60 or so outlay I'm pleased with them. They sound pretty good, image superbly as desktop speakers, look very presentable. I picked up an old Rel sub to fill the bottom end in, which should sort things nicely I hope.
The drivers settled down a bit with some hours on them. I started cleaning up the cabinets to powder coat, only to realise the previous owner had painted them black... rather badly. The Anodised aluminium underneath was in pretty decent nick really once the paint was removed. I had some melamine acoustic foam so redid the bits round the tweeters, the grilles were sanded a bit with a dremel to clear the driver frames and new grille cloth fitted with hotmelt glue.
Overall for my £60 or so outlay I'm pleased with them. They sound pretty good, image superbly as desktop speakers, look very presentable. I picked up an old Rel sub to fill the bottom end in, which should sort things nicely I hope.