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Multi-Way Conventional loudspeakers with crossovers

B&O 5702 Upgrade Project
B&O 5702 Upgrade Project
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Old 8th November 2017, 06:16 PM   #1
snoopy33 is offline snoopy33  Ajman
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Default B&O 5702 Upgrade Project

Hi,

In The 70's B&O produced these huge, heavy and very expensive speakers. They used Celestion drivers from the top-range Dittons, which many considered the best in the world at the time. By today's standards they are still very good.

DIN power handling capacity 60 watts
Music power handling capacity 100 watts
Impedance 4 ohms
Frequency range 35 - 20,000 Hz
Harmonic distortion < 1 %
Sensitivity 3 watts
Net volume 45 litre
Woofer: 22,5cm and ABR 25cm
Mid-range 6cm Dome
Tweeter 2cm Dome
Crossover frequency 600 - 6000 Hz
Dimensions W x H x D: 36 x 66 x 30 cm
Weight 22.5 kg

They also used an outstanding woofer by Philips. I can't find any details on it but I've tested it against modern Celestion woofers of the same size (10") and the Philips blows them away. It's low-hz extension is superb.

B&O fell flat using an ABR which IMO is a gimmick. In this case the Kef BD139. They also used a Celestion version in the similar 5700 model. The ABR gives a lazy sound, poor bass extension and just doesn't work.

I set to work removing it and filling in the void. I've restored the crossover and replaced the perished base domes. Although I've tried several mods I'm not quite happy with the bass extension. The driver is obviously able but the enclosure isn't matched. Here are my findings;

1. With all the sound deadening material removed (there was a lot) the bass increases but at the expense of dampening. There's now too much low-mid range. Bass is not quite hitting the 40Hz level (which this speaker can easily do).

2. The most bass I've managed comes without a tube in the bottom hole (aka reflex). This reduces the dampening control even further and doesn't sound great.

My question to the experts is whether from these two findings it is possible to determine a course of action for modifying the cabinet to suit the woofers potential. To me removing the fluff and seeing an improvement indicates the 45 Litre (!) is too small.

Would an internal baffle plate work? I've seen some where they section off the lower half of the speaker and stick a hole in it several cm's wide.

Or if bass reflex is possible, can it be calculated with a driver of unknown characteristics?

Regards,

Andrew

BeoVox 5700/5702 Passive Loudspeakers
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Old 9th November 2017, 08:28 PM   #2
Fernando R is offline Fernando R  United States
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Have you tested to obtain TS parameters? Without them you are just guessing. The woofer looks like a Philips AD10100W (AD1056W if magnet is alnico). I had a 12 inch version in the 70s. I used it in a sealed system. The cone was paper but not very stiff.
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Old 9th November 2017, 09:07 PM   #3
balerit is offline balerit  South Africa
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The fibre filling/stuffing actually increases the cabinet volume, maybe you should re-stuff it. I also once tried to use a B&O crossover but it never worked properly, better to measure the T/S parameters and make your own crossovers.
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Old 10th November 2017, 12:49 PM   #4
snoopy33 is offline snoopy33  Ajman
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Interesting, the woofer hasn't been identified before on forums. There's no marking on the back but the encasing is aluminium.

B&O will have got the crossover's right, they were experts back in the 70's. No freqencies are missing, it's just that the bass rolls off incorrectly. You can hear the levels down to 30Hz but the cabinet is just not working for them. Also, it gets worse as stuffing is added.

I'd prefer use math rather than guess work but I have no woofer parameters to go off. I'll start investigating now there's a possible model number.
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Old 10th November 2017, 01:01 PM   #5
snoopy33 is offline snoopy33  Ajman
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Model is AD1056/W8

Seeks specs for old Philips woofer

Last edited by snoopy33; 10th November 2017 at 01:23 PM.
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Old 10th November 2017, 04:54 PM   #6
Fernando R is offline Fernando R  United States
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That was the earlier Alnico version. I would expect stuffing to make it worse. You should not stuff a vented box. My 12 inch version was in a 40 liter box. The resonance in the box was about 52 Hz but system Qt was only around .6. Stuffing the box lowered resonance below 50Hz but it sounded terrible. Best results was with just a lining on the walls. I never tried it vented. The 10 and the 12 inch versions had identical motors. I would think the 10" version would be even more overdamped with lower Mms. Try to get your TS parameters.
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Old 10th November 2017, 05:55 PM   #7
snoopy33 is offline snoopy33  Ajman
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I've scoured the internet but could only find Ts for a similar (but different) version, plus the guy took readings from three drivers and they were all different. Philips didin't publish Ts back in the 70's.

The 5702 wasn't vented per say but had a Kef BD137 Radiator on the front. This didn't work at all and made the sound woolly (plus absorbed bass energy). I filled this up and stuck a hole in the front to see what a bass reflex port would do. The best I got was the hole with no port.

In all cases stuffing makes the bass roll off worse, however removing it increases the drivers efficiency which will need a reconfig of the crossover to compensate. First though I have to make the cabinet work. It's 45 litres. Someone said (could be hearsay) that the maths for a similar Philips driver indicated 100 litres, though Philips recommended a more realistic 40 litres.
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Old 10th November 2017, 05:58 PM   #8
snoopy33 is offline snoopy33  Ajman
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Easier would be to use a modern driver but I've tried some of Celestions 10" current models and they sounded awful in comparison, a significant lack of bass extension compared to the elderly Philips driver.
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Old 10th November 2017, 06:36 PM   #9
Fernando R is offline Fernando R  United States
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I actually still have my old Philips design booklet from 1973 as well as a later version. The one from 73 has the AD10100W which was the AD1056W with the ceramic magnet. They have 24 different designs. The one with the AD10100W uses a 35 liter closed box. The system resonance is given as 52 Hz while the driver's Fs was given as 20Hz. These were loose suspensions more geared to closed boxes which was more the norm at the time. The book shows lining the walls with fiberglass, no stuffing. The theory for vented and ABR systems was just beginning to be understood. I first read Richard Small's paper at the college library in 1972. I think B&O used the ABR because it provided better excursion control below the box resonance. These drivers were quite floppy.


Since you have the Alnico version, another thing you need to consider is possible demagnetization. Alnico magnets suffered from that when exposed to high currents. You should get the speakers measured. Even if you don't know what the numbers are supposed to be, inconsistency between them should give you an alert.
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Old 10th November 2017, 06:50 PM   #10
Fernando R is offline Fernando R  United States
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I meant that ABR provided better excursion control compared to vented not closed box. If demagnetization is a problem, perhaps you can find a pair of AD10100Ws with the ferrite magnets.


Another possible thing to try would be aperiodic loading. I once had a Peerless 12" that I was not happy with either vented or closed. A pair of the Scan Speak aperiodic ports did the trick. This is essentially the Dynaco A25 loading.
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