Modifying my Mission 765i with big Heils. I could use some advice

[Broadwayautoclinic]

Hello all. I need some technical advice, and I know I'm in the right place for that.

I own a set of Mission 765is that I bought in the early 90s. I love them, but the highs are not up to snuff for todays music, or maybe I'm getting a little deaf. Today, I bought a used pair of big Heils with the original crossovers from ESS AMT monitor speakers. I am told they are all in mint condition, and I'll know soon enough when I receive them. I had a pair of ESS speakers in the 80's and I loved the mids and highs they produced. I am hoping to meld the smooth bass and mid-bass from the Missions,with the midrange and treble of the Heils.

My question is, what is the best way to to go about hooking them up to my Missions? I am driving my Missions with a Adcom 5802 amp. I also have a McIntosh 2300 I could use as well, but currently it is driving my surrounds. Both amps can drive down to 2 ohms.


Should I leave the Missions as is, and run another wire from my amp to the ESS crossovers, and then to the Heils, or should I use the ESS crossover to replace the crossover that come with the Missions, and disconnect the Mission tweeter? I am not sure how this would effect the impedance. The Missions use a two way design, with two 8" drivers and a dome tweeter.

Thank-you in advance,

Rick

[Broadwayautoclinic]

Anyone?

[AllenB]

Short of building new crossovers, I would suggest you start by disconnecting your mission tweeters, and running the heils from a separate amp. This will help you to take care of the difference in level. Although I have neither of these speakers, I believe the heils are sensitive.

Secondly. you'll need to adjust at least one of the crossovers to meet up with the other, if they don't just work straight off. It would be tempting to leave the heil crossover alone and adjust the mission woofers but this is something you may need to work out on your own. Do you have the mission crossover schematic or a photo?

[Broadwayautoclinic]

No Allen, I do not have have the Mission schematic. However, the ESS crossover does have an adjustment pot for the Heils. I believe it is + - 3db. Could I use the ESS crossover in place of the Missions altogether?

[Loren42]

This is not a simple process. There are many factors that go into driver selection for a speaker.

It is more than simply level matching the Heil to the Missions, so the ±3 dB pot is not going to cut it.

Some of the factors that you must consider in the process are:

Level
Crossover point
Phase
Matching horizontal dispersion angles between drivers
Proximity to other drivers
Impedances

The suggestion of using a dedicated amp with an electronic crossover (optimally a digital one) would give you the best chance of success.

You will also need to do comprehensive testing to validate your work. So, a microphone, audio adapter, PC, and associated software will be needed (along with knowledge on how to test loudspeakers). You can't do this with your ears.

A simpler route would be to see if you can get the Missions fixed.

[AllenB]

Originally Posted by Broadwayautoclinic

I believe it is + - 3db. Could I use the ESS crossover in place of the Missions altogether?

I doubt that 3dB will be enough.

Building crossovers can be a very involved process. If you are prepared to accept less than perfection and take it one step at a time then you have many options open. You could probably just use the heil crossover but you said you liked the midbass of the missions and it would seem a shame to just ditch the mission crossover without at least 'learning its secrets'.

[Broadwayautoclinic]

The Missions are two way. I think the AMT monitors are also two way ? Not sure. But what would happen if I used the ESS crossover to drive the Mission drivers? would I necessarily loose the good characteristics of the Mission crossover? I do not have the schematic for the Missions. But I am not super critical. I have a mish mash of amps and speakers . Polk lsi9 and Sonas Faber Concertos for the sourrounds Polks driven by a Mac 2200 and a Mac 2300 for the Concertos.

[c2cthomas]

Hi Rick! and Welcome to diyAudio!!!! :

Check out this link for a crossover schematic to think over.
ESS amt 1 am crossover
The xovers ESS used were designed for a lot of adjustment to account for room placement and thus the user could "tweak" 'em to fit their needs. One problem is the age of the components comes into question - and the fact that the components used are not of the quality available today. I would suggest that you seriously consider replacing the electrolytic cap's and take a careful check of the pots, resistors, connectors, etc. for aging.

With my Great Heil's I went the simple rout - crossed over high - 6KHz - using a 6.8uf cap and to even out the SPL's I tossed in a 10Watt 4 ohm resistor.
2-Way Crossover Designer / Calculator

I hope that this is of some help to you!!

[Broadwayautoclinic]

I just bought a BBE digital external crossover. I hope it does the trick

[Broadwayautoclinic]

Originally Posted by c2cthomas

Hi Rick! and Welcome to diyAudio!!!! :

Check out this link for a crossover schematic to think over.
ESS amt 1 am crossover
The xovers ESS used were designed for a lot of adjustment to account for room placement and thus the user could "tweak" 'em to fit their needs. One problem is the age of the components comes into question - and the fact that the components used are not of the quality available today. I would suggest that you seriously consider replacing the electrolytic cap's and take a careful check of the pots, resistors, connectors, etc. for aging.

With my Great Heil's I went the simple rout - crossed over high - 6KHz - using a 6.8uf cap and to even out the SPL's I tossed in a 10Watt 4 ohm resistor.
2-Way Crossover Designer / Calculator

I hope that this is of some help to you!!

Wow, that is an interesting setup you have there. How does it sound?

I am a little too hasty, because I didn't realize what the heck I was buying when I bought the BBE DS26. I thought it was an adjustable crossover that hooked directly to the drivers. My preamp doesnt even have balanced inputs! I hope I don't get stuck with it