Yes Qts below 0.5 yields a start of roll off that is higher (given the same Fs) than higher Q which results in a higher -3dB frequency. But looking a response simulations the difference in -10dB points is not as great and I suspect that the -10dB point is really the more pertinent figure especially when room gain is taken into account. But on top of that many times the low Q drivers tend to have lower fs which further mitigates the issue. It may even be that the low Q slope more closely matches the slope of room gain in normal "leaky" rooms.
I may need to do a bit of experimentation. Have you guys found the bass extension of low Q sealed enclosures to be really lacking or not as bad as it looks? Thoughts?
I may need to do a bit of experimentation. Have you guys found the bass extension of low Q sealed enclosures to be really lacking or not as bad as it looks? Thoughts?
Much would depend on the type and size of the room one has and how it is built. I feel no lack of bass with sealed subs in my room. I would say the room is well sealed compared to most rooms and all surfaces are stiff and heavy. In theory / simulation in open air: Qtc is around 0,36, F3 around 118 Hz and FB around 49 Hz. Still, because of room gain and pressure gain, the bass is actually louder at 10 Hz than at 120 Hz. The UMIK 1 shows about 6 dB too low value at 10 Hz according to the calibration file which came with it. Link to my simulations and actual REW measurements: https://www.diyaudio.com/community/threads/active-basstraps.331145/post-6836275 (f I remember correctly crossover was set at 120 Hz.)
Thanks, good info. IIRC my room is about 12'x14' and leaky. Look forward to hearing any experiences with these types of woofer/subwoofer setups.
"suck vs. not-suck" is a one-dimensional metric taken out of context.
what you want to look at is the cabinets low frequency response (dominated by woofer roll-off slope defined by the driver/box resonant system)
adding with room gain (and other resonant peaks and cancellations from boundary interference)
it all adds up to an in-room response that may or may not be what you are looking for
if you are doing a passive setup with no EQ, simulate the enclosure size with your woofer of choice to get the response you want
remember this will also be dependent on the speaker position in room (distance from walls,etc) and your listening position.
it will be an iterative process because you will need to build the box to measure it (or I suppose you can use some fancy simulation software)
"modern" method is to put a low Q woofer in manageable sized box and EQ to optimal response with lots of power and DSP.
then you are able to attack the room modes as well as shape the roll-off.
low Q woofers usually have stronger magnets, higher Xmax and power handling and therefore take well to EQ boost
which allows you to get any response you want within limits of Xmax, power, etc.
even if you are dedicated to passive XO for the mids and highs there is a strong case for doing this for the low end.
what you want to look at is the cabinets low frequency response (dominated by woofer roll-off slope defined by the driver/box resonant system)
adding with room gain (and other resonant peaks and cancellations from boundary interference)
it all adds up to an in-room response that may or may not be what you are looking for
if you are doing a passive setup with no EQ, simulate the enclosure size with your woofer of choice to get the response you want
remember this will also be dependent on the speaker position in room (distance from walls,etc) and your listening position.
it will be an iterative process because you will need to build the box to measure it (or I suppose you can use some fancy simulation software)
"modern" method is to put a low Q woofer in manageable sized box and EQ to optimal response with lots of power and DSP.
then you are able to attack the room modes as well as shape the roll-off.
low Q woofers usually have stronger magnets, higher Xmax and power handling and therefore take well to EQ boost
which allows you to get any response you want within limits of Xmax, power, etc.
even if you are dedicated to passive XO for the mids and highs there is a strong case for doing this for the low end.
Room gain is theoretical. It is a myth in practice, even if you were to try to seal your room.
The higher the system Q, the higher the (undesirable - but how undesirable?) group delay. One reason that OB bass is so well liked??? (I'm assuming that most OB systems use decent drivers which tend to have lower than optimal Qts.)
High Q also implies low magnetic flux, which implies lower sensitivity and higher distortion - everything else being equal, of course.
High Q also implies low magnetic flux, which implies lower sensitivity and higher distortion - everything else being equal, of course.
keithj01, since open baffle bass is usually falling at 6dB/oct, wouldn't you equalise it and wouldn't you choose to make it look like some other well known alignment?
Yes, it's an interesting point as to how much effect the usual 6dB/octave EQ would have. Would we expect a sealed-box to have superior group delay characteristics to an OB with the same frequency response?
Anyway, the main point is that low Q will usually result in lower group delay - though at frequencies where it may not matter too much (in terms of audibility).
Would you expect them to be different? (Of course the cabinet edges could affect the impulse but that could be beyond the point..)
That won't be an issue. The response and the EQ are both minimum phase, so the total remains the same.
Can we say that, when the mechanism causing the falling OB response is the delay associated with the acoustic short-circuit?
Edit: "rising OB response" would be a better description, I suppose.
Edit: "rising OB response" would be a better description, I suppose.
No, room and pressure gain is not a myth. The simulation I made for sealed subs showed a 29 dB drop from about 120 Hz to about 90 dB at 10 Hz. The shape of the simulated curve does not show much of similarity at all to the actual measured room response curve. -A proof of the influence of room dependent room and pressure gain. (The link in post #2).
A lack of room and pressure gain (or little of it) can be a fact though. That would be dependent on room construction and the room’s longest dimension. A very large dimension would give no pressure gain at audible frequencies. A bass leaky room with light weight walls / many windows and doors, not much of room gain in the low frequencies. This can be good too, low frequency room modes with long decay time can be a problem.
I guess there is some confusion on 4/2/1 pi radiation vs. resonances from modal patterns here. Room gain isn’t theoretical from our ears’ perspective. The question is which kind of it is beneficial.
The differences between 4 or 2 or 1 pi radiation ( or even smaller angles) apply not only to bass frequencies. Think ‘horn’ 😉
The differences between 4 or 2 or 1 pi radiation ( or even smaller angles) apply not only to bass frequencies. Think ‘horn’ 😉
The mechanism is loss that occurs below the modal region, so in that sense it is a lack of significant delay that is needed.
I'm sorry, were you responding to me? Neither of these things has to do with room gain.
If you can tweak the amplifier or don't mind reducing efficiency, you can always increase Q by increasing the driving resistance by either using a combination of series and shunt feedback or a series resistor. It should also reduce distortion and compression effects to some extent (similar to current drive, but probably to a lesser extent, as resistive drive is in between current and voltage drive).
You have me clueless there. So what is room gain?
Below the modal region SPL in an enclosed space is spread quite homogenuous and defined by the room volume change that a speaker volume displacement causes. Think of Boyle-Gay Lussac. Leaks will be of influence, like losses of less than perfect stiff boundaries.