Horn vs Open baffle bass

[paulspencer]

Trans I'm sure this is part of it, but not all. The ceiling is timber, it's all quite solid, but this can't describe it fully. Obviously something is happening that is more than just stored energy in the room, or room modes ...

[ThorstenL]

Konnichiwa,

Originally posted by paulspencer
The problem with midbass being exaggerated is for small rooms, correct?

Depends upon you definition of "mid bass". Severe room modes often exist in the 50-100Hz range. If the speaker used still outputs a lot of energy in this range and is well coupled to room modes (due to the invariable near corner placement) you get severe resonances in the range where a lot of "Bass" instruments actually have notes. This overwhelming "one note" Bass will obscure really low stuff unless dealt with (by equalising or using dipoles).

Originally posted by paulspencer
There is a room where the Melbourne Audio Club meets, and I'm not sure I understand why, but it is a terrible room for bass. It is large enough to seat perhaps 200, the rear wall is all glass with a heavy curtain in front, the floor is carpet and the side walls are brick. The ceiling is high, as in 4 or 5 m. The bass is terrible.
Tiny speakers sound as if they have a lot of bass, and larger speakers which would normally be fine have boomy bass. Any idea why this might be the case?

The ceiling to floor mode may be the responsible one, as all other modes should be below the musical range. In a normal room both speaker and listener tend to be near the "null" of the vertical mode, as the rooms are usually 2.5 - 3m High. Make the room much higher and you are asking for trouble with the vertical mode, instead of any of the lateral one.

It is hard to be more specific without doing a full acoustical analysis of the room.

There is a good program and some more resources here:

http://www.rivesaudio.com/CARAquick/CARAframe.html

Originally posted by paulspencer
So how should a horn be designed in a room for maximum fidelity? Suppose it were integrated into the construction of the room and the room was large.

The Horn mouth must point towards the listener and have enough surface area to retain pattern control at the lowest frequency related to a room mode.

Originally posted by paulspencer
I would say based on the transient response that dipoles of the same SPL capability would be more dynamic than horns, as horns still compress the peak slightly.

That is entierly possible. However, truely "uncompromised" Horns and Dipoles tend to be structurally of a nature that makes them extremely rare beasties. While I love discussing the absolute, in reality we usually deal with the relative.

And for domestically aceptable structures a "unipole" arrangement is in my view the best LF module, as horns will be too small to be usefull.

Sayonara

[paulspencer]

Is unipole attainable? If so how do you achieve it?

[ThorstenL]

Konnchiwa,

Originally posted by paulspencer
Is unipole attainable? If so how do you achieve it?

Actually, I'm taking liberties here.... The true "unipole" is a design by wvier audio and combines a dipole and a monopole, with adjustable group delay and levels, so in effect ANY directivity pattern, from dipole over various cardiods to omnipole can be produced.

What I am refering to is perhaps best called "limited unipole".

I detailed it earlier somewhere. My argument is that at very low frequencies (below the lowest room mode) an omnidirectional super/infra-woofer is desirable, with as low a cutoff as attainable. With rising frequency this "omni" woofer should hand over to a dipole woofer.

Now if we design a crossover proper, with (say) 3rd order acoustic slopes we can let our dipole roll out naturally if we select the driver suitably for resonance frequcny and Qt (there may still be a need for some EQ of course). At the nominal crossover our dipole will be 6db down in SPL, as will be our super/infra-woofer.

In other word, the same amount of SPL is generated by a (more or less) co-incidental dipole and monopole, giving a (hyper) cardiod response with in theory full cancellation of any rear output and full doubeling up of the front output, giving a flat spl response.

Using our 3rd order slopes the "transitory" region through which the radiation patter changes from omni to dipole will be around 1 Octave, so perhaps from 35-70Hz centered around 50Hz (as it is currently the case for my own system).

The combination can deliver very powerfull low bass output with excellent speed and control of low notes falling into the room mode region and with the classic "chest crushing" pressure often missing from Dipoles even with a very low cutoff (eg. Carver "Amazing").

I guess I have to call it something else than "unipole", but I can't come up with any better term.

I hope this helps.

Sayonara

[qxlxp]

i think there is some apple to oranges comparisons going on here. i have heard multiple interations/generations of magnetar's rigs and i was magnetar's house this last weekend during a "beers & ears" party he was hosting.

when you mention the carver amazing loudspeaker, it is apparent to me that your concept of acceptable output levels are entirely different than magnetar's. just the horn mouth area for his mid to upper bass horns appear to be approx the same surface area as about 3.5 x 18" woofers (and that is a single channel)

his system is really in a different league than what 99% of people have in their homes (i am giving the remaining 1% the benefit of the doubt). i liken it to the best small club sound system available, but with the resolution expected in a high-end, audiophile type speaker. so, when he talks about "live" listening levels, he means it.

i have listened to the martin-logan statements for an hour or so, and they seemed to have the same kind of feeling of unlimited dynamic range, but they were crossing over their dynamic dipole array of 8 x 7" woofers at 60hz to a bipolar/monopole column of 8 x 12".

i have a gut feeling that to reasonably match the output of magnetar's horn rig you would need to go at least with 8 x15" in stacked linkwitz w-baffles and even then i suspect you would have trouble in the 20hz-35hz range.

[RHosch]

Which is why KWY suggests transitioning to a monopole source (sealed box) below the first room eigenvalue. There is no need for a dipole array to attempt 25Hz reproduction in the size of a typical home's room. You might expect the first mode to be around ~40Hz and above for most people's room sizes, and perhaps ~35hz for a large one. Dipole sub systems capable of prodigous output to 40Hz need not be physically intimidating (at least compared to your suggestion of 16 15" drivers), and sealed enclosures matching the output of even Magnetar's horns at 20Hz and below will seem quaint in size compared to his solution. On this point, I can only agree with KWY emphatically.

The only fly in the ointment is the loss of flat(ish) power response paralleling a flat amplitude response at the listening position (which dipoles provide) below the dipole/monopole transition frequency. With the behavior of rooms in response to pressurization below frequencies in which standing waves can develop, the impact of this shift in power response is unclear. Combined with our reduced hearing acuity, it would not seem to be a problem, but it is an area that I intend to more fully explore.

[qi]

qxdxp:

his system is really in a different league than what 99% of people have in their homes (i am giving the remaining 1% the benefit of the doubt). i liken it to the best small club sound system available, but with the resolution expected in a high-end, audiophile type speaker. so, when he talks about "live" listening levels, he means it.

Are there pictures, or of similar rigs, that you can point me to?

[qi]

...no worries -- found em

[Magnetar]

Hello Curtis (it is you isn't it? --

I actually have made some progress on the system since Saturday. We were listening yesterday and felt the subhorn to basshorn transition was a bit off -- What I changed was

1) the large tube traps at the intersection of the subhorns/wall/basshorn have been raised from the submouth to where they now meet the ceiling rather than sitting in front of outside horns mouths on the floor.

2) moved the tractrix satellite horns to the OUTSIDE and the bass horns off the side walls to the inside of the satellites.

3) raised the crossover frequency between the sub and bass horns to 50 cycles as opposed to the old 40 cycle point -- the bass horns aren't loaded as well on the very bottom of their range since they aren't coupled to the sidewalls anymore.

The benefits are clearly audible. For one the soundstage opened up even further (well beyond the room walls) where instruments that used to be on the edge of the stage were a bit out of focus now have much clearer focus with 'flesh and bones' and dimension, the 60 cycle hole that was directly behind the sofa has been raised to almost flat, and the transition between the horns is as transparent as I have been able to obtain in my room.

All in All it was worth the 2 hours I spent moving these beasts around -- They really opened up.

I have usesd eight JBL 2235H 15's before in a dipole (as well as infinite baffle and reflex) -- It was good by 'high end' standards but not like this. IE -- pitch, impact, overhang, power, weight, "speed" are better with the horns.

Originally posted by qxlxp
i think there is some apple to oranges comparisons going on here. i have heard multiple interations/generations of magnetar's rigs and i was magnetar's house this last weekend during a "beers & ears" party he was hosting.

when you mention the carver amazing loudspeaker, it is apparent to me that your concept of acceptable output levels are entirely different than magnetar's. just the horn mouth area for his mid to upper bass horns appear to be approx the same surface area as about 3.5 x 18" woofers (and that is a single channel)

his system is really in a different league than what 99% of people have in their homes (i am giving the remaining 1% the benefit of the doubt). i liken it to the best small club sound system available, but with the resolution expected in a high-end, audiophile type speaker. so, when he talks about "live" listening levels, he means it.

i have listened to the martin-logan statements for an hour or so, and they seemed to have the same kind of feeling of unlimited dynamic range, but they were crossing over their dynamic dipole array of 8 x 7" woofers at 60hz to a bipolar/monopole column of 8 x 12".

i have a gut feeling that to reasonably match the output of magnetar's horn rig you would need to go at least with 8 x15" in stacked linkwitz w-baffles and even then i suspect you would have trouble in the 20hz-35hz range.

[RHosch]

Originally posted by Magnetar

I have usesd eight JBL 2235H 15's before in a dipole (as well as infinite baffle and reflex) -- It was good by 'high end' standards but not like this. IE -- pitch, impact, overhang, power, weight, "speed" are better with the horns.

Pitch... hmm... only things that can possibly affect the perception of pitch is doppler distortion (unlikely, since the warble is centered) or harmonic distortion. Doppler distortion Horns have an advantage in, harmonic they do not. Not sure what could have accounted for your perception of inferior "pitch" definition with dipoles.

Overhang... hmm... horns have measurable inferior transient response. Compared to dipoles, they do have more overhang or ringing. It is a fact.

As for impact, power, weight, and "speed"... well, those are entirely subjective terms that more often than not really have no basis in reality. The "speed" of a subwoofer is nonsensical. Power and impact are defined by SPL capability and power compression attributes. For a given SPL, a dipole sub should have more impact above the room's first eigenmode, perhaps less below, which is why I agree with KWY that transitioning to a monopole below that frequency is advantageous. Perhaps you equate impact with raw SPL output ability? And as for weight, I really can't fathom what that is supposed to convey, but as there is no shortage of audiophile terminology in use I'm sure it has some commonly used definition somewhere.