new member, new sub design critique

[hopkid929]

Hello All,

I've been browsing for the past few weeks, reading and learning. I am in the process of building my own H.T. setup. I need some help with a subwoofer design. I just picked up 2 of the mcm 300w plate amps. I would like to put each amp w/ 2 NHT npt-11-075-2, 10" woofers, ported... 5.2cuft @ 21Hz. I am boarderline understanding about system impedence and spl output. I figure w/ 2 driver per box I can keep the size reasonable for some nice end tables and still have decent sound. I know three drivers would increase the output (lowering the impedance and increasing Sd), but I'm not sure I'd need the extra db's since I'll have 2. I'm only using an onkyo sr605 for a receiver powering the other speakers.

Anyway any suggestions with these amps would be helpful, or current design. Before I was thinking about a single elemental designs 13kv.2, but I think I can achieve a little more with the nht drivers... cheaper too.

[BoomieMCT]

Man, I'm jealous. I wanted so bad to mate three of the NHT drivers on sale with the MCM amp on sale. Since almost every room in my house has a sub now I'd have a hard time justifying that cost though!

Anyway since you want to do with two NHT driver's per sub I'd go with a lightly stuffed sealed enclosure of 3.0 cubic feet. I think those NHT drivers work best with sealed enclosures. You should get an F3 of 34Hz. Unless your room is very large and/or open you should pick up a lot of the low end with room gain. With two amps and four drivers you shouldn't have to drive them very hard either.

As always, I'd suggest getting a BFD if you don't have one to tame any room issues you might have.

[hopkid929]

BoomieMCT wrote:

As always, I'd suggest getting a BFD if you don't have one to tame any room issues you might have.

Please inform.. what is a BFD?

I never really understood sealed enclosures?... why not just go ported? I'll be underpowered anyway, no chance of over excursion, and I will get another 10-20hz on the low end of response. These are subwoofers. What makes these drivers better for 'sealed application'?

I suppose I could go with 3 drivers per enlosure, I just don't see the benefits other than SPL. Heck, I could play with a 3driver ported and sealed setup. I'll just have to make bigger end-tables. Room size is about 2500cuft.

[BoomieMCT]

hopkid929 wrote:

Please inform.. what is a BFD?

Behringer Feedback Destroyer. Basically a reasonably priced digital parametric equalizer. You can get them cheap on ebay, Parts Express or (right now) Guitar Center is selling theirs off cheap with their in-store clearance (they aren't carrying Behringer products anymore so they are very cheap there). There are many thread in this forum about using these with Room EQ wizard (free software) to reduce room modes. There is probably a link to this information at the top of your page.

hopkid929 wrote:

I never really understood sealed enclosures?... why not just go ported? I'll be underpowered anyway, no chance of over excursion, and I will get another 10-20hz on the low end of response. These are subwoofers. What makes these drivers better for 'sealed application'?

Those drivers have nearly ideal characteristics for sealed enclosures. You can still make a ported enclosure and it will sound good, but for the same size (not counting the port volume) you'll be getting more like 5 Hz more extension, not 10-20Hz. You can run the numbers in WinISD or Unibox - I could be wrong.

hopkid929 wrote:

I suppose I could go with 3 drivers per enlosure, I just don't see the benefits other than SPL. Heck, I could play with a 3driver ported and sealed setup. I'll just have to make bigger end-tables. Room size is about 2500cuft.

Three drivers could give you more SPL (good for HT), or you can run it at the same volume and be pushing each driver less (good for music).

[BoomieMCT]

I apoligize. The graph and statements I made above is for the 11-083-2. The 11-075-2 "needs" a smaller enclosure but will have a higher F3 point. Yeah, you'd get about 10Hz advantage off a ported enclosure.

[audio newbie]

Ive used the NHT's sealed and ported.

I used 2 10's in sealed boxes that were approx 1.5 cu ft each. I'm now using 8 10's in a vented box that is 25 cu ft.

According to WINISD the ported configuration gives 13db more at 20hz, 6db more at 30hz, 3db at 40hz.
According to another program the ported is up 6db at 20hz, 3db at 30hz.

I cant make a fair comparison on sound quality because the sealed boxes were not used in the same room location as the vented.

If I have time, I will try to hook up my sealed 10's and run a REW on them (the vented box has already been measured). I can also do a back to back listening comparison at that time.

[hopkid929]

Thanks for the input guys... I can see your point w/ three subs working better for sound quality.

audio newbie - that would be great on a direct sealed/ported comparison.

I guess I need to find a way 3 10's would look good in an end table... I'd like to keep it all hidden. Gloss is just under 5%... might go with all three on the side. I need to look at the cuft and size of my couch.

[Warmon]

hopkid929 wrote:

I guess I need to find a way 3 10's would look good in an end table... I'd like to keep it all hidden..

Dave, these subs will work in a down fired configuration...sag is a little less than 4.5%...

[hopkid929]

Warmon wrote:

Dave, these subs will work in a down fired configuration...sag is a little less than 4.5%...

Yeah I noticed that, I don't know if I can fit all three facing down. Rough outside dimensions look to be around 34"x23"x23". My couch is about 35" deep. I could put all three in a diagonal, or in an L shape. I think I'll look around for some pictures. 7.75ft^3 @ 21hz: 105db @ 20hz;108db@25; 110@35; 111dbs from 45-100hz. Bracing will be a trick.

[Warmon]

Just out of curiousity, what alignment does WinISD want to put these in by default?...and what is the bandwidth quotient? I run Linux on a laptop, so I have to knock a kid off to get to a Windows box. You said your room is 2500 cf - what's that like?, heavily furnished, carpeted, hardwood, sparse, etc.???

I'm very interested in your thread as I'm gonna be using these same drivers and amp for my next build.

BTW, welcome to The Shack...

[hopkid929]

Warmon wrote:

Just out of curiousity, what alignment does WinISD want to put these in by default?...and what is the bandwidth quotient? I run Linux on a laptop, so I have to knock a kid off to get to a Windows box. You said your room is 2500 cf - what's that like?, heavily furnished, carpeted, hardwood, sparse, etc.???

I'm very interested in your thread as I'm gonna be using these same drivers and amp for my next build.

BTW, welcome to The Shack...

EBP=48.4 according to my parameters. Winisd pro will not let you input the parameters as listed from the .xls sheet because they are not 'perfect'. So it's just slightly prefered as a sealed enclosure per winisd.

I have been using Bassbox longer than winisd, for strictly automotive application, and it highly suggests a sealed enclosure... although with the same setup, 3 in parrallel, the avg. impedance is down ~60% for sealed application, but the -3db is around 52hz vs ~25hz with a vented enclosure.

The room is hardwood, pretty open, open doorways to 3 other rooms. I do have a few chairs, couch, fireplace,... it is all a work in progress.

[Jack Hidley]

Hopkid,

I just entered the parameters for the npt-11-075-2 into Winisd Pro. I didn't have any problems. The Auto calculate unknowns box was checked by default. I didn't try it without the box checked. I suggest entering all of the parameters in the Electro-Mechanical parameters section first. A couple of these aren't in the Excel spreadsheet. Don't worry about that. Then enter the Qms value in the Thiele/Small parameters section. Winisd will calculate all of the other Thiele/Small parameters. You can check these against the Excel file. They may be 1% or so different. This is due to different assumptions about air density, temperature, speed of sound, etc. that Winisd makes compared to my measurement software that generated the parameters in the Excel file. This is completely normal and nothing to worry about.

Regarding placing subwoofers near the listening position. It's not a great idea. From your description, each subwoofer will be at the end of the couch, which is going to be close to the listener. Assume the listener is seated in the center of the couch. That may make them 4' from each subwoofer. Assume that each left and right main speaker is 8-9' from the listener. Soundwaves from point source direct radiator loudspeakers propagate spherically, so the sound pressure level they generate changes 6dB each time the distance is doubled or halved from the sound source. Now adjust the subwoofer output level so that the SPL it produces matches the SPL from the L and R speaker at the listening position. Everything is good.

Now move 2' to either side on the couch. The distance from the listener to the L and R speakers has barely changed, but the distance from the listener to the subwoofer has changed by a factor of 2 (4'/2'), so the subwoofer SPL has gone up by 6dB. The system now sounds very bass heavy. This explanation is very simplified to make it clear. Your other subwoofer is going to help some, soundfields in small acoustic spaces don't obey the inverse square law, blah, blah, blah. The point is that as a general rule, you need all of the sounds coming from a given channel in the system to be as coincident as possible to guarantee that as the listener moves around the room, the tonal balance doesn't change drastically. Obviously this can't be done perfectly, but the closer you can get to it, the better system performance you will have. It is one of the main advantages of full range speakers over subwoofer satellite systems.

[audio newbie]

Here are the near field and in room REW's for sealed and ported configurations. I was in a hurry trying to do this at 5AM before going to work. I forgot to unplug the mains on one of the tests, so ignore the differneces above 100hz.

Looking at the charts, the ported box has a flatter response and extends deeper. The closest I could get the sealed boxes to the ported boxes was about 4ft away from each other which pretty much makes a listening comparison invalad. With that being said, they sound very similar. What I percieved at the listening position did not at all reflect what the charts show. You could feel the ported sub more, but it didnt sound any deeper. Maybe my ears are a lot worse than I thought Without back to back switching between the two I would have a very difficult time identifying which one was playing. The ported sub definately shakes the house more during movies though

Hope that was helpfull.

[Warmon]

hopkid929 wrote:

I have been using Bassbox longer than winisd, for strictly automotive application, and it highly suggests a sealed enclosure... although with the same setup, 3 in parrallel, the avg. impedance is down ~60% for sealed application, but the -3db is around 52hz vs ~25hz with a vented enclosure.

Somethings wrong if it's giving you an F3 of 52hz sealed. You want to make sure you are modeling a maximally flat .707 box - which will give the lowest -3db possible.

[hopkid929]

Jack Hidley wrote:

Regarding placing subwoofers near the listening position.....It is one of the main advantages of full range speakers over subwoofer satellite systems.

Well you learn something everyday, Thanks! Lately, on this subject, I've been learning quite a bit. I didn't know about the half/double rule, but it makes sense. I assumed since the low frequencies aren't directional, it wouldn't matter. This certianly brings up some creative thinking though: where to put 6 10" subwoofers. I suppose the center of the room, or center of the seating arrangement would be near perfect.

audio newbie wrote:

Here are the near field and in room REW's for sealed and ported configurations. I was in a hurry trying to do this at 5AM before going to work. I forgot to unplug the mains on one of the tests, so ignore the differneces above 100hz.

Looking at the charts, the ported box has a flatter response and extends deeper.... Without back to back switching between the two I would have a very difficult time identifying which one was playing. The ported sub definately shakes the house more during movies though

Hope that was helpfull.

Very helpful, thanks. I'm definately going ported. The low's can't be beat for H.T. and besides, I have the extra room. What does you enclosure/setup look like? I'm hate to just take up room with huge enlosures.. thats why I was thinking of and end table setup.

Warmon wrote:

Somethings wrong if it's giving you an F3 of 52hz sealed. You want to make sure you are modeling a maximally flat .707 box - which will give the lowest -3bd possible.

I was using .707... I had bass box set with heavy damping material though (more volume). With minimal it is 44.9hz at -3db. Winisd is saying -3db at 41.6hz.

[audio newbie]

hopkid929 - here is a link to the install. Its a little different, but high on the WAF.
http://home.comcast.net/~jhidley/Subwoofers/index2.html

I honestly dont think you can go wrong with sealed or ported. They both sound great... probably because these speakers arent biased heavily toward either one.

[Ricci]

Jack Hidley wrote:

Hopkid,

I just entered the parameters for the npt-11-075-2 into Winisd Pro. I didn't have any problems. The Auto calculate unknowns box was checked by default. I didn't try it without the box checked. I suggest entering all of the parameters in the Electro-Mechanical parameters section first. A couple of these aren't in the Excel spreadsheet. Don't worry about that. Then enter the Qms value in the Thiele/Small parameters section. Winisd will calculate all of the other Thiele/Small parameters. You can check these against the Excel file. They may be 1% or so different. This is due to different assumptions about air density, temperature, speed of sound, etc. that Winisd makes compared to my measurement software that generated the parameters in the Excel file. This is completely normal and nothing to worry about.

Regarding placing subwoofers near the listening position. It's not a great idea. From your description, each subwoofer will be at the end of the couch, which is going to be close to the listener. Assume the listener is seated in the center of the couch. That may make them 4' from each subwoofer. Assume that each left and right main speaker is 8-9' from the listener. Soundwaves from point source direct radiator loudspeakers propagate spherically, so the sound pressure level they generate changes 6dB each time the distance is doubled or halved from the sound source. Now adjust the subwoofer output level so that the SPL it produces matches the SPL from the L and R speaker at the listening position. Everything is good.

Now move 2' to either side on the couch. The distance from the listener to the L and R speakers has barely changed, but the distance from the listener to the subwoofer has changed by a factor of 2 (4'/2'), so the subwoofer SPL has gone up by 6dB. The system now sounds very bass heavy. This explanation is very simplified to make it clear. Your other subwoofer is going to help some, soundfields in small acoustic spaces don't obey the inverse square law, blah, blah, blah. The point is that as a general rule, you need all of the sounds coming from a given channel in the system to be as coincident as possible to guarantee that as the listener moves around the room, the tonal balance doesn't change drastically. Obviously this can't be done perfectly, but the closer you can get to it, the better system performance you will have. It is one of the main advantages of full range speakers over subwoofer satellite systems.

Great post Jack.

[Warmon]

Here's an interesting build worth looking at: http://www.toshistation.com/thunder/default.htm

I did the end table thing with one 12" sealed on each side of the couch. I don't get a sense that one side is louder than the other, but I do have a third one under the RF Main and that probably helps some. Music is just great and I am getting plenty of low output for movies [enough for me anyway]. The train scene in 3:10 to Yuma - yeah, I swear that thing came thru the living room...

[brent_s]

I know Jack has probably forgotten more about acoustics than I'll ever know, but (you knew that was coming), I think this is more of a theoretical problem than real life. And you do mention that rooms tend to make the theory harder to apply. Before anyone goes obsessive trying to rearrange their setups, the same proximity issue would apply to all speakers in a given system since equal SPL calibration can only be performed from one location. Any listening position outside of the one use for calibration will suffer an imbalance. I would think subs would be least effected due to the wave lengths involved.

In room REW measurements, at least for my room, don't seem to vary drastically in the roughly 3'-10' seating distance from my rear corner sub placement. Looking at measurements made on the right arm rest (closest to sub), center headrest, and left arm rest looks like a deviation of about 3-4dB with the headrest as the median. It's quite interesting to see how the SPL by frequency is room influenced. The left armrest (most distance to sub) actually has the highest SPL below 16hz. FWIW, my ancient processor also doesn't have the benefit of a sub channel distance delay as most (all?) current processors do.

-Brent

[Warmon]

Hey hopkid929,

How's it going? Figure out what you are going to do yet? I've been playing around with a ported pull pull isobaric design. Looks like one could shave off roughly 2/3 cubic foot over a typical single driver ported design and still get a nice response - albeit less SPL, but still quite acceptable. Down side is long ports because of the small volume of the vented space. It would take some real creativity to route the ports and keep the box reasonably small enough for an end table or night stand. I figure, I'll play around with this some more, but probably go with 2 drivers sealed.

[hopkid929]

Warmon wrote: