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Multi-Way Conventional loudspeakers with crossovers

Weaker low-range response of 3-way speaker
Weaker low-range response of 3-way speaker
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Old 11th April 2018, 07:22 PM   #11
DonVK is offline DonVK  Canada
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Are those photos of your prototype ? It's hard to tell how the baffle is held on or what the internal structure of the box is like.

The midrange requires its own separate enclosure (volume) within the speaker box otherwise it will act like a passive radiator and effect the woofers LF performance.


P.S. If you use the advanced "manage attachments" you can insert the photos right into thread. Links always end up breaking over time.
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Old 11th April 2018, 08:15 PM   #12
adason is offline adason  United States
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Quote:
Originally Posted by krasnypixel View Post
Hi guys,
Im new to this forum so apologies for asking maybe mundane question.

I have decided to build my second DIY audio project, 3 way ported loudspeaker.

Components selected for the build were
Lows - Dayton Audio RS225-8 8" Reference Woofer
Mids - HiVi F5 5" Bass/Midrange
Highs - Dayton Audio PT2C-8 Planar Tweeter

Im crossing the drivers using Eminence PXB3:3K5 crossover at 500/3500 hz with 2nd order slope for woofer, 1st order filter for midrange and 3rd order for tweeter

Box and port were calculated in WinISD software. Port is tuned for 30hz in 42 litres enclosure (7.5 cm (3in) diameter, cca 31c (12in) length - flared)

Midrange enclosure is separated from woofer, for the sake of the prototype building however, larger than suggested cabinet size was used (14 litres instead of 5 litres) and was properly damped.

After building prototype enclosure for the speaker and testing the speaker i was

a) Amazed by performance in mid and high range, clarity and separation of instruments is very nice, especially considering that the prototype build is rough.
b) Weak low-range performance. Bass is clear , however it lacks any depth and "punchiness" . Im not talking about groundshaking performance, but overall, the bass is weak.

This was confirmed by measurement which has shown 6-7db lower performance across the band, up to the 500hz crossover frequency.

When I adjusted preamplifier to +7db for lows and -7db for highs, sound started to appear more balanced, but I still was a little bit disappointed by the overall performance.

I was rather surprised by this issue, as this is my second build (first was 2way speaker) , and It was calculated the same way. First build has amazing bass considering that it uses only 4inch midwoofer drivers.

Could you please advise me what could I do wrong? Many thanks for your replies.
No problem, just insert simple L-pads for mid and tweeter.
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Old 15th April 2018, 12:23 PM   #13
krasnypixel is offline krasnypixel  Slovakia
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Quote:
Originally Posted by DonVK View Post
Are those photos of your prototype ? It's hard to tell how the baffle is held on or what the internal structure of the box is like.

The midrange requires its own separate enclosure (volume) within the speaker box otherwise it will act like a passive radiator and effect the woofers LF performance.


P.S. If you use the advanced "manage attachments" you can insert the photos right into thread. Links always end up breaking over time.
Hi. Thanks for your response. Yes those are photos of the prototype loudspeaker. I have double checked the cabinet and re-sealed cable holes and some tiny leaks. Afterwards, I have re-tested the speaker and I must conclude that situation is much better

I have measured response of the drivers and following are the results.

Response of the speaker port (20-200hz) measured from 10cm
Port_Response.jpg

Response of the speaker woofer (20-200hz) measured from 10cm
woofer response.jpg

Combined system response (20-10,000hz) measured from 1 meter. With 6db reduction of trebles on preamplifier in order to simulate performance of installed L-pads
combined response.jpg

I am much happier with the performance, however I think something is still not 100% OK. Probably it is the port. Although WinISD suggest 30cm depth, it is installed 30cm with one flared end. Effective length is thus probably slightly lower.

I have noticed that the subjective bass intensity was much higher on the sides of the speaker than in front of it. When I was in the hallway 4 meters left to the speaker (which was perpendicularly positioned to me) I have felt ground trembling under my feet. Could this be because of front positioned port?

Many thanks for your replies
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Old 15th April 2018, 01:51 PM   #14
DonVK is offline DonVK  Canada
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It should not matter if the port is in the front. It does look like the tuning is higher than predicted. In your graph#2 the dip is around 45Hz and it should be around 30Hz (see graph below). I've attached a HornResp sim for the driver output. You will get a better graph of just the driver if you measure closer (4cm).

The box tuning may be higher due to a smaller volume (its <42L) or the midrange is not entirely separated and is acting like a passive radiator, or the port tube is restricted. How much distance from the rear tube to the rear cabinet wall?

If you measure with the box against the wall or on the floor you will get more bass. It's better to have it on a stand, away from a wall (1m) for more accurate measurements. You may also want to apply an IR window (-20,40ms) and smoothing (1/12 octave) to your graph to make it less noisy,.. everyone has their favourite settings.
Attached Images
File Type: jpg BR Driver SPL.jpg (44.7 KB, 106 views)
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Old 15th April 2018, 03:32 PM   #15
krasnypixel is offline krasnypixel  Slovakia
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Quote:
Originally Posted by DonVK View Post
It should not matter if the port is in the front. It does look like the tuning is higher than predicted. In your graph#2 the dip is around 45Hz and it should be around 30Hz (see graph below). I've attached a HornResp sim for the driver output. You will get a better graph of just the driver if you measure closer (4cm).

The box tuning may be higher due to a smaller volume (its <42L) or the midrange is not entirely separated and is acting like a passive radiator, or the port tube is restricted. How much distance from the rear tube to the rear cabinet wall?

If you measure with the box against the wall or on the floor you will get more bass. It's better to have it on a stand, away from a wall (1m) for more accurate measurements. You may also want to apply an IR window (-20,40ms) and smoothing (1/12 octave) to your graph to make it less noisy,.. everyone has their favourite settings.
Thanks for advice,
Box itself is 42,8l, however port itself as well as woofer should account for 1-2 litres volume substraction. I have made new measurements with speaker standing on 50cm stand and cca 80cm from the wall.

port_woofer.jpg

Blue is the response of the port and red is response of the woofer. As you can see. SPL is -10db in the range 35-55 db.
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Old 15th April 2018, 04:25 PM   #16
DonVK is offline DonVK  Canada
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That does not look right. You should see a port peak at 30hz and a driver dip at 30Hz. It looks like the box is leaking. I added the port output below, and the driver output was in previous post.

Try to open the IR window (left 50, right 100) and enable FDW=6. The window may be too small.
Attached Images
File Type: jpg BR Port SPL.jpg (45.5 KB, 94 views)

Last edited by DonVK; 15th April 2018 at 04:27 PM. Reason: added port output
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Old 15th April 2018, 04:25 PM   #17
Dissi is offline Dissi  Switzerland
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Hi,

I wouldn't worry about the bass as long as mid and tweeter levels are too high.

Attached is a simulation of your current setup. Due to baffle step the woofer only reaches a sensitivity of 84 dB.

Beside the level issue, I also think that the first order crossover in the midrange section doesn't work satisfactorily.
Attached Images
File Type: jpg SimulationKrasnypixel.jpg (107.1 KB, 82 views)
File Type: jpg CrossoverKrasnypixel.jpg (48.2 KB, 82 views)
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Old 15th April 2018, 07:58 PM   #18
krasnypixel is offline krasnypixel  Slovakia
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Thank you both for replies.
I am pretty sure that the box is now properly sealed. If there are any leaks, these should be really tiny.

The space behind the back of the port tube is approx. 5-6cm, port with diameter 7.5 cm should then work properly (i guess).

Thanks for suggestions DonVK. I will remeasure the performance tomorrow. Its 21pm here already and I dont want to disturb neighbours

Dissi, final speaker build should of course have flushed drivers and faceted front baffle. Do you think it will anyhow improve the low bass response?

Thanks
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Old 16th April 2018, 09:32 AM   #19
giralfino is offline giralfino  Italy
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If you want to measure port and woofer bass output, you should place the mic very near, some half cm from the membrane. Only in this case you won't catch the unwanted box reflections effect.
If your box works as intended your measured curves should look like here (green and blue curves on the fig 4): Monitor Audio Silver 300 loudspeaker Measurements | Stereophile.com

Quote:
The space behind the back of the port tube is approx. 5-6cm, port with diameter 7.5 cm should then work properly (i guess).
I'm not sure that 5 cm is enough as a clearance.

Quote:
Dissi, final speaker build should of course have flushed drivers and faceted front baffle. Do you think it will anyhow improve the low bass response?
Not flush drivers is a problem only for tweeters. I'm not sure what you mean for faceted front baffle, but if it something like here SP44 this won't affect the bass performance at all, it will only change the diffraction profile, and can provide benefits for that.

Ralf
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Old 30th April 2018, 06:36 PM   #20
krasnypixel is offline krasnypixel  Slovakia
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Quote:
Originally Posted by DonVK View Post
That does not look right. You should see a port peak at 30hz and a driver dip at 30Hz. It looks like the box is leaking. I added the port output below, and the driver output was in previous post.

Try to open the IR window (left 50, right 100) and enable FDW=6. The window may be too small.
Hi,
It took me a while but I have adjusted the speaker port, added knee bend and made it slightly longer.

After subjective hearing test , one must note that the bass situation has improved. When i added +4-5 db on my preamp, it has started to sound just right.

Measurement confirmed that the speaker port is now performing as it should have, started fully kicking in at 30hz frequency.

What is however still puzzling me, is why the system response without adding 4-5 db on pre-amp so weak untill approx 60db.

Attached are measurements of the port (2cm distance) and system measurement with and without 4-5db adjustment on pre-amp (1m distance) in room conditions.

Can anyone please adwise where could be some hidden error? I was guessing whether this could be caused by slightly lower port diameter (approx 2-3mm) compared to original port, or by adding a knee on the port.

port.jpg

system_4db.jpg

Many thanks in advance

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