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Author Topic: This or that  (Read 8908 times)

Rob Spence

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Re: This or that
« Reply #10 on: January 12, 2017, 11:58:04 AM »

Hey guys. Looking for anyone with real experiences on running a sub setup with the X1 type design from Rog Mogale. Any significant advantages/disadvantages over a standard front loaded reflex system?
Assuming the same 18" driver used.
Sound quality is #1 priority.

Not often can you use the same driver in two different designs.


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Jim McKeveny

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Re: This or that
« Reply #11 on: January 13, 2017, 08:09:11 AM »

Bandpass designs demonstrate encouraging sensitivity advantage in a narrow passband, but if we dig further down the prediction & measurement chain we discover less-than-ideal Group Delay characteristics. This measurement is often credited as an identifier of the tradeoff between steady state v. transient response.

So (to quote Ivan) "It depends"..

BTW- Ivan should host his own forum here. His primary sponsor? Proctor & Gamble's DEPENDS....
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Jim McKeveny

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Re: This or that
« Reply #12 on: January 13, 2017, 08:26:40 AM »

To me-sound quality means something that accurately reproduces what is coming into it.

And since absolute accuracy is not currently possible, endeavor to minimize distortions and effort to render those remainers de minimus and even-order harmonic in content.

Eeeeasy!. Right?
« Last Edit: January 13, 2017, 08:32:36 AM by Jim McKeveny »
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Roland Clarke

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Re: This or that
« Reply #13 on: January 14, 2017, 04:35:40 PM »

Here's an old rule of thumb.

All things being as equal as possible in the design, a sealed sub will sound better than a vented sub, which will sound better than a sixth order sub.

The best sounding sub is a well designed horn, with the one caveat being that delay thru the sub is greater and needs to be dealt with when tuning the whole system.

There are always tradeoffs.  Rog is a talented designer, I'd make sure to follow his plans and driver specs closely to see results that I would hope have been verified by him and others who have already built this model.

Best regards,

John

I'm usually with Ivan on the "it depends" bench, however, I can tell you that in all my years working audio, I've never heard a decent band pass box, from any maker or designer.  The jokes about one note bass aren't accident.  If by quality you mean reasonable reproduction fidelity look elsewhere.

The ultimate I've ever heard in bass fidelity is not a horn but a quarter wave transmission line.  Forget about the TLs of old, some amazing work was done about 17 years ago by George Auspurger and Martin King working independently, both came up with predictable mathematical models.  I have a pair of monitors based on these principles that are head and shoulders above anything else I've ever heard.  No good for PA systems, but Tom Danley's tapped horns use some of the same principles.
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Chris Grimshaw

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Re: This or that
« Reply #14 on: January 17, 2017, 09:21:27 AM »

I'm usually with Ivan on the "it depends" bench, however, I can tell you that in all my years working audio, I've never heard a decent band pass box, from any maker or designer.  The jokes about one note bass aren't accident.  If by quality you mean reasonable reproduction fidelity look elsewhere.

The ultimate I've ever heard in bass fidelity is not a horn but a quarter wave transmission line.  Forget about the TLs of old, some amazing work was done about 17 years ago by George Auspurger and Martin King working independently, both came up with predictable mathematical models.  I have a pair of monitors based on these principles that are head and shoulders above anything else I've ever heard.  No good for PA systems, but Tom Danley's tapped horns use some of the same principles.

I quite liked my Tannoy T40 until I blew it, though I've moved on to nicer things since.

FWIW, a quarter-wave TL is perfectly usable in a PA situation. I recently built and tested one. 123dB continuous from 38Hz upwards from a single 15", in a cab you could carry (just) with one hand. Since you can keep the port area pretty big, there was minimal compression showing up until the amplifier clipped.

Chris
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Roland Clarke

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Re: This or that
« Reply #15 on: January 17, 2017, 09:38:03 PM »

I quite liked my Tannoy T40 until I blew it, though I've moved on to nicer things since.

FWIW, a quarter-wave TL is perfectly usable in a PA situation. I recently built and tested one. 123dB continuous from 38Hz upwards from a single 15", in a cab you could carry (just) with one hand. Since you can keep the port area pretty big, there was minimal compression showing up until the amplifier clipped.

Chris

The trouble is preventing overexcursion of the cone.  Mine will move with a 7hz signal put through them.  I believe that even with the tapped horns they have to put a steep hpf in.  I would expect that in reality it would be very difficult to satisfactorily achieve the spl's we are used to with other sub systems, although contrary to popular myth tl's do not need to be as long or large as was once considered.
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Chris Grimshaw

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Re: This or that
« Reply #16 on: January 18, 2017, 06:29:26 AM »

The trouble is preventing overexcursion of the cone.  Mine will move with a 7hz signal put through them.  I believe that even with the tapped horns they have to put a steep hpf in.  I would expect that in reality it would be very difficult to satisfactorily achieve the spl's we are used to with other sub systems, although contrary to popular myth tl's do not need to be as long or large as was once considered.

Unloading below tuning will happen with anything that doesn't have a sealed chamber. Ported boxes, 6th order bandpass, tapped horns, back loaded horns... You name it. They all suffer below their bottom tuning frequency. Front-loaded horns and sealed boxes are the only ones that don't.

Transmission lines are weird, with a lot of different cabinets having that name attributed to them. Mine are simply a slightly-tapering line that's tuned for a quarter-wave resonance in the high-30s. A traditional TL is optimally damped to totally flatten the low-frequency impedance peak. The ones that do manage that will effectively have an infinite baffle response, since the enclosure just absorbs the back wave. With modern drivers, that's not particularly useful - their motors are much stronger than drivers of old, so they don't need to see an infinite enclosure to get decent LF response. You can use a smallish sealed box and get basically the same thing, without having to move that huge enclosure. Most TLs in use today are quarter-wave resonators, which will provide reinforcement at the bottom end, like a ported box will.
The quarter-wave one I built (others are available) responds in a similar way to a ported box. Indeed, you can remove a couple of internal panels and get a ported box. I'll be trying that to see if there's much difference between the two, taking a hole saw to the panels.

Chris
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Roland Clarke

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Re: This or that
« Reply #17 on: January 19, 2017, 06:51:53 AM »

Unloading below tuning will happen with anything that doesn't have a sealed chamber. Ported boxes, 6th order bandpass, tapped horns, back loaded horns... You name it. They all suffer below their bottom tuning frequency. Front-loaded horns and sealed boxes are the only ones that don't.

Transmission lines are weird, with a lot of different cabinets having that name attributed to them. Mine are simply a slightly-tapering line that's tuned for a quarter-wave resonance in the high-30s. A traditional TL is optimally damped to totally flatten the low-frequency impedance peak. The ones that do manage that will effectively have an infinite baffle response, since the enclosure just absorbs the back wave. With modern drivers, that's not particularly useful - their motors are much stronger than drivers of old, so they don't need to see an infinite enclosure to get decent LF response. You can use a smallish sealed box and get basically the same thing, without having to move that huge enclosure. Most TLs in use today are quarter-wave resonators, which will provide reinforcement at the bottom end, like a ported box will.
The quarter-wave one I built (others are available) responds in a similar way to a ported box. Indeed, you can remove a couple of internal panels and get a ported box. I'll be trying that to see if there's much difference between the two, taking a hole saw to the panels.

Chris

Whilst a lot of that is true,  generally, tl's are generally shorten than 1/4 wave these days.  The big mistake of old was the general consensus that the damping within the cabinet slowed the speed of the sound.  When this assumption was eventually disproved the maths started to work and a lot of the "rule of thumb" and "trial and error", design.  Martin Kings worksheets are a great starting place.
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Chris Grimshaw

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Re: This or that
« Reply #18 on: January 19, 2017, 09:37:42 AM »

Whilst a lot of that is true,  generally, tl's are generally shorten than 1/4 wave these days.

Tapering them will push the tuning frequency down a bit, though there are limits of course. FWIW I use Hornresp, but keep meaning to learn Akabak.

Chris
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Roland Clarke

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Re: This or that
« Reply #19 on: January 19, 2017, 12:31:46 PM »

Tapering them will push the tuning frequency down a bit, though there are limits of course. FWIW I use Hornresp, but keep meaning to learn Akabak.

Chris


http://leonardaudio.co.uk/transmission-line/help-file/

For TL's the Leonard audio program works and seems to correlate with Martins own calculations.
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Re: This or that
« Reply #19 on: January 19, 2017, 12:31:46 PM »


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