Just did an initial listen to the miniDSP vs a prototype Ryan Sound Lab crossover. This was done on my 2nd system which consists of an RSL 72, Mivera Class D power amps, and DIY transmission line speakers. Here are a few key specs of each xover setup:
miniDSP: 2x4 HD model with best processor (Shark)
-Linkwitz-Riley 8-pole filters (48db/octave slope)
-setup as stereo 2-way crossover @ 3400 Hz. (nominally -6db points for L-R type filter).
-adjusted actual crossover points for constant power output (-3db at 3400Hz): low freq = 3700Hz, high freq = 3100Hz. (this gives flat power through the pass band).
-did not adjust for time delay (might make a difference since the -3db points are no longer the same).
-tweeter output adjusted down -2db - about the same to my ears as turning the tweeters down manually to balance with the woofer-mid.
RSL prototype xover: 2-way
-Bessel 3-pole filters (18db/octave slope - same as NAXO)
-Crossover point is 3400Hz also adjusted for constant power across passband. (-3db points: low freq = 3600Hz, high freq = 3200Hz approximately)
-tweeter turned down for balance by ear.
Setup: same amps, speakers, source, and preamp for both xovers. No change in volume setting on the preamp when switching (both xovers have unity gain).
I won't elaborate here on setting up the miniDSP. Only need to mention that after the initial hassles with downloading software and understanding how to use it, the process of controlling the miniDSP is amazingly easy - selecting curve types, # of filter poles, frequencies, etc. Nicely done package.
Initial listening reaction using CD and LP sources:
- miniDSP is pretty decent but not great. Voices have added coarseness and a slightly hollow, metallic sound. Not terrible but a bit irritating. Same with piano - leaner, meaner - lacking in great tonality. On the plus side, the dynamics seem to be all there, at least on this system which is not my best one.
-RSL xover has all the dynamics plus the smoothness and tonality you expect from an analog system. Not to say it's perfect but not fatiguing like the miniDSP for sure.
There are dozens of possible filter setups for the miniDSP and I should try a couple of others to see what that does to the sound. Maybe these defects can be ameliorated by careful selection of parameters.
Then, there is the whole equalization feature which I didn't even look at (although I have the microphone to try it sometime). Since that was a constant between the two components, at least the initial impressions weren't affected by that.
I'm thinking of moving this evaluation to my primary system (Isobariks) to get more revealing information. Since a single miniDSP can only do one 3-way system (or two 2-way systems) I will try putting it on the woofer and midranges first, while leaving the tweeter on the existing analog xover to start.
More reports to follow!
Hi,
I think i saw that you mentioned that the 4th order had a dip in the middle - i think you were referring to the Linkwitz-Riley filter. This is the optimal filter, since although there is a dip in the middle at the crossover frequency, the sum of the filters responses means that the overall response is flat.
In addition to this, the Linkwitz-Riley ensures correct phase response at the crossover frequency.
https://en.wikipedia.org/wiki/Linkwitz–Riley_filter
http://www.linkwitzlab.com/crossovers.htm
I use a program called Crossover-Pro by Harris Technologies for passive loudspeaker design, which allows for non Linkwitz-Riley crossover approaches with different orders - and lets you see if the magnitude and phase of the system with the drivers used- from the database of drivers.
I was going to take the approach you have in regards to the analogue crossover - but with the orders required using multiple "2nd order single opamp implementations", and the delay filters, the number of opamps to be used was high, and the frequencies are set based on the cutoff frequencies for each filter. You can change the frequencies by changing the resistor values - but it is a pain, given that you may or may not like the change.
My preference would be to progress with a DSP solution - i am surprised the MiniDSP gave the results you have mentioned. Did you use digital in, and analogue out ? This is my aim - to use a digital input, and the Analog Device ADAU1452 device which provides 4 stereo outputs. I will connect these to the Texas Instruments 32bit DAC's for upto a 4-way crossover, and implement the volume control in the ADAU1452, programmed to allow for the generic pre-amplifier remote controls (most remote controls for audio follow a standard such as RC-5). With the DSP solution - the ease and flexibility are much greater than an analogue filter approach.
For the tweeter crossover frequency - i am using the SB Acoustics Satori TW29RN-B - and the power rating in the datasheet can be misleading. They are using an IEC filter cutoff at 2.6kHz, for a specific input power of 80watts. The entire 80watts is NOT applied to the tweeter, but a smaller percentage of this as per the 2.6kHz high pass filters. What i am getting to - is that careful consideration of the cut off frequency for the tweeter (high pass) is required to ensure that the signal applied does not contain too low frequency energy and hence too much high power. The tweeter travels +/- 0.5mm based on the input signal, where as the midrange i am using travels +/- 5.5mm.
How did you set up the drivers for the correct signal level ??
I too will have to purchase a microphone - so i can adjust each driver volume level when setting up the crossover. I was going to use the laptop - with a tone sweep generator - to see what the response is across the band. Probably in the back garden - to stop reflections etc., within the room.
You seem to be much further along than me - so hope it goes ok.
Regards,
Shadders.