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Discussion Starter #1
Hi,

I am investigating how to get best possible impulse response from a sub that will go all the way or close to 20Hz. Ideally I want to play 20Hz square-wave and it will still look as a square-wave when I measure it with a good microphone.
My first approach was that a horn loudspeaker would be ideal for this.
But when doing some simulations with a vented box of a fraction of the size actually had better impulse response!

Do anyone has any comments regarding this?
My expectation was that a horn would have a much better impulse response than a vented box. The horn is not a resonant system in the same way as a vented box and the general comments and experiences (including my own) is that horns are much more direct and punchy and not at all boomy in the same way as many vented boxes.
If this punchyness do not come from a better impulse response, what is it then that that makes bass horns so direct?
 

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It maybe just me but I would NOT be playing a square wave through your sub the speaker will not care one bit for it and depending on the amp it will not either.

What amp are you going to use and why would you ever want to reproduce something your driver should never see.
 

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Discussion Starter #3
The important thing is not playing square waves and listening to them.
The important thing is to play music with perfect transient information intact and no ringing.
I want to be able to play a square-wave and have it reproduced perfectly because it shows that the system do not have phase distortion issues.
It is perfectly harmless to play square-waves through any loudspeaker system, just listen to any track containing a Moog synthesizer.
Of course it depends on the level. If you are playing a square-wave because your 2000W amp is clipping then it is probably not so good. But if you are playing a square-wave at 1 Vrms or 2,83 Vrms most system will not have any problem with it.
The problem is that most systems will not be able to play a 20 Hz square-wave that still looks like a square-wave!
 

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Square wave reproduction requires a wide frequency response because the wave consists of the primary frequency and an infinite number of odd-order harmonics. The poor result of the horn-loaded system reflects a more limited operating bandwidth compared to the vented subwoofer. The best test would be how each performs with optimized satellites, crossovers and delay (if applicable) in place. Not many systems can produce good square waves at any frequency and/or listening position and the significance of the characteristic is hotly debated among audiophiles.
 

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Have you hooked your amp up to a scope and looked at the output and see if it can make a perfect square wave? Most amps have issues with that. What amp are you using that can make a perfect square wave on a quality scope please post some pics of it as I have seen many amps measured and most have issues and I am not talking cheep class D amps.

Even the Parasound Hca-3500 that I own does not produce a perfect square wave are you using a $5000 + amp for a subwoofer?

Also what are you using to make the square wave, are you using a sound card on a computer that will in most test I have seen fail to do such correctly or are you using a high quality generator that can do such?

What kind of test equipment do you own? I used to service electronic's and have a bench setup with stuff and from what I have measured over the years finding a piece of gear that can do such is not common.
 

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Discussion Starter #6
Thanks for the inputs.
I should maybe clarify a bit more. These two speakers are simulations. I have not built them yet.
I was more looking for a theoretical discussion on how speaker parameters effect group delay, impulse response but more importantly audible parameters such as "punch" or "depth".
When measuring I can borrow a Audio Precision, Clio or Klippel system from work, but first I want all the theoretical stuff to add up.

My feeling is that I have always loved the punch of horn loaded subs. But looking at these simulated responses, the vented sub actually gives the impression of being the more punchy arrangement.
Any comments on this?
 

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With ringing if you remove the box from the equation and look at the driver the driver with the higher mass in theory take more time to stop moving.

A lot of horn subs seem to use cones that are lighter in mass then say a ported subwoofer.

However with that being said the amps ability to control the driver is based on a lot of factors and where it all may end up is hard to say.

The ported subs I have spent time with that sounded bad were not built correct and we're in too large or small of a box. My guess is that a subwoofer that is in too large of a box would cause it to ring a bit more then one that is in a smaller box and the same could be said with sealed sub. The air acts as a cushion and if I recall helps control the driver too much air being able to easily be moved and the sub can keep playing. This is a guess however and I could be very wrong on that.
 

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Thanks for the inputs.
I should maybe clarify a bit more. These two speakers are simulations. I have not built them yet.
I was more looking for a theoretical discussion on how speaker parameters effect group delay, impulse response but more importantly audible parameters such as "punch" or "depth".
When measuring I can borrow a Audio Precision, Clio or Klippel system from work, but first I want all the theoretical stuff to add up.

My feeling is that I have always loved the punch of horn loaded subs. But looking at these simulated responses, the vented sub actually gives the impression of being the more punchy arrangement.
Any comments on this?
Subwoofers with the lowest group delay are generally critically damped sealed box designs. These have a large box volume by commercial standards and can produce excellent results - very clean and musical. "Punchy" often means exaggerated and may wear thin quickly. Accurate and deep are the most desirable traits in a subwoofer. The best results are usually in a treated room with two or (preferably) more subwoofers placed in locations that smooth the response at the listening position and make the best use of room gain. Electronic room correction can add icing to the cake, but is not a panacea.

My current home theater uses four Acoustic Elegance SBP-15 subwoofers each in large sealed enclosures (about 8 cubic feet) and driven by an SVS STA-800H amplifier in a large acoustically treated room. Capable of plumbing the depths of any source material at levels that would drive any sane person from the room, the low distortion and smooth frequency response of this system is among the best I've encountered in a domestic environment. Measurement equipment (Dayton Audio Omnimic system and a wide range of test material) confirm the results and greatly aided in achieving the best sound.
 

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This sounds like a valuable discussion here because accuracy in subs is not easy to attain. If I can comment on LLT enclosures: If you tune your enclosure low enough the worst part of the group delay is located under 20Hz. The peak of the delay may be very high but (with music at least) you wont hear it because its typically much lower by 25HZ and up. So as a ported enclosure goes this may be a good choice?
 

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Off topic how low can you get while still having a flat response and what size room are you working with?
The native response of the subwoofer sytem in my rough;y 24'x19'x10' vaulted ceiling room extends to the low teens with the inherent eoom gain. The overall response is slightly down-sloped, falls about 4 db by 18 kHz and is very linear when measured at the listening position using 1/12 octave smoothiing.
 

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Discussion Starter #13
Here is the output of the horn and the vented sub for 1W input and for 1000W input.
The RCF LF18X400 speaker is used as driver in both examples.
 

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Discussion Starter #14
My room will be about 9m x 7m. It is not built yet.
The subwoofer will be built into the front wall. The idea is a critical listening room/studio control room.
 

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Discussion Starter #15
My problem with subwoofers is that I really dislike them!
In most cases I would rather not have the bass extension instead of turning the sub on.
I think most sub-woofers on the market just smear the music and sound terrible.
A lot of it has to do that in general the only parameters that are specified is the wattage and the frequency response. But these parameters say extremely little on how it will sound when playing music.

I believe that transient response is the most important parameter for a sub. If it is not quick a bass drum beat will sound the same as a bass guitar note and the music will just be a general blur below 60Hz.
That is why I want to build a super fast subwoofer, so that I can finally enjoy the lowest octaves in music!
 

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What is the purpose of this system? Is it for 2 channel music a home studio for mastering?

What kind of treatment is in the room as of now? Many subs have sounded very bad when placed in a room that did not have proper bass traps setup.

Also just a other thought what subs have you played with and we're they in a well treated room and properly setup and aligned with the mains and was this confirmed with measurement software?

Besides just bad subs and they are out there a lot of issues seem to be room related placement or poor matching to the phase of the mains. If the bass from the sub lags behind the mains it is going to sound slow.
 

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Discussion Starter #18
The room is going to be used for two channel stereo material. The "subwoofers" will actually be part of the main stereo setup, so there will be one sub on each side supporting a large studio monitor with the lowest 2 octaves.
So it is a bit like a PA system where a stereo setup is supported by multiple boxes.

It will be used mainly as a critical listening room to judge recordings and changes made to equipment. It will also be used as a studio control room for mixing and recording.

I think my main complaint with subwoofers is that they are usually made to get the most bass out of a as small as possible box volume. This usually lead to some bandpass design or a high Q tuning vented box. This usually means a boomy ringing bass. Even most of the "professional" subwoofer such as Genelec and KRK have this problem. On the Hi-fi side I have tested one of DynAudios bigger subs and was very disappointed. I think most subs that I have tried suffer from "one note bass" to some degree.
I also do not like long throw woofers. When you see a speaker moving like crazy already at normal listening levels you just know that that speaker will run out of headroom fast when there is a transient and there will be distortion as a result and the music will sound compressed and boring. I like large subwoofer, more like PA subwoofers where the cone is almost standing still for most of the playback, but this type of speaker is very rare in a domestic enviroment I think, largely due to it's size.
For some reason fullrange speakers do not suffer as much from this problem, maybe because bass extension is not the primary design goal, so a roll off may be accepted as a good compromise when it comes to over all performance.

My goal is kind of to have PA sound levels with Hi-fi performance. PA speakers are usually very efficient, but few of them play good bass below 30Hz, and they usually have a bit more distortion than Hi-Fi speakers. I want to go all the way dowmn to 20Hz and still be able to support peaks of 120dBSPL without ringing and a lot of distortion.

I would love to try a large overunder damped subwoofer tuned to a Bessel response. But these are mostly found in big cinemas where they do sound very good indeed. Ironically I think that some cinemas are the only place left to hear real audio quality for music playback. Even concert PA systems seems to be designed for a lot of other things than sound quality. A good cinema is still a place were you can hear a wide dynamic response at high SPL with low distortion.
To bad they mostly show movies there...
 

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If the goal is high output with low distortion then a few well designed horns would do what your looking for.

No need to tell you that horns for 20 hz will not be small and as long as your fine with such I don't see a issue hitting that spl with a few of them depending on how far you plan on sitting from them.

Do you have the equipment to offset the proper delay for your mains sense the horns will will have a larger latency then the mains will.
 

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Discussion Starter #20
My thought exactly!

Yes I know they will be big...
I will get a digital delay line for the other drivers, since the horn will add up to 20ms of delay for the lowest frequencies.

But back to my initial question; I thought horns would definitely be the way to go, but when simulating, the horns actually have worse transient response then a vented cabinet, and I do not want to start building anything before I am happy with my simulation results!

This simulation result does not really add up to my subjective experience with horns as being very fast and direct, and not having a lot of overhang, so now I'm confused...
 
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