Sound quality vs SPL parameters

[Triticum Agricolam]

Ive read a few articles saying that a good indicator of a sub that has good SQ is what you said Le/Re, a high sensitivity, low QTS, light moving mass and a strong motor to control the direction of the cone quickly... If you were reading a review on a particular sub you havent heard, what are the specs that do matter?

Things like higher QTS don't necessarily indicate a sub will have poor SQ. QTS is more of an indicator of what style of box a sub will work well in.

A big part of getting of getting good sound quality (IMHO) is achieving smooth frequency response. Smooth doesn't always mean flat, we just want to avoid big peaks or dips if we can. A lot of subs that claim to be SQ focused end up having very peaky output, which kind of defeats the purpose, this is especially true with smaller subs. One spec I look at is Vas. Vas is a measurement of the suspension stiffness. Higher Vas subs generally make it easier to achieve smooth frequency response whereas low Vas subs will usually have peaky output. Cabin gain is going to change the frequency response of a system significantly, so you have to account for that too.

[MyNameIsNoob]

Yea theres a small void on each side to recess most of the box into and i was planning to tilt it forward ab 22 degrees so i can get the rest of my airspace toward the back of firewall... i can mount the box to the bracing on firewall and theres a bar further forward i can use for front of box... it may be tricky, but im pretty sure (i hope) itll be good, otherwise i gta use the plan B, that i dont have yet bc i dont wna mod any visible panels if i can help it...

So from what im understanding, for a sub to sound good the biggest determining factor (besides a flat frequency response, Vas and Le/Re), is the enclosure the specs tell me to build... and that the specs listed on the websites are there to help sell products to someone like me who doesnt know better lol. I jus want the tightest detailed bass i can get up front... My current sub is amazingly tight for a 15 and being a cheaper product, but ive compared the specs to what ive thought to be SQ oriented n besides the sensitivity, it wasnt what they say is "ideal"... idk, i guess "every sub is different, gta listen to em" is more true than i was hoping for lol I was hoping it would be more cut n dry tho :/

[ShadeTreeMechanic]

Well if you are going to keep the 15 along with the 8s up front, then the 8s boxes could be tuned to play higher than the 15 and give more punch. This will also keep the boxes on the small side especially if they are sealed. Ported boxes are generally bigger. The trick then is to figure out the box frequency. Maybe 60Hz? Then find a driver that gives the box Fs as 60Hz when the selected box Q is .7 for the flatest response (or slightly higher for more output but it might make it harder to blend with mids). Below F3 would be covered by your 15.

[MyNameIsNoob]

Yea im gna use the 8's and a sealed box to give it some kick for rock, country, etc and also so i can cross my components up front a lil higher, but id like them to also have a full sound so i can keep my bass knob down at least till i want to show it off lol but yea thats what im looking for.

So if i want it to sound full on a wide range of music, without the 15 goin, how does that change the fs recommendations?

*edit* - should i find one w an fs at ab 40 or so?

[Triticum Agricolam]

If you aren't already using box modeling software (like WinISD, BassBoxPro), it will probably help you answer a lot of the questions you have.

[MyNameIsNoob]

Yea i have WinISD, but ive only used it 3 times, so im still learning. I jus hate not knowing why im doin somethin... I used it on this current box n it sounds much better than my last in the same car w the same sub and amp... idk how much of that is attributed to the boundary loading, cabin gain w it being downfire, port back now vs rear facing sub and port in the previous box. I know according to the software i got a theoretical 3 db more w a flatter curve the way it is now vs before tho

[ShadeTreeMechanic]

Well Fs is only the driver in free air. The Fb will depend on the size of the box. If it were my system I would find 8s that would tune to 60hz in a small box (would be more of a woofer than a subwoofer, single voice coil or dual) and use the 15 to fill in the lows at the same time. The only way to find the right 8s would be to run the numbers on the 8s that you see in your price range and see what they look like on paper.

[lutkeveld]

I'm sure someone can shed light on this. I have heard that T/S parameters are just theory and can change once a driver is broken in. They don't take into account the coil being powered either. This is why a driver might look like the specs are crazy and it ends up being perfect for what you are doing. I would recommend figuring out the boxes and tuning for each one to get a feel for what the different parameters do. The old way of pencil and paper is best to help see. Calculator if you must. My 2 cents.

You could measure the T/S parameters at higher power, but it's a small signal based system. All models (simulators like WinISD included) assume that it's measured with ~1V applied. Things like Re will increase drastically as the coil heats up, just an example. If you know the parasitic side effects high power has you can compensate for them.

Same with effects like cabin gain, if you already let the response peak in the low end the cabin gain will only make it worse.

You're better off using a bass shelf alignment and letting the gain fill in the dip (if a deep, flat response is what you're after).

[ShadeTreeMechanic]

T/S is also based on the companies R&D sample and will vary slightly in production. Hardcore guys break the driver in and then measure parameters for themselves. Any SQ system will have to be dialed in if that's what you are after. Some people balance it until it sounds good to them. That's ok too if that's what they want.

[MyNameIsNoob]

Thx guys, good info here!

So i guess thats why im tryna get a better understanding of how to read the specs, so i can have a better indication of what will suit my needs before i do any upgrades... So after i decide on a sub, if the factory specs have enough deviation to not trust em, how would I go ab gettin the actual parameters after i break the speaker in (so i can adjust my box if need be)?

...and one more question (i know i ask too many lol)

but out of the subs i listed, how would you rate them based on frequency response, tightness, volume, quality, etc...?

(i dont wna spend more than 325-350 on a sub, so im not stuck on these, but somethin similar in the 1500 rms range will do me good)

Brand / Model........................Size...........RMS.......... SPL........ Xmax........ FS........ QTS.......... Magnet

Massive Audio Hippo152....... 15"........... 2000......... 98............ 15mm...... 34.2..... .374.......... 320 oz

Sundown ZV.4REV.2..............15"............1750......... 86.5........ 35 mm................... .45.....................

Soundqubed HDC3.115 ........15"............1500......... 91.5........ 36 mm...... 38......... .419......... 340 oz

American Bass HD15D2 ........15"............1500.......... 91.5....... 30 mm...... 31.7...... .382.........300 oz

FI BL15.................................. 15"...........1500......... 91.8.........18mm....... 33.8..... .27............ 261 oz

RE SXXV215D2..................... 15"........... 1200......... 90.6......... 24mm.................... .38......................

NVX VCW152.........................15"........... 1000......... 87............ 20mm...... 24......... .36............195 oz