Bose Cubes without Acoustimass connected to a non-Bose Amp

 

New member
Username: The_rug

Post Number: 2
Registered: Jun-10
Was asked to repost this in the sub-woofer forum:

Hi Everyone,

This is a post to share my research and experience on connecting Bose Cubes to a Yamaha amp without the Acoustimass module. I thought I would make this post as I searched for hours to collect the necessary info, and to share my results.

Please note: this is not a debate over whether Bose are better, this is just information for those that are curious as to whether this is possible and how.

History:
About 15 years ago I purchased a Bose Lifestyle 25 II system. Recently a lightning strike blew up my Acoustimass module. After many hours of cursing and realising that it wasn't salvageable, I decided to embark on replacing the system.

Requirements:
I didn't have a huge budget, so re-using the cube speakers as satellite speakers made sense. I admit the biggest downfall of the lifestyle systems is that if one part of it dies, you pretty much have to replace the whole thing (unless you eBay the specific item), so purchasing separate equipment was also on my agenda.

The specifications of the Bose speakers:
In order for me to research what I could purchase/use, I had to find out what I had first. Here is what I found online:
Frequency Responses:
Bose Cubes: 280Hz to 13,300Hz
Bose Acoustimass: 46Hz to 200Hz
These are the most accurate figures I have found, without testing the speakers myself (as I don't have the equipment to do this).
Bose Cube Ohm Rating:
According to most Internet sources: 4 ohm According to the shop I bought my new amp from: 2 ohm According to MY multimeter plugged into MY Bose cubes: 6.6 ohm

Note: My cubes are from a LifeStyle 25 II system - the ohm rating on the newer cubes may be different. I highly recommend investing in a cheap multi-meter with an Ohm setting so you know for sure what you are working with.

Finding the right amp:
From my research, the Ohm rating on the speakers is very important. It specifies how much resistance the speaker has, and therefore how much power it will draw from the amplifier - a lower number means less resistance, meaning more power is being drawn. You *can* connect a 4 Ohm speaker to a 6 Ohm amp, but chances are you will blow the amp as the speaker causes it to overheat.
It is therefore important to ensure that your amp can handle your speaker's Ohm rating. I have found that some amps have a lower amp rating for the main (front stereo) speakers, but a higher rating for the surround speakers - keep an eye on this!
For example, my new Yamaha RX-V595 can do 4 Ohm front speakers, but surround is only 6 Ohm.
As you can see, my Bose Cubes have a 6.6 Ohm rating and my amp can support as low as 6 Ohm (surround speakers), hence I was confident my amp would not blow up if I connected them.

Finding the right speakers & sub:
Now going back to the frequency responses I mentioned earlier - this is the sound that your speakers can reproduce. So as a whole, the LifeStyle 25 II system could reproduce sounds from 46Hz through to 13,300Hz with a gap from 200Hz to 280Hz. My thinking was that my next set of speakers would have to be able to cover more than that as I had noticed at times the LifeStyle lacked some 'oomf'. My research had
shown:
The average sub can produce: 20Hz to 150Hz The average front mains produce: 50hz to 20,000Hz Meaning the LifeStyle was missing lower bass frequencies, the 'gap'
was being missed and there was a higher frequency range being missed as well.
I have had my eye on a pair of Bose 301 series V for a while now, and their specs show they can do 30Hz to 20,000Hz - which I thought their ability to produce a bit more bass than the average front mains would help compensate for the Bose Cubes I was planning on using.

Result:
I now have my Bose Cubes configured for Centre and Left & Right surround and my Yamaha amp has auto-speaker configuration, so it knows how 'weak' they are. The sound level from them is fine and the quality is fine. As expected from such a small speaker, they sound a little tinny, but as I have a decent sub and as my stereo fronts have good bass reproduction, it isn't much of a problem.
I will, however, in the future replace these speakers with 'better'
surrounds, but for now I am enjoying a full 5.1 experience without such an initial outlay by re-using my otherwise useless Bose Cubes.

Suggestions:
If you can afford a completely new speaker setup, then don't bother with the cubes - they really only come into their own when attached to an Acoustimass unit. But if you're a cheap bugger like me, then they certainly will do the job.
Also, when hooking them up, just be extra careful. Connect one at a time, play a movie for a while (to ensure you're using that channel), then see how hot your amp is running. If you are happy it is not working too hot, connect another cube and do the same.

I hope that this information helps anyone else who is looking at doing the same.

I also hope that this does not fire up the Bose bashers and spark another debate over which speakers are better - I have noticed that every forum thread that mentions Bose has at least one comment about how rubbish they are. Let's face it, it all comes down to personal choice, so let that person make their choice.

Thanks,
Rug
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 14927
Registered: May-04
.

A few points:

Your measurement of the cubes as taken with a simple DVOM only indicates a "nominal" impedance for the system. The actual impedance of the system varies first with frequency and secondly with any passive components employed - resistors, capacitors and inductors - which make the system operate as designed by Bose. If the system has a roll out stated at 280Hz, there must be either an active (powered by AC voltage) component in the entire system which actuates this rollout or there must be a passive component - in this case either an inductor or less likely a cap - to roll out the response in order to save the very tiny drivers from any large excursion low frequencies. My experience with Bose cubes is they are totally passive in their operation (as are more consumer loudspeakers) and a large inductor is typically placed in line with the satellite speakers. This passive component would influenece the actual impedance of the system at the point where it begins to roll out the response. This large value component rolling out the response will also affect the electrical phase angle of the signal which will, when combined with the low impedance of the system, present a fairly difficult load to any amplifier. Rather than taking a meter to the terminals of a speaker you would be best advised to rely on more comprehensive information, in this case assume at least the four Ohm rating and, if the shop which claims two Ohms is familiar with the Bose system and not just blowing smoke to push you off their use, then I would believe the lower impedance. Impedance and resistance are not the same thing, if you do not understand the difference, it would be worth your time to do some investigation.


This impedance plus phase angle draws not just more "power" from an amplifier but more current and current (amperage) is just what most HT receivers cannot do well. Buying more "power" in your amplifier does not in any way ensure you will also gain more amperage capacity. There is no such thing as a "6 Ohm amplifier". There are only amplifiers which have higher degrees of capacity to feed current into a low impedance load over longer time periods. You are correct when you say the impedance rating on the amplifier matters and any amplifier which implies it cannot drive low impedance loads should be overlooked unless you are absolutely certain the load you are intending to attach to the ammplifier is a very benign load (at all frequencies) when combining the actual lowest impedance point and the electrical phase angle; http://www.ecoustics.com/electronics/forum/home-audio/628565.html


As far as frequency response is concerned Bose is quite notorious for not stating any +/- points when giving frequency repsonse specs. Without any knowledge of where the actual -3dB or -6 dB points are in the real world frequency response of the system all you are being told is the drivers respond to say, a 280Hz input. Responding and reproducing useable information are two vastly different things - as different as impedance and resistance. One of the constant issues against Bose is their lack of technical information which would allow an honest and transparent comparison to their competition. In this case, say the response is -10dB at 280Hz, that would imply a possible roll out beginning as 600Hz thought the stated 280Hz "response" would technically be correct. If the rollout is made steeper by employing higher order filters, then the total impedance is likely to be affected also. Even at a generously suggested roll off of -6dB at 280Hz, this leaves out huge chunks of midrange and vocal material; http://www.psbspeakers.com/audio-topics/The-Frequencies-of-Music

As you can see the male voice can reach down into the 60Hz range and the heart of most vocals, male and female, is centered at roughly 250Hz. Leave out the range between the top of your subwoofer's range and the bottom of the Bose range and you're missing substantial amounts of vital information not to mention placing what does exist in the vocal range now originating from both the subwoofer placed away from the satellites which can create a very disconcerting effect for most listeners as vocals no longer have an anchored position in the soundfield.


Please take what I have just said and apply some common sense to your suggestion a pair of Bose 301's can "do 30Hz to 20,000Hz". They cannot. If you require clarification of this statement, please ask. Moreover, the suggestion by Bose that the larger 301 can respond to lower frequencies does not inherently imply the 301 will "do more bass". Once again you are comparing apples to orangutans.



Do not take this as "Bose bashing", this is meant only to clear up some technical points which you have wrong. Speaker selection is about personal preferences, I have no problem with that and I have no problem if Bose is your solution to your personal needs and desires. However, speaker selection should also, IMO, be made with a modicum of knowledge about how the system - amplifier and speakers combined - will operate. In your case, you've misconstrued many items which are important to the total results of a system's operation.

If you have any comments are questions about my post, please feel free to express your opinions. I do agree this should not become a bash Bose thread and any such comments are out of line.



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Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 14928
Registered: May-04
.

I really shouldn't type until the coffee has hit home.


Unfortunately, in my case, that requires multiple (large) cups and doesn't really "get'r done" until about three in the afternoon.



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