Out with the old, in with the new (Bose 901 eq. topic)

sprins

sprins

Active Member
Today I replaced my 901 active equalizers (2, for left/right/center setup) for a Bose ESP-88 DSP (yay eBay!). I did this to be able to add two MB4 subs into the equation to get a little more oomph in the lows.

I had to dial in the 901 (series III have I) equalizer curve myself since the ESP-88 only has pro gear presets. But since it's possible to enter any parametric EQ setting I managed to reproduce the 901 settings from online documentation and by hearing.

In the process I found out that the 901s have pretty sweet bass reproduction by themselves so I ended up with a crossover frequency at 60Hz (with a very steep roll-off) and a low cut filter around 35Hz for the subs. Seems like a lot ado about almost nothing but it does add something that wasn't there to begin with. And I had a good day or so to tinker :beatnik:

It's not as hefty as my man-cave setup but at home I have neighbors to take into account :pistols:

The 'old' (series VI) Bose 901 equalizers:
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The ESP-88 connected to the Marantz MM9000:
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This combo drives the L/R/C and two MB4 speakers (3 in 5 out setup). The surround satellites are driven by the surround receiver.

The MB4 bass units (some overkill):
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Very interesting! How has the sound changed with the subs added and with the 60 Hz x/o from the 901's?

My one experiment with adding subs (Velodyne DLS4000R's) to my 901's failed. Of course, I had no way to hi-pass the 901's so regardless of how low I rolled the subs in, there was just too much bass.
 
In the end the sound is the same, there is just more lower frequencies.

If I set the crossover freq higher (I tested 160/120/100/80) it changes the bass reproduction too much. It works but the 901 bass is just incredible and better balanced by itself here in the living room. Until 60Hz. There the subs take over perfectly.

You could just add an active crossover before the 901 equalizer. Better make it a digital one as you want a very steep roll off at the crossover point (I did 48db per octave, while 12db per octave is more common).
I bypass the subwoofer output of the surround receiver completely (no SW configured) so that the external DSP does all the work. I reckon the SR internal DSP is more a general propose surround chip, besides none of the tinkering was possible anyway with that.

I guess any good DSP will do. MiniDSP for ex. I just thought it was fun to use Bose gear in the setup. That DSP might also take the 901 eq out of the chain as a DSP can reproduce that functionality, but that's another chapter.

These subs I got don't even go that low. If your velodyne does 20hz you'll really have a blast!
 
My Velos, while satisfactory for my uses, do not plumb the depths. In fact they are internally limited below 29Hz. Above that they're pretty good. They kept up with my Klipsch La Scala II's that I had for a short while.

Here's the set-up from when I did my version of the "901/subwoofer" experiment: I put a "Y" connector on my pre's sub out and ran to the two subs. I had no way to filter the output to the 901's other than using the Bose EQ and/or the tone controls on my NAD pre. I tried every combination of settings possible; cutting bass at the pre (100Hz, +/- 5dB), using the bass cut switch on the Bose EQ (-6dB @ 35Hz) and also playing with the phase, x/o and levels of the subs. No combination I could find sounded as good as the 901's by themselves, so I gave up and put the subs back in my HT rig. I took comfort in my conclusion that the Bose 901's have pretty impressive bass on their own! My take is I would need one or two really, really GOOD subs to significantly better what the 901's will do, plus a good way to integrate them. Your idea of a separate x/o inserted in a processor loop ahead ofthe Bose EQ sounds good. I have considered those in-line resistors that Parts Express sells, but I don't think you can get a very steep x/o with those.

Another option I've considered as an upgrade path is just to add another pair of 901's. Imagine two or even three pairs of stacked 901's. Oh...my...goodness. :rockon: ...but then the purist in me is afraid there might be some weird comb-filtering from the spaced front drivers. I don't know if that would be an issue or not but it might be fun finding out.

ps: I just clicked on your man-cave link. I didn't realize who I was talking to. If I wore a hat, I'd take it off. But, I don't, so... :ntwrthy:
 
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Hehe, yeah I get carried away with this stuff. Although the setups are fairly (over)complete now.

Before I found all the pro gear I experimented with stacked 901s myself. That actually works pretty good for me. I noticed no unwanted side effects. It just gives a lot of sound pressure. It's like stacking the 802 speakers I guess. And if you have a 4 ohm stable amp you can start by connecting two 901s in parallel per channel.

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One of the better 901 installations I recall doing used 4 901s in a front wall/side wall configuration documented in some of the Super Bose marketing literature for the Series IIs.

In this arrangement, 2 901s would be placed on the opposite wall of the listener. Then an additional set would be placed on the side walls. The 2 left hand 901s connected to that channel and the other 2 connected to the right channel in order to throw a very wide sound stage.

The key to getting the most out of this configuration, however, was to have _lots_ of space around all 4 901s. This was the challenge in most home situations. The typical living room would not accommodate such a system, thereby compromising the sound stage.

Alternate arrangements included suspending one set of 901s from the ceiling directly overhead of the 2 floor mounted 901s. If the room had taller than normal ceilings, this would work _if_ the listener was well back from the speakers in order to experience the soundstage - or rather, the wall of sound.

Just stacking 901s, however, were difficult with the tulip stands, rendering the top-heavy 901s even more precarious. Use of small tables tended to help in installations like these but, again, most living rooms (and their decor owners!) didn't take to setups like these.

As for EQing extended bass, the 901 EQs did a good job as long as sufficient power was behind the 901s. The amount of power required is a function of the room size - not necessarily the efficiency of the speakers. As our OP has discovered, the roll off points require some steep curves in crossovers that were not generally available to most consumers in the mid-70s when I dealt with this stuff.

Lastly, the cost of adding subs and electronic crossovers to a large 901 installation did not generally result in a good Return On Investment for most well-heeled consumers that could afford such a Super Bose system.

Cheers,

David
 
All points well taken...still my inner audiophool wants to play; wants to tinker with happiness. I say that because I'm really very happy with my 901's, but happy is a relative term and one that has a somewhat different meaning in the audiophile world. "I'm happy, but..." There's always a but! "The system's great and I love it, but what if I just _____?" I'm sure you all know exactly where I'm coming from.

Sprins' systems really make me want to do...something. Even if it's wrong. Maybe I'll find a good pair of VI's on ebay and try stacking in my main system. I'm sure my amp is up to the task, but I would definitely have to build some stands. And if the stacked pairs don't work out, I could hang one pair in my HT room and leave the other where they are in my 2-channel system in the family room. It's a win/win!:banana:
 
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You can start testing by stacking the two you have. It'll be a mono setup, but might give you some ideas.
 
I'll have to find something to stack my pair on...actually, I think I still have a stand I made for a 27" crt TV years ago. I'm sure it's stout enough to hold a couple of stacked 901's. First chance I get I'll drag it out of storage and see what happens. I've got plenty of good-sounding mono CD's I could use for test purposes. My trusty old STEREOPHILE test CD's might come in handy, too. Can I expect a 6 dB boost in output across the spectrum when running two stacked, or will it just be below a certain threshold like 200 or 300 Hz?

One difficulty may be getting two stacked 901's to look good. I think the stand will be key in that.

I don't know that doubling or tripling Bose 901's will really make a practical improvement other than in the bass. And even then, bass would not be extended. Maximum output should go up and distortion should go down per a given output. Is that what you've found? Maybe a pair of really good subs and a way to hi-pass the 901's really is the best to go? It might have a higher WAF, too. I still don't see how to do the hi-pass filter though. The Bose EQ needs to be in a processor or tape loop, while a sub needs to be fed a pre-amp level signal. It looks like I'd need some sort of hi-pass filter to insert between the preamp and the amplifier driving the 901's, right?
 
I placed the bose eq (and now the DSP) between the pre and power amp. Since there is gain on my power amp I set that to half to reduce hiss from the speakers.

If you have a tape or processor loop you could tap in there as well for the crossover before the bose eq. (both in that loop connected together) as long as the sub is powered or has an amp of its own.

Your regular amp will then get the upper frequencies with the correct bose eq curve. Your subs the lower ones.

Stacking just gives you more sound pressure. Not sure if 3 or 6db but it will be all across the frequency scale.
 
I owned a double pair of 901s set up as David described with one pair using the wall opposite the listener and the other pair split and facing each other on the side walls. I used two McIntosh Mc 2100s at first and then switched to an Mc2300 for power and a C26 preamp. This system sounded very good, but as David said it took up a lot of space. The ideal spacing was to have the speakers all equidistant from the corners and about 24" out from the walls. I always wanted to do this again, but never had the room for it. I still have a pair of 901s, the Lifestyle series, which is a Series VI with the amp built into the base of the left speaker and the cabinets in ebony black. I like these speakers a lot. Unfortunately they are in storage at the moment.
 
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