Suggestions on raising Qts

[Mikett]

I've been looking for 6 1/2 midwoofers for my car. Most of the brand name stuff have high Fs. I see Madisound has one with a low Fs (28Hz) for a 6 1/2" and has high sensitivity and low impedance. The only issue is that the Qts looks high for mounting on a door (.28)

Any ideas on how I can modify this for door use? I want a deep bass but no subs, separate amps and no high SPL.

[richie00boy]

Linkwitz Transform, or make the inductor you use for the crossover (assuming passive x-over) have a high DC resistance. I can't remember the exact relationship between adding resistance and Q, but I think it's detailed in Loudspeaker Cookbook by Vance Dickason and/or David Weems Speaker Projects book.

[BobEllis]

you could build an appropriately sized enclosure to fit in the door. Linkwitz transform if the space available is too small.

[kelticwizard]

Originally posted by BobEllis
you could build an appropriately sized enclosure to fit in the door. Linkwitz transform if the space available is too small.

True, but any ported or sealed enclosure he builds for the door will have an F3 considerably above 28 Hz. On the other hand, a small enclosure still might be a good idea if you are willing to accept an F3 somewhat above 28 Hz, which is very low.

Using a crossover inductor with a high resistance will raise the Qts, true. The only problem there is that they correspondingly cut sensitivity. It's a little like "adding bass" simply by cutting the midrange and treble.

Not familiar with how the Linkwitz Transform works, so I won't comment on it as a possible solution.

I should point out that even if your F3 is 42 Hz, that is pretty good for a pair of 6½" midwoofers. I don't know if they will go that low mounted in the door, but if they do, that isn't bad bass at all. The lowest note on the electric bass is 42 Hz.

[kelticwizard]

For that matter, what are the Thiele-Small parameters of this 6½?

[BobEllis]

Originally posted by kelticwizard

I should point out that even if your F3 is 42 Hz, that is pretty good for a pair of 6½" midwoofers. I don't know if they will go that low mounted in the door, but if they do, that isn't bad bass at all. The lowest note on the electric bass is 42 Hz.

Wizard,

You made very good point that I forgot to make - with the "room" gain in anything much short of a minivan, a free air f3 in the low 40s should give nice response down to the 20's, even without a Linkwitz transform. Adding the transform (at least based on free air response) to such a system could result in one of those nasty bass-mobiles and may not be healthy for the woofers.

If you find that you want a little more bass extension you might try the less aggressive boost offered by a baffle step correction filter tuned to your in car f3. It only gives a 6db/octave step, to the Linkwitz's 12db/octave. see http://www.t-linespeakers.org/tech/index.html for some ideas on implementation and design.

[JOE DIRT®]

the internal door cavity will provide enough volume for the driver to reach its lower fs.....a small "buildout" and a properly damped inner cavity will yeild great results.

[Mikett]

The driver I found is one of the "sledgehammer series" from Madisound - I think it is a house brand.
The x max is only 3.5 mm and I'm hoping that is enough excursion since I don't do high SPLs and the car is relatively quiet.
I was hoping that the Cabin Gain and door footwell mounting would give me a fuller bottom end and a midrange droop from absorption from the auto carpet.

I was going to use a pair of those neodynium 1" silk domes for the upper range.

If the specs are true, it is an excellent driver for the car as all the other branded speakers don't come close to bass extension and they carry cheesy tweeters too for much more money.

Thanks for the suggestions, I'll try some "high resistance" coils and make sure that I use smaller gauge connection wire.

[sreten]

Qts is only valid in free air. As is Fs. Vas is very is important.

The Q of the bass alignment is modified by the enclosed air
volume, basically the Q goes up as the F frequency is raised.

Nearly allways the enclosed air volume is much less than the
equivalent air volume of the suspension Vas, however Vas
determines the free air resonance frequency, so a large Vas
(floppy suspension) gives a low free air Fs but the actual F in
the door is dominated by the door volume as this is nearly
allways much smaller than the Vas equivalent air volume.


Ideally you need to know the door volume. For a Q of 0.3 you
need a door volume ~ 1/3 to a ~1/4 of Vas, to give a Q of ~ 0.7
and to ~ double the F to 2xFs.
But a lower door volume will still give good results as long as
the Q is not raised above ~ 1 and F to ~ 3Fs, up to 1/9 of Vas.

Low Fs and high Vas are not bad things for a sealed box mounting,
in fact they are good, (but they are not good for reflex loading.)
But they are very misleading parameters regarding the end result.

For sealed box loading a drivers Q is allways apparently too low,
this is because it has a huge Vas, actual F will depend on the real
enclosed air volume which is much smaller, and this raised F will
also increase the effective Q.

So door mountings speakers should have a low Q - 0.25 to 0.4.
Conversely speakers for the rear shelf in a hatchback, with no
real air volume shoud have a Q of 0.7 to 1.0.

hope this helps, /sreten.

[Mikett]

The TS parameters are Fs= 29 Hz Qts=.26 Vas=77 liters

I have a similar 8" driver I am using now in the rear parcel shelf

Fs=29 Hz Qts=.26 and Vas=70 liters. I was initially attracted by the Fs but with the Q so low, the bass seems anemic.

Your point is good about the door volume but I suspect that since doors are leaky, it would probably seem more like a leaky box thus leading to greater bass losses.