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<blockquote data-quote="JohnEJanowitz" data-source="post: 3741260" data-attributes="member: 584636">In reality you want many of the same things for both an SQ and SPL driver.&nbsp; Just for different reasons.&nbsp; Parameters often aren&#039;t that telling in a woofer unless we are looking at everything.&nbsp; Many people look at Fs at Qts only but don&#039;t look at anything else.&nbsp; Those don&#039;t tell us a whole lot in general.&nbsp; I can make 3 different drivers with different size coils and motors all come out with the same Fs and qts while they are drastically different drivers.&nbsp; Looking at the design goals tells us much more about the woofer.Whether you are looking for an SPL or SQ woofer you are going to want a linear, symmetrical BL curve.&nbsp; You are going to want good heat transfer and cooling.&nbsp; If you don&#039;t have those&nbsp; things, which unfortunately many drivers don&#039;t, they probably aren&#039;t going to be good for SQ or SPL.For the SQ option you want the linear BL curve for low distortion.&nbsp; As your BL changes throughout the stroke, or if it is non-symmetrical on the inward and outward stroke, you have a large amount of distortion.&nbsp; Obviously not desireable for SQ applications.&nbsp; In an SPL woofer you want the linear BL curve because you want more force throughout the stroke to excite the resonance in the port, giving you more efficiency and output.&nbsp; More efficiency means less power is wasted as heat.&nbsp; This means less input power to reach the same levels, and less power means less heat.&nbsp; Less heat means less power compression which again means you&#039;re getting more output for the amount of power you put in.&nbsp; It&#039;s somewhat of a chain reaction.Heat transfer is also important and often overlooked.&nbsp; As the temperature of your coil rises, so does the resistance.&nbsp; As the resistance rises, your amp needs to put out more power to reach the same output levels.&nbsp; As it is putting out more power, the coil is then also heating up more, requiring more and more input power to get the same levels.&nbsp; This is what&#039;s known as power compression.&nbsp; This is bad for both SQ and SPL applications.&nbsp; For SPL, it is obvious.&nbsp; You are losing output.&nbsp; That is why in most cases you hit significantly higher levels on initial runs.&nbsp; As the coil heats up you just can&#039;t deliver as much power to it.&nbsp; For SQ, this heating again leads to higher distortion.That all said, in general an SPL woofer will be used in a vented enclosure where you are expecting the woofer to excite the resonance of the port to create output.&nbsp; You are operating at and around the tuning frequency so the driver doesn&#039;t need to travel a long distance.&nbsp; You&#039;re more excited about exciting the resonance than moving long distances.&nbsp; You want a very linear stroke, but not a very long stroke.&nbsp; You&#039;ll typically want high motor strength and large cone area to do this.&nbsp; Since you aren&#039;t moving long distances, huge surrounds are not a benefit.&nbsp; The more cone area you have, the better you can excite the resonance.John</blockquote>

[QUOTE="JohnEJanowitz, post: 3741260, member: 584636"] In reality you want many of the same things for both an SQ and SPL driver. Just for different reasons. Parameters often aren't that telling in a woofer unless we are looking at everything. Many people look at Fs at Qts only but don't look at anything else. Those don't tell us a whole lot in general. I can make 3 different drivers with different size coils and motors all come out with the same Fs and qts while they are drastically different drivers. Looking at the design goals tells us much more about the woofer. Whether you are looking for an SPL or SQ woofer you are going to want a linear, symmetrical BL curve. You are going to want good heat transfer and cooling. If you don't have those things, which unfortunately many drivers don't, they probably aren't going to be good for SQ or SPL. For the SQ option you want the linear BL curve for low distortion. As your BL changes throughout the stroke, or if it is non-symmetrical on the inward and outward stroke, you have a large amount of distortion. Obviously not desireable for SQ applications. In an SPL woofer you want the linear BL curve because you want more force throughout the stroke to excite the resonance in the port, giving you more efficiency and output. More efficiency means less power is wasted as heat. This means less input power to reach the same levels, and less power means less heat. Less heat means less power compression which again means you're getting more output for the amount of power you put in. It's somewhat of a chain reaction. Heat transfer is also important and often overlooked. As the temperature of your coil rises, so does the resistance. As the resistance rises, your amp needs to put out more power to reach the same output levels. As it is putting out more power, the coil is then also heating up more, requiring more and more input power to get the same levels. This is what's known as power compression. This is bad for both SQ and SPL applications. For SPL, it is obvious. You are losing output. That is why in most cases you hit significantly higher levels on initial runs. As the coil heats up you just can't deliver as much power to it. For SQ, this heating again leads to higher distortion. That all said, in general an SPL woofer will be used in a vented enclosure where you are expecting the woofer to excite the resonance of the port to create output. You are operating at and around the tuning frequency so the driver doesn't need to travel a long distance. You're more excited about exciting the resonance than moving long distances. You want a very linear stroke, but not a very long stroke. You'll typically want high motor strength and large cone area to do this. Since you aren't moving long distances, huge surrounds are not a benefit. The more cone area you have, the better you can excite the resonance. John [/QUOTE]

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