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Old 22nd September 2012, 11:09 AM   #1
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Default Active filtering or new cross-over for DIY 15 inch homecinema speakers?

Hello!

I recently built my first pair of DIY speakers!

A 86 litres bass-reflex cabinet with the following drivers:

low: eminence delta 15 lfa (sensitivity: 96db)
mid: electro-voice 1823M (sensitivity: 118db)
high: JBL 2402 (sensitivity 110db)

The cabinet is inspired by a document called 'cabinet recommendations for eminence delta 15 lfa', found on the eminence website.

I bought two DAP cross-overs ( DAP PCX-4 Passive Crossovers | Geluid, Dj-gear, Speakers, Mixers, CD-spelers, Licht - Pioneer, JBL, Sennheiser - SoundXplosion.nl )

the cross-over points at are 800hz and 6000hz


The speakers sound amazing and are a big step forward regarding my older (but good) akai speakers.

Here some pictures:

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(need to paint the bass-reflex ports! Movies are projected on the white wall. The little lcd is for News only )

If the pictures don't show up, click this link: https://picasaweb.google.com/1136711.../Luidsprekers# !


Now here is my problem. I recently did a SPL test, and it turned out that the curve isn't straight at all.
The mids are too loud, and there is a severe peak at 800hz (that makes the sound a bit like it is in a church)
I tried fixing this with an equalizer, but that didn't work very good. Besides, there is no 800hz frequency meter at the equalizer..

So, I want to fix this. What is the best solution?
Active filtering and bi-amping (mids and highs together/ lows separated)
Or a new DIY passive cross-over? The problem is that I don't know how to make a cross-over.

Could someone help me?

Thank you very much in advance!!!

Last edited by vandevoordekoen; 22nd September 2012 at 11:55 AM. Reason: fixing image-link
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Old 22nd September 2012, 11:22 AM   #2
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I would always recommend active crossovers as they are so much easier to tune to get right, and cheaper and faster once you start tuning. But the question is, can you dedicate 6 amp channels? If not then you have no option but to go passive.
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Old 22nd September 2012, 11:44 AM   #3
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Thank you for your answer.
This would mean that I need two active cross-over and 3 stereo amps, right?
Is that cheaper than a passive cross-over?

I would consider this investment, if it works good and finetuning is easy and effective.
Is there a big quality difference in active cross-overs?
What trade mark do you recommend regarding price/quality?

Thank you in advance!
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Old 22nd September 2012, 12:13 PM   #4
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You need one 3-way active crossover and 3 stereo amps, or one 6 channel amp.

If you buy used amps it can be about the same price as two or three attempts at a passive crossover. And the quality is better.
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Old 22nd September 2012, 12:57 PM   #5
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Some attenuation on the midrange will probably help (do a search on Lpad's) You can place it after your crossover. The tweeter probably needs some as well.

If you don't want to go fully active you could get a second amp and still use passive on the mid/tweeter and an active crossover for the bass to mid/treble. This should help with the biggest efficiency difference you have with the 15" drivers only being 96db (it feels wrong saying only there). Taking into account baffle step losses as well you are probably around 20db down compared to your tweeter level and a staggering 28db compared to the midrange!

I'm assuming your off the shelf crossover has no attenuation in it whatsoever.

You would only need a relatively small amp for the mid/tweeter due to the insanely high efficiency of the drivers.

So for a quick (and cheap) fix for the inbalance (without thinking about fixing all all of the inadequacies of an off the shelf crossover) some lpad's on the midrange especially and also the tweeter would probably make a big difference to the overall tonal balance.

edit: I just checked the datasheet for the mid, the spl levels are 1M at 90W input!! not comparing apples with apples... I don't know the formula to translate that back to 1W / 1M to get something comparable to the eminence spec...

edit2: also I don't know which horn you are using with the mid, but both the spl graphs in the datasheet I would not want to cross it much higher than 3000Hz...
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Last edited by wintermute; 22nd September 2012 at 01:04 PM. Reason: add comment about misleading specs.
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Old 22nd September 2012, 03:34 PM   #6
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Thank you very much for the answers!
I appreciate this!

Indeed, the midrange falls off after 3000hz! I hadn't seen that before! Thank you for noticing.

It was a bit stupid buying cheap off the shelf X-overs, while the drivers costed a lot more, even used..
It seems that the X-overs ruin the capabilities of the drivers.

I'll try both options:

- active filtering (in a prototype setup) --> I found a program on internet called "foobar2000" with an active cross-over plug-in which converts the stereo, surround and center/sub outputs of my 7.1 soundcard into 3 seperate stereo channels, each providing the signal of a defined frequency-band. It is possible to configure the gain of each band, and of course to define where each band starts and stops.
A time ago, I made a 6 channel amplifier for a surround equipment (that I don't use anymore). It's not very high end, but good. It will give an idea I guess. I'll use 4 channels of this amplifier (for the mids and the highs). And my marantz for the low frequencies (because of its good damping factor).

Before I connect everything, two more questions:
a. can I damage the diaphragma of the electrovoices and the JBL's? Or can't this happen because the frequencies are adapted to the drivers?
b. Can I bridge the passive X-over by connecting the drivers directly to the amps? Or is this dangerous and shoud I disconnect each driver from the passive X-over?

- passive filtering: when I don't find an active X-over and one or two more amps for a reasonable price, I'll stay with the Lpads to attenuate the enthousiastic mid and high-drivers. But this is step 2...


Thank you in advance!

Last edited by vandevoordekoen; 22nd September 2012 at 03:43 PM.
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Old 22nd September 2012, 04:47 PM   #7
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Yes you can damage the mid and high if you set their high pass filter frequency too low or too shallow slope. See if you can find datasheets for them and look up their resonance frequency (Fs). Keep the filter frequency at least double this.

You should be disconnect the crossovers as you may get some signal passthrough the wrong way.

Ensure that the amp you will use for mid and high does not have any turn on thump or cone movement.
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Old 22nd September 2012, 06:04 PM   #8
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I tried the active X-over setup.
Wow, that's a difference!
I tried it with one of the speakers, so I could only test mono.
But now I know looking for an active X-over is worth it!
I don't know if I have to go active for the 3 speakers. Does it makes a big difference or could I also split low and mid-high with an active filter (passive filtering mid and high) without a lot of qualityloss?

Thanks in advance!
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Old 23rd September 2012, 09:47 AM   #9
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Looking for an active X-over to experiment with, I found a used 'Inkel DIV 23' active cross-over.
The cross-over has XLR-connections, but the input of my amps are rca.. Is there a proper way to connect rca output to XLR input?

While experimenting with the active x-over (on computer with the program foobar2000), I connected all the drivers (15 inch woofer, electrovice mid, jbl high) with the (budget) DIY amp. The woofer didn't sound good (muddy), but the mids/highs sounded acceptable.
So I connected the 15 inch woofer with the marantz (and the mid/high with the budget DIY amp). That was better! The woofer sounded dry and defined and the mids/highs sounded very acceptable.
Will there be a big difference in detail if I connect the mids/highs also to an amp like the Marantz? Or is there no such difference in the higher frequencies as in the lower frequencies and could I stay wit the DIY amp for the mids and highs?

Thanks in advance!
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Old 23rd September 2012, 10:23 AM   #10
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I also came across this active X-over with jack 6.3mm connections:

http://www.unika.com.tw/archive/prod...5892515423.jpg

http://www.unika.com.tw/archive/prod...1edaa34012.jpg

Is it easier to connect rca to jack?
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