How do I measure subwoofer SPL and frequency response?

[Eric_C]

I'm picking out some idea's for a couple of subs for my room and want to compare to what I currently have.

I have Def Tech 7002's which have 1 300 watt active 12" sub and 2 12" passives.

I've been reading and now know how to read the charts and know what to look for.

I'm just trying to figure out how big I want to go.

I do want BIG sound The room is 20x20x20 and is open air to the upstairs and foyer.

I thought of some of the short sonotubes I could put in place of tables I current have at the ends of the room.

Will be doing sealed since music is a bigger concern than movies.

I would like to go large enough sealed though to get closer to a ported sub for feel if that makes any sense.

Edit: thread renamed by moderator to reflect content.

[ThomasW]

I've been reading and now know how to read the charts and know what to look for

What charts are you talking about?

Yes the room is big, but that's not the primary consideration.

What's important is the distance from the listening position to the sub, unless you feel the need to have the same SPL thoughout the room. If that's the case you're going to need to rethink this entire project, and be prepared to spend CUBIC amounts of money.

[Eric_C]

I was referring to the response charts on HZ/DB.

I'd like to see where mine start to fall off and see how much farther I want to go.

Our sectional that we sit on is 14' long. Each sub will be at the end of the couch, level with the arms.

For movies I'll be sitting at the very end, for music I usually sit in the tuned position which is the center of the sectional.

I would like the sound to be equal across the sectional which follows the back wall.

right now the 2 subs are located 3' in on each end of the sectional, 14' across the room.

Define dollars too...I was looking at about $1,000 to $1,300 for a pair and will be doing the work myself.

[ThomasW]

I was referring to the response charts on HZ/DB.

You haven't provided a link, a Google search for 'HZ/DB' turns up nothing useful, and I wasn't born with psychic powers. So this is going to be a really short thread.

[---k---]

I think he is referring to the frequency response charts. Something like the attached???

There are lots of ways to do it. Probably the best way to do it, for your first attempt is to use the Avia DVD and a Radio Shack SPL meter. Write down the readings from the RS meter and then put it into an excel speadsheet to plot.

If you go to http://bfdguide.ws/ (ignore all the stuff about the BFD for now), they have some excel spreadsheet with the correction factors and everything already in them. They also have some test tones you can download and burn to a CD, if you don't have the Avia DVD yet.

Once you understand the graph, you can generate it using a computer. It just takes a little bit more cabling and if you're using a laptop, likely an external soundcard. For info on generating the graph with a computer, look at Room EQ Wizard.

[Eric_C]

hz/db chart certaintly did make sense to me since one axis shows db and the other axis shows hz

Thanks. I have an SPL meter but no AVIA disk, have to get one of them. I've borrowed one in the past to setup the TV.

Can I use any of the THX setup programs on some THX DVD's?

[ThomasW]

You're talking about understanding a plot?




Read this link

http://home.comcast.net/~thomasw-2/SubwooferSetupandEQpage3.html

[---k---]

To get the big low low end, I think you are looking for, and if you want to use sealed subs, you are definitely going to need EQ/LT to really extend the low end. Without corner loading the subs and with a room that big, you may not get a ton of room gain, without LT/EQ. Think DEQ2496 or a BASSIS.

Check out the Sub Showcase in the Mission Accomplished forum.

Currently, I think the standard response to your question is two RL-P15 or TC-2000 drivers in two sealed enclosures with an EP2500 AMP and a Beringer DEQ2496 EQ, each in a 100L enclosure.

That should meet your budget, size, and sealed requirements.

[Eric_C]

Thanks.

I understand the plots. I was looking to measure what I currently have against some plots for some of the kits out there.

I for sure want a more musical sub.

I picked up The Beatles Love DVD-A and it has some of the best engineering in a DVD-A I've heard, especially on the low end and a more musical sub would really shine.

I checked out those parts. Just to be clear. The amp is a 2x1200, so I only need one and split it between the two? I do want to run stereo subs since my setup can utilize them, will this still allow it? I would say yes since its a 2 channel.

How big roughly would a 100liter sub need to be in physical dimension?

[Dennis H]

I for sure want a more musical sub

You'll find people around here don't know what "musical" means. Either a sub sounds good or it doesn't. Any well-designed sub, with a low-distortion driver and adequate SPL capability for the job at hand, will perform equally well for HT or music.

[Eric_C]

By more musical I mean tight.

Something hard with a fast response.

That is what I consider musical. I have a Solobaric in my car that is very fast and has a good tight sound to it.

I downloaded the software and made a test CD from 10hz to 80hz in 5hz increments.

Of course my batteries are dead in the SPL meter but I did play around with it.

I can not hear or perceive anything below 20hz. At 25hz its very minor, not very loud. 30hz is a bit louder, 35 starts to fall off until about 55, then its up from there.

I'll get some batteries for the meter and plot it out tomorrow to see how it comes out.

Is 85db the reference level? At what hz do I set the reference level at?

[Dennis H]

Sorry Eric, we don't know what tight, hard or fast mean either. I don't mean to give you a hard time; I'm trying to help. Those are subjective audiobabble terms that have no objective meaning. Your opening question is on the right track. Frequency response and distortion curves tell you all you need to know about a sub. Leave the descriptive adjectives for the next wine tasting.

[Eric_C]

By tight or fast I mean when you hear a sound or instrument that plays a short note that is in the range that the sub plays it plays for the exact duration.

There is no reverb or lasting effects.

What I've been told, and experienced, is that sealed subs are faster and ported subs are slower and are better for movies since they produce more of a rumble effect.

I can see how this is a problem because when we goto the wine store the guy there has no idea what I'm trying to describe either

[soho54]

By tight or fast I mean when you hear a sound or instrument that plays a short note that is in the range that the sub plays it plays for the exact duration.

There is no reverb or lasting effects.

That would be the subs impulse-response.
The problem is that it is a factor both the room and sub contribute to.

... and lets not forget it's frequency dependent also. :roll:
Here is a small primer Audio Measurement Basics

[Dennis H]

"Fast" bass is an audio-myth. It's a crude attempt to categorize "good" bass. Sealed and ported designs, if done well, can both produce good bass. Both types can produce bad bass if done poorly. There's a lot of mysticism to unlearn when you want to actually start designing a good sub. Start with a clean slate. Flat frequency response down to the lowest frequency you want to play. Low distortion at all frequencies at the loudest SPL you need. That's it; nothing else.

[Eric_C]

What I've heard all my time being involved with this is good speakers are the ones you like to listen to.

I like the setup in my car, which I would characterize as fast...so I want a fast sub

I read the primer and I understand that what I am looking for in a room with my kind of volume might be difficult and require some work but if I am going to replace my entire setup then I want to shoot for a solid improvement in an area where I feel its lacking.

I know where you coming from, I refuse to let some people use some words in my line of proficiency but I can't seem to stop them from doing it either.

We're leaving in a bit for breakfast and a battery for the meter. What sound level do I set my receiver and subs at to test with?

Do I set it to 0db and 50 percent on the sub?

Or is there a reference db and I keep a whitenoise tone and keep turning it up until I hit that db and then switch to the low frequency stuff?

Thanks for the information, I was looking to describe the things in that article and it makes a lot more sense, as do the idea behind room treatments.

[crackyflipside]

Ok, forget most of those terms you have heard in car audio or other audio magazines. What really matters for your subwoofer is that you have a capable driver that plays with low distortion, and that your enclosure is properly designed. 'Fast' bass is a myth, just follow certain guidelines and model the enclosure correctly and you will have a good sounding subwoofer.

Flat frequency response down to the lowest frequency you want to play. Low distortion at all frequencies at the loudest SPL you need. That's it; nothing else.

As for setting up your sub and calibrating it to your system, buy a Radioshack SPL meter and we'll walk you through set-up.

[ThomasW]

We're leaving in a bit for breakfast and a battery for the meter. What sound level do I set my receiver and subs at to test with?

Do I set it to 0db and 50 percent on the sub?

Or is there a reference db and I keep a whitenoise tone and keep turning it up until I hit that db and then switch to the low frequency stuff?

Thanks for the information, I was looking to describe the things in that article and it makes a lot more sense, as do the idea behind room treatments.

First you want to use pink-noise instead of white-noise.

Second the 'settings' on the receiver and sub amp don't really matter. To make life simple choose settings in the middle of the available range for each (these can be fine tuned, (adjusted) later) .

When testing for frequency response (as opposed to max SPL) use something 'reasonable' like 70dB-80dB at 80Hz as a starting point. Don't run the tones for a long time, 15sec is more than enough to get a good reading.

Set the meter on 'slow' and 'C' weighting.

If you read the link I posted above then move to the next page

http://home.comcast.net/~thomasw-2/SubwooferSetupandEQpage4.html

Scroll down to where it says "Initial Measurements, don't work in a vacuum, start with a near-field plot..."

Now you don't even need to use Excel or any other software program. You can simply write each frequency and the output beside it for a quick and dirt test.

[Eric_C]

Thanks again for the help. The more I read the more I understand.

I did the readings based on the previous link and see a difference in how the room is effecting things.

I wasn't sure exactly where to place the SLP meter to get a 80db reference on the near field so I put it in front of the mid range where the pink noise was coming from, 2" away and set the receiver until I hit a solid 80db. Then I moved it to the side where the sub is, 2" away and came up with the results attached.

I then put it on a tripod in my listening spot on the couch at ear level, again set the receiver until I hit 80db and then ran the sequence again.

Charts are attached....so now what does all this mean?

These subs are built into the tower, the new subs will be 6' left and right of the listening position on the floor. The current subs flank my TV and fire towards each other. I can swap them and have them fire out but this was recommended to me by Definitive. They must fire side to side since the midrange and tweeters are on the front of the speaker.

I was shocked to see how much ambient noise we have in the house. I am not sure if my my meter is out of whack. I turned off the furnace, put up the dogs, etc and it was pretty quite in here but still registed pretty high with nothing on. I remember getting readings of around 65db but now see 72-73 with nothing running in the house and it being quiet.

Thanks

[---k---]

Sounds like you did the tests correct.

Make sure db is on the vertical, and hz is on the horizontal. Also, make sure you are adding the correction factors for the RS meter. I posted a link above with the excel spreadsheets already made, including the correction factors.

It looks like your current woofers are good to about 35hz, where they start to drop off rapidly. Room gain starts to kick in below this, so we can't tell how much you may get. With a big open room, probably should design a sub to be flat to whatever freq. you want. Most here like to be flat to under 20hz, this adds the thump in the rump.

You may want to experiment with putting your current speakers in the position where you plan to put the subs and do the test again. The room will respond differntly depending on where the subs are placed, so you may want to try two or three locations if it will have an impact on the size/shape of the subs (some people can build bigger subs for corners, etc.)

[ThomasW]

On the links I provided, there are down-loadable spreadsheets they have the corrections for the inaccuracies inherent in the older Radio shack SPL meters.

It's not unusual to see ambient noise levels of 60-70dB in the average house.

Although sold as 'subwoofers' the Def-Tech side firing speakers are in truth woofers, not subwoofers. Over the years learning this has been a surprise to more than one owner.

Obviously the main issue with this arrangement is the inability to optimize placement for the output of the woofers, while maintaining optimal placment for the higher frequencies. A separate stand-alone sub or two will eliminate most of those problems

[Eric_C]

I downloaded the sheet but haven't had a chance to redo it.

So where do I go from here based on what I am looking for?

Someone suggested a EP2500 AMP and a Beringer DEQ2496 EQ. How about a driver. Are the Rythmic drivers any better than the RL or TC drivers mentioned above?

If I draw up a box is there some consideration I should keep in mind with the design? As I said I'd like to do some kind of end table arrangement. I've saw one where they filled the top portion with cement to keep things steady on the table surface.

I'd like to start on the box construction as soon as I pick a driver and order a couple.

What kind of improvements can I expect over the charts shown above in response and sound?

Thanks

[---k---]

You said that you want to do a small (in terms of what we build) sealed sub. I'm not going to try and talk you ou of that. The RL-p15 and the TC2000 (very similar drivers) are very commonly recommended and people are happy with them. They are big, beefy, and can handle lots of EQ being applied to extend the low end.

I used to have two sealed RL-p15 w/ the DEQ. It worked really well. I would highly recommend it.

I have no experance with the Rythmic, so I can't say. I don't think you will get as much output per driver as with the RL-p or the TC2k.

If you build your box right with double layer 3/4" MDF, bracing and decent joints, it will be very heavy and very stiff. You won't need cement or granite or anything like that on top. My 19x24x20 boxes weighed about 90lbs each.

Keep it simple.

You have read through my or SteveNN or one of the other sealed sub design threads, right??? They are long to read, but most questions have been answered and there are pictures to look at. Please make sure you check at least one out. Refer to Mission Acomplished Forum if you haven't done so already.

[ThomasW]

FYI, the Rythmik and SoundSplinter drivers are both made by TC-Sounds.

Any sub you build will increase the bass output in the room

[Eric_C]

I'll read through that thread more closely and come back with a more exact set of questions.

Are the Soundsplinter or Rythmik any better/worse than the ones mentioned?

Thanks

[ThomasW]

Are the Soundsplinter or Rythmik any better/worse than the ones mentioned?

Thanks

Once more, there is no "better or worse". All TC-Sounds drivers are handmade in their factory in San Diego. TC-Sounds is known for making high quality drivers not 'cheap', 'crappy' drivers.

The differences in SoundSplinter or Rythmik or TC-Sounds house brands are simply what spec's are chosen by who orders them. Obviously RL-p15"s aren't the same as Rythmik. That doesn't make one better or worse, they're just different.

IMO unless one intends on taking advantage of their servo and LT circuitry, there's little point to ordering Rythmik's drivers, If one want's those functions, then buy their driver/amp/LT package since it's designed as a 'system'.

[SteveCallas]

I remember getting readings of around 65db but now see 72-73 with nothing running in the house and it being quiet.

It's not unusual to see ambient noise levels of 60-70dB in the average house.

Yikes, that's crazy :E

What master volume do you typically listen at in order to hear dialog and music intelligibly?

[Eric_C]

I read through some of those threads but could not find one on sealed designs.

I did hear a lot of interest in tubes...Assuming I have room, no complaints from the wife(she prefers function over form), is a sonotube a better way to go?

A pair of them?

My only concern is due to the room design the sonotubes would sit about 1.5 feet from my rear's and very near walls, like 3-4 inches.

[ThomasW]

http://www.htguide.com/forum/showthread.php4?t=18218