parallel or series connection?

**vince** · **11-02-07, 12:05 AM**

Hello, I am working on biulding an electronic x-over to replace the passives in my Diffinitve Technology speakers. I have the direct firing Dappolito array mains each with two 6.5 in. woffers and one 1 in. fabic dome tweeter. My question is after I complete the x-over I am not sure if I sould wire the 6.5's in parallel or series? My Rotel amps will operate in 4 ohm's and be stable, but would rather run them at a 8 ohm load. After I open up my factory speakers to bi-amp them, sould I just measure the simple DC resistance of the voice coil and use this value to make my determination? I know that resistance changes with frequency but in an electronic x-over sittuation is this a factor or not? Will my amp see just the DC resistance with active setup? I guess if the DC resistance is 4 ohm's then I had better go series! I guess my ultimate question is will the impeadance dip below the measured DC resistance or not in an electronic x-over setup???

Thanks,
Vince

**drf** · **11-02-07, 01:48 AM**

The impedance of the drivers should only effect your amps, not the crossover.

Yes, the dc resistance (resistance at rest) will be an indicator of the coils nominal impedence, e.g 3.2 ohms will indicat a 4ohm driver and 7.6 ohms will indicate an 8ohm.

If they are 8ohm drivers I would wire them in parralel to get 4 ohms, other wise you are going to have to push your levels up to get the same SPL from a 16ohm ohm arrangment. If they are 4ohm drivers then go series and have them presenting an 8 ohm load to the amp.

BTW what allignment are you using for the X-over and are you making it variable?

**vince** · **11-02-07, 10:20 PM**

The x-over is an electronic 24db per octave. I am using seven boards "XM-1'S from Marchand Electronice" I have used there stuff before, excelent build quality. I have also implemented seven 12 step rotary swithces on the front panel with 1% metal film resitors to control tweeter level in relation to the woofer. Each position changes tweeters 1db. I am looking forward to the difference this sould make. There will be no passives in any of the speakers in my home theater now! All speakers will have there own dedicated amp obviously. All driven by Rotel gear.
Vince

**F1 fan** · **11-02-07, 11:42 PM**

Hi Vince, it will be interesting to hear about the results after changing your DT's to fully active status.I'm a fan of active systems and believe they have many advantages.
I agree with drf as long as the impedance is not below about 4 ohm's use the parrallel connection for the mid bass drivers.The nice thing about the D'appolito MTM arangement is you do not have to compensate for the effects of lobing in your crossover design as the lobing will be symetrical above and below the tweeter axis.

However you do have to consider a couple of other important things namely,adding delay to the tweeter so that it is time aligned (or in phase) with the midbass units and baffle step compensation.These latter two things can easily be done actively and added to your crossover circuits (I m sure Mr Marchand could help you with this).

The original passive crossover designer would have compensated for both of these when optimising his design, so even though you are going active they still need to be dealt with if you want to get the best results.
Good luck on your project and please keep us posted on your progress.

**vince** · **11-03-07, 02:05 AM**

Thanks guys for the input. I will keep you posted after build. As far as time delay of the tweeter, I did not consider this

wonder if R+D software can help me measure this, might have to ask Doug at acousisoft. Im sure there is a function in the software, perhaps just an impulse response of the woofer to tweeter using the same exact locations for all hardware but just swithcing the two drivers at speaker levels like Doug says in his manuel. Anyway I will try and post some pics. Just got the prodject box back from powder coater today, looks very nice. You know, amps cost aside, I don't think that I could build passives for all my speaker in the HT for what I paid to make this piece, about $700, well maybe a 6db per octave setup, but I don't think anything real elaborate as some passive designs can get! Thanks again for the input and as far as baffle step and tweeter delay, I will try and research and implement something

Thanks,
Vince

P.S. To answer drf's question, will they be variable? No the XM-1's use four 1% metal film resistors on a DIP module that just plugs into a socket on the board. I purchased the 2000Hz and the 2500Hz module's. They will make any frequency you specify. They cost three dollars each if you solder them yourself, takes about ten minutes to make one.

**F1 fan** · **11-03-07, 09:04 AM**

For tweeter delay you will need an all pass circuit as shown in #4 in this link. http://www.linkwitzlab.com/filters.htm#4 You most likely can use Doug's software to determine the amount of delay needed.Or you can get close just by visually guestimating the distance the midwoofers voicecoils are behind the tweeters voicecoil when mounted on the baffle.
Baffle step can be corrected by using the circuits shown in #5 of the above link.Also here is an informative link regarding baffle step compensation.http://trueaudio.com/st_diff1.htm

**drf** · **11-03-07, 05:56 PM**

Quote:

vince wrote:

I am looking forward to the difference this sould make. There will be no passives in any of the speakers in my home theater now! All speakers will have there own dedicated amp obviously. All driven by Rotel gear.
Vince

There should be a very noticable difference, I am doing exactely the same thing in my theatre currently except that my amps and speakers are all DIY. Other than with cost active X-overs are, (in my humble opinion), the only way to go.

**F1 fan** · **11-03-07, 07:47 PM**

Quote:

drf wrote:

Other than with cost active X-overs are, (in my humble opinion), the only way to go.

I couldn't agree more,Im using a DIY active set up and I know that I could not have achieved the same results had I tried to design my own passive crossovers.There are big performance gains to be had with the active approach.

**vince** · **11-03-07, 11:57 PM**

Thanks for the links guys, I will be checking into this more for tweeter delay. As far as baffle step I might just try and EQ this out if possible. My goal is to have a dedicated DSP Parametric for every channel. Currently I just have the DSP1124P on my sub and center. Its Iteresting you have all DIY stuff, thats respectible. What equipment are you using? I checked out the Marchand stuff, but don't have that much coin laying around! I'm sure it's nice build quality though, they say stable at "ANY" load! I want to eventually do a scan speak MTM setup all around. Maybe next year when my wallet recovers

Regards
Vince

**F1 fan** · **11-04-07, 11:06 AM**

Quote:

vince wrote:

Thanks for the links guys

Your welcome,

Quote:

I will be checking into this more for tweeter delay. As far as baffle step I might just try and EQ this out if possible.

I checked the XM1 schematic on the Marchand site to see if it could be easily modded to add baffle step comp but unfortunately it is not.You would have to add another dual op-amp per channel to incorporate both the BSC and delay.This could be built on to a little circuit board available at Radio Shack.Im using 4 db of BSC in my unit and I would be glad to supply resistor and capacitor values if you are interested.

Quote:

What equipment are you using?

Here is a listing of my stuff.http://www.hometheatershack.com/foru...830-my-ht.html

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