Home audio sub using 18" passive

[eRiCdWoNg]

...I have a rather heavy sub I used to use in my car, but it was too heavy. It it this one: a 15" thats essentially a Kove Audio Z15D car audio sub. I got it from parts express, I will post a link when their site works again. Its a great sub but its just too darn heavy so I took it out of the car. Soooooo... here comes my next wild idea. I've never used a passive radiator before and would like to try. I know not many manufacturers make 18" PR's but I found this one:

http://yellow.mynethost.com/~bv1263...id=38&osCsid=7ec7efaf58864aa6fbbb16566df0dbf0

Its not terribly expensive and I don't care how large of a box I would need to use, but the tunability with weights and no port noise and low end response of a PR is appealing. The next question is I have no idea how to begin designing one of these except the passive should be larger then the active. I'd use this for home theater where ultra low infrasonics will be required.

The woofer has a good amount of excursion and power handling although its Fs is a little high, probably because it is a car audio sub. Can I touch the 20's maybe teens in FR?

 

[LineSource]

I think the most common solution is to build a small sealed, well braced, box and use equalization like a Linkwitz transform circuit to get low freq bass extension at the cost of much higher power(watts).

The math says you can only have two of these three features.

1) low frequency bass
2) low power (efficiency)
3) small cabinet


If you want a small cabinet and low frequency, you will need high power amplifier and equalization.

 

[bigwill]

I'll pick 1 & 3 then

 

[eRiCdWoNg]

Thanks for the response, but I dont think I will be going sealed on this design. Ive done sealed boxes before and want to try a passive radiator. Since I am shooting for low bass, I think it will be better then a port which would loose control of the woofer below its resonate freq.

I want low frequency bass no matter what the cost (almost). I have a Crown MacroTech 5000VZ as a bass amp (5000 watts continuous, 4 ohms bridged) so power is not a problem. I also have a graphic and parametric EQ's to use if needed. Box size, I don't care if it is the size of a refridgerator, if thats what it takes. So small size does not matter either. Any tips on calculating the box size/weights to use on the PR?

 

[95Honda]

Figure on 2x the driver displacement for passive radiator displacement.

If you don't care about box size, then you could build a port big enough to not worry about any noise......

 

[simon5]

You should order your passive radiator from Acoustic Vision website, someone heard that Acoustic Elegance is mostly stalled right now.

It's the same one and it's in stock.
http://www.acoustic-visions.com/~acoustic/products/passive_radiators/stryke_pr18/

To find the correct box size, you could download WinISD Pro or Unibox and find by yourself.

 

[Ron E]

...I... want to try a passive radiator. Since I am shooting for low bass, I think it will be better then a port which would loose control of the woofer below its resonate freq.

Any tips on calculating the box size/weights to use on the PR?

PR's unload below tuning the same as a port. Depending on size not quite to the extent, but very near so. It is fine to want to try something new, but PR's are not much different from ports excepting the ease with which they may tune a mall box to a low frequency. If you want something that protects the driver at low frequencies, try a 4th order bandpass.

To design a PR box, simply design with a ported box calculator. Find out how long a port must be that is the same diameter as the PR piston. Calculate the volume of the port, then the mass of the air in a cylinder the length of the port plus approx 0,75 times diameter of port. Subtract this value from the PR stock mass and that is the amount of mass you must add.

 

[kelticwizard]

You can download Subwoofer Simulator and find the mass which needs to be added to the passive radiator, (Drone Cone).

Or you can give us the Thiele-Small parameters of the subwoof you are referring to and we can make recommendations.

 

[eRiCdWoNg]

Thanks for the replys guys. This is the woofer, now the PE page is working again:

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=299-665

An externally hosted image should be here but it was not working when we last tested it.

Specifications: *Power handling: 1050 watts RMS *VCdia: 3" *Le: 2.8 mH *Nominal impedance: 4 ohms per coil *Re: 3.0 ohms per coil *Frequency response: 20-250 Hz. *Magnet weight: 192 oz. *Fs: 37 Hz *SPL: 90 dB 2.83V/1m *Vas: 2.63 cu. ft. *Qes: 0.53 *Qts: 0.48 *Xmax: 20mm *Manufacturer model number: Z15D *Dimensions: Overall Diameter: 15-1/2", Cutout Diameter: 13-7/8", Mounting Depth: 7-1/2", Magnet Diameter: 7-3/4", Magnet Height: 3"

 

[tade]

have you purchased that sub yet? i was curious as to its performance.

 

[JinMTVT]

try something nice fresh and new ..

make a folded horn with a nice comp driver..something like 6 to8"
wich permits a nice design in size

we don't see that much folded horns in cars do we ?
that would be awsome i'm sure!

and if designed properly, you could prolly get good sound out of it..but hey, i don't know much about horns ;p

 

[paulspencer]

The only way to say what you can get is to model it in winISD. I did a quick sim and found that you can actually get plenty of low end on this thing. Due to the very high fs, and high Qts you get a strange response, so you actually need some filtering to get that response. What you can do is make an EBS tuning it well below fs, and setting the crossover so that you effectively get a low F3.

For a HT beast I'd do something like this:

150L vented box tuned @ 22 Hz

This can achieve 112db @ 20 Hz with 1kw and an F3 @ 20 Hz

You need a 3rd order highpass (rumble filter) @ 20 Hz to prevent chuffing and excursion problems, and a 2nd order lowpass @ 45 Hz to get this response (-3db points at 20 and 75 Hz).

Two 120mm diameter vents with a 50mm flare radius should mean no chuffing (840mm length). Dual 150mm vents would be even better, but require 1.3m length each.

Yes you can do this with a passive radiator, but in a box big enough to get you that deep bass, you can easily get vents that won't chuff. Normally a driver like this would run out of power before excursion, but this driver with such a high thermal rating is an exception. I say don't waste your money on a passive radiator! Where you have a properly designed vented box, a passive radiator has NO performance advantage. In fact the performance is slightly inferior as a PR has slightly higher group delay.

 

[eRiCdWoNg]

have you purchased that sub yet? i was curious as to its performance.

Yes, I've had the sub for quite a while actually. It WAS in my car. Keyword WAS. its performance was awesome. Good quality sound, GREAT SPL, good efficiency. HOWEVER it was way too heavy. It weighted down my car, it made a noticeable difference in the handling and ride quality.

try something nice fresh and new ..

make a folded horn with a nice comp driver..something like 6 to8"
wich permits a nice design in size

we don't see that much folded horns in cars do we ?
that would be awsome i'm sure!

and if designed properly, you could prolly get good sound out of it..but hey, i don't know much about horns ;p

Haha, me neither, but this is actually for the house, not the car.

The only way to say what you can get is to model it in winISD. I did a quick sim and found that you can actually get plenty of low end on this thing. Due to the very high fs, and high Qts you get a strange response, so you actually need some filtering to get that response. What you can do is make an EBS tuning it well below fs, and setting the crossover so that you effectively get a low F3.

For a HT beast I'd do something like this:

150L vented box tuned @ 22 Hz

This can achieve 112db @ 20 Hz with 1kw and an F3 @ 20 Hz

You need a 3rd order highpass (rumble filter) @ 20 Hz to prevent chuffing and excursion problems, and a 2nd order lowpass @ 45 Hz to get this response (-3db points at 20 and 75 Hz).

Two 120mm diameter vents with a 50mm flare radius should mean no chuffing (840mm length). Dual 150mm vents would be even better, but require 1.3m length each.

Yes you can do this with a passive radiator, but in a box big enough to get you that deep bass, you can easily get vents that won't chuff. Normally a driver like this would run out of power before excursion, but this driver with such a high thermal rating is an exception. I say don't waste your money on a passive radiator! Where you have a properly designed vented box, a passive radiator has NO performance advantage. In fact the performance is slightly inferior as a PR has slightly higher group delay.

Good thoughts. I'll do some other box calculations. Right now I have a commercially made twin 10" 400 watt sub, which plays good to around 30 Hz or so. If I can reinforce that last octave, it would be the bomb.

 

[Ed B. 1979]

Do you think a box similiar in size/style to this:

http://www.partsexpress.com/projectshowcase/whtsub.htm

would work for this sub? im thinking it would be pretty cool having this behind a couch in a home theatre. For me its this vs 2 12" Dayton high fi subs in sealed enclosures. What do you guys reccomend?

 

[paulspencer]

2 single subs are more flexible than one large one in terms of placement.

A design like that one limits placement to places that might turn out to be less than optimal.

I wouldn't consider behind the couch to be a very optimal location. I think you are better to stay as close to mains as possible. If you are using two, then dual mono, each close to the mains is a good idea, or possibly stereo if you are crossing high ie 80 Hz.

Harmonic distortion can localise a sub. Even crossed low at 40 Hz, a 40 Hz tone can produce 3rd order harmonic distortion products at 120 Hz which is clearly audible. Higher order distortion products will get up into the lower midrange. This can mess with imaging.

 

[GM]

I wouldn't consider behind the couch to be a very optimal location. I think you are better to stay as close to mains as possible. If you are using two, then dual mono, each close to the mains is a good idea, or possibly stereo if you are crossing high ie 80 Hz.

Greets!

Can't say as I agree with such a dogmatic stance since I've had much success with it, though there are design considerations other than the one you listed that make it untenable, with the major one IMO being that the XO point/slope sets the listening distance from the mains if there's no adjustable phase control.

Since the LFE signal is mono and stereo recordings are summed mono below ~150 Hz, what's the difference between dual mono and 'stereo' subs? Anyway, for two subs, the midpoint between the front/back walls is the best compromise positions according to a fairly exhaustive study by Harmon-Kardon.

GM

 

[paulspencer]

Well, I don't know where you read dogmatic into my post, but my listening impressions and theory on this agree.

I've seen that study but can't really agree on their conclusion. IMO there aren't many locations that don't compromise imaging. I have heard a good system which had one rear subwoofer and 4 across the front, and it has a sophisticated phase correction system. I'd call it an exception.

Since the LFE signal is mono and stereo recordings are summed mono below ~150 Hz,

What's your source on that?

I've heard a lot of conflicting views on this. I recall a discussion of this some time ago, in which someone claimed that modern recordings do in fact have stereo bass information, and that in the past they were summed mono due to the limitations of vinyl. This person appeared to have some credible link to recording studios in some form, but it's hard to know what to believe, since there are a lot of assertions being thrown around. Sometimes it's a case of someone who heard someone who sounded like he knew what he was talking about because his friend's brother's wife's dog's pervious owner once went to a recording studio!

 

[GM]

Well, I don't know where you read dogmatic into my post, but my listening impressions and theory on this agree.

Greets!

"I wouldn't consider......." sounds pretty dogmatic to me, especially considering my contrary experience. WRT staying close to the mains, if you want the subs to be in 'time', then they need to be well in front of them. For instance, with an 80 Hz/4th order XO (1 Hz offset), we're talking ~169.5"/12.5 ms, or further than some room's longest dim. and way more than can be electronically corrected for with inexpensive units. So yeah, for low XO point/high order slopes, I agree.

I've seen that study but can't really agree on their conclusion. IMO there aren't many locations that don't compromise imaging. I have heard a good system which had one rear subwoofer and 4 across the front, and it has a sophisticated phase correction system. I'd call it an exception.

Me neither, but I don't have any documented proof to back up my opinion that their conclusions are questionable so don't have much choice but to offer it up and let those who try it decide for themselves. I gather that you don't either.

What's your source on that?

I've heard a lot of conflicting views on this. I recall a discussion of this some time ago, in which someone claimed that modern recordings do in fact have stereo bass information, and that in the past they were summed mono due to the limitations of vinyl. This person appeared to have some credible link to recording studios in some form, but it's hard to know what to believe, since there are a lot of assertions being thrown around. Sometimes it's a case of someone who heard someone who sounded like he knew what he was talking about because his friend's brother's wife's dog's pervious owner once went to a recording studio!

Can't imagine why there's conflicting views on something that's well documented in various places from back 'in the day', but I can't quote title/issue # at this late date. I'm not a recording engineer, but I've spent many an hour learning from them back when analog was the only 'game in town', though on-line that doesn't count for much without the credentials and/or documentation to back it up, so I guess you'll have to find your own sources if no 'pro' chimes in.

There are some early special effects analog (RTR tape mostly, though there's some vinyl with stereo midbass) and digital recordings (CD) that have a stereo signal below ~150 Hz, but I don't know why they bother since a typical size HT and/or hi-fi room will screw them up so bad that you won't recognize them as being anything but summed mono. Even if the room's big enough, there's still the problem of the speaker's directivity down low, or the lack thereof with all but the largest practical midbass/LF horn systems. I mean just dropping the stereo to 80 Hz requires a ~139" wide WG to confine it to 90 deg, or about the max angle for HT and/or hi-fi apps, with 60 deg better in many apps, but now we need a ~208" wide mouth/channel!

WRT the LFE channel, download Dolby's 'LFE' pdf, or for more in-depth info, their '5.1 Channel Production Guidelines', both of which describe it in such a way (at least to my satisfaction) that <120 Hz is mono, though I don't recall them saying it bluntly.

Correct, vinyl can barely handle a mono LF track, the grooves get too big, so no way to cut stereo. I do have one album with a 32 Hz groove in it, but a hi-fi stylus just drops down and drags/bounces around the bottom so it comes out as a bunch of summed higher harmonics of various origins. I have a Capitol LP demo with a bit of stereo midbass, "The Big Sound Of The Drags" circa 1962, but AFAIK it wasn't released that way.

Bottom line, between the room and our hearing acuity down low, we neither want nor need stereo LF in a typical home app. What we do need is controlled directivity/flat power response in our acute hearing BW, which in turn gives a sense of LF 'stereo' by controlling its harmonic structure, which is considerable since the lower the frequency, the wider its BW and why the lower the system Fc, the 'fuller'/'richer'/more 'extended' it sounds.

GM

 

[BassAwdyO]

With regard to the bass being mixed mono...

It is done this way in greater than 90% of professional recordings. I have heard a few tracks that have been mixed with stereo bass, but audibly there isn't really a difference.

It is true that we localize the harmonics of the fundemental low frequency and we use the localization of those harmonics to percieve the location of the fundemental.

For instance, if you had a stereo recording where a 30hz fundemental was played on the left side and it's harmonics were played on the right side, you would localize the fundemental as coming from the right.