Axiom Home Page Forums General Discussion Technical Questions DSP vs EQ

I've been wondering for a while. Whats the difference bwetween the dsp that is applied on subs an what an equalizer does? Is this just two different names for the same thing?

When you stick a driver in a box and plot the SPL vs. frequency of that system (ie. the frequncy response), the graph will be "all over the place". By programming equation coefficients into a DSP, the desired response is produced. For frequencies where the graph is too high, the DSP will compensate by requesting less power from the amp. For frequencies where the graph is too low, the DSP will compensate by requesting more power from the amp. While this sounds great in theory, in practice it can introduce problems like phase delays and harmonic distortion.

Now when you take a sub like the 600 which was designed for a flat frequency response and stick it in a room and graph the frequency response, the graph will likely not be flat because the DSP has no knowledge of the room. Enter the equalizer. If you know where your peaks and valleys are, you can knock them down or bring them up by adjusting the equalizer. This again sounds good in theory but in practice you don't have discrete control over each and every frequency using an equalizer.

The EP350 dosn't have dsp. Why is it not "all over the place"?

I think what you are saying is that dsp circuitry and an equalizer are more or less the same thing. The DSP is hard wired, where as an eqalizer allows you to adjust those 'power requests' for specific frequencies/bands. Is this correct?

That's correct.

The 350 is not all over the place but it's also not flat. Filters using discrete components (capacitors, resistors, inductors) were used to "tame" the raw response. Axiom did a great job on that one!

Hmm... equalization of another sort. So all subs do equalization of some sort then??

I've been wondering about the range of comments I see on various subs including the EP500 and 600. There seems to be more than the usual amount of bias out there around subs so it becomes hard to sort out what the relative performance of various subs is.

All subs have some form of equalizer, yes. The only way to sort out the relative performance is to listen to them. And just because some are popular doesn't necessarily make them better than others. The SVS PB12 (I think that's the name) that Jason brought over is a popular sub at a popular price and although it's great for movies, I got sick of the thumping when it came to music. The 350 in my opinion is a better sub.

Was the "thumping" you refer to anything close to the "chest thump" you've mentioned before that is missing from your 600?

Yea. I've just finished reading a thread over on audioholics by someone who upgraded from the PB12 to PB13. He commented on how he never liked the PB12 with certain music because stuff like kickdrums just didn't sound right.

After my visit to Axiom, I was considering the SVS PB10 as a reasonable alternative, but given the above comments on the PB12 I suspect I may be dissapointed.

Given the choices here in Canada, as things stand I will end up with the EP350.

I wonder If Axiom will go from dsp to eq in the 500 and 600. If you are going to equalize, it would seem to make sense to do so for the room the sub ends up in.

The DSP is a tool used to obtain the flattest response (and go low with the same +/- 1.5db) at a lower price (after a 5 minutes search, I did not manage to find back the post from Ian talking specifically about that).

The flattest the sub, the easiest it becomes to place in a room (unless you just happen to have a room that compensates exactly for a non-flat sub; it can happen!), and even more so when you want 2 or more subs as they will blend more easily. If there is problem in the room, then you can use an equalizer to further compensate.

If I remember right it is. I seem to remember Mojo saying,"now that is what I am talking about".

I seem to have tamed the PB12 enough that I like it now. I run the XO at 60 and I repositioned it so it is firing into the side of my couch, instead of across the front of the M80s from a corner. It is blending much better. I am still waiting for the PB13 to ship so I can do a comparison.

Yes, it certainly has a great thump that the 600 is missing but I was surprised that I got tired of it after a few minutes.

The 350 has thump too but it's not annoying. And my cheap Sony sub has a nice thump too that I really like.

Ever since you 1st mentioned the 'thump' issue, I've been paying close attention. While the EP500 and SMS-1 get fairly close to what I'm looking for, I don't know if I need a second sub, more room treatments, some more attempts at sub placement, or yet MORE experimentation to get what I want. It's a difficult puzzle to solve.

Your bass 'needs' appear to be similar to mine.. I don't however, have as many opportunities/means as you do to explore the possibilities...so I'll be eagerly lurking!

A second sub won't give you more thump unless it's a thumping kind of sub . The best advice I can give you is to get out and listen to more subs so that you can better understand what you may be missing. As for room treatments, I don't know what kind of treatment would absorb frequencies below 100Hz.

The most pleasing thump I've heard so far is from my cheap Sony. I get a lot of listening pleasure from the Sony paired up with the audiobytes. A close second is the EP350. All around, the 350 is a better sub though.

I was hoping by now that Randy would give us some more feedback on his EP600 equipped with the 150Hz filter. I've been waiting anxiously to find out if that leads to a touch more snap in the sound.

I kinda figured that dsp might be less costly. Maybe eq. is a lot more expensive?

Spoiler. I think a lot of us will be interested in how the PB13 performs.

The DSP is used to perform equalization within the sub components. EQ just means equalization, which is usually done using a DSP in your receiver.

I have 2 EP500's and my initial reads using REW confirm a large bump in the 60-70Hz range (+15db!). I think that this bump is causing a "false read" using Denon Audessy because even when I have the subs down to the 6pm position, the receiver still wants to take another 2db off. I just turn the level up on the subs afterwards.

The DSP in the subs can only do so much to adjust for the room. The EQ in the receiver can do a little more, but my receiver only has one adjustable band in the sub range (63Hz). I ordered a Behringer FBQ2496 last week online (new $135 shipped). It should be here this week, so I'll let you all know how a dedicated parametric equalizer helped out my situation. I already ran the REW analysis, and 6 filters in the sub range should get me to the +/- 1.5 db goal from 20-100Hz.

Keep us posted.

I'd like more info on your attempts, if you can spare the time:

1) What are your results when you turn on only one sub at a time? They might be cross-firing a tad too much.
2) Did you play with the sub's phases?
3) Did you try removing your mains from the equation and set their XO at 100Hz?

I was amazed that some of these humps are caused becuase my mains are the same distance from the side and front walls. Adjusting your mains so this is not the case, can help greatly. Also, moving them out from the front wall, and playing with toe in helps as well. It is not always the sub causing the humps.

The DSP cannot adjust for your room as it has no knowledge of its characteristics.

Mojo, you're right of course. What I meant to say was that the DSP can only do so much to produce a flat curve in a perfect room. Without the DSP, a sub's natural peak may be accentuated by your room's dynamics.

I have mys subs next to my mains, toed in. The drivers' centerline are about 2 ft off side wall, and 3 ft off front wall. I've tried moving them around, and it made some, but mot much difference to the response.

I have not tried one sub at a time, but I have tried adjusting phase. With one at 0 and the other at 180, the response was smoother, but much lower. With both at 180, the response again was similar to both at 0.

I've tried XO at 60, 80 and 100. 60 was too low, as there was a big dip between 100 and 60 (natural rolloff of the M80s I guess). Both 80 and 100 showed the peak in the 60-70 range.

After hours and hours of trying, this is how I have the Denon set now for "best" sound and response:

1) Denon Sub set to LFE+main
2) Denon XOs at 80 for all channels (and LFE)
3) Denon EQ in Manual (copied the flat curve over). I had to do this because Audessy insists on setting my M80s as large. Even when you manually switch them back to small, the bass still does not go to the sub. Manual EQ setting however allows it.
4) Subs both at 7pm gain position.
5) Subs set FLAT
6) Subs XO at 150 (bypass)
7) Subs at 0 deg (both)

With these settings, the sound is quite pleasant, but I can tell there is a bump in thr 60-70 range from listening. With the FBQ, I'm hoping to drop the bump down so I can increase the subs' levels to get a bigger gain in the 20-30 Hz range.

Unless it's a Cylon.

Just a quick update... The BFD came in the mail yesterday. I was able to play around with it for an hour or so last night, and just by manually applying 3 filters I was able to drastically improve the REW response (I had to enter parameters manually because the MIDI cable has not yet arrived).

I applied 2 reductions at 28Hz and 72Hz, and one gain at 45Hz and the resultant REW curve appears to be within +/- 2db of my programmed house curve from 20-100Hz. This was a heck of a lot easier than I thought it would be (even entering the parameters manually), and was certainly easier than constantly moving the EP500s around the room (with much better results).

I'll post some details and REW screen shots this weekend after I have some time to fine tune things and really get them where I want them to be. But for 60 mins work and only 3 filters, I'm very happy at this point.

One thing I did notice however was that the BFD appeared to apply a 9db gain across the board from 20-100Hz, even with no filters programmed. I had to attentuate the SW output in the Denon to adjust for this. Is this normal? I am using the 1/4" jack input/output with 1/4" to female RCA adaptors, and using the -10db setting on the back of the unit. Is this happening because I am mixing balanced / unbalanced inputs?

Very interesting thread. It is inspiring me to maybe download the freebee version of TrueRTA just to get a rough baseline of what current, square, hard floored, relatively empty room looks like compared to the new HT room when it's done.

If it works OK with my setup mike from the Denon, I would imagine I will have to spring for one of the more powerful versions than the free one as 1 octave measurements are probably not going to give me much of a comparison.

Would that be safe to say? If so, what would be reasonable for basic room comparisons and maybe a little curious tweaking down the road?
1/3, 1/6,....1/24th ?

Some part of me is telling me this is a bad idea but that voice has never been one I listened to in the past. Why start now?

Okay, I was able to work with REW and the BFD last night. The results are pretty staggering. This is my 20-100 Hz response before (2 EP500's, 0 Degrees, Full, XO Bypass on Sub and 90 Hz in AVR). Note that the more straight line is my goal, a 75db hard knee house curve that adds 6db between 20-30Hz:



And here are the results after the adjustments.



I used 4 filters:
26.98Hz, -9.0db, 0.500 (9.5Hz BW)
37.67Hz, 2.5db, 0.333 (8.9Hz BW)
49.66Hz, -4.5db, 0.200 (7.0Hz BW)
69.35Hz, -7.0db, 0.250 (12.3Hz BW)

I tried lower XO settings in the AVR, but the responses were always better to start with at 90 Hz. Plus, I'm able to control more of the curve with the XO higher. Interesting note. Before the adjustments (the 1st curve), my AVR was set at -12db for the sub (with the subs at 6:30pm). After adjustments (2nd curve), the AVR is now set at -6db (subs again at 6:30pm).

This adjustment was very easy to do, and actually pretty fun. The improvement in the bass was very obvious. It sounds much cleaner and tighter now. Although the low frequencies were by and large reduced, the bass actually sounds lower now, and much more realistic.

Interesting. Especially that it did not sound like an expensive box. Thanks for sharing.

have you tried the 500's on flat versus full, will help reduce your hump in the 30hz area.

Sroo,

I haven't played around with equalizers so forgive me for asking basic questions. How did you choose the goal line? Why for example didn't you select a flat goal line? Have you tried a single sub as opposed to two?

REW accounts for the RS meters flaws, and creates a slope goal.

Looking good though I would suggest half trim rather than full, if only to avoid that boost of 37.67Hz, 2.5db, 0.333 (8.9Hz BW). Boosting filters may make that line look flatter but it comes at the cost of eating into amp headroom and introducing more ringing and phase errors. Hopefully at half trim you can remove that boost entirely and just rely on cuts to get a nice flat curve.

Thanks for the input guys. I did try half and flat, but even at half, I dropped way off in the 40Hz-60Hz range by like -7db. The room is eating up 40-60Hz, and amplifying >60Hz range.

I do want to try to remove the +2.5 Hz gain. I may wind up narrowing the BW of the 26.98Hz filter and maybe moving it down a Hz or two. The +2.5 gain is necessary now due to the -9db at 26.98.

I chose a +6db house filter to adjust for the human ear's reduced sensitivity in the 20-30Hz range. I tried a flat curve, an this sounded much better to me. There are advocates of house curves, and of the flat response. In the end, you wind up setting it the way it sounds better to you. Randy's right to. REW has adjustments that you load in to account for your measureing equipment. I loaded the Radio Shack sound meter adjustment, and also calibrated my sound card (though that was not as much of an adjustment as the meter).

But overall, this is a 2x improvement from pre-equalization.

One more fun bit of info. My wife is not much of an audiophile, is happy watching movies in our living room (61" DLP, no audio setup), but as I said in other posts, is very supportive of my hobby and is happy to see me happy listening to music and watching movies in the theater.

With the new speaker setup, I had been brining my 4 year old in to watch exciting scenes from different movies, and listening to music. She would poke her head in once in a while to see what was going on. Yesterday, she caught us watching one of my son's favorite scenes right now, Apollo 13, the liftoff. With everything properly calibrated now, it is absolutely awesome. So much so that she actually stuck around to watch a scene or two (which she rarely, if ever does). Afterwards she said she would love to see that movie (never had before).

Well, we made Saturday night our movie night last night. We put the kids down, took the baby monitor to the theater, and I popped in Apollo 13. Watching her experience the movie was almost as much of a treat as watching my son's expressions! She had her hands to her mouth at the suspenseful scenes, and was totally brought into the movie. Is is the first time I have ever seen her react this way. She was so drawn into the movie that she actually became interested in the space program and asked me questions about how things worked, and why they did the things they did. Yes, Axiom allowed us to have one of our first adult conversations in months (we have an 11 month old as well).

It was such an enjoyable night that we have a date next Saturday to watch another movie together in our theater. She now wholeheartedly agrees that nothing compares to watching a movie on the bigger screen, but more importantly, with the right sound.

Baby steps... But steps in the right direction nonetheless!

Wow... what a great post! It's wonderful that your wife is supportive of your hobby, and was then drawn into the movie and your system in that way. Very cool. Love Apollo 13 BTW.