Bump...a little help? Anybody?

I'm in a similar situation trying to decide on the BM15P and figuring which amp to use. I think what you have would work as long as you don't max out the volume. I've owned the BM6A and can tell you if you are a bass player they won't cut it. BM15 all the way man!

Technically(Or maybe not very?) any good amp should be fine with them.

Too much power? Don't "crank em' up" too much(Ha!).

Room size? Hard to say..? Room treatment, in a room of any size, may help tame problem areas... Whether ANY system is "monitor quality", generally depends on the ENTIRE system! Room, speakers, amp, source and --- ears... As you say, you'll at least have a neat-o stereo setup..! You can work toward making the room and the rest of the system all it can be for critical monitoring......

TG

I currently have BM5A's but I guess I'm gonna upgrade to passive BM15's soon. I just bought a second hand Rotel RB980BX amp today. The manual says: 2x 120W RMS @ 8 ohms, 2x 220W RMS @ 4 ohms, damping factor: 1000 (20-20000 Hz @ 8 ohms), Peak current: 80 A

Btw, here's a picture of the amp: http://www.quandace… link

I also found out that the amplifier has been a Stereophile recommended amplifier. So what do you think...Will this be a good amp for the BM15's? I cannot test the amp yet because I don't have any passive speakers before I get the BM15's.

Hmm... The crown - not so much. PA amps are designed for PA work. They really sound quite a bit different than a standard audio power amp. Not to mention the noisy fan.

The Rotel is a solid winner!!

For my BM15Ps, I use either a Hafler PA3000 or a Rotel RMB-1075. Both sound nice, the Rotel sounds liquidy and buttery smooth - as beautiful as an amp should be. The Hafler is accurate and clean - nothing wrong, just not near as smooth as the Rotel.

J.

Ok, great!

I still have one more question...

Is it ok if use my MOTU 828 mk2 as a pre amp for the Rotel power amp or do I need a "real" pre amp to get the best possible sound? I have heard that some audio interfaces reduce bits when changing the output volume. Do you know if this is true with the 828 mk2 or do I get a full 24bit output altough I have the output set to -60dB ?

F5D wrote: I
Btw, here's a picture of the amp: http://www.quandace…

I'm a bit stumped.. the Rotel does have a level control.. hidden away ?

Sidhu

F5D wrote: Ok, great!

I still have one more question...

Is it ok if use my MOTU 828 mk2 as a pre amp for the Rotel power amp or do I need a "real" pre amp to get the best possible sound? I have heard that some audio interfaces reduce bits when changing the output volume. Do you know if this is true with the 828 mk2 or do I get a full 24bit output altough I have the output set to -60dB ?

You should be able to use the MOTU as the preamp. I'm not familiar with anything reducing bits though when outputting different volumes. That doesn't mean that it doesn't, I'm just not familiar with this.

I've recently started using a Presonus Central Station as my "preamp" and it works beautifully. Of course, there are tons of monitor controllers from companies like SPL and others too.

Enjoy.

J.

F5D wrote: Ok, great!

I still have one more question...

Is it ok if use my MOTU 828 mk2 as a pre amp for the Rotel power amp or do I need a "real" pre amp to get the best possible sound? I have heard that some audio interfaces reduce bits when changing the output volume. Do you know if this is true with the 828 mk2 or do I get a full 24bit output altough I have the output set to -60dB ?

I know what you are saying, and in your extreme case I would get some kind of passive monitor volume controller to avoid any resolution loss at your software output mixer. -60 is pretty low, even if your software mixer runs at 32 bit or something. It might be something worth testing at least, and see if you can hear the difference.

Sidhu wrote: [quote=F5D]I
Btw, here's a picture of the amp: http://www.quandace…

I'm a bit stumped.. the Rotel does have a level control.. hidden away ?

Sidhu No, it's just a power amplifier. You can only turn it on/off and select between bridged/stereo operation. I use a motu 828 mk2 to control the volume.

Reggie wrote: I know what you are saying, and in your extreme case I would get some kind of passive monitor volume controller to avoid any resolution loss at your software output mixer. -60 is pretty low, even if your software mixer runs at 32 bit or something. It might be something worth testing at least, and see if you can hear the difference.

I will do some testing and if it seems to ruin the sound I will buy a pre amp.

Ok, I found something about the reduced resolution at the 828 mk2's output when controlling the volume digitally...From SOS article:

As usual, our first job (after attending to the tea and chocolate biscuits) was to listen to the monitoring system exactly as it was. Initially, this was done using the MOTU 828 MkII's volume control, but this proved frustrating to control, and the resolution fell off at low volume settings. So Hugh quickly set about patching in the Samson C*Control instead, with the MOTU monitoring outputs set at full level to achieve the best D-A resolution

I guess this is just what I have already heard with my BM5A's. So I will get the BM15's in 2 weeks, bought the Rotel and also ordered good quality 4mm^2 speaker cables and gold plated signal cables so I will also need a pre amp or maybe a passive volume controller if I want to get the best possible sound out of the system.

I found a very interesting Russian? website with measurements of BM15 passives. Here's the link: http://

I guess the 1. picture is impedance (green) and phase (yellow). Don't know about what the different colors at the second picture mean but some kind of frequency responses. The 3rd picture is the frequency response again but is the yellow line with port engaged and the green line using the plug? There seems to be a 6dB drop at about 3.5kHz, a little above the crossover frequency, hmm...

I also found the thiele small parameters of the 24W100 woofer and it seems that there's a 3dB boost between 50-80Hz in this enclosure when the port is engaged. In fact the measurements look very close to the ones I simulated.

With BM5A's I tuned the ports 5Hz lower and the heavy mid bass (might be the room) wasn't troubling me anymore and the monitors played a little lower. I guess I will try the same trick with BM15's and see if it works (if it's even needed).

Of course the sound may already be very good and doesn't need any fixing at all but I am always interested in tuning speakers and a passive design makes it alot easier than active design if needed.

Ok, I got the BM15's a week ago. I didn't do a run in with pink noise like some of you guys have done. The instructions say that it's enough if you play music at medium levels over a week. Well, I guess the run in is almost over now because the sound really has improved dramatically. In fact the sound was not so good at first day. So I have just been running them in with music.

And the bass... In my room (about 23 m^2) the BM15's are a little too boomy with ports open and if I use the foam plugs the bass is weak. I also found out that my room is very difficult with bass but this is what I did...

I have 0.5 meters behind the monitors and about 0.7 meters between side walls. And I had to do the same as I did with BM5A's. I calculated that the ports of the BM15's are tuned at about 52Hz which is very high imo and that's the main reason why there's also a bass boost in the simulated frequency response at about 50-80Hz (which you can also hear very easily). So, I opened the monitors and extended the ports to make the length about double the original and I can say that the bass is playing alot better now. The ports are now tuned at about 41Hz. The boominess is gone and I can hear all the notes very well, the bass level is good and the speakers are still playing the transients very well. I didn't notice any differences there. I attached the port extensions with tape so I can take them away any day I want. The original BM15 bass ports only have that rounded trumpet end in front of the monitor but not inside. However my plastic port extensions have a trumpet end now too.

I guess the monitors are still breaking in and the sound still gets better and better but I guess I can already say something about the sound. Compared to BM5A's, the BM15's are _very_ different. The BM5A's are alot brighter and IMO the BM15's have larger and flatter sound. The sound is still not absolutely flat and I guess that the frequency response measurements of the Russian website (which I posted earlier) are very close to what I'm hearing. So, with BM5A's I was sometimes missing the lowest bass but now with BM15's I have enough bass.

With my current monitoring position I have run several sine sweeps and it seems that there's a boost around 130Hz and and the bass goes to around 30Hz but the level of the bass is not very strong in my room but well enough for my needs. I use a software eq to attenuate the 130Hz in Logic and in iTunes and I found it to be very important to get as flat bass response in this room as possible.

So I am happy with the bass and so am I with the overall performance too. Altough the sound is not so hyped as the BM5A's had, everything I hear now is somehow alot more precise but still not fatiguing. The most important thing I have noticed is the sound field between the monitors. There isn't a hole between the monitors like I sometimes felt with BM5A's. Some vocals and percussions sound incredibly real and come from between the speakers. The sound is bigger, wider and more uniform (is this the right word? :) ) between the monitors. One thing which is still bothering me a little is the frequency response above 10kHz which seems to be attenuating before 20kHz a little and it can also be heard. It's not huge but it still is there. I don't know how the breaking in affects the drivers and if it does something to the highs later. But I have already used to the sound and that there is not so much treble like the BM5A's had.

And maybe the most important thing with the BM15's is that you can tell alot easier if a mix is good or bad compared to BM5A's. I have already listened to many bad mixes and they really sound like rubbish but if you play a well mixed song the sound is huge. Both BM15 and BM5A seem to have that Dynaudio sound but imo the BM15's have a more realistic non-hyped sound and they reveal a bad mix easily. For smaller rooms the BM5A's and BM6A's may work better and for my room I had to extend the BM15 bass ports but it was worth it. These definitely sound good (if the mix is good).

cheers,
F5D