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X15 crossover freqs

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norty303 View Drop Down
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    Posted: 30 March 2005 at 6:04pm

I've decided that my X15's (SN-15MB & bm-d450) don't sound right in the midrange with vocal especially sounding very harsh.  PAP were out of the correct crossovers at the time and sent VX4's (3.2k) which i think are the cause of the problem as the sound is noticeably coming from the 15" driver.

I've decided i'm probably going to run them active but i've no idea about how to go about finding the best slopes and frequencies, etc.  Is it normal practise to use shallower slopes and have a gap between the hi and lo cutoffs?

Anyone running theirs active? What are you doing with them?

Thanks lots

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Tom Umney View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tom Umney Quote  Post ReplyReply Direct Link To This Post Posted: 30 March 2005 at 6:55pm

Although I don't have those cabs but as for the active crossover:

I'd make sure the crossover point overlaps so there is no gaps, or you get dead spots.

Eg : a 50hz-3khz 15 incher and a 1.5khz-15khz 1.5 inch driver inch driver. I'd cross it over at 2 khz , so that the roll off slope had no sudden gaps or dips in the response in it like if you did crossover at 3khz, where the 15 incher breaks up. 

Well now not the examples the real thing!!!!!!

P.Audio SN-15MB 33hz-3khz, P.Audio bm-d450 1.5khz-18khz.

So I'd cross over at 2khz. Best of both worlds that way, hf handles a bit more power and some of the harshness taken off the 15 incher.

And then if 15 incher still sounded harsh on vocals-- take a 31 band eq and cut those frequencies a bit that sound harsh.



Edited by ToXiC
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Dom View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dom Quote  Post ReplyReply Direct Link To This Post Posted: 30 March 2005 at 7:27pm

Have a search around on the web and you'll find pages of information of the pros and cons of different crossover slopes and the effect they have on summing and phase.  You can get a flat response, no phase shift or group delay, but you can't get everything so there's no magic answer.

Your best bet is stick on some music you know well and experiment with a variety of types and see for yourself what difference they make....

 

"It sounded like a million fire engines chasing ten million ambulances through a war zone and it was played at a volume that made the empty chair beside me bleed."
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norty303 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote norty303 Quote  Post ReplyReply Direct Link To This Post Posted: 30 March 2005 at 7:44pm

I understand about group delay now but what is this 'phase shift' of which you speak?  And what does it sound like in the real world?

@ Toxic - I've already tried to cut the EQ on the problem frequencies, it just makes them quieter but still rough so i want to eliminate them from being played by that driver completely (or at least audibly)

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Timber_MG Quote  Post ReplyReply Direct Link To This Post Posted: 31 March 2005 at 5:12am
The BMD is alright crossed at 2k on the PH-220, but if you use that 1.5" driver, I'd cross much, much lower, say 1k2 (though I don't know the PH-3220 horn all that well). The SN-15MB is not bad at all and yes it does respond up to 3k and a touch beyond, but I'd prefer no to have it run beyond 1k8.

On the bottom it goes rather well with a 100Hz crossover. It all boils down to a matter of power handling and how your subs sound crossed higher up. A bit of a gap and less steep crossover frequencies don't hurt.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lasse Lukkari Quote  Post ReplyReply Direct Link To This Post Posted: 31 March 2005 at 5:38am

Moved from General Forum



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Post Options Post Options   Thanks (0) Thanks(0)   Quote owentec Quote  Post ReplyReply Direct Link To This Post Posted: 01 April 2005 at 5:41am

Hi Norty,

This is the technique I use to get the best xover points and slopes. You will need a LMS of some type (Behringer one is better than nothing), and some type of loudspeaker measuring setup (if you haven't got one, see what you can borrow).

Setup the measuring mic to measure the on-axis response. Its best to do this in a very dead room, or outside, but you can do quite well almost anywhere if you keep the mic close to the speaker. Taking each driver in turn, setup the lms to output the manufacturers suggested frequency range (or more... but be weary of sending very low frequencies to compression drivers and don't go below the cut-off frequency of the horn you are using) and use the highest order xovers you have available. Look at the response of each one, and use the output parametric eq's in the LMS to achieve a reasonably flat response. Expect to apply CD horn equalisation as appropriate when you come to do the top end driver. Perhaps the most important part is to maintain a flat response at the extremes (eg your 15" might start a gentle roll off  around 2k, correct this so it stays flat to 3k). That might seem pointless if you are eventually going to cross over at 1k2, but it isn't (this out-of-band eq is very common on manufacturer supplied LMS settings (EAW kf850ef settings come to mind)). Don't go overboard trying to get it crazy flat, I've never used the components you have, but I guess +/-3dB is achievable.

Next, match the amp gains for each band, and use the band gain controls on the LMS to match the sensitivity of the drivers. This is likely to be the difference between the sensitivity claimed by the component manufacturer, although there can be some variation.

As I'm sure you know, large drivers like 15"ers get beamy near the top of their response. The best crossover point to use is where the dispersion pattern of the low frequency driver matches that of the horn. This gives the smoothest transition off-axis. If you happen to have TEF, this is dead easy, because it does normalised polar response measurements. Assuming you don't, setup your measurement mic at the horizontal dispersion angle of the horn (45 degrees for a 90 degree horn). Again, look at each passband in turn, and you should find that with the same eq you applied on axis the 15" response falls off with increasing frequency. With your matched on-axis sensitivity, you should find that the 15" is louder than the hf in most places, until around 1-2kHz (hopefully). That frequency is your ideal crossover point. Now, things can get tricky here, because you might find that you need a crossover point below the manufacturers minimum crossover point. This basically means you've chosen the wrong components in your design, but since Rog came up with this match, I'm trusting it won't happen. Incidentally, have a try at a couple of different distances and vary the angle slightly... off-axis response is usually very choppy, so the frequency can vary a bit especially without anechoic conditions.

Set the crossover points to your chosen value, and use the Linkwitz-Riley 24dB/octave slopes (a safe bet). Turn on both bands at the same time (should be the first time you've done this). Hopefully, you have a phase response measurement on your measuring rig, turn it on. With the measurement mic on-axis, have a look at the phase response through the crossover point. I can almost guarantee that you'll have a steep part here. This is because each speaker is generating the same frequencies, but they aren't time-aligned, so you get this smearing effect. Flip the polarity in the LMS on the bass driver. Start applying delay to the bass driver band, you should see the amplitude response drop at the crossover frequency, set the delay to the point where the drop is greatest (should be 10dB or more). This means that the sound from each driver is cancelling out the most amount. Flip the polarity back to normal, and it should go away, be a nice looking frequency response, and your phase plot should be reasonably flat through the crossover. The phase response for the whole box should look like a big smiley face... if it drops off at one end or the other, you have introduced a delay of more than one wavelength at the crossover frequency, which you didn't want to do. Theoretically speaking, your parametric eq's group delay could actually mean you need to delay the top-end driver instead, but I've never seen that happen.

Have a listen with a CD. If you've done it right, this should be the best the speakers have ever sounded. Unfortunately, you'll probably be used to however they sounded before, and you might've done something wrong anyway, so expect to be under-whelmed. Its not uncommon! Try finding a set of good studio monitors and doing some side by side listening. If you have more than one box, compare the off-axis response of a passive box with your biamped one. The difference should be apparent. Get other people to have a listen. Ultimately, if it sounds like poo, then it is poo... so start over.

Have a play with some other slope types and orders, but I do recommend you keep them symmetric. I almost invariably end up using L-R 24 everywhere apart from sub-band HPF anyway. This seems to be true for most manufacturers.

Err, well, that's it. Hope its some use to you.

Owen



Edited by owentec
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norty303 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote norty303 Quote  Post ReplyReply Direct Link To This Post Posted: 01 April 2005 at 6:42am

Blimey, that some read, but thanks for taking the time to post it.  I don't have a measuring rig yet but i do have an ultradrive and measurement mic so i think i'll try setting up by ear as far as frequencies are concerned and use the auto phase alignment functions of the LMS to correct that.  I've got a gig next saturday where we can load in in the afternoon so i'll have a fair few hours to play at someone else's expense.

I'm using the 2513 horn rather than the recommended 220 which is 100x65 iirc.  I'll have alook at the specs for it on the p-audio site

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Timber_MG Quote  Post ReplyReply Direct Link To This Post Posted: 03 April 2005 at 7:29pm
Get yourself ETF demo and the Behringer mic and hook the two up to your desk (you need a return signal back to your PC. You'll not look back (trust me). Set up your gate and set it to RTA type MLS mode on sequential measurement and you can tweak to your hearts content. Just have a look to gate your measurements properly.

I have set it up +- 1.5dB (3rd ocatve smoothed) on axis before, but your mileage may vary. That horn isn't particularily big or deep, so a guess would be 2.3kHz electrical crossover to end up at something like 1.8khz - 2Khz acoustic crossover (depending on the horn). I generally also use LR-24, but sometime use bessel or Butterworth for some free EQ just sbove crossover.

Regards

Martin
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Post Options Post Options   Thanks (0) Thanks(0)   Quote norty303 Quote  Post ReplyReply Direct Link To This Post Posted: 17 April 2005 at 6:22am

Just to feedback, after running them active for 2 weekends now i have to say i'm completely converted to running active if i can.  The problems with the breakup of the sound have bee cured now i can set the x-over poinyt manually.  Currently at 2khz but there will be some experimenting to come.

Vocals are now shiny transparent and the punch and clarity in lower range is just incredible.  They're incredibly hifi and i've not really had to push them on the amp yet

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Post Options Post Options   Thanks (0) Thanks(0)   Quote JD01 Quote  Post ReplyReply Direct Link To This Post Posted: 17 April 2005 at 11:32am
IIRC there was a big gap. Something like the HF drivers highpass at 2kHz with 12dB/Oct. and the 15s lowpass at 1200Hz with 12dB/Oct. I remember Rog saying that the BMD has a big hump in response below 2kHz and it was smoothened out that way ans the acoustical crossover was around 1400Hz or something... Must be around here on the board.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Timber_MG Quote  Post ReplyReply Direct Link To This Post Posted: 17 April 2005 at 3:08pm
I am busy working on a passive 1" X-15 (PAP x-over) and will report on the results along with detailed measurements of the cab. For those interrested I can provide some measurements on the raw drivers.
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