Frequency Response/Roll-off

[Zafsk]

This is a pretty amateur question, but I couldn't find the answer I was exactly looking for. I think I have a handle on it, but I'm not quite sure, so here goes:

I understand that the F3 variable represents the -3dB half power frequency, which indicates the beginning of low end roll off. I'm looking to set up my first pair of multi-way speakers, and I'm trying to set up a two-way system (I'd rather not try to crossover three drivers on my first go-around) so I'm trying to figure out the recommended frequency response for this driver.

https://www.madisound.com/store/prod...oducts_id=8772

The F3 in a sealed system with an enclosure around .85 cubic feet would be 59 Hz, correct? Additionally, would the total Q of the woofer at Fs be .34? I'm still trying to get all the nomenclature down, but I'm obviously having a hard time. I'm trying to build a speaker system with a Qts of around .90, .95, for a warmer sound. Am I on the right track?

That said, I'm trying to read this frequency response graph and trying to deduce where it rolls off.




I'm thinking it rolls off at around 1.5kHz? I'm probably reading the log scale wrong. Would this make the recommended frequency range 20Hz - 1500Hz? I'm not very confident in my results, any help would be greatly appreciated.

Also, on a separate note, for a two-way speaker, would this be an appropriate woofer? Any recommendations for a tweeter? Thanks for putting up with the inane questions, I'm just having a hard time figuring it all out.

[gfiandy]

Hi,

Qts relates to the drive unit total system not the driver and box combination. I imagine that the 0.85 cubic feet box will be a butter worth alignment which means it will have a Q of approximately 0.7.

To increase the Q you need to make the box smaller this will rase Fs from 59Hz but will increase the peak in the response before roll off. To simualte this download the Linearteam tool shown below

If you want a warm mid bass it would probably be better to do this using baffle step compensation in the crossover. (Search for BSC on this site for lots of details)

This speakers response would be from arround 60Hz to 5KHz in the 0.85 cubic foot box on axis (however the off axis response falls away quickly ay 5KHz as shown by the green and red traces. (A simulation would confirm this for th bass response) If you want lower bass with a single 8 inch driver you will need to use a port but it will still only get you down to about 40Hz I would think. To achive 20Hz with a single 8 inch driver would require very large excursions of the driver and probably active bass equalisation.

This driver should probably be crossed over at about 1.5KHz for a good off axis response. Not many tweeters are happy down to 1.5KHz so you may want to choose a 6 inch driver for your first design as this will be much easier to get a tweeter to work with.

From another thread I posted in in some helpfull links, the linear team link will alow you to simulate the Q of the system in any size box. Do read the help and follow it exactly when entering your drivers parameters:


LinearTeam
Good free box design program (you need the T-S parameters from the speaker you want to use) Follow the help exactly to enter the parameters or it will not allow you to complete the entry.

Speaker Workshop Download
Probably the best free speaker design package but it is evil to learn how to use.
Speaker Workshop Tutorial
one of several tutorial on how to use it (search the web for others)

HOLM Acoustics
Probably the best free measurement software and fairly easy to use. You will need a microphone and a half decent sound card but that is all.

FRD Consortium
Collection of very usefull simulation tools mostly in Excell. Th Baffle Step compenation program is really good for demonstrating how just moving a drive unit a few cm in a cabinet can significantly affect the frequency response.

John Conover: Using the Panasonic WM61A as a Measurement Microphone
How to build a really cheap but flatish response microphone for only a few £ or $. If you only take one peice of advice from me it would be don't try to build speakers without a microphone. It would be like setting sail without even a compass, you can use the sun but its not really that much help unless you have years of experience, your ears are much the same.

Regards,
Andy

[Zafsk]

I actually own a copy of LspCAD Pro v6 I just have no idea how to use it. A friend passed it on to me. I've tried going through the manual but I'm utterly lost.

As far as microphones go, however, I actually have a decent cardioid reference microphone that does a good job at giving a flat response. I typically use it for recording in studio, but it should do the trick.

Would crossing over a three-way speaker be much harder? I'd rather not go down to a 6 inch if I don't have to. I was looking forward to putting together a larger speaker, sort of in the spirit of an early Acoustic Research but with modern dynamics, if that makes any sense.

If I went with a 10" or an 8" woofer, would I have to go three way to make a decent set of speakers or is it possible to find a tweeter that could come down that low.

https://www.madisound.com/store/prod...oducts_id=8497

Something like that maybe?

[wolf_teeth]

First off, 8" 2-ways can be rather difficult, unless you use drivers that are very well behaved, and have an extended frequency response.

A 10" 2-way is virtually inconceivable, unless you find a rare-bird. I think the only ones I know that might do that are the Morel 1075 and the Dayton DC300. BUT- you have to have a tweeter that is equally capable of that task. It will have to reach to 1.2kHz or lower, and that is a tough load to haul. Most 'robust' tweeters are good to about 1.8 kHz, LR4 acoustic.

All that said- your 8" you chose looks like it could be fairly benign. Using the right coil/cap to round off the short rise from 1-3 kHz might fare you very well. The thing with 8" woofers, is that they really are only good to about 1.5 kHz before they start beaming. The problem with xovering this low is that the tweeter may require a slope to get there. You won't be doing it wih 12dB electrical filters. I suspect a 4th electrical is a must on the tweeter, and you will require a term of playing on the system to get it tuned in right. The power response and off-axis issues on an 8" 2-way are more difficult to dial in than anything smaller.

However- if you get it right, the soundstage will be massive, and they will have a very large sound.

While I know this is a metal woofer, this will give you an idea what I went through to get this one right:

MAX pictures by wolf_teeth_speaker - Photobucket





If you value your sanity (), don't use a metal woofer in an 8" 2-way....

Later,
Wolf

[sreten]

Hi,

Just bide your time and wait for someone to publish a decent design.
it seems a good unit and someone will at some point, likely with a
well matching tweeter, keep checking the various design forums.

Keep searching on the driver number for information.

/Sreten.

[Zafsk]

Well, I'm realizing now that this is going to be a tougher undertaking than I originally though (when is it not?) I think I'm still going to try for a 8" two-way. I think you guys have noted that it would take a bit of experimenting, but I'm up for it.

I've been searching for the past couple of hours for a decent combo, but I'm still stumbling around in the dark, it feels like. I'm excited about the possible result, however. I may end up just moving down to a 6" woofer for my first actual design if this proves too complex, but I'm going to jump in feet first.

I saw another Woofer that caught my eye, it goes a bit lower and has a decent frequency range all together.



https://www.madisound.com/store/prod...oducts_id=1600

The tweeter: https://www.madisound.com/store/prod...roducts_id=288

It has a frequency response from 800Hz to 30kHz. I think I could cross it over at around 1.5kHz. I could be wrong, in fact, I probably am.

[sreten]

Hi,

You cannot just pick drivers based on limited paper specifications.

Find an established design with drivers you like or the approach appeals.

Take a look at Zaph|Audio

/sreten.

[Zafsk]

I'm familiar with Zaph, though, I'm a bit curious. What specifications are required when picking out drivers? I understand the designs he has are far superior than anything I could come up with, but what information do I need to understand before I can start putting together my own -- because honestly, that's why I love audio. The customization that is individual to me, something I chose.

I'm inclined to shy away from templates someone else made, and I'd like to understand the concepts behind choosing drivers that would complement each other. I don't just want to get the ingredients and make something without understanding the process behind the design and production of it. I'm not under the influence that their quality is poor or anything of the such, I'd just like to design something myself.

All that said, what specifications do I need to understand to start putting together my own? I've been brushing up my math skills to try to get through Loudspeaker Design Cookbook and understand it, and I have been for the most part. If you could give me some advice in regards to picking drivers, I'd greatly appreciate it. Thanks!

[PeteMcK]

Unibox is good tool to download (free) and easy to use, to show how a driver will interact with box size/tuning (needs Excel); the parameters you need to input into Unibox are the ones you need to know about.

At the high end, you need to concentrate on the impedance curve to give you the impedance values to use in your calculations, and the freq response curve to help choose the xover point (the off axis curves are a good clue)

The SEAS driver you have chosen will probably be easier to xover because of the cone material; I’d consider using a SEAS tweeter too, these have a very good rep.

[Zafsk]

Thanks for the information.

https://www.madisound.com/store/prod...roducts_id=778

Are you talking about something like that? From what I understand, the underhung voice coil (1.5 mm) will make it easier to xover, correct?