dear confused (chris661) not an expert, but my take on things
compliance and power...and mass (and dampening factor)
Ok, here's my "infamous " car suspension analogy:
Consider a car suspension. A bunch of factors affect how well a car handles. Primarily if a wheel loses contact with the ground, it's a bad thing. Control of the suspension allows the maximum contact while being responsive without being overly harsh: the softest suspension that allows this contact to be maintained for the maximum amount of time is the most effective. Herb Adams (former GM suspension designer responsible for the 2nd generation GM "F" bodies and founder of "Herb Adams VSE") took this to the maximum when he left the confines of GM and started his own company. He felt that the non-WS6 suspension as found on Pontiac TransAm (and the Cheverolet equivalent as used on the Camaro Z-28), which had softer spring rates allowed the suspension to do it's job more effectively. Rather than use heavier spring rates, He chose to use larger (and I mean huge) anti-roll bars and shocks that were optimized for those spring rates.
The result: his cars' suspension was vastly superior to the stock cars' suspensions (as "re-tuned" after he left GM). His most significant set-up included reducing the "unsprung" weight (via lighter wheels and "+zero" tire sizing ), using the standard (more) compliant springs (non-HD or "WS-6"), much larger anti-roll bars, and more effective damping (via better tune shock absorbers). Everything else remained the same. His suspension tuned cars bettered the skidpad numbers of the stock car by some 15-20%. His street tuned cars approached 1.0g of lateral acceleration at a time when most race cars didn't hit that number while remaining comfortable to drive on everyday streets. The relation of all this to turntable (my fave topic) and loudspeaker design is not insignificant.
chris (and others):The relationship here is easy enough to establish. The loudspeaker designer/manufacturer must make some assumptions regarding the amount of (reasonable) power that needs to be applied to the loudspeaker driver to get it to move. Inertia must be over come. Overcoming inertia is how we get a driver to move and change direction. The most significant factor that can be designed in (or if you prefer designed out as per Colin Chapman) is lightness
. So a reduction in mass is really about the only thing that can be easily controlled as well as the motor system strength. Compliance also plays a role in Inertia requirements to start and stop a driver's motion (think of it as the spring). But how does this all get controlled?
Control is established through the amount of power applied to the voice coil and the amplifier's dampening factor. And here is the issue using large drivers: the loudspeaker designer/manufacturer makes assumptions based on the intended use of their products and amplifiers with a reasonable dampening factor (often between 70 and 100) . Sway from their assumptions too much and the results can be things like "slow bass". So if a driver is operated outside of its design parameters with an amplifier that does not meet the basic criteria as recommended (without doing any modifications to the driver), one ought not expect good results. That's why for example, a driver with a high Qts can maintain a note for a relatively long period of time, and why many drivers with a much lower Qts can't. Then bring a miss-matched amplifier with too low (or too high) a dampening factor for a particular driver into the equation and it is easy to see how "too slow" bass can happen.
Again, I'm no expert, so take this all with a grain of salt. I'll leave Pano ( Michael, is your wife the "audiophile's wife"?) and others to be the experts (which I truly believe many on this site are).
To all: Merry Christmas, Happy Hannukah and Kwanzaa (or whatever winter you observe).
compliance and power...and mass (and dampening factor)
Hi, could you expand a little?
I don't see how one can draw such a conclusion, when surely moving a diaphram of any diamater any distance is rather dependent on the compliance of the suspension.
Perhaps I haven't understood.
Ok, here's my "infamous " car suspension analogy:
Consider a car suspension. A bunch of factors affect how well a car handles. Primarily if a wheel loses contact with the ground, it's a bad thing. Control of the suspension allows the maximum contact while being responsive without being overly harsh: the softest suspension that allows this contact to be maintained for the maximum amount of time is the most effective. Herb Adams (former GM suspension designer responsible for the 2nd generation GM "F" bodies and founder of "Herb Adams VSE") took this to the maximum when he left the confines of GM and started his own company. He felt that the non-WS6 suspension as found on Pontiac TransAm (and the Cheverolet equivalent as used on the Camaro Z-28), which had softer spring rates allowed the suspension to do it's job more effectively. Rather than use heavier spring rates, He chose to use larger (and I mean huge) anti-roll bars and shocks that were optimized for those spring rates.
The result: his cars' suspension was vastly superior to the stock cars' suspensions (as "re-tuned" after he left GM). His most significant set-up included reducing the "unsprung" weight (via lighter wheels and "+zero" tire sizing ), using the standard (more) compliant springs (non-HD or "WS-6"), much larger anti-roll bars, and more effective damping (via better tune shock absorbers). Everything else remained the same. His suspension tuned cars bettered the skidpad numbers of the stock car by some 15-20%. His street tuned cars approached 1.0g of lateral acceleration at a time when most race cars didn't hit that number while remaining comfortable to drive on everyday streets. The relation of all this to turntable (my fave topic) and loudspeaker design is not insignificant.
chris (and others):The relationship here is easy enough to establish. The loudspeaker designer/manufacturer must make some assumptions regarding the amount of (reasonable) power that needs to be applied to the loudspeaker driver to get it to move. Inertia must be over come. Overcoming inertia is how we get a driver to move and change direction. The most significant factor that can be designed in (or if you prefer designed out as per Colin Chapman) is lightness
. So a reduction in mass is really about the only thing that can be easily controlled as well as the motor system strength. Compliance also plays a role in Inertia requirements to start and stop a driver's motion (think of it as the spring). But how does this all get controlled? Control is established through the amount of power applied to the voice coil and the amplifier's dampening factor. And here is the issue using large drivers: the loudspeaker designer/manufacturer makes assumptions based on the intended use of their products and amplifiers with a reasonable dampening factor (often between 70 and 100) . Sway from their assumptions too much and the results can be things like "slow bass". So if a driver is operated outside of its design parameters with an amplifier that does not meet the basic criteria as recommended (without doing any modifications to the driver), one ought not expect good results. That's why for example, a driver with a high Qts can maintain a note for a relatively long period of time, and why many drivers with a much lower Qts can't. Then bring a miss-matched amplifier with too low (or too high) a dampening factor for a particular driver into the equation and it is easy to see how "too slow" bass can happen.
Again, I'm no expert, so take this all with a grain of salt. I'll leave Pano ( Michael, is your wife the "audiophile's wife"?) and others to be the experts (which I truly believe many on this site are).
To all: Merry Christmas, Happy Hannukah and Kwanzaa (or whatever winter you observe).
I know its a pain but you may find more joy selling/swapping your Alpha's for single pair of Beta15's. I know its a different kettle of fish but I used mine in a sealed box
and they were tight as a drum
Thats the plan right now. I've been looking at possible drivers till my eyes cross, and it seem a good candidate...not to pricey. if they work out then I'll take a look at the amp. Someone asked about wires....I used two strands of Cat5 for the test...wondering if I should add the whole 8.
and they were tight as a drum
Thats the plan right now. I've been looking at possible drivers till my eyes cross, and it seem a good candidate...not to pricey. if they work out then I'll take a look at the amp. Someone asked about wires....I used two strands of Cat5 for the test...wondering if I should add the whole 8.
I was sure i'd seen that too but had a search through my pics and the nearest I found was this...
Attachments
It was a woofer on 2'nd floor, BAF 2008. On 1'st floor when they played 18 Hz sine we heard the building rattling.
You may find it helpful to read MJK's papers on design of a small passive OB and comparison of three different woofers for OB use at:
Quarter Wavelength Loudspeaker Design
Look under OB theory and project sections.
Cheers, Jim
Quarter Wavelength Loudspeaker Design
Look under OB theory and project sections.
Cheers, Jim
Last edited:
Let me try (fail alert!!)
if you drive your Alphas with exactly 50w and play a sweeping test tone from upper bass to low bass, some frequencies would be louder than others. All drivers(?) have natural peaks in their output. Because of that you can use the peak to overcome the crossover frequency and smooth out the sound.
The crossover frequency of 70hz doesn't mean that nothing above 70hz gets through. Rather the crossover can be viewed as the top of a slope. Your driver gets 100% of the signal from 70hz downwards but sill gets some of the signal above 70hz. The amount of that extra signal is determined by the slope of the crossover. The slope can be gentle or very steep. If your slope is gentle enough your driver will still be receiving information at 200hz but maybe only at 40% of full signal. When you take into account that your driver is already more efficient around 200hz, with only 40% of the signal you can achieve a practically flat response.
(all frequencies assumed)
if you drive your Alphas with exactly 50w and play a sweeping test tone from upper bass to low bass, some frequencies would be louder than others. All drivers(?) have natural peaks in their output. Because of that you can use the peak to overcome the crossover frequency and smooth out the sound.
The crossover frequency of 70hz doesn't mean that nothing above 70hz gets through. Rather the crossover can be viewed as the top of a slope. Your driver gets 100% of the signal from 70hz downwards but sill gets some of the signal above 70hz. The amount of that extra signal is determined by the slope of the crossover. The slope can be gentle or very steep. If your slope is gentle enough your driver will still be receiving information at 200hz but maybe only at 40% of full signal. When you take into account that your driver is already more efficient around 200hz, with only 40% of the signal you can achieve a practically flat response.
(all frequencies assumed)
The problem with the Alphas is that the magnet is far too small to properly control a 15" cone. I suggest staying away from any driver with a qt. above 1. Everyone here is trying to explain the slow phenomenon with umpteen reasons all circling around the target but not hitting it. The simplest explanation is usually the right one! If you want good bass transients, you need a strong motor. Don't overthink it. The Alphas and the Betas are like Cadillacs with VW beetle engines.
Look for a 15" driver with the best compromise of moving mass, magnet weight and qt. Try to shoot for something under 150g, at least 50oz mag and at least .6 qt. Few woofers out there meet these specs, but they're out there. And they work magic on OB.
Look for a 15" driver with the best compromise of moving mass, magnet weight and qt. Try to shoot for something under 150g, at least 50oz mag and at least .6 qt. Few woofers out there meet these specs, but they're out there. And they work magic on OB.
An approximation of what to expect with the Alpha 15 in OB.
System Q = 1.266
This implies that the woofer doesn't come to a stop fast enough. There is some degree of ringing, hence the "slowness/ woolyness".
Attachments
if you can manage to get the driver tuned to a MEASURED Qtc of 1.306 and feed it through a highpass filter with the same resonanzfrequency (as your MOUNTED and MEASURED driver in the OB ) and tune the filter to a Q of 0.541 you get a 4th butterworth impulse-response (wich is about the same as the response of a Butterworth tuned reflex box).
But that is about the best you can get from this driver.
But that is about the best you can get from this driver.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.