WIth an isobarik setup the sensitivity is half

What you say is true as (assuming one has a minimum phase speaker) but so is what Mike E. said about the transient action of the various alignments he listed.

The reason is that regardless of how the response shape (transfer function) is obtained, it is the amplitude and phase of those slopes which govern impulse response.
The steeper the slope at band edges, the greater the phase shift and so the signal is spread out in time more.
Extending Low frequency response alone does not adversely effect impulse response but increasing the slope at either end or narrowing the bandwidth does.
Taken alone, a wider bandwidth system (with the same band edge slopes) automatically has better impulse response.
While one might associate the increasing group delay numbers with lower frequency alignments with a "problem", one has to remember that in the context of the wave period, a nominal 2nd order alignment at 40 Hz and another at 20Hz, both exhibit a 180 degree rotation in phase through resonance while (because of the period) the lower one has twice the GD. Passing a complex or impulsive signal through both shows as before, the wider BW system has better impulse response, not to mention reproducing the parts of the music the 40 Hz system was too far down in level to produce audibly.

The real problem with Bandpass speakers is twofold. First that they are limited Bandwidth (if they have gain) and so automatically suffer "in time".
If ported, the real big problem shows up which are the organ pipe resonance’s which can be of greater amplitude than the main response and also make for terrible impulse measurements due to the ringing.
These (just like the duct in a normal vented box) are at the half wave length multiples for the duct and can present 20 dB + of acoustic gain..
The issue is that keeping them high in frequency (way above the crossover) means a short port, small diameter duct, one which will also choke off (falling Qb) easily even at low powers.
Really, a passive radiator is the fix for this and its impulse response can be the same as an ideally acting ported system with out the organ pipe resonance’s.
Nice forum Wayne.
Best,

Tom Danley

^too bad they spelt inadaquate wrong^

Hi Tom

Can you reccomend a text book on areas like this? Does Olsen mention much of this? Or AES loudspeaker anthology?I enjoy solid facts such as this.I cant go into the local bookstore and flick through all the different audio textbooks and chose one with detail i require-I can order the cookbook-which i dont need :P

BTW the forum layout is familiar,simple,and effective. Makes the prosoundweb.com forums look unnatural and complex.

Cheers
Mike.e

• home

Yes, it's two ways of saying the same thing. I think sometimes people get a negative impression of certain traits that "just are." It's like talking about how friction is bad because it wears things out. But without friction, there would be nothing to push against. Same thing with properties like "resonance" or "group delay" or "phase." Sometimes they are excessive, but sometimes, they aren't. Your illustration is a good one:

While one might associate the increasing group delay numbers with lower frequency alignments with a "problem", one has to remember that in the context of the wave period, a nominal 2nd order alignment at 40 Hz and another at 20Hz, both exhibit a 180 degree rotation in phase through resonance while (because of the period) the lower one has twice the GD.

Wayne

I'm certainly not saying that these things are the last word in deep bass reproduction, but neither my cousin nor I have experienced any real problems with one-note bass or similar distortion problems. I think, as with any design, it's a matter of making the right compromises. I'm very satisfied with mine - especially since they've made it possible for me to get real extended deep end with little cost. They cost ~$150 to build.

I must say thatI think that some of the reason for the bad reputation this principle have, is that it's so widely used in cheap 'package type stereo & HT systems, where it's mainly used to at least give an impression of bass to very small satelite speakers with no sound under ~250Hz...

Ofcourse given the choice id have both horn + sealed/dipole ,none of that high order roll off rubbish

What I like about my BP is, that it doesn't exagerate - I've heard way too many subs, that were very busy telling the whole world they were here. My sub delivers when it's supposed to. I think it's 'Q' is about similar to a closed box with Q=1 - not great, but not bad, either. An interesting point is, that my sub isn't exactly small, in hifi terms at least. Btw., the roll-off of my sub IS 12dB/octave a bit down - the initial is probably close to 15dB/oct.

What people often don't consider is the influence of the room. It's close to impossible to judge a sub if one don't take that into consideration - the 'Q' from various room modes can make a sub sound quite different, for better or worse, than it's specs will tell you.

I always walk away from these kind of discussions with an empty feeling - Like why do people think that there is a single best way to do anything in audio given the huge number of compromises that any system involves? And a list of what types of systems sound best? Where is the data to support such a claim? "Sounds good to me"?

My opinion, the room makes more of an effect than any of the factors that are being thrown arround here. Bandpass, ported, sealed, they all have their benefits and drawbacks.

What do I do? Actually I use them all. Thats right, I have five LF drivers in my Home Theater. Two are closed, one ported and two more are bandpass. Five woofers spread around the room makes for a very smooth low end with an effortless sound quality. I don't know muddy from slipery, or slimy, but I do know that the more LF sources there are in a room the smoother the frequency and spatial response will be. And transient response - in a woofer? Does that even have any meaning?

I'd like to participate in the discussion but I don't really follow it.