to add a subwoofer or not to a full-range stereo speaker system?

[atomant]

Hello,

I have large 9 cubic foot speakers, homemade in 1975. The woofer is 15 inches. There is no crossover with coils and capacitors. Instead, there is an active crossover , and each pair of speakers is driven by its own stereo amplifier. It's a 3-way system. 50 WRMS/channel. The frequency response for the room was adjusted with REW.

Would it be appropriate to add a Polk XT12 subwoofer?

It seems counterintuitive to me, given that the frequency response of the main speakers extends to 24 Hz, just like the XT12. But it was still recommended that I add a subwoofer, and I would notice the difference.

Your opinion?

 

[theREALdotnet]

What problem are you trying to solve?

It seems like the ~45Hz boundary interference that the left speaker suffers isn't affecting the right speaker. You could EQ the right speaker up a little there, to compensate.

 

[staticV3]

Subwoofers can achieve three things:

Extend LFX

Reduce distortion in the Mains

(With multiple bass sources combined with Multi Sub Optimizer or similar):
Reduce positional variation in bass response

If none of these interest you because you're already satisfied with your system's performance in these aspects, then buying a subwoofer would be pointless.

 

[DVDdoug]

The only reason you'd "need" a subwoofer is for movies with surround sound. The "point one" LFE channel isn't included in the downmix so you only get the regular bass from the other channels. And you can configure an AVR to bypass the bass management (crossover) so the bass from the other channels is not re-directed to the sub and it's only used for the LFE. (That's how real movie theaters are set up.)

 

[atomant]

What problem are you trying to solve?

Nothing in particular, I've been recommended to add one. Period. According to this source, every system would benefit from it. I'm skeptikal therefore I'm asking advice here.

It seems like the ~45Hz boundary interference that the left speaker suffers isn't affecting the right speaker. You could EQ the right speaker up a little there, to compensate.

It's a null, it can't be corrected with EQ. Even if I boost it, it still will be a null.

 

[atomant]

The only reason you'd "need" a subwoofer is for movies with surround sound. The "point one" LFE channel isn't included in the downmix so you only get the regular bass from the other channels. And you can configure an AVR to bypass the bass management (crossover) so the bass from the other channels is not re-directed to the sub and it's only used for the LFE. (That's how real movie theaters are set up.)

Thanks for your interest,
I already have a 'movie' room and setup. And it does include a 5.1 setup.
This thread is for my stereo syetem, in another room. I don't watch movies here. Only music. And the XT12 can accept speaker level inputs and has speaker level outputs to redirect to the original woofers. The system would become a 4-way instead of a 3-way.

Therefore, no benefit?

 

[atomant]

Subwoofers can achieve three things:

Extend LFX

Reduce distortion in the Mains

Hi,

Thanks for your reply.

I guess I'd like to address both points. The woofers I have, even though they have been reconed since , are vintage 1975 era (i.e. 50 years old) models 15 inches speakers. They don't seem to move as much air as my 8 inches subwoofer I have for my home theater setup. They don't have large cone excursion. Just an impression. Enclosures are bass-reflex.

 

[RDoc]

Because low frequencies have such long wavelengths there can be various phase interference effects as you move around the room. If that's a concern, a third low frequency source could lessen the effects by adding another phase. Assuming your curves are at your preferred listening location, I'm pretty doubtful you'd hear much difference. It looks very good as it is.

 

[atomant]

your preferred listening location, I'm pretty doubtful you'd hear much difference. It looks very good as it is.

That is correct. All I could do is to absorb or reflect at the nodes to fine tune the actual result. There is already a lot of work positioning the speakers and adjusting the frequency response for this room with REW. Thanks for your opinion.

 

[theREALdotnet]

Nothing in particular, I've been recommended to add one. Period. According to this source, every system would benefit from it. I'm skeptikal therefore I'm asking advice here.

I'd be sceptical, too. If there is no problem you don't need a solution.

It's a null, it can't be corrected with EQ. Even if I boost it, it still will be a null.

That's not quite right. Since it looks like an SBIR null that affects only the left speaker, you can compensate by EQing the right speaker up a bit. This would even out the overall frequency response in that region.

 

[smygolf]

Who suggested to add a sub, your response looks good imo.
XT12 is a small sub o my guess is that it cant keep upp att higher volumes.
Off course it comes down to if the current setup has the same response att higher volumes.

 

[FrantzM]

Hi

It is clear to me that you know how to wield a measurements mike and REW... It will be challenging but you could add a sub. yes.. It mus be able to keep up in SPL (down low ) with your main speakers.. I'd suggest a ported one. Say an SVS PB 2000 Pro or equivalent to or could DIY, something similar , then you would need some DSP. It will take some time to integrate this well but .. You may find the rsults immensely satisfying, as the PB2000 or equivalent ,could help extending your overall bass response in SPL and reach ..
Best

 

[atomant]

the right speaker

Hi,

Sorry, I misread the first time. Interesting approach. It deserves testing. I wouldn't have think of that.

 

[atomant]

Who suggested to add a sub, your response looks good imo.

1) Someone selling subs. 2) Someone else repairing customer grade electronics for years and who added a sub to its hi-fi system, circa Y2K, and the difference was audible. Of course he doesn't have main enclosures as large as I do and they go down to 40 Hz give or take.

XT12 is a small sub o my guess is that it cant keep upp att higher volumes.

I would agree.

 

[atomant]

would need some DSP

Using CamillaDSP for my home theater and EasyEffects on my stereo system (convolution filters). That's right, all is driven by computers running a variety or another of Linux.
Having already bass-reflex enclosures, I also think a ported sub would be preferable, less expensive and smaller should one be added. I only need that extra touch below 30 Hz that require hard work for my 50 years old woofers
Thanks for your kind intervention and the suggestion for sub.

 

[Hear Here]

Hello,




View attachment 466688

Would it be appropriate to add a Polk XT12 subwoofer?

It seems counterintuitive to me, given that the frequency response of the main speakers extends to 24 Hz, just like the XT12. But it was still recommended that I add a subwoofer, and I would notice the difference.

Your opinion?

Are you using 1975-vintage bass drivers or modern ones? I've had similar vintage speakers with old 15" drivers and I now consider that they are nowhere near as good at delivering tight, detailed bass as modern 12" ones. My speakers were Wharfedale Airedale (self-built from Gilbert Briggs' drawings in one of his books) and Westrex 2326A studio monitors of similar vintage. Neither, by modern standards, offered bass anywhere near that of my Avantgarde speakers (twin 12" or twin 10"), or even my earlier Martin Logans (twin 10"), or much earlier KEF Reference 107s (twin 10")

The trouble with large diameter drivers (15" and 18") is the tendency for a "ripple" to develop as the cone reacts to the initial coil movement. The further the distance between the coil and the extremity of the cone, the bigger this problem becomes and the result is "flabby" bass. The best modern large bass drivers partly overcome this by using very large diameter coils but these are very costly. The latest Avantgarde 12" driver uses a 6" diameter coil. My old Wharfedale 15" driver had a 2" coil and I doubt the hugely costly Westrex one was more than 3".

After a decade or so with my Airedales, I decided to change all the drivers from Wharfedale of KEF. The new bass driver was the well-respected "racetrack" B139 (13” x 9") and this delivered noticeably improved bass.

Have you considered upgrading your big speakers with new drivers? 9 cu ft is huge and unnecessary now with modern materials and design, but if you like them and wish to keep them, I'd look at introducing new modern but smaller bass drivers, probable a pair of 10" or 12" ones and forget using subs that will hugely complicate your system and will be difficult to set up optimally with your mains. Also they are unlikely to improve the bass performance. I'm about to sell my REL S812 subs as they contribute nothing to the sound I get from my full-range speakers with their twin 12" drivers.

Good luck with your venture.

 

[krabapple]

Subwoofers can achieve three things:

Extend LFX

Reduce distortion in the Mains

(With multiple bass sources combined with Multi Sub Optimizer or similar):
Reduce positional variation in bass response

If none of these interest you because you're already satisfied with your system's performance in these aspects, then buying a subwoofer would be pointless.

You can also change the modal profile at your single listening position, by adjusting subwoofer position/number.
E.g., the Toole 'trick' of placing two subs at 1/4 positions on the front wall.

Anyway the only thing the OP needs to 'fix' in his graph from the measured position, is the left channel null at 45Hz and the both-channels dip at 250Hz.

 

[krabapple]

The only reason you'd "need" a subwoofer is for movies with surround sound. The "point one" LFE channel isn't included in the downmix so you only get the regular bass from the other channels. And you can configure an AVR to bypass the bass management (crossover) so the bass from the other channels is not re-directed to the sub and it's only used for the LFE. (That's how real movie theaters are set up.)

That's Dolby spec, and your AVR will do it that way if the source is Dolby-encoded (AC3, and I'm guessing, any other flavor of Dolby, whether lossy or lossless)

Whether that is true of other x.1 formats found on DVDA, SACD, and BluRay, I don't know. I would *guess* DTS sources work the same way?

 

[Keith_W]

Subwoofers can achieve three things:

Extend LFX

Reduce distortion in the Mains

(With multiple bass sources combined with Multi Sub Optimizer or similar):
Reduce positional variation in bass response

If none of these interest you because you're already satisfied with your system's performance in these aspects, then buying a subwoofer would be pointless.

This is the answer you need. Well, I would also add "drains your bank account" and "provide hours of DSP fun" but that's just me

We still don't know a few things about your system. Using @staticV3's points:

- Extend LFX: it is clear that your main speakers are capable of low freqs so this point is moot.
- Reduce distortion: take your measurement at normal listening volume, and take a sweep. Then increase by 10dB and take another sweep. Change the distortion scale to %, and if distortion remains <1% it's good. I generally give a bit more leeway for subs, so I accept 2%.
- Reduce positional variation: this is only true if you have multiple bass sources. For e.g. if you add multiple subwoofers, you will get less variation. But it's rather pointless if you add only one sub, unless you don't high pass your main speakers. We don't know whether your system suffers from this. I usually take a measurement at every point where someone is likely to sit. On my listening sofa, I measure over a 60cm area (2 feet) because that's where my head is likely to be when i'm listening by myself.

 

[atomant]

Are you using 1975-vintage bass drivers or modern ones?

Yeah, these are old 1973 Radio Shack 40-1301 (free-air resonance 20 Hz) 15-inch speakers. Not to be confused with the 40-1315 (free-air resonance 45 Hz). They were properly reconed around the year 2000.



They were very good at the time, but the technology has improved a lot since then.

I think your description of the problem applies perfectly to my case. The frequency response is definitely there, but they seem to lack punch compared to modern speakers. They originally sounded great in a small room measuring 10 by 12 feet or 13 by 13 feet, but they're currently in a room measuring 15 by 30 feet.

They were installed in an enclosure I built myself based on plans published in a 1973 book by Gilles Poirier. These were enclosures designed for the BBC. The front and rear panels were filled with compacted sand to eliminate vibrations and were nearly 2 inches thick. For this reason, I'm considering keeping them and will consider your suggestion of replacing them with something more compact and modern.

Thanks for your interest.