Dual Subs advice ???

[Alaric]

Hi there,

Is it a co-inky-dink that the BFD has two chanels ??? I've just ended up with two subs, my Paradigm Servo 15 and a Mirage BP150i (it came as set of speakers i picked up on ebay - and it would be rude not to use it).

My yamaha DSP-AX1 has a dual output for subs, though i'm not sure if this is best or a splitter cable (though i'm also spilting for Buttkickers etc).

I have a second XLR to phono cable comming and have placed the second sub behind the screen wall in prep.

However thats probably as far as my thinking has got, so advice is more than welcome.

I guess that just outputting tones from a disc for balencing audio levels, i can't set one, then the other, otherwise i'd have twice the bass (although actualy that probably isn't true as sound is totaly addative).

What about room eq with the REW can that be done sperately, but will i also have to check together etc ???

Ta,
Lee

[brucek]

and it would be rude not to use it

Don't get me wrong, but it would be rude to use the BP in the same room as a Servo-15. They're not even in the same league I'm afraid.

Combining two subs is quite difficult, but can be done if they are the same model and even easier if they are the same model and co-located.

Trying to equalize two subs, of which one is inferior to the other simply drags down the better sub, specifically in the area where the lesser sub is wanting.

Use the Servo by itself - you'll be pleased......

brucek

[Sonnie]

I have to agree here... I'd probably try to sell the Mirage sub. That Servo 15 is known to be a very fine sub and as brucek eluded to, miles ahead of the Mirage. You could use the Mirage in a second room or again... sell it for something maybe. If you gotta have two subs, which I'm a fan of, I'd get another Servo 15... then watch out for the slobber.

[Alaric]

Hi There,

You suprise me to some extent. When they were both on sale here in the UK, the Servo 15 was probably cheaper than the BP150i !

I must admit looking at the size of the two and knowing the wattage of the servo (400 vs 150) i was also retisent to do much with the BP however when i pluged it in to test, it put out quite a lot of Ooomph, i was quite pleasantly suprised.

I know the Servo15 sacrifices some low end grunt for acuracy and was hoping that the BP may make up for this. I also don't know how much the tonal qualities affect things....The rest of my set-up is mirage.

I guess the BP400 would be a better fit, but they are a pain to get hold of, so i may look for a second servo...I have heard of someone using four and corner loading a room up !!!

You really don't think its worth experimenting ?

Ta,
Lee

[brucek]

the Servo 15 was probably cheaper than the BP150i

Hopefully, we're talking about the same products here. The Mirage BPS-150i was a dual 8" mid priced sub that sold for about $600US and had a response that was down 3dB at 22Hz. The spec sheet is here

The Paradigm Servo-15 is a servo controlled 15" sub that sold for about $1500US and had a response down to 14Hz.

I know the Servo15 sacrifices some low end grunt for acuracy

Not at all - it is known for its low end extension capabilities.

You really don't think its worth experimenting ?

Sure, but let me tell you what will likely happen. You can easily verify this with Room EQ Wizard.
The desire is to have a smooth response, so hopefully both subs are contributing a certain spl level across the low frequency spectrum.
Let's look at 50Hz. Both subs can easily produce this frequency and lets say each contributes evenly to the final spl level of 50Hz in the room.
Now consider what happens at 15Hz when the Servo outputs the same level it outputs at 50Hz and the Mirage output has dropped off the map. You need both subs to contribute to the overall level and one isn't doing the job, so the overall spl level is lower at 15Hz. If you had used the Servo by itself you would draw from its headroom and use it alone to contribute to the desired level in the room producing and even response down to 15Hz. Two or more subs only add headroom (if needed), but can be a response killer if the two subs don't match.

brucek

[Alaric]

Hi There,

Yep we are talking about the same products, however the Servo got handled by a discount chain called Richer Sounds over here, they are actualy the largest specialist retailer and they work out of tiny shops piled really high, but also tend to sell last years models at silly prices. Hence my Servo cost £400 me IIRC. Mirage is a rare beast here and very much a premium brand.

http://www.homecinemachoice.com/revi...geBPS-1501.php
December 2001 £700

http://www.homecinemachoice.com/revi...gmServo-15.php
May 1999 Price £799

So over in the UK, they would have been quite cost comparitable, and when RS got them, a silly bargain.

I must admit, just putting the pair in the same room, the mirage looks less potent and it was only when i rigged it up to check it worked etc, that it really did suprise me. I guess to dual 8" cones do add up to a reasonable excursion and at a guess are substantialy quicker than a 15" one.

You explanation of why two mismatched subs would actualy reduce the sound is as ever simple and concise and i understand the logic. In some respects i also gather it could be an argument for not using even two matched subs, as room acoustics will invaiably mean that one is loaded differently and as such could cause a drop in overall levels.

I still like the idea of dual subs, i guess a pair of Servos are probably the way to aim for....I'd like to hear a BP400 as i guess that would be a better match for my system, but they are v. rare here.

Thanks,
Lee

[Wayne A. Pflughaupt]

In some respects i also gather it could be an argument for not using even two matched subs, as room acoustics will invaiably mean that one is loaded differently and as such could cause a drop in overall levels.

Not a drop in overall level – that will actually increase. What suffers is overall response. It’s tricky to explain. This comes up pretty often, so I think a visual is really needed. I’ve been meaning to do a graph to show what happens the past couple days, but haven’t managed to. Maybe tomorrow or this weekend. Stay tuned.

Regards,
Wayne

[Wayne A. Pflughaupt]

I hope someone appreciates this, because it cost me dinner and a movie for my wife to create these charts for me! (Sonnie, maybe you can tell me why they look so bad? We modified the charts for our subwoofer review, but they didn’t look like this.)

Okay, first we have to address a few “givens” here. The first is that two subs’ measured response in a given room will be very much the same, except at the lowest frequencies. This is because most of a sub’s in-room response is determined by the room itself - it’s modes, cancellations, etc. The reason subs will deviate most in the lowest frequencies is obviously because the most prodigious subs will have more output down there.

You can see what I’m talking about in this graph from my subwoofer review:





As the graph plainly shows, the Infinity and Velodyne subs had better extension than the JBL, while the SVS sub handily bested all the others in this regard. Sure, there are some deviations in the upper frequencies, but they are minor. They are minor enough, in fact, that you probably won’t hear the difference. I certainly could not tell a difference in these subs’ performance in the 38-70 Hz region when I listened to them.

The other given is that if you place two subs in the same location - we’ll use a corner for sake of argument - there will be about a 6 dB gain in output over their combined operating response. Notice I said “combined” operating response. Obviously at frequencies where one sub is deficient, you won’t get the full 6-dB gain.

So, let’s take the case of two theoretical mismatched subs.





As you can see, Sub 1 has good output all the way down to, and below, 20 Hz. Sub 2, on the other hand, rolls out pretty hard below 30 Hz or so.

(Sub 2’s response had been shifted downward 2 dB, for the sake of clarity. For the sake of this presentation, both subs have the same maximum output. As noted in the first chart, the two subs’ response won’t be as identical as this. It was just easier for the sake of this presentation [read preparing graphs] to have them mirror each other.)

Okay, what do we get when we stack the two subs in the same corner? Something like this:





As you can see, we get a 6-dB gain in output over the “combined” operating range. In this case, that means everything above 30 Hz is up 6 dB compared to either sub by itself (remember in the first chart we shifted Sub 2’s response only for the sake of clarity). Notice what happens below 30 Hz, where Sub 2’s response fall out. At those frequencies Sub 1 is carrying the mail all by itself, so everything is 6 dB lower compared to above 30 Hz.

So what do we have? Sub 1 by itself gave us nice smooth response, with great extension. But when you combine the mismatched subs, overall response suffers considerably below 30 Hz. You can be that the problem will be audible!

Trying to fix the problem is “iffy,” even with equalization. Boosting either sub’s ultra-low frequency response to take up the slack may overdrive it, but you might get away with it if you have plenty of headroom. However, the best thing to do is simply to ditch the lesser sub and either go with the one good one, or if you really need the output, make your Sub 2 another Sub 1.

Regards,
Wayne

[Sonnie]

(Sonnie, maybe you can tell me why they look so bad? We modified the charts for our subwoofer review, but they didn’t look like this.)

Looks like you shrunk them down in an image editor to me. It might be better to shrink them within Excel by clicking on it and dragging the edges inward. Then right click the outer blue area and copy, then paste into an image editor as is. When you shrink them in the image editor they distort somethimes, depending on how much you shrink it.


Btw... good explanation and examples.

[josh]

Hey Alaric

I have recently experimented with my Servo 15 and a JBL 18" sub, I found that the low end rumble that is so deliciously awesome on the Servo 15 when playing Yello The Eye/Junior B, a must have song to show off that low end rumble, I completely lost the lows when using both subs, no amount of tweaking and adjusting could even come close to the Paradigm Servo 15 alone.

It didn't take long, a coupla hours to realise that the Servo 15 alone is far better in pitch and accuracy than trying to use it with another sub and I have my wonderful window/couch rattling rumble back now.

I've tried a lot of subs, including Velodynes and nothing even comes close to the Servo 15, I haven't had the opportunity to try the SVS subs that are so popular in this forum, and would appreciate a subjective evaluation of SVS versus Servo 15 if anyone has compared them

[vierling]

In these acoustic predictions, We have a 100´ X 130´sound-field,
The reason for this is that I want You to understand how low-freq´s can expand.
This is a plan view projected with two subwoofers working together @ 40Hz, with the same specs, amps, and x-over filters.
Each one has 2 X 18" speakers, with a freq response of 28 Hz - 150Hz @ +-3dB, with a 600W amp.
All the sub´s have the same coverage (omni) so We can expect almost the same behavior in big or small speakers.

At the front ( X to the right ) is a microphone which can give us the freq response in that field, at 68º F and 20% relative humidity.

You can see that they expand to 360º when they are mounted one against the other.

In number 2 and 3 of these predictions You will see what happens if You separate the sub´s from each other.
Energy collapses to the center and starts to have deep cancellations in some areas, and sums energy in others,

Imagine that the reflected sound acts as a "virtual" speaker that is working in a different phase and time, against the original source.

Note: I am NOT calculating the reflections ( wall´s, floor or ceiling ) in this case, but if anyone would like to see another prediction, maybe with other dimensions, or freq´s, Just let me know !

[Blaser]

Wayne,

I appreciate your clarifications... I am also against use of different subs simultaneously. I don't know if you are aware of the HSU new mid bass module, which has a freq. response ranging from 40 and up...And everybody's beginning to follow a new fashion of adding a MBM module in the nearfield to have additional headrooms and punch in th mid bass region. I even saw people add an MBM to an SVS Pb12+/2 (the SVS is already very dynamic in the midbass and stronger than freq. below 20).... Pls see these threads: http://www.avsforum.com/avs-vb/showthread.php?t=768725 and http://www.avsforum.com/avs-vb/showthread.php?t=786627 and

I wonder what happens at high listening levels where one would have ample headroom in the midbass and being near compression at lower frequencies... sound will get muddy IMO

am I nuts?????

[Chrisbee]

I spent some time trying to match my SVS to my IB using REW.

I got a deep ditch that refused to fill and wandered up and down in frequency as I adjusted the phase on the SVS.

This is just an example.



Ignore the meter correction curve. I forgot to change the correction files for my meter for this one. So the graph seriously exaggerates the low bass.

And another.

[brucek]

Ignore the meter correction curve. I forgot to change the correction files for my meter for this one. So the graph seriously exaggerates the low bass.

That makes it fairly hard to interpret any graph then.....

brucek

[Chrisbee]

With respect brucek it doesn't alter the presence of the phase-related notch.

I have so many graph images saved already from REW that I don't always remember to save a new test situation.

Even finding new names for the graph images (which still means something to me a few weeks later) is becoming creatively challenging.

For example: My typical graph image names would look like this:

"ib plus bfd trgt 80 db cx 75hz 4 fltrs boost 16db at 20hz 3ft frntofchrpos ear ht plus svs phse 180 cxbypsd nrml rmpos gain 12oclck.

[Wayne A. Pflughaupt]

Chrisbee wrote:

"ib plus bfd trgt 80 db cx 75hz 4 fltrs boost 16db at 20hz 3ft frntofchrpos ear ht plus svs phse 180 cxbypsd nrml rmpos gain 12oclck.

[brucek]

I have so many graph images saved already from REW that I don't always remember to save a new test situation

Fair enough, but compensating a measurement with an incorrect calibration file can exaggerate comparisons where different frequencies are involved, since the calibration files offer non-linear correction. The comparison of the old analog cal file vs new analog cal file varies 19.7dB at 10Hz but only 4.5dB at 30Hz. It tends to skew the results and the interpretation.

I guess my comment was couched in the bigger idea that inaccurate measurements and testing procedures are one of the biggest problems with REW (or any testing for that matter). I'm not singling you out, but I see a lot of conclusions drawn by other forum members that are simply a result of testing or graphing error. I think it's important to remove as many variables as we can in the testing.

brucek

[Ciscokid]

Hello. After reading your post Wayne I decided to runs some tests on my setup. I wanted to see if my subs respond in the same manner as logic would dictate.

I have an EP500 and an old Cambridge Soundworks sub. I had been running just the EP500 for the longest time. Since my other sub was just sitting around collecting dust, I decided to hook it up. I wanted to help balance out the bass sound in my room so that it would not appear so localized. Both subs are in opposite front corners of my room.


The graph Shows the EP500 in blue, Cambridge in purple, and both subs in green. If you look from about 15 Hz to 20 Hz the EP500 rises very quickly. The Purple(Cambridge) line takes on a much more gradual rise. When I put them together my low end at 15 Hz to 20 Hz picks up around 10dB.In turn between 30 Hz and 40 Hz I get around a 7dB drop. When running both subs independent the rise between 30 Hz and 40 Hz was hirer.


Why, when combining them does my over all dB’s drop in the 30Hz to 40Hz region?

So based on the graphs information, is having both subs helping me?

Will I really notice that 10dB in the 15 Hz to 20 Hz region audible? (And the dip between 30 Hz and 40 Hz?)

[brucek]

I think since the two subs aren't co-located, that the phase of the signal at any frequency as it arrives at the microphone is a **** shoot. It may add and it may subtract. Move the mic around (a.k.a the listening positions) and it's a problem that results in very different responses.

Co-locating subs solves this problem, but since one of the subs is different than the other, the overall response will gravitate toward the challenged one.

Of course, Wayne may have an entirely different idea.

brucek

[Wayne A. Pflughaupt]

Of course, Wayne may have an entirely different idea.

Not really!

I see at least three places where the blue and purple diverge significantly, which may well be phase issues, but overall you can see that the EP500 has “dumbed down” response to use a term brucek coined (I love that, brucek – I’ve even used it on other Forums – hope you don’t mind ).

Will I really notice that 10dB in the 15 Hz to 20 Hz region audible? (And the dip between 30 Hz and 40 Hz?)

Can’t tell you about the first question, as I’ve never had a sub that would go below 20 Hz. As for the dip – turns into a hump with the subs combined.

By the way, when you said they’re in the front corners – is your room symmetrical (i.e., shoe-box dimensions)? That’s really the only scenario that you should be using both front corners - or maybe if at least the front of the room is symmetrical. If there is say, an opening near one of the corners, or some other irregularity like that – it pretty much destroys response when you separate the subs.

Regards,
Wayne