Curious about passive subwoofers – who’s using them and how?

[Flaesh]

anechoic frequency response

of my sub (calculated, 2pi):

and measured LF response approximately at "sweet spot". As always (unless otherwise specified) no smooting, without eq\correction, with long default window:

For example.
(copied from my thread)

 

[LF78]

and measured LF response approximately at "sweet spot"

So basically what you're suggesting is that the anechoic FR is totally not relevant compared to the in-room FR, am I correct?

 

[Flaesh]

I don't think anechoic equalization is necessary or particularly useful for home subwoofers.

 

[levimax]

of my sub (calculated, 2pi):
View attachment 486589
and measured LF response approximately at "sweet spot". As always (unless otherwise specified) no smooting, without eq\correction, with long default window:
View attachment 486590
For example.
(copied from my thread)

I am not sure I understand the first graph as it appears to be a "calculated" anechoic response rather than a measured anechoic response. I am not sure of the calculation method but it almost appears to be for just the driver and not the enclosure? In any case I do agree the calculated results you show have no use but actual anechoic measurements are always helpful.

 

[montyliam]

I think that a linear anechoic frequency response is a good starting point on which to add room correction: am I wrong?

Yes. The linear anechoic frequency response will never be so when the subwoofer is placed within a room. You do not EQ the natural subwoofer response but the subwoofer response as a result of the room influence in which it is in. Using the anechoic response of the subwoofers can help you understand what the influence of the room is (likely increased low end output + lots of peaks and nulls in the response), but should not be used as a basis for EQ.

 

[Flaesh]

just the driver and not the enclosure?

Driver in 200 l sealed enclosure (that's how they are used in reality), calculated for half spase. It's possible to measure quasi-anechoicity in the near field. Or take four 200-liter boxes to the stadium and measure them ground-plane. But why? This won't change the frequency and time response in the listening room.

 

[LF78]

Using the anechoic response of the subwoofers can help you understand what the influence of the room is (likely increased low end output + lots of peaks and nulls in the response), but should not be used as a basis for EQ.

Ok got it. But this is different for example for bookshelf speakers and left/right channel as far as I know, where the anechoic response is the basis for the first correction (see for example sites like spinorama.org).

 

[levimax]

Driver in 200 l sealed enclosure (that's how they are used in reality), calculated for half spase. It's possible to measure quasi-anechoicity in the near field. Or take four 200-liter boxes to the stadium and measure them ground-plane. But why? This won't change the frequency and time response in the listening room.

I understand your point but for instance if you have a "dip" in the measured in-room response it would be helpful to know if it is caused by the speaker or the room. If the speaker you can boost the dip to fix the response, if the room is causing the dip boosting dips is generally counterproductive. The more accurate information you have the better as in room measurements at LF are unreliable and can be difficult to interpret.

 

[Flaesh]

or the room

The room of course. The same applies to peaks. Any realistic speaker driver in a reasonable simple box does not produce dips and [big] peaks.

 

[levimax]

The room of course. The same applies to peaks. Any realistic speaker driver in a reasonable simple box does not produce dips and [big] peaks.

Again I understand your point, especially for a sealed sub (for a ported DIY sub a lot can go wrong and I would like to confirm it is working as expected before I started taking in room measurements). I like to have as much information as possible as when integrating subs as even under the best indoor measurements scenario the measurements are limited at best. Now when you talk about dragging a 200 liter sealed sub outside to measure it is the added information worth the trouble? Probably not unless you enjoy that kind of thing.

 

[Flaesh]

about dragging a 200 liter sealed sub outside

Four subs !! BTW, maybe I'll make and add four more..

 

[EngineerNate]

I like keeping the amp separate because it means I only have to run one wire (pair) to where the sub lives instead of power+signal. Makes positioning optimally easier.

 

[Bruce Morgen]

I use passive subs for the 2.1 systems connected to two of our smart TVs. One is an old Infinity PS-10 that I converted to passive -- when its plate amp failed for the second time -- and the other is a refugee from an old Samsung 5.1 package that I picked up for peanuts on eBay. Both systems are powered with sub-$100 2.1 chip amps and are more than adequate for the very small spaces they serve.

 

[DVDdoug]

I am new to this forum and would appreciate any help in finding a passive subwoofer

They are rare in home audio. Most home theater or hi-fi subs are active. It seems like most pro/PA subs are also active these days...

AVRs (Audio Video Receivers) have amplifier-outputs for 5 or more passive speakers (sometimes additional "preamp outputs") but only a line-level output for a powered sub. Of course you can use a passive sub with an AVR if you have an amplifier for it.

And you need a way to integrate it... A lot of active subs have a built-in line-level pass-through crossover (to filter the bass out of the signal to the amplifier for your main speakers). (ALL active subs have a low-pass filter.)

With a passive sub, if you don't have a receiver with a crossover ("bass management") you may need an active crossover.

(and especially instructions on how to convert a powered sub to passive)

Just open it up, disconnect the amplifier from the driver(s) and connect the driver(s) to some kind of connector. These are pretty standard. Or if it has speaker inputs you may be able to disconnect those from the amplifier input and use those. (That won't be as easy if it's all on one PC board).

Note that most active subs have built-in EQ (analog or DSP) that's customized to smooth and extend the bass and you'd be bypassing that. (It will likely sound WORSE.)

I've tried Klipsch and Polk powered subs, but find that I cannot control the bass level (it's either booming or not there depending on the record being played).

If it's connected correctly, obviously, the level should change when you adjust the volume. And active subs always have a "gain" control.

There are some "bad" subwoofers but the issue is PROBABLY standing waves in the room. The direct and reflected waves combine in-and-out of phase at different frequencies at different places in the room. Standing waves are worse at low frequencies and they are difficult to deal with. The bumps (standing wave anti-nodes) can be knocked-down with EQ. The dips (standing wave nodes where the waves cancel) can't really be corrected with EQ because it takes "infinite power" and "infinitely large" subwoofers to overcome the cancelation. The good news is that the dips tend to be less annoying than the bumps. (The "pro solution" is bass traps to absorb the bass that would otherwise be reflected. They can help to smooth the dips and the bumps.)

Different subwoofer locations will make a difference and multiple subs (in different locations) can help... And it can get complicated...

I'm an advanced woodworker but novice with audio gear.

You could easily build a subwoofer! Before you buy a woofer (driver) you can look-up the specs which usually include the Thiele/Small parameters. You can plug the parameters into speaker design software (WinISD is free) to optimize cabinet design and experiment with different cabinet volumes and compare/model ported and sealed designs, etc.

...And if you wanted to make it active you can get a Plate Amplifier.

 

[EJ3]

Hey everyone,

I’ve been seeing that while most people go with active subs these days, there are still quite a few who stick with passive subwoofers. I’m really curious to learn from those of you who use them.

A few things I’d love to hear about:

• Why passive? What made you choose a passive sub over an active one? (flexibility with amps/DSP, reliability, DIY, cost, etc.)
• Your setup – Which passive subwoofer(s) are you running, and what amp do you pair them with?
• Use cases – Do you mainly use it for home theater, music, gaming, or a mix?
• Amps – For using dedicated subwoofer amps, which features do you find essential (power output, filters, phase, DSP, auto on/off, trigger, etc.) and which ones are just nice-to-have?
• Good and bad – what’s been great (or frustrating) about today’s subwoofer amps?

I’m not looking for measurements or lab-style analysis (though always welcome on ASR!), but more your personal experiences and what you’ve learned from using passive subs in the real world.

Looking forward to hearing your setups and lessons learned — I feel like this is an area where shared experiences can really help others considering the same path.

Why Passive: with six NAD 2200 amps that can do this: 460 W RMS a channel into 8 ohms, 700+ W RMS a channel into 4 ohms, 800+ W RMS a channel into 2 ohms all @ 40 Hz & can be bridged mono for double the power at either 8 or 4 Ohms, I had to give 2 of them something to do.
My setup: one amp running 4 Ohm stereo for my pair of Dahlquist M-905's (unequilized FR +-2DB from 26 Hz-20 KHz [see HiFi Classsic review if interested]) and one 2200 running 4 Ohm bridged mono for each of 2 subs.
Back in the day, Radio Shack made 2 different floor firing, ported subwoofers (both 12" [one a smaller box tuned for maybe 40 HZ & one larger box tuned for 29 Hz]). Of course, Radio Shack's 12" speakers (even the better one in the larger box) where not that great (& neither was their crossover).
So, around 2008, I bought the best Pioneer 12" automotive competition, dual 4 Ohm voice coil speakers that they made at the time (with a 96 DB @ 1 watt 4 Ohms, 1400 RMS continuous and 2400 watt RMS max), with an FR of 20-80 Hz. And made a circuit that gave me 4 Ohm nominal with the 2 voice coils bridged together. I did this to both subs and ran each sub from it's own bridged mono at 4 Ohm NAD 2200.
My APT Holman PRE OUT 1 goes into a Harison Labs PFMOD (with Highpass set at 70Hz and my Low Pass set at 55Hz:

The Dahlqusts sit on top of the subwoofer box's on a container pad (40FT/80FT container corner pads for the concrete to container interface) 11 inches above the floor, with a backward tilt of 3.5 degrees for optimum coverage of the listening area. Like most free-standing speakers, the M-905 gives its best performance when it is placed at least a foot from the wall and angled slightly inward toward the listener, Quasi-anechoic FFT measurements have shown an overall group-delay variation of about 0.1 millisecond between 4,000 and 20,000 Hz and 0.5 ms between 1,000 and 20.000 Hz, convincing evidence of the attention paid to the phase characteristics of the M-905.
Use cases: mostly stereo but sometimes I configure into quad similar two this manner (ending up being a 4.2 system):
Quadraphonic Synthesis
With two Holman Preamplifiers, you can synthesis and control four output channels from just two input channels.

Apply all your inputs to the first Holman Preamplifier. Use it for all your tone controls, filters and source and tape selections. Leave its Stereo Mode in Stereo.

Connect the first Holman Preamplifier's MAIN 1 output to one power amplifier and your two front speakers.

Connect the first Holman Preamplifier's MAIN 2 output to any line-level input of the second Holman Preamplifier.

Connect the second Holman Preamplifier's MAIN 1 output to the power amplifier for your two rear speakers.

Rotate the second Holman Preamplifier's stereo mode control to L-R, and start by setting it to about unity gain or a bit less, and keep its tone controls flat. The tone and filter settings of the first Holman Preamplifier are fed automatically to the second Holman Preamplifier.

Set balance on the first preamp. Set front-rear balance on the Volume control of the second preamp.

Leave the power switch of the second preamp ON, and plug its power cord into a switched outlet of the first Holman Preamplifier. Now the power is controlled by the first Holman Preamplifier, too.

I use the tone controls & filters to adust the signal to taste (no EQ, DSP, etc.):

Frequency Responses, Bass Control (normal ">--") at 12, 1, 2, 3, 4 and 5 o'clock

Frequency Responses, Treble Control, Apt Holman Preamplifier.

Frequency Response, Normal (left) and 15 Hz filter (right), Apt Holman Preamplifier.

15 Hz filter (only) response.​

The low-frequency response is the same with the tone controls either defeated or engaged, for all inputs and all outputs.

The 15 Hz filter is selected with a rear-panel switch.

It's -1/2 dB at 20 Hz, -1 dB at 17.5 Hz, -2 dB at 15 Hz, -3 dB at 14 Hz, - 5 dB at 12 Hz and -10 dB at 10 Hz.

Frequency Response, High Filter (lowest trace), Normal (middle), and Tone Defeated (top), Apt Holman Preamplifier.

The 8 kHz High Filter is only active when the tone controls are engaged. If the tone controls are active but the High Filter isn't selected, then the middle 40 kHz filter is active.

If the tone controls are defeated, then the -3 dB frequency is 150 kHz as seen in the highest curve.

I have a pair of these (bought new & restomodded to newer, better specs (not that they were slouches, by any means but around 46-47 years later, it's likely that one or two things could be deteriated and need renewing or been done slightly better (but for sure, not by much):

Apt Corporation Holman Preamp, designed in 1978 by Tomlison Holman (THX founder and inventor of 5.1 surround).​

AMPS- (and everything else in my system) are on a pair of dedicated 20 amp outlets with a USPS between them & the outlet. Tun both USPS's on and it all comes on.
There is no TV in this house (we have not had one since 2007, at my wife's request) & there are no remotes to the stereo system.

Good & Bad: All good, the system does exactly what I want it to do. People who visit ask "How can it sound so great and you only have a couple of speakers & cobbled together subs?" & I answer: "Well, it's simple: you start out by buying great gear that will stand the test of time and add to it as you go along".

 

[Bugal1998]

Better late than never...

Running:
(4) JBL 5628 subwoofers powered by a single Crown 4x3500HD
(4) SI IB-24 subs powered by a Crown 5000HD

Passives selected for:

-Ease of wiring (only speaker cable needes at eachnsub location and saves on electrical work)
-Ease of repair (amp can be pulled from the rack)
-Ease of tuning (amps are IP controlled so no need to move bulky subs to acess controls)
-Lifetime repairability since any suitable amp can power the subs without fitment considerations
-Built-in DSP/crossovers/delays and signal pass through
-Price to performance (Only 2 amps needed for 6 channels of subwoofer amplification)

Use is in dedicated home media room, roughly 90% 2-channel music, 9% movie, 1% multi-channel atmos music.

This amp/sub setup has been wonderfully flexible and easy to tune and integrate; I have zero interest in going back to powered subs.Just wish EQ center frequency range extended to 10hz instead of 20hz in the amps.

 

[Shrek6]

I am using a passive sub because it's the one I had in high school for my car stereo like 20 years ago. It's an Ascendant Acoustics Atlas 15", in a sealed box I built. The company no longer exists and hasn't for a long time. I'm using some ****** class-d amp I bought on amazon from Kinter I had laying around. Luckily these subs were pretty efficient but It's far from ideal.

I'm currently debating what my next move should be, subwoofer-wise. I know this subwoofer was considered to have good sound quality for the money back when I bought it. It's unclear if it would be worth throwing money at this thing in terms of a new amplifier and refining the enclosure (it's currently in a carpeted MDF box with no bracing), or if I should just sell it locally along with the Elemental car audio amplifier (also out of business) I have. I could get a Dayton powered 12" sub for $180

 

[Chrispy]

Wow, an Ascendant sub, predecessor to the Epiks IIRC

 

[jonfitch]

I imagine passive subs have huge advantages in noise and would be really effective for a nearfield setup. Most subs I find have too much self-noise when you sit near them. There was a thread here on ASR where someone took their SVS SB1000 and hooked it up to an Aiyama amp and all the self-noise coming out of the sub went away.

 

[EJ3]

I am using a passive sub because it's the one I had in high school for my car stereo like 20 years ago. It's an Ascendant Acoustics Atlas 15", in a sealed box I built. The company no longer exists and hasn't for a long time. I'm using some ****** class-d amp I bought on amazon from Kinter I had laying around. Luckily these subs were pretty efficient but It's far from ideal.

I'm currently debating what my next move should be, subwoofer-wise. I know this subwoofer was considered to have good sound quality for the money back when I bought it. It's unclear if it would be worth throwing money at this thing in terms of a new amplifier and refining the enclosure (it's currently in a carpeted MDF box with no bracing), or if I should just sell it locally along with the Elemental car audio amplifier (also out of business) I have. I could get a Dayton powered 12" sub for $180

Something like this might help??:

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