Limitations of a 5.5" driver on an Open Baffle?.

[kbgl]

How low can a 5.5" midbass with 4 mm x-max be used on an OB? My room is small, and SPL for music is usually limited to 90 dB. I want to use it as a mid in a 3-way crossed at about 400 hz. I also have some 8" drivers that I could use. I would like to cross to a dome tweeter at 2k. This will be a passive speaker used with a sub.

[oublie]

have you any thiele small parameters? you could try modelling it in edge software just using the size and tweaking the baffle to see what you get

[picowallspeaker]

Wouldn't the 8" be enough for a small room ? I use 2 x 6,5" in isobaric and they fill the room with bass . It depends on the drivers you have ,or you are going to obtain .
Some use GOOD 8" for mids in OB ,even crossed at 2500 Hz .Lots of work for obtaining a flat freq response in the crossover network .
X-max of a driver is only a part of the story...it is the result in linear pistonic motion of various forces and springs ,but it doesn't say anything of the sound ,or useful application of the driver on a baffle. Indeed ,it is important for woofers in OB ,since the acoustic load is nearly null and there isn't the air-spring effect as in sealed boxes .

[Dr.EM]

Crossed at 400Hz I'd think it'd be alright, with 12dB or more electrical roll-off. The mid covers a quite a small bandwidth though from just 400Hz to 2Khz. The woofer with a 4" fullrange in a 2-way system may work better.

[BobEllis]

The godfather of open baffles has a calculator on his website that allows you to plug in Sd and X max to determine output and see how low you can cross the driver at your target SPL. http://www.linkwitzlab.com/spl_max1.xls

[kbgl]

Originally Posted by Dr.EM

Crossed at 400Hz I'd think it'd be alright, with 12dB or more electrical roll-off. The mid covers a quite a small bandwidth though from just 400Hz to 2Khz. The woofer with a 4" fullrange in a 2-way system may work better.

I have two different Peerless HDS midbass drivers to choose from. One is the one used by SL in the Pluto speaker. 850488 I think. The other is more current. I don't recall the model number, but it is the GFC (glass fiber cone) version. I think the GFC sounds better than the 488 as a mid, but the 488 is a couple dB more sensitive, and can take more abuse I believe.

I have a couple Peerless 8 inch woofers that I could use. I refer to them by the last 3 digits of their part numbers. One (***136) is a low Q and good for a 2k x-over, the other (***709) is higher Q and really needs a midrange. These have an f3 in a sealed box of about 70 hz and 45 hz respectively. I know that goes out the window without a box behind them. The 136 is in a speaker right now, so I would have to rob it. (Something I do all the time!) I prefer to use one of the 5.5" drivers. I'm pretty good with passive x-overs, and can measure.

Did you have an issue with using a dome tweeter due to off axis response differences. I'm trying not to spend any money. I have a lot of parts on the shelf.

[StigErik]

You didn't say anything about baffle size. The bigger the baffle, the lower you can go, but it will lead to worse off-axis response, but generally a baffle 2x the size of the driver can work well.

I run two 5" without any baffle at all down to 500 Hz - the cones barely move at all. I'd expect 400 Hz is easy with a baffle some 20-30 cm wide.

[oublie]

you could run the better of the hds up to 2k ish and use the second one to augment down to 45hz crossing around 200hz then get a tweeter to handle the 2k up range?

[kbgl]

Originally Posted by StigErik

You didn't say anything about baffle size. The bigger the baffle, the lower you can go, but it will lead to worse off-axis response, but generally a baffle 2x the size of the driver can work well.

I run two 5" without any baffle at all down to 500 Hz - the cones barely move at all. I'd expect 400 Hz is easy with a baffle some 20-30 cm wide.

The baffle I have in mind for a first try would be 11" x 30", possibly with the top 3rd tappering down to about 8".

[kbgl]

Originally Posted by oublie

have you any thiele small parameters? you could try modelling it in edge software just using the size and tweaking the baffle to see what you get

Here's the specs on the 488.

* Power handling: 110 watts RMS/155 watts max * Voice coil diameter: 1" * Voice coil inductance: 1.0 mH * Nominal Impedance: 8 ohms * DC resistance: 5.7 ohms * Frequency response: 62-5,500 Hz * Fs: 61.1 Hz * SPL: 89.2 dB 2.83V/1m * Vas: .27 cu. ft. * Qms: 2.07 * Qes: .41 * Qts: .34 * Xmax: 4mm * Net weight: 2.4 lbs. * Dimensions: Overall Diameter: 6", Cutout Diameter: 5", Mounting Depth: 2-5/8", Magnet Diameter: 3-1/2".

Here's the GFC

*Power handling: 30 watts (IEC 2685 18.1) *VCdia: 1" *Le: 0.33 mH *Impedance: 8 ohms *Re: 6.0 ohms *Frequency response: 66-7,000 Hz *Fs: 66 Hz *SPL: 87 dB 2.83V/1m *Vas: 0.24 cu. ft. *Qms: 3.0 *Qes: 0.58 *Qts: 0.49 *Xmax: 4.55 mm *Dimensions: Overall diameter 6", 5.275" across flats, Cutout diamter 4.75", Depth 2.75".

• Truncated cast aluminum frame
• Glass-Fibre Composite (GFC) cone with half-roll rubber surround
• Long-throw voice coil
• Shorting rings for reduced distortion
• Under-spider and voice coil ventilation