Group delay

Posted by: lemarchand on 10 January 2002

First of all I would like to say hello to everyone since this is my first post in the forum and I would like to thank you for my membership approval.I would be glad to know if there is any technical expert around on whether the group delay is getting increased after the use of a crossover.If yes, for how many milliseconds is it getting increased?Thanks in advance.

I am really sorry for my english but I am Greek

[This message was edited by lemarchand on FRIDAY 11 January 2002 at 03:53.]

Posted on: 10 January 2002 by David Dever

What crossover? (Microseconds might be a more reasonable order of magnitude)

Posted on: 10 January 2002 by lemarchand

Thanks a lot for your reply David.Oops, you may be right.It should be microseconds.The crossover should be of 2nd order if I remember well.Cheers.

Posted on: 10 January 2002 by Steve Toy

Does crossover circuitry slow down the bass?

Is that the question, I wonder?

Is that why most of us here seem go for simple two-way speakers, and eschew biwiring, bi-amping and active crossovers etc?

Next: sealed box versus ported versus transmission loading...

This tecchie stuff is picklin' me brain... confused

It's always a nice day for it Have a good one!
Steve.
It's good to get back to normal.

Posted on: 10 January 2002 by lemarchand

Yes Steve,that is the question in other words.Group delay determines how "fast" the bass will be.Sealed subwoofers have less group delay than ported ones for instance.Bandpass subwoofers are even worse than ported ones in that sense.I am really curious on what is better in terms of group delay, sealed ones or TL ones!?

Posted on: 10 January 2002 by Manu

Sealed boxes generaly have a shorter group delay than TL and bass reflex. BUT it is closely linked to the alignment chosen. And G.D. is not constant with frequency. It can be a very weird curve.
Phase linear alignments (like bessel) gives "maximaly flat delay". The vast majority of speaker designer will favorize the best low frequency extension at the expense of weird group delay. This will give a speaker with low PRAT in the bass (sorry, you are a junior member, you have to make some research, use the search engine for PRAT).
The group delay due to accoustic tunning (alignment) is an order of magnitude superior to the group delay due to the crossover. As David says milliseconds vs microseconds.
An other factor of delay in speakers are the non vertical plane of speakers accoustic centers.
(except on slopped baffle). But very few specialists still believe in vertical alignment of speakers.
All this is very theorical, let the PHD's play with all these maths.
Chose your speakers by ear. And enjoy the music.

Emmanuel

Posted on: 10 January 2002 by Steve Toy

No matter how crappy your (my) tastes may be, the subjective listening approach is always best.

lemarchand

I will therefore be interested to hear that sub of yours for subjective listening evaluation...

Will the bass extend below that of my Naos, and will overall PR&T be maintained?

It's always a nice day for it Have a good one!
Steve.
It's good to get back to normal.

Posted on: 10 January 2002 by lemarchand

Manu - If I remember well from Steven Toy Prat is Pitch, rhythm and timing, is that correct?
Well Manu, I choose speakers by ear from now and on, but having had a B&W ASW1000 subwoofer at the past I realised that it is easy to create the "tsiki tsiki boom boom" factor but the music will be wrecked big time. After some proper research mainly from the "Loudspeaker Design Cookbook" I decided to make my own subwoofer and try to make a "fast" subwoofer with decent output capability. My project will be done in one week time, I will give it one week to have a go and then I will let you know. A professional box designer has done the box design after I told him what my aim is. I will use a BK 200wrms sub-bass module amplifier with built-in active crossover and a JL Audio 10W0 driver.

Steve - "Will the bass extend below that of my Naos, and will overall PR&T be maintained?"

Well, that would be nice if it could happen. As we have discussed at the past in my opinion Rega makes speakers with minimum group delay in mind, so it would be a difficult task for me

frederick charles - Thank you very much. When I refer to group delay I always have low frequencies in mind. The group delay is determined by the type of the box design, its construction maybe, the box's size and possibly by how the specific driver behaves within the certain type of enclosure. What I don't know is if the addition of the crossover adds group delay or not. Theory such as "big drivers are slow and small drivers are fast" is non-sense. The bigger drivers usually require bigger enclosures. If you stick the wrong driver in the wrong enclosure then yes the bass will be crap. Sorry, I have never heard of the Sara 9 speakers. If you want some more info about the above issues you could always purchase the above book I mentioned and have it a go.Cheers.

Posted on: 11 January 2002 by Steve Toy

That's the book you gave to me!

"The loudspeaker design cookbook" by Vance Dickison, Audio Amateur press, Peterborough, New Hampshire.

It's always a nice day for it Have a good one!
Steve.
It's good to get back to normal.

[This message was edited by Steven Toy on FRIDAY 11 January 2002 at 17:09.]

Posted on: 11 January 2002 by Manu

Lemarchand
Do you know the meaning of your french name?
Good luck for your project.

Some advices:
Don't know this driver. IMHO a paper cone is better for speed. Stiffer and lighter than polypropylen, never try Kevlar but should worth a try.
Use a software to calculate all parameters, i would recommand LSPCAD (a light version was available for free some time ago).
If you can, make all mesurements of the speaker parameters on the driver you get; there are big variations of them from unit to unit.
The "Loudspeaker design handbook" is a kind of bible, follow the advices. Also have a look at the "Loudspeaker design cookbook" by the same author.
Take very good care of the impulse response of your design.
Don't try to go down to 20 Hz with a 10", concentrate on good sound down to 30/35.
As your sub will be amplified, don't bother with efficiency, concentrate on good impulse response.
Closed boxes sounds better.
Spend time to try various stuffing materials. Rubberised dampers used for cars give good results but vapors they produce burn speakers.
Double veneered (outside and inside the box) panels are good for vibration control.
Natural wool gives good results.

And don't hurry, try, listen, retry....

Emmanuel

Posted on: 11 January 2002 by Steve Toy

He does.

I already told him.

It means "shopkeeper" no less!

As for the loudspeaker cookbook, I have his copy, but the sub he's built is nearly ready anyway...

Je suppose que t'es canadien qui parle le francais en premiere langue.

It's always a nice day for it Have a good one!
Steve.
It's good to get back to normal.

Posted on: 11 January 2002 by lemarchand

Manu - Rega uses paper cone and IMHO they are after minimum group delay in their speakers. Another issue is that of the linearity of the driver though. Paper cone may be "faster" but can the paper remain linear after long pressure? In subwoofers there are several issues. IMHO car audio drivers for low frequencies are much better than the home ones. They have done proper research and they are in business and competitions almost 10 years more than in home audio world. The box design has already been made by a professional designer through computer modelling. The box will be closed with a Qtc of around 0.65. The dampening material will be egg-box type carpet underlay. There will be an internal port I have no idea what for. It will have two purposes. The first one will be as a brace and the second one is in musical terms, but the designer told me "Let's say it is an unchartered territory". A Finnish guy I know said that a similar technique is used by someone he knew and this improved the group delay. I do not really know more stuff to tell you Manu. The box will be of 18mm thickness MDF and I expect to have in room 0.0db at 38-39 hz. Well,the box is ready and has been shipped to me. As I said in 15 days we shall know after the results...

Posted on: 12 January 2002 by Manu

Steven,
Oui, cela ce voit tellement dans ma "litterature"?.
In fact I'm a "french man in Montreal".

Lemarchand,
Can't agree with your comments about car speakers.
Most of the car speakers are cheap. Made to work with a big air volume, low sensitivity, 4 ohms.
Home/pro speakers are more advanced if you look at scandinavian, british, french, american (for Pro) companies.

Paper cones are good if treated with carbon fibers, making them stiff. Their break-up point is higher than plastic ones.
Is the inside port just a cylinder inside the box or a real port between 2 closed cavities. If it's the second option it looks like Naim speakers (SBL, NBL, DBL).
Tell us informed of the progress

Emmanuel

Posted on: 12 January 2002 by Steve Toy

quote:

Steven,
Oui, cela ce voit tellement dans ma "litterature"?.

Non, pas trop!

It's always a nice day for it Have a good one!
Steve.
It's good to get back to normal.

Posted on: 12 January 2002 by lemarchand

Manu - I strongly disagree with you in that matter. Car subwoofers are by far more advanced than the home ones. I do not know which ones you have in mind but there are not only single 4ohm or "cheap" subs out there. There are dual voice subwoofers and you choose the impedance they will have. If you have doubts about how the car subwoofers are today then please check this and let me know what you think. These are the latest subwoofers from JL Audio, the W7 series. Do they look cheap?

The 13,5" one costs $950, has over 20kgs weight and has over 30mm Xmax one-way...

Bear in mind I am speaking about low frequency drivers here Manu only. The box is a dual chamber one with a port between them, so it is "Naim style". I am more confident now . Cheers

Posted on: 14 January 2002 by Manu

Looks good, at that price i hope it does't only look good.
Serious basket.

Emmanuel