I have a pair of Bose 901 speakers that I inherited but does not have the Active Equalizer that comes with it. The speakers are working fine but I would like to find a solution for the missing Active Equalizer. Not sure if it will be possible to get a new Bose Active Equaliser and so would it be possible to get one from another company and connect it to the speakers and the receiver?
Bose 910 Active Equalizer
- Thread starter Chipman
- Start date
IndianEars
Well-Known Member
I knew these speakers well, & have even repaired them, 40 years ago, when the company I worked for (NELCO) provided free support in India for all BOSE users, since Mr Ratan Tata was a personal friend of Amar Bose.
The 901 Speakers were the Top-Of-The-Line speakers from BOSE.
Each speaker enclosure had 9 drivers of 4 inch diameter each ( 4+4 facing the front + 1 rear ). A 9 drivers were exactly the same. They were manufactured in Taiwan (That day's equivalent of today, China's low cost manufacturing). They were designed for large voice coil excursions. The 901s had no tweeter or woofer.
As you can imagine, the 9 small drivers were mainly good only for mid range frequencies. To force them to deliver Low & High Frequencies, an active equaliser was used at the Line In level (Pre amplifier signal level).
The active equaliser provided an Low Frequency Boost of approx 12 dB and a High Freq boost of also 12 dB. The exact amount of boost and the EQ shape varied with the version (Called Series) of the 901 ... I think there were Series 1 to 5 or 6... But to generalise, the boost was approx similar.
Below is a typical, simplified EQ curve.
You can buy an appropriate (depending on your 901 Series 1 to 6 EQ from E-Bay) but a
Simple quick and dirty fix will be to turn up your Bass & Treble Controls on your integrated amp to Full.
Do note that such LF boost will HUGELY increase the power output demand on yr amplifier, so you may have to keep the volume down.
At that time, BOSE offered a 500 Watt Solid state stereo power amp as the recommended amplification for the 901!
THE 901 SPEAKER
The drivers (individual speakers in each enclosure) use Goam surrounds that completely crumble in 3 to 5 years, and that decay is accelerated in high humidity locations like Mumbai, Chennai & Kolkata.
Below is a picture showing a 901 speaker with foam surrounds that have completely disintegrated (Very typical)
Foam Surrounds are not available locally (to the best of my knowledge). There are Many sources abroad, including from Amazon, etc.
Do keep in mind that even the replacements will have a life of about 3 years!
I would recommend that you simply get the drivers repaired here in India... they will use the usual rubber (bextrene) surrounds and the cost will be minimal.
You will need a Hex Nut Socket / Driver (available in India, often as part of a Chinese Screwdriver kit for Rs 200) to unscrew the drivers.
I would encourage you to remove the Front Grill (simply pull out the cloth grill) and visually examine your drivers, even if you think they are OK. Repairing the drivers will make a HUGE difference.
All The Best.
The 901 Speakers were the Top-Of-The-Line speakers from BOSE.
Each speaker enclosure had 9 drivers of 4 inch diameter each ( 4+4 facing the front + 1 rear ). A 9 drivers were exactly the same. They were manufactured in Taiwan (That day's equivalent of today, China's low cost manufacturing). They were designed for large voice coil excursions. The 901s had no tweeter or woofer.
As you can imagine, the 9 small drivers were mainly good only for mid range frequencies. To force them to deliver Low & High Frequencies, an active equaliser was used at the Line In level (Pre amplifier signal level).
The active equaliser provided an Low Frequency Boost of approx 12 dB and a High Freq boost of also 12 dB. The exact amount of boost and the EQ shape varied with the version (Called Series) of the 901 ... I think there were Series 1 to 5 or 6... But to generalise, the boost was approx similar.
Below is a typical, simplified EQ curve.
You can buy an appropriate (depending on your 901 Series 1 to 6 EQ from E-Bay) but a
Simple quick and dirty fix will be to turn up your Bass & Treble Controls on your integrated amp to Full.
Do note that such LF boost will HUGELY increase the power output demand on yr amplifier, so you may have to keep the volume down.
At that time, BOSE offered a 500 Watt Solid state stereo power amp as the recommended amplification for the 901!
THE 901 SPEAKER
The drivers (individual speakers in each enclosure) use Goam surrounds that completely crumble in 3 to 5 years, and that decay is accelerated in high humidity locations like Mumbai, Chennai & Kolkata.
Below is a picture showing a 901 speaker with foam surrounds that have completely disintegrated (Very typical)
Foam Surrounds are not available locally (to the best of my knowledge). There are Many sources abroad, including from Amazon, etc.
Do keep in mind that even the replacements will have a life of about 3 years!
I would recommend that you simply get the drivers repaired here in India... they will use the usual rubber (bextrene) surrounds and the cost will be minimal.
You will need a Hex Nut Socket / Driver (available in India, often as part of a Chinese Screwdriver kit for Rs 200) to unscrew the drivers.
I would encourage you to remove the Front Grill (simply pull out the cloth grill) and visually examine your drivers, even if you think they are OK. Repairing the drivers will make a HUGE difference.
All The Best.
Thanks a bunch for this detailed reply. It is incredibly helpful to know that you have good understanding of this speaker. I am also on the verge of replacing my amp and will take your guidance on the power requirements. I have a question - How do I know which series it is? I looked at the back and on the bottom of the speakers and could not find the model number - series etc. It is on a pedestal like picture below. Should I unscrew the pedestal and see? Also, is it safe and reliable to buy these active equilizer from ebay in India or should I look for one from a different company, since this Bose speakers are at least 35+ years old.
greenhorn
Well-Known Member
If you are using a PC as your source, you can use either a calibration mic or the published eq curves or schematic to reverse engineer the eq needed using a parametric eq app like peace (windows) or wavelet (Android)
IndianEars
Well-Known Member
Chipman,
Visually, the speaker Stands point to a Series 5 or Series 6. They are black anodised. However Its not clear to me if you have photographed your actual speaker of posted a typical speaker pic.
No, unscrewing the pedestal will not reveal anything.
There is no eBay India. You will need to import the appropriate equaliser.
There is a fair amount of info on the net on these speakers and Equalisers for sale abroad. Google should be your friend!
My suggestion, as made earlier is to FIRST examine the drivers, by taking off the front grill. Repairing the drivers will make the GREATEST impact. This should be your top priority. If your existing amp has tone control, set them to max and listen to them AFTER you repair the drivers. Then take a call if these speakers are what you want to keep and spend more on.
BOSE is a lifestyle brand, and is often Phoo-Phooed by audiophiles.
They produce a wall of sound, and there is no precise imaging.... As one reviewer had famously said "Ella Fitzgerald had a 9 feet wide mouth"
Visually, the speaker Stands point to a Series 5 or Series 6. They are black anodised. However Its not clear to me if you have photographed your actual speaker of posted a typical speaker pic.
No, unscrewing the pedestal will not reveal anything.
There is no eBay India. You will need to import the appropriate equaliser.
There is a fair amount of info on the net on these speakers and Equalisers for sale abroad. Google should be your friend!
My suggestion, as made earlier is to FIRST examine the drivers, by taking off the front grill. Repairing the drivers will make the GREATEST impact. This should be your top priority. If your existing amp has tone control, set them to max and listen to them AFTER you repair the drivers. Then take a call if these speakers are what you want to keep and spend more on.
BOSE is a lifestyle brand, and is often Phoo-Phooed by audiophiles.
They produce a wall of sound, and there is no precise imaging.... As one reviewer had famously said "Ella Fitzgerald had a 9 feet wide mouth"
IndianEars, They are my own speakers. I quickly took a photo last evening and posted it. These speakers are really old but I like them and don't feel like changing them any time soon. Good point about checking out the drivers. Looks like it is easy to remove the front cloth covers to access these drivers. I will try my hand this weekend and see if they are damaged (it is possible because these speakers were at my parents' home in Cochin for 20+ years) and I saw in one of your previous post about ordering the foam surrounds. Also any recommendation on a new receiver? One of the channels of my Onkyo receiver is not working any more and it is also quite old. Will any of the currently available Yamaha receivers power these speakers? Any recommendations? I would like to buy one soon - in the next week or two.
IndianEars
Well-Known Member
Given Cochin's high humidity, the speaker surrounds would almost certainly have discussed integrated.
Any reason why you are considering only receivers, and not stereo integrated amps?
You also plan a Home Theatre?
IndianEars
Well-Known Member
Typo in my above post... Sorry, should have read
Given Cochin's high humidity, the speaker surrounds would almost certainly have DISintegrated.
Given Cochin's high humidity, the speaker surrounds would almost certainly have DISintegrated.
I used the words receivers and stereo integrated amp interchangeably (not much of a hifi expert but a generally likes to listen to a lot of music and occasionally hosts parties at home). What I need is a good amp for these speakers and the source will be a mac or phone via bluetooth. I don't plan to connect my TV etc to this amp/speaker.
kapvin
Well-Known Member
I have always been fascinated by 901s. and always wondered how the concept would work if executed with modern drivers and dsp. I have never heard the 901s seriously but have heard 801s in many clubs (from the time that clubs were my thing) and they could play at really loud levels cleanly. if you ever decide its not worth the effort, please do connect to see how I could take them off your hands..
greenhorn
Well-Known Member
Chipman, where are you located?
IndianEars
Well-Known Member
Yes, I agree, the Bose Professional Audio (PA) series are rugged and play Clean & Loud.
As far as I know, they never used foam surrounds
Interesting design features in these (801 series) speakers were:
1. (Like the 901s) No Tweeters ( Tweeters being the most fragile ). In fact No woofers either ... they just used High Power, High Excursion 4 inch drivers.
2. MOST INTERESTING .... the use of a Car Headlamp incandescent bulb in series with the (PA) Speaker Input!
At normal operational levels, the car bulb would remain cool and have only a small resistance. But if Excessive power was delivered into the speakers (eg microphone dropped), the larger current would heat the bulb filament and VERY Sharply increase the resistance in series with the drivers, protecting them. Once the overload is removed, the lamp would go Off & effectively "disappear" from the circuit.
Incidentally, the Resistance of an incandescent lamp typically increases proportional to I^4 i.e. IxIxIxIxI ...
so if the Current Doubles, the Resistance increases 16 Times!
The combination of 1 & 2 made these speakers indestructible.... ( Though the Huge Non Linearity of the incandescent bulb, made them distinctly Non Audiophile fare)
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IndianEars
Well-Known Member
The BOSE 901 would be happy with any Stereo Solid State amplifier of 100 Watts + ... 200 Watts RMS per channel would be ideal. Class D amps would match well, I speculate.
The Equaliser would have to be placed between the Pre & power amplifier sections or between the CD Player / DAC and the amplifier.
In the 'Olden Days" it was placed in the Tape Loop of the amplifier ....
I am based in Bangalore
greenhorn
Well-Known Member
Ah ok. I have a calibration mic and a 901 series 4 pending restoration in trivandrum. Figured if you were nearby....
Check the bottom of the speaker to find out the series. Some of them don't need new surrounds
Check the bottom of the speaker to find out the series. Some of them don't need new surrounds
Buy from India's official online dealer!
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