Tryin this distributed bass thing..have ?

[tomlinmgt]

I have two DIY subs and an older Velodyne servo (what does that mean?) sub that I want to use to try and assemble a distributed bass set up. The DIY subs use a ported Parts Express sub box, 12" Soundstream subwoofer, and 240wpc Dayton plate amp. The twenty plus year-old Velodyne has a 12" sub driver in a very large sealed enclosure and I think its' around 100wpc. My question is this.... The DIY subs are very musical and the mid bass on these is wonderful but they really don't put out a lot of db below 60hz (the don't "rumble" per se). The Velodyne can get down very low, but because it's only 100wpc it can't dominate at higher volume levels. Do all the subs in a distributed bass set up need to have VLF capability to get a truly effective distributed bass system, or is it prefered to have the subs occupy different territory in the LF bandwidth?

 

[sealy]

Servo-feed back is essentially a sensing circuit or feedback mechanism, sometimes in the form of an accelerometer, which is built into a sub in an attempt to control bass distortion. Velodyne used that system a ways back. I'm not sure if they still use it. It has proven to be failure-prone. The two Velodyne subs I had needed repairs to the servo mechanisms. Velodyne made, and I guess still makes great subs, so I guess the circuit was doing its job, although like any other company of modern times, Velodyne also has mediocre product on the market.

So-called "subwoofers" that can only go down to 60 hz are not really subwoofers. If you want to use various drivers to augment various frequencies, go for it. In my opinion, you're simply compounding the already complex problem of properly enjoining the lows with the rest of the frequency band. I'd stick with a single or double set of identical subwoofers and forget the stepped, bass response idea.

The Soundstream is a car subwoofer is it not? I've yet to hear a car sub in a home environment that can match a good-quality sub designed specifically for that purpose.

 

[89grand]

The subwoofer being a "car" subwoofer really wouldn't matter. The enclosure is what actually tailors the response. Assuming the car sub has a reasonably low Fs and decent X-max it should work just fine.

I'm think the OP isn't really looking for a stepped response, but rather a mutli-sub, distributed bass setup which should easy trounce a single sub setup...as long as the subs woofers actually produce low bass. If they don't, well then sealy is right that it would cause more issues most likely.

 

[dumptruck]

Are you sure the PE boxes are appropriately sized and tuned for those woofers? Maybe some simulation is in order. I would guess, perhaps wrongly, that any subwoofer driver made by a company like soundstream would be capable of playing very loud at 35-40Hz, if not lower. It is kind of their mission.

 

[89grand]

In fact, I would be inclined to blame the ported enclosures. Do you know what the Sounstream subs t/s parameters are, and do you know the specs of the enclosures, ie internal volume, port length and diameter? I'd guess the enclosures simply are not suited to those subs. For some reason, many prefab ported encloures are tuned way too high.

 

[tomlinmgt]

In fact, I would be inclined to blame the ported enclosures. Do you know what the Sounstream subs t/s parameters are, and do you know the specs of the enclosures, ie internal volume, port length and diameter? I'd guess the enclosures simply are not suited to those subs. For some reason, many prefab ported encloures are tuned way too high.

Yes, as a matter of fact Soundstream provided a very nice "installation guide/booklet" that gives all specifications for the driver and also several different frequency response curves for a variety of box designs (ported, sealed, bandpass), volumes, and port volumes for ported boxes. The PE box volume falls right in the middle of their recommended volume (except I think I calculated the slot port on the PE box to be a little larger than they recommend) but IIRC the sealed box has better db below 40hz than the ported box at the expense of overall db. I'll have to study the charts again and perhaps modify the PE enclosures to maximize LF db. I did try to play with port tuning a bit and partially stuffed the slotted ports with some towels and this helped bring in a little more bottom end but more noticeably tightened and cleaned up the mid-bass.
But what I'm getting so far from your responses is that ideally all (or majority?) of the subs in a distributed bass set up need to have good response down to VLF (sub 40hz). Correct?

 

[89grand]

One thing to remember too, is given that the Soundstream sub's are actually for the car, their recommended enclosures will not be ideal for the home. The low frequency response of a given enclosure in the car will be much stronger than in the home. The enclosure will more than likely be larger for home use.

Do they give the actual t/s parameters? If so, that's of much more use than listed "recommended" enclosures. Many car sub manufacturers list smaller than ideal enclosure because everyone wants some magic speaker that only needs a tiny box, but in reality, Hoffmans Iron law already dictates that you can have any two of the three, low bass, small enclosure volume, high sensitivity. So if a sub uses a small enclosure and can produce low bass, it needs a lot of power.

And yes, frequency response at least down to 35hz or a little lower is ideal. Not much music has any information below 30hz anyway.

 

[tomlinmgt]

And about the suitability of this driver in a non-mobile audio application...the "installation guide/booklet" actually makes suggestions for it's employment as a home theater sub. I also called Soundstream and they said these drivers do not rely on cabin gain to get the measured results. The drivers are very nicely constructed. The frames aren't cast, but they are a robust stamped steel design that's powder coated to reduce resonances and the magnet is huge with a vented voice coil. They have nice, beefy spiders and the cone material is much like that of the 2214 JBL drivers in my L100T3's and the surround is fat and fairly rigid. They were made in the USA at their California facility...as opposed to their newer Chinese stuff. They look quite nice and as I said are very, very musical.
I suppose I could knock the divider that is the ceiling of the slot port out of the inside of the enclosure and increase the volume and close the port to create a sealed design if need be.
I played them alongside my JBL L100T3's last night and they seemed to reinforce the bass rather than add something the JBL's weren't providing. As a matter of fact, the JBL's bass seemed larger, fuller and more robust where the DIY subs were more musical with nice, articualte and clear bass notes. Of course, the cabinet volume of the JBLs is probably at least twice that of the PE enclosures.

 

[dumptruck]

If you post the relevant model numbers and dimensions, us geeks can run our simulations and then get off your case if the enclosures aren't the problem.

 

[tomlinmgt]

If you post the relevant model numbers and dimensions, us geeks can run our simulations and then get off your case if the enclosures aren't the problem.

Absolutely! I'll do that as soon as I get home where the relevant literature is. If there's one thing I've learned since messin with this vintage audio stuff (and computers) it's VERY beneficial if you have a few geeks in your corner!

 

[tomlinmgt]

Specifications:
*Power Handling: 300 watts RMS
*VCdia: 2"
*Le: 1.2 mH
*Nominal impedance: 4 ohms per coil
*Re: 3.1 ohms per coil
*Frequency response: 28-500 Hz.
*Magnet weight: 63 oz.
*Fs: 28 Hz
*SPL: 94 dB 2.83V/1m
*Vas: 2.72 cu. ft.
*Qms: 7.83
*Qes: 0.30
*Qts: 0.39
*Xmax: 6.6mm

Highlights
Dual 4-ohm 4-layer voice coils for increased application flexibility
Kapton former for higher power handling
Vented pole piece for better heat dissipation
Custom-design high strength spider to control large cone excursion
Flat dust dome for greater rigidity
Made in the USA
Part #: 299-674 Weight: 15.00 lbs.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=299-674


And the box....

Overview
Goldwood's E-12SP 12" ported box is CNC machine cut from 3/4" MDF and glued air tight, then ported to extended low frequency response. High quality, black polyester carpet adds the finishing touch. Approximately 1.5 ft³.
Highlights
1.5 ft³ cabinet
Slotted port design
3/4" MDF construction
All joints glued and caulked
Black carpet covering

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=260-630

Oh, and I did add some internal bracing (1x2x12 and 1x2x14) to the inside of the box which displaced almost .03 cuft.

 

[kb9qkc]

from what i read youll need at least 3 subs placed at diffrent points of the room,to do it right. i thought you would have the cuttoffs for each slightly diffrent. but then again that might only be for if your using 3 diffrent subs, and want to limit the lesser sub of its duties. anyways hope it goes good for you, hope you find a setup that works for you.

 

[tomlinmgt]

"IMO if you have proper speakers you wont need a sub."

I don't know man...from what I read I'm starting to think some VLF reinforcement with total distribution throughout the listening area could benefit just about any speaker(s) if done properly. Seems those that have gotten it right become very strong proponents of the method and my impression is they aren't exactly spring chickens when it comes to experience with "proper" speakers.

 

[89grand]

The ideal ported enclosure with a tuning frequency of 29hz is 2.43 ft3.

Your enclosure is too small resulting in a high tuning frequency, that's why it sounds like it's strong at 60hz...because it is, and it over powers the lower frequencies.

You'd be better off totally sealing off the enclosure and turning it into a sealed enclosure. For home use 1.5-2 ft3 sealed would work fine, but you'd lose some sensitivity. It's no where near the 94db advertised.

2.83v @ 1m into 8 ohms is 1 watt, but since it's a dual 4 ohm, they are measuring it with the coils in parallel. 2.83v @ 2 ohms is 4 watts. In reality the sensitivity is closer to 88db.

Oh yeah, no speaker I know off doesn't benefit from one or more good subwoofers.

 

[tomlinmgt]

The ideal ported enclosure with a tuning frequency of 29hz is 2.43 ft3.

Your enclosure is too small resulting in a high tuning frequency, that's why it sounds like it's strong at 60hz...because it is, and it over powers the lower frequencies.

You'd be better off totally sealing off the enclosure and turning it into a sealed enclosure. For home use 1.5-2 ft3 sealed would work fine, but you'd lose some sensitivity. It's no where near the 94db advertised.

2.83v @ 1m into 8 ohms is 1 watt, but since it's a dual 4 ohm, they are measuring it with the coils in parallel. 2.83v @ 2 ohms is 4 watts. In reality the sensitivity is closer to 88db.

Oh yeah, no speaker I know off doesn't benefit from one or more good subwoofers.

So with the lower sensitivity I'd just have to run the plate amps a little harder (hotter) for any given volume setting, correct?

 

[skywave-rider]

"IMO if you have proper speakers you wont need a sub."

I don't know man...from what I read I'm starting to think some VLF reinforcement with total distribution throughout the listening area could benefit just about any speaker(s) if done properly. Seems those that have gotten it right become very strong proponents of the method and my impression is they aren't exactly spring chickens when it comes to experience with "proper" speakers.

Read this: Room modes, multisubs and flanking subs.

Parham is saying you use subs flanking the mains crossed over fairly high (about 150Hz) and more distant subs at a lower frequency (80 Hz or so.) He explains why.

 

[kb9qkc]

Oh yeah, no speaker I know off doesn't benefit from one or more good subwoofers.

that might be true for some. but this isnt the discussion of this thread. sorry if you guys interpreted my signature text as part of the post. makes it look like im trying to thread crap. but i just meant to give postive encouragment and help the OP with the previous post i made.

 

[89grand]

that might be true for some. but this isnt the discussion of this thread. sorry if you guys interpreted my signature text as part of the post. makes it look like im trying to thread crap. but i just meant to give postive encouragment and help the OP with the previous post i made.

I just saw it quoted, and responded, then tried to find who said it, then I realized after I posted that it was your sig, not a post. Anyway, some people feel as you do, some as I do, it's cool.

 

[Navydoc]

Read this: Room modes, multisubs and flanking subs.

Parham is saying you use subs flanking the mains crossed over fairly high (about 150Hz) and more distant subs at a lower frequency (80 Hz or so.) He explains why.

I am running two flanking subs (Eminence LAB-12 based sealed, -3 dB @ 45 Hz) via Parham crossed over at 120 (that's as high as my receiver allows) and one old Paradigm PDR 12 crossed over at 60 located on a side wall and elevated about a foot.

The sound is much better than just the one Paradigm sub. It is also better than my previous room with a 24" sealed enclosure w/ a Maelstrom-X 18" driver powered with 700 W.

I really like Parham's implementation of distributed subs. I would bet that Geddes and Toole's approaches also work well. I will never use less than three subs again as distributed bass works so well at canceling out peaks and nulls. I have zero localization issues and a lot of impact when called upon. I like that on recordings with weak bass the system sounds like it has weak bass, accurate - not bloated - bass is my goal.

I plan on replacing the two sealed LAB-12 subs with four standard 3 Pi subs (LAB-12 based Parham designs, vented, ~22 Hz tuning) subs, two will be used as flanking and two as distant. I will augment below 20 Hz with a massive T-TQWP beast using the Mal-X driver that will be capable of putting out >125 dB @ 13 Hz w/ 1300 W (no cone excursion issue when used with a 12 Hz 4th order HPF).

 

[dumptruck]

Here ya go. Sims of the soundstream driver in the PE box.

blue = as-is
yellow = as-is but with 14" external extension to slot port
green = 3 ft³ tuned to 32 Hz

frequency response:

frequency response with dayton plate amp set to 80Hz low-pass:

level of output at 1m when simulated xmax is hit at > 34 Hz, i.e. your approximate maximum music volume if you had a larger amp:
(blue@70W, yellow@270W, green@140W - you don't have that much power, but the relative diff. is what matters)

Do you have the dayton amp with bass boost or without? If you have the boost one, this is not accurate.