Room Measurements

Maybe it should be pointed out that the active crossovers are made adjustable to help with room placement. For example, if the MB2 were soffit wall mounted then the bass section of the crossover would need to go down by about 5dB to account for this. It would also change the mid frequencies due to baffle step. Again, a small adjustment on the crossover can help this.

MLS can help with background noise, but I don't find it represents the bass section as you will hear it as well as a solid-state tone does.

 

The prior installation was a treated room with the speakers flush against a rear wall.

 

Backed up against the wall or do you mean actually sitting in a hole in the wall so the front is flush?

If the latter, the no wonder it was bass light to begin with.

 

Well, if you're only interested in setting the gain of each band, why not do it by ear? If you feel that your system is too bright (or whatever) then having a measurement - no matter what the graph looks like - isn't going to change your mind is it?

What are you using for phantom power?

 

Well I just wanted to be rigourous

I have a behringer DI box.

It looks like the recording input is being rerouted internally on the sound card to the sound card output rather than the microphone input. The sounding track records the noise of the noise track even if the digital output to the behringer is disconnected and the system is silent! If a silent track is played then the sounding track records nothing so I am not measuring some bogus sound. The option in cool edit pro only allows you to choose between the sound card, the usb mic or the bluetooth headset. It appears it defaults to the internal soundcard output feed redirection so I need to find a way to make it take the mic input. The mic works fine in windows outside of cool edit pro.

 

I think it has to be considered that PMC are setting the crossover to a very different criteria. For a start they will be setting crossover frequencies and slopes not just levels, also they will be making each unit consistant with a norm. As soon as you are adjusting in a particular room then it is not unreasonable to adjust each crossover taking the room into account optimising it for the room.

 

You can only adjust the level on the customised bryston crossover supplied with the pmc actives (it is also tweaked to improve the sound) the frequencies are fixed

 

The odd thing is that the slopes are fixed too... real pity. Though I suppose it doesn’t matter once you have the DEQ

 

The sound card is realtek on motherboard. It maps to a pci slot back plate and also the sound card panel slot nearer the top of the case. All of the i/o can be flexibly mapped according to requirements by changing the settings on the driver. It is this "virtual hardware configuration" that is confusing the cool edit pro software I think. It might be best just to buy a usb mic input and connect to that if its possible...

 

Indeed. But perhaps they dont matter as much?

 

Something like this usb microphone preamp...

http://www.piedog.com/musical_instruments/computer/hardware/m_audio-mobilepre_usb.htm?tf_6292

It would then be picked up just as seperate usb feed in cool edit pro. Something simpler and cheaper would be a big plus!

 

Holy cow, this sounds complex.

Hopefully when it's set up you will resist the urge to fiddle and just relax back into the music. :MILD:

 

Its only complex because it isn't working

 

No, it's a good thing the slopes (and crossover points) are fixed, otherwise you'd have a serious engineering exercise on your hands to optimize both the on-axis and power response of the speaker.

If you are going to start diddling with crossover design, you may as well start building a new speaker, because by just fiddling with the crossover you are inherently limited by other design compromises that have already been made elsewherein the choice and placement of the drivers, cabinet design etc..

"Going Active" is not a way to improve a poorly conceived passive deisgn. Moreover, it's unlikely to yield radical improvements in a well executed passive design, as the other choices in that design will inherently limit your options with respect to active operation.

While it's possible to design and build a speaker at home that "works" in the sense that it makes noise, it's hard to build a really good speaker without optimizing and measuring (accurately) a large number of parameters.

 

Thats what I thought. Hence the slopes and points screws have been removed and only the level screw remains.

Well I replaced the triamped passive with equivalent active and it is a huge improvement. Not least that it freed me up to try generic pres. The passive wasnt poor in any respect but the active is just much better.

I just want to get the level screws set right. I dont want to build my own speaker. That would be very tricky.

 

Umm.. not really. If you had a bass peak at 40Hz and a crossover point of 150Hz you can not really just alter the level, as the whole range will change. If you can change the slope so it rolls off more sharply then you can counter the lower bass peak while keeping 50-100Hz pretty much as they should be.

Even just adjusting them by ear, it is no worse than putting a random passive speaker in a random room, which is essentially what most people are doing. You can do it if you want. Besides, its not like BBV can't put it all back the way it came if he wants.

I should probably add, I wouldn't want to change the midrange slope much... that could be tricky!

 

What do you mean? The exact same crossover implemented in an active configuration would yield many improvements.

 

What are these "many improvements" of which you speak? Go on list them... but please note the bold emphasis I've added to your text [BTW I'll know if you're quoting the section from Dickason's "cookbook"]

 

Oooo. This could well be a very long thread if every aspect falls under such close scrutiny. It tickles me that brizonbiovizier hasn't even got his kit set up to take the first reading and it's already fisticuffs at dawn. I presume there is a bit of history here, I will have to check out some old threads.

I can't quite see what harm could come from mucking about with one level pot. Especially if brizonbiovizier intends to do some subsequent room eq. I would be tempted to do a nearfield measurement for setting the crossover level, something like 0.5 metres from the speaker and reduce the window. Probably best to try to take the room out of the equation as much as possible just for setting the crossover level, or am I being too old fashioned?

Martin

 

That sounds like a very good idea... as soon as I get a mic preamp. I have found a usb one - but I am looking for a pci one preferably... then the fun can really begin!