Help required with setting crossover DCX2496

[Beast_of_burden]

Hey Guys,

My system is a biamped setup using a digital active cross over, the DCX2496. Since I mostly listen to FLAC and radio streamed over a squeezebox, using a digital x-over has its advantages. The woofers are custom Fostex FW305s in BR boxes built based on Wayne Parham's recommendation, driven by an Onkyo stereo amp. Woofers low-passed at 225Hz. Running Lowther DX3 in DIY TP1 Isis front horns without any cross-over with rear attenuated using a thick wad of foam. So there is no rear chamber for these horns, I need to understand the impact of a rear chamber on the system, subject for a different thread. Lowthers are run using a quality T-amp, soon to be replaced by Viren's 2A3 SET.

The Lowther horns roll off around 225Hz as seen on the DEQ2496 whilst playing pink noise. It all sounds very good with the speakers placed in corners and toed into the room, it does lots of things right. Sound stage and imaging are good if not outstanding. The cross over region could use some cleaning up though, perhaps a bit more precision. The EQ is definitely compensating and helping with the integration for sure, but still.

Here are the questions - the horns will start rolling off below 225Hz and I would like to utilize the natural roll-off from the horn system. How do I figure out the roll-off characteristics of the horns? Are there tools which can predict the roll-off curve atleast in theory for the horns? So that I have an educated starting point.

Secondly, I am utterly clueless about phase angles, cross-over types etc. I am quite sure cross-over isnt just about setting the low-pass frequency and choosing the rate at which it rolls off.

Please restrict discussion to the subject of the cross-over only. I am somewhat familiar with the features of the DCX2496, but willing to be educated.

 

[kapvin]

Hey Guys,

My system is a biamped setup using a digital active cross over, the DCX2496. Since I mostly listen to FLAC and radio streamed over a squeezebox, using a digital x-over has its advantages. The woofers are custom Fostex FW305s in BR boxes built based on Wayne Parham's recommendation, driven by an Onkyo stereo amp. Woofers low-passed at 225Hz. Running Lowther DX3 in DIY TP1 Isis front horns without any cross-over with rear attenuated using a thick wad of foam. So there is no rear chamber for these horns, I need to understand the impact of a rear chamber on the system, subject for a different thread. Lowthers are run using a quality T-amp, soon to be replaced by Viren's 2A3 SET.

The Lowther horns roll off around 225Hz as seen on the DEQ2496 whilst playing pink noise. It all sounds very good with the speakers placed in corners and toed into the room, it does lots of things right. Sound stage and imaging are good if not outstanding. The cross over region could use some cleaning up though, perhaps a bit more precision. The EQ is definitely compensating and helping with the integration for sure, but still.

Here are the questions - the horns will start rolling off below 225Hz and I would like to utilize the natural roll-off from the horn system. How do I figure out the roll-off characteristics of the horns? Are there tools which can predict the roll-off curve atleast in theory for the horns? So that I have an educated starting point.

Secondly, I am utterly clueless about phase angles, cross-over types etc. I am quite sure cross-over isnt just about setting the low-pass frequency and choosing the rate at which it rolls off.

Please restrict discussion to the subject of the cross-over only. I am somewhat familiar with the features of the DCX2496, but willing to be educated.

do you have a mic or is the roll off estimated by "ear"? a mic connected to a laptop is critical to getting the best of out of the DCX

but fundamentally speaking, while you can use the drooping response of the horns below 225hz (or whatever), it would be one part. of the accoustic slope. you'd still need to run a high pass to get the correct electrical slope. (you really do not want to get the LF into your horns)

i.e if you have a 1st order natural acoustic rolloff post crossover, the crossover can add a 1st order electrical to get a 2nd order acoustic slope. then you can match the crossover slope of woofer to a 2nd order electrical.

the crossover type is defined by the "q" you want to achieve. again, for simplicity, for the horn, try to match the horn filter function at rollout.

Linkwitz is q=.5 (critically damped); butterworth q is .707 (maximally flat).

for second order slopes, remember to invert the polarity of one set of drivers.

again, no substitute for a mic + laptop.

have fun

 

[Beast_of_burden]

do you have a mic or is the roll off estimated by "ear"? a mic connected to a laptop is critical to getting the best of out of the DCX

but fundamentally speaking, while you can use the drooping response of the horns below 225hz (or whatever), it would be one part. of the accoustic slope. you'd still need to run a high pass to get the correct electrical slope. (you really do not want to get the LF into your horns)

i.e if you have a 1st order natural acoustic rolloff post crossover, the crossover can add a 1st order electrical to get a 2nd order acoustic slope. then you can match the crossover slope of woofer to a 2nd order electrical.

the crossover type is defined by the "q" you want to achieve. again, for simplicity, for the horn, try to match the horn filter function at rollout.

Linkwitz is q=.5 (critically damped); butterworth q is .707 (maximally flat).

for second order slopes, remember to invert the polarity of one set of drivers.

again, no substitute for a mic + laptop.

have fun

Yes, I do have the Behringer calibration mic and also an external soundcard /pre. I am assuming I will need some kind of software,please let me know what I need to do.

Ok, I will try 1st order for the horns and the 2nd order for the woofers and report back with the results. I may have to set the low pass for the woofer somewhat higher at 300 Hz while retaining the high pass at 225Hz so as to avoid a huge dip at the crossover point. This is something I had noticed when the high and low pass were linked in the DCX. I can reverse polarity in the device itself.

I want to understand this a bit better "try to match the horn filter function at rollout". Did you mean to say, whatever the slope chosen for the horn I need to choose the same for the woofer.

 

[anilva]

You need to use TrueRTA software to get the frequency response plots on your PC.

Cheers.

 

[kapvin]

You need to use TrueRTA software to get the frequency response plots on your PC.

Cheers.

I am using Rew. For now.

 

[kapvin]

Yes, I do have the Behringer calibration mic and also an external soundcard /pre. I am assuming I will need some kind of software,please let me know what I need to do.

Ok, I will try 1st order for the horns and the 2nd order for the woofers and report back with the results. I may have to set the low pass for the woofer somewhat higher at 300 Hz while retaining the high pass at 225Hz so as to avoid a huge dip at the crossover point. This is something I had noticed when the high and low pass were linked in the DCX. I can reverse polarity in the device itself.

I want to understand this a bit better "try to match the horn filter function at rollout". Did you mean to say, whatever the slope chosen for the horn I need to choose the same for the woofer.

No. That was an example.

I would not recommend a 1st order electrical u less you cross over higher unless you are sure of the capabilities if your diver

All depends on the drivers. If you want, i will be happy to offer my limited perspective on what crossover. just pm me the links to driver specs.

Am in chennai today for some event, so may not reply immediately.

 

[Beast_of_burden]

Hi Kapvin,


PM sent with the specs. I have installed REW and mucking around.

 

[Beast_of_burden]

Installed REW and started doing some measurements. I dont have a SPL meter to calibrate but I pressed on neverthelss. Here is a screenshot from a sweep done from 20 to 1Khz.


The box is tuned to 55Hz and there is a dip here. Kapvin has been helping me with suggestions, but I can share pics such as this one. Not sure I can read much from this, I will make no secret of being a total noob here.

 

[kapvin]

Installed REW and started doing some measurements. I dont have a SPL meter to calibrate but I pressed on neverthelss. Here is a screenshot from a sweep done from 20 to 1Khz.


The box is tuned to 55Hz and there is a dip here. Kapvin has been helping me with suggestions, but I can share pics such as this one. Not sure I can read much from this, I will make no secret of being a total noob here.

sorry, i have not replied so far.

spl meter is req for calibrating absolute SPL levels. but you are just fine without it otherwise.

one way your could do this is (if you have a DEQ) is to set the mic sensitivity in the setup, connect the mic to the DEQ use the pink noise to get the sql using the DEQ RTA . using the same level, calibrate REW.

hower, be sure to use the mic calibration file to calibrate the ECM (it does not have a flat response). if you do not have a .cal file, you can download a generic ecm .cal file from HTS.

for this graph, you'll also need to extract min phase.

but overall for a live room this is not too bad at all when you smooth it 1/12 octave, it'll look really nice. Most speaker manufacturers give anechoic of smoothed at 1/6 octave response curves.

ps - is this for both speakers or only one? is it "in place" or have you moved it around for measuring? there is a bit of a rising response around in 500-800hz. might have your speakers sound a bit "honky"

pps - that 58hz thing looks like a room null. note that you have a similar null exactly 1 octave higher. also that phase response between 80 and 100hz is odd. have you done any eq there?

 

[Beast_of_burden]

That is unequalized without any contribution from the deq. It was also before running any auto alignment on the DCx.

The mic was placed about 1m from one channel and the measurement recorded.

I have now run auto alignment for all 4 outputs and it does sound a bit cleaner. It added delay to 3 outputs except the first horn. I am wondering if I should run auto align for two outputs representing one channel at a time. I have to plot the response with the auto alignment in place.

And then I am going to try the LeCleach crossover method for the Dcx.

 

[Beast_of_burden]

I ran the auto align with produced a short delay of ~12 inch on the woofers. woofer cutoff at 200Hz. Here is the SPL and phase response for the aligned setup. I think phase response does look better, your feedback please. BTW, no EQ applied.

 

[kapvin]

I ran the auto align with produced a short delay of ~12 inch on the woofers. woofer cutoff at 200Hz. Here is the SPL and phase response for the aligned setup. I think phase response does look better, your feedback please. BTW, no EQ applied.

definitely better upto 200hz.

have you upped the resolution of your sweep. I use 1m or 512k. how much are you using?