The trials and tribulations of trying to install a sub (part 1 - long)

[maxg]

I got an offer on a sub that looked too good to be true from Antonis at Stepcom. It usually retails for something like 3500 euros - but as it has been in his stock since time began he is letting it go for a song - so I decided to try it.

http://www.backesmueller.de/index.php?CNT=PROD&ID=SUB2&LANG=DE

Prior to delivery I decided to measure (as best I could) my bass response in room - at my listening position with the trusty Radio Shack digital meter. Now I know that these things are not very accurate below 50Hz but the measurements do seem to match my observations. So we started with:

20 Hz - 54 dB

25 Hz - 63 dB

32 Hz - 75 dB

40 Hz - 63 dB

50 Hz - 76 dB

63 Hz - 85 dB

80 Hz - 82 dB

The only thing you can say about the above is that the measurements are all over the place. I have always assumed this was largely as a result of using a home built and improperly designed set of speakers with the room being responsible for the dropout at 40 Hz.

Anyway Antonis arrived at about 10 in the evening - running horribly late as usual and schleped the sub in on his own (no mean feat - it weights 45 Kilos out of the box (about 100 lbs) and it was in the box.

As my speakers use 8 inch drivers in sealed enclosures we decided the best way to install the sub was to use its built in high pass filter and cut my speakers off at the low pass point of the sub. To do this you connect the pre-amp to the sub and then the power amp to the output from the sub via either RCA or balanced connection (RCA in my case).

Having done the connections and powered up the sub we put the test CD in and started playing tones and measuring results varying the 2 cross-over points between 50 and 100 Hz.

We then played with the phase settings and attempted to get a fairly balanced bass output level.

After 3 hours of this we got to:

20 Hz - 66 dB

25 Hz - 75 dB

32 Hz - 76 dB

40 Hz - 74 dB

50 Hz - 85 dB

63 Hz - 90 dB

80 Hz - 84 dB

As you can see from the above the 40 Hz dip is fixed - but the peak at 63 dB remains. In other words the thing I thought was room based wasnt and the thing I thought was speaker based wasnt either.

In a word - bugger!

At about 1 am we gave up on the balancing and started to listen to some music. Disasterous. And it was not the bass that was the problem.

The whole presentation was lifeless - dead - like a 128 Kb MP3.

Switch out the sub and it all returns. Weird.

So we decide that the problem is the introduction of the high pass crossover into the path between amp and pre.

We re-cable.

This time we direct connect the amp back to the preamp and parralel connect the sub to the pre on the second set of outputs.

No change.

Cant be no change - but it is. Sub on - loads of bass but dead music. Sub off and the music just soars.

The only good news thus far - the increase in bass levels is not unduely muddying the bass. In other words this is one FAST sub and it is keeping up with the 8 inch drivers in the main speakers.

Must be a power issue - we are running everything from a single outlet in the living room - the sub is obviously drawing so much juice it is killing the power to the amp. So I grab an extension chord and run the sub to another outlet.

Same thing.

Another outlet - in the kitchen this time - definitely on a separate line to the fuse box.

Same thing.

WTF??

OK - so we return the sub power to its original place and disconnect it from the system. We then pull the RCA's out of the back and power it on with the system playing. Not a squeek. Sound exactly the same. It is therefore not a power issue.

It is now 2 am. Antonis is starting to look like he has been run over by a truck - he has had a long day and I can tell he is terrified I am about to tell him to pull the unit entirely.

We switch the sub off and listen to the Tchaikovsky Violin Concerto whilst we think.

The only conclusion we have come to now is that the sub kills the pre-amp. Something about its connection to the pre sucks the life out of it. I cannot, as yet fathom the why's and wherefore's of this but there is no other explanation readily available.

With the sub in the sound is crapola - without it the sound it magic. There is a definite volume drop when it is switched in but even when we raise the volume on the pre to compensate we just get louder crap.

As it happens the sub supports speaker input too. Our final attempt with this thing is to run 2 speaker cables from the amp to the sub and see how it works. Last night we just didn't have the energy to try it so that will be tonight's game.

I am hoping that the impact of this connection is negligible on the amp - it is a 200 watt unit for heaven's sakes and as the sub is powered - how much juice can it really take?

Well I will see tonight. If there is a way to keep my mids and highs and merely extend the bass I will be one happy bunny - if not it is back to the drawing board and the sub back to Antonis.

That's all for now - not as long as I thought it might be.

[lwhaples]

Max, Can't wait for part 2. You sure gave it a good try ,and write very

well for 2:00 a.m. Hope to see it all works out! Happy Holidays!

Larry

[Doug C]

Connecting your sub via the Speaker Level inputs (Speaker Cables) will draw virtually no power from the amp since the sub has it's own volume control (gain) and amp. I'm connected in this fashion using a 2-watt tube amp and no problems. I always run my mains full range for best sound quality. Going through the sub crossover and then to the mains is just another set of electronics (and more cable) to do bad things to the sound.

Looking at your SLP readings, this is not out of line from my experience. I have room induced dips and peaks that I smooth out (but never get completely rid of) the best I can with a combination of sub placement and phase setting. I have a particularly nasty room induced peak in a narrow band around 36hz. With sub placement and phase setting I'm able to minimize it to about a +10db peak.

I'm with you, can't understand how the sub could affect the pre-amp if it's using a completely different power circuit?

Doug C

[maxg]

Max-- Since you have the sub and your amp connected in parallel to the preamp, you may be loading the preamp output below its capacity. What is the input impedance of your sub? Your amp? What kind of output is in the preamp? md

I guess you mean loading the preamp ouput above its capacity. Almost certainly true - but remember that the exact same thing happened when the sub was the only directly connected unit to the pre-amp with the amp taking its input from the sub itself - using its built in Xover.

I am checking into the imut impedances and such now - but I know the answer is - not right for the combination.

Do you know of any pre-amp that might do better - perchance?[]

[Duke Spinner]

a Peach will surely solve your impedance problem...

now you have a reason to justify buying one .....[6]

funny how trying something new in a system, always causes at least twice the expediture you counted on ...

[rigma]

Max-- Since you have the sub and your amp connected in parallel to the preamp, you may be loading the preamp output below its capacity. What is the input impedance of your sub? Your amp? What kind of output is in the preamp? md

Mark,

How do you measure the output impedance of a tube preamp if it is not known? I have had similar problems.

Rigma

[Doug C]

As it happens the sub supports speaker input too. Our final attempt with this thing is to run 2 speaker cables from the amp to the sub and see how it works. Last night we just didn't have the energy to try it so that will be tonight's game.

maxg,

Try the speaker level connection to the sub, If that solves the problem then it confirms a problem with the Preamp driving the amp and sub at line level at the same time.

Doug C

[maxg]

Mark,

Interesting point on the pre-amp ->sub ->speaker connection. I had assumed that the sub would then be taking the load of the amp from the pre but you are right - it may not be the case.

Anyway I am now at home and have just connected the sub to the speaker level connections from the back fo the amp. Sounds promising - certainly no comparison to the garbled mess I had last night. Funnily enough - there is now no volume drop - quite the contrary. I need to measure this but I think I just gained about 3-4 dB from somewhere....this gets weirder and weirder.

I have had to turn the bass right down already - a sure sign it is working better (from 3 o'clock on the dial to 9 o'clock).

Now all I have to do is to re-measure, sort out the volume and phase issues, check there is no muddying of the bass, ensure mids and highs are as they should be, try to address some of the peaks and troughs and cancel that order for a Peach[]

Anyway Mark - a Peach??? For me???? We are not thinking today methinks. I think you will find I ocasionally listen to ....er.......vinyl??!!!!

Doug,

Yup!

[Invidiosulus]

Maybe you should go back to your Sansui speakers.

I jest.

[maxg]

"well, hey, don't you all use "separate" phono stages over there? "

Only because no-one sells built in phono stages over here. Actually they are starting to - but for MM cartridges - how useful is that?

Anyway - current state of play is:

Maria Callas sounds wondrous - up one

Guitars and violins both excellent.

Numbers still not good:

20 Hz - 78

25 Hz - 78

31.5 Hz - 91 (! gulp !)

40 Hz - 82

50 Hz - 76

63 Hz - 99 (! gulp 2!)

80 Hz - 94

100 Hz - 82

Hmm - 31.5 times 2 is 63 - think this must be a room mode that I was not exciting previously as I did not have enough power down there.

Switching the phase 90 degrees makes everything worse. 180 degrees improves 50 Hz by about 8 dB - but 63 goes to 101. 270 degrees same as 90.

Right now it is all flat with the low pass xover set to about 80 Hz. this is the next thing to play with but I think the rest of the play will take days.

I am of the opinion at the moment that all I am doing is proving I need either a parametric equalizer or room treatments. Neither option fills me with glee - although parametrics are cool toys to play with.

[Doug C]

Sounds like your sub has a variable phase knob? Suggest you play the 63hz tone and have someone slowly rotate the phase knob from 0 to 180 as you monitor the Db's. By doing this you should be able to get the peak down a bit. If you flaten the peak completely then you will probably find the problem has shifted to a different frequency, so split the difference.

Was also wondering where your sub is positioned in the room? Sub position has a lot to do with what frequencies are reinforced and by how much.

I have used a Rane Parametric equalizer before and they are not difficult to use and let you dial right into the offending frequency range. I found however that the bass was tighter (more natural) without the EQ in the signal path.

Doug C

[DrWho]

Using test tones and an SPL meter to "measure" your subwoofer is a most awful approach...

The next time you take some measurements, try moving your meter around; everywhere within arm's reach from your listening position. You will notice +-10dB just by the position of your meter!

So really your measurements aren't telling you anything as I'm most certain you don't always have the meter in the exact same spot. The best you could do would be comparison measurements where you put the meter on a tripod and then measure the difference that changes on the subwoofer make....this will only tell you what you're doing - NOT what is the ideal.

But tuning a subwoofer by ear is a most simple thing to do....first invert the phase of your mains and set your subwoofer crossover pretty high (above the point where the mains start to roll off). Try to match the volume and then play some bass heavy material and adjust the phase on the subwoofer until you hear as little bass as possible. Once achieved, invert the phase of your mains back to normal and now you've got the phase aligned perfectly (it's much easier to hear full cancellation than it is +6dB). Now adjust the crossover point - typically I like to start with the lowest crossover possible, bringing the level up until I can just notice the subwoofer...and then back down one notch. Then finally adjust the gain as necessary and you should be 95% of the way there. If it doesn't sound right, then move the sub to a new location and start the entire process over.

[tigerwoodKhorns]

"funny how trying something new in a system, always causes at least twice the expediture you counted on ..."

LMAO!!

You are so right. My Khorn purchase brought about a complete replacement of my entire system.

Chris

[maxg]

Using test tones and an SPL meter to "measure" your subwoofer is a most awful approach...

The next time you take some measurements, try moving your meter around; everywhere within arm's reach from your listening position. You will notice +-10dB just by the position of your meter!

So really your measurements aren't telling you anything as I'm most certain you don't always have the meter in the exact same spot. The best you could do would be comparison measurements where you put the meter on a tripod and then measure the difference that changes on the subwoofer make....this will only tell you what you're doing - NOT what is the ideal.

But tuning a subwoofer by ear is a most simple thing to do....first invert the phase of your mains and set your subwoofer crossover pretty high (above the point where the mains start to roll off). Try to match the volume and then play some bass heavy material and adjust the phase on the subwoofer until you hear as little bass as possible. Once achieved, invert the phase of your mains back to normal and now you've got the phase aligned perfectly (it's much easier to hear full cancellation than it is +6dB). Now adjust the crossover point - typically I like to start with the lowest crossover possible, bringing the level up until I can just notice the subwoofer...and then back down one notch. Then finally adjust the gain as necessary and you should be 95% of the way there. If it doesn't sound right, then move the sub to a new location and start the entire process over.

Where were you last night when I needed you?

Ya mean I just wasted 6 hours playing on this thing? How's a guy supposed to know?

I printed this answer - thanks.

[DrWho]

Where were you last night when I needed you?

Ya mean I just wasted 6 hours playing on this thing? How's a guy supposed to know?

I printed this answer - thanks.

lol, I hope it works out

btw, I wouldn't consider your 6 hours a complete waste of time...If you took your time and tried to pay attention to what you're doing, you might find it was a most educational experience.

Heck, this is the first time I've ever heard of impedance mismatches being an issue...which I find to be a most interesting problem (though you probably don't feel that way) []

[maxg]

Where were you last night when I needed you?

Ya mean I just wasted 6 hours playing on this thing? How's a guy supposed to know?

I printed this answer - thanks.

lol, I hope it works out

btw, I wouldn't consider your 6 hours a complete waste of time...If you took your time and tried to pay attention to what you're doing, you might find it was a most educational experience.

Heck, this is the first time I've ever heard of impedance mismatches being an issue...which I find to be a most interesting problem (though you probably don't feel that way) []

Funnily enough - once we found out what the problem was - and as you can see from the first post it took some time - I too was fascinated by it.

Now that I have a solution to the problem and the sub is in and working - more so.

For reference the pre-amp I am using is the DECWARE ZTPRE running a pair of 6N1P Svetlanas.

Further, this is not the first time we have had a very disappointing listening experience with it - now that I think about it. When we connected Tony's Yamaha MX-D1 500 wpc digital amp the sound went to crapola real quick.

Some amps it likes - some it don't. I guess it was designed with tubes in mind and maybe I just got lucky with the SS amp I have now.

Too many thoughts on this one to list really. Boggles the mind that a sub and pre cant co-exist on a system.

[maxg]

Well its now 1 am and I think I am finished listening for the night. In all probability this sub is staying. I still do not have it dialed in perfectly - but following the advice of a timelord I am now pretty close.

Dvorak's Cello has just finished - tis a wonderful piece - one of the best cello works ever written (some might say the best) and at times it really shows what a reasonably integrated sub can add to the music.

Simply put - the is just a lot more mass to instruments - they are bigger and more credible ultimately. Its like moving from Row P to row B.

Thus far - very impressed - and it is as quick as the devil. First sub I ever heard that would show a clean pair of heels to a REL Strata 3.

That must be why they put 2 8 inch drivers (which look more like 10's to me - but never mind) in a sealed box. Clever stuff.

I think extension down to 20 Hz may be a little over-optimistic - but they come on strong from 25 and up - and that is plenty range for me.

[Timmikid]

Max, this thread read like a Christmas Carol. Great that it seems to work out and thanks for showing that trial and the other thing pays of together with a little help from timelords. It appears that there really is no end to upgrading, but what's more important if done wisely, it pays off!!! Thank you very much. [:@]Michael would probably have said: "Wallectomy is inevitable". Happy new year to the whole forum and I wish this forum gets a more than statistically expected share of winnings at the newyears lotteries, because I know we will spend it on a good cause (and a little on charity ofcourse). []

[maxg]

2 things of interest to note from the following picture:

1. How well the sub fits into the gap I had.

2. Max has a new digital camera.

The old Sony DSC-P1 has had its chips - the battery is dead and not only difficult to get hold of - they are charging a fortune over here.

So for just about twice the price of the battery I got me a Casio EX-S500 on 10 easy and interest free payments. This is a small camera - almost fits in my wallet. I am bound to lose it.

Oh - the pic is reduced to 800*600 for the forum - the original is a 5 megapixel monster.

[Doug C]

maxg,

Is that your sub between the TV and your left speaker? Not much wall behind it or to the left side to reinforce the sub output evenly? Just for comparison purposes, I sugesst you try it tucked tight into the corner to the right of your right speaker. With low frequencies it won't matter if the right speaker seems to be blocking the front of it.

In my system the sub is slam tight in the front left corner. This corner shares the two longest walls in my room giving the maximum reinforcement across all frequencies. This position also produces the most consistent bass levels throughout the room. From my listening position the front of the sub is completely obstructed by my left main but the bass is still great.

Doug C