Rebuilding 15yr old speakers, and other questions...

[servicetech]

I've got some speakers I've built in the early 90's and I considering rebuilding them. These are from a "kit" that MCM used to sell. Components are 55-1465 woofer, 50-650 crossover ( I can't believe they still sell these) a 1" titanium dome tweeter similar to PE 270-150 (looks the same, original was MCM brand) and a 2" textile dome tweeter MCM no longer sells. Everything mounted in a 3.5 cuft cabinet ported to about 35HZ (4" pipe, 5" long). Bass/Midbass is very strong since apparently the mids/tweeters aren't running the 95-96 db/w they were originally rated. Woofer seems to be close to 95-96 db 2.83V/m running the 8 ohm coils in parallel. They still sound fairly decent but not as good as a recent center channel project I completed (MTM using Dayton 295-305/275-070)

Are the old speakers worth rebuilding or would you just sell them and start over? I was thinking replace the tweeters w/275-070 and rebuild the crossovers. In redesigning the crossovers I'm looking at running one of the coils for low bass only and the other crossing over at 800hz. I know grilles are a no-no theses days but with an 18 month running around they are a necessary evil.

Images not available

[servicetech]

I'm looking at possibly some Dayton 275-045's instead of the 275-070's for a bit more treble.
Which tweeter would you go with?
Or should I just sell the set and start over?

[ThomasW]

These aren't 'classics' like old Advents, rebuilding them isn't a good investment. So my advise is gut them and put in one of the proven designs in the Missions Accomplished section of the forum.

[servicetech]

If you are suggesting salvage the cabinets and replace the drivers/crossovers, what in the mission accomplished section would use a 12" woofer and a 3.5 cu ft cabinet? I've even though of reusing the cabinets/woofers and replacing the crossovers/midranges/tweeters.

[ThomasW]

Obviously there is no 12" 3-way in the Missions Accomplished section, but there are certainly other options.

One option would be to use the existing box as a bass bin and put a MT or MTM on top of it...

If there's someone willing to buy them that gives you cash and a clean slate to start off....

So it all depends on what you want to do and the budget.

[servicetech]

As a quick fix I've ordered a pair of Hi-Vi tweeters @ $12.60 each, and picked up a 47uf cap and 4ohm resistor for the woofer zobel.

Not as elaborate as building a nice system from scratch, but I should be able to get a few more years before building a new set.

As an added note I used this website as the PE referral source on the order page, hopefully HTguide will benefit somehow.

[servicetech]

Just did the Hi-Vi tweeter swap out and added a zobel to the woofer. I can't believe the difference in sound, well worth the $40 per pair spent.

Only 2 bad things:
1: There seems to be bigger differences in sound quality from CD to CD.
2: I can tell the effects the grills have on the sound, before the upgrade you couldn't really tell much difference.

I've only done one speaker, I'll have to do some more testing once both speakers are finished.

[servicetech]

What Gives ?

Since doing my recent speaker rebuild I finally had the house to myself and was able to really test the speakers out. What I've found is some of my CD's some awesome, I'm hearing things I've never heard before. Other CD's seem to sound worse than before I rebuilt my speakers. Before the rebuild some CD's sounded better than others, not now there is a big difference in sound, especially in the treble. I thought some of the recordings just had a low treble level but upping the treble control didn't make it sound cleaner, just brighter. Some my CD's sound like old cassette tapes :cry:

Has anybody else had this happen after a new speaker build/rebuild? Is there really THAT much difference in CD recording/master quality? I've tried Popular/Unpopular, Old/New, Rock/Top40/R&B, it doesn't matter. There doesn't seem to be any rhyme or reason to what recordings will sound good or bad, the only way to know is to stick it in the CD player and try it.

Chicago, Eagles, and The Police sounded great.
Rush sounded bad, Boston "OK". AC/DC sounded OK.
Run DMC, some good some bad. Janet Jackson sounded good.
Beatles sounded good considering the recording is 40yrs old, better than many of the newer recordings.

[joecarrow]

There really is

It's sad, really- you know how some people really believe "These MP3s are CD quality!"? My wife thought I was crazy when I told her I still buy CDs because I can hear the difference between them and MP3s- but I tell you, with anything less than a 320kbps (the highest encoding quality), I can very easily tell which is which in a blind test.

It was sad for me when I built some good speakers and had to realize that some of my favorite songs just weren't recorded very well. Still, I think it's worth it when you hear how great it can really sound when it's done right. That extra level on some songs, it kind of makes up for it.

[---k---]

Yep.

What your saying is quite common. I'm sure those that have been around these parts for a while have all lost count of the number of people who have built one of Jon's designs and then complained that it made all of their rock recordings suck! Good speakers will revel bad recordings.

But, it just isn't all bad recordings (mostly). It could be the instruments/effects used in a recording emphasis a specific frequency that just so happens to line up with a null or hump.

[ThomasW]

The old axiom is.... the better the equipment, the worse the bad recordings sound, and the better the best recordings sound...

As a general rule so called 'pop' recordings have the worst sound quality. There are of course exceptions to this but they're rare.

Moderator's note.

From now on I'm merging your threads. IMO it makes no sense to open a new thread for every question being asked...

[stangbat]

One of the pitfalls of good equipment. Crappy CDs now sound...crappy. Welcome to the Loudness War. Rush's Vapor Trails is widely criticized for sounding terrible.

As for AC/DC, the new re-masters are criticized for lack of dynamic range. AC/DC's Ballbreaker is not a great recording, and Stiff Upper Lip isn't much better. However, I have an old (circa late 80s) CD of Back in Black that is very good. The rest of the older AC/DC stuff I have that was mastered a while ago, which means Thunderstruck and older, is pretty good.

[servicetech]

It's sad, really- you know how some people really believe "These MP3s are CD quality!"? My wife thought I was crazy when I told her I still buy CDs because I can hear the difference between them and MP3s- but I tell you, with anything less than a 320kbps (the highest encoding quality), I can very easily tell which is which in a blind test.

My heart dropped when I read this, a lot of my stuff is MP3s'. I just had to have a listen after reading this. I'm pretty fortunate, the MP3's are fairly good quality for the most part. Not quite as good as some of my CD's but not as bad as some of the bad CD's. The good MP3's sounds good enough for me, the bad ones are probably from CD's that were recorded bad to begin with.

As for AC/DC, the new re-masters are criticized for lack of dynamic range. AC/DC's Ballbreaker is not a great recording, and Stiff Upper Lip isn't much better. However, I have an old (circa late 80s) CD of Back in Black that is very good. The rest of the older AC/DC stuff I have that was mastered a while ago, which means Thunderstruck and older, is pretty good.

I was using "Who made Who", I'll have to give the others a try.

What your saying is quite common. I'm sure those that have been around these parts for a while have all lost count of the number of people who have built one of Jon's designs and then complained that it made all of their rock recordings suck! Good speakers will revel bad recordings.

But, it just isn't all bad recordings (mostly). It could be the instruments/effects used in a recording emphasis a specific frequency that just so happens to line up with a null or hump.

On the "bad recordings" do you guys boost the treble to try to compensate or just live with the weak sound? I hate to ruin my good recordings by boosting the treble or be constantly messing with the controls. Speaking of bass/treble controls, do you guys run them "flat" or adjust them to taste? Since the rebuild my system sound great flat for the most part, I do have the bass EQ turned on just because I like a bit more low bass. No subwoofer in my system just yet.

I've also had a chance to try out the HT aspects of the speakers. WOW, what a difference, I can really pinpoint the location of the sounds. Sound effects are much more real. Volume doesn't have to be as loud to make out voices (I know this probably doesn't make sense since 90% of vocals come from the center).

[stangbat]

I did a quick comparison between the "Who Made Who" CD and some other CDs that contain the same songs. It is hard to say for sure, but I thought "You Shook Me" was about the same. I'm not sure about "For Those About to Rock". And I don't think the song "Who Made Who" is a very good master. It is kind of dead sounding. This is one problem with compilation CDs, they are sometimes all over the place.

I went back and listened to some other AC/DC discs and I have to say that "Flick of the Switch" is probably the worst sounding CD I have. Absolutely terrible. Pretty much unlistenable. I wonder if there are better masters out there. "Let There Be Rock" isn't very good either.

[servicetech]

Some more testing has revealed that the system sounds better with the bass boost turned OFF. I took a look at the schematic and found that there is a a bypass relay that kicks in when the bass boost, EQ, and sound fields are all turned off. The signal goes to the volume control, balance control, then on to the main power amps, bypassing all other circuits. This is only true for analog inputs, digital inputs still go through processing. With 12" woofers the bass boost isn't really needed anyways.

Tried out some Country CD's, most of them are recorded very good. I was a bit surprised.

[servicetech]

Looks like Midranges also need updating...

Apparently the midrange speakers are also worn out. For a quick test I hooked up some 5.25" full range speakers in place of the 2" dome midranges, the full range speaker sounded clearer and was a bit stronger also. I'm looking at some 280-240's for a low cost replacement that will fit the 4 7/8" hole. Has anybody used these midrange speakers? Where could I find performance specs on the drivers?

Also are "stock crossovers" typically Butterworth, LR, or just whatever the manufacturer feels like making?

[servicetech]

How about a Dome Midrange?

I found another candidate, the Hi-Vi DMB-A that also would fit nicely in the hole. It's a few more $$$ than the 282-240 but I really like the Hi-Vi SD1.1A that I used for the tweeters. Has anybody used either of these drivers in a project?

Since both speakers are 5.5 ohm some crossover adjustments are going to be needed, I was thinking crossing @ 3,500hz 6db/octave since both drivers have a flat response well above/below the crossover frequency. Both drivers are close in sensitivity, a nice added bonus. The midrange is about 8 ohms @ 800hz so the existing low pass should work. According to the crossover calculator I need a .25mh coil and 8uf cap, now the question is to wire in series or parallel.

[servicetech]

Stock crossover suck.

I just pulled the x-overs to find out what the component values were and of course the coils weren't marked and the caps were turned so you couldn't read the values. I turned the caps so I could read the values and don't see how they are getting a 4,500hz crossover point @ 8ohms with a 4uf cap in a 12db/oct configuration. My calculations show closer to a 3,500hz x-over point if they used a butterworth setup. The midrange uses a 22uf cap which runs it down to 650hz in a 12db/oct setup and a 4.7uf cap which cuts the high end @ 3,000hz. the woofer uses a 30uf cap which would be 950hz @ 4 ohm, it's the only cap that even gets close to the rated x-over frequency. I hate to think what inductor values they used. Never again will I buy a stock crossover !!

If I put in a new crossover, midrange, and tweeter I'll basically have a new set of speakers. Only the woofer will remain from the old setup.

It's looking like a brand new crossover from scratch, at which point I'm wondering if I should pull the tweeters and just start a new project. Are there any proven designs that I could reuse the Hi-Vi SD1.1A's in with enough bass response that I wouldn't need a sub?

[servicetech]

Midranges Ordered

I decided to go with the Hi-Vi mids.
Now it's a waiting game until the parts come in.

Once I did some more calculations it turns out the original crossover was designed for 4 ohms on ALL the drivers, not just the woofer as listed in the MCM catalog. Of course this will be corrected to Hi-Vi's 5 ohms with a few new crossover parts. I decided on doing a 12/db oct @ 800hz for the midrange high pass, and 3500hz crossover @ 6db/oct series crossover for the mid/high. I was able to "recycle" most of the old crossover except the caps. Some of old caps were electrolytic so they needed to go anyways. I did a side by side test on electrolytic vs/mylar, HUGE audible difference especially at high frequencies.

[servicetech]

One Down, One to go.

Replaced one of the midrange speakers and have noticed clearer vocals. The Hi-Vi mids seem to have more sensitivity than the originals, some of this may be from the reduced impedance. Not as a dramatic difference as changing the tweeters though. The overall sound is close to that of the center channel. Had to bump the center speaker +3db relative to the mains to even the level out.

I'm assuming the woofer be wired "in phase" and the midrange/tweeter network be out of phase with the woofer. Should the mid/tweeter be in or out of phase with each other?

[Dennis H]

I'm assuming the woofer be wired "in phase" and the midrange/tweeter network be out of phase with the woofer. Should the mid/tweeter be in or out of phase with each other?

I don't know how any of us could answer that. You may have noticed we're a "science" board here. That means measuring the drivers (SPL, phase, impedance) in the box, plugging the measurements into crossover simulation software, and designing a crossover that gives you the desired acoustical SPL and phase response considering how the SPL and impedance of the drivers vary with frequency. Everybody has been pretty polite about your "try a new driver and some textbook filters and see how it sounds" approach but I'm afraid you won't get a lot of help with it. Textbook filters assume SPL and impedance are flat with varying frequency but neither is true. Textbook phase assumes all the drivers' acoustical centers are the same distance from your ears and that isn't true either.

[servicetech]

I'm relatively new to high tech audio testing, my specialty is actually video displays (what I do for a living). One day I'd like to get some more equipment and have the means to really do some deep testing like you guys do. I did consider impedance curves when selecting component values, the phase thing still is a bit of mystery to me. I understand what phase is from doing video work, I'm just not sure how the theory applies to audio systems.

My next project will probably just be a tried design somebody else has done, it's a lot easier than the trial/error method I've been using for 20+ years. I'm done with 3 ways, future projects will be much cheaper and simpler 2 ways. Today's tweeters play much lower than years ago and the small woofers can get decent bass response now. Of course I'll need to build a sub to pick up the deepest bass for HT use.

I've noticed many of the designs on the PE projects use textbook crossovers, even stock crossovers. How are they getting good results? The featured design is a $300 project that uses $2 tweeters and $7 midranges, and this is considered cheap for a 3-way. Supposedly goes down to 36hz, but I don't know how considering the woofer has an FS of 45hz and is in a sealed box.

[ThomasW]

I've noticed many of the designs on the PE projects use textbook crossovers, even stock crossovers. How are they getting good results?

Who said they're getting good results?

With rare exception (like Curt's TriTrix and a couple others) when one looks at the projects on the PE page they're so bad PE should be should be embarrassed to host them. But it's business and if someone is ignorant enough to build them, PE is willing to sell the parts.

[Dennis H]

I understand what phase is from doing video work, I'm just not sure how the theory applies to audio systems.

The thing that really mucks up phase for a speaker is the acoustical center of the woofer may be as much as 2" behind the tweeter (roughly where the voice coil attaches to the base of the cone.) So you may need a steeper filter on the tweeter to delay the phase to match the woofer at the crossover frequency. And remember, when we talk about filter slopes, we're talking about the acoustical response. It's not uncommon for a 2nd order electrical filter to give a 4th order acoustical response when you add in the driver's SPL, so you can't just look at the electrical transfer function.

The whole thing is really complicated but these days it's really simple (sorta). You need a mic, a mic preamp, a computer with a sound card, and some free or pretty cheap software. The good old days of breaking out the signal generator and plotting points on graph paper are long gone, thank goodness.

[servicetech]

Phase issues, cont.

Apparently I didn't get it right, the center doesn't "lock" to the left speaker in the AVIA phase test. The woofers are wired correctly, tested with the "D Cell" method.

My center channel originally had the tweeter out of phase, connecting in phase helped lock the image to the left speaker. I'm not sure if "in phase" or "out of phase" is the "correct" way to wire the center. The center has a simple 6db/oct series crossover w/zobel for the woofer.

From this point where do I go? Reverse mid and Tweeter on one main or just the mid? According to the phase data provided by Hi-Vi both tweeter and mid are about 20 degree "positive" on the phase at the 3500hz x-over frequency. How does a series crossover affect phase?

[servicetech]

Who said they're getting good results?

With rare exception (like Curt's TriTrix and a couple others) when one looks at the projects on the PE page they're so bad PE should be should be embarrassed to host them. But it's business and if someone is ignorant enough to build them, PE is willing to sells the parts.

What gets me is some of those projects cost as much as the designs in the "mission accomplished" section over here. It's not like they are doing the PE build to save money.

[servicetech]

Center MTM correct, now onto the mains

The Dayton MTM is correct with the tweeter out of phase, I tried both ways. When the tweeter is out of phase the voice locks to the screen, when the tweeter is in phase the voice seems to come from all 3 front speakers.

The mains also benefited from having the mid/tweeter out of phase with each other, the sound seems to "lock" from the speaker instead of "floating". However the mains and center still fail the AVIA DVD "phase test" even though the Woofer/DC is correct. Reversing the leads on the center speaker will get it to pass the AVIA phase test but then it fails the DC test. I guess the only thing left to do is reverse the mid and tweeter on the mains and hope if doesn't throw the woofer/mid phase off too much. Who knows, maybe the woofer/mid phase might actually work better with the mids wired "in phase", instead of using the conventional wisdom of running the mids "out of phase" for 12/db crossovers.

[servicetech]

Lost on this phase thing

How do you "read" phase data from the MFG charts?
The frequency response and the impedance charts give totally different data, is there a way to manually incorporate this into crossover design? Is there a way to predict response w/o using a software program?

Are the days of manually calculating crossovers done and if you don't have software you can't design one? I tried a demo of the Leap 5.0 program and it's WAY over my head, I don't even know where to start.

Does anybody know of any proven designs that utilize the Hi-Vi dome mids/tweeters? Before I started visiting this site I didn't even think of phase any more than + to + and - to -, I guess ignorance is bliss to some extent..