Subs - are two smaller ones best

Bloody hell. These would be to go with the Altecs?
Don't do it.
Get those woofer cabs off of Merlin and find a pair of JBL 15" drivers. Weenie boy hifi subs won't cut it.

 

joel, it can do 115 db at 20hz!

http://www.avrev.com/equip/revelb15sub/index.html

 

I recommended a pair of JBL 4645 but to no avail Joel. Something to do with 16 cu. ft eating into his living space.

 

To those of you selling subs, what are you going to build instead? Not something even larger?...

 

Chris, it's not a question of absolute volume or extension. It's a question of quality.
You *know* that.

 

Joel,

Having a lot of extra reserve means what happens at normal operation is of hiogher quality, this applies to practically all mechanical systems. The lack of reserves and headroom invariably impacts on quality.

You *know* that.

Ciao T

 

Actually Chris, that means little without knowing the distortion figures as well, as I'm sure Thorsten *knows*. And it was 113db I thought.

FWIW, the JBL's can do 116db at the same frequency with surprisingly low distortion. A pair of 4645 will offer 140 db - so by Thorsten's reckoning, they would be vastly superior having a lot more in reserve ;-)

 

Hi,

Well, a friend of mine has huge transmission lines with 18" Altec drivers. These deliver something in the 120db/1m range each at 20Hz reasonably cleanly (in practice). The reserve sure shows up.

My other friends double 18" Dipoles cannot quite hold pace, but integrate better with his dipole main speakers. I suspect stakin g four dipoles per side would redress the balance though and then the Sub's would match the main speakers in hight....

No, honestly, if you can have extra headroom at ANY frequency it's worth having. Truely uncompressed classical recordings have around 20db crest factor on the crescendi, attendant with aroundwell over 90db average SPL. Less civilised music tends towards higher peak SPL's (average too).

Ciao T

 

No I don't. Although as Merlin mentions the JBLs and many others go more than loud enough to make the listener deaf.

 

Hi,

As pointed out, it is not about loud enough to make you deaf.

Most dynamic cone speakers have between 0.3 to 1% Distrotions for one watt applied (there are certain geometric relaitionships between distortion and power as well, equally with respect to frequency and also of course the ear becomes less sensitive to sound, for a given SPL with falling frequency below around 500Hz.

All this means in a room like mine (small) a pair of 12" Pro Audio Drivers (High SPL, low distortion) which, with their around 400W drive power in tow and realistic 102db/2.83V at 100Hz and 2nd order rolloff at 60Hz (compensated mostly by the room gain which is around 10db @ 30Hz) and can produce a good deal of SPL (128db/1m @ 100Hz, 123db/1m @ 30Hz including room gain) is actually more marginal than ideal, if you prefer low distortion.

Ciao T

 

thorsten,

have you had the distortion components of you home made subwoofers measured in any meaningful fashion?

 

Hi,

My home made subs have a good deal of distortion (like so many others) at power levels above around 1 Watt applied. Actually, due to their Pro Audio Nature the levels where the exceed 1% THD and 1db compression is probably closer to 10 Watt.

The "1 Watt" ballpark applies usually to the toy voice-coils and magnets on so-called "High Fidelity" drivers (including supposedly "serious" subwoofers). Most "HiFi" drivers exceed 1% THD @ 100Hz somewhere in the 1-3 Watt region and 1db compression almost invariably above 1 Watt.

Measurements by Tom Noisaine, Bascom H King and others for the long lamented "Audio" Mag more then illustrate my point. The basic laws of physics more than underscore it.

Any system that requires significantly more than a single Watt for realistic sound pressure levels MUST produce elevated levels of distortions at realistic sound pressure levels. The fact that high efficiency is present however does not mean low distortion is inherently present (low compression will be though), but the fact low efficiency is present means that high distortion and compression is unavoidable.

Ciao T

 

At what frequency and what level measured at 1m anechoic if I might ask? (or at least discounting room gain)

 

Hi,

I do not measure (pseudo)anechonically myself, as I am not operating anything in anechonic chamber. traditional anechonic measurements are virtually useless to tell us anything relevant.

The distortion and compression levels are estimates extrapolated from the data given in the manufacturers datasheets for my own drivers.

My generalisation come mostly from the excellent measurements in Audio, which where so valuable because they profiled THD vs input power in a 3D FFT graph. Most excellent. I also include data from a number of other sources, an excellent resource for measurements of speakers available on line is here:

http://www.geocities.com/sanchez_raoul2/measurements.htm

Ciao T

 

Sorry I'm just getting a load of Stereophile reviews on you link, nothing relating to your subwoofers or how they perform theoretically or in practice.

Traditional (pseudo) anechoic measurements are useful for comparative purposes because they are traditional

 

Hi,

Note what I wrote:

"The distortion and compression levels are estimates extrapolated from the data given in the manufacturers datasheets for my own drivers."

All the notes you need to derive what you seek where below....

102db/2.83V/1m
(theoretically in the selected box)
-3db @ 60Hz
-15db @ 30Hz

that is 99db/2.83V/1m @ 60Hz and 87db/2.83V/1m @ 30Hz

based on extrapolation from manufacturers data the driver has around 1% HD at around 100Hz and 10 Watt Input which will (invariably) rise towards lower frequencies with around a 2nd order curve (as the motor nonlinearities remain constant but SPL output falls notably, so I'd expect around 4% HD @ 30Hz and 10 Watt input (which produces btw. 94db/1m @ 30Hz anechonically and around 104db/1m @30Hz including room gain).

Yet equally, if we take the drivers Xmax10 the System can produce much higher SPL's at elevated levels of distortion, in fact for Xmax10 the Subwoofers output is only limited by the applied power and we then find indeed "deafening" SPL's in room, but with distortion levels between 10 -40% (100 & 30Hz respectively).

Of course much of this is extrapolation.

It is also easy to see how this system is really quite inadequate in absolute terms, as it lacks the ability to produce high SPL's with low distortion, yet at more sedate SPL's (say 90db average at the listening position) it offers quite low levels of distortion.

And before you ask, yes, this single sub with dual 12" drivers goes louder much cleaner than a pair of REL Quake's.

Ciao T

 

Sorry Thorsten but you haven't mentioned the drivers you are using from what I can see. Do you have a link to the specifications?

 

Hi,

The drivers are OEM for a friends company, not generally available. They are nothing too special, fairly average, fairly long throw pro audio 12" Woofers, low Vas, moderate Qts and 45Hz resonance.

Not sure what would be close in generic available drivers, they where specified for the application in a compact, below resonance sub.

Ciao T

 

I said can not will.

Chris:
Get a listen to merlin's various JBLs before parting with any cash.

 

I think the point is that good low distortion bass costs money.

To give an idea, it seems that most loudspeakers display between 10% and 30% THD at 30hz when played at levels around 94db. Even the professional loudspeakers like the ME 901 has about 18% at these levels.

Getting low distortion bass, means subwoofers from what I can see, along with the use of high pass filters on the main speakers. But subs such as the midprice Rels can be worse than normal loudspeakers when it comes to distortion - truly awful. When you get to home builds like Thorsten's, it is possible to get into single figures at semi realistic levels. Going one step further, it seems the likes of the Velodyne DD series halve the levels of THD inherent in designs like Thorsten's.

So really low distortion bass suitable for a domestic enviroment is neccessarily expensive.

But JBL bass is addictive.